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The epidural blood patch. Resolving the controversies. Duffy PJ, Crosby ET. Can J Anaesth 1999 Sep;46(9):878-86. Department of Anesthesiology, University of Ottawa and the Ottawa Hospital, Ontario, Canada. E-mail: pduffy@anesthesia.org
PURPOSE:To review the literature regarding epidural blood patch (EBP) to generate conclusion relating to the controversial issues surrounding its application.
SOURCE: A Medline search was made for relevant publications using keywords epidural blood patch,
prophylactic epidural blood patch, dural puncture, and postdural puncture headache. Bibliographies of retrieved articles were hand-searched for relevant articles. Case series and comparative trials were emphasized in the
analyses. These were culled and those deemed relevant were reviewed.
PRINCIPAL FINDINGS: The majority of the literature consists of observational reports: there are few comparative studies. Headache most likely results from cerebrospinal fluid (CSF) loss leading to intracranial content shift and traction on pain sensitive structures; cerebrovascular alterations may be implicated. An EBP with 10-15 ml blood is indicated and effective therapy for severe headache after dural puncture. There is conflicting evidence regarding larger volume blood injections or delaying EBP for 24 hr or more after the diagnosis of postdural puncture headache (PDPH). Efficacy of EBP is related to a "patch effect" as well as transmission of increased epidural space pressure to the CSF space. Previous estimates of EBP efficacy were overgenerous; persistent symptomatic relief can be expected in 61-75% of patients with initial EBP. Patching with non-blood solutions, although initially effective, is associated with a high incidence of headache recurrence. Prophylactic injection of saline or blood decreases the incidence of severe headache after dural puncture. 
CONCLUSION: Blood-patching is an effective treatment of PDPH but further research is required regarding its mechanisms and prophylaxis  [citas]
Oxygen "cure" for anaesthesia sickness.
Many patients feel ill after general anaesthesia. Giving patients extra oxygen during and after surgery can halve the chance of them developing nausea as a result of general anaesthesia, say US researchers. As many as seven out of 10 people are thought to experience nausea after general anaesthesia, but two studies in the journal Anaesthesiology suggest this can be dramatically reduced without any significant side effects. The research by the University of California in San Francisco and at hospitals in Vienna found that increasing the level of oxygen in anaesthesia gas during surgery and two hours afterwards halved sickness. The research was conducted on 231 colon surgery patients in Vienna. Half were given 30% oxygen, considered the normal level, and half were given 80%. Normally the only solution for combatting post-anaesthesia nausea is anti-nausea drugs. However, these are only given to people who are vomiting and they only stand a 50% chance of working. In addition, they cost $30 a go while oxygen is almost cost free. Researchers also found that it had no side effects and could be given to all patients. Dr Daniel Sessler, professor of anesthesia and perioperative care at the University of California and senior author of both studies, said: "The take-home message from the new studies is that extra oxygen is cheap, risk-free and reduces the incidence of nausea as well as any known drug." The researchers are not sure why extra oxygen has this effect, but they speculate that it may be because the intestines do not get enough oxygen during surgery because of organ interference and cutting. This could lead to the body believing it is experiencing a life-threatening problem, triggering chemical messengers which cause nausea, they say. The research is part of ongoing studies by an international science team, the Outcomes Research Group. It is looking at accepted practice in anaesthesiology to determine if simple improvements can produce major benefits. For example, previous research led by Dr Sessler found that general anaesthesia lowered body temperature and that keeping patients' bodies warmer could cut the rate of post-operative infection threefold. This procedure has now become standard practice during general anaesthesia [citas]
Shared spinal cord scenario: paraplegia following abdominal aortic surgery under combined and epidural anaesthesia. Rutter SV, Jeevananthan V, Souter R, Cowen MJ. Eur J Anaesthesiol 1999 Sep;16(9): 646-9.Milton Keynes Hospital, UK.
Serious neurological complications of abdominal aortic vascular surgery are rare but devastating for all involved. When epidural blockade is part of the anaesthetic technique such complications may be attributed to needles, catheters or drugs. We present a patient who developed paraplegia following an elective abdominal aortic aneurysm repair. Continuous epidural blockade was part of the anaesthetic technique and postoperative analgesia. In this case the spinal cord damage was explained by ischaemia caused by the aortic surgery. This event has made us aware of a rare complication associated with abdominal aortic surgery and highlighted safety aspects of epidural anaesthesia in such patients [citas]
Preoperative dextrose does not affect spinal-induced hypotension in elective Cesarean section. Wilson D, Douglas J, Heid R, Rurak D. Can J Anaesth 1999 Nov; 46 (11):1021-29. Department of Anaesthesia, BC Women's Hospital and Health Centre, Vancouver, Canada.
PURPOSE: To determine if preoperative intravenous dextrose affects the incidence and ease of treatment of spinal-induced hypotension in parturients having elective cesarean section under spinal anesthesia.
METHODS: In this prospective, double-blind study, following informed consent, 119 ASA I,II parturients for elective cesarean section were randomized to receive intravenously either dextrose 5% in normal saline (Group D) or normal saline (Group NS) at 125 ml/hr for two hours prior to delivery. Following a bolus of 15 ml/kg normal saline iv, spinal anesthesia was induced with hyperbaric bupivacaine 0.75%, fentanyl and morphine. Hypotension (systolic blood pressure <100 mm Hg or >20% decrease) was treated with fluids and/or vasopressor. Data collected: demographics, blood glucose concentrations (fasting, time of spinal, delivery), blood pressure (baseline, one minute intervals from spinal to delivery), neonatal Apgar scores, umbilical blood gas analyses, glucose and lactate concentrations.
RESULTS: There was no difference between the two groups in the rate of hypotension (P = 0.272). All parturients who experienced hypotension received fluids, and there was also no difference between the groups in vasopressor requirement [mean dose of ephedrine: Group D = 21.6 mg (95% CI 15.1-28.2),
Group NS = 16 mg (95% CI 12.0-20.5)].
CONCLUSION: The routine administration of dextrose 5% at a rate of 5.22 g x hr(-1) preoperatively does not affect the hypotension rate, or make it easier to treat [citas]
Significant reducton in post-lumbar puncture headache using an atraumatic needle. A double-blind, controlled clinical trial. Kleyweg RP, Hertzberger LI, Carbaat PA. Cephalalgia 1998 Nov;18 (9): 635-7; discussion 591.Department of Neurology, Merwedeziekenhuis, Dordrecht, The Netherlands.
A characteristic headache occurs in about 36-55% of patients after lumbar puncture, and many of these patients need bed rest for one or more days to get relief. In a double-blind randomized trial we compared a new 22-gauge atraumatic puncture needle with the most widely used 20-gauge "conventional" needle. In 49 patients randomized to the atraumatic needle, post-lumbar puncture headache occurred in 6%,whereas in the 50 patients randomized to the conventional needle this occurred in 32% (p = 0.001). On the basis of these results we recommend use of the atraumatic needle in order to diminish the frequency of post-lumbar puncture headache [citas]
Post-dural puncture related complications after diagnostic lumbar puncture, myelography and spinal anaesthesia. Acta Neurol Scand 1998 Dec; 98 (6):445-51. Flaatten H, Krakenes J, Vedeler C. Department of Anaesthesia and Intensive care, Haukeland University Hospital, Bergen, Norway.
OBJECTIVES: This study was conducted to investigate complications after dural puncture. 
MATERIAL AND METHODS: A 15 months' prospective observation study of routine clinical practice with dural puncture at a university hospital was conducted. Quincke spinal needles 0.90 to 1.0 mm O.D. (20-19 g) were used for diagnostic lumbar puncture, 0.70 mm O.D. (22 g) for myelography and 0.40 to 0.50 mm O.D. (27-25 g) for spinal anaesthesia. A questionnaire aboutpost-puncture discomfort was given to the patients, to be returned after 1 week.
RESULTS: Of 679 questionnaires 537 (79.1%) were returned. Discomfort was experienced by 53.8% of the patients, most often after diagnostic lumbar puncture and myelography. The difference in incidence of headache after diagnostic lumbar puncture and myelography compared with spinal anaesthesia were 27.9% (95% CI: 18.6 to 37.2) and 18.3% (95% CI: 9.1 to 27.5).
CONCLUSION: Small diameter and atraumatic spinal needles will reduce patients' discomfort after dural puncture [citas]
Effects of epidural steroids on lumbar dura material properties.Slucky AV, Sacks MS, Pallares VS, Malinin T. J Spinal Disord, 1999 Aug;12 (4):331-40. Department of Orthopedics and Rehabilitation, University of Miami School of Medicine, Florida USA. 
Epidural steroid injections are commonly used in the treatment of low back pain and radiculopathy  based on their antiinflammatory and analgesic benefits. However, steroids are known to affect collagen  synthesis, material strength, and tissue healing. The purpose of this study was to assess the effects of  serial epidural steroid injections on the material properties of the lumbar dura mater. Serial epidural steroid injections of saline or methylprednisolone at 2-week intervals were performed in three paired  groups of canines; a separate noninjected group was used as controls. Postmortem, dural sample  testing to failure and histologic analysis was performed. Mechanical failure testing revealed no clinically  significant change in the transverse dorsal dura tensile strength between all saline-injected, steroid-injected, or noninjected controls. Histologic analysis demonstrated no overt disruption of  collagen matrix organization; however, electron microscopy demonstrated a significant decrease in the  number of intracytoplasmic mitochondria of dural fibroblasts in steroid-injected animals, suggesting a metabolic inhibitory effect within steroid-injected dura mater. In the clinical time frame of this study,  serial epidural steroid injections appeared to produce no significant material or matrix changes in the  lumbar dura [citas]
Epidurography and therapeutic epidural injections: technical considerations and experience with 5334 cases. AJNR Am J Neuroradiol 1999 Apr;20(4):697-705. Johnson BA, Schellhas KP, Pollei SR. Center for Diagnostic Imaging, St Louis Park, MN 55416, USA.
BACKGROUND AND PURPOSE: Even in experienced hands, blind epidural steroid injections result in 
inaccurate needle placement in up to 30% of cases. The use of fluoroscopy and radiologic contrast material provides confirmation of accurate needle placement within the epidural space. We describe our technique and experience with contrast epidurography and therapeutic epidural steroid injections, and review the frequency of systemic and neurologic complications. 
METHODS: Epidural steroid injections were performed in 5489 consecutive outpatients over a period of 5 1/2 years by three procedural neuroradiologists. In 155 cases (2.8%), the injections were done without contrast material owing to either confirmed or suspected allergy. The remaining 5334 injections were performed after epidurography through the same needle. Patients and referring clinicians were instructed to contact us first regarding complications or any problem potentially related to the injection. In addition, the referring clinicians' offices were instructed to contact us regarding any conceivable procedure-related complications.
