Cardiovascular and respiratory effects of ketamine in the neonatal lamb.

To determine the cardiovascular and respiratory effects of intravenous ketamine in the neonatal lamb we studied six unpremedicated chronic neonatal lamb preparations. Each lamb was anaesthetized with ketamine 15 mg [corrected] X kg-1, allowed to recover and then anaesthetized with ketamine 30 mg [corrected] X kg-1. Mean arterial pressure, mean pulmonary artery pressure, mean left atrial pressure, pulmonary bloodflow, heart rate, respiratory rate and arterial blood gases were measured before and at one, two, four, six, eight and ten minutes after the administration of each dose of ketamine. Pulmonary vascular resistance, systemic vascular resistance and the ratio of pulmonary to systemic vascular resistance were also determined. After the administration of either dose of ketamine, only respiratory rate changed significantly (p less than or equal to 0.05), reaching a maximum after two minutes. This change was not associated with any arterial blood gas abnormalities. We conclude that in the presence of adequate ventilation, ketamine produces no significant cardiovascular effects in neonatal lambs.