10. Cooling the heat emergency – April 2015
Heat stroke is a life threatening problem. Body temperature is raised over 40°C by the environment or by exertion. Thermoregulation fails and life threatening muscle and organ failure follows. Cooling must occur quickly, usually within thirty minutes, to return the temperature below 39°C. There are a number of pre-hospital options available.
Cold water immersion can cool but has pre-hospital difficulties. Ice packs to the vascular groin, armpits, chest and abdomen can help lose heat but be very uncomfortable. Both these conduction methods can make the skin sense cold and trigger reflex shivering reflex if overzealous. This will produce more unwanted heat. Spraying water on the patient then blowing air over them uses evaporation and convection. Both means together are efficient and less likely to lead to overcooling. Where they are not quick enough the addition of cold (<8°C) intravenous fluid therapy can hasten cooling and hydration.
Cooling of heat emergencies recognises that thermoregulation is lost and the body needs urgent help. This is very different from fever. In contrast, this is a normal body response to infection. The hypothalamus is very much in control and has reset normal temperature. Shivering, rigours, feeling cold are all part of becoming intentionally hotter. Sometimes as hot as heat stroke. Fever is widely held to be advantageous. It does not need cooling unless perhaps in septic shock where there is high metabolic oxygen demand and a need for vasopressor support. Infection can include delirium making it difficult to differentiate from non exertional heat stroke with altered conscious state.
Jeff Kenneally – www.prehemt.com