RESULTS: Only 10 patients in the entire series required either oral (n = 5) or intravenous (n = 5) sedation. Four complications (0.07%) required either transport to an emergency room (n = 2) or hospitalization (n = 2). None of the complications required surgical intervention, and all were self-limited with regard to symptoms and imaging manifestations. Fluoroscopic needle placement and epidurography provided visual confirmation of accurate needle placement, distribution of the injectate, and depiction of epidural space disease.
CONCLUSION: Epidurography in conjunction with epidural steroid injections provides for safe and accurate therapeutic injection and is associated with an exceedingly low frequency of untoward sequelae. It can be performed safely on an outpatient basis and does not require sedation or special monitoring [citas]
Efficacy of epidural steroids in low back pain and sciatica. A critical appraisal by a French Task Force of randomized trials. Critical Analysis Group of the French Society for Rheumatology. Rozenberg S, Dubourg G, Khalifa P, Paolozzi L, Maheu E, Ravaud P. Department of Rheumatology, Pitie Teaching Hospital, Paris, France. Rev Rhum Engl Ed 1999 Feb;66(2):79-85.
OBJECTIVE: Several randomized trials have suggested recently that epidural steroid injections may not 
be a valid treatment in common low back pain and sciatica. To clarify this issue, we conducted a critical appraisal of relevant randomized trials published up to 1997. Attention was directed to methodological quality, results, and clinical implications. 
METHODS: A Medline search identified 13 trials published between 1966 and 1997. Trial methodology was evaluated using a 100-point grid based on four groups of items, namely study population, therapeutic intervention, evaluation method, and data presentation and analysis. 
RESULTS: Methodology quality scores ranged from 12 to 84 and were unrelated to the results of epidural steroid therapy. Five trials demonstrated greater pain relief within the first month in the steroid group as compared to the control group. Eight trials found no measurable benefits. Obstacles to meaningful comparisons across studies included differences in the patient populations, steroid used, volume injected, and number of injections. None of the published studies used the injection modalities that are standard practice in France. 
CONCLUSION: Whether epidural steroids are effective in common low back pain and sciatica cannot be determined based on our review [citas]
Cervical epidural steroid injection with intrinsic spinal cord damage. Two case reports. Hodges SD, Castleberg RL, Miller T, Ward R, Thornburg C. Chattanooga Orthopaedic Group, Foundation for Research, Tennessee, USA.
STUDY DESIGN: Intrinsic cervical spinal cord damage represents the serious and permanent complications that can occur if cervical epidural steroid injections are administered while the patient is sedated. Two case reports are presented. 
OBJECTIVES: To draw attention to the dangerous consequences that can arise from sedating a patient before administering a cervical epidural steroid injection.
SUMMARY OF BACKGROUND DATA: Reported complications of cervical epidural steroid injections have been minor and infrequent. No reports of intrinsic cervical cord damage could be found in a comprehensive English language literature search.
METHODS: Two case reports of permanent intrinsic cervical cord damage in patients who had been administered cervical epidural steroid injections while under intravenous sedation are presented. Magnetic resonance imaging was performed before and after the administration of cervical epidural steroid injections. Each patient had herniated nucleus pulposus before they received cervical epidural steroid injections and intrinsic cord damage on postinjection magnetic resonance images. 
RESULTS: Both patients developed increased pain and neurologic symptoms within 24 hours of injection. To date, these symptoms appear to be permanent. However, Patient 1 had pain relief in her right arm and shoulder after undergoing a microdiscectomy, but pain was still persistent in her left leg, and she has developed a positive Lhermitte's sign. 
CONCLUSION: These case reports indicate fluoroscopic guidance will not insure or prevent intrathecal 
perforation or spinal cord penetration during the administration of cervical epidural steroid injections. In addition, although intravenous sedations during cervical epidural steroid injections have been used numerous times without reported complications, it appears intravenous sedation in these two cases resulted in the inability of the patient to experience the expected pain and paresthesias at the time of spinal cord irritation. Therefore, the authors conclude that the patient should be fully awake during the administration of cervical epidural steroid injections, with only local anesthetic in the skin used for analgesia[citas]
An epidural scoring scale for arm movements (ESSAM) in patients receiving high thoracic epidural analgesia for coronary artery bypass grafting.Anaesthesia 1999 Nov;54(11):1104-9. Abd Elrazek E, Scott NB, Vohra A Clinical Fellow in Cardiac Anaesthesia.
Thoracic epidural analgesia appears to improve the outcome of patients undergoing coronary artery bypass graft surgery. Cranial extension of nerve blockade involving the third, fourth and fifth cervical nerve roots can cause apnoea. However, progressive paraesthesia and weakness due to cephalad spread of thoracic epidural analgesia will affect the arms before the diaphragm. A scale was designed to test three active movements of the arms bilaterally: hand grip (T1/C8), wrist flexion (C8/7) and elbow flexion (C6/5). This epidural scoring scale for arm movements (ESSAM) consists of four grades (0-3) based on the number of absent movements, and suggests appropriate action. The reliability of this scale was tested in 40 patients undergoing coronary artery bypass surgery. Twelve of the 40 patients had their epidural infusion reduced on the basis of the scale. Of these 12 patients, eight had a worst ESSAM score of 1, three had a worst score of 2 and one had a worst score of 3. In each patient, motor power returned following the reduction in infusion rate, taking between 30 min and 3 h. This scale appears to be a simple and reliable method for the early detection of the cephalad spread of thoracic epidural analgesia  [citas]
Effects of epidural anaesthesia on microcirculatory blood flow in free flaps in patients under general anaesthesia. Erni D, Banic A, Signer C, Sigurdsson GH. Eur J Anaesthesiol 1999 Oct; 16(10): 692-698.
It has been suggested that epidural anaesthesia may increase blood flow in free flaps on the lower extremity. The objective of the present study was to test this hypothesis in 21 patients undergoing reconstructive surgery of the lower extremity with free muscle (n=8),fasciocutaneous (n=6) or musculoIcutaneous (n=7) flaps. Microcirculatory blood flow was measured continuously with a multichannel laser Doppler flowmetry, both in muscle and skin of the free flap as well as in the intact skin and muscle on the same extremity. After completion of surgery, general anaesthesia was continued and the epidural block was induced by an injection of 2%lignocaine hydrochloride into a pre-operatively inserted and tested epidural catheter. The epiduralblock caused no change in microcirculatory flow in the intact skin and muscle, however, it resulted in a marked decrease in microIcirculatory blood flow in all the free flaps studied (20-30%; P <0.05). The epidural block also caused a significant decrease in mean arterial blood pressure, from 85(+/-2.8) mmHg to 68 (+/-2.8)mmHg (P < 0.01). It was concluded that epidural anaesthesia may decrease microcirculatory blood flow in free flaps on the lower extremity by diverting flow away from the flap to normal intact tissues (a steal phenomenon)  [citas]
Nitroglycerin relieves laryngospasm. Acta Anaesthesiol Scand 1999 Nov;43(10):1081-3. Sibai AN, Yamout I. Department of Anesthesiology, American University of Beirut-Medical Center, Lebanon.
Two young healthy non-asthmatic non-smoking patients developed partial laryngospasm directly post-anaesthesia extubation after routine varicocelectomy and perianal abscess drainage operations under general anaesthesia. Nitroglycerin was administered intravenously in a dose of 4 microg/kg for both cases. The laryngospasm was completely relieved within a minute of nitroglycerin administration in both cases and the relief was maintained thereafter. The two cases suggest that nitroglycerin can be effective in the treatment of post-extubation partial laryngospasm in ASA (class I) patients[citas]
An investigation of the possible neurotoxic effects of intrathecal midazolam combined with fentanyl in the rat. Bahar M, Cohen ML, Grinshpoon Y, Kopolovic U, Herbert M, Nass D, Chanimov M.  Eur J Anaesthesiol 1998 Nov;15(6):695-701. Department of Anaesthesiology, Assaf Harofeh Medical Centre, Zerifin, Israel. 
In previous work, midazolam was injected intrathecally and produced reversible, segmental, spinally mediated anti-nociception sufficient for abdominal surgery in a rat model. The neurotoxic effect of midazolam, alone or combined with fentanyl, injected intrathecally repeatedly on 15 occasions over a period of 1 month, was studied in the same model. We sought to establish whether this would produce neurological damage or neurotoxic injury. Histopathological examination of the excised spinal cord and paraspinal tissues was carried out. Thirty Wistar strain rats with nylon catheters chronically implanted in the lumbar subarachnoid space were divided into five groups: group 1 (n = 6) received 40 microL of  midazolam 0.1%; group 2 (n = 6) received 40 microL of fentanyl 0.005%; group 3 (n = 6) received 20 microL of midazolam 0.1% plus 20 microL of fentanyl 0.005%; group 4 (n = 6) received 40 microL of  lignocaine 2%; group 5 (n = 6) received 40 microL of phenol in water. All substances were injected through the implanted catheters. The neurological recovery of all the animals in the four groups that received intrathecal midazolam alone, fentanyl alone, midazolam plus fentanyl and lignocaine alone was similar and complete. There were no significant differences in the histological changes in the neural tissues of these groups, despite repeated application of the test substances. Group 5 demonstrated the typical neurolytic lesions of phenol when injected intentionally into the subarachnoid space  [citas]
Spinal anaesthesia with midazolam in the rat. Can J Anaesth 1997 Feb;44(2):208-15. Bahar M, Cohen ML, Grinshpon Y, Chanimov M. Department of Anaesthesiology, Assaf Harofeh, Medical Centre, Zerifin, Israel.
PURPOSE: This study examined in an animal model whether intrathecal midazolam, alone or with fentanyl, can achieve anaesthesia sufficient for laparotomy, comparable to lidocaine. Effects on consciousness and whether anaesthesia was segmental were also examined. The haemodynamic and respiratory changes were compared with those of intrathecal lidocaine or intrathecal fentanyl alone. 
METHODS: Sixty Wistar strain rats, with nylon catheters chronically implanted in the lumbar subarachnoid theca, were divided into six groups. Group 1 (n = 12) received 75 microL intrathecal lidocaine 2%. Group 2 (n = 12) received 75 microL intrathecal midazolam 0.1%, Group 3 (n = 12) received intrathecal 37.5 microL midazolam 0.1%, plus 37.5 microL fentanyl 0.005%. Group 4 (n = 12) received intrathecal 50 microL fentanyl 0.005%. Group 5 (n = 6) received 75 microL midazolam 0.1% iv. Group 6 (n = 6) received halothane 0.6% in oxygen by inhalation. 
RESULTS: Both groups that received intrathecal midazolam, alone or combined with fentanyl, developed effective segmental sensory and motor blockade of the hind limbs and abdominal wall, sufficient for a pain-free laparotomy procedure. Neither of these groups, unlike the group that received intrathecal lidocaine, developed a reduction in blood pressure or change in heart rate at the time of maximal sensory or motor blockade, nor were there changes in the arterial blood gases or respiratory rate.
