Blood pressure measurement in patients with cardiogenic shock: the effect of norepinephrine.

BACKGROUND: Before arterial cannulation for invasive blood pressure monitoring, clinical decision-making depends on non-invasive blood pressure in critically ill patients. Whether non-invasive blood pressure is comparable to invasive measurement is not clearly elucidated. We address this issue as it relates to the use of norepinephrine in patients with cardiogenic shock. METHODS: We analysed invasive and non-invasive blood pressure in 85 patients admitted to the Coronary-Care Unit for cardiogenic shock. We compared initial blood pressure measurement (just after radial artery cannulation) and blood pressure taken during the first 72 hours after admission. Invasive blood pressure was used as the reference method. RESULTS: Initial invasive mean and systolic arterial pressures were in a good agreement with oscillometric blood pressure; mean differences were -0.4 ± 8.8 and +6.1 ± 14.4 mmHg with correlation coefficients of 0.76 and 0.74. Doses of norepinephrine were significant negative determinants of invasive/oscillometric blood pressure differences. The invasive/oscillometric mean arterial pressures and SBP differences were +0.1 ± 3.4 and 7.6 ± 1.6 mmHg in patients treated with nothing or a maximum norepinephrine dose of 0.6 µg/kg/min. However, treatment with very high doses of norepinephrine was associated with a steep rise in mean arterial pressures and SBP invasive/oscillometric differences (-9.5 ± 3.3 and -8.5 ± 5.2 mmHg). In a total of 967 sets of blood pressure measurements, invasive/oscillometric differences were relatively stable across blood pressure categories, with the exception of measurements assessed after very high norepinephrine doses. CONCLUSIONS: Non-invasive BP is a sufficient substitute for invasive measurement in cardiogenic shock patients, with the exception of those receiving very high doses of norepinephrine.