a b s t r a c t

Background: Rapid rewarming of an acutely frostbitten extremity has been the standard treatment for nearly 60 years, however, there are no existing practical recommendations to create a warm water bath. Our study de- scribes a novel approach to rapid rewarming using a sous vide cooking device to create and maintain a circulating warm water bath at a desired set temperature.

Methods: A series of in vitro experiments were performed to assess the efficacy of different methods of maintain- ing constant water temperature while rapidly rewarming a simulated frostbitten extremity (frozen pig’s foot). An Anova Sous Vide Precision Cooker(R) was attached to a 5 gallon bucket and used to circulate and maintain the water at 104 ?F while rewarming a frozen pig’s foot. This method was compared to manual exchange of water to maintain the temperature at 104 ?F and to a control with no water exchanged. During each experiment, the temperature of the water was recorded every 2 min and the pliability of the pig’s foot was assessed after 30 min. Results: The sous vide method maintained circulating water at a constant temperature of 104 ?F for 30 min. At 30 min the frozen pig’s foot was warm, soft, and pliable. The manual method resulted in temperature fluctuations requiring frequent large volume water exchanges. When no water was exchanged, the water cooled quickly and the pig’s foot remained partially frozen.

Conclusion: Sous vide rewarming is a Novel method that easily creates and maintains a warm water bath ideal for rapid rewarming of a frostbitten extremity.

(C) 2019

Introduction

Rapid rewarming in a warm water bath has been a mainstay of acute treatment for a frostbitten extremity for the last 58 years. In their land- mark publication in 1960, Mills and Whaley described rapid rewarming of the frostbitten extremity in a whirlpool bath at 42-48 ?C (107.6-118

?F) until brought to body temperature [1-3]. A later animal study deter- mined the ideal temperature of a warm water bath for rapid rewarming was 37-39 ?C (98.6-102.2 ?F) with lower temperatures delaying rewarming and higher temperatures causing increased tissue damage [4]. Subsequently published Treatment protocols have recommended variable temperatures for rapid rewarming ranging from 38 to 42 ?C (100.4-107.6?F) [5-10].

? We have no conflicts of interest to disclose and this manuscript is not undergoing review at any other journal at this time. All authors meet the criteria for authorship stated in the Uniform Requirements for Manuscripts Submitted to Biomedical journals (ICMJE) and all listed authors approve of the final manuscript.

?? No prior presentations.

* Corresponding author at: Stroger Cook county hospital, Department of Emergency Medicine, Professional Building, 1950 W. Polk Street, Room 7106, Chicago, IL 60612, United States of America.

E-mail address: [email protected] (J. Weber).

While differences of opinion on ideal water temperature exist, rapid rewarming in a warm water bath remains the standard initial treatment for the frostbitten extremity. Despite this universal recommendation, there are few descriptions in the literature about the best method to achieve the warm water bath. Mills and Whaley simply describe a “whirlpool bath.” Recently published treatment protocols also call for a “whirlpool bath” [7,8] while other foundational publications upon which most treatment protocols are based only mention “rapid rewarming in warm water” [5,6]. The Wilderness Medical Society pro- vides the most detailed description of rapid rewarming in their 2014 update with recommendations to use a thermometer to avoid iatro- genic injury, circulation of the water to help maintain the correct tem- perature, and careful continual warming of the water to target temperature as the water may cool quickly [9]. However, no practical recommendations are given on how to achieve these goals. There is agreement throughout the literature that rapid rewarming should con- tinue for 30 min or until the affected tissues are pliable.

Our study aims to describe a novel approach to rapid rewarming by creation of a warm water whirlpool bath using a sous vide cooking de- vice. This device, which is typically used for cooking, has the ability to circulate and maintain water at a desired set temperature quickly and easily. We assessed the ability of the sous vide device to circulate and

https://doi.org/10.1016/j.ajem.2019.05.009

0735-6757/(C) 2019

464 A.N. Fiutko et al. / American Journal of Emergency Medicine 38 (2020) 463–465

maintain water at 40 ?C (104 ?F) while rewarming a simulated frostbit- ten extremity.

