Surgical complications occur more frequently, often are more preventable, and their consequences can be more severe than other types of complications. Thus, predictive factors for surgical complications have been extensively studied. In a recent systematic review addressing predictive factors for the development of operative complications in adult patients undergoing gastrointestinal, vascular, or general surgery, Visser et al.[12] identified, categorized, and ranked various patient- and surgery-related risk factors for complications: prolonged operative time was considered among the top three surgery-related factors.
This evidence was confirmed by Cheng et al.[5] who reported on the association between operative duration and complications across various surgical specialties and procedure types, showing that likelihood of complications increased significantly with prolonged operative duration, approximately doubling with operative time thresholds exceeding 2 or more hours. Meta-analyses also demonstrated a 14% increase in the likelihood of complications for every 30 min of additional operating time.
In recent years, spine surgery has emerged as a critical intervention for addressing a myriad of spinal conditions; however, the complexity of these procedures often accompanies a risk of complications that can significantly impact patients’ outcomes and quality of life. In general, the complication rate after spinal surgery ranges between 7 and 20% [2][13][14]while orthopedic surgery generally has a mean rate of complications of 5%[2].
We recently classified adverse events occurring in a tertiary reference center for spinal surgery according to SAVES v2 system[9], [10]and analysed risk factors for surgical complications and prolonged length of hospital stay[3], highlighting the prevalent role of operative time longer than 3 hours as risk factor for complications. Our population included patients affected by oncological and degenerative spinal diseases mainly located at thoracic and lumbar level, but the same results were achieved by Ondeck et al[6] on a population undergoing a 1-level anterior cervical discectomy and fusion and by Hersey et al[15] who identified that longer operative duration was associated with more complications among patients ≥ 65 years undergoing posterior lumbar fusion procedures.
In the present study we proposed to further investigate on the relationship between surgical duration and adverse events via logistic regression models. In order to reduce the impact of other variables on surgical complications, we analyzed a population of patients surgically treated for degenerative spinal diseases in a single center, where confounding factors (diagnosis, comorbidities, type of surgery) were minimized. Although previous studies have noted that increased operative time (as a binary variable) is associated with the total rate of adverse events, most of them have not attempted to quantify the increased risk associated with greater operative duration across the entire range of operative times or been specific about which categories of adverse events are increased.
In our population surgical time was considered as continuous variable and was confirmed as a relevant risk factor for the occurrence of any complication across the spectrum of operative times.
At univariate analysis both CCI and ASA score did not result as risk factors for complications in our population of degenerative patients[3], in contrast with Withmore et al[16] who previously reported the association of increasing CCI and ASA grade with complications and societal costs in spinal surgery.
We observed here that lower scores of CCI (≤ 2) and ASA (≤ 2) and age less than 60 years old were associated with an increased surgical time (Table 4A-B). In fact, the age-related medical comorbidities affect not only the decision to undertake a surgical procedure but also the magnitude of the procedure and consequently its duration. In our study complicated and elderly patients were eligible for less complex and invasive surgeries, while healthier and younger patients usually underwent to longer surgical procedure in order to improve their overall survival and outcomes. Likewise, procedural times are often reflective of case complexity, another factor heralded as influential in the risk of complications. We observed that the rate of complicated patients increased with increasing operative time (Table 5 and Fig. 1) and almost all the intra-operative and post-operative adverse events occurred in surgeries lasting more than 2 hours (Table 6 and Fig. 2). As we found a significantly lower age, CCI and ASA score in the group of patients who underwent surgeries longer than 3 hours with respect to patients undergoing surgeries with OT less than 3 hours (Table 4A-B), the relevant increase of AEs can be attributed to increasing operative time and not to other possible influencing factors. We show that an increase of 30 minutes in operating time can increase the complication rate, even if a nonlinear increase of risk is observed across increasing time intervals (Fig. 3). Ondeck et al.[2] previously observed that each additional 15 minutes of operating time raised the risk for having any adverse events after anterior cervical discectomy and fusion by an average of 10%. In our population, patients were affected by degenerative spine diseases, mainly localized at thoracic and lumbar levels, and posterior stabilization with or without decompression was the most frequent surgery.
