Inaccuracies and variability of indirect pressure measurements during cardioplegia administration.

This study shows cardioplegic delivery requires direct measurement of intravascular pressure, rather than its estimation by calibration of individual delivery systems or by aortic palpation. The effects of temperature, hematocrit, flow rate, and cannula type were tested in vitro after recording intravascular pressure during routine cardiac operations. Inaccuracies were introduced by estimating intravascular pressure, as changes in blood viscosity are affected by hematocrit and temperature, and delivery system pressure varied in relation with the type of cannula, direction of perfusion, and flow rate. Additionally, clinical delivery introduces the variable of intravascular resistance. The variability of direct intravascular pressure versus predicted pressure increased as flow rate was raised. These inaccuracies were overcome completely by directly monitoring intravascular pressure from the side ports of antegrade and retrograde cannulas. We conclude that (1) monitoring cardioplegic delivery device pressure is useful primarily to detect potential obstruction in the delivery system that must be corrected intraoperatively and (2) predicted pressure (by either palpation or in vitro calibration) is an unreliable method of determining intravascular pressure during cardioplegic delivery.