Category Archives: heat

You can overdo heat stroke treatment

Heat stroke can kill. This isn’t debatable. And mortality is linked to duration of hyperthermia. Thus, prehospital treatment of heat stroke improves mortality. Due to this, many EMS agencies will start with cooling patients using low-tech methods such as ice packs and ice water laden towels or sheets. The problem with these methods is that many agencies do not have the ability to continuously monitor core temperatures.

This case report has an example of just such a problem. Their patient was found ataxic and confused during a 17km march in the mild climate of the Texas hill country. His rectal temperature was 42.3°C. They correctly undressed him and placed ice in the axillae and groin. He also got 1L of saline that was room temperature. The issue comes from the extended travel time to the hospital, at 34 minutes. No further temperatures were checked en route. When the patient arrived at the ED, his temperature was 38.1°C.

Now it gets weird. Not many of use would have much of a problem with that temperature, but the astute physician was concerned about afterdrop from rapid cooling. All of the ice was removed, and the patient was placed under a forced air warming blanked and received 43.0°C normal saline. Even with all of this, the temperature continued to drop, hitting a nadir of 36.0°C.

I know what you’re saying. The patient didn’t actually even become hypothermic. And true, we don’t know how cold the patient would have gotten if they had simply stopped cooling and not initiated active rewarming. But clearly if the transport time had been longer or they had failed to check the temperature early on, the patient could have developed a degree of hypothermia. Whether or not the patient would be harmed by this (at best) mild hypothermia is also undetermined.

Take home points should be that you should be continuously monitoring the core temperature of any patient, whether you’re cooling them or warming them, and also the endpoint at which you should cease active cooling is 38.9°C. They do offer a good point that in the absence of ability to measure temperatures, such as the austere or prehospital environments, use shivering as your endpoint or only do any measure for 15 minutes at a time.

Dangers of Prehospital Cooling: A Case Report of Afterdrop in a Patient with Exertional Heat Stroke
http://www.jem-journal.com/article/S0736-4679(15)00615-0/abstract

Ice vs chemical cold packs

Heat illness needs fast treatment, and to accomplish this many EMS agencies carry chemical cold packs.  These are convenient in that they have long shelf lives, don’t require cold storage, and don’t leak or drip fluids.

According to this article, there really isn’t any prior testing to compare them to ice packs in human testing. This hasn’t changed with this paper, but they do directly compare the cooling effectiveness of CCPs to similarly sized ice packs in an insulated water bath. What they found might seem intuitive, just never documented.  Cold packs do get cool quickly, but they don’t really get very cold, and they don’t last more than about 5 minutes.  Ice packs remain cold significantly longer and perform better by reducing the temperature of the water bath more.

The authors use this data to extrapolate that 6 CCPs, strategically placed, would reduce the temperature of a hyperthermic male by less than 0.5°C. Ice would perform better, reducing the temperature by 2.5°C.  They do discuss the logistical problems of using ice in the pre-hospital setting, and recommend more frequent checking and replacement of CCPs based on their short effective times.  One limitation of the study is that they didn’t use more than one source of CCPs, so there could be a large difference in performance of other samples. The authors also present other treatments of hyperthemia in the discussion part of the article, so it’s worth a read.

Chemical cold packs may provide insufficient enthalpy change for treatment of hyperthermia
http://www.ncbi.nlm.nih.gov/pubmed/23312558

Posting from #ACEP13 Council meeting.