a) List the clinical signs associated with severe (< 28ºC) hypothermia. (30% marks)
b) Outline the considerations in providing advanced cardiac life support (ACLS) in a severely hypothermic patient. (70% marks)
Neuro: Loss of cerebrovascular regulation, coma, loss of ocular reflexes
CVS: Decline in BP and cardiac output, VF (<28°C) bradycardia and asystole (<20°C)
Respiratory: Pulmonary oedema, apnoea
Musculoskeletal: Pseudo-rigor mortis (may appear dead)
Metabolic: Decreased metabolic rate, hyper or hypoglycaemia
Considerations in providing ACLS
Decision to start
May commence cardiac life support in an apparently “dead” hypothermic patient. Beware that very slow, irregular small volume pulse may be present and an unrecordable blood pressure. The brain can tolerate cardiac arrest for long periods at 18°C.
Patients need to be actively rewarmed while resuscitation is being continued.
Extra-corporeal support, not mandated, but can be mentioned
More emphasis on the continuing re-warming, an issue of priority, should state early
Temperature should be measured centrally
Hypothermia can cause stiffness of chest wall making ventilation and chest compression difficult – early use of mechanical devices as resuscitation attempts are likely to be prolonged.
Be aware that interventions (e.g. CPR, central line placement, endotracheal intubation) may precipitate arrhythmias
Consider withholding drugs (e.g. Adrenaline) until core temp > 30°C and then double the interval between giving the drugs (i.e. give adrenaline every 4th cycle compared with every 2nd cycle) until temperature 35°C
The hypothermic heart may be unresponsive to cardioactive drugs, electrical pacing and defibrillation. Arrhythmias
Arrhythmias other than VF tend to revert spontaneously as temperature rises. Bradycardia does not usually need treatment as it is physiological in severe hypothermia
VF therapy: unclear at which temp shocking should be first attempted. After 3 shocks if no response, consider delaying further attempts at defibrillation until temperature > 28-30°C
In part a), candidates listed things that were not clinical signs e.g. ECG changes and ETCO2, and there was also a focus on the CVS aspect which showed a limited breadth of clinical signs, and hence limited marks. In part b), many candidates did not show a breadth of considerations, and focussed mainly on the rewarming in great depth, hence did not score well on this section. Also, candidates often listed their management rather than outline their considerations, so the aspects they discussed also often lacked depth.
The cranky CICM examiners complained that, when asked for clinical signs, many of the candidates "listed things that were not clinical signs e.g. ECG changes and ETCO2" And then they themselves had listed "loss of cerebrovascular regulation", "decline in ... cardiac output" and "decreased metabolic rate" in their model answer. Looking at their list, one might come to the conclusion that the question asked for the physiological consequences of hypothermia.
Anyway, the clinical signs are:
Now, as for the management of cardiac arrest in hypothermia. "Outline the considerations", judging by the wording of the model answer, appears to mean "discuss all the ways hypothermic arrest is different". Though the college question asks specifically about ACLS, the college answer also discusses some BLS material. The ideal reference for this would probably have to be the AHA "Special Circumstances" section from the 2015 cardiac arrest guidelines. Following the AHA's own structure:
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