Postoperative drains have been used by surgeons to minimize complications of lumbar spine surgery in over 10% of patients [1]. However, the use of postoperative drains continues to engender significant debate over their efficacy and impact on patient outcomes. The primary theoretical benefit of drain utilization is minimization of hematoma formation, which may reduce postoperative pain, neurologic compression, and reduce the risk of surgical site infections (SSI) [2,3]. While drains can reduce the saturation rate of wound dressing and the incidence and size of postoperative hematomas, the risk of anemia and allogeneic blood transfusions increase [4–8]. Additionally, clinical outcomes, hematoma formation, or SSI are not significantly different between patients with and without drains [9,10].

Drains continue to be used in spine surgery despite the greater risk of blood loss and the subsequent elevated transfusion rates, as well as retained drain fragments requiring reoperation and cerebrospinal fluid (CSF) leaks [11,12]. The relationship between drain utilization and increased transfusion requirements may increase the risk for SSI due to immunosuppressive response to the allogeneic blood [4,8,13]. Currently, there is conflicting evidence regarding the increased risk of SSI due to drain placement, although most evidence points to no significant differences based on drain use [7,14–16].

At present, a consensus on protocols for the management of postoperative lumbar spine drains is lacking, specifically for determining when they should be used and when they should be discontinued [2]. Therefore, this study was aimed to determine whether specific drain usage variables can predict hospital readmission, postoperative blood transfusion, or postoperative anemia.

Of the 1,166 total patients included in the cohort, there were 111 (9.5%) hospital readmissions, of which 44 were classified as surgical complications and 38 required reoperation. Of those with a reoperation, five were for symptomatic hematomas and 16 were for SSI. The remaining reoperations were unrelated to drain placement and included persistent CSF leaks that occurred during the surgical procedure and recurrent stenosis. Of the remaining hospital readmissions not deemed surgical complications, none required blood transfusions or required supportive measures due to perceived hypotension potentially caused by the surgery or drain placement. Patients who were readmitted had a higher CCI (1.16 versus 0.77, p<0.001) as well as decreased penultimate 8-hour drain output (39.4 mL versus 40.8 mL, p=0.030). There were no other significant differences among groups (Table 1).

When stratifying by the final 8-hour drain output, 344 patients (29.5%) were placed into the GDO group, while the remaining 822 (70.5%) were in the LDO group. By definition, the final 8-hour drain output was larger in the GDO group (65.6 mL versus 14.9 mL, p<0.001) than the LDO group. However, demographic characteristics, hospital readmissions (GDO [7.85%] versus LDO [10.2%], p=0.251), postoperative blood transfusions (GDO 7.85% versus LDO 9.25%, p=0.513), or postoperative anemia (GDO 13.4% versus LDO 16.1%, p=0.283) were not significantly different (Table 2).

When recategorizing patients by drain duration, 480 patients (41.2%) had a drain duration longer than 2 days, while 686 (58.8%) had a drain duration of 2 days or less. The >2-day drain duration group was significantly older (65.1 years versus 63.4 years, p=0.029) and had a higher proportion of women (54.2% versus 46.1%, p=0.008), significantly longer length of hospital stay (4.86 versus 2.99, p<0.001), more levels fused (2.31 versus 1.57, p<0.001) and decompressed (2.33 versus 2.05, p<0.001), and higher rate of postoperative blood transfusions (15.6% versus 4.08%, p<0.001) and postoperative anemia (21.9% versus 10.6%, p<0.001). Meanwhile, readmission rate was not significantly different between groups (>2 days [10.2%] versus ≤2 days [9.04%], p=0.569) (Table 3).

Results of multivariate logistic regression analysis revealed that none of the drain variables were independent predictors of hospital readmission, postoperative blood transfusion, or postoperative anemia (Table 4). An ROC curve was generated for each drain variable with the goal of predicting hospital readmission. The last 8-hour drain output had the highest AUC with a value of 0.524 (sensitivity, 61.3%; specificity, 49.9%) (Fig. 1). ROC curve analysis aimed at identifying risk factors for postoperative blood transfusions found drain duration to have the highest AUC, with a value of 0.729 (sensitivity, 72.8%; specificity, 61.9%) (Fig. 2). Similarly, ROC curve analysis targeted at identifying the greatest predictor for postoperative anemia found drain duration to have the highest AUC, with a value of 0.646 (sensitivity, 58.9%; specificity, 62.0%) (Fig. 3, Table 5).

Drains have historically been used after spine surgery to reduce postoperative epidural hematomas that can potentially compress the spinal cord or nerve roots. These complications are associated with significant patient morbidity and can lead to increased health care costs and resource utilization [17]. However, the utility of postoperative drains in preventing wound complications and readmissions in spinal surgery has been controversial [14,18]. Our data suggest there may not be a benefit to drain usage in decreasing readmission rates, and the majority of drain variables were more accurate in predicting postoperative blood transfusions or anemia rather than hospital readmission.

