Precipitate formed by thiopentone and vecuronium causes pulmonary embolism

Abstract

Purpose: To examine the effects of a bolus injection of the precipitate formed by thiopentone and vecuronium on the pharmacokinetic behaviour of thiopentone, cardiopulmonary physiology, and lung histology. Methods: Of 16 female rabbits (2.9 to 3.1 kg), eight were injected with a precipitate formed by a mixture of 5 mg · kg-1 thiopentone and 0.67 mg · kg-1 vecuronium via the external jugular vein. Eight control rabbits were injected with 5 mg · kg-1 thiopentone alone. Plasma thiopentone concentration, systolic arterial pressure and PaO2 were measured for 60 min after injection. Histological changes in the lungs were evaluated at one and 60 min. Results: Maximum blood thiopentone concentration in the precipitate group was lower than in the control group (12.9 ± 4.5 vs 17.0 ± 1.6 μg · ml, P < 0.05), although the half-life of thiopentone in the precipitate group was longer (32.3 ± 8.5 vs 21.7 ± 8.2 min. P < 0.05) and the area under the time concentration curve was similar between the two groups. However, the mean residence time was 28% longer in the precipitate group than in controls (P < 0.05). The PaO2 was lower in the precipitate group than in controls one minute after injection (431 ± 27 vs 464 ± 18 mmHg, P < 0.05) but not subsequently. Histologically, crystals (30-150 μm in diameter) obstructed small arteries in the lungs at one minute but not at 60 min after injection. Conclusion: Intravenous injection of precipitate causes pulmonary microembolism, with a small transient decrease in PaO2.