CONCLUSION: Midazolam, when injected intrathecally, produces reversible, segmental, spinally mediated antinociception, sufficient to provide balanced anaesthesia for abdominal surgery [citas]
Subarachnoid midazolam: histologic study in rats and report of its effect on chronic pain in humans.  Reg Anesth 1991 Nov-Dec;16(6):329-32. Department of Anesthesiology, University Hospital, Clermont-Ferrand, France.
Subarachnoid administration via a catheter of a water-soluble benzodiazepine, midazolam, was tested in the control of cancer pain. First, the lack of its toxicity during constant subarachnoid administration (50 mcg/day) was assessed in the rat. After 15 days of treatment, a histologic examination of  the spinal cord revealed the same amount of fibrosis, infiltration, and deformation in the control group (n = 14), which had received only saline, as in the test group (n = 18), treated with subarachnoid midazolam. Therefore, the histologic changes observed in the spinal cord probably are related to the presence of the catheter. After these results, a mixture of 2 mg midazolam and a variable dose of subarachnoid morphine was injected in two patients presenting chronic neoplastic pain resistant to high doses of morphine. In these two cases, the addition of midazolam appeared to be effective in controlling intractable neoplastic pain [citas]
On the mechanism by which midazolam causes spinally mediated analgesia.Edwards M, Serrao JM, Gent JP, Goodchild CS. Anesthesiology 1990 Aug;73(2):273-7. Department of Pharmacology, University of Leeds, England. 
The electrical current thresholds for pain (ECTP) in the skin of the neck and tail were measured in rats with chronically implanted lumbar subarachnoid catheters. The effects of a benzodiazepine antagonist and a gamma-aminobutyric acid (GABA) antagonist on the analgesic effects of equivalent doses of midazolam, fentanyl, and ketocyclazocine were studied. These were the minimum doses producing maximal segmental analgesia when given intrathecally (i.e., they all caused a significant and maximum increase in ECTP in the tail, which was similar for all three drugs, but no significant change in the ECTP in the neck). Flumazenil (Ro 15-1788) administration caused a parallel shift to the right of the dose-response curve for midazolam spinal analgesia. Segmental analgesia following midazolam was also significantly attenuated (P less than 0.05) when the selective GABA antagonist bicuculline was given intrathecally at the same time as midazolam. The highest dose of bicuculline used (50 pmol) caused no significant attenuation of the segmental analgesic effects of either ketocyclazocine or fentanyl. The authors concluded that the segmental analgesia produced by intrathecal midazolam is mediated by the benzodiazepine-GABA receptor complex that is involved in other benzodiazepine actions  [citas]
Intrathecal midazolam and fentanyl in the rat: evidence for different spinal antinociceptive effects. Serrao JM, Stubbs SC, Goodchild CS, Gent JP. Anesthesiology 1989 May;70(5):780-6. Department of Anaesthesia, University of Leeds, United Kingdom. Published erratum appears in Anesthesiology 1989
Sep;71(3):482.
The effects of intrathecal midazolam and fentanyl on electrical current threshold for pain were measured using stimulating electrodes in the neck and tail of rats with chronically implanted lumbar subarachnoid catheters. This involved the measurement of the minimum current (50 Hz 2 ms pulses 0-5 mA), which made the rat squeak when applied alternately to electrodes at each skin site. The responses measured in milliamperes were expressed as a number of times control readings. Equieffective doses of both midazolam and fentanyl produced a significant increase in electrical threshold for pain in the tail (mean +/- SEM 3.14 +/- 0.51 and 2.89 +/- 0.35: P less than 0.05; Wilcoxon sum rank test) in the absence of any change in the neck (mean +/- SEM 1.28 +/- 0.13 and 0.96 +/- 0.12, NS), thus demonstrating a spinal effect. Fentanyl caused a significant simultaneous increase in tail flick latency (mean +/- SEM 67.8 +/- 20.1%, P less than 0.05), but midazolam did not (mean +/- SEM 4.22 +/- 2.76%, NS). Intraperitoneal injections of naloxone (0.25 mg/kg) blocked the response to fentanyl in both tests and did not affect the response to midazolam. Intraperitoneal flumazenil (5 mg/kg) blocked the midazolam antinociceptive effect but did not affect the response to fentanyl in either test. Tail withdrawal in response to non-noxious stimulation was preserved in all animals with spinal analgesia, indicating that myelinated afferent and efferent pathways were still functioning. Righting reflex, coordination, motor power, and alertness were also preserved in the presence of both drugs. Both drugs caused spinally mediated antinociceptive effects that were qualitatively different  [citas]
Intrathecal midazolam in the rat: evidence for spinally-mediated analgesia.Br J Anaesth 1987 Dec;59(12):1563-70. Department of Anaesthesia, University of Leeds. 
This study investigated the possible analgesic effect of midazolam as a result of interruption of those spinal cord pathways taken by pain afferents. Experiments were performed on 15 male Wistar rats with chronically implanted lumbar subarachnoid catheters. The threshold for pain induced by brief passage of electric current between pairs of electrodes placed on the tail and the skin of the neck was measured before and after subarachnoid injections of midazolam. Intrathecal midazolam caused a significant (P less than 0.02) increase in the threshold for pain in the tail, but not in the neck; this response was not produced by intrathecal injections of vehicle and was blocked by prior intraperitoneal injections of the benzodiazepine antagonist RO 15-1788. We also performed experiments on frog sciatic nerves which showed that midazolam did not have a local anaesthetic action. We conclude that intrathecal midazolam causes spinally-mediated analgesia by binding to benzodiazepine receptors in the spinal cord
Postdural puncture headache andtransient neurologic symptoms in children after spinal anaesthesia using cutting and pencil point paediatric spinal needles.H. Kokki, H. Hendolin and M. Turunen. Acta Anaesthesiol Scand.1998; 42: 1076-1082.
This is an open-randomised, parallel groups, prospective study comparing the puncture quality, success rate and post puncture characteristics of dural puncture in 200 children age 2 to 128 months. The authors compared two cutting point needles, a 25G Quincke nd a 26G Atraucan, with two pencil point needles; a 27G Whitacre and 24G Sprotte needle. Spinal puncture was successful in 96% of children. The authors felt that cutting point needles were easier to insert through the skin and ligaments but that the pencil point needles gave a better indication of dural passage. Spinal block was completed in less than 3 minutes in 96% of the cases with no differences between the needles. Seventeen (9%)children developed a headache, 10 (5%) of which were classified as post dural puncture headache. Three of these occurred with a Sprotte, three with a Quincke and four with an Atraucan needle. The authors concluded that postdural puncture headache is as common in children (5%) as in adults although it is most often mild in nature andshorter lasting. There was no discussion of the treatment of postdural puncture headache  [citas]
Postdural puncture headache in paediatric oncology patients. Napoleaon Burt MD, B. Hugh Dorman PhD MD, et. al. Canadian Journal of Anaesthesia 1998; 45:8(741-745).
This was a prospective study analysing the incidence of postdural puncture headache and atypical headache in a population of 66 paediatric oncology patients undergoing 128 consecutive procedures (these included 99 lumbar punctures and 29 bone marrow aspirations without concomitant lumbar puncture). Patients were randomised into four groups: Group 1, preteens under going lumbar puncture, Group 2 adolescents (13-21 years) undergoing lumbar puncture, Group 3 preteens undergoing bone marrow aspiration and Group 4 adolescents undergoing bone marrow aspirations. There was an increase in the incidence of headache (9.1%) after lumbar puncture in both groups less than 21 years of age relative to patients undergoing bone marrow aspiration (P <0.05). Interestingly the incidence of postdural puncture headache as was 5.7% in the pre teens and 17% for those patients aged 13-21. The incidence of atypical headache was approximately twice that of postdural puncture headaches and there was no difference in the incidence after dural puncture or bone marrow aspiration amongst the preteens or adolescents. The incidence of atypical headache was not increased in patients who underwent dural puncture. All dural punctures were performed with a 20 or 22g needle, presumably a cutting needle. Five to 10cc. of CSF fluid were routinely removed during the dural puncture and intrathecal chemotherapy was administered to 87% of patients. There was no discussion as to the treatment of postdural puncture headaches.
Comments: These two papers in different paediatric populations (also the one above) confirm that postdural puncture headaches occur in children as it does in adults. In the first study no difference was found between cutting point and pencil point needles and the incidence of postdural puncture headache was similar to that encountered in the adult population. In the second paper in which paediatric oncology patients were studied and a larger cutting needle was used, the incidence of headache was approximately twice that found in the other study. Whether this is due to the increased needle size or patient population is not possible to answer. Collectively these papers suggest that postdural puncture headache dues occur in children but the duration and severity is not as severe as in adults. When an epidural blood patch should be used in the treatment of these headaches is unfortunately not addressed by either paper [citas]
Nitrous oxide does not alter bispectral index: study with nitrous oxide as sole agent and as an adjunct to i.v. anaesthesia. Barr G, Jakobsson JG, Owall A, Anderson RE Br J Anaesth 1999 Jun;82(6):827-30. Department of Cardiothoracic Anaesthetics and Intensive Care, Karolinska Hospital, Stockholm,Sweden.
We have studied the effect of nitrous oxide on bispectral index (BIS), calculated from a bipolar encephalogram. Inhalation of 70% nitrous oxide resulted in loss of consciousness in all healthy volunteers (n = 10) but no change in BIS. Brief inhalation up to 1.2% sevoflurane also resulted in loss of consciousness in volunteers (n = 5), but with sevoflurane, BIS decreased. BIS and the haemodynamic effects of adding nitrous oxide were also measured during coronary artery bypass surgery in patients (n= 10) receiving midazolam and fentanyl infusions. Measurements were made after 0%, 33%, 66% and 0% nitrous oxide, just before skin incision and after sternotomy. Nitrous oxide caused no change in BIS. BIS may indicate a sufficient hypnotic depth to prevent awareness during surgery, but our study demonstrated that pharmacological unconsciousness-hypnosis can also be reached by mechanisms to which BIS is not sensitive. Thus BIS is a sufficient but not a necessary criterion for adequate depth of anaesthesia or prevention of awareness  [citas]
Incidence of Epidural Abscess after Epidural Analgesia. Lars P. Wang, M.D.*; John Hauerberg, M.D.†; Jes F. Schmidt, M.D., Ph.D.‡, ANESTHESIOLOGY 1999;91:1928-1936. *Staff Anesthesiologist, Department of Neuroanesthesiology. †Senior Registrar, Department of Neurosurgery. ‡Head, Department of Neuroanesthesiology. Received from the National University Hospital, Copenhagen, Denmark.
Submitted for publication October 14, 1998. Accepted for publication June 29, 1999. Address reprint requests to Dr. Wang: Department of Anesthesia and Intensive Care, Odense University Hospital, DK-5000 Odense, Denmark. Address electronic mail to: lpw@med.ou.dk. Key words: Complications; epidural catheters; neurologic deficits outcome.

