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Field torso-warming modalities: a comparative study using a human model
Umeå University, Faculty of Medicine, Department of Surgical and Perioperative Sciences, Surgery.
Umeå University, Faculty of Medicine, Department of Surgical and Perioperative Sciences, Surgery.
Laboratory for Exercise and Environmental Medicine, University of Manitoba, Winnipeg, Manitoba, Canada.
Laboratory for Exercise and Environmental Medicine, University of Manitoba, Winnipeg, Manitoba, Canada.
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2009 (English)In: Prehospital Emergency Care, ISSN 1090-3127, E-ISSN 1545-0066, Vol. 13, no 3, 371-378 p.Article in journal (Refereed) Published
Abstract [en]

Objective: To compare four field-appropriate torso warming modalities, that do not require AC electrical power, using a human model of non-shivering hypothermia.

Methods: Five subjects, serving as their own controls, were cooled four times in 8ºC water, for 10-30 minutes. Shivering was inhibited by Buspirone (30 mg) taken orally prior to cooling and IV Meperidine (1.25 mg/kg) at the end of immersion. Subjects were hoisted out of the water, dried, insulated and then underwent 120 min of either: spontaneous warming only; a charcoal heater on the chest; two flexible hot water bags (total4 liters of water at55°C, replenished every 20 minutes) applied to the chest and upper back; or two chemical heat pads applied to the chest and upper back. Supplemental meperidine (maximum cumulative dose of 3.5 mg/kg) was administered as required to inhibit shivering.

Results:  Post-cooling afterdrop was compared to spontaneous warming (2.2°C) less for chemical heat pads (1.5°C) and hot water bags (1.6°C, p < 0.05), and was1.8°C with the charcoal heater.  Subsequent core rewarming rates, the hot water bags (0.7°C/h) and the charcoal heater (0.6°C/h), tended to be higher than chemical heat pads (0.2°C/h, p = 0.055) and was significantly greater than spontaneous warming (0.1°C/h, p < 0.05).

Conclusion: In subjects with shivering suppressed, greater sources of external heat were effective in attenuating core temperature afterdrop whereas sustained sources of external heat effectively established core rewarming. Depending on scenario and available resources, we advice to use charcoal heaters, chemical heat pads or hot water bags as effective means for treating cold patients in the field or during transport to definitive care.

Place, publisher, year, edition, pages
Informa Healthcare, 2009. Vol. 13, no 3, 371-378 p.
Keyword [en]
Hypothermia
National Category
Surgery
Research subject
Surgery
Identifiers
URN: urn:nbn:se:umu:diva-54277DOI: 10.1080/10903120902935348OAI: oai:DiVA.org:umu-54277DiVA: diva2:517560
Available from: 2012-04-24 Created: 2012-04-23 Last updated: 2017-12-07Bibliographically approved
In thesis
1. Protection and treatment of hypothermia in prehospital trauma care: with emphasis on active warming
Open this publication in new window or tab >>Protection and treatment of hypothermia in prehospital trauma care: with emphasis on active warming
2012 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Background: In prehospital trauma care active warming is recommended to aid in protection from further cooling. However, scientific evidence of the effectiveness of active warming in a clinical setting is scarce. Also, evaluating the effectiveness of active warming, especially in harsh ambient conditions, by objective measures, is difficult.

Objective: To evaluate the effectiveness of field applicabe heat sources (I) and to evaluate active warming intervention in a prehospital clinical setting (II and III).

To evaluate reliability and validity of the Cold Discomfort Scale (CDS), a subjective judgement scale for assessment of the thermal state of patients in a cold environment (IV).

Methods: In a laboratory trial, non-shivering hypothermic subjects (n=5), were cooled in 8 ºC water followed by spontaneous warming, a charcoal heater, two flexible hot-water bags or two chemical heat pads, all applied to the chest and upper back (I). Oesophageal temperature, skin temperature, heat flux, oxygen consumption, respiratory rate and, heart rate were measured.

In two clinical randomized trials, shivering patients during road and air ambulance transport (II) and during field treatment (III) were randomized to either passive warming alone (n=22 and n=9) or to passive warming with the addition of a chemical heat pad (n=26 and n=11). Body core temperature, respiratory rate, heart rate, blood pressure (II) and the patients’ subjective sensation of thermal comfort (II and III) were measured.

In a laboratory trial, shivering subjects were exposed to – 20 ºC (n=22). The CDS was evaluated regarding reliability, defined as test-retest stability, and criterion validity, defined as the ability to detect changes in cold discomfort due to changes in cumulative cold stress (IV).

Results: In non-shivering hypothermic subjects postcooling afterdrop was significantly less for the chemical heat pads, but not for the hot water bags and the charcoal heater, compared to spontaneous warming (I). Temperature drop during the entire warming phase was significantly less for all the heat sources respectively, compared to spontaneous warming (I).

During road and air ambulance transport, ear canal temperature was significantly increased and cold discomfort significantly decreased, both in patients assigned to passive warming only, and in patients assigned to additional active warming (II). During field treatment, cold discomfort was significantly reduced in patients assigned to additional active warming, but remained the same in patients assigned to passive warming only (III).

Weighted kappa coefficient, describing test-retest stability, was 0.84 (IV). CDS ratings were significantly increased during each 30 minutes interval (IV).

Conclusion: In non-shivering hypothermic subjects, heat sources were effective to attenuate afterdrop, when providing high heat content over a large surface area and effective to continue to increase body core temperature when providing sustained high heat content. In shivering trauma patients, adequate passive warming were sufficient treatment to prevent afterdrop, to slowly increase body core temperature, and to reduce cold discomfort. If inadequate passive warming, additional active warming was required to reduce cold discomfort. The CDS, a subjective judgement scale for assessment of the thermal state of patients in a cold environment seemed to be reliable regarding test-retest stability and valid regarding ability to detect change in cumulative cold stress.

Place, publisher, year, edition, pages
Umeå universitet, 2012. 51 p.
Series
Umeå University medical dissertations, ISSN 0346-6612 ; 1502
Keyword
Hypothermia
National Category
Surgery
Research subject
Surgery
Identifiers
urn:nbn:se:umu:diva-54304 (URN)978-91-7459-424-9 (ISBN)
Public defence
2012-05-16, Tandläkarhögskolan sal B, byggnad 1D, 9 tr, 08:30 (English)
Opponent
Supervisors
Available from: 2012-04-24 Created: 2012-04-24 Last updated: 2012-04-24Bibliographically approved

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