The effect of patient body mass on renal function in multilevel spinal fusion for adult spinal deformity to prevent acute kidney injury.

Objective: Adult spinal deformity (ASD), a condition characterized by spinal degeneration resulting in abnormal spinal curvature and pain, can be treated with multilevel spinal fusion. Perioperative acute kidney injury (AKI) is associated with prolonged hospital stays, death, and overall poor surgical outcomes. High-volume fluid resuscitation can prevent AKI, however. It is contraindicated in surgeries such as spinal fusion for ASD, given the risk of elevated intraocular pressure resulting in ocular damage when a patient is positioned prone. This study aimed to evaluate how preoperative renal function affects outcomes in ASD spinal fusion and to determine the incidence of and risk factors for developing perioperative AKI in ASD surgery.

Methods: Patients with ASD who underwent long-segment thoracolumbar fusion for abnormal spinal curvature between 2016 and 2021 were included. Blood urea nitrogen and creatinine values from within 24 hours prior to surgery were used. KDIGO (Kidney Disease Improving Global Outcomes) guidelines were used to define AKI, and the Cockroft-Gault equation was used to calculate creatinine clearance. Univariate analyses assessed perioperative factors affecting AKI development and associations with chronic kidney disease.

Results: A total of 235 consecutive patients were included, of whom 155 were women. The average age was 69.6 years (SD 8.0 years). Forty patients (17%) developed AKI postoperatively. Anesthesia duration (289.2 vs 293.3 minutes, p = 0.739), blood loss (1.65 vs 1.58 L, p = 0.663), and number of levels fused (9.0 vs 9.4, p = 0.459) were similar in patients with and without AKI. Patients developing AKI were more likely to have higher BMI (31.8 vs 27.5 kg/m2, p < 0.001). Intraoperative colloid (1.10 vs 1.07 L, p = 0.771), crystalloid (2.35 vs 2.61 L, p = 0.160), and total fluid volumes (4.92 vs 5.08 L, p = 0.702) were similar in patients with and without AKI. Multivariate analysis found that total fluid volume (p = 0.404) and weight-adjusted total fluid volume (p = 0.249) were not significantly predictive of AKI when controlling for BMI. Patients with BMI > 27.34 kg/m2 were more likely to develop AKI. Patients with chronic kidney disease (7.23%) did not develop AKI at a higher rate than patients without it (p = 0.200).

Conclusions: Perioperative AKI occurred regardless of the volume of colloid, crystalloid, or total fluid administered intraoperatively. Therefore, a more cautious approach to fluid resuscitation is recommended to mitigate the risk of ocular damage in patients undergoing spinal fusion for ASD.