Underestimation of postoperative ileus as a benign complication in spine surgery: a case-control study in a major spine surgery centre in Saudi Arabia

Introduction

With the increasing prevalence of complex spine surgeries, cases of postoperative ileus (POI) have become more prominent (1-4). POI is a recognized complication of spine surgery. While various definitions exist in the literature, most experts concur that it represents a temporary physiological condition characterized by a reversible slowdown in gastrointestinal tract movement following surgery (5). POI is a common postoperative complication, affecting approximately 3.5–12% of patients who undergo all types of spinal procedures (6). POI can lead to symptoms such as abdominal distention, vomiting, nausea, delayed bowel movements and passing of gas, as well as postponed resumption of oral intake. This can result in extended hospital stays for patients. These consequences can place additional strain on the health care system and reduce patient satisfaction after surgery. Normally, small intestine motility resumes within a few hours after surgery, while colonic motility returns within 48 hours. However, if this condition lasts for over 48 hours, it is considered a pathological condition (3).

The causes of POI are multifaceted and include factors such as surgical stress, release of inflammatory agents, presence of natural opioids in the gastrointestinal tract, alterations in hormone levels, and imbalances in electrolytes and fluids (5). It is important to distinguish POI from mechanical obstruction, which is a more common occurrence after abdominal surgery (6). Notably, POI can also follow procedures that do not involve breaching the peritoneum, particularly spine surgeries (7). These intricacies emphasize the limited available information on the incidence and risk factors for POI after spine surgery. While certain studies have reported on the occurrence and potential contributing factors of POI following spinal surgery, there remains a dearth of definitive research on its frequency; thus, the underlying mechanisms of POI after spinal surgery remain largely uncharted territory (4). To the best of our knowledge, there has never been any study to showcase the risk of POI following spine surgery in the Middle East. In addition, the characterization of surgical procedures and various risk factors has not been done together in a single study before this. We present this article in accordance with the STROBE reporting checklist (available at https://jss.amegroups.com/article/view/10.21037/jss-25-23/rc).

Methods

This study utilized a case-control method. Every file of patients who underwent spine surgery in King Abdulaziz Medical City was obtained for the period 2016–2022. We manually screened for those who developed POI and selected a near-matched cohort of those who did not develop POI using a random computer selection method. Our POI cohort was required to have evidence of POI on documentation as per the reviewed standard POI definition. We excluded patients with any previous spine surgeries and any medical condition known to be related to developing POI (e.g., constipation, biliary and renal colic, and cardiopulmonary failure). Furthermore, we have excluded anterior lumbar surgeries. Finally, we also excluded any oncology-related and infectious spine cases.

The following risk factors and outcomes were assessed in each patient: age, sex, and smoking and alcohol history. In addition, our data collection included comorbidities, surgical indication (e.g., trauma, scoliosis, and degenerative disease), pre-operative and post-operative medications used, post-operative bowel regimens used, blood transfusions, perioperative blood work (e.g., albumin, hemoglobin, and creatinine), as well as intensive care unit (ICU) admission and mobilization documentation.

Ethical statement

This study was approved by the Institutional Review Board of King Abdullah International Medical Research Centre, Riyadh, Saudi Arabia (protocol number NRC 21R/181/05) and individual consent for this retrospective analysis was waived due to the retrospective nature. The study was conducted in accordance with the Declaration of Helsinki and its subsequent amendments.

Statistical analysis

A bivariable analysis was employed to identify POI cases and controls related to risk factors. Categorial data are presented as frequencies and percentages, while continuous data are presented as means and standard deviations (SDs). Categorical data was analyzed using a Chi-squared test, and continuous data was analyzed using Student’s t-test. The standard Student’s t-test was applied for continuous variables, based on the assumption of equal variances between groups. To validate the appropriateness of this test, the distribution of continuous variables was assessed using the Shapiro-Francia test and the Lilliefors test. Categorical and continuous analyses were conducted with multivariant logistic regression models adjusted for documented risk factors. A value of P<0.05 was considered statistically significant at a 95% confidence interval (CI). Data collection and analysis were performed using Microsoft Excel (Microsoft Corp., Redmond, WA, USA) and IBM SPSS Statistics for Windows, version 26.0 (IBM Corp., Armonk, NY, USA).

