Hidden Hypothermia in Outborn Very Low Birthweight Infants

Background: The neonatal golden hour is defined as the first 60 minutes of postnatal life in premature infants. Hypothermia during that time has been identified as a critical indicator of significant morbidity and mortality. The issue of hypothermia also effects infants born in other facilities (outborn). Outborn infants requiring transport to a higher level of care are often hours old by the time of admission and represent a population at risk for hypothermia. The aim of this study was to identify hypothermia risk factors and to identify areas of improvement for future intervention.

Methods: This is a retrospective review of very low birthweight (VLBW, <1500 gm) infants transported by the Vanderbilt Children’s Hospital Neonatal Transport team from August 2017 to June 2021. There were 107 infants transported with 6 excluded due to incomplete data (total 101). Pre-identified potential risk factors for hypothermia ( <36.5°C) were collected and compared among the hypothermic (44) and normothermic (57) patients. The data was compared using the student’s T and Chi square tests when indicated.

Results: There were 44 infants (43.6%) who had documented hypothermia, however NICU admission hypothermia was only detected in 21 (20.8%) infants. Of the hypothermic patients, 38 (86.4%) had an initial temperature <36.5°C on arrival of the transport team and 6 (13.6%) developed hypothermia during transport. Prior to team arrival 6 patients were hyperthermic (>37.5°C) and 6 patients were hyperthermic on arrival to the NICU. Temperatures were not affected by arrival time of the transport team at the referring hospital, transit time or time of life the infant arrived to the NICU (Table 1). Hypothermia was associated with lower gestational age and birthweight, delivery hospital level of care, total bedside time and need for intubation (Table 1). The need for >2 bedside procedures was associated with a longer bedside time (123. 3 vs 93.9 min, p<0.01), initial hypothermia (36.1 vs 36.8, p<0.01) and a non-clinically significant difference in admission temperature (36.6 vs 36.9, p=0.02).

Conclusion: Hypothermia was prevalent among outborn VLBW infants prior to the arrival of the transport team. Over half of these infants achieved normothermia by arrival to the NICU, representing improved thermoregulatory control. Hypothermic infants were younger, smaller and likely more critical, as indicated by the need for intubation. We hypothesize that the longer bedside time in the hypothermic infants directly relates to critical illness and the need for multiple procedures. Care must be taken during procedures to mitigate heat loss. These infants were more likely to deliver at level 1 nurseries not equipped to provide intensive thermoregulation. This emphasizes the importance of community education and the need for more detailed counseling on thermoregulation by the medical control physician.