In 2005, a retrospective database study of 14,932 patients undergoing spinal surgery found that drains were not associated with a decreased risk of postoperative spinal epidural hematoma [19]. Instead, multiple operative levels, anemia, and excessive blood loss were predictive of epidural hematoma formation, the results of which have been corroborated by a National Surgical Quality Improvement Program study of 75,878 lumbar decompression procedures [20]. A multicenter study has also questioned the degree to which drains reduce development of epidural hematomas, citing that symptomatic hematomas still occurred in the majority of patients managed with postoperative drains [21]. Accordingly, patient selection and perioperative factors such as medical management of bleeding and surgical hemostasis may play a more significant role than drains in reducing SSI and hematoma formation. While a prospective randomized study demonstrated that both the incidence and size of postoperative hematomas decreased after a drain was inserted following lumbar disc surgery and that late clinical outcomes were not significantly different between patients with and without a drain, the incidence of symptomatic hematomas or SSI was not determined [6]. Therefore, postoperative drains do function to reduce the size of postoperative hematomas, but their use does not appear to have clinical relevance in reducing postoperative complications from the hematoma formation.

Despite the aforementioned evidence, many surgeons continue to postoperatively use drains. Therefore, evidence-based guidelines should be established to determine how long drains need to remain in place when used postoperatively. A retrospective case-control analysis of SSIs following posterior spine fusion found that the risk for SSI increased for every 1.6 days that a drain was present [15]. Another retrospective case-control study of both laminectomy and fusion procedures identified drain duration of greater than 3 days as a risk factor for SSI [22]. Our study found that using a 2-day threshold for drain removal was not associated with an increase readmission rate after surgery. Additionally, multivariate regression and ROC analysis utilizing drain duration as a continuous variable demonstrated that removing a drain after 2 postoperative days was not an effective predictor of hospital readmission (AUC: 0.494), but it was a strong predictor of requiring postoperative blood transfusion (AUC: 0.729). This has major implications for clinical practice, especially for the patient who are medically cleared for discharge but remain in the hospital due to the presence of a drain. These findings also suggest that drains in lumbar spine surgery can be removed within the first 2 days regardless of drain output without increasing complication rates including readmission. Further, our results demonstrate that patients in the GDO group had drains in place for a significantly shorter period of time and had a shorter hospital stay, while patients with drains maintained for greater than 2 days had significantly longer lengths of stay. A retrospective cohort study of multilevel anterior cervical discectomy and fusion in 321 patients similarly observed an almost two-fold longer length of stay for patients with postoperative drain placement. Moreover, the incidence of postoperative hematomas or SSI were not significantly different in patients with and without drains [23].

While many studies have compared the absence or presence of a drain, none have proposed recommended thresholds for removal based on drain output volumes. A retrospective case-control study found that postoperative drain output was a risk factor for symptomatic epidural hematomas (SEH) after lumbar decompression. However, the mean drain output for patients that developed SEH was actually less than patients that did not develop SEH [24]. While the exact reason for this finding is unclear, it could be possible that those who developed SEH may have had technical issues with their drains. Regardless, it complicates the interpretation of drain outputs in the postoperative spine patient. Drains are susceptible to many technical issues once placed, including loss of suction, clotting of the drain, or unintended premature removal. An additional retrospective case-control study found that the most important tool for early diagnosis of postoperative epidural hematomas was the clinical evaluation, not drain output [19]. In our study, we collected data on the drain output over the last 8-hour shift prior to drain removal and the penultimate 8-hour period and found that the GDO group did not have a higher incidence of readmissions, readmissions due to wound complications, or surgery if they were readmitted. Furthermore, multivariate regression and ROC analysis demonstrated that drain output over the last 8-hour shift was not an effective predictor of readmission. The findings of the present study are consistent with those of other studies that have demonstrated that drains do not significantly influence rates of symptomatic hematoma formation, neurologic deficit, or SSI, in that the maximum drain output or minimum drain duration are not necessary clinical parameters to determine when to pull drains [25,26]. If surgeons are inclined to place a postoperative drain, the drain may be pulled on the first postoperative day without concern for increasing postoperative complications. Further, early drain removal may minimize blood loss, while reducing the hospital length of stay.

The study had some limitations, including those inherent to retrospective study design. Wound drainage that did not require a revision surgery and the preoperative use of anticoagulants were not evaluated. While general comorbidity indexes were compared, specific factors such as tobacco use, diabetes, malignancy, history of spine trauma, and prior spine surgery have been identified as potential risk factors for increased postoperative bleeding and wound complications and these were not specifically evaluated in our analysis [15,19,20,27,28]. Further, on ROC analysis, surgical characteristics, such as the number of levels fused or decompressed, were not adjusted, which might have introduced bias to our findings. Therefore, while this study may be generalizable to short construct lumbar fusion, our data should be cautiously interpreted for longer construct lumbar fusions or thoracolumbar fusions, especially for adult deformity procedures.

Drain output and drain duration are not accurate predictors for postoperative complications or hospital readmission due to hematoma formation. Surgeons should consider prompt removal of drains, especially in short construct lumbar fusions, to minimize blood loss and hospital length of stay.