Effects of the automated management of hypertension after open heart surgery. The relevance of the initial systemic vascular resistance as index for predicting hemodynamic response to computer-controlled nitroprusside infusion.

In the study of hemodynamics of hypertensive patients with low-output syndrome after open-heart surgery (the closed loop control of mean arterial pressure with nitroprusside, n = 14), evidence was obtained that the baseline SVR is a valuable index for predicting the response to vasodilation. Patients with markedly elevated SVR (n = 11) (1800 dyn. s. cm-5) responded favorably to vasodilation with SVR fall (from 2300 +/- 500 dyn X cm-5 to 1400 +/- 300 dyn X cm-5, p less than 0.005, -37%), cardiac index rise (from 2.1 +/- 0.3 to 2.4 +/- 0.4 l/min. m2, p less than 0.05 + 14%), or stroke volume index elevation (from 23.4 to 26.7 ml/m2, p less than 0.05, +14%). In patients with slightly raised SVR close to the normal range a mild SVR reduction (by 10%) occurred but no cardiac index increase with vasodilation alone. These patients derived their hemodynamic benefit from a combination of NP with preload augmentation and possibly direct inotropic stimulation. By assessing SVR before and during treatment with nitroprusside we were able to monitor more closely the course of automated afterload reduction and provide an additional important parameter for this regulation.