Epidural analgesia is most often used for postoperative pain relief, whereas it is no longer so commonly used for long-term treatment of pain from malignant diseases. For perioperative use, the epidural catheter is most frequently inserted before induction of anesthesia while the patient is awake, although there has recently been some debate as to whether regional techniques should or should not be performed during general anesthesia (1). Side effects of epidural analgesia are common (2), but the majority are innocuous and well known to anesthesiologists. However, two serious complications of epidural analgesia may result in severe morbidity: the spinal epidural hematoma and the spinal epidural abscess. In a recent editorial (3) the incidence of spinal epidural hematoma after epidural analgesia in association with the use of low-molecular-weight heparin was estimated to vary from 1:1,000 to 1:10,000 epidural procedures, which is much higher than previously thought. The incidence of spinal epidural abscess after epidural analgesia remains unknown but has been reported to vary widely. No cases of epidural abscess were found in a large Swedish study of 9,232 epidural procedures (4),  whereas there were two cases of abscess formation among 13,000 epidural procedures in a German report (5) and 3% of the patients in a smaller North American study developed epidural abscess after long-term epidural treatment of chronic pain (6). The incidence has also been reported to vary from 0.6 to 0.77 per 1,000 catheter days (7,8).

The present study was undertaken to estimate the incidence of epidural abscess after epidural analgesia in Denmark during a 1-yr period and to evaluate the overall use of epidural analgesia during the same period. We further wished to analyze the treatment and outcome in patients with spinal epidural abscess.

