Radial artery pressure monitoring underestimates central arterial pressure during vasopressor therapy in critically ill surgical patients

Objectives: Radial artery pressure is known to differ from central arterial pressure in normal patients (distal pulse amplification) and in the early postcardiopulmonary bypass period. The adequacy of the radial artery as a site for blood pressure monitoring in critically ill patients receiving high dose vasopressors has not been carefully examined. Design: Prospective observational study comparing simultaneous intra arterial measurements of radial (peripheral) and femoral artery (central) pressures. Setting: Clinical investigation in a university based surgical intensive care unit. Patients: Fourteen critically ill patients with presumed sepsis who received norepinephrine infusions at a rate of greater than or equal to 5 mu g/min. Interventions: All patients were managed in accordance with our standard practice for presumed sepsis, which consisted of intravascular volume repletion followed by vasopressor administration titrated to a mean arterial pressure of greater than or equal to 60 mm Hg. Measurements and Main Results: Systolic and mean arterial pressures were significantly higher when measured from the femoral vs, radial site (p <.005). The higher mean arterial pressures enabled an immediate reduction in norepinephrine infusions in 11 of the 14 patients. No change in cardiac output or pulmonary artery occlusion pressure was noted after dose reduction. In the two patients in whom simultaneous recordings were made after discontinuation of norepinephrine infusions, equalization of mean arterial pressures was observed. Conclusions: Radial artery pressure underestimates central pressure in hypotensive septic patients receiving high dose vaso presser therapy. Clinical management, based on radial pressures, may lead to excessive vasopressor administration. Awareness of this phenomena may help minimize adverse effects of these potent agents by enabling dosage reduction.