Precipitate formed by thiopentone and vecuronium causes pulmonary embolism

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.

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.

Maximum blood thiopentone concentration in the precipitate group was lower than in the control group (12.9 +/- 4.5 vs 17.0 +/- 1.6 micrograms.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 microns in diameter) obstructed small arteries in the lungs at one minute but not at 60 min after injection.

Intravenous injection of precipitate causes pulmonary microembolism, with a small transient decrease in PaO2.