Treatment of Isolated Serosanguinous Incision Drainage after Thoracolumbar Surgery: Is Surgical Management Always Necessary?

Abstract

Background:

There is no consensus regarding how to care for a patient presenting with early isolated incision drainage after thoracolumbar spine surgery. Although drainage is the most common presenting symptom of surgical site infection (SSI), it has low specificity for SSI in the absence of other symptoms. Given that invasive treatment for SSI is costly and high risk, it would be beneficial to determine whether antibiotic treatment alone is sufficient for isolated drainage and what factors predispose to failure of this conservative strategy.

Methods:

The authors retrospectively reviewed a clinical database of patients who underwent thoracolumbar spine surgery at a single center between 2012–2017. Patients were included if serosanguinous drainage was present within six weeks of surgery without other signs and symptoms of infection such as fever, chills, purulent discharge, fluctuance, wound dehiscence, or erythema.

Results:

Fifty-eight patients met the study inclusion criteria. After initial conservative management with antibiotics, drainage resolved in 51 patients. The seven patients with drainage that did not resolve were treated with operative surgical washout. Although the groups were similar in most respects, there was a significant difference in the American Society of Anesthesiologists (ASA) score, which is a marker of overall health (surgical group score 2.89 ± 0.33 versus 2.06 ± 0.61; p < 0.0001). In addition, patients with greater estimated blood loss, length of hospital stay, operative time, and spinal levels treated were more likely to require surgical washout, although these differences were not statistically significant. Groups were similar with respect to age, Body Mass Index, smoking status, diabetes mellitus status, revision versus primary surgery, and drainage latency.

Conclusion:

Most patients who present with isolated serosanguinous incision drainage within six weeks of surgery may be managed successfully using antibiotics only. Patients who fail to respond to conservative therapy have significantly worse general health, as indicated by the ASA score.

Acute surgical site infection (SSI), defined as a hospital-acquired infection of the skin, soft tissue, or bone, is a common and potentially serious complication of lumbar spine surgery. This complication increases morbidity and mortality rates and often leads to poor surgical outcomes, additional surgery, and increased costs [1 -5]. It is the most common complication of lumbar decompression and microdiscectomy operations, affecting 0.9%–3.5% of patients [2,6]. Risk factors for an SSI are diabetes mellitus, ischemic heart disease, dysrhythmia, chronic liver disease, autoimmune disease, older age, and high body mass index (BMI) [2,4].

Cases of known SSI typically are treated aggressively with removal of instrumentation, surgical debridement with wide margins, and site irrigation followed by prolonged antibiotic therapy [3,7,8]. This approach often is instituted empirically, particularly if the patient has risk factors for treatment failure, such as delayed presentation, deep SSI, polymicrobial infection, or greater spinal levels of operation [3,7]. In the absence of these risk factors, however, studies have demonstrated that antibiotic therapy alone may be sufficient to achieve resolution of the infection [3,9].

Diagnosis of SSI often is clinical, with the most common presenting symptoms being fever, pain, erythema, swelling, warmth, tenderness to palpation, and incision drainage [9]. The clinical diagnosis of SSI based on these signs often is complicated, however, because few cases present with overwhelming positive clinical signs. Additionally, these signs may be present in benign post-operative conditions such as seroma [9,10]. On the basis of the current literature, the most common presenting symptom is serosanguinous incision drainage, but the specificity of this finding for the diagnosis of SSI in the absence of other symptoms of infection is low [10]. For this reason, many patients with presumed infection as judged by borderline clinical signs such as isolated drainage undergo empiric surgical debridement when antibiotic therapy alone would have been sufficient. Conversely, some patients with borderline clinical signs of SSI suffer a delay in surgical debridement after unsuccessful initial treatment with antibiotics alone. Avoidance of surgical debridement in patients with a benign etiology of drainage would be immensely beneficial, as it would reduce the morbidity and cost associated with additional surgery. However, delay of needed surgery could lead to poorer outcomes and progression of the infection.

In the present study, we sought to determine which patients would benefit most from antibiotic therapy or observation alone versus surgical debridement in the presence of early post-operative incision drainage without other clinical signs of SSI. This study was exempt from a need for Institutional Review Board approval.

Patients and Methods

The authors reviewed retrospectively the clinical data of adult and pediatric patients who underwent thoracolumbar spine surgery at a single center from 2012–2017. The patients were identified using a data-mining software program (Clinical Looking Glass, Streamline Health Solutions Inc., Atlanta, GA). Once relevant cases were identified, patient data were gathered manually from the notes in the electronic medical record.

Patients included in the study were those who underwent thoracolumbar spine surgery and presented with serosanguinous incision drainage at follow-up visit within six weeks of surgery. Patients were excluded if they were human immunodeficiency virus positive, taking immunosuppressive drugs, or presented with clear signs of SSI, including frank pus, induration, and erythema at the incision site.

