Sodium nitroprusside-induced, but not desflurane-induced, hypotension decreases myocardial tissue oxygenation in dogs anesthetized with 8% desflurane.

Objective: To compare sodium nitroprusside (SNP)-induced hypotension with desflurane-induced hypotension for the effects on myocardial blood flow and tissue oxygenation in dogs.

Design: Prospective, randomized, crossover, nonblinded.

Setting: University teaching hospital.

Participants: Male nonpurpose-bred hounds (n = 8).

Interventions: Dogs were anesthetized with 8% desflurane. Catheters were inserted into the femoral artery and coronary sinus. A flow probe was placed in the left anterior descending (LAD) branch of the coronary artery. A sensor that measured myocardial oxygen pressure (PmO(2)) was inserted into the myocardium of the left ventricle. Myocardial oxygen consumption (MVO(2)) was calculated as LAD flow x arterial - coronary sinus oxygen content.

Measurements And Main Results: Measurements were made at baseline blood pressure levels of 99 mmHg (measure 1), during hypotension to 62 to 66 mmHg using intravenous SNP or 14% desflurane (measure 2), and during SNP or 14% desflurane with blood pressure support using phenylephrine (measure 3). Each dog randomly received both hypotensive treatments, separated by 1 hour. Baseline measures were PmO(2) = 46 +/- 9 mmHg, LAD flow = 43 +/- 11 mL/min, and MVO(2) = 2.47 +/- 0.73 mL O(2)/min. During hypotension induced with SNP, PmO(2) decreased 30% (p < 0.05), LAD flow increased 40% (p < 0.05), and MVO(2) did not change. During hypotension induced with 14% desflurane, PmO(2) did not change, and LAD flow and MVO(2) decreased 25% and 40% (p < 0.05). Blood pressure support with phenylephrine increased LAD flow and MVO(2) but did not change PmO(2) during SNP or 14% desflurane treatment.

Conclusion: SNP-induced hypotension produced myocardial vasodilation, but tissue oxygenation was impaired. PmO(2) was maintained during desflurane-induced hypotension.