Abstract
Despite efforts to maintain a meticulous aseptic environment, wound infection is one of the most common complications following surgery and may be related to dehiscence, haemorrhage, infection, and/or poor surgical technique. With the appearance of new wound closure techniques and suture materials, we felt compelled to perform a retrospective study on our institution's neurosurgical population to determine how our institution compared to others in terms of incidence of surgical site infection (SSI). A retrospective analysis was performed at our single institution for all patients that had cranial or spine surgery by a neurosurgeon for the past 15 years. The data were extracted via Crimson Continuum of Care software program and analysed using χ 2 and relative risk. The data retrieval software program collected a total of 1184 cranial and spinal surgeries. Of these 1184 cases, 12 resulted in post‐operative wound infections. Using these collected values, we compared the results with published values in the literature. Prior studies have shown that up to 33% of surgical cases have post‐operative infections. Using this reported value in comparison with our data, χ 2 testing equals 547.893 with 1 df, P = .0001 (confidence interval = 0.05), which demonstrated statistical significance when compared with surgical literature. The results from this retrospective analysis demonstrated that the rate of neurosurgical post‐operative SSI falls within the range consistent with the literature, which has shown rates of infection from <1% up to 15% depending on the type of surgery, surgical technique, and patient characteristics. SSIs can be an unfortunate and costly post‐operative complication. Risks factors in the past have been studied, but introspection by each institution is an important metric to ensure accountability and provide optimal patient care in comparison with established data and guidelines. No deviation from current techniques is deemed necessary at our institution based on the results.
Keywords: neurosurgery, post‐operative complications, surgical site infections, wound infection
1. INTRODUCTION
Despite efforts to maintain a meticulous aseptic environment, wound infection is one of the most common complications following surgery and may be related to dehiscence, haemorrhage, infection, and/or poor surgical technique. 1 Margin approximation involves closure with a variety of options including sutures, staples, or novel closure techniques with zippers or adhesives. The ideal method for closure should have a high tensile strength to hold wound edges together until healing is complete, should not be allergenic or cause tissue inflammation, and if done with suture, then it should be placed with sound knotting techniques.
Surgical site infections (SSIs), as opposed to traumatic wound infections, may be classified as either superficial or deep, and occur within 30 days after the operation. 2 The primary pathogens in acute infections are gram‐positive cocci, specifically Staphylococcus aureus, B‐hemolytic Streptococci, and Staphylococcus epidermidis. 3 Diabetics with poor glycaemic control, elderly age, smoking, obesity, malignancy, and/or an immunosuppressed state increase the proclivity for a SSI.4, 5, 6, 7 SSIs occur in 2% to 5% of patients undergoing inpatient surgery and are associated with an average increased length of stay of 9.7 days and a 2‐ to 11‐fold increase in mortality.8, 9, 10, 11 The financial burden resulting from SSIs in the United States is estimated to be between 3.5 billion to 10 billion dollars. 4
Recently, there has been a growth in alternative suture materials including antimicrobial sutures, bio‐active sutures with either drug‐eluting stents or stem cell‐seeded sutures, and electronic smart sutures. 12 The goal of these new suture materials extends beyond simple tissue apposition, to a biological deliverable drug with potentially immense application to improve the entire wound healing process. Comparative research studies have shown a reduction in post‐operative wound infections with the use of antimicrobial sutures compared to traditional sutures.1, 13 A recent meta‐analysis has demonstrated a decrease in the risk of SSI with the use of triclosan antibiotic suture compared with a standard suture; triclosan‐coated suture is now a standard of care for all clean and contaminated abdominal cases. 14 With the appearance of all these new options, we felt compelled to perform a retrospective study on our institution's neurosurgical population to determine how our institution when compared to others in terms of incidence of SSI, and second if we needed to adopt the usage of novel suture materials or closure techniques.
Post‐operative wound infections have been extensively studied in patients following general or oncologic surgery. Limited studies following craniotomy have shown that prior neurosurgical procedures, concomitant infections, cerebrospinal fluid (CSF) leak, and venous sinus entry pose the greatest risk towards SSI. The use of external CSF devices has also been shown to be a significant risk factor for the development of SSI with a higher 90‐day mortality.15, 16 Most of these studies have focused on the demographics of the patient and/or the procedure and less on the mechanism by which the wound was closed. 17 Our study focuses on all primary closure neurosurgical cases, including craniotomies, and spinal surgery, with attention to the type of closure material used. The aim of this retrospective analysis was to review our experience with patients following neurosurgical intervention using a contemporary wound closure approach, evaluate for trends in the data, and to determine if antibiotic sutures should be offered at our institution as an alternative by comparing our data to other studies with antibiotic sutures.