Materials and Methods: All anesthetic departments in Denmark were invited in writing to participate in a prospective 1-yr study of patients with epidural abscess after epidural analgesia from May 1, 1997, to April 30, 1998. After a reminder was sent to departments that failed to respond to the initial invitation, a questionnaire was
distributed to the participating departments. The questionnaire was to be completed when a patient developed an epidural abscess after epidural analgesia, and in each department a local coordinator was responsible for the collection and transfer of data for the relevant patients. Because the anticipated total number of epidural procedures during the 1-yr study period was high, only information about patients who developed an epidural abscess or in whom the diagnosis was suspected (i.e., were referred for neurosurgery) was requested. Epidural catheterization was classified as complicated (multiple attempts) or uncomplicated (straightforward).
     
     No single method was used at all departments to identify all patients with complications after epidural
catheterization. All Danish physicians were informed about the ongoing study through the Danish Medical Journal (9) and the coordinators were reminded at regular intervals of the progress of the study. Patients with indwelling (long-term) epidural catheters were examined on a regular basis by an anesthesiologist according to local routines to ensure that the epidural analgesia was working and to renew the content of the epidural infusion pump.
     
     A national identification system (Central Personal Registry) based on a person’s date of birth plus a four-digit number, which, taken together, is unique to that person, is used in all cases of contact with the Danish health care system. This central identification facilitates subsequent tracking of any given individual within the society.        Furthermore, a national coding system of diagnoses and surgical procedures facilitates cross-checking information about specific hospital admissions. The Danish population of 5.5 million people is predominantly white and may be considered fairly homogenous from racial and social points of view. Therefore, the study population was relatively closed and well documented.
     
     At the end of the study period, the number of epidural catheters used in each department was calculated. Patients who developed epidural abscess at the end of the study period, after an epidural catheter had been inserted during the study period, were to be included (n = 0). The follow-up of patients with spinal epidural abscess was terminated at the most recent hospital discharge as documented in the patients’ notes. The ethics committee waived the need for consent.

Data Verification: Local variations in the facilities available for departmental recording of anesthetic activities during the study period accounted for interhospital differences in the calculation of the number of epidural catheters. The number of catheters used during the study period may either be calculated from number of catheters in stock on May 1, 1997, plus the catheters purchased during the study minus the stock on April 30, 1998, or may be derived from computerized registration of epidural anesthetics. The validity of the latter method was tested at one university hospital where 88% of the purchased catheters (2,900 of 3,285) were used during the 1-yr period. Allowing for a 10% waste rate (e.g., because of technical problems), this figure suggests an acceptable correlation between the two numbers. As for patients with epidural abscess after epidural analgesia, the combination of a national system of coding of diagnoses and surgical procedures and the Central Personal Registry made it possible to identify all patients referred to neurosurgical departments with a diagnosis of spinal epidural abscess during the study period, and to cross-match admitted patients and operating lists with the patients with epidural abscess. This analysis of data was performed by the authors. A manual review of the neurosurgical operating lists at six neurosurgical departments was performed by the authors in four cases and by the chiefs of neurosurgical departments in two cases.
     
     After the study period, three subgroups of epidural procedures were analyzed: (1) catheterization time was studied in 343 epidural procedures from one university hospital; (2) level of catheterization was investigated in a subgroup of 2,171 patients from two university hospitals and two nonuniversity hospitals; and (3) indications for epidural analgesia were studied in 1,795 patients from one university hospital and four nonuniversity hospitals.

Statistics: Results are presented as mean ± SD. Intergroup comparisons were analyzed by chi-square test with
 Yates correction and P values < 0.05 were considered indicative of statistical significance.

Results: Forty-six of 59 departments participated in the study. This represents 78% of anesthesia departments
 in Denmark, covering a population of 4.5 million people. There were 12 participating university departments and 34 nonuniversity departments; two university departments and 11 nonuniversity departments chose not to participate. Sixty-eight percent of the epidural procedures were performed at the university departments. Twenty-three of 44 anesthetic departments (52%) possessed computerized registration of epidural anesthetics, and 21 departments (48%) used stock recording for calculation of the number of catheters used. Two departments did not use epidural anesthesia. A total of 17,372 epidural catheters were used during the 1-yr period.

     Data from 12 patients with possible epidural abscess formation were collected. Nine of these 12 patients had developed a true spinal epidural abscess, two had subcutaneous infections, and one suffered from sequelae from a misplaced epidural catheter. However, only the nine cases of epidural abscess are considered here. These cases occurred at eight different departments. No cases were identified in neurosurgical departments that had not already been registered by the coordinators. The incidence of spinal epidural abscess after epidural analgesia was 1:1,930 catheters. The incidence of epidural abscess was 1:5,661 catheters at the participating university
hospitals, and 1:796 catheters at the nonuniversity (community) hospitals (P < 0.01). Case reports of the
nine patients with epidural abscess are presented in the appendix.

Catheterization Time: The catheters remained in situ for a mean of 11 days (11.2 ± 3.6 days) and a median of 6 days (range, 3–31 days).

Level of Catheterization: Of the nine patients with epidural abscess, five had a thoracic catheter placement, whereas a lumbar epidural catheter was inserted in the other four patients.

Indication for Epidural Analgesia: In the nine patients with epidural abscess, 67% received epidural
analgesia for perioperative pain relief, 22% for cancer pain, and 11% for trauma-related pain. Low-molecular-weight heparin was given as thromboprophylaxis before epidural catheterization in six of nine patients.

     Symptoms and signs of meningitis (fever, meningismus, headache) were found in 11% of the patients, 56% of the patients were febrile, and 67% had signs of local infection. Sixty-seven percent complained of localized back pain, and 78% developed neurologic disturbances such as lower-limb paraplegia, urinary or fecal incontinence, or irradiating pain. The time from appearance of the initial symptoms of development of an epidural abscess to the time diagnosis was established varied from 1 to 32 days (mean, 8.2 ± 9.9 days; median, 5 days). For patients undergoing neurosurgical decompression of the spinal cord (n=7), the mean time from first symptoms to confirmation of the diagnosis was 5.9 ± 4.0 days (median, 5 days). Staphylococcus aureus was isolated in six patients (67%). Coagulase-negative cocci were found in one patient, and no bacteria were found in two patients. Bacteremia was diagnosed in two patients (S. aureus in one case and Staphylococcus epidermidis in one). All patients received intravenous antibiotic treatment.

