Admission hypo- and hyperthermia are associated with increased mortality and morbidity in very preterm infants

[EBNEO]

We, EBNEO, would like to share one of our latest commentaries, this time on a study on admission temperature and risk of adverse outcomes, written by Julia Maletzki, Stephanie Adzikah, Christoph Rüegger, and Dirk Bassler, at the University Hospital of Zurich, Switzerland.

Find the full EBNEO review on ebneo.org!

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Even though the pathophysiologic mechanisms of hypo- and hyperthermia and their impact on infants’ outcome have been known for a long time, most previous research merely covers one end of the temperature scale, namely hypothermia.

In this Canadian Neonatal Network study, Lyu et al. retrospectively investigated the effect of admission body temperature (low and high) on adverse outcomes of preterm infants. The nation-wide participation resulted in an impressive number of included infants with only very few drop outs. Nevertheless, there are a few comments to make.

The authors define the admission temperature as the temperature taken with the first vital signs within the first hour of the infant’s admission to the NICU. Information about the infant’s chronological age when admission temperature was measured is missing.

There is no standard protocol to measure the admission temperature. Not only does the location of temperature acquisition vary (rectal vs. axillary) but also the temperature detecting device. The authors cite Craig et al., who concluded that there is a pooled mean temperature difference of 0.17 °C between axillary and rectal temperature. This indicates only a small – probably not significant – difference between the two measurement locations. They forgot to mention that the range of temperature difference was wide and that the temperature measurement device (mercury vs. electronic) plays an important role. Mercury thermometers had narrower limits of agreement when comparing axillary vs. rectal temperature. Other studies also come to the conclusion that axillary and rectal temperatures are not interchangeable in preterm infants.

Important, but not documented, are possible confounders like the mother´s temperature at birth or the time needed to transport the baby from the delivery room to the NICU. Other confounders like ventilation with a dry circuit or the use of fluids for resuscitation are not mentioned, as well. The authors included factors like these in their infants´ characteristics (Apgar score < 7 with 5 minutes, SNAP II > 20, resuscitation needed) and applied a univariate analysis which showed that these factors were associated with admission temperature.

In addition, the primary composite outcome may contain too many individual components. Schmidt et al presented a count of 3 major neonatal morbidities, namely bronchopulmonary dysplasia, brain injury and severe retinopathy of prematurity as the most important prognostic factors for neurodevelopmental outcome at 18 months. Bassler et al. showed that necrotizing enterocolitis and sepsis (except meningitis) are weaker predictors of a poor long-term outcome. Late-onset sepsis, on the other hand, has been shown to be inversely correlated with hypothermia, which might have been the reason for adding sepsis to the composite primary outcome.

For the secondary outcome the authors calculated the admission temperature at which each single adverse outcome was at its lowest rate. This is interesting on a theoretical basis, but not applicable for clinical everyday life.

In conclusion, the authors found an association between hypo- and hyperthermia and an adverse neonatal outcome, which calls for continuous monitoring of body temperature in extremely preterm infants as part of routine resuscitation.