All patients were treated initially with empirical antibiotics (defined as conservative treatment). Those patients who had persistent drainage or clinical worsening after two weeks of conservative treatment underwent surgical debridement/washout with 2 L of physiologic saline in addition to antibiotic therapy. Patients were grouped according to whether conservative treatment alone was successful at resolving the drainage or whether surgical intervention was needed. Variables that were analyzed were age, BMI, smoking status, diabetes mellitus status, revision versus primary surgery, number of levels operated on, estimated blood loss, total operative time, number of days in the hospital, latency between the operation and drainage, and American Society of Anesthesiologists (ASA) score (Tables 1 and 2). Variables in the two groups were compared using two-tailed t-tests.

Table 1.

Comparison of Variables between Washout and Non-Washout Groups

	Non-wash out group	Wash out group	p
No. of patients	51	7
Mean age (y)	33.82 ± 20.52	26.04 ± 20.43	0.37
Body Mass Index	28.55 ± 6.84	25.0 ± 8.13	0.35
Smoking status			0.94
Current	8	0
Former	6	0
Never	37	7
Diabetes mellitus status			0.29
Yes	5	2
No	46	5
Surgery status			0.10
Revision	6	3
Primary	45	6
No. of levels	7.22 ± 5.02	8.42 ± 4.86	0.56
Estimated blood loss (mL)	485.59 ± 415.44	664.3 ± 499.8	0.33
Operative time (min)	326.46 ± 187.20	451.3 ± 350.1	0.60
Total length of hospital stay (d)	5.24 ± 3.67	8.0 ± 4.93	0.60
Drainage latency (d)	15.00 ± 9.60	14.4 ± 12.5	0.20
Blood transfusions	6	1	0.85
Mean ASA score	2.06 ± 0.61	2.89 ± 0.33	<0.001

Table 2.

American Society of Anesthesiologists Classification Score

Class I	Patient is completely healthy and fit
Class II	Patient has mild systemic disease
Class III	Patient has severe systemic disease that is not incapacitating
Class IV	Patient has incapacitating disease that is a constant threat to life
Class V	Patient is moribund and not expected to live 24 h with or without surgery

Results

A total of 58 patients met the inclusion criteria. Twenty-nine patients were above the age of 18 at the time of surgery. After conservative management, serosanguinous incision drainage resolved in 51 patients (non-washout group). Seven patients had drainage that did not resolve with conservative management, requiring surgical washout (washout group). The mean follow-up time for all patients was 29.4 months, 27.0 months in the non-washout group and 46.7 months in the washout group.

Typical antibiotics regimens prescribed were 1–2 g of oral cephalexin for 10 to 14 days. Groups were similar in terms of age (non-washout group 33.82 ± 20.52 years versus washout group: 26.04 ± 20.52; p = 0.37), BMI (non-washout group 28.55 ± 6.84 versus washout group 25.0 ± 8.13; p = 0.35), smoking status (non-washout group eight current and 37 never smokers versus washout group seven never smokers; p = 0.94), diabetes mellitus status (non-washout group five yes, 46 no versus washout group two yes, five no; p = 0.29), type of surgery (non-washout group six revision and 45 primary operations vs. washout group three revision and six primary operations; p = 0.10), number of spinal levels operated on (non-washout group 7.22 ± 5.02 versus washout group 8.42 ± 4.86; p = 0.56), estimated blood loss (non-washout group 485.6 ± 415.4 mL vs. washout group 664.29 ± 499.8 mL; p = 0.33), operative time (non-washout group 326.5 ± 187.20 minutes versus washout group: 451.33 ± 350.51 minutes; p = 0.60), days in the hospital (non-washout group 5.24 ± 6.67 versus washout group 8.00 ± 4.93; p = 0.60), blood transfusion need (non-washout group six versus washout group one; p = 0.85), and drainage latency (non-washout group 15.0 ± 9.6 days versus washout group 14.4 ± 12.5 days; p = 0.20). Drainage latency was defined as the time between discharge and presentation to the clinic or emergency room with incision drainage.

Higher ASA score was a significant predictor of conservative treatment failure (non-washout group 2.06 ± 0.61 versus washout group 2.89 ± 0.3; p < 0.0001). Table 3 lists the systemic diseases present in patients who required surgical washout. Further characteristics describing the washout group are detailed in Table 4.

Table 3.

Systemic Diseases in Patients Who Underwent Surgical Washout

Patient	Systemic Disease(s)	ASA Score
1	Asthma, ulcerative colitis, chronic cystitis	3
2	Asthma	2
3	Spinal muscular dystrophy Type 2	3
4	Cerebral palsy	3
5	Diabetes mellitus Type 2, chronic kidney disease, non-alcoholic liver disease, hypertension	3
6	Cerebral palsy, epilepsy	3
7	Diabetes mellitus Type 2, anxiety disorder	3

Table 4.

Characteristics of Patients Having Washout

Patient	Incision Culture Results	Closure
1	Negative	Primary
2	Methicillin-sensitive Staphylococcus aureus	Primary
3	Methicillin-sensitive S. aureus	Primary
4	Polymicrobial	Paraspinal flap
5	S. epidermitis	Paraspinal flap
6	Pseudomonas and S. epidermidis	Primary
7	S. epidermidis	Primary

Instrumentation was retained in all patients.

