Does radial artery pressure accurately reflect aortic pressure?

STUDY OBJECTIVE Our objective was to determine whether the systolic, diastolic, and mean arterial pressures measured in the radial artery accurately reflect corresponding pressures in the ascending aorta in narcotic-anesthetized patients with known obstructive coronary artery disease, before being subjected to cardiopulmonary bypass (CPB). DESIGN This was a prospective study. SETTING The cardiac operating room of a large, tertiary-care university medical center. PARTICIPANTS Fifty-one patients (45 men and six women; age range, 48 to 77 years) with documented atherosclerotic coronary artery disease were studied. All patients underwent elective coronary artery bypass grafting after the study. INTERVENTIONS Patients were premedicated with lorazepam and morphine 60 min before administration of Fentanyl-pancuronium anesthesia. The radial artery was cannulated before induction of anesthesia and the aorta approximately 45 min later. Comparisons of radial and aortic pressures were then performed. MEASUREMENTS AND RESULTS Radial and aortic pressures were recorded through standard, fluid-filled, high-pressure, 91-cm (36-in) long tubing and disposable transducers, meticulously cleared of air bubbles. Additional measurements included cardiac output, central venous pressure, core temperature, blood gas levels, and hematocrit reading. Radial-aortic pressure differences were as follows: systolic arterial pressure (SAP), 12 +/- 1 mm Hg; mean arterial pressure (MAP), -0.8 +/- 0.3 mm Hg; and diastolic arterial pressure (DAP), -1.0 +/- 0.3 mm Hg. All were significant (p < 0.001), but the SAP difference was more than ten times that of either the MAP or the DAP values. The coefficients of determination (r2) indicated that the radial-aortic dependence was 0.44 for the SAP, 0.90 for the DAP, and 0.98 for the MAP relationship. Plotting the respective differences against the arithmetic mean of simultaneously measured pressures indicated that the radial SAP was 4 to 35 mm Hg higher than the aortic in 42 patients (82 percent) and was 10 to 35 mm Hg higher in 26 patients (51 percent); radial-aortic MAP differences clustered within 3 mm Hg in 47 patients (92 percent); radial DAP was +/- 3 mm Hg different from the aortic in 46 patients (90 percent). The largest MAP difference was -6 mm Hg in one patient. The largest DAP difference was +/- 5 mm Hg in three patients. CONCLUSIONS In this group of patients, who were studied before undergoing CPB, the radial SAP gave a poor estimate of that present in the ascending aorta, since in more than 50 percent of the cases, the radial SAP was 10 to 35 mm Hg higher than that in the aorta. The radial MAP and DAP are reliable, since in 90 percent and 92 percent of the patients, respectively, the pressure differences were within +/- 3 mm Hg of those in the aorta.