2. METHODS
A retrospective analysis was performed at our single institution for all patients that had cranial or spine surgery by a neurosurgeon for the past 15 years. Inclusion criteria include the following: (a) patients age 18 and over, (b) patients who had a neurosurgical procedure, and (c) patients who had primary wound closure at our institution with suture or staple technique. Exclusion criteria include the following: (a) patients age under 18, (b) patients who did not have a neurosurgical procedure, and (c) patients whose closure was performed outside the institution.
The data were extracted via the Crimson Continuum of Care software program. Additional information was collected from electronic medical records and that information was organised and stored in a Microsoft Excel spreadsheet. The data collected included medical record number, gender, age, smoking status, diabetes, IV drug usage, body mass index (BMI), date of surgery, type of surgery, type of closure, time of infection after surgery, type of infection, co‐existing infection, and treatment (surgery versus antibiotics). The data were analysed using χ 2 test and relative risk (RR) using Microsoft Excel.
3. RESULTS
The data retrieval software program collected a total of 1184 patients who underwent cranial and spinal surgeries. Of these 1184 cases, 12 resulted in post‐operative wound infections. Using these collected values, we compared the results with published values in the literature. Prior studies have shown up to 33% of surgical cases have post‐operative infections. 18 Using this reported value in comparison with our data, the χ 2 testing value equals 547.893 with 1° of freedom, P = .0001 (confidence interval = 0.05). Our SSI incidence demonstrated statistical significance when compared with surgical literature (Table 1). When evaluating for specific SSI, Kolpa et al reported an incidence of 1.5%. Our data did not show any statistical significance, with an incidence of 1.0%, when compared with quoted literature (χ 2 value 2.031, P‐value = .1541). 18
TABLE 1.
Chi‐squared and relative risk analysis for surgical site infections (SSIs) at our institution versus reported literature values
| Our Institution | Kolpa et al 18 | Chaudhary et al 19 | Ueno et al 20 | De Jonge et al 21 | χ 2 | |
|---|---|---|---|---|---|---|
| SSI | 1% | 1.5% | 2.031, P‐value = .1541 | |||
| Spinal SSI | 0.05% | (2.2%—did not use for statistical analysis) | 3% | 25.272, P‐value <.0001 | ||
| Spinal SSI | 0.05% | 4.15% | 39.364, P‐value = .0001 | |||
| Cranial SSI | 0.05% | 1.4% | 12.334, P‐value = .0004 | |||
| RR | 0.80 | 0.75 |
Abbreviation: RR, relative risk.
In evaluating rates of infection comparing spinal surgery with literature in two separate publications, quoting 3% for all spinal surgeries and 4.15% of infection noted on spinal surgeries, 20 our data (0.05% infection incidence) was statistically significant regardless of the rate reported χ 2 25.272, P‐value <.0001 and 39.364, and P‐value = .0001, respectively. 19 When parsing out cranial surgery infection, again our data with an infection rate of 0.05% demonstrated statistical significance when comparing quoted data of 1.4%, χ 2 12.334, P‐value = .0004. 18 de Jonge et al reported an RR of 0.75 in regard to SSI. 21 Our data demonstrated a similar finding of 0.80 in regard to RR.
Of those 12 patients who experienced a post‐operative infection, 10 were males (83.33%) and 2 were females (16.67%) (Figure 1). Half of the patients (50%) were found to be in the age group of 51 to 65 years (Figure 2). We then evaluated certain demographics that have been shown to increase the risk of infection. Of those patients, 0% of patients were noted to have a BMI <18.5, while the remainder were evenly distributed, 33.3% were noted to have a BMI >30.1 (Figure 3). Half of the patients (50%) with infection were found to be either active or former smokers (Figure 4). Two patients admitted to intravenous drug abuse (IVDA) (16.7%), 1 (8%) stated they were former IVDA (Figure 5). Only one patient (8%) was diagnosed with diabetes mellitus (DM) (Figure 6). When evaluating surgical specifics, equal patients had spinal versus cranial surgery, six of each case type (Figure 7). In relation to closure material, sutures, and staples were used in equal amounts five for each material and two in combination (10 without closure information) (Figure 8). Thus, our data demonstrate no difference when comparing the type of closure or surgical procedure. Of the patients who did experience SSI, 50% of the post‐operative infection occurred 11 to 30 days after surgery, “N/A" represents a patient who had purulent debris in the wound that was found on a washout surgery but cultures were not taken (Figure 9). And 66.7% of patients required repeated surgical intervention, in addition to antibiotic treatment (Figure 10).
FIGURE 1.
Gender ratio of patients with post‐operative wound infection
FIGURE 2.