Results

A total of 294 patients who met the criteria underwent spine surgery from 2016 to 2022, out of which 40.8% developed POI (Table 1). The female gender accounted for most POI cases at 75% vs. 54.6% for the non-POI group (P<0.001). Mean age ± SD was 40.5±22.35 and 46.1±20.96 years for POI and non-POI, respectively (P=0.03). The mean body mass index (BMI) ± SD in the POI group was 27.049±8.47 and 28.16±6.91 kg/m² in the non-POI group (P=0.21). Table 1 presents baseline factors and comorbidities, with asthma being significantly associated with POI development [15% vs. 2.9%, odds ratio (OR) =5.9, 95% CI: 2.14–16.55, P<0.001]. Interestingly, diabetes was found to be protective against POI (20% vs. 33.9%, OR =0.48, 95% CI: 0.28–0.842, P=0.009). The use of narcotics (43.3% vs. 40.2%) and PPI (50.8% vs. 46.6%) was not associated with POI development (P=0.59 and P=0.47, respectively).

In Table 2, various perioperative medications are illustrated as analgesia and bowel preps. Fentanyl was associated with POI development (97.5% vs. 85%, OR =6.89, 95% CI: 2.03–23.35, P<0.001). Patient-controlled analgesia (PCA) morphine also had a significant association (65% vs. 49.4%, OR =1.9, 95% CI: 1.17–3.06, P=0.008). On the other hand, the use of nonsteroidal anti-inflammatory drugs (NSAIDs), gabapentin, and Percocet was associated with lower incidence of POI development; however, the sample size in each group is exceedingly small to draw a clinical correlation. With regard to bowel prep, only glycerin (73.3% vs. 42%, OR =3.805, 95% CI: 2.2–6.3, P<0.001) and enema (66.7% vs. 28.2%, OR =5.1, 95% CI: 3.0–8.4) use was statistically associated with POI.

Surgical features and postoperative outcomes

Table 3 presents various surgeries performed per the main spinal segments. The most common surgeries performed were those for degenerative spinal canal stenosis (n=104), scoliosis (n=87), trauma (n=70), disc herniation (n=45), spondylolisthesis (n=42), degenerative disc disease (n=26), and spondylosis (n=4). It is important to note that numerous patients have overlapping concurrent diseases (such as degenerative vertebrae with stenosis) and, thus, we grouped them into isolated scoliosis (n=84), isolated trauma (n=70), and grouped all other diseases under “degenerative disc disease” (n=140). Scoliosis was the only statistically significant type to be strongly associated with POI development (45% vs. 19%, OR =3.49, 95% CI: 2.07–5.89, P<0.001). Similarly, in terms of spine location, there was an overlap in disease location, with lumbar being most common (n=253), followed by thoracic (n=137), and cervical (n=13). Isolating only vertebral areas for analysis could not be done due to the nature of diseases (i.e., scoliosis spanning the end of the thoracic and beginning of the lumbar). Thoracic has the highest POI association (61.7% vs. 36.2%, OR =2.83, 95% CI: 1.75–4.58, P<0.001), followed by lumbar (90.8% vs. 82.8%, OR =2.064, 95% CI: 0.991–4.302, P=0.049). Lumbar significance barely crossed p value significance, and the true range for the significance of both might be revealed upon isolation. Spine fusion (95% vs. 78.7%) and an increasing number of levels fused [7.35 (SD =4.66) vs. 5.34 (SD =3.89)] are both associated with POI development (both P<0.001). Finally, an increase in surgery duration is statistically significant for the presence of POI [mean 5.09 (SD =1.75) hours vs. mean 4.23 (SD =2.14) hours, P<0.001].