     Seven patients with neurologic deficits underwent neurosurgical decompression of the spinal cord within 24 h of verification of the diagnosis, and two patients were treated successfully with antibiotics and were discharged free of neurologic symptoms. Four of the patients who underwent surgery developed persisting neurologic deficits; two patients suffered severe paraplegia, and two developed paraparesis. The risk of persisting neurologic deficits was 1:4,343 catheters. Magnetic resonance imaging (MRI) was used in eight of nine patients to establish the diagnosis of spinal epidural abscess, and computed tomography plus myelography was used in one patient.

     For comparison, three subgroups of patients were analyzed. A subgroup of 343 catheters at one university hospital was analyzed for details of the catheterization period. In this group, the median and mean catheterization time was 3 days (range, 1–10 days) and 3.5 days, respectively. A subgroup consisting of epidural procedures from two university and two nonuniversity departments were analyzed in detail with respect to the level of catheterization. At the university hospitals, 863 catheters were used; 80% of these were thoracic and 20% lumbar. At the nonuniversity departments, a total of 1,308 epidural catheters were inserted: 33% thoracic and 67% lumbar. The indications for epidural catheterization were analyzed in a subgroup of 1,795 patients. Eighty-seven percent of the epidural catheters were inserted for perioperative pain relief (including obstetric analgesia), 9% of the patients were trauma victims, and 4% had an epidural catheter inserted for relief of cancer related pain. The findings of these comparisons may not be entirely representative of the total study population. However, the hospitals were selected at random, and the total number of catheters in the subgroups included 24.8% of all epidural procedures.

Discussion: The large majority of the anesthetic departments indicated that registration and later follow-up of every epidural anesthetic procedure would not be possible. Subsequently, we planned the study so that a staff member at each department immediately conveyed data of patients who developed epidural abscess after epidural analgesia to the authors. Furthermore, the medical community was informed of the study in an article appearing in the Danish Medical Journal (9), which is received by all Danish physicians. Because of the severity of the complication, we believe it is unlikely that cases were not reported, but because of the study design, the true incidence of epidural abscess may be even higher than calculated here. However, no further patients were admitted to the neurosurgical departments, and in our opinion, the incidence reported here is nearly accurate.

     During a 1 year period, a total of 17,372 epidural catheters were used in a population of 4.5 million people.
 Approximately 400,000 anesthetics are given in Denmark each year (10). Subsequently, epidural analgesia was used alone or in combination with general anesthesia in 6% of all anesthetic procedures. In a recent review of the European anesthesiology literature from 1974 to 1996, a total of 42 cases of epidural abscess after epidural analgesia were reported (11); this number probably represents a significant degree of underestimation of the problem. In this series, the incidence of epidural abscess after epidural analgesia was 1:1,930 catheters, which is higher than previously quoted estimates of approximately 1:5,000 catheters (5). However, epidural abscess was associated with simultaneous occurrence of long duration of catheterization, possible immunosuppression, and low-dose
anticoagulation in the large majority of patients.

     Epidural abscess formation may occur spontaneously in approximately 1:10,000 hospital admissions in
 the United States (12). We believe it to be unlikely that patients with previous epidural catheterization should develop a spontaneous abscess unrelated to the epidural catheter, because the abscesses in all patients were found at the same level as the previous catheter, and they occurred within a relatively short interval of the epidural catheter insertion.

     Our results suggest that the use of thoracic versus lumbar epidural analgesia is similar. Epidural catheterization is performed after surgical hand wash, and the procedure includes wearing a hat, face mask, and sterile gloves, disinfecting the patient’s skin twice with a chlorohexidine/70% alcohol solution (most often from a multiuse bottle), and using disposable epidural kits and drapes. When intraoperative epidural analgesia is used, it is likely to extend into the postoperative phase, and prolonged epidural catheterization (3 days) is generally accepted for major general and orthopedic surgery in Denmark. Subsequently, segmental analgesia and segmental placement of the epidural catheter is the most commonly accepted procedure. This is further supported by the results of an international study of the use of spinal opioid analgesia in which 75% of the respondents preferred segmental analgesia for postoperative pain relief (13). In accordance with this approach, we observed an 80% frequency of thoracic epidural catheterization at two university departments and a lower frequency at nonuniversity departments. Although these figures are the result of a subgroup analysis of 2,171 catheters, we believe that they are a reliable representation of the national anesthetic activity and of the use of segmental epidural analgesia. The distribution of the epidural abscesses presented here reflects the distribution of the epidural catheters, and our results do not support the assumption that thoracic epidural analgesia is more likely to result in symptomatic abscess formation than the lumbar approach. However, the absolute number of abscesses is, in this respect, low.

     Eight of nine patients experienced uncomplicated catheter insertion. Therefore, our results do not support the anticipation that a technically difficult catheter insertion may predispose the patient to development of infectious complications. It has been suggested that multiple needle insertions carry a risk of asymptomatic epidural hematoma formation that may later become the focus of bacterial colonization (11). This remains undocumented, however, and hematogenous colonization of an epidural catheter is believed to be most unusual (14). Two thirds of patients with epidural abscess received low-dose or low-molecular-weight heparin as thromboprophylaxis before epidural catheterization. Thromboprophylaxis for surgical patients has attracted much attention in Denmark. An analysis of periodic questionnaire surveys from 1981 to 1990 showed that 68% of all surgical departments had included regimens for thromboprophylaxis in departmental instructions.15 This figure compares well to the finding of 66% of patients who received thromboprophylaxis in this study. However, our results can not establish a cause-and-effect relationship between the use of low-molecular-weight heparin and the observed incidence of epidural abscess. Furthermore, our findings do not permit differentiation between an epidural abscess and an infected epidural hematoma, because MRI studies may be unable to distinguish the signals from a primary epidural abscess from those of a degrading hematoma with infection.

     All patients in this study with spinal epidural abscess had epidural catheters in situ for 3 days, and there are still no reports of abscess formation in patients with short-term epidural analgesia (2 days). Figure 1 illustrates that patients with epidural abscess had the catheter in situthree times longer than the mean catheterization time in 343 patients from one hospital (11.2 vs. 3.5 days). However, the figure also shows that in this group of 343 patients, most had the catheter in situ for 3 days, as was the case in one third of the patients with epidural abscess; therefore, although there are no reports of abscess formation after 2 days of catheterization, it seems that a catheterization time of 3 days does not eliminate the risk of epidural infection.

     Patients in need of long-term epidural pain relief are by necessity severely ill. In our study, only one patient had no complicating disease, whereas four patients suffered from malignant disease, two had non insulin-dependent diabetes mellitus, and two patients suffered from multiple trauma and chronic obstructive airways disease, respectively. This predominance of immunocompromised patients has also been found in previous studies (8,11,16). Because long-term (3 days) postoperative epidural pain relief most often is used after surgery for cancer, it is not surprising to find malignancy as a complicating disease in patients with epidural abscess. However, our findings do not permit the opposite conclusion, that epidural abscess is more likely to occur in patients with cancer than in patients without malignancy.

     Seven patients underwent neurosurgery for evacuation of the abscess, and four were discharged with
neurologic sequelae in the form of paraparesis of varying degrees. The patients who were treated with antibiotics only were discharged free of symptoms. The approach is in accordance with the results of Du Pen et al. (8), who described successful antibiotic treatment of 15 nonsurgical patients with epidural infection after long-term epidural catheters in the absence of neurologic deficits. The overall outcome in patients with epidural abscess after prolonged epidural analgesia is grave, because 44% of these patients left the hospital with a persisting neurologic deficit. Larger studies of the outcome after epidural abscess after epidural analgesia have shown a similar incidence of neurologic deficits, and apparently no improvement in outcome has occurred since the period from 1947 to 1974 (11).

