Heat illness, hypothermia and environmental emergencies — formative SAQs

SAQ 1 — Exertional heat stroke: recognition and rapid cooling (10 marks)

A 15-year-old cross-country runner collapses 5 kilometres into a race on a 39-degree summer afternoon. On arrival in the emergency department his rectal temperature is 41.5 degrees Celsius, he is confused and combative, his skin is hot and sweating profusely, his pulse is 140 beats per minute, and his capillary glucose is 6.2 mmol per litre. Cold-water immersion is available in the department. [1] [3]

Questions

1. Define heat stroke and justify the diagnosis in this athlete, including why the profuse sweating does not exclude it. (4 marks) [1]

2. Outline your immediate management with the cooling target, the cooling method, and the drugs you would NOT give and why. (6 marks) [3]

Model answer

Definition and diagnosis (4). Heat stroke is defined as a core temperature above forty degrees Celsius accompanied by central nervous system dysfunction — confusion, agitation, ataxia, seizure or coma — and the central nervous system state is the pivot that separates heat exhaustion (mental state intact) from heat stroke. This athlete has a core of 41.5 degrees with confusion and combativeness, which is heat stroke. The subtype is exertional heat stroke, occurring in a young athlete during intense exercise in heat, and in the exertional form sweating is often still present and profuse, so a hot, sweating skin must not be used to exclude the diagnosis; the absent-sweating (hot, dry) picture is typical of classic non-exertional heat stroke, not this athlete. The history of exertion, the rapid onset, and the preserved sweating all point to exertional heat stroke. [1] [2]

Management (6). My priority is to remove the heat load and begin cooling immediately, because the duration above forty degrees is the chief determinant of survival — I do not wait for investigations. I remove his clothing, secure the airway and give oxygen, establish intravenous access, and begin cold-water immersion, which is the gold standard for exertional heat stroke, cooling at roughly 0.15 degrees per minute. My target, from the National Athletic Trainers' Association position statement, is a core below thirty-nine degrees within thirty minutes — the cool-first, transport-second principle. I check and continue to monitor the glucose, treat the hypovolaemia with warmed intravenous crystalloid titrated to perfusion, and cool to the target before transfer. I would NOT give antipyretics (paracetamol, non-steroidal anti-inflammatory drugs) or dantrolene: the hypothalamic set point is normal in heat stroke, so antipyretics do not lower the temperature and paracetamol may compound the heat-stroke liver injury, and dantrolene has not shown benefit. Once cooled, I monitor for the multi-organ injury — rhabdomyolysis, acute kidney and liver injury, disseminated intravascular coagulation — and admit to a paediatric intensive care unit. [3] [1]

SAQ 2 — Accidental environmental hypothermia and the hypothermic arrest (10 marks)

A 7-year-old with a developmental disability is found cold and unconscious in a field in winter after a wandering episode of unknown duration. In the emergency department his rectal temperature is 27 degrees Celsius, he is unconscious but has detectable vital signs initially, and then loses his pulse — the monitor shows ventricular fibrillation. Cardiopulmonary resuscitation is in progress and intraosseous access is in place. [5] [7]

Questions

1. Stage this child by the Swiss classification at first presentation, and state the matching rewarming strategy before he arrested. (5 marks) [5]

2. State the defibrillation and adrenaline rules for his hypothermic ventricular fibrillation, the temperature at which resuscitation may be terminated, and the principle that governs this. (5 marks) [7]

Model answer

Staging and rewarming (5). The Swiss classification pairs the core temperature with the clinical state: stage one is thirty-five to thirty-two degrees (conscious, shivering), stage two is thirty-two to twenty-eight degrees (impaired consciousness), stage three is twenty-eight to twenty-four degrees (unconscious with vital signs present), and stage four is below twenty-four degrees (no vital signs). At a core of twenty-seven degrees he is, by temperature, at the boundary of stage two and three, and because he is unconscious with vital signs still present he is Swiss stage three (severe). The matching rewarming strategy for stage three is active internal rewarming: warmed humidified oxygen at forty-two to forty-six degrees, warmed intravenous crystalloid at approximately forty degrees, and consideration of body cavity lavage, with monitoring for the afterdrop and rewarming shock, and gentle handling throughout to avoid precipitating ventricular fibrillation. I would also remove his wet clothing, dry and insulate him, check and treat the glucose, and arrange early liaison with retrieval and an extracorporeal service because of his risk of deterioration. [5]

Defibrillation, drugs and termination (5). The core is below thirty degrees, so the cold myocardium is refractory to defibrillation and to drugs. Following the European Resuscitation Council 2021 guidance, I deliver a single shock at the standard paediatric energy of four joules per kilogram for the ventricular fibrillation, and if it fails I withhold further shocks and adrenaline until the core rises above thirty degrees, continuing chest compressions and active rewarming throughout. Once above thirty degrees, I resume standard shocks and adrenaline, but I lengthen the interval between adrenaline doses because drug clearance is slowed in hypothermia. I continue resuscitation until the core reaches at least thirty-two degrees before considering termination, because the maxim holds that nobody is dead until they are warm and dead — profound hypothermia, once rewarmed, is one of the few reversible causes of prolonged cardiac arrest. I escalate to extracorporeal rewarming as early as the system allows, and I would involve the family early with honest prognostic discussion. [7] [5]