Cooling Overview

Malcolm Battin

Feb
2010

Cooling has been recognised as an effective intervention to decrease adverse neuro-developmental outcomes following perinatal asphyxia ^1-5. There are no studies that have performed direct comparison between selective head cooling and whole body cooling and it is generally considered that both techniques provide neuroprotection.

Indications:

Cooling may be indicated in infants with moderate to severe neonatal encephalopathy following a perinatal asphyxia episode. Each case should be discussed with the attending neonatologist but in general infants should fulfil the following criteria.
Greater than or equal to 36 weeks corrected gestational age
Evidence of perinatal asphyxial episode including one of the following:
- pH < 7.0 or base deficit of -12 mmol/l or more
- Ongoing resuscitation requirement including positive pressure ventilation after 10 mins
- Apgar score < 6 at 10 mins
Less than 6 hrs of age (Babies between 6 and 12 hrs of age may be cooled at individual consultant discretion)
Clinical signs consistent with moderate or severe encephalopathy

It is essential that infants should be adequately resuscitated prior to active cooling.

Severe congenital malformations may be a relative contraindication and would need to be assessed on individual merit. Ano-rectal malformations may mean it is not possible to monitor rectal temperature.

For infants who are moribund and considered likely to die imminently cooling should not be initiated and the focus should be on either further resuscitation or terminal care.

Infants from peripheral centres may require transfer for cooling. For a short distance transfer within the city passive cooling is likely to be adequate, particularly if the infant is transferred quickly to the level 3 centre for cooling.

NB. Infants should not be cooled without monitoring of core temperature.

Although cooling is generally well tolerated there are a number of potential complications that should be anticipated.

Complications:

Bradycardia
Potential for pulmonary hypertension
Potential increase in BP support
Potential increase in requirement for blood products
Potential disturbance of coagulation cascade

NB. hypothermia will potentially slow down the metabolism and / or excretion of drugs including opiates ⁶, anticonvulsants and aminoglycoside antibiotics. Thus care should be taken with dosing and monitoring of levels to avoid excessive accumulation.

Application of Cooling

Care is taken to not overheat the infant prior to cooling

Infant should be nursed on a radiant heat table
Turn off radiant heat source and allow to cool passively
Umbilical venous and arterial lines should be inserted as venous access may not be easy to establish once the infant is cooled and frequent blood samples +/- invasive BP monitoring may be required
Insert approved rectal probe to 5 cm
Turn off radiant heat source and allow to cool passively
Follow link to specific instructions for Criticool body cooling or selective head cooling set up and instructions.
Cooling normally continues for a period of 72 hours before careful rewarming
Infants are nil by mouth for the duration of cooling

Follow up of baby after cooling completed

Step	Action
1	Neurological examination of the baby and head circumference, weight and length measurements Electroencephalogram and magnetic resonance imaging (MRI) to be done when clinically possible Any tests that were abnormal at 72 hours, such as an elevated creatinine level should be repeated.
2	Review at 3 months of age: At 3 months there should be follow up clinic visits with the paediatrician with neurodevelopmental examination and measurements of head circumference, weight and length. Audiology assessment as outpatient
3	Age 18 months to two years: Neurodevelopmental examination by a paediatrician, measurement of head circumferences, weight and length. Formal psychometric testing by a clinical psychologist

References

1	Hypothermia to treat neonatal hypoxic ischemic encephalopathy: systematic review. Shah PS, Ohlsson A, Perlman M. Arch Pediatr Adolesc Med. 2007;161(10):951-8
2	Cooling for newborns with hypoxic ischaemic encephalopathy. Jacobs S, Hunt R, Tarnow-Mordi W, Inder T, Davis P. Cochrane Database Syst Rev. 2007;(4):CD003311.
3	A systematic review of cooling for neuroprotection in neonates with hypoxic ischemic encephalopathy - are we there yet? Schulzke SM, Rao S, Patole SK. BMC Pediatr. 2007;7:30.
4	Whole-body hypothermia for neonates with hypoxic-ischemic encephalopathy. Shankaran S, Laptook AR, Ehrenkranz RA, et al. National Institute of Child Health and Human Development Neonatal Research Network. N Engl J Med. 2005;353:1574-84
5	Selective head cooling with mild systemic hypothermia after neonatal encephalopathy: multicentre randomised trial. Gluckman PD, Wyatt JS, Azzopardi D, et al. Lancet. 2005;365(9460):663-70
6	Elevated morphine concentrations in neonates treated with morphine and prolonged hypothermia for hypoxic ischemic encephalopathy. Róka A, Melinda KT, Vásárhelyi B, Machay T, Azzopardi D, Szabó M. Pediatrics. 2008 Apr;121(4):e844-9.