     It is generally accepted that decompression of the spinal cord should be performed as soon as possible should signs of medullary affection occur (12,17). In our study, there was a 6-day delay in the referral and neurosurgical treatment of patients. The outcome after epidural abscess is related to preoperative impairment (17) which emphasizes the importance of vigilance and early diagnosis. It is therefore possible that the delayed recognition and intervention may have contributed to the high incidence of adverse outcomes in this series. One may speculate that there is a potential risk of delayed referral to neurosurgical departments of patients from
nonuniversity hospitals. However, this was not demonstrated in the present study.

     Signs of localized infection occurred in 67% of our patients, whereas 56% complained of back pain, and 56% had fever. One patient (11%) had symptoms and signs of meningitis, and neurologic deficits were found in 78%. Our results are in accordance with those of an analysis of patients admitted to a neurosurgical department with epidural abscess in which 10%, 62%, and 69% suffered from meningitis, fever, and neurologic deficits, respectively (17). Therefore, the most common signs and symptoms of epidural abscess after epidural catheterization consist of neurologic deficits, elevated body temperature, and back pain, whereas meningitis is uncommon.

     S. aureus was isolated in 67% of patients, which is in accordance with other reports (5,16,18,1920,21). All
patients received antibiotic treatment, which is in line with United States recommendations for treatment of spinal epidural abscess (17). Two patients were treated with antibiotics only. It has been suggested that this treatment is acceptable in patients with a lumbar epidural abscess without neurologic symptoms in whom the causative bacteria is known (17).

The findings of this study suggest that: 1. The indications for epidural analgesia in the nine patients reflected those in the total population; 2. The patients with epidural abscess had a longer mean catheterization time than the populatio mean; 3. The majority of the patients with epidural abscess were immunocompromised by one or more complicating diseases; 4. The level of catheter insertion is not critical to the likelihood of abscess formation;
5. The long period from diagnosis of a postepidural spinal abscess to intervention may, in part, explain the severe outcome of these patients; and 6. the use of perioperative anticoagulant therapy was involved in most cases of epidural abscess, but the diagnostic neuroimaging techniques and the intraoperative neurosurgical findings did not verify the differential diagnosis of infected epidural hematomas.

     There was a statistically significant difference in the frequency of epidural abscess at university versus community hospitals. However, the study design does not permit disclosure of interhospital differences in the indications and management of patients with epidural catheters, and further analysis of the reasons for the observed difference exceeds the scope of this study.

     Epidural analgesia was used in 6% of all anesthetic procedures in Denmark. There is little doubt that epidural analgesia is a very effective method of pain treatment, and it is the responsibility of each anesthesiologist together with the patient to agree on the best and the most acceptable method of postoperative pain relief. It is hoped that the results of this study may assist the anesthesiologist in making that decision. A forthcoming national Danish database of all anesthetics given in the country may assist in the determination of the incidence of spinal epidural
abscess after epidural catheters in relation to the catheterization period.

     The authors thank the following colleagues at anesthesiology and *neurosurgery departments in Denmark for their assistance in data collection: N. E. O. Andersen, J. Astrup,* A. B. Bach, A. Bendtsen, D. Bigler, M. Brandt, E. Bonsing, P. A. Christensen, S. Clemensen, M. Crawford, J. B. Dahl, P. Dalager, H. Degn, B. Dilling-Hansen, N. E. Drenck, K. Egsgaard, J. P. Gyrn, B. Hansen, S. Henneberg, J. Jacobsen, F. Jensen, Y. Juncker, N. O. Klausen, C. Koch-Jensen,* T. Krantz, Jan Kristensen, J. Kristensen, J. Koch, A. Kyst, H. J. Ladegaard-Pedersen, L. Malmstrom, J. Viby Mogensen, J. Molgaard, S. R. Nielsen, T. Palm, T. K. Petersen M. Primdahl, A. Risbo, T. Rosendal, L. Rybro, K. Schultz-Moller, B. A. Schurizek, M. Smedebol, M. Weber, M. Werner, and F. Wiberg-Jorgensen.

References:
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2. Rygnestad T, Borchgrevink PC, Eide E: Postoperative epidural infusion of morphine and bupivacaine is safe on surgical wards: Organisation of the treatment, effects and side effects in 2,000 consecutive patients. Acta Anaesthesiol Scand 1997;41:868–76
3. Horlocker TT, Wedel DJ: Spinal and epidural blockade and perioperative low molecular weight heparin: Smooth sailing on the Titanic (editorial). Anesth Analg 1998;86:1153–6
4. Dahlgren N, Törnebrandt K: Neurological complications after anaesthesia: A follow-up of 18,000 spinal and epidural anaesthetics performed over three years. Acta Anaesthesiol Scand
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6. Strong WE: Epidural abscess associated with epidural catheterization: A rare event? Report of two cases with markedly delayed presentation. ANESTHESIOLOGY 1991;74;943–6
7. Byers K, Axelrod P, Michael S, Rosen S: Infections complicating tunneled intraspinal catheter systems used to treat chronic pain. Clin Infect Dis 1995;21:403–8.
8. Du Pen L, Peterson DG, Williams A, Bogosian AJ: Infection during chronic epidural catheterization: Diagnosis and treatment. ANESTHESIOLOGY 1990;73:905–9.
9. Wang LP, Schmidt JF: Severe infections following epidural catheterisation (in Danish). Ugeskr Laeger 1998;160:3202–6.
10. Møller JT, Jørgensen BC: Anesthetic mortality (editorial, in Danish). Ugeskr Laeger 1995;157:6559.
11. Kindler CH, Seeberger MD, Staender SE: Epidural abscess complicating epidural anaesthesia and analgesia: A review of the literature. Acta Anaesthesiol Scand 1998;42:609–13.
12. Hlavin ML, Kaminski HJ, Ross JS, Ganz E: Spinal epidural abscess: A ten-year perspective. Neurosurgery
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13. Rawal N, Allvin R: Epidural and intrathecal opioids for postoperative pain management in Europe: A 17-nation questionnaire study of selected hospitals. Acta Anaesthesiol Scand 1996;40:1119–26.
14. Jakobsen KB, Christensen MK, Carlsson PS: Extradural anaesthesia for repeated surgical treatment in the presence of infection. Br J Anaesth 1995;75:536–40.
15. Rasmussen HM, Lausen IM, Wille-Jorgensen PA, Jorgensen T, Hauch O: The development in attitudes towards thromboprphylaxis in Danish surgical departments during a ten year period. Dan Med Bull 1994; 41:240–2.
16. Ngan Kee WD, Jones MR, Thomas P, Worth RJ: Extradural abscess complicating extradural anaesthesia for caesarian section. Br J Anaesth 1992;60:647–52.
17. Del Curling O, Gower DJ, McWorther JM: Changing concepts in spinal epidural abscess: A report of 29 cases. Neurosurgery 1990;27:185–91.
18. Holt HH, Andersen SS, Andersen O, Gahrn-Hansen B, Siboni K: Infections following epidural catheterizations. J Hosp Inf 1995;30:253–60.
19. Dawson P, Rosenfeld JP, Murphy MA, Hellyar AG: Epidural abscess associated with postoperative epidural analgesia. Anaesth Intens Care 1991;19:569–91.

Appendix (case reports):

     Case #1: A 70-yr-old man with a medical history of chronic obstructive airways disease and arterial hypertension was admitted for removal of a right-sided renal tumor with general anesthesia. Beginning the night before surgery, the patient received prophylactic low-molecular-weight heparin throughout the perioperative course. Immediately before induction of anesthesia, an epidural catheter was inserted at the T9/10 interspace. Intraoperative antibiotics were not used. Postoperatively, a second (new) catheter was inserted one level above because of insufficient analgesia from the initial epidural catheter. The catheter was used for postoperative analgesia for 3 days and was thereafter removed. Four days later the patient was febrile, the epidural site was inflamed, and after another 4 days a bilateral paraparalysis was noted by the surgeon along with a sensory deficit distal to the upper abdomen. A computed tomography scan supplemented with a myelography revealed an epidural abscess at the T9/10 level. The patient was transferred to a neurosurgical department and underwent surgery immediately. S. aureus was isolated from the abscess, and antibiotic treatment with cephalosporine and aminoglycoside was commenced. Two months later the patient suffered from fecal and urinary incontinence and inability to stand, and was subsequently wheel-chair bound. The patient died 11 months after the neurosurgical procedure after several readmissions for bedsores.

