CALCULATED MEAN ARTERIAL-PRESSURE IN THE POSTERIOR TIBIAL AND RADIAL ARTERY PRESSURE WAVE IN NEWBORN-INFANTS

Mean arterial pressure (MAP) is the area under the pressure wave avera ged over the cardiac cycle, and therefore depends on pressure wave con tour. A generally used rule of thumb to estimate MAP of peripheral art eries in adults is adding one-third of the arterial pulse pressure (PP ) to diastolic arterial pressure (DAP). As peripheral pressure wave fo rms in neonates do not resemble adult peripheral wave forms, it may be expected that this rule of thumb does not hold for neonates. Previous ly, we found that MAP can be calculated by adding 50% PP to DAP in rad ial artery waves in neonates. In the present study, we investigated in neonates how MAP in the posterior tibial artery depends on systolic a nd diastolic pressure and we compared these findings to those found in the radial artery. Forty infants admitted for intensive care were stu died. We analyzed 5000 invasively and accurately obtained blood pressu re waves in the posterior tibial artery of 20 neonates and another 500 0 waves similarly obtained from the radial artery in another group of 20 neonates. We found that MAP in posterior tibial artery waves is wel l approximated by adding 41.5 +/- 2.0% of PP to DAP, whereas MAP in ra dial artery waves can be calculated by adding 46.7 +/- 1.7% of PP to D AP These values are significantly different (p < 0.0001). In conclusio n, the rule of thumb as used in the adult to find MAP, where 33% PP is added to DAP, does not hold for the newborn. We recommend to calculat e MAP in the tibial artery by adding 40% of PP to DAP and in the radia l artery by adding 50% of PP to DAP.