Methods

We performed a series of in vitro experiments to assess the efficacy of different methods of maintaining constant water temperature while rapidly rewarming a simulated frostbitten extremity. A frozen pig’s foot was used to simulate a frostbitten extremity.

The sous vide (su-‘ved) device is a self-contained, portable, immer- sion circulator that pulls water through its internal heating element and circulates the water at a set temperature (range 77 to 212.5 ?F). An Anova Sous Vide Precision Cooker(R) was attached to the side of a standard 5-gal utility bucket filled with 5 gal of tap water at a tempera- ture of 40 ?C (104 ?F). This temperature was chosen as it was in the mid- range of the most commonly cited temperatures for rapid rewarming. The sous vide device was then set for 104? F and turned on, circulating the water and maintaining a constant temperature of 104 ?F. A frozen 0.615 kg (1.3 lb) pig’s foot was then submerged in the water. Two addi- tional thermometers (Oxo(R) electronic insta-read, Taylor(R) candy) were used to ensure accuracy of water temperature as measured by the sous vide device (Fig. 1). The water temperature was then assessed and re- corded every 2 min for a total of 30 min, which is the duration of rewarming that current protocols recommend.

A manual comparison was also performed using a standard 5-gallon utility bucket filled with 5 gal of tap water at a temperature of 40 ?C (104

?F). A frozen 0.615 kg (1.3 lb) pig’s foot was then submerged in the water. Two thermometers (Oxo(R) electronic insta-read, Taylor(R) candy) were used to ensure accuracy of the water temperature which was measured every 2 min for a total of 30 min. As the water

Fig. 1. Sous vide device attached to 5-gallon bucket with additional thermometers attached. Frozen pig’s foot in foreground.

temperature cooled below 104 ?F a smaller bucket was used to remove some of the cooling water and exchange it with warm tap water in an attempt to maintain water temperature as close to 104? F as possible.

Finally, a standard 5-gal utility bucket was filled with 5 gal of tap water at a temperature of 40 ?C (104 ?F). A frozen 0.615 kg (1.3 lb) pig’s foot was then submerged in the water. Two thermometers (Oxo(R) electronic insta-read, Taylor(R) candy) were used to ensure accu- racy of the water temperature which was measured every 2 min for a total of 30 min. No water was added or removed.

All data were analyzed using descriptive statistics. All three experi- ments and data collection were performed by two investigators (AF, CS). This study was deemed exempt from review by the Cook County Health Institutional Review Board.

Results (Graph 1)

The sous vide method maintained circulating water at a constant temperature of 104 ?F for 30 consecutive minutes. After 30 min the fro- zen pig’s foot became warm, soft, and pliable. For comparison, the man- ual method had a water temperature decrease to 102.7 ?F at 8 min requiring the exchange of 3 l of warm water resulting in a temperature overshoot to 105 ?F. At 18 min the water temperature again decreased to 102.7 ?F resulting in additional water exchanges of 2 l at both 18 and 20 min. The water remained slightly below the target temperature for the remaining 10 min. After 30 min the frozen pig’s foot was more pliable with some areas remaining firm and cool. Finally, when no inter- ventions were made the water temperature steadily decreased to 98.2

?F at the 30-min time mark. After 30 min the pig’s foot remained par- tially frozen.

Discussion

We found that the sous vide method of rapid rewarming maintained a constant water temperature and achieved the greatest rewarming and tissue pliability as compared to the traditional manual method.

Rapid rewarming in a warm water bath remains the mainstay of treatment for the acutely frostbitten extremity. However, published lit- erature and expert opinion provide little guidance on how to administer this limb saving therapy in a practical way. Previously published guid- ance cautions against overly warm or cool water which may either in- duce Iatrogenic injury or negate the benefits of rapid rewarming. Manual temperature regulation using a standard thermometer and tap water requires frequent temperature monitoring with frequent ex- change of water in an attempt to maintain the desired temperature; fur- thermore, recommended water circulation must be performed manually. Most emergency departments do not have the equipment necessary to create and monitor a warm water bath readily available.

