Venous air embolism during semi-sitting craniotomy evokes thrombocytopenia.

Venous air embolism activates platelets in vitro and can evoke platelet dysfunction in swine. We tested the hypothesis that venous air embolism during semi-sitting craniotomy induces thrombocytopenia in humans. We analysed the charts of 799 patients who had an elective craniotomy in the semi-sitting position between 1990 and June 2009. Venous air embolism occurred in 52 patients (6.5%) and was associated with a decrease in mean (SD) in platelet count from 270 (75) × 10⁹ l⁻¹ to 194 (62) × 10⁹ l⁻¹ (p < 0.001). In age-matched controls without venous air embolism mean (SD) platelet count did not change (254 (82) × 10⁹ l⁻¹ vs. 250 (97) × 10⁹ l⁻¹ (NS). While mean (SD) haematocrit fell slightly in both groups (venous air embolism: 0.40 (0.05) to 0.32 (0.04), p <0.001; no venous air embolism: 0.41 (0.04) to 0.35 (0.05), p < 0.001), normalising platelet count to haematocrit did not alter the results.