Comparing Axillary and Rectal Temperature Measurements in Very Preterm Infants: A Prospective Observational Study

Abstract

<b><i>Purpose:</i></b> The agreement between axillary temperature (AT) and rectal temperature (RT) measurements has not been well established in preterm infants. Therefore, our study aimed to evaluate the agreement between AT and RT measurements in very preterm infants. <b><i>Methods:</i></b> Preterm infants &#x3c;32 weeks of gestational age were prospectively included. The infants’ body temperature (BT) was measured twice a day from day 1 to day 6. A paired <i>t</i>-test and the Bland-Altman method were used to analyze the difference between the AT and RT. A linear regression model was used to explore the effects of environmental factors on the differences of BT between the axillary and rectal measurements and to calibrate the RT according to the AT. <b><i>Results:</i></b> Eighty infants each underwent 6 paired axillary and rectal measurements. The gestational age varied from 22 to 31 weeks (mean 28 weeks). The birth weight varied from 302 to 1,770 g (mean 1,025 g). The AT was significantly lower than the RT. The difference between the RT and AT significantly increased with increasing RT. The AT and RT demonstrated poor agreement overall; however, the RT can be estimated using the AT with the following equation: RT = −4.033 + 1.116 × AT. Environmental factors, including the incubator temperature, incubator humidity, phototherapy, and application of invasive mechanical ventilation did not affect the differences between the AT and RT measurements. <b><i>Conclusion:</i></b> AT measurements cannot be interchangeably used with RT measurements in very preterm infants.