Incidence of Spinal Epidural Abscess after Epidural Analgesia

Abstract

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. 1Side effects of epidural analgesia are common, 2but 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, 3the 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, 4whereas there were two cases of abscess formation among 13,000 epidural procedures in a German report, 5and 3% of the patients in a smaller North American study developed epidural abscess after long-term epidural treatment of chronic pain. 6The incidence has also been reported to vary from 0.6 to 0.77 per 1,000 catheter days. 7,8The 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.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 , 9and 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.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.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.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.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;table 1).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 (table 1).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 (table 1). 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 (table 1).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 (table 1). 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 (table 1); 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 (fig. 1). 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.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 , 9which 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-yr 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. 10Subsequently, 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. 11This 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. 5However, 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. 12We 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 that the use of thoracic lumbar epidural analgesia is Epidural catheterization is performed after surgical and the procedure a and the with a often from a and epidural and epidural analgesia is it is to the postoperative and epidural catheterization 3 days) is for general and surgery in Subsequently, analgesia and of the epidural catheter is the most commonly This is further by the of an study of the use of spinal analgesia in which of the analgesia for postoperative pain with this we an 80% of thoracic epidural catheterization at two university departments and a at nonuniversity departments. these are the result of a subgroup analysis of 2,171 catheters, we believe that they are a of the national anesthetic and of the use of epidural The of the epidural abscesses presented here the of the epidural catheters, and our not the that thoracic epidural analgesia is to result in abscess formation than the lumbar However, the number of abscesses in this of nine patients uncomplicated catheter Therefore, our not the that a catheter may the patient to development of has been that a risk of epidural hematoma formation that may later the of 11This remains and of an epidural catheter is to be most of patients with epidural abscess received low-dose or low-molecular-weight heparin as thromboprophylaxis before epidural catheterization. for surgical patients has much in analysis of questionnaire from to that of all surgical departments had included for thromboprophylaxis in departmental figure well to the of of patients who received thromboprophylaxis in this study. However, our establish a between the use of low-molecular-weight heparin and the incidence of epidural abscess. Furthermore, our findings not between an epidural abscess and an epidural because may be to the from a epidural abscess from of a hematoma with patients in this study with spinal epidural abscess had epidural catheters in situ for 3 days, and there are no reports of abscess formation in patients with epidural analgesia days). that patients with epidural abscess had the catheter in situ three longer than the mean catheterization time in 343 patients from one hospital (11.2 3.5 days). However, the figure also that in this of 343 patients, most had the catheter in situ for 3 days, as was the case in one of the patients with epidural although there are no reports of abscess formation after days of catheterization, it that a catheterization time of 3 days not the risk of epidural in need of long-term epidural pain relief are by In our only one patient had no whereas four patients suffered from malignant two had and two patients suffered from trauma and chronic This of patients has also been found in previous long-term 3 days) postoperative epidural pain relief most often is used after surgery for it is not to as a in patients with epidural abscess. However, our findings not the that epidural abscess is to occur in patients with cancer than in patients patients underwent for of the abscess, and four were discharged with neurologic sequelae in the of of The patients who were treated with antibiotics only were discharged free of symptoms. The is in with the of , antibiotic treatment of patients with epidural infection after long-term epidural catheters in the of neurologic The overall outcome in patients with epidural abscess after epidural analgesia is because of these patients the hospital with a persisting neurologic of the outcome after epidural abscess after epidural analgesia a incidence of neurologic and no in outcome has occurred the period from to is that decompression of the spinal cord should be performed as as possible should signs of our there was a in the and neurosurgical treatment of patients. The outcome after epidural abscess is related to the of and is possible that the and may to the incidence of in this may that there is a risk of to neurosurgical departments of patients from nonuniversity However, this was not in the present of localized infection occurred in 67% of our patients, whereas 56% complained of back pain, and 56% had patient had symptoms and signs of and neurologic deficits were found in are in with of an analysis of patients admitted to a neurosurgical department with epidural abscess in which and suffered from and neurologic the most signs and symptoms of epidural abscess after epidural catheterization of neurologic and back pain, whereas meningitis is aureus was isolated in 67% of patients, which is in with other patients received antibiotic which is in with United for treatment of spinal epidural abscess. patients were treated with antibiotics has been that this treatment is acceptable in patients with a lumbar epidural abscess neurologic symptoms in whom the bacteria is