Indian Journal of Anaesthesia

: 2007  |  Volume : 51  |  Issue : 6  |  Page : 496--500

Bacterial colonization and infection of epidural catheters: a prospective study of incidence and risk factors in surgical patients

Uma Srivastava1, Parul Chandra2, Surekha Saxena1, Aditya Kumar1, Ashish Kannaujia3, Shiv Pratap Singh Rana2, Hompriya Issar4,  
1 MD,Professor, Department of Anaesthesia & Critical Care, S. N. Medical College, Agra, India
2 MD, Ex-Resident, Department of Anaesthesia & Critical Care, S. N. Medical College, Agra, India
3 MD, Lecturer, Department of Anaesthesia & Critical Care, S. N. Medical College, Agra, India
4 DNB (Surgery) Resident, Agra, India

Correspondence Address:
Uma Srivastava
Department of Anaesthesia & Critical Care, 15, Master Plan Road, New Lajpat Kunj, Agra-282002


Infection of the epidural space is a rare but serious complication of catheter placement. The purpose of the present study was to determine the incidence of bacterial colonization of epidural catheters, the co-relation between colonization and infection and to identify the risk factors associated with colonization.Aprospective observational trial was carried out on 272 adult patients receiving epidural catheterization for anaesthesia and post-operative analgesia. Patients undergoing a variety of surgical proce­dures (abdominal, thoracic, urological, orthopaedic, gynaecological and obstetric) both elective and emergency were recruited. The tips of epidural catheters after removal were sent aseptically for culture. Of 261 tips sent for culture 11 (4.2%) showed positive culture, the most prevalent microorganism being Staphylococcus epidermidis. None of the patients had signs and symptoms of local or epidural space infection. Twelve potential risk factors were entered in the step-wise logistic regression analysis to identify factors associated with catheter colonization. Out of these only the duration of catheterization (P<0.01, odd ratio 3.39, 95% confidence interval 0.12-1.5) was found to be significant. Summarizing the results, the incidence of bacterial colonization was 4.2% with no case of epidural space infection. The chances of colonization increased with duration of placement beyond 96 hours and this was found to be a potential risk factor for colonization but not infection. The positive cultures did not equate with infection.

How to cite this article:
Srivastava U, Chandra P, Saxena S, Kumar A, Kannaujia A, Singh Rana SP, Issar H. Bacterial colonization and infection of epidural catheters: a prospective study of incidence and risk factors in surgical patients.Indian J Anaesth 2007;51:496-500

How to cite this URL:
Srivastava U, Chandra P, Saxena S, Kumar A, Kannaujia A, Singh Rana SP, Issar H. Bacterial colonization and infection of epidural catheters: a prospective study of incidence and risk factors in surgical patients. Indian J Anaesth [serial online] 2007 [cited 2021 Jun 24 ];51:496-500
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Although many retrospective & prospective stud­ies found epidural anaesthesia to be safe with regard to infectious complications [1],[2],[3] ,serious infections have been reported after central neuraxial blockade [4],[5],[6] . A recent study reported the incidence of epidural abscess of 0.2­2 cases per 10,000 hospital admissions [7] . The precise mechanism of epidural space infection associated with epidural block is not yet clear; several possible routes have been proposed [8] . The micro-organism may reach the epidural space during needle or catheter insertion, alongthe catheter tract, bycontaminated syringes or medi­cation or by local or haematogenous spread from else­where in the body [8] . While the bacterial colonization of catheter tips after removal is frequently obtained, the incidence of epidural space infection is very low [3],[9],[10]. The predisposing factors, which play a key role in colo­nization and infection, are not well defined. In a meta­analysis, Reihsaus & colleagues (2000) [7] found certain risk factors to be associated with higher chances of in­fection but the degree of risk associated with each fac­tor was not clear [11] .The aim of this study was to pro­spectively determine the incidence of epidural catheter tip colonization and infections as well as to identify risk factors associated with bacterial colonization in adult sur­gical patients who received epidural anaesthesia & post­operative epidural analgesia for longer than 48 hours.


This prospective observational study was conducted between January '04 and November '06 after approval from the Institution's Ethical Committee and informed written consent from the patients. All the adult patients in whom epidural catheter was placed for surgery and post-operative analgesia for more than 48 hours were eligible for the study. Exclusion criteria included patient's refusal, coagulation abnormality and local or systemic infection. Types of surgical procedures performed in­cluded abdominal, urological, orthopaedic, and obstetri­cal (both elective & emergency). The epidural catheter was inserted at lumbar or thoracic epidural site. Hospital's prepared trays containing autoclaved epidural needles (16-18 G) were used. A sterile disposable catheter with filter was included in the tray after it was opened.

