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 for neonatal arterial blood pressure (ABP) measurement, using a catheter-manometer system (CMS) for accurate intraarterial measurement. We aimed to describe the influence of the radial artery wave shape on oscillometric ABP determination, as pressure wave-shape influences the relationships between systolic arterial pressure (SAP), diastolic arterial pressure (DAP) and mean arterial pressure (MAP) in the wave. These relationships are part of the algorithms contributing to the final ABP determination in the oscillometric device.

DESIGN

Intra-patient comparison of two blood pressure measurement systems.

SETTING

Neonatal intensive care unit.

PATIENTS

In 51 critically ill newborn infants, ABP was determined oscillometrically in the brachial artery and, simultaneously, invasively in the radial artery using a high-fidelity CMS. Clinical data of the infants were: gestational age: 29 (25-41) weeks; birthweight: 1200 (500-3675) g, postnatal age: 6 (2-46) h.

METHODS

Statistical analysis was performed with the paired Student's t-test. Multiple regression analysis was used to determine the influence of birthweight and height of the blood pressure on the results.

MEASUREMENTS AND MAIN RESULTS

In 51 infants, 255 paired values of SAP, DAP and MAP were recorded. In all recordings, we determined the relationship between SAP, 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 were significantly different from zero (P < 0.001) and the limits of agreement for SAP, DAP and MAP were wide: 18.8 mmHg, 17.2 mmHg and 15.2 mmHg respectively. The relationship between invasive and noninvasive values is only partly (7-19%) influenced by the height of the blood pressure; low values of SAP, DAP and MAP tend to give overestimated oscillometric values. In the relationship between SAP, DAP and MAP, alpha was 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 oscillometric device may be partly explained by the incorporation of an inappropriately fixed algorithm for final ABP determination in newborns. Care should be taken when interpreting the oscillometrically derived values in critically ill newborn infants.