Table 4 presents the postoperative outcomes. Classical signs and symptoms of ileus such as nausea, vomiting, delay in passing motion, abdominal distention, delay in passing flatus, and imaging evidence are all evident and predictive of ileus development (Table 4). ICU admission and duration were not associated with ileus development (P=0.60 and P=0.79, respectively). With regard to mobilization, there was no difference when mobilizing early (day 0, P=0.09; day 1, P=0.15; day 2, P=0.82) for POI development. Further, post-op blood transfusion was significant for the development of ileus (19.2% vs. 8.6%, OR =2.51, 95% CI: 1.25–5.05, P=0.008). Table 5 presents various pre- and post-operative laboratory values. A decrease in pre- and post-op hemoglobin levels was associated with POI development (mean ± SD levels: pre-op, 125.3±17.49 vs. 131.2±17.9, P=0.005; post-op, 102.38±16.1 vs. 112.85±19, P<0.001).

Regression analysis

We performed a multivariable logistic regression analysis to identify independent predictors of POI. The model included age, gender, gastroesophageal reflux disease (GERD), diabetes, asthma, intraoperative blood loss, length of hospital stay, surgery duration, ICU admission, number of levels fused, and early mobilization. ORs and 95% CIs were calculated for each predictor. We selected variables based on clinical relevance and significant findings from bivariable analysis. The final model showed asthma was statistically significant for developing POI (OR =4.984, P=0.004, 95% CI: 1.67–14.82) as well as increasing levels of fusion (OR =1.13, 95% CI: 1.025–1.246, P=0.01). Diabetes continued to be associated with a lower incidence of POI development when controlled for the above variables (OR =0.404, 95% CI: 0.188–0.869, P=0.02) (Table 6).

Discussion

Our results demonstrate that almost half of the spine cases included in our study were associated with POI. Notably, asthma was the most significant risk factor for developing POI, even when adjusted with regression analysis. The female gender was also univariately significant; however, the significance was not apparent in regression. From a surgery perspective, scoliosis had the highest association, most prominently in the thoracic region. Numerous studies have been conducted to showcase unique risk factors for developing POI in spine surgeries in the literature. Prominently, Kiely et al. conducted a study on demographic and laboratory risk factors in addition to comorbidities (3). Moreover, Ohyama et al. found POI corresponds to the degree of mechanical correction (8). Another paper by Al Maaieh et al. focused on the anatomical fusion approach as a risk factor (9). Further, Yilmaz et al. conducted a retrospective case-control study that illustrated that patients with POI were at a higher risk of ICU management, readmission, and delayed hospital discharge (5). Additionally, POI was highly associated with length of hospital stay, lumbar surgery, and major spine surgery of more than three levels. In 2019, Wright et al. found that from among 174 patients who underwent adult complex spine surgeries, 32 (18.4%) were identified as having POI. Moreover, patients who developed POI had a lower mean BMI and there was no difference between genders (P=0.871). They reported that postoperative deep vein thrombosis (DVT)/pulmonary embolism (PE) was surprisingly less frequent among patients with POI (10).

In addition, diabetes was peculiarly associated with a lower incidence of POI, even after controlling for other variables. This is unheard of, as much of the existing literature on POI from surgery, in general, is known to be a contributing risk factor (10,11). However, these studies are extrapolated from abdominal and general surgeries. Manipulation of the gastrointestinal tract can worsen the nerve damage from the already existing diabetes. For spine cases, this additional insult is not evident (11,12). In spine literature, diabetes was insignificant in Yilmaz’s cohort. A few aspects can explain our result. First, documentation errors could have explained this, and we took necessary precautions to double-check the past medical history of all patients. Second, many of the patients, particularly the younger ones, could have good control of their levels with medications. Finally, the effect of spine surgeries on gastric nerve motility is minimal, as stated above, and diabetes might be insignificant or protective. More definitive studies are required to examine appropriate diabetes associations in spine surgery to confirm this finding.