Age of patients with post‐operative wound infection
FIGURE 3.
Body mass index
FIGURE 4.
Smoking status
FIGURE 5.
Intravenous drug abuse
FIGURE 6.
Diabetes mellitus
FIGURE 7.
Type of surgery
FIGURE 8.
Closure material
FIGURE 9.
Days after surgery of infection
FIGURE 10.
Patients requiring re‐operation
4. DISCUSSION
The results from this retrospective analysis demonstrated that the rate of neurosurgical post‐operative SSI falls within the range consistent with the literature, which has shown rates of infection from <1% to 15% depending on the type of surgery, surgical technique, and patient characteristics.15, 22 In comparison to meta‐analyses reviewing the typical rate of SSI in spinal and cranial surgeries, χ 2 analyses of our rates of infection for both spinal and cranial surgeries were below the expected rates in a statistically significant fashion (P < .0001 and P < .0004, respectively). When attempting to explain the low incidence of SSI in this group of 1184 patients, it is important to first consider what variables may contribute to the incidence of SSI overall.
There have been several meta‐analyses and systematic reviews, done compiling trials that review risk factors that affect the incidence of post‐surgical infections in neurosurgical operations.15, 22, 23, 24, 25 In evaluating risk for post‐operative SSI, there exist variables both related to the technique and protocol of the procedure (what we refer to here as “intrinsic” variables), as well as variables unrelated to the procedure but rather specific to the patient's profile and overall health (what we refer to as “extrinsic” variables). These meta‐analyses and systematic reviews incorporate several variables that fall into both categories (intrinsic and extrinsic factors) impacting the incidence of SSI, some of which have been shown to do so in a statistically significant way. Among the publications referenced above, intrinsic risk factors demonstrated to impact SSI incidence in a statistically significant way are included in Table 2.
TABLE 2.
Intrinsic risk factors impacting the incidence of SSI
| Variable | Increase versus decrease in SSI | Reported P‐value | References |
|---|---|---|---|
| CSF leak | Increase; increase | P = 0; P < .0001 | Fang et al 15 ; Meng et al 22 |
| CSF drainage | Increase; increase | P = 0; P < .001 | Fang et al 15 ; Schipmann et al 23 |
| Prolonged duration of operation (>4 h) | Increase; increase | P = .001; P = .009 | Fang et al 15 ; Fei et al 24 |
| Venous sinus entry | Increase | P = .007 | Fang et al 15 |
| Implantation of foreign material | Increase | P < .001 | Schipmann et al 23 |
| Posterior approach to spinal surgery | Increase | P = .009 | Fei et al 24 |
| Spinal surgeries involving seven or more intervertebral levels | Increase | P = .023 | Fei et al 24 |
| Surgical scrub with antiseptic foam | Increase | P = .01 | Sarmey et al 25 |
| Omission of 5% chlorhexidine hair wash | Increase | P = .051 | Sarmey et al 25 |
| Antibiotic‐impregnated sutures | Decrease | P = .038 | Sarmey et al 25 |
| Lack of hair shaving in ventriculoperitoneal shunt (VPS) placement | Decrease | P > .05 | Sarmey et al 25 |
| Double gloving with change of gloves prior to shunt handling | Decrease | P = .046 | Sarmey et al 25 |
Abbreviation: SSI, surgical site infection.
With this in mind, the factors intrinsic to surgery that we evaluated among our cohort included the type of surgery (spinal versus cranial), type of closure material (staples, sutures, or a combination of both), and the number of days post‐operation. These were chosen because each has been previously analysed in the literature and could be applied to all of the procedures reviewed in this retrospective analysis. In reviewing these intrinsic variables with regard to each case of post‐operative infection in our retrospective analysis, our results demonstrated no statistically significant difference in SSI incidence between spinal or cranial surgeries, type of closure material, or the number of days post‐operation. These results are similar to meta‐analyses and reviews that are done in the literature surveying these variables as none of these three variables have been shown to consistently impact SSI in a statistically significant way.
As mentioned previously, extrinsic factors include those unrelated to the technique or specific details of the procedure and rather refer to patient characteristics that predispose one to infection, such as gender, age, BMI, smoking status, IVDU, and history of DM (Table 3). Among the aforementioned compilation of meta‐analyses and systematic reviews, extrinsic risk factors shown to affect SSI incidence include male gender, number of previous neurosurgical operations, tobacco smoking, diabetes, BMI >35, urinary tract infection, and hypertension. The tabulated risk factors and their impact on SSI are shown in the table below.
TABLE 3.
