Presented at the Neonatal Society 2009 Autumn Meeting.
Hoque N, Chakkarapani E, Liu X, Thoresen M
Department of Child Health, University of Bristol, Bristol, UK
Background: Therapeutic hypothermia has been shown to improve outcome following perinatal asphyxia in three large clinical trials(1-3). Although the principles of cooling infants remain the same the method of cooling has differed greatly both within and outside the trial setting. It is unclear whether there are differences in temperature and haemodynamic stability between methods.
Aim: To compare cooling methods during therapeutic hypothermia for moderate or severe perinatal asphyxia with regard to temperature and haemodynamic stability.
Methods: A total of 73 newborns received therapeutic hypothermia in our centre between July 1999 and January 2009. We compared all four methods used: selective head cooling with mild systemic hypothermia using cap (SHC) (n=20), whole body cooling with mattress manually-controlled (WBCmc) (n=23), whole body cooling with body wrap servo-controlled (WBCsc) (n=28) and whole body cooling with water-filled gloves (n=2). Target rectal temperatures (Trec) were 34.5± 0.5°C (SHC) and 33.5±0.5°C (WBC). Hourly data were collected on Trec, mean arterial blood pressure (MABP) and heart rate (HR).
Results: Groups were similar with respect to baseline characteristics and condition at birth. Trec was maintained within target temperature ± 0.5°C for 97% of the time in WBCsc infants, 81% in WBCmc infants, 76% in SHC infants and 66% in infants cooled with gloves. There was marked overshoot in WBCmc and SHC groups during onset of cooling. Mean maximum overshoot was 0.3°C for WBCsc, 1.3°C for WBCmc and 0.8°C for SHC groups. There was no difference in mean MABP during the maintenance of cooling between groups (49mmHg[8] for SHC, 51mmHg [8] for WBCmc, 51mmHg[9] for WBCsc) and nor was there difference in mean HR between groups (107bpm[22] for WBCsc, 105bpm[16] for WBCmc, 103bpm[16] for SHC). There was greater variation in Trec during rewarming in SHC compared with WBCsc group (p<0.01).
Conclusion: Use of manually-controlled cooling systems is associated with greater variability in Trec compared with servo-controlled systems. A manual mattress often causes overcooling during onset of therapy. It is unknown whether large variation in temperature adversely affects the neuroprotection of therapeutic hypothermia. The small variability observed in MABP and HR with all methods is unlikely to be clinically significant.
References
1. Gluckman PD, et al. Selective head cooling with mild systemic hypothermia after neonatal encephalopathy: multicentre randomised trial. Lancet. 2005;365(9460):663–70.
2. Shankaran S, et al. Whole-body hypothermia for neonates with hypoxic-ischemic encephalopathy. NEJM. 2005;353(15):1574–84.
3. Azzopardi DV, et al. Moderate hypothermia to treat perinatal asphyxial encephalopathy. NEJM. 2009;361(14):1349-58.