POI poses a strain not only on patients but also in the form of a larger healthcare cost spectrum. These two factors intertwine through a long cascade of events. Patients who are diagnosed with POI often undergo prolonged hospitalization periods, which leads to increased healthcare costs and resource utilization. The financial implications are substantial, as revealed by the recent meta-analysis by Traeger et al. (13). From the patient’s perspective, a prolonged stay can lead to various complications—ranging from dehydration, electrolyte imbalances, infections, and, most seriously, an increased risk of thromboses (14). Efforts to mitigate the healthcare burden of POI revolve around prevention strategies and early detection. Enhanced recovery after surgery (ERAS) protocols, which include measures such as early ambulation—optimized pain management, and careful fluid administration—have shown promise in influencing the incidence and severity of POI, which can consequently reduce hospital stay and associated complications (15,16). It is important to note that many of these studies that examine POI burden were focused on abdominal surgeries, as spine-focused papers are scarce. A properly run registry that is prospectively collected should be present at major spine centers. These registries can provide details of the financial cost for each case, which may reveal spine-specific factors that are possibly overlooked otherwise. Our paper has limitations. First, the retrospective nature inherits its own bias and thus causality could not be established. Proper documentation relates to it as well, as patients could have been falsely labelled as POI or had their signs and symptoms not written. Second, we could not evaluate the proper trends in electrolyte disturbances and their timing with POI diagnosis postoperatively. Another limitation is the severity of POI was not addressed, as well as detailed management. Another limitation is the inclusion of hospital length of stay in our regression model. As POI may inherently increase hospital stay, this could introduce reverse causality and bias the associations observed. Future prospective studies should consider alternative designs or time-to-event analyses to better account for this potential bias.

Conclusions

In conclusion, this study sheds light on the significant prevalence and risk factors associated with POI following spine surgery, a complication that can lead to prolonged hospital stays and diminished patient satisfaction. This study found that almost half of the patients undergoing spine surgery developed POI. In addition, asthma was identified as the most significant risk factor for POI, while diabetes revealed an unexpected protective association. Additionally, scoliosis, particularly in the thoracic region, was strongly associated with POI. Perioperative factors such as the use of certain medications and bowel preparation techniques were also linked to POI development. These findings highlight the complexity of POI etiology in spine surgery patients and emphasize the need for tailored perioperative management strategies to mitigate this complication and improve patient outcomes.

Acknowledgments

A shortened abstract has been presented in 2023 as part of the Journal of Spine Practice local Saudi meeting for training residents and fellows.

Footnote

Reporting Checklist: The authors have completed the STROBE reporting checklist. Available at https://jss.amegroups.com/article/view/10.21037/jss-25-23/rc

Data Sharing Statement: Available at https://jss.amegroups.com/article/view/10.21037/jss-25-23/dss

Peer Review File: Available at https://jss.amegroups.com/article/view/10.21037/jss-25-23/prf

Funding: None.

Conflicts of Interest: All authors have completed the ICMJE uniform disclosure form (available at https://jss.amegroups.com/article/view/10.21037/jss-25-23/coif). The authors have no conflicts of interest to declare.

Ethical Statement: The authors are accountable for all aspects of the work in ensuring that questions related to the accuracy or integrity of any part of the work are appropriately investigated and resolved. The study was conducted in accordance with the Declaration of Helsinki and its subsequent amendments. The study was approved by the Institutional Review Board of King Abdullah International Medical Research Centre, Riyadh, Saudi Arabia (protocol number NRC 21R/181/05) and individual consent for this retrospective analysis was waived due to the retrospective nature.

Open Access Statement: This is an Open Access article distributed in accordance with the Creative Commons Attribution-NonCommercial-NoDerivs 4.0 International License (CC BY-NC-ND 4.0), which permits the non-commercial replication and distribution of the article with the strict proviso that no changes or edits are made and the original work is properly cited (including links to both the formal publication through the relevant DOI and the license). See: https://creativecommons.org/licenses/by-nc-nd/4.0/.

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