Accuracy of pulse oximetry in hypothermic neonates and infants undergoing cardiac surgery

To assess the accuracy of pulse oximetry under hypothermic conditions in neonates and infants undergoing cardiac surgery, and to assess the effect of probe site as well as probe site skin temperature on the reliability of pulse oximetry.

Prospective Study.

Cardiac operating room and intensive care unit of children's hospital.

Twenty-five infants <3 months of age undergoing cardiac surgery with cardiopulmonary bypass.

Pulse oximeter readings (Sp O2) from probes placed on the hand and foot were recorded at various skin temperatures and compared with hemoximeter oxygen saturations (Sa O2) obtained on simultaneously drawn arterial blood samples. Core temperature, arterial pressure and vasodilator use were recorded simultaneously.

Pulse oximetry bias (Sp O2 - Sa O2) increased to an unacceptable range (>+3% or <-3%) in 45.5% of the readings at foot probe site temperatures of <27 degrees. Pulse oximetry bias was within an acceptable range in 94.7% of the readings at temperatures >29 degrees. There was no significant difference between oximeter readings obtained from two probe sites (hand and foot). Administration of phenoxybenzamine improved the accuracy of pulse oximetry in ten infants at skin temperature of <27 degrees.

Pulse oximetry readings in small infants are likely to be unreliable at skin temperatures of <27 degrees, irrespective of probe site. Intravenous phenoxybenzamine appeared to improve the accuracy of pulse oximetry at low temperatures.