Dr Katherine Taylor | Dr Nandiran Ratnavel
Midnight on NICU. The crash call suddenly goes out on labour ward. As you run by, a midwife calls out ‘it’s a shoulder dystocia…’ Your team arrives to find a blue, floppy baby with no heart rate, and while you start giving breaths, intubation equipment is being frantically prepared. You have a bad feeling about where this is heading.
Perinatal asphyxia leading to Hypoxic Iscahemic Encephalopathy (HIE) happens in 3/1000 births in the UK. Therapeutic hypothermia, or total body cooling, is now the standard of treatment for babies with moderate to severe hypoxic brain injuries at birth. If you’re already in a tertiary level unit that offers cooling therapy, this is pretty simple to arrange. But for the neonatal team in a smaller district general hospital where you have to transfer your babies out to another hospital for cooling, this can be trickier. Obviously time is of the essence, so discussions about ‘passive cooling’ often come up. So… should we be passively cooling all of these babies, and what guidance should we be following?
The evidence for cooling comes from the TOBY trial (as well as other international studies) which showed that lowering body temperature by 3-5 degrees after perinatal asphyxia reduces the risk of cerebral injury and improves long-term neurological outcome. The results showed significant improvement in survival with neurology abnormalities and improved neurodevelopmental outcomes in babies with moderate to severe HIE. The treatment protocol for the trial was 72 hours of total body cooling, aiming for a core temperature of 33-34 degrees celcius (monitored continuously by rectal thermometer) using cooling blankets, or cold air/water circulated through a cap, blanket or mattress.
Cooling should be started in any baby that meets criteria A and B below. The cause of the hypoxic injury might be obvious at the time of birth – shoulder dystocia, cord prolapse, massive APH – but you can be faced with a baby born in a poor condition very unexpectedly if there has been an antenatal insult.
Note: Babies with evidence of encephalopathy but that do not fulfil the criteria should still be discussed as cooling may still be considered.
As soon as initial resuscitation is finished, you should be starting your assessment for cooling, speaking to your local cooling centre and/or transport team. Current evidence is that cooling is unlikely to work if started more than six to eight hours after birth.
What are the risks?
Hypoxia doesn’t just affect the brain- babies that have had a hypoxic injury around the time of birth can also have multi-system organ damage which can make it difficult to optimise your management. Some of the negative effects of cooling include bradycardia, thromobocytopenia, coagulopathy, hypotension and hypocalcaemia. These could lead to poor respiratory or cardiovascular outcomes, so cooling should be used with caution in babies who are clinically unstable. Basic life support is the priority – if there is severe hypoxaemia that can’t be managed, cooling might have to be stopped.
Cooling might be not appropriate if:
- The baby is likely to require surgery during the first 3 days after birth
- There are other abnormalities indicative of poor long term outcome
- The baby appears moribund, or has persistent severe encephalopathy such that further treatment is likely to be futile, for example if the aEEG/EEG is isoelectric beyond 12-24 hours of age
- There is severe ongoing hypoxaemia
- There is coagulopathy or evidence of bleeding
Clinical management (based on NTS Cooling Toolkit)
- Do you need more help? This baby is likely to need your full attention, and will be easier to manage if you are not challenged with competing tasks.
- Is the airway secure? Not all babies that require cooling need intubation, but consider it.
- Is the baby saturating well? Measure pre & post ductal saturations (a difference of 5% or greater may indicate right to left ductal shunting, i.e. PPHN)
- If ventilated – is the baby normocarbic? (Aim 4.5kPa – 6kPa)
- Cerebral blood flow is extremely sensitive to CO2 variations, so ventilation should be carefully monitored to help maintain normal CO2 levels.
- Is the baby cardiovascularly stable? Whilst fluid restriction to 40ml/kg/day is the accepted standard in cooled babies, correct hypovolaemia where necessary. A baby who has a suboptimal blood pressure and is poorly perfused may need inotropes.
- Are the blood sugars acceptable? Aim for normoglycaemia.
- What kind of access do you need – central lines may not be a priority in a baby who is stable
- Make sure Hb is over 120g/L. Check platelets and coagulation, correct them if necessary. Discuss with tertiary centre if severely coagulopathic as cooling might be contraindicated.