We observed that intra-operative complications as well as early and late post-operative complications were associated to prolonged operating time. Concerning intra-operative AEs,the most common was dural tear (6.7%). In spinal surgery, accidental dural tears have been documented as a noteworthy adverse event, with an incidence ranging from 0.4–15.8%[17]. Interestingly, centers conducting a substantial number of surgical procedures tended to report lower rates of dural tears, while those with fewer procedures reported higher incidence rates[3], [17], [18]. In our cohort 9 out of 14 dural tears occurred in operative time longer than 6 hours; this could be partially explained with an increase of the operative time due to the additional procedure of dural tear’s repair. In fact, Weber et al[19] investigated dural tears after elective spinal surgery and they reported that the operative time significantly increased from 116 minutes to 153 minutes when they occurred (P < .0001). Moreover, the occurrence of dural tear has been associated to other perioperative complications in spinal surgery[20]. When assessing operative time some intra-operative complications may not be the consequence of increased duration, but instead may be one of the contributing factors to increase time, and this is difficult to be quantified, as for massive blood loss intra-operative AE. “Major” or “massive” blood loss is defined as the loss of 1 volume of the patient’s total blood (60mL/kg in adults) in < 24 hours[21]. In our study this complication was recorded in 18.1% of patients with OT ≥ 3 hours in the oncological group. Generally, the first reason that can cause surgical blood loss is a hypervascularized tumor even if treated with a pre-embolization. In spinal procedures that require decompression, laminectomy can result in epidural bleeding.
Even if intra-operative complications could be a contributing factors for increasing operative time, numerous studies described a putative relation between longer operative time and post-operative complications, with an increased risk both for surgical and medical complications[1], [22]. Kim et al. [23], focusing on single-level lumbar fusion/instrumentation procedure, analyzed the effect of operative duration on postoperative adverse event showing that most postoperative complications exhibited a nonlinear increase in risk across the increasing groups. Similar to the findings by Kim et al, the current descriptive analysis showed that the risk of postoperative complications raised through surgical duration: early post-operative AEs were more common where OT was between 2 and 3.59 hours, while late post operative AEs were more frequent in OT interval times longer than > 4 hours. Thus, the surgical duration results to be strictly related to post-operative complications, that increase the length of hospital stay [3] and impair the clinical outcomes and the patient’s quality of life in the follow period, while impairing on healthcare system expenditure.
Early post- operative adverse events represent the most frequent category of complications in our cohort (135/206, 65.5%). Even if we used SAVES-V2 capture system to collect AEs, 83 out of 135 early post-operative complications fitted into the category “other”, comprehensive of a large variety of medical complications. Fever represented 11/83 early post operative adverse events with an onset of 2–3 days post-surgery. Seo et al[24] showed in their study that post-operative fever without infection in long operative or trauma surgery is a normal medical sequalae, caused by a greater degree of tissue inflammation. Oncological group showed several pulmonary complications (pneumonia and pleural effusion) into “other” category. As reported, the incidence of pulmonary complications following spine surgery for metastases ranged from 1 to 18%[25] and, this AE has been related to the prolonged anesthesia procedure.
Concerning late post-operative adverse events identified in this patients’ cohort, they result to be similar to those previously identified in elderly spine patients[26] and all patients undergoing spinal fusion[23]. For the oncological group deep wound infection represented 28.5% of adverse events associated with longer operative time. Operative time has also been cited as a risk factor for surgical deep wound infection in abdominal surgery. In spinal surgery, the correlation between deep wound infection and prolonged operative duration can be attributable to various time-related factors such as prolonged microbial exposure, diminished efficacy of antimicrobial prophylaxis over time, increased tissue retraction leading to tissue ischemia, necrosis, and desiccation, and increased opportunities for violations in sterile technique[5], [27]. Common mechanisms for construct failure, with or without loss of correction, registered in degenerative patients were rod breakage, pedicle screw pull-out, proximal junctional kyphosis (PJK) and proximal junctional failure (PJF). These types of complications occurred in particular in long spinal instrumentation.
Despite limitations due to the retrospective analysis and the small sample size, this study highlights the relevant problem of complications in spinal surgeries and its strong correlation with prolonged operative time, focusing on a homogenous cohort of patients treated in the same tertiary center by the same surgeons.