Comparison among manual, computer-assisted, and closed-loop control of blood pressure after cardiac surgery

Forty-five patients who required vasodilator therapy for systemic arterial hypertension following cardiac surgery were randomly allocated to receive: (1) manual control of a sodium nitroprusside (SNP) infusion; (2) computer-assisted control where the nurse was provided with a color graphical display of performance; or (3) automatic closed-loop control. Limits of acceptable systolic pressure were prescribed for each patient, and the percentage time spent outside these limits was calculated for each patient. The closed-loop computer system (CLCS) produced significantly better control than either manual or computer-assisted systems for the time spent outside the prescribed limits (P less than 0.001), and better control for the time spent outside the limits +/- 10 mmHg (manual P less than 0.001; assisted P less than 0.01). While the CLCS proved more satisfactory than manual control for the limits +/- 20 mmHg and +/- 30 mmHg (+/- 20 mmHg P less than 0.001; +/- 30 mmHg P less than 0.01), there was no significant difference in the quality of control between the CLCS and computer-assisted systems for these limits. The results suggest that the quality of blood pressure control achieved by nurses can be improved by providing them with a clear graphical display of their performance. Better control of blood pressure should reduce the adverse effects of hypotension and hypertension following cardiac surgery.