High Altitude Is an Independent Risk Factor for Developing a Pulmonary Embolism, but Not a Deep Vein Thrombosis Following a 1- to 2-Level Lumbar Fusion

Study Design: Retrospective study. Objective: To identify if a 1- to 2-level posterior lumbar fusion at higher altitude is an independent risk factor for postoperative deep vein thrombosis (DVT) and pulmonary embolism (PE). Methods: A national Medicare database was queried for all patients undergoing 1- to 2-level lumbar fusions from 2005 to 2014. Those with a prior history of DVT, PE, coagulopathy, or peripheral vascular complications were excluded to better isolate altitude as the dependent variable. The groups were matched 1:1 based on age, gender, and comorbidities to limit potential cofounders. Using ZIP codes of the hospitals where the procedure occurred, we separated our patients into high (>4000 feet) and low (<100 feet) altitudes to investigate postoperative rates of DVTs and PEs at 90 days. Results: Compared with lumbar fusions performed at low-altitude centers, patients undergoing the same procedure at high altitude had significantly higher PE rates (P =.010) at 90 days postoperatively, and similar rates of 90-day postoperative DVTs (P =.078). There were no significant differences in age or comorbidities between these cohorts due to our strict matching process (P = 1.00). Conclusion: Spinal fusions performed at altitudes >4000 feet incurred higher PE rates in the first 90 days compared with patients receiving the same surgery at <100 feet but did not incur higher rates of postoperative DVTs.