Objective: We investigated the reliability of the plethysmographic waveform of the pulse oximeter to measure systolic blood pressure in sick neonates.
Methods: Fifty infants admitted to the neonatal intensive care unit, with indwelling arterial catheters placed for their ongoing care, were enrolled. Median gestational age was 31 weeks (range, 24 to 40 weeks), and the mean birth weight was 1711 gm (range, 546 to 3856 gm). Blood pressure was recorded by an oscillometric method as well as from a transducer connected to an arterial catheter. Additionally, pulse oximeter blood pressures were obtained by gradually inflating an appropriately sized blood pressure cuff in increments of 2 to 5 mm Hg, on the same extremity as the oximeter probe, until the waveform just disappeared. The cuff was then rapidly inflated another 20 mm Hg and then gradually deflated in increments of 2 to 5 mm Hg until the waveform reappeared on the oximeter screen display. The pulse oximeter blood pressures were calculated both as the blood pressure noted at disappearance of the pulse oximeter waveform and as the blood pressure noted by the average pulse oximeter blood pressure at the disappearance and reappearance of the waveform. The mean intraarterial systolic blood pressure was 54 mm Hg (range, 36 to 82 mm Hg).
Results: Blood pressures obtained by pulse oximetry showed a significantly better correlation with intraarterial measurements in comparison with those obtained by oscillometric instruments. Additionally, the limits of agreement (mean difference +/- 2 SD) between blood pressures obtained by intraarterial measurements and those obtained by pulse oximetry were within a clinically acceptable range as opposed to those obtained by the comparison of intraarterial and oscillometric methods.
Conclusion: Measurements of blood pressure in the neonate by means of pulse oximetry waveform analysis are easily obtainable and more accurate than those obtained by the oscillometric method.