Blood pressure variability in surgical and intensive care patients: Is there a potential for closed-loop vasopressor administration?

Blood pressure management in the operating rooms (OR) and intensive care units (ICU) frequently involves manually titrated vasopressor therapy to an optimal range of mean arterial pressure (MAP). Ideally, changes in vasopressor infusion rates have to quickly follow variations in blood pressure measurements. However, such a tightly controlled feedback loop is difficult to achieve. Few studies have examined blood pressure control when vasopressor therapy is administered manually in OR and ICU patients. We extracted MAP data from 3623 patients (2530 from the ORs and 1093 from the ICU) on vasopressors from our electronic medical records. Coefficient of variation (= standard deviation/mean value) *100) was calculated and the values were additionally categorized into different MAP ranges (MAP < 60 mmHg, 60 < MAP < 80 and MAP > 80 mmHg). There was no statistically significant difference between both centres for MAP across all time points (80 ± 12 vs. 80 ± 16, P = 0.996, 95% CI -6 to 6). The coefficients of variation of MAP were 13.7 ± 5.4% and 18.4 ± 9.8% in the OR and in ICU respectively. Patients on vasopressors spent 48.8% treatment time with a MAP between 60 and 80 mmHg (11.2% time with MAP < 60 mmHg, and 40% with MAP > 80 mmHg). These results provide a reasonable baseline from which to establish whether 'reduced variability' may be achieved with a closed-loop vasopressor administration system.