We used a sous vide device to create a circulating warm water bath as originally described by Mills and Whaley in 1960. The sous vide de- vice maintained a circulating warm water bath at a constant tempera- ture of 104 ?F for 30 min resulting in complete thawing and warming of our simulated frostbitten extremity. In comparison, the manual method resulted in temperature drops and overshoots requiring Close monitoring of water temperature and multiple water exchanges over 30 min. This method was more labor-intensive than the use of the sous vide device, and additionally the pig’s foot remained cold and firm in some areas. Finally, when no water was exchanged the water quickly dropped below our target temperature and resulted in a par- tially frozen pig’s foot at 30 min.

The sous vide device is a self-contained heating immersion circulator that is small and portable and can be attached to any large bucket, tub, or cooler allowing submersion and rapid rewarming of upper or lower extremities (Fig. 2). It is extremely quick and easy to set up and requires minimal monitoring creating a whirlpool bath that can continue for as long as needed to achieve tissue pliability. Additionally, it has bluetooth

A.N. Fiutko et al. / American Journal of Emergency Medicine 38 (2020) 463–465 465

Graph 1. Comparison of water temperatures during rapid rewarming of a simulated frostbitten extremity with the sous vide method, manual water exchange, and no water exchange.

capability allowing remote temperature monitoring using any smartphone.

Some limitations in our pilot in vitro study need to be acknowledged. First, the sous vide device was not created or approved by the U.S. Food and Drug administration for clinical use. However, the Anova(R) sous vide precision cooker was originally created by a scientific equipment manufacturer of Temperature control products for laboratories world- wide. Additionally, the sterility of this product and the ability for it to be sterilized is unknown. However, the necessity of sterility for this ap- plication is unknown, and due to the low cost of this product it could be stocked as a single use device. At less than $100 dollars, it is comparable

Fig. 2. Sous vide device close up.

to other single use items in emergency departments, especially in the context of the other more expensive therapies used to treat frostbite and the devastating morbidity that results from an untreated frostbitten extremity. Finally, our study used a frozen pig’s foot as a simulated frost- bitten extremity. While a pig’s foot is not identical to a human extremity in anatomic characteristics and weight, the presence of bone, soft tissue, and skin allowed the assessment of tissue pliability that is recom- mended when assessing a rewarmed frostbitten extremity.

Conclusion

Sous vide rewarming is a novel method to create a warm water whirlpool bath ideal for the rapid rewarming of a frostbitten extremity. Further research is necessary to determine the safety and efficacy of its use in the clinical environment.

References

1. Mills, W J, and R Whaley. “Frostbite: experience with rapid rewarming and ultra- sonic therapy: part I. 1960.” Alaska Med, 35(1):6-9, 1993.
2. Mills WJ, Whaley R, Fish W. Frostbite: experience with rapid rewarming and ultra- sonic therapy: part II. 1960. Alaska Med 1993;35(1):10-8.
3. Mills WJ, Whaley R, Fish W. Frostbite: experience with rapid rewarming and ultra- sonic therapy: part III. Alaska Med 1961;35(1):19-27, 1993.
4. Malhotra MS, Mathew L. Effect of rewarming at various water bath temperatures in experimental frostbite. Aviat Space Environ Med 1978;49(7):874-6.
5. McCauley Robert L, et al. Frostbite injuries. J Trauma Injury Infect Crit Care 1983;23 (2):143-7.
6. Murphy James V, et al. Frostbite: pathogenesis and treatment. J Trauma Injury Infect Crit Care 2000;48(1):171-8 Jan.
7. Handford Charles, et al. Frostbite: a practical approach to hospital management. Ex- treme Physiol Med 2014;3(7)www.extremephysiolmed.com/content/3/1/7.
8. Charles Handford, et al. Frostbite. Emerg Med Clin North Am 2017;35(2):281-99.
9. Mcintosh Scott E, et al. Wilderness medical society practice guidelines for the pre- vention and treatment of frostbite: 2014 update. Wilderness Environ Med 2014;25 (4).
10. Nygaard Rachel M, et al. Time matters in severe frostbite. J Burn Care Res 2017;38 (1):53-9.