All catheter insertions were done in the operation theatre with full aseptic precautions. The operator's hands were washed and a cap and mask, sterile gown and sterile gloves were worn. The patient's skin was prepared with cetavlon, 10% povidone-iodine solutionand rectified spirit and then covered with sterile drapes. The area was allowed to dry between each anti-septic appli­cation. The epidural space was identified using the "loss of resistance" technique with air & epidural catheter was advanced about 4-5 cm into the epidural space. A dry sterile gauze pad was applied at the insertion site with the adhesive tape. The exposed length of the cath­eter was directed cephalad over the patient's back and fixed with adhesive tape over the shoulder after attach­ing bacterial filter. The filter was enclosed in a sterile bag. The operations were performed under epidural ana­esthesia alone or combined with general anaesthesia as required.All patients received peri-operative antibiotics viz. ceftriaxone, gentamicin/ amikacin, metronidazole, ciprofloxacin, ceftazidime in various combinations. The first dose of antibiotic was administered before place­ment of epidural catheter. The resident anaesthesiologist, observing complete asepsis provided post-operative an­algesia. The anaesthetist visited each patient twice a day and inspected and palpated the catheter dressing for any discharge, staining or tenderness. The dressing was not changed routinely unless required. The patients were screened daily for symptoms/signs that would suggest the presence of epidural space infection which included pain in back, tenderness, root pain, sensory or motor deficit, fever etc. Catheter related infection was sus­pected if the patient became febrile without any other obvious cause. Epidural catheter was left in place for a minimum of 48 hours but was removed earlier if analge­sia was no longer required, was malfunctioning, acci­dentally removed or if local or epidural space infection was suspected. The catheter was removed in the gen­eral ward without prior antiseptic skin preparation. The distal 2 cm of the catheter was aseptically cut with ster­ile scissors keeping the tip of the catheter upward and away from the skin surface. The cut portion was trans­ported in a sterile tube for immediate culture onto the culture medium in the microbiology laboratory. In the lab, each catheter segment was cultured at 37 0 C under aerobic conditions for 48 hours and identified by stan­dard methods and criteria. Positive culture was defined as > 15 colony forming units. The patients were visited daily till discharge from the hospital, checked regarding symptoms and signs of epidural space infection & instructed to report to the PAC clinic if anyof above mentioned symp­toms appeared after the discharge from the hospital.

The characteristics of the patients are expressed as median, range or as the number of patients. Twelve po­tentially relevant variables studied as the risk factor were entered into a step-wise backward logistic regression analysis using the maximum likelihood method. The fac­tors included: age, sex,ASA grade, type of surgery (elec­tive/emergency), site of insertion (thoracic/lumbar), num­ber of attempts for epidural puncture, duration of catheter in situ, diabetes mellitus, chronic drug abuse, malignancy, corticosteroid therapy and alcoholism.All analyses were performed using Lotus software for Windows.


A total of 272 epidural catheters were inserted in 272 patients, the majority (70%)were placed for elective surgery. The main non-elective indications were caesar­ean section & exploratory laparotomy.About half the pa­tients had undergone abdominal surgery followed by or­thopaedic, caesarean section, urological & thoracic sur­gery. Out of 272 catheters only 36 were placed in the thoracic region [Table 1]. About 1/3 rd of patients had one or more risk factors or conditions known or suspected to predispose to infective complications of epidural catheter such as diabetes, malignancy, alcoholism or had received steroids.

Majority of the catheters were removed after 52 hours after insertion. Two hundred sixty one catheter tips were sent for microbial culture, as rest were re­moved accidentally or earlier than 48 hours. The cath­eters removed earlier than 48 hours were not sent for culture, as they were not eligible for the study. Out of these, 250 were sterile while 11 showed positive culture. The commonest microorganism grown was coagulase­negative Staphylococcus epidermidis present in 64% of positive cultures. The clinical & bacteriological data of the patients with positive epidural catheter tip culture are presented in [Table 2]. Most of the patients had their catheters in epidural space for equal or more than 90 hours. No patient had signs of local infection such as erythema, tenderness or discharge etc. Also, none of the patients showed clinical signs & symptoms of epidu­ral space infection including those with positive cultures.

The stepwise regression analysis revealed that out of 12 potential risk factors, only one remained in the fi­nal model as statistically significant. Duration of cath­eterization was associated with increased incidence of bacterial colonization (P [10],[12],[13] while others have evidenced higher rates [3],[9],[14],[15],[16]. Wide variation in results could be due to methodological dif­ferences among the studies, making inter-study compari­son difficult [17] . Low incidence of colonization in our study could be due to the use of peri-operative antibiotics which have been shown to lower the risk of catheter related infectious complications [13],[18],[19] .

