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Canadian Journal of Anesthesia, Vol 32, 119-123, Copyright © 1985 by Canadian Anesthesiologists' Society

Intrapulmonary Shunting during Deliberate Hypotension with Nifedipine, Diltiazem and Labetalol in Dogs

PIERRE A. CASTHELY MD1, RAYMOND VILLANUEVA MD1, LAWRENCE RABINOWITZ MD1, PRAVINCHANDRA GANDHI MD1, BRAD LITWAK MD1, and PHILLIP N. FYMAN MD1

1 Department of Anaesthesiology, State University Hospital, Downstate Medical Center, Brooklyn, New York

Address correspondence to: Dr. Pierre A. Casthely, Department of Anesthesiology, State University Hospital, Downstate Medical Center, 450 Clarkson Avenue, Box 6, Brooklyn, New York 11203.

Pulmonary shunt (Qs/Qt) was calculated in 49 mongrel dogs weighing 18-20 kg during mechanical ventilation, before and during deliberate hypotension with either nifedipine (group N), diltiazem (group D), labetalol (group L), or ethyl alcohol and polyethylene glycol (group E). A 30 per cent decrease in mean arterial blood pressure occurred after two minutes of nifedipine infusion, two minutes after diltiazem, and three minutes after labetalol; these effects lasted two hours after nifedipine administraiton, 90 minutes after diltiazem and three hours after labetalol. There was an accompanying significant decrease in systemic and pulmonary vascular resistance.

Qs/Qt and cardiac output increased significantly after nifedipine infusion. Shunt increased (mean ± S.E.) from 9.7 ± 0.8 to 18.25 ± 1.05 per cent at two minutes (p < 0.005); 19.05 ± 1.2 per cent at 30 minutes (p < 0.005); 17.5 ± 1.6 per cent at two hours (p < 0.01); and 12 ± 1.1 per cent at three hours (p < 0.025). No increase in shunt occurred after the administration of diltiazem, labetalol or polyethylene glycol and ethyl alcohol. Arterial oxygen tension (PaO2) decreased significantly after nifedipine infusion from 146 ± 11.5 to 105 ± 3.5 mmHg two minutes after infusion; to 89.5 ± 3 mmHg 30 minutes after; 115 ± 4.75 mmHg two hours after; and 130 ± 10.75 mmHg three hours later. PaO2 was not significantly different after diltiazem, labetalol, or polyethylene glycol and ethyl alcohol administration. With nifedipine cardiac output increased from 2.25 ± 0.3 to 3.95 ± 0.25 after two minutes (p < 0.005) to 3.85 ± 0.35 after 30 minutes (p < 0.005), 3.7 ± 3 after two hours (p < 0.01) to 2.9 ± 1.1 after three hours. No significant increase in cardiac output occurred in groups D or L.

These results suggest that only nifedipine infusion significantly alters oxygenation in dogs and therefore its use warrants caution in the presence of a preexisting abnormal Qs/Qt.

Key Words: ANAESTHETIC TECHNIQUES: hypotension, induced • BLOOD PRESSURE, DRUG EFFECTS: nifedipine, diltiazem, labetalol






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Copyright © 1985 by the Canadian Anesthesiologists' Society.