1594. Impact of Hypothyroidism on In-Hospital Mortality and Cardiac Complications for Lumbar Spinal Fusions

Authors: Evan Luther, MD; Roberto Perez-Roman, MD; David McCarthy; Josh Burks, MD; Andrew Buskard; Karthik Madhavan; Steven Vanni, DO; Michael Wang, MD (Miami, FL)

Introduction: The prevalence of hypothyroidism in the United States is 1-4% and is associated with an increased risk of developing comorbidities including hypertension, cardiovascular disease, osteoporosis, peripheral neuropathy, and muscular weakness. However, the impact of hypothyroidism on perioperative morbidity in patients undergoing lumbar spinal fusion is limited. Methods: We performed a retrospective analysis of the Nationwide Inpatient Sample between 2004-2014. Patients who had an ICD-9-CM procedure code indicating a lumbar spinal fusion (81.04-81.08, 81.34-81.38) were included. Patients in this cohort with an ICD-9-CM diagnosis code indicating hypothyroidism (244.x) were compared to euthyroid patients. Primary outcome measures were defined as specific short-term post-surgical complications. Patient, hospital, and Elixhauser comorbidity variables were assessed in univariate analysis to test covariates predictive of specific complications and mortality. Factors predictive in univariate analysis (p<0.2) were utilized to construct a multivariate logistic regression model to analyze the effect of hypothyroidism on complications and mortality. Results: A total of 2,467,320 patients underwent lumbar spinal fusion from 2004-2014 for which 251,475 (10.19%) carried a diagnosis of hypothyroidism. Although hypothyroid patients had increased risk of developing acute postoperative anemia (OR 1.176, 95% CI 1.160 to 1.192, p < 0.0001), they exhibited decreased in-hospital mortality (OR .643, 95% CI .551 to .746, p < 0.0001) and decreased risk of developing MI (OR .851, 95% CI .810 to .893, p < 0.0001). Conclusion: Hypothyroid patients undergoing lumbar spinal fusion demonstrated lower rates of in-hospital mortality and MI when compared to their euthyroid counterparts. This suggests that hypothyroidism offers protection against all-cause mortality and acute cardiac complications in the post-operative lumbar spinal fusion patient. The mechanism is poorly understood but may be secondary to either decreased oxygen demand and thus reduced cardiac workload in the hypothyroid-induced hypometabolic state or by the known antithrombotics effects of thyroid hormone supplementation.