ACCURACY OF OSCILLOMETRIC BLOOD-PRESSURE MEASUREMENT IN CRITICALLY ILL NEONATES WITH REFERENCE TO THE ARTERIAL-PRESSURE WAVE SHAPE

Objective: To perform further evaluation of the oscillometric device f or neonatal arterial blood pressure (ABP) measurement, using a cathete r-manometer system (CMS) for accurate intraarterial measurement. We ai med to describe the influence of the radial artery wave shape on oscil lometric ABP determination, as pressure wave-shape influences the rela tionships between systolic arterial pressure (SAP), diastolic arterial pressure (DAP) and mean arterial pressure (MAP) in the wave. These re lationships are part of the algorithms contributing to the final ABP d etermination in the oscillometric device. Design: Intra-patient compar ison of two blood pressure measurement systems. Setting: Neonatal inte nsive care unit. Patients: In 51 critically ill newborn infants, ABP w as determined oscillometrically in the brachial artery and, simultaneo usly, invasively in the radial artery using a high-fidelity CMS. Clini cal data of the infants were: gestational age: 29 (25-41) weeks; birth weight: 1200 (500-3675) g, postnatal age: 6 (2-46) h. Methods: Statist ical analysis was performed with the paired Student's t-test. Multiple regression analysis was used to determine the influence of birthweigh t and height of the blood pressure on the results. Measurements and ma in results: In 51 infants, 255 paired values of SAP, DAP and MAP were recorded. In all recordings, we determined the relationship between SA P, DAP and MAP, using the equation: MAP = alpha%(SAP - DAP) + DAP. For SAP, DAP, MAP and alpha, we computed mean differences (bias) and the limits of agreement (precision). Biases for SAP, DAP, MAP and alpha we re significantly different from zero (P < 0.001) and the limits of agr eement for SAP, DAP and MAP were wide: 18.8 mmHg, 17.2 mmHg and 15.2 m mHg respectively. The relationship between invasive and noninvasive va lues is only partly (7-19%) influenced by the height of the blood pres sure; low values of SAP, DAP and MAP tend to give overestimated oscill ometric values. In the relationship between SAP, DAP and MAP, alpha wa s found to be 47% invasively (as generally found in the radial artery in newborns) and 34% noninvasively (as generally found in the brachial /radial artery in adults). Conclusions: Inaccuracy of the oscillometri c device may be partly explained by the incorporation of an inappropri ately fixed algorithm for final ABP determination in newborns. Care sh ould be taken when interpreting the oscillometrically derived values i n critically ill newborn infants.