Study design: Retrospective review of prospectively collected data.
Objective: To determine a cutoff below which worsening renal function is associated with increased risk of morbidity and to determine the types and magnitude of morbidity associated with renal impairment.
Summary of background data: Renal impairment is associated with an increased risk of morbidity after lumbar spine surgery. However, the degree to which increasing levels of renal dysfunction are associated with morbidity has not been well defined.
Methods: A large, multicenter, clinical registry was queried for all adult patients undergoing lumbar spine surgery in 2012, and 13,576 cases were identified. An estimated glomerular filtration rate (eGFR) was calculated for each patient. Propensity scores were used to match patients on the basis of preoperative comorbidities and the procedure-type performed. The incidence of 30-day morbidity was then compared between patients with no or mild renal impairment (eGFR ≥60 mL/min/1.73 m) and those with moderate or severe disease (eGFR <60 mL/min/1.73 m). Separately, the morbidity risk associated with eGFR was analyzed as a continuous variable.
Results: The risk of morbidity increased with worsening eGFR in an inverse-logarithmic fashion (R = 0.84), and the magnitude of risk increased substantially for eGFR below 60 mL/min/1.73 m (odds ratio of ≥1.8). There was a 26% relative increase in morbidity for patients with moderate to severe renal impairment, as compared with the propensity score-matched cohort of patients with no or mild disease (5% absolute increase, 24% vs. 19%, P = 0.004). Wound complications (3% vs. 2.1%), reoperation rates (4.6% vs. 3.3%), and need for blood transfusions (16.3% vs. 12.8%) trended higher in patients with moderate or severe disease, but only the need for blood transfusion reached significance. Patients with preoperative moderate or serve renal impairment were 10 times more likely to develop acute renal failure postoperatively (0.6% vs. 0.06%, P = 0.01).
Conclusion: Thirty-day morbidity risk after lumbar spine surgery is strongly associated with renal impairment. These data may be useful for preoperative patient counseling, and surgeons should consider the relative magnitude of risks and benefits before operating on a patient with severe renal disease, particularly in elective cases.
Level of evidence: 3.