      Case #2: A 73-yr-old man with a medical history of ischemic heart disease, severe chronic obstructive airways disease, and non–insulin-dependent diabetes mellitus was admitted for exchange operation of a previously inserted left-sided hip arthroplasty with epidural analgesia. Prophylactic low-molecular-weight heparin and dicloxacillin were administered. An epidural catheter was inserted at the L3/4 interspace and was left in situ for postoperative pain treatment. The catheter was removed on postoperative day 3. The postoperative course was complicated by severe respiratory worsening and a perforated gastric ulcer. On postoperative day 15, urinary retention was noted along with a persisting fever. Leukocyte scanning showed accumulation in the lumbar spine. Five days later, an MRI scan showed an epidural abscess at the L2 level, and the patient was transferred to a neurosurgical department 41 days after the epidural procedure and underwent surgery the same day. Preoperative blood cultures revealed the presence of S. aureus, and antibiotic treatment with meticillin and fusidin was commenced. The patient was discharged from neurosurgery with minimal motor deficits in the legs, with the right leg weaker than the left. At a 1-yr follow-up examination, the patient was unable to walk without crutches and suffered severe lumbar back pain.

     Case #3: A 55-yr-old man with a medical history of heavy smoking was admitted for resection of a lung tumor
with general and epidural analgesia. The epidural catheter was inserted at the T4/5 level and was left for postoperative pain relief. Prophylactic low-molecular-weight heparin was not used, whereas a single dose of penicillin and gentamycin was given preoperatively. The catheter was removed after 6 days because of localized back pain. The patient was discharged from the hospital but was readmitted after another 6 days because of increasing back pain. The patient was examined by the anesthesiologist and was referred for MRI, which revealed an epidural abscess at the T1–T4 level. Later that day, the patient underwent decompressive laminectomy of the same spinal segments. Postoperatively, a minor bilateral lower-limb weakness was noted, and the patient was able to walk with crutches. Antibiotic treatment consisted of meticillin and fusidin for S. aureus.

     Case #4: A 74-yr-old woman with a medical history of non–insulin-dependent diabetes mellitus was admitted for insertion of a knee prosthesis with epidural analgesia. Prophylactic low-molecular-weight heparin was given on the night before surgery. The epidural catheter was inserted at the L3/4 interspace and left in situ for postoperative pain treatment during mobilization. Seven days postoperatively the patient complained of lumbar back pain, and over the following 9 days the pain worsened. Fever, local back pain at percussion, and cutaneous inflammation at the insertion site were noted. During the next 6 days the patient developed irradiating pain in both legs to the level of the ankles in addition to urinary retention. Blood cultures grew S. aureus. The patient was transferred to another hospital for MRI and  subsequent neurosurgical decompression of an epidural abscess at the L2–L4 level. Antibiotic treatment consisted of cloxacillin and meticillin. The postoperative course was complicated by cardiac failure, pneumonia, and cystitis. Six days postoperatively a right leg paralysis was still observed, but the sphincter function was normal. The patient was readmitted to the neurosurgical department 11 days later for a presumed recurrent epidural abscess, but instead a diagnosis of pyelonephritis was made.

     Case #5: A 75-yr-old man with no complicating diseases was admitted for insertion of a knee prosthesis with
epidural analgesia. The patient received prophylactic low-molecular-weight heparin starting on the night before surgery, and a single dose of dicloxacillin was given preoperatively. An epidural catheter was inserted in the L4/5 interspace and remained in situ for postoperative use during mobilization. Six days postoperatively the patient complained of back pain and fever. On examination the insertion site showed signs of inflammation, and pus was noted along the catheter. Moderate hip flexion weakness on the side of the operated leg was also found on examination. That day the patient underwent surgical debridement of a large subcutaneous abscess at the catheter insertion site. MRI was performed 2 days later, and a diagnosis of epidural abscess was made. The patient was transferred to another hospital for neurosurgical removal of the abscess at the L3 level. S. aureus was isolated from the catheter tip as well as the abscess, and treatment with dicloxacillin was commenced. Postoperatively, no motor deficits were observed. One month later the patient was readmitted for neurosurgical revision of the subcutaneous cavity.

     Case #6: A 53-yr-old man with a medical history of dilated cardiomyopathy sustained a severe trauma with
multiple rib fractures, lung contusion, fractures of right humerus and scapula, and hepatic contusion. The humerus fracture was treated with external fixation, and prophylactic dicloxacillin was given along with low molecular weight heparin. An epidural catheter was inserted at the T6/7 interspace for pain relief during weaning from ventilatory support. The patient was afebrile at the time of epidural catheterization. Because of fever and local signs of infection at the site of the epidural catheter, it was removed after 16 days. S. aureus was isolated from the catheter tip. During the following 4 days the patient developed bilateral paralysis of the legs and fecal incontinence. The patient was transferred to another hospital for MRI, which demonstrated an epidural abscess at the T3–T7 segments. Subsequent neurosurgical decompression of the spinal cord was performed the same day, but the paraparalysis subsided only slowly. Five days postoperatively only minor hip and knee flexion was observed. Antibiotic treatment consisted of meticillin. The postoperative course was complicated by a total atelectasis of the left lung, necessitating a further period of positive pressure ventilation.

     Case #7: A 48-yr-old woman with breast cancer with dissemination to the lungs, liver, and the lumbar spine, for which she received repeated chemotherapy, underwent epidural catheter insertion at the T7/8 interspace for long-term treatment of cancer pain. Sixteen days later the patient complained of pain at injection site, weakness of the right leg, and paresthesiae. Over the next 5 days two doses of epidural steroid were administered, and the catheter was removed on day 31. After another 9 days (day 40), inspection of the catheter site showed inflammation and frank pus, and the patient developed signs of meningitis (fever, meningismus, headache). There were no neurologic deficits, but the backache increased over the following 8 days. An MRI performed on day 48 showed an epidural abscess extending from T5 to T11. S. epidermidis was isolated from the catheter tip and as well as from the pus, and antibiotic treatment consisted of dicloxacillin, penicillin, and gentamycin. After neurosurgical review, surgery was deferred because of a lack of neurologic deficits. A follow-up examination 2 months later showed no residual signs of infection and no neurologic deficits.

     Case #8: A 71-yr-old woman with previous good health was admitted for a left-sided hemicolectomy for cancer with general and epidural anesthesia. Low-molecular-weight heparin and antibiotics were administered prophylactically. The epidural catheter was inserted at the T8/9 interspace and was left in situ postoperatively for pain relief. On the fourth postoperative day the patient complained of weakness of the left leg. On inspection, no signs of local inflammation at the catheter insertion site were noted. An MRI scan showed a posterior epidural collection at the T7/8 level without displacement of the spinal cord. Computed tomography scan of the brain was normal. No bacteria were isolated, but antibiotic treatment with ampicillin, cefuroxime, and gentamycin was commenced.

     Case #9: An 80-yr-old man with a medical history of bladder cancer, for which he had undergone radiation
therapy and transurethral resection of the prostate on several occasions, received sulphamethiazole for asymptomatic urinary tract infection. An epidural catheter was inserted at the L2/3 interspace for long-term pain relief. Three weeks later the patient developed lumbar back pain and increasing irradiating pain in the lateral left femur along with altered perception in the same dermatome. The patient was readmitted after another 4 days with increasing pain. No systemic or local signs of infection were observed; however, an MRI scan performed at a different hospital on the following day showed an epidural abscess situated to the left of the L2 vertebra. Subsequent neurosurgical decompression of the spinal cord was performed on the same day. The neurologic signs normalized, but the postoperative course was complicated by signs of gastrointestinal perforation. Because of old  age, the patient was treated conservatively with nasogastric decompression of the gut, intravenous  omeprazole, and broad spectrum antibiotics, and he recovered slowly. Complications of the previous radiation therapy were suspected as the underlying cause [citas]