Reliability of the radial arterial pressure during anesthesia. Is wrist compression a possible diagnostic test?

STUDY OBJECTIVE: To evaluate wrist compression as a test to identify low radial from low systemic pressure and to see if the gradient found after cardiopulmonary bypass is also present whenever hand vascular resistance may decrease.

DESIGN: This was a prospective study.

SETTING: Operating room area of a university medical center.

PARTICIPANTS: (1) Forty patients undergoing coronary bypass grafting studied at discontinuation of cardiopulmonary bypass. (2) Twenty-six patients received isoflurane anesthesia before major noncardiac operations. (3) Hydraulic model: a fluid container with a tube 66-cm long, 6- to 1.8-mm internal diameter, connected at its base.

INTERVENTIONS: Before induction of anesthesia, the radial artery was cannulated and, in the first group, the aorta or femoral arteries as well. The radial pressure was compared consecutively with and without wrist compression. In the model, the pressure was recorded simultaneously at three sites along the tube while different flows ran through its distal end.

MEASUREMENTS AND RESULTS: Overall, wrist compression increased radial (p < 0.001) systolic, diastolic, and mean arterial pressures. In the first group, compression reduced the femoral/aortic-radial mean pressure difference by 50 percent and never produced higher radial than central mean pressure. Plot of the pressure difference produced by wrist compression against the average of the (compared) radial pressures and considering increases > or = 4 mm Hg as real, showed that, in the first group, systolic arterial pressure (SAP) increased 13 +/- 1.4 mm Hg in 22 of 40 patients; diastolic arterial pressure (DAP) increased 7.8 +/- 1.1 mm Hg in 4; and mean arterial pressure (MAP) increased 7.7 +/- 1.6 mm Hg in 9 patients. In the second group, SAP increased 16.0 +/- 1.7 mm Hg in 24 of 26 patients, DAP increased 6.0 +/- 1.4 mm Hg in 5, and MAP increased 7.0 +/- 0.7 mm Hg in 18 of 26 patients. In the model, base pressure at 94 mm Hg, the pressures were 1.2 to 28.1 mm Hg lower for flows ranging from 10 to 122 ml/min at the 54-cm distance (wrist equivalent).

CONCLUSION: The systemic-radial artery pressure gradient seen at the end of cardiopulmonary bypass seems to be a phenomenon common to patients with decreased hand vascular resistance. Wrist compression decreases or abolishes the gradient in most cases. It does not produce false positives, so an increase indicates a greater aortic than radial pressure. The difference is likely to be only temporary.