1595. Impact of Hypothyroidism on In-Hospital Mortality for Cervical Spinal Fusions

Authors: Evan Luther, MD; Roberto Perez-Roman, MD; David McCarthy; Josh Burks, MD; Andrew Buskard; Karthik Madhavan, MD; 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 many comorbidities including hypertension, cardiovascular disease, osteoporosis, peripheral neuropathy, and muscular weakness. However, the impact of hypothyroidism on perioperative morbidity in patients undergoing cervical spinal fusion is limited. It was the aim of this study to elucidate this relationship. 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 cervical spinal fusion (81.0x and 81.3x) were included. Patients in this cohort with an ICD-9-CM diagnosis code indicating hypothyroidism (244.x) were compared to euthyroid patients. Defined primary outcome measures were short-term post-surgical complications [neurological, respiratory, cardiac, gastro-intestinal, wound complication and infections, venous thromboembolism, and acute-renal failure (ARF)]. 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 1,681,805 patients underwent cervical spinal fusion from 2004-2014 for which 138,495 (8.2%) carried a diagnosis of hypothyroidism. Although hypothyroid patients had increased risk of developing acute postoperative anemia (OR 1.162, 95% CI 1.114 to 1.212, p < 0.0001), they exhibited decreased in-hospital mortality (OR .643, 95% CI .506 to .720, p < 0.0001). Conclusion: Hypothyroid patients undergoing cervical spinal fusion demonstrated lower rates of in-hospital mortality when compared to their euthyroid counterparts. This suggests that hypothyroidism offers protection against all-cause mortality in the post-operative cervical 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.