The impact of stratified hypoalbuminemia and dialysis on morbidity/mortality after posterior spinal fusion surgery: An ACS-NSQIP study.

Background: Preoperative optimization in patients undergoing posterior spinal fusion is essential to limit the number and severity of postoperative complications. Here, we, additionally, evaluated the impact of hypoalbuminemia on morbidity and mortality after posterior spinal fusion surgery.
Methods: This retrospective analysis was performed using data from a prospective multicentric database (ACSNSQIP:2015-2020) regarding patients undergoing posterior spinal fusions. Factors studied included; baseline demographics and 30-day postoperative complications (i.e., reoperations, readmissions, and mortality rates).
Results: There were 6805 patients who met the inclusion criteria. They averaged 62 years of age and had an average BMI of 30.2. Within the 30-day postoperative period, 634 (9.3%) sustained complications; 467 (6.9%) were readmitted, 263 (3.9%) required reoperations, and 37 (0.5%) expired. Although multiple preoperative risk factors were analyzed, hypoalbuminemia, severe hypoalbuminemia, and dialysis were the strongest independent risk factors associated with complications (i.e., reoperations, readmissions, and mortality).
Conclusion: Hypoalbuminemia, severe hypoalbuminemia, and dialysis were significant predictors for morbidity and mortality after posterior spinal fusion surgery. Copyright:

INTRODUCTION

Multiple preoperative risk factors have already been identified as contributing to postoperative complications following posterior spinal fusions.[1,3,4] These have typically included; older age, elevated BMI, and multiple medical comorbidities. Here, however, we, additionally, analyzed the negative impact of hypoalbuminemia/severe hypoalbuminemia on the 30-day postoperative reoperation, readmission, and mortality rates following posterior spinal fusions.

MATERIALS AND METHODS

Study design and criteria

This was a descriptive retrospective study performed using the American College of Surgeons’ National Surgical Quality Improvement Program (ACS-NSQIP) database for patients undergoing posterior spinal fusions for degenerative disease/ deformity between 2015 and 2020. Patients were selected based on primary Current Procedural Terminology codes, then further filtered based on International Classification of Diseases 9 and 10 codes [Table 1]. Exclusion criteria included simultaneous anterior spinal fusions or insufficient perioperative/postoperative data.

Table 1:

ICD 9th and 10th codes and CPT codes.

Baseline characteristics

Between 2015 and 2020, 6805 of 16,219 patients from the NSQIP database undergoing posterior spinal fusion met our inclusion criteria. The 3455 males and 3350 females averaged 62 years of age [Table 2]. Multiple clinical and preoperative comorbidities were identified, including dialysis status. Patients were classified based on preoperative albumin levels into three groups; normoalbuminemia, ≥3.5 g/dL; mild hypoalbuminemia, <3.5 and >2.5 g/dL; and severe hypoalbuminemia ≤2.5 g/dL. The most common spinal fusion location was the lumbar followed by the cervical spine. The overall complication rate, unplanned readmission rate, reoperation rate, and mortality rates occurring within 30 days postoperatively were all recorded [Table 3].

Table 2:

Baseline general and per group parameters.

Table 3:

Univariate analysis of complications, reoperation, and readmission.

Statistical analysis

Outcomes were analyzed utilizing univariate analysis based on demographics, preoperative comorbidities, and other surgical variables. Comparisons were performed using Chi-square tests, Fisher’s exact tests, or Student t-tests.

RESULTS

Overall complications, wound-related complications, and mortality

Notably, 634 patients (9.3%) suffered at least one postoperative complication [Table 2]. The three most common complications included; wound-related complications in 167 patients (2.3%; superficial wound infections comprising 1.3% of these), urinary tract infections (1.7%), and pneumonia (1.3%). Univariate analysis showed significant differences in complication rates among patients in the mild hypoalbuminemia and severe hypoalbuminemia groups versus those with normoalbuminemia [Table 3]. Multivariate analysis demonstrated that mild and severe hypoalbuminemia were also significantly associated with overall complications, but not with significant wound complications [Table 4]. The mortality rate was 0.5% (i.e., 37 patients) within 30 days postoperatively and was significantly associated with mild hypoalbuminemia (OR = 3.4), severe hypoalbuminemia (OR = 8.9), and dialysis (OR = 4.5) [Table 4].

Table 4:

Multivariate analysis of overall complications and mortality.

Reoperation and readmission

There were 467 patients (6.9%) who had unplanned readmissions within the 30-postoperative days, with 263 (3.9%) requiring reoperations. Dialysis was the main risk factor for both readmissions (OR = 5.4, P = 0.00) and reoperations (OR = 3, P = 0.025) while hypoalbuminemia was not (i.e., based upon multivariate analysis) [Table 5].

Table 5:

Multivariate analysis for reoperation and unplanned readmission.

DISCUSSION

Albumin’s role in healing process

In our study, mild hypoalbuminemia and severe hypoalbuminemia were significantly associated with higher rates of overall complications and mortality compared with normoalbuminemic patients undergoing posterior spinal fusions. These findings are consistent with existing literature.[5,10] However, we did not find an association between hypoalbuminemia and wound-related complications on multivariate analysis. Gelfand et al.[4] analyzed the impact of hypoalbuminemia and severe hypoalbuminemia in 700 patients undergoing surgery for metastatic spine disease; they found a direct correlation between lower albumin levels and 30-day mortality rates.

Other studies have demonstrated albumin’s role in the healing process and associated hypoalbuminemia with wound-related complications.[6,8] He et al. showed a significant correlation between lower albumin levels and delayed wound healing in 554 patients undergoing single-level posterior lumbar fusion surgery.[6] Others found low albumin levels contributed to higher risks of major complications in spine surgery.[9]

No association between hypoalbuminemia and reoperations/unplanned readmission

Interestingly, we found no significant association between hypoalbuminemia and reoperations or unplanned readmissions. Alternatively, Phan et al.,[9] in an ACS-NSIQP study of 2410 patients undergoing elective posterior lumbar fusions, found significantly higher unplanned readmission rates, hospital length of stay, and perioperative complications for those with low albumin levels, while others viewed similar findings with cervical surgery.[8]

Impact of dialysis

In our study, dialysis was an independent risk factor significantly contributing to complication, readmission, reoperation, and mortality, rates. These findings have been reported in other studies.[2,8]

Risk factors increasing mortality rates for spinal fusions

We found other independent risk factors such as operative time, ASA III-IV, thoracic location, and diabetes that increased mortality rates for spinal fusions. However, these factors demonstrated a weaker significant association when compared to hypoalbuminemia and dialysis. These finding were also previously reported in the literature.[7]

CONCLUSION

Mild hypoalbuminemia, severe hypoalbuminemia, and dialysis significantly increase morbidity and mortality rates for patients undergoing posterior spinal fusions. These results support the fact that albumin levels should be optimized in the preoperative setting to improve outcomes.