HIGH ALTITUDE AND VENOUS THROMBOSIS: FREQUENCY AND RISK FACTORS

Objective: To determine the effect of high altitude on frequency and risk factors of venous thrombosis inindividuals ascending to high altitude Study Design: Cross-sectional analytical study. Place and Duration of Study: Armed Forces Bone Marrow Transplant Centre, Combined Military HospitalSkardu, from Apr 2015 to Aug 2018. Methodology: High Altitude was taken as height equal to or more than 8000 feet. Polycythemia as hemoglobin>16.5 g/dl OR hematocrit >49%. Medical records of all patients evacuated from high altitude through CombinedMilitary Hospital Skardu were analyzed retrospectively. A proforma was designed to include necessary variables. Results: We evaluated medical records of 539 individuals and found frequency of 86 (15.9%) for venous thromboembolism (VTE) at high altitude. Cerebral venous sinus thrombosis (CVST) was most common thrombotic complication seen in 39 patients (46%). Majority of thrombotic episodes occurred at >18000 feet (likelihood ratio (LR) 5.99, p-value 0.009). Majority of thrombotic episodes 34 (39%) occurred within first 45 days of ascent to high altitude. Thrombosis was linked to smoking 47 (55%) (likelihood ratio 21.3 and p-value <0.001) and use of melted snow as a source of drinking water 56 (65%) (likelihood ratio 57.6 and p-value <0.001). Conclusion: This study showed a very high frequency of thrombotic complications at high altitude. There isa need for a robust prospective study covering epidemiology, clinical information and diagnostics in order todevelop appropriate standard operating procedures and guidelines for prevention of thrombosis at HA