Critically evaluate the role of induced hypothermia in the management of traumatic brain injury.
Induced hypothermia refers to the use of techniques to intentionally lower the core body temperature below a physiological level (i.e. <36 degrees), in this case, in a patient with a traumatic brain injury.
• Reduction in metabolic rate
• Reduction in oedema
• Modification of the inflammatory response
Therapeutic (for the management of elevated intracranial pressure)
• Reduction in core body temperature is associated with a reduction in cerebral metabolic
rate and reduction in cerebral blood flow
• Will be associated with a reduction in intracranial pressure
• Noted cerebral protective effect in animal models and in case reports of survival with good
neurological recovery in hypoxic ischaemic encephalopathy in patients with severe
• Known that hyperthermia is associated with worse neurological outcomes
• Requires sedation and neuromuscular blockade with the attendant adverse effects
• Lower temperature predisposes to infective complications, in particular pneumonia
• Cardiac dysrhythmias
• Overshoot can expose patients to adverse effects of more severe hypothermia
o Diuresis and electrolyte disturbance
o Immune suppression
• Adverse effects of cooling devices (loss of skin integrity) and monitoring devices
• Cost of prolonged ICU stay and increased requirement for intervention and monitoring
• Initial studies and meta-analysis showed promising results with regards to improved
• Subsequent studies are less positive
Cochrane Systematic Review 2009
No evidence of benefit.
Significant benefit shown in low quality trials with tendency to over-estimate the treatment effect
• Nine class I and II studies, and 3 Class III studies summarised in BTF.
• Since then two paediatric studies and a Japanese study have been published
Brain Trauma Foundation (2016):
“Level II B: Early (within 2.5 hours), short-term (48 hours post-injury) prophylactic hypothermia is not recommended to improve outcomes in patients with diffuse injury”.
Elevated ICP management:
• EUROTHERM-3235 study
o Induced hypothermia has an effect on reducing intracranial pressure, but the effect on
outcome is variable
o Little clinical evidence on the effect on other important aspects of cerebral physiology
e.g. cerebral blood flow or cellular metabolism
• It is important to avoid hyperthermia
• Routine use of induced hypothermia in all TBI patients is not warranted
• Careful reduction in core body temperature may help control ICP in selected severe TBI
patients who may otherwise be at risk of a decompressive craniectomy.
• Await results of high-quality RCTs
- Induced hypothermia in traumatic brain injury is the therapeutic or prophylactic use of lower body temperature, to prevent secondary brain injury or to relieve refractory raised ICP.
- Decreased cellular injury
- Decreased inflammatory response and oedema
- Decreased cerebral metabolic rate, with many benefits:
- Decrease oxygen and glucose consumption by the oedematous brain tissue (by 6-10% per 1°C - Polderman, 2001 )
- Decreased intracranial pressure (thus, improved perfusion of the healthy brain)
Arguments against the use of hypothermia in TBI
- The studies exploring its benefits have been either human case series or animal data
- The technique is not without risk (i.e. even mild hypothermia has a rate of significant complications):
- Arrhythmias (AF, bradycardia)
- Diuresis, hypokalemia
- Need for paralysis and sedation
- Poor neutrophil function: the rate of infectious complications is relatively high, eg. pneumonia (POLAR, 2018 had 70% vs 57% in the normothermic group)
- Higher catecholamine reuqirements (POLAR, 2018): Catecholamine responsiveness is diminished at low temperature, making CPP more difficult to achieve with noradrenaline
- The deeper the hypothermia, the greater the risk of complications
- Haemodynamic instability in hypothermia may decrease CPP
- Decreased platelet function may lead to expansion of conservatively managed haemorrhages or contusions
Evidence for and against hypothermia in TBI
- Eurotherm 3235 trial (2015):
- Enrolled 387 patients;
- Hypothermia was used as a second-line therapy to reduce ICP.
- No survival benefit was observed.
- Recruitment was suspended early owing to safety concerns.
- ICP control was in fact better in the hypothermia group (they required rescue therapies less frequently) but this seems to have made no difference to mortality.
- "Cochrane Systematic Review 2009" probably refers to Sydenham et al (2009). A new update was published by Lewis et al in 2017. Neither meta-analysis found any benefit (the 2009 version recommended that hypothermia should be relegated to the realm of experimental trial interventions rather than established practice).
- POLAR (2018)
- Enrolled 511 patients
- Hypothermia was commenced early and sustained for at least 72 hours
- There was no difference in neurological outcome between the groups
- "These findings do not support the use of early prophylactic hypothermia in patients with severe traumatic brain injury", they concluded
- Prophylactic hypothermia for severe TBI is not indicated in routine practice
- Therapeutic hypothermia for severe TBI with refractory raised ICP may reduce the ICP, and is an alternative or adjunct to decompressive craniectomy
If the college examiners had any investment in the process of writing these answers, they'd probably have offered their trainees some references beyond "two paediatric studies and a Japanese study". At least one of the "two paediatric studies" is Hutchison et al (2008), who concluded that prophylactic hypothermia "does not improve the neurologic outcome and may increase mortality". The other paediatric trial may be Li et al (2009), which came to totally opposite conclusions ( "moderate hypothermia provided neuronal protection for children with severe TBI, and maintaining the intracranial temperature at 34.5°C for 72 h was safe"). Looking at the list of trials undergoing meta-analysis in Lewis et al (2017), the "Japanese study" is probably Hifumi et al (2016), whose B-HYPO trial did not find any significant difference in mortality or neurological outcome among 135 adult patients.
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