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Three Part Question

In [patients presenting with classic heat stroke at mass gathering events] is [fine mist water spraying and evaporation more effective than ice packs] at [reducing core body temperature and decreasing ongoing cerebral dysfunction]

Clinical Scenario

39 year old male presents to the medical facility at an international air show having spent the day on grass and concrete watching the air show. Clinically he presents with significant confusion, disorientation, tachycardia, tachypnoea, and absence of sweating. On initial assessment he is found to have a rectal temperature of 41.2 degrees and HR of 118.
Following rapid assessment he is taken to the decontamination shelter where he is taken through the tent which is spraying cool water - he is passed along the tent twice and following this his rectal temperature is 39.3 degrees. He returns to the P1 (resuscitation) area and cooling and treatment continues with fine mist water spraying (plant sprayers), blow by air and IV fluids. After 1 hour of treatment his core body temperature has returned to normal and he is alert and orientated.

Search Strategy

Medline (Ovid)
Exp Heat stress disorders/ OR exp heat exhaustion/ OR exp heat stroke/ or heat illness.mp
AND
Exp body temperature/ OR body temperature regulation/ OR cooling.mp
AND
Evaporation.mp
Limit to humans and English language

Ovid Nursing Database
Heat stroke.mp OR heat stroke/
AND
Exp Body temperature/ OR cooling.mp

CINAHL (EBSCOHOST)
(MH “heat stroke”) OR “heat stroke” OR (MH “heat stress disorders”) OR (MH “Heat Exhaustion”)
AND
(MH "Heat Stroke") OR (MH "Heat Exhaustion") OR "cooling"
AND
“Evaporation”

Medline – 24 results of which 2 were useful
OVID Nursing Database – 47 results of which 4 were useful
CINAHL – 4 results of which 2 were useful

Out of all the useful results 5 were deemed of good enough quality for inclusion. Any duplicate articles that were found during the searching were removed.

Search Outcome

Medline – 24 results of which 2 were useful
OVID Nursing Database – 47 results of which 4 were useful
CINAHL – 4 results of which 2 were useful

Out of all the useful results 5 were deemed of good enough quality for inclusion. Any duplicate articles that were found during the searching were removed.

Relevant Paper(s)

Author, date and country	Patient group	Study type (level of evidence)	Outcomes	Key results	Study Weaknesses
Yeo 2004 USA	Classic Heat stroke Exertional heat stroke	Review	Normothermia	Evaporative cooling methods are safest – best tolerated by all patient groups	Doesn’t clearly show type of studies reviewed nor does it show populations’ sizes. Lacks rigour in assessment of outcomes. Non therapy driven paper.
			Reduction in CNS dysfunction	Treatment should include fluid resuscitation preferably with isotonic sodium chloride
			Reduction in organ damage	The use of benzodiazepines to sedate and reduce shivering or chlorpromazine to reduce shivering may help reduce time to normothermia by preventing increased heat production.
Harker and Gibson 1995 UK	Patients suffering from heat stroke	Comparative review	Preferential cooling modality	Evaporative cooling outperforms cold water immersion. Key feature of evaporative cooling is to maintain skin warmth, aiming to avoid vasoconstriction and shivering	No definition of type of study reviewed or total populations. Highlights lack of direct comparative evidence between cooling modalities.
Bouchama et al 2007 Saudi Arabia	556 total patients in 19 studies subdivided as below: Classic Heat stroke - 386 Exertional heat stroke - 170	Level 1 Systematic Review of RCT’s and case series.	Classic Heat stroke (CHS)	No clear best method for cooling. Although Iced water immersion suggest increased morbidity and mortality. Both evaporative and conductive non-invasive techniques comparable in efficacy	Failed to effectively compare conduction and evaporation methods in EHS. Lack of high level studies included – may lead to lack of reliability
			Exertional Heat stroke (EHS)	Conduction (iced-water immersion) is only method reviewed for EHS. Shown to be effective.
			Temperature for stopping cooling	No clear end point temperature for cessation of cooling identified
Glazer 2005 USA	Heat-related illness in humans	Review	Pre-hospital management of heat-related illness	Cooling by evaporation is most effective method in pre-hospital environment with cooling rates of up to 0.31 degrees C/minute compared to 0.15 degrees C/minute in conduction methods.	Review of literature fails to demonstrate strength of literature included. Key recommendations come from less rigorous data than may be hoped.
				Patients are more accessible when being cooled by evaporation
				Immersion may trigger mammalian diving reflex
Hadad et al 2004 Israel	11 studies reviewed Cold water immersion – 3 Evaporation – 3 Dantrolene - 5	Level 2 review	Overall best modality for rapid and safe cooling	Evaporative cooling was better in 2 out of 3 controlled trials reviewed	Small cohorts in studies reviewed. Participant numbers not included and no mention to statistical significance
				There is no clear preferential modality for cooling however, evaporation techniques are more tolerable and available pre-hospitally
				In patients who may not be fit and healthy evaporative techniques are preferred

Comment(s)

Heat stroke is a heat related illness defined by a core body temperature in excess of 40.6°C due to environmental heat exposure (McGugan, 2001). It is characterised by a failure of the body’s thermoregulatory system in the presence of high core body temperature. Heat stroke may be divided into exertional (may not need high environmental temperatures) and non-exertional (classic) heat stroke. Classic heat stroke occurs during extreme heat waves, the elderly and young being particularly vulnerable. The methods of cooling patients with heat stroke is still highly contentious. The number and quality of available studies is significantly lacking. Much research has been published in the assessment and management of exertional heat stroke but little in comparison has been done for classic heat stroke with those studies that have been done being rather old. The pre-hospital environment poses many challenges to clinicians and even more challenges can be seen at mass gathering events like air shows. In this environment it is imperative that patients are rapidly cooled in a safe and effective manner especially given that a large number of heat related casualties may present in a very short period of time. Further consideration needs to be given to the siting of onsite facilities to give best access to required resources in order to provide optimal care to patients.

Clinical Bottom Line

There is as yet not enough evidence to fully support either method for cooling patients. More good quality controlled trials need to be done comparing evaporation with convection techniques as at present both techniques appear equally efficacious. In the clinical setting detailed above it is preferable that the use of evaporation techniques in conjunction with cardiovascular support in the form of cooled IV fluids is used to rapidly cool the patient with heat stroke in order to minimise ongoing cerebral dysfunction and further organ damage.

Level of Evidence

Level 2 - Studies considered were neither 1 or 3.

References

1. Yeo, T.P 'Heat stroke: a comprehensive review.' AACN Clin Issues April - June 2004; pp 280-293
2. Harker, J. and Gibson, P. 'Heat-stroke: a review of rapid cooling techniques.' Intensive Critical Care Nurse August 1995; pp 198-202
3. Bouchama, A. et al 'Cooling and haemodynamic management in heatstroke: practical recommendations.' Critical Care 2007; p R54
4. Glazer, J. L. 'Management of heatstroke and heat exhaustion.' American Family Phycisian June 2005; pp 2133 - 2140
5. Hadad, E. et al 'Heat stroke : a review of cooling methods.' Sports Medicine 2004; pp 501-511