The commonest microorganism identified in this study was coagulase negative Staphylococcus epidermidis, a prominent human skin commensal gener­ally regarded as a pathogen of little clinical significance. It represented about 64 % of cultured pathogens. These results concur with other studies showing it to be the most common agent of epidural catheter tip culture [5],[9],[10],[12],[17],[20]. However, the findings of culture of Kleb­siella, Enterobacter and Staphylococcus aureus in our study and Pseudomonas and Eschericia coli in other stud­ies [9],[13],[16] emphasize the possibility that more virulent mi­croorganism could colonize easily leading to epidural space infection. Raedler et al (1999) [21] found that 17.9% of spinal and epidural needles were colonized when sent for culture immediately after use in spite of full aseptic precautions. In the present study the catheters were removed in the general ward without applying any anti­septic. Thus catheter tips probably got contaminated by skin flora during withdrawal [15] . As such, it is impossible to exclude catheter contamination that could have oc­curred during withdrawal [9],[20].

Despite colonization of the catheter tip with vari­ous microorganisms, we did not encounter any patient with clinical findings of epidural space infection, a find­ing in agreement with many studies [1],[2],[10],[13],[15] . Thus posi­tive culture is not a reliable predictor of epidural space infection [3],[9],[10],[15],[16] suggesting routine culture of catheter tips unnecessary. The infection can occur even in the absence of a positive culture.

Although direct relation between colonization and infection of epidural space is uncertain some risk fac­tors have been suspected to abet this [11],[19]. These include age, I/V drug abuse, steroid administration, diabetes, chronic renal failure, alcoholism, immuno compromise due to malignancy, sepsis, type of surgery, site and dura­tion of catheterization and number of attempts during catheter insertion etc. Out of these we selected 12 po­tential risk factors for logistic regression model to deter­mine the effects of these factors on incidence of cath­eter colonization. The analysis showed that of these 12 factors, only one i.e. "the duration of catheterization" remained in the final model as statistically significant. Longer the catheter remained in epidural space, more were the chances of colonization [5],[22],[23] .Out of 11 pa­tients who had positive culture, 7 had their catheters in the epidural space for equal or more than 90 hours.

Currently there is not adequate data to suggest a duration beyond which the risk of infection increases [4] . But the data on I/V devices suggests that majority of the infections occur after 5 days, lending some support to wide spread practice of withdrawal of epidural catheter by the 5th day [11] ; if its use is required beyond 4 days, the risk/benefit ratio must be assessed [11] .

All other patient related factors (age, sex, malig­nancy, chronic drug abuse, site & number of attempts, steroid administration etc) were removed as non-signifi­cant suggesting that frequency of colonization was inde­pendent of these factors. The results indicate that it is difficult to predict which patient will have a positive cul­ture [15],[19]. Of all the pre-existing diseases, diabetes has been shown to be one of the most important risk factors [7] followed by I/V drug abuse [24] and remote infection 7 . But we failed to demonstrate any such association. This could be due to the small number of patients with such co-morbid conditions.

There were certain methodological limitations to this study. Many potential risk factors that were entered in the stepwise logistic regression correlated with each other such asASAstatus on one hand and steroid therapy or malignancy on the other hand. Thus, if one of such factors is removed during stepwise exclusion process a certain part of information of the removed factor is trans­ferred to the correlated factors still in model. Therefore the risk factor remaining as significant in the final model might not be truly significant [19] .The other limitation was a relatively small sample size which might be insuffi­cient to detect a rare complication like epidural abscess. Insufficient follow-up data was another limitation as the symptoms of catheter related infection may present so late that the condition might escape detection [25] . Though all patients and surgical teams were instructed to report any complication, no patient turned up.

To summarize, the incidence of bacterial coloniza­tion was 4.2% with Staphylococcus epidermidis being the most prevalent microorganism. No clinical infection of epidural space was observed in any patient. Among the riskfactors studied, onlythe duration of catheter place­ment upto or beyond 90 hours was found to increase the likelihood of bacterial colonization of epidural catheter tips. Therefore we suggest that the epidural catheter should be removed by the 4th day unless deemed neces­sary.Although we did not find any case of epidural space infection or abscess, sporadic cases are being published. Therefore, all the anesthesiologists practicing epidural anaesthesia & analgesia should maintain a high index of suspicion [25] regarding this potential complication.


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