All but one patient had a positive wound culture that yielded methicillin-sensitive S. aureus (n = 2), S. epidermidis (n = 2), Pseudomonas, S. epidermidis (n = 1), or unspecified polymicrobial (n = 1). All patients had mild or moderate amounts of pus and a small quantity of blood at the operative site on washout. Two patients underwent paraspinal flap closures of the incision. Five patients underwent primary closure of the incision after washout. All patients retained instrumentation, and no patient required an additional spine operation during the follow-up period.

Discussion

The present study sought to determine whether patients who present with a questionable diagnosis of SSI evidenced only serosanguinous incision drainage could be managed effectively with antibiotic therapy alone and to identify factors associated with failure of this strategy. A variety of variables, including demographic data (age, gender, BMI), known pre-operative risk factors for incision complications (ASA score, diabetes mellitus status, smoking status, and revision surgery), intra-operative parameters (operative time, estimated blood loss, number of spinal levels operated on), and post-operative parameters (length of hospital stay and drainage latency), were investigated. After statistical analysis, the ASA score was found to be significantly higher in patients who failed conservative management.

The ASA score, also known as the ASA physical status classification, was developed in 1963 as a tool to allow anesthesiologists to stratify patients on the basis of the severity of their illnesses [11]. The score was intended to be used a predictive tool to identify patients who might experience complications both intra-operatively and post-operatively. It is a subjective assessment typically performed by the attending anesthesiologist and includes five classes (see Table 2). “E” is placed after the roman numeral to indicate that the anticipated surgery is an emergency operation.

The ASA score is intended to measure the physical status, severity of existing medical disease, and physiologic stability of the patient [11 -14]. Moreover, the score has been shown to be a significant predictor of surgical morbidity and death in several studies [15 -18]. It has proved to be a valuable tool for predicting post-operative outcomes in patients undergoing spinal surgery. One 2017 study investigated the predictive value of several variables, including ASA score, in patients undergoing elective lumbar spine surgery and concluded that higher ASA scores were a statistically significant predictor of increased disability, reduced quality of life, and persistent back and leg pain 12 months after surgery (p < 0.0001, p < 0.0001, p = 0.0002, and p = 0.0049, respectively) [19]. Another 2017 study using the Quality Outcomes Database sought to identify factors that predicted time to return to work after lumbar surgery for degenerative disc disease. The investigators included 4,694 patients and concluded that higher ASA scores significantly predicted delayed return to work after surgery (p < 0.008) [20].

The ASA score also has been demonstrated to predict incision infections well after a variety of surgical procedures. One study reported on a cohort of 382 patients undergoing abdominal surgery of various degrees of acuteness and with various incision classes (clean, clean-contaminated, etc.) who received antibiotic prophylaxis with cefotaxime and metronidazole. The ASA score and incision category significantly predicted the likelihood of a post-operative incision infection (p = 0.002 and p = 0.034, respectively) [21]. Other observational studies involving a broad range of patients, procedures, and antibiotic protocols also have shown the ASA score to be a significant predictor of post-operative incision infection [22,23].

The ASA score considers the impact of systemic disease on the patient's overall health. Given that SSIs occur when bacterial pathogens overwhelm host immune defenses, higher ASA scores, which imply reduced global health, may correlate with impaired host immune defenses. Conservative management of post-operative drainage with antibiotics in the setting of incision management relies at least partly on host immune defenses. Reliance on host defenses is more critical when conservative treatment does not include antibiotics. Reduced host immune system function in patients with compromised global health may explain the greater propensity for failure of conservative treatment in patients with higher ASA scores in our study.

Patients who underwent surgical washout in our study presented to the clinic with serosanguinous incision drainage that was comparable to that of those who did not receive washout. However, there were several statistically insignificant, but nonetheless notable, differences in the pre-operative characteristics of these groups. Specifically, the mean estimated blood loss was roughly 200 mL greater in the washout than the non-washout group (p = 0.33). Similarly, patients in the washout group had an average operative time more than 100 minutes longer than the non-washout group (p = 0.60). Finally, the average hospital stay in the washout group was an average of 2.7 days longer than in the non-washout group (p = 0.20). Although these differences may not be statistically meaningful, they do indicate that our study population obeys the rule that several previously recognized risk factors increase the likelihood of post-operative SSI.

Our analysis has several limitations that must be acknowledged. These include a relatively small cohort, which reduced the statistical power of our study. Our study also included data from a single institution, which may limit the generalizability of our findings to clinical centers with significantly different patient demographics. Future studies might seek to investigate which patients who present with serosanguinous drainage would benefit from dry dressings alone versus antibiotics and whether the drugs should be orally versus intravenously administered.

In conclusion, our study demonstrates that the majority of patients who present with isolated incision drainage within six weeks of thoracolumbar spine surgery can be managed effectively with antibiotics alone. Those patients who failed conservative management and required invasive treatment for SSI had significantly worse overall health, as indicated by a higher ASA score. Surgeons faced with the decision of proceeding to the operating room in instances of isolated drainage therefore are advised to attempt conservative management in patients with general overall good health and to consider higher ASA scores as an indicator of the likely need for surgical management.

Author Disclosure Statement

The authors have no conflicts of interest with regard to this manuscript.

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