Comparison of haemodynamic effects during venous air infusion and after decompression in pigs

We have compared haemodynamic effects of venous gas emboli during continuous air infusion into the right atrium and after rapid decompression in pigs. Eight anaesthetized and spontaneously breathing pigs received continuous air infusion at a rate of either 0.05 ml.kg-1.min-1 (six pigs, air infusion group) or 0.10 ml.kg-1.min-1 (two pigs). Another eight pigs (decompression group) underwent a 30-min compression to 5 bar (500 kPa, absolute pressure), followed by a rapid decompression (2 bar.min-1). Haemodynamic variables were measured or calculated, and bubbles in the pulmonary artery were monitored using transoesophageal echocardiography. The results showed less variation in the maximal increase in mean pulmonary arterial pressure (BPa,pulm) during air infusion (0.05 ml.kg-1.min-1) than after decompression, although the mean maximal increase did not differ between the two groups [28.0 mmHg (3.73 kPa), 95% confidence interval (CI) 23.5-32.5, vs 32.0 mmHg (4.27 kPa), 95% CI 25.3-38.7, P = 0.3]. The BPa,pulm stabilized or decreased very slowly after peak values were reached in the air infusion group, whereas the BPa,pulm decreased rapidly during the same period in the decompression group. No significant changes in mean arterial pressure were observed during air infusion (0.05 ml.kg-1.min-1), in contrast to the rapid increase and the subsequent decrease, that appeared after decompression. Finally, the maximal bubble count was much lower in the air infusion group than in most of the pigs in the decompression group. The two pigs that received 0.10 ml.kg-1.min-1 stopped breathing after 5-min infusion, developed arterial hypotension and died.