THERMOREGULATORY AND ANESTHETIC-INDUCED ALTERATIONS IN THE DIFFERENCES AMONG FEMORAL, RADIAL, AND OSCILLOMETRIC BLOOD PRESSURES

Background: A decrease in radial artery blood pressure relative to cen tral arterial blood pressure Is commonly associated with the rewarming phase of cardiopulmonary bypass. Decreased hand vascular resistance h as been suggested as a possible mechanism. Although decreased blood vi scosity due to hemodilution may contribute to decreased hand vascular resistance, thermoregulatory vascular responses to core hyperthermia a lso may be important. Methods: Seven healthy volunteers were studied. Volunteers first were cooled until thermoregulatory vasoconstriction w as evident. Next, each was warmed until intense sweating developed. Af ter a cool-down period, general anesthesia was induced with propofol a nd N2O. Femoral artery pressure (a surrogate for central arterial pres sure) and radial artery and oscillometric (brachial artery) pressures were compared during each of six defined thermoregulatory and anesthet ic study conditions. To determine the effect of hand vascular resistan ce on blood pressure differences, measurements were compared before an d after occlusion of hand blood flow. Upper-extremity blood flow was e valuated by forearm and fingertip plethysmography and laser Doppler fl owmetry. Results: Forearm, fingertip, and cutaneous blood now increase d significantly during warming and were maximal during intense sweatin g. During thermoregulatory vasoconstriction, femoral, radial, and osci llometric mean blood pressures were similar. In contrast, radial arter y mean pressure was 5 +/- 1 mmHg less than femoral artery mean pressur e and 12 +/- 8 mmHg less than oscillometric mean pressure during inten se sweating. Hand compression reduced these differences. The contour o f the radial artery pressure waveform was dramatically altered by ther moregulatory and anesthetic conditions. Radial artery systolic pressur e exceeded both femoral artery and oscillometric systolic pressures du ring vasoconstriction but was less than these during intense sweating. Hand compression reestablished the exaggerated radial artery systolic pressure during all study conditions. Conclusions: Thermoregulatory a nd anesthetic-induced alterations in upper-extremity blood now substan tially influence the relations among femoral artery, radial artery, an d oscillometric blood pressure measurements.