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Three Part Question

In [immobile casualties, in the pre-hospital environment], is [bubble wrap better than other non-active warming methods] at [preventing or treating hypothermia]?

Clinical Scenario

Search and rescue services locate a missing adult male, who is found to have reduced consciousness and a core temperature of 32 degrees. Preparing for hospital transfer, the team insulate the casualty to prevent further heat loss.

Search Strategy

Natural language and controlled vocabulary (MeSH) search of PubMED database on 24th January 2017. Subsequent backward (reference list) and forward (prospective citation) searches were performed on the papers found
PubMED (natural language): ((((bubble) AND wrap)) OR bubblewrap) AND ((hypothermia) OR ((pre-hospital) OR prehospital))

PubMED (controlled vocabulary - MeSH): (Hypothermia/prevention and control) AND (Transportation of patients)

Search Outcome

38 papers found, of which 35 were excluded as they did not evaluate bubble wrap in managing prehospital hypothermia. A further publication was found using a reference list search which was an oral publication not listed on PubMED that was relevant and therefore included. The table lists the 4 publications found

Relevant Paper(s)

Author, date and country	Patient group	Study type (level of evidence)	Outcomes	Key results	Study Weaknesses
Thomassen, Ø et al 2011 Norway	8 healthy adults (7 completed the trial) in a 5 ⁰C climatic chamber with 3 m/s wind, wearing wet clothing, lying supine. Wrapped with either bubble wrap, ambulance blankets or a combination of dry insulation and vapour-tight layer (Hibler's method)	Randomised controlled trial	Core temperature	No significant differences between coverings	Core temperature never went below 36.5 degrees. Not blinded
			Skin temperature	Bubble wrap not as effective as Hibler's method or ambulance blankets in preventing drop in skin temperature
			Shivering and metabolic heat production	Bubble wrap required a higher metabolic rate and higher level of shivering from the subjects than other methods of covering
Jussila, K et al. 2014 Finland	Part 1 of the study: Thermal manikin set at 34⁰C wrapped in 10 different covering systems in a climatic chamber at -5⁰C, with wind speeds of 0.3 m/s and 4.0 m/s, in both dry and wet conditions Part 2 of study used the most effective covering from Part 1 on a healthy human trial, but was excluded from this literature review as bubble wrap was not evaluated in part 2	Randomised Controlled Trial	Standard Thermal Insulation of Bubble Wrap when dry in calm conditions	0.26 m^2K/W (relating to sleeping bag rating of 18-20.4 ⁰C). This was lower than all other methods tested in dry calm conditions	Not blinded. Thermal manikin lacking human physiological responses to cold. Study results do not indicate statistical significance
			% Reduction of thermal heat loss in Wind and Wet conditions	Bubble wrap is better at maintaining thermal properties than blankets in wind/wet (bubble wrap showed 21% reduction in thermal properties compared to 45% loss with blankets), but is outperformed by some purpose-designed rescue bags
Zasa et al 2016 United Kingdom	6 torso models, composed of 5.5 litre fluid-filled bags with indwelling thermometers, heated to 37 degrees, then randomly allocated to a heat preservation system or control, and placed onto airfield on 10 separate days with outdoor temperatures ranging -3 ⁰C to 5 ⁰C	Randomised Controlled study	Rate of temperature decline in torso model	Bubble wrap performed better than ambulance blanket or space blanket, but not as well as Blizzard blanket or Ready-Heat II (active warming) blankets	Fluid-bags used as model, lacking human physiological responses to cold
Vangberg et al 2009 Norway	Thermal manikin in climatic chamber wrapped in either 3 cotton ambulance-style blankets, or standard 3-layer industrial bubble wrap	Randomised Controlled Trial	Standard Thermal Insulation	0.27 m^2K/W for bubble wrap (compared to 0.40 m^2K/W for 3 cotton blankets) which is equivalent to sleeping bag rating of 18-20.4 ⁰C	Thermal manikin lacking human physiological responses to cold

Comment(s)

Despite widespread use of bubble wrap in prehospital services, the evidence for effectiveness is limited. The evidence that is available suggests that the dry insulating properties of bubble wrap is worse, or at least no better, than simple ambulance blankets and purpose-built rescue bags. However in wet and windy conditions, bubble wrap maintains thermal properties better than ambulance blankets, and at least as well as some rescue bags. By acting as a vapour-tight layer bubble wrap therefore has potential use in wet/windy conditions. None of these studies investigated bubble wrap in combination with further insulation or active warming.

Clinical Bottom Line

Bubble wrap is a poor insulating layer when compared to purpose built rescue bags, and even simple ambulance blankets, but it does provide a useful vapour-tight layer reducing evaporative heat loss in wet/windy conditions. It is therefore advisable that if bubble wrap is used, it should be combined with additional dry insulation. Further research into this use is warranted

Level of Evidence

Level 3 - Small numbers of small studies or great heterogeneity or very different population.

References

1. Thomassen, Ø et al Comparison of three different prehospital wrapping methods for preventing hypothermia--a crossover study in humans Scandinavian journal of trauma, resuscitation and emergency medicine 2011; 19:41
2. Jussila, K et al. Evaluating cold, wind and moisture protection of different coverings for prehospital maritime transportation-a thermal manikin and human study Prehospital and disaster medicine 2014; 29(6), pp. 580–8
3. Zasa et al A torso model comparison of temperature preservation devices for use in the prehospital environment Emergency Medicine Journal 2016; 33(6), pp. 418–422
4. Vangberg et al Bubblewrap for hypothermia prevention - the ultimate solution or yet another fancy gadget? Scandinavian journal of trauma, resuscitation and emergency medicine 2009; 17(Suppl 3)