A new sodium-nitroprusside-infusion controller for the regulation of arterial blood pressure

Automatic optimization of the infusion rate of sodium nitroprusside (SNP) is achieved by an integrated hardware-software closed-loop controller implemented as a small bedside device. A microprocessor-based blood pressure monitor controls an infusion pump. The shape of the arterial pressure wave is digitally sampled; its analysis incorporates artifact-detection and -rejection routines. The implemented algorithm applies a rule-based closed-loop control that incorporates fuzzy logic. The system models the decision-making ability of the expert, instead of trying to model the patient's physiologic dynamics. Several internal fuzzy-state variables are defined to achieve a clear understanding of mean arterial pressure (MAP) evolution with time. The system performance is very robust, employing, under all possible situations, a sort of "common sense." A clinical trial of the controller was conducted in 60 patients requiring vasodilation therapy for systemic arterial hypertension following cardiac surgery, 20 who had conventional manual control by an experienced nursing staff and 40 who had automated closed-loop control. The first 240 minutes of the postoperative period were closely watched, taking into account 1) the percentage of time during which MAP was within the 10-mmHg wide frame above the target pressure (target gap); 2) the mean difference of pressure values that crossed the boundary of the target gap; 3) the mean SNP-infusion rate. With automatic control, the time mean arterial pressure values were located in the target gap during the first hour amounted to 72.8 +/- 6.7%, vs 51.2 +/- 10.3% in the manual-control group. In the second hour, it was 79.3 +/- 2.5% vs 67.4 +/- 11.7% (p < 0.005).(ABSTRACT TRUNCATED AT 250 WORDS)