Extrinsic risk factors include those unrelated to the technique or specific details of the procedure
| Variable | Increase versus decrease in SSI | Reported P‐value | References |
|---|---|---|---|
| Male gender | Increase | P = .091 | Fang et al 15 |
| Number of previous neurosurgeries | Increase | P = .02; P = .000; P < .001 | Fang et al 15 ; Schipmann et al 23 ; Meng et al 22 |
| Tobacco smoking | Increase | P < .10; P = .015 | Kong et al 26 ; Meng et al 22 |
| Diabetes | Increase | P < .001; P = .001 | Meng et al 22 ; Fei et al 24 |
| BMI >35 | Increase | P < .001; P = .015 | Meng et al 22 ; Fei et al 24 |
| Urinary tract infection | Increase | P < .001 | Meng et al 22 |
| Hypertension | Increase | P < .001 | Meng et al 22 |
Abbreviations: BMI, body mass index; SSI, surgical site infection.
In reference to the extrinsic variables analysed, our results did not highlight any particular risk factor present among the 12 patients that correlated well with the incidence of SSI. However, the group size of 12 patients with SSI was likely too small to be able to adequately discern variables that more prominently impacted these results. Nevertheless, our study's reported incidence of SSI falls within the range of typical post‐operative infection rates in neurosurgical cases, thus providing valuable data that adds to the current literature documenting risk factors for neurosurgical rates of SSI.
Although our results demonstrated a low‐average SSI incidence and did not elucidate a clear correlation between particular intrinsic or extrinsic vfariables and the development of SSI, there are important conclusions to take away from this study. Namely, it is important to highlight that our retrospective analysis of post‐operative SSI incidence in patients receiving spinal or cranial surgery at our institution demonstrated outcomes on the low end of the spectrum of documented SSI rates in neurosurgery. The low infection rate from our institution can be attributed to the processes from our practice in an effort to decrease infection rates. We maintain sterility of operative site from draping to dressing, although no strict protocol is mandated. The initial intent of the study was to survey our cohort of prior neurosurgical cases and identify the need for quality improvement potential. Options for quality improvement included alternative closure materials, such as antibiotic sutures to reduce SSI incidence, as the use of such sutures has demonstrated an association with decreased incidence of SSI in the literature. 25 However, our analysis highlighted that conventional surgical closure methods at our institution are indeed very safe, and do not currently necessitate any major deviations from standard practice or technique without further studies demonstrating the outcome benefit and cost‐effectiveness of that change. Perhaps the most important role our study can play in the literature is to provide a framework for hospitals and academic institutions to review and analyse their own success in preventing SSI through a similar retrospective analysis with risk‐stratified groups. Our methodology is certainly reproducible by other hospital systems looking to explore ways to improve post‐surgical outcomes for their patients and concomitantly reduce care costs. The results of those analyses would likely lay the groundwork for future studies exploring the potential benefits of alternative closure methods and/or materials.
Our study does carry limitations that require addressing. Given the data collected spans 15 years, it is reasonable to expect that changes in surgical skill or technique might have occurred throughout this timeframe, likely influencing the incidence of SSIs. However, that is not limited to our study and is a valid expectation in all cohort studies reviewing the incidence of SSI over time. Moreover, given this is a medical chart review analysis, it accompanies all limitations inherent to a retrospective study. These potential limitations include incomplete or inconsistent documentation at the time of each surgical case and errors in data gathering attributed to the data retrieval software utilised. However, based on large sample size and even distribution of data, we find this retrospective review to be reliable.
5. CONCLUSION
SSI can be an unfortunate and costly post‐operative complication. Risk factors in the past have been studied, but introspection by each institution is an important metric to ensure accountability and provide optimal patient care in comparison with established data and guidelines. This study highlights that at our institution, neurosurgical wound infections is comparable to various reported literature and data on the same topic. In fact, when analysed, our rates were statistically significantly lower than reported averages. Therefore, no necessary deviation from current techniques, such as the implementation of antibiotic sutures usage is of necessity considering our institution exceeds the standard of care and does so without paying the elevated cost for antibiotic sutures compared to the price of non‐antibiotic sutures. However, a future study could replicate other studies by directly comparing SSI in non‐antibiotic suture cohort versus antibiotic suture cohort to find if there is an institutional benefit. The manner in which this study was conducted was deemed both reliable and sound and would serve as a framework for other institutions to replicate and analyse their own SSI for quality improvement.
CONFLICT OF INTEREST
The authors declare no potential conflict of interest.
Fiani B, Cathel A, Sarhadi KJ, Cohen J, Siddiqi J. Neurosurgical Post‐Operative Wound Infections: A retrospective study on surgical site infections for quality improvement. Int Wound J. 2020;17:1039–1046. 10.1111/iwj.13367
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