Therapeutic hypothermia for hypoxic ischaemic encephalopathy: initiation in special care nurseries

Controlled passive hypothermia is the technique used in SCNs in Victoria, under the guidance of PIPER, to initiate hypothermia treatment during stabilisation prior to retrieval and transport to the NICU. It allows the baby to cool naturally at ambient environmental temperature by removing all external heat sources (baby undressed with overhead radiant warmer turned off) and adding low-technology devices (refrigerated gel packs as in the ICE trial) to ‘actively’ lower the infant’s temperature. Temperature is manually controlled to maintain the continuously monitored core (rectal) temperature in the target range of 33°C–34°C.

It is suggested controlled passive hypothermia requires 1:1 nursing care to observe the baby’s temperature and to make frequent adjustments to the radiant warmer thermostat or to apply the gel packs; even with this, overshoot below the target range is common.

• Ensure adequate resuscitation and support for the baby, including attention to airway, breathing, circulation and glucose. Target an oxygen saturation of 91–95 per cent, an arterial pCO2 between 35–45 mmHg, a mean blood pressure of 40–50 mmHg, and true blood glucose of 3–7 mmol/L.
• Hypothermia is an adjunct therapy. The ability to commence hypothermia should not influence decisions to discontinue resuscitation attempts at birth.
• Assess criteria to consider hypothermia treatment. It is only considered for babies ≥ 35 weeks’ gestation at birth and should not be undertaken for preterm babies born before 35 weeks.
• Hypothermia should only be commenced following referral to PIPER and discussion with the PIPER neonatal consultant.
• Discuss asphyxia, HIE and hypothermia treatment with the parents; give parents the information sheet.

1. Moderate or severe encephalopathy between one and six hours after birth: seizures or the presence of signs in three of the six bolded categories in either the ‘Moderate encephalopathy’ or the ‘Severe encephalopathy’ in the modified Sarnat criteria checklist.

1. Evidence of perinatal hypoxia-ischaemia (asphyxia) as defined by the presence of at least two of the following:
   1. Apgar score of 5 or less at 10 minutes
   2. ongoing resuscitation (chest compressions) or ventilation (endotracheal tube or mask) at 10 minutes
   3. cord pH < 7.0 or if cord pH not available, blood gas pH < 7.0 or base deficit ≥ 12 within one hour of birth
2. Gestation ≥ 35 weeks
3. Less than six hours of age
4. None of:
   1. birthweight < 1.8 kg
   2. major (or suspected major) congenital abnormalities that are likely to result in death
   3. overt bleeding (including subgaleal haemorrhage)
   4. death is considered imminent

During cooling, continuous rectal temperature monitoring is recommended. If continual monitoring is not possible, rectal temperature should be measured and recorded every 15 minutes.

Procedure for continuous rectal temperature monitoring

1. Insert the rectal probe (for example, disposable/ single use ‘Vital temp general purpose probe 9 FR’) ≥ 5 cm into the anus tape the probe at the 10 cm (first) mark to the upper inner thigh.
2. Attach the probe to the cable and connect to the temperature module and/or monitor.
3. Ensure temperature alarm limits are set at 33°C (low) and 34°C (high) during the cooling period.
4. Leave the rectal probe in until the PIPER team arrives.

Large variability between rectal and axillary temperature measurements preclude the use of either intermittent axillary or continuous skin temperature measurements as a surrogate for continuous core (rectal) temperature monitoring during whole body therapeutic hypothermia.

Significant adverse effects have been reported in babies undergoing uncontrolled passive hypothermia with temperatures < 32°C. Hypothermia is not a benign treatment.

The odds of death or disability are increased up to four-fold for each 1°C increase in core temperature > 37.5°C. Hyperthermia, at any time, should be avoided.

The procedure for controlled passive hypothermia is as follows:

1. Nurse the baby naked on a radiant warmer with the warmer turned off and ensure:
   • no sheepskin
   • do not dress, or use a hat or any form of wrap (plastic or cloth)
   • leave the nappy unfastened.
2. Full cardiorespiratory, saturation and blood pressure monitoring.
3. If ventilated, use normal humidifier settings.
4. Monitor rectal temperature:
   • continuously, or
   • intermittently every 15 minutes with thermometer.
5. Record the time hypothermia treatment commenced and rectal temperature every 15 minutes.
6. All other documentation/care/treatment should be the same as in any asphyxiated baby with HIE waiting for transport by PIPER.
7. If rectal temperature drops below 33.5°C, set radiant warmer on manual and gradually adjust heater output to maintain rectal temperature between 33°C and 34°C.
8. If hypothermia has been underway for one hour and the rectal temperature is still > 35.5°C, discuss the use of refrigerated gel packs (active hypothermia) with the PIPER neonatal consultant.
9. If using refrigerated gel packs (for example, ‘hot/cold’ blue gel packs, Nexcare™ First Aid, 3M), ensure the packs are:
   • refrigerated at ~ 4°C (never frozen)
   •  wrapped in cotton covers or equivalent (for example, daylees); they should never be applied directly to the skin
   • placed:
     • one under the shoulders/upper back/head
     • the second across the chest/body.

Note: Using more than two packs prevents radiant loss of heat into the environment and makes it more difficult to cool the baby 

10. Record the time the gel packs were applied and continue to record rectal temperature every 15 minutes.

Algorithm to achieve the 33°C–34°C target rectal temperature range

11. If rectal temperature drops below 33.5°C, remove all gel packs and repeat temperature in 15 minutes. If the temperature continues to fall, set radiant warmer on manual and gradually adjust heater output to maintain rectal temperature at 33.0°C–34.0°C.

12. The aim is to achieve the target rectal temperature range 33.0°C–34.0°C within one hour, but more importantly, to continue to manage airway, breathing, circulation.

13. Advise/reassure parents about their baby’s appearance and that the baby will feel cool to touch.

14. The transport team will bring all the necessary equipment to continue the cooling process during transport.

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Commencement of therapeutic hypothermia in a special care nursery in a non-tertiary hospital

Clinical

• Jacobs SE, Berg M, Hunt R, Tarnow-Mordi WO, Inder TE, Davis PG. Cooling for newborns with hypoxic ischaemic encephalopathy. Cochrane Database of Systematic Reviews 2013, Issue 1. Art. No.:CD003311.DOI: 10.1002/14651858.CD003311.pub3
• Jacobs SE, Morley CJ, Inder TE, Stewart MJ, Smith KR, McNamara PJ, Wright IMR, Kirpalani HM, Darlow BA, Doyle LW; Infant Cooling Evaluation collaboration. Whole-body hypothermia for term and near-term newborns with hypoxic-ischemic encephalopathy. A randomized trial. Archives of Pediatrics and Adolescent Medicine. 2011;165(8):692-700
• Jacobs SE. Hypothermia during patient transport. In: Edwards AD, Azzopardi DV, Gunn AJ, editors. Neonatal Neural Rescue: A Clinical Guide: Cambridge University Press; 2013. p. 95-106.
• Landry MA, Doyle LW, Lee KJ, Jacobs SE. Axillary temperature measurement during hypothermia treatment for neonatal hypoxic-ischaemic encephalopathy. Archives of Diseases in Childhood Fetal Neonatal Edition. 2013;98(1):F54-F58
• New South Wales Department of Health. Whole body cooling - neonates suspected moderate or severe hypoxic ischaemic encephalopathy (HIE) Policy Directive 2010_006. 22-January-2010
• Sarnat HB, Sarnat MS. Neonatal encephalopathy following fetal distress. A clinical and electrographic study. Arch neurol 1976:33(10);696-705