Effects of the Temperature of Inspired Gases on Arterial Oxygen Saturation and the Accuracy of a Pulse Oximeter in Intubated Newborn Piglets

Abstract

The effects of cold stress on the newborn, especially on peripheral perfusion, are well documented. We studied the effects of varying airway temperatures on (1) the arterial oxygen saturation as measured by in-vitro oximetry (SaO₂) and (2) the accuracy of pulse oximeter arterial oxygen saturation measurements (SpO₂) in newborns because adequate perfusion is necessary to successfully measure SpO₂. Method: Six intubated newborn piglets ranging in age from 3 to 5 days and weighing 1300-1840 grams were studied. We maintained their core temperature above 36 °C and randomly varied and controlled the temperature of the inspired gases at 30 °C, 33 °C, and 36°C. We sampled blood from the descending aorta, measured the SaO₂ on an Instrumentation Laboratory 282 CO-Oximeter and simultaneously measured SpO₂ with an Ohmeda Biox III pulse oximeter. We compared the two measurements of oxygen saturation at each airway temperature (the SaO₂ at 36 °C and 30 °C, and the SpO₂ at 36 °C and 30 °C) and tested the significance of the differences with the Student's t test for paired samples at an alpha level of 0.05. Results: At 30 °C, mean SpO₂ was 86.2 ± 5.52% (mean ± SD), and mean SaO₂ was 90.4 ± 2.43%. At 33 °C, mean SpO₂ was 87.3 ± 5.98%, and mean SaO₂ was 91.0 ± 2.99%. At 36 °C, mean SpO₂ was 91.9 ±3.41%, and mean SaO₂ was 90.9 ± 2.64%. Although there were no statistically significant differences between SpO₂ and SaO₂ at any of these three airway temperatures, SpO₂ was significantly lower at 30 °C than at 36 °C (P<0.05), even though SaO₂ did not differ at these temperatures. Conclusions: We conclude that (1) short term exposure to inspired gases as low as 30 °C does not affect arterial oxygenation, and (2) measurements of SpO₂ may be less accurate than SaO₂ measurements in intubated newborns with airway temperatures of 30 °C or less. At airway temperatures of 30 °C, clinical decision making may be affected if pulse oximetry alone is used as the indicator of arterial oxygen saturation. (Respir Care 1988;33:188-192.)