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.