findings of this study was a significant in the of epidural abscess at university community However, the study not of interhospital differences in the indications and of patients with epidural catheters, and further analysis of the for the the of this analgesia was used in 6% of all anesthetic procedures in There is that epidural analgesia is a method of pain and it is the of each anesthesiologist with the patient to on the and the most acceptable method of postoperative pain is that the of this study may the anesthesiologist in that A national Danish of all anesthetics given in the may in the of the incidence of spinal epidural abscess after epidural catheters in to the catheterization authors the at anesthesiology and departments in Denmark for in data and with a medical of chronic and was admitted for of a with general anesthesia. the before the patient received low-molecular-weight heparin the perioperative before induction of an epidural catheter was inserted at the antibiotics were not used. a catheter was inserted one level because of analgesia from the initial epidural catheter. The catheter was used for postoperative analgesia for 3 days and was Four days later the patient was febrile, the epidural was and after days a was by the with a to the A computed tomography with a myelography an epidural abscess at the The patient was to a neurosurgical department and underwent surgery aureus was isolated from the abscess, and antibiotic treatment with and was Two later the patient suffered from fecal and urinary and to and was The patient 11 after the neurosurgical procedure after for with a medical of severe chronic and was admitted for of a previously inserted with epidural low-molecular-weight heparin and were epidural catheter was inserted at the and was in situ for postoperative pain The catheter was on postoperative The postoperative was complicated by severe and a postoperative urinary was with a persisting in the lumbar days an an epidural abscess at the and the patient was to a neurosurgical department days after the epidural procedure and underwent surgery the same the of aureus , and antibiotic treatment with and was The patient was discharged from with deficits in the with the than the At a 1-yr follow-up the patient was to and suffered severe lumbar back with a medical of was admitted for of a with general and epidural The epidural catheter was inserted at the level and was for postoperative pain low-molecular-weight heparin was not whereas a single of and was given The catheter was after 6 days because of localized back pain. The patient was discharged from the hospital but was after 6 days because of back pain. The patient was examined by the anesthesiologist and was referred for which an epidural abscess at the that the patient underwent of the same spinal a lower-limb was and the patient was to with treatment of and for aureus with a medical of was admitted for of a with epidural low-molecular-weight heparin was given on the before The epidural catheter was inserted at the and in situ for postoperative pain treatment during days the patient complained of lumbar back pain, and the days the pain local back pain at and at the were the 6 days the patient developed irradiating pain in to the level of the in to urinary aureus The patient was to hospital for and subsequent neurosurgical decompression of an epidural abscess at the treatment of and The postoperative was complicated by and days a was but the was The patient was to the neurosurgical department 11 days later for a epidural abscess, but a diagnosis of was with no was admitted for of a with epidural The patient received low-molecular-weight heparin on the before and a single of was given epidural catheter was inserted in the and remained in situ for postoperative use during days the patient complained of back pain and the signs of and was the catheter. on the of the was also found on the patient underwent surgical of a large subcutaneous abscess at the catheter was performed days and a diagnosis of epidural abscess was The patient was to hospital for neurosurgical of the abscess at the aureus was isolated from the catheter as well as the abscess, and treatment with was no deficits were later the patient was for neurosurgical of the subcutaneous with a medical of a severe trauma with of and and The was treated with and was given with low-molecular-weight epidural catheter was inserted at the for pain relief during from The patient was at the time of epidural catheterization. Because of and local signs of infection at the of the epidural catheter, it was after days. aureus was isolated from the catheter the days the patient developed of the and fecal The patient was to hospital for which an epidural abscess at the neurosurgical decompression of the spinal cord was performed the same but the only days only and was treatment of The postoperative was complicated by a total of the a further period of with cancer with to the and the lumbar for which received underwent epidural catheter at the for long-term treatment of cancer pain. days later the patient complained of pain at of the and the 5 days two of epidural were and the catheter was on After days of the catheter and and the patient developed signs of meningitis (fever, meningismus, There were no neurologic but the the days. performed on an epidural abscess from to epidermidis was isolated from the catheter and as well as from the and antibiotic treatment of and After neurosurgical surgery was because of a of neurologic A follow-up later no signs of infection and no neurologic with previous health was admitted for a for cancer with general and epidural anesthesia. Low-molecular-weight heparin and antibiotics were The epidural catheter was inserted at the and was in situ for pain the postoperative the patient complained of of the no signs of local at the catheter were a epidural collection at the level of the spinal tomography of the was No bacteria were but antibiotic treatment with and was with a medical of for which had and of the on received for urinary epidural catheter was inserted at the for long-term pain later the patient developed lumbar back pain and irradiating pain in the with in the same The patient was after days with pain. No or local signs of infection were an performed at a different hospital on the an epidural abscess to the of the neurosurgical decompression of the spinal cord was performed on the same The neurologic signs but the postoperative was complicated by signs of Because of the patient was treated with decompression of the intravenous and and of the previous were suspected as the