- Is CFM monitoring available? Have you done a cranial ultrasound? (transport increases the risk of IVH)
- Cooling is uncomfortable – consider sedation
- Documentation – BADGER summary (including a Sarnat or Thompson score neurological assessment!) is a priority if baby is to be transferred.
The TOBY group has strict guidance on starting passive cooling while waiting for the arrival of the retrieval team, emphasising the importance of initial basic resuscitation. Here’s a quick summary:
- Assessment for cooling should be done as early as possible using the TOBY criteria
- While making initial referral for cooling the team should aim for standard intensive care and normal body temperature
- Passive cooling to only commence once cooling cot accepted
- Once passive cooling is commenced, aim to start continuous rectal temp
- If rectal monitoring not available, measure axillary temp every 15 mins
- Turn incubator off, have baby naked except for nappy and open portholes
- Ensure temp does not fall below 33ºC
- If passive measures are not working, ask advice about active cooling measures such as a fan but these can overcool, so use with caution
There are 18 transport services across the UK. 15 of these have active cooling units on board for use during transfers.
London’s Neonatal Transfer Service (NTS) has transferred hundreds of babies for cooling and has published several research studies. In 2010 they found that passive cooling was simple and effective for starting therapeutic hypothermia before and during transport, and meant that therapy could start earlier (1). However, rectal (or at the very least axilla temperature monitoring every 15 minutes) was essential – some babies were cooled to under 33°C. A later study in 2017 compared active vs passive cooling during transfer, with servo-controlled cooling mattress equipment (2). This study found that active cooling got to the baby to target temperature in a shorter period than passive cooling, and there was better temperature stability.
The Acute Neonatal Transfer Service (ANTS, for the East of England) looked at active vs passive cooling during neonatal transport in 2013 (3) – they saw that servo-controlled active cooling reduced the transfer time to the regional unit and there was better temperature stability on arrival (39% of infants who were passively cooled were within target temperature range, compared to 100% of those infants who were actively cooled).
The Newborn Emergency Stabilisation and Transport team (NEST, based in Bristol) compared passive cooling, active cooling with adjuncts and active cooling with a purpose built cooling machine (4). They found that a purpose-built cooling machine was the most reliable way to get adequate therapeutic hypothermia during transport. Cooling with adjuncts and passive cooling often failed to get temperatures within the right range.
As of 1st April 2017 all trusts have to report any babies diagnosed with grade 3 HIE or who are therapeutically cooled within 30 days to the trust’s legal services, so an investigation can take place. That means it is absolutely essential that the clinical decisions about cooling (and meeting criteria A and B) are clearly documented, and that neurological examinations are fully documented.
- ABCDE approach first and foremost. Good quality resuscitation and stabilization is key
- Early discussions with cooling centre and transports teams
- Aim for normothermia until there is a decision about therapeutic cooling
- Active cooling is more effective and more reliable at achieving target temperature than passive cooling
- Most transport teams have active cooling facilities on board, meaning active cooling can be commenced in most babies within the 6 hour window.
- If in doubt, maintain normothermia
For more detailed guidance, look at “UK TOBY cooling register clinicians handbook, version 4, May 2010”.
Dr Katherine Taylor (Paediatric ST7), Dr Nandiran Ratnavel (Consultant Neonatologist; Neonatal Transport Consultant with NTS)
1) Arch Dis Child Fetal Neonatal Ed. 2010 Nov;95(6):F408-12. Passive cooling for initiation of therapeutic hypothermia in neonatal encephalopathy. doi: 10.1136/adc.2010.187211.
2) Am J Perinatol. 2017 Jan;34(1):19-25. doi: 10.1055/s-0036-1584151. Comparison of Passive and Servo-Controlled Active Cooling for Infants with Hypoxic-Ischemic Encephalopathy during Neonatal Transfers.
3) Pediatrics. 2013 Nov;132(5): Active Versus Passive Cooling During Neonatal Transport
4) Acta Paediatr. 2011 Aug;100(8):1084-6; Therapeutic hypothermia during neonatal transport. discussion e49. doi: 10.1111/j.1651-2227.2011.02249.x