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Active versus passive cooling during neonatal transfer

Presented at the Neonatal Society 2012 Autumn Meeting (programme).

Chaudhary R1, Broster S1, Farrer K1, Austin T2

1 Acute Neonatal Transfer Service for the East of England, UK
2 Neonatal Intensive Care Unit, Rosie Hospital, Cambridge University Hospitals NHS Foundation Trust, UK

Background: Therapeutic hypothermia is now recommended as the standard of care for the management of infants with moderate or severe hypoxic – ischaemic encephalopathy (HIE) (1). Current practice in the UK is that most infants are treated in regional neonatal intensive care units (NICUs). Evidence suggests treatment should begin as soon as possible after birth thus cooling should be initiated at the referring hospital and continued during transfer to the regional NICU. A number of small series have reported the experience of passive and active cooling during transfer of these infants, but to date there is no published large comparative series or recommended consensus on the optimal method for maintaini ng hypothermia during transfer (2,3).

Methods: The Acute Neonatal Transfer Service (ANTS) for the East of England have delivered therapeutic hypothermia during transfer since June 2009. In October 2009 the service hours increased to 24 hours daily. Initially infants were stabilised and transferred using passive cooling methods. Since March 2011 infants have been actively cooled using a servo-controlled mattress.

The aim of this retrospective observational study was to compare the effectiveness of passive and active cooling during transfer. The key outcome measurements were: time to target temperature, stabilisation time and temperature stability during transfer. Target temperature range was defined as 33.0-34.0ºC. As a marker of temperature stability the percentage of time within this range during transfer was calculated for each infant. Unpaired t-test was used to compare the differences between the two different groups.

Results: Between June 2009 and May 2012 a total of 143 infants with HIE requiring cooling were referred for transfer and 134 transferred. Passive cooling methods were used in all infants by the referring hospital to initiate therapeutic hypothermia. Following arrival of the ANTS team, cooling was maintained passively in 64 infants until arrival at the regional NICU and 70 were actively cooled using the servo-controlled Tecotherm Neo (Inspiration Healthcare). There was no significant difference in gestation, birthweight, sex, or age at referral between the two groups. The mean (+/ – SD) time cooling was initiated in the passive group was 141 (+/-121) min ute s and 80 (+/-85) minutes in the active group (t=3.31, p=0.001). The mean (+/-SD) stabilisation time in the passive group was 178 (+/-81 ) minutes and 151 (+/-77) minutes in the active group (t=2.03, p=0.04). The mean (+/-SD) time within target temperature range in the passive group was 45.8 (+/-35.8)% and 81.2 (+/-21.5)% (t= 6.53, p=0.0001). 34.4% of infants transferred passively cooled were overcooled (temperature <33ºC) compated with 11.2% of infants actively cooled.

Conclusion: These data suggest that while initiation of therapeutic hypothermia is achievable with passive methods, maintenance and stability of temperature is significantly enhanced using a servo-controlled cooling mattress. Additionally the thermal stability of the active method results in a significant reduction in stabilisation time and allows the transfer team to focus on other aspects of the infants’ management. Furthermore active cooling during the journey prevents potentially serious over-cooling. Servo-controlled cooling should be considered by all transfer teams as a safe and effective way of managing infants with HIE during transfer. 

Corresponding author: topun.austin@nhs.net

References
1. NICE IPG374: Therapeutic hypothermia with intracorporeal temperature monitoring for hypoxic perinatal brain injury: guidance. Issued May 2010http://www.nice.org.uk/nicemedia/live/11315/48809/48809.pdf
2. Kendall GS, Kapetanakis A, Ratnavel N, et al. Passive cooling for initiation of therapeutic hypothermia in neonatal encephalopathy. Arch Dis Child Fetal Neonatal Ed. 2010; 95 :F408-12.
3. O’Reilly K, Tooley J, Winterbottom S. Therapeutic hypothermia during neonatal transport. ActaPaediatrica 2011; 100 :1084 – 6.

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