Human Responses to 5 Heated Hypothermia Wrap Systems in a Cold Environment.

INTRODUCTION: We compared the effectiveness of 5 heated hypothermia wrap systems. METHODS: Physiologic and subjective responses were determined in 5 normothermic subjects (1 female) for 5 heated hypothermia wraps (with vapor barrier and chemical heat sources) during 60 min of exposure to a temperature of -22°C. The 5 systems were 1) user-assembled; 2) Doctor Down Rescue Wrap; 3) hypothermia prevention and management kit (HPMK); 4) MARSARS Hypothermia Stabilizer Bag; and 5) Wiggy's Victims Casualty Hypothermia Bag. Core and skin temperature, metabolic heat production, skin heat loss, and body net heat gain were determined. Subjective responses were also evaluated for whole body cold discomfort, overall shivering rating, overall temperature rating, and preferential ranking. RESULTS: The Doctor Down and user-assembled systems were generally more effective, with higher skin temperatures and lower metabolic heat production; they allowed less heat loss, resulting in higher net heat gain (P<0.05). HPMK had the lowest skin temperature and highest shivering heat production and scored worse than the other 4 systems for the "whole body cold discomfort" and "overall temperature" ratings (P<0.05). CONCLUSIONS: The user-assembled and Doctor Down systems were most effective, and subjects were coldest with the HPMK system. However, it is likely that any of the tested systems would be viable options for wilderness responders, and the choice would depend on considerations of cost; volume, as it relates to available space; and weight, as it relates to ability to carry or transport the system to the patient.

Efficacy of Head and Torso Rewarming Using a Human Model for Severe Hypothermia.

INTRODUCTION: To evaluate the rewarming effectiveness of a similar amount of heat (from a charcoal heater) applied to either the head or torso in a human model for severe hypothermia in which shivering is pharmacologically inhibited in mildly hypothermic subjects. METHODS: Six male subjects were cooled on 3 different occasions, each in 8°C water for 60 min, or to a lowest core temperature of 35°C. Shivering was inhibited by intravenous meperidine (1.5 mg·kg-1), administered during the last 10 min of the cold-water immersion. Subjects then exited from the cold water, were dried, and were placed in a 3-season sleeping bag for 120 min in one of the following conditions: spontaneous rewarming only, charcoal heater on the head, or charcoal heater on the torso. Supplemental meperidine (to a maximum cumulative dose of 3.3 mg·kg-1) was administered as required during rewarming to suppress shivering. RESULTS: No significant differences were found in the postcooling afterdrop amount or core rewarming rates among the 3 conditions (0.8°C·h-1). During the last 30 min of rewarming the net heat gain was significantly higher in the head (85.8±25.3 W) and torso (81.5±6.3 W) conditions compared with the spontaneous condition (56.9±12 W) (P<0.05). CONCLUSIONS: In our study, head and torso warming had the same core rewarming rates when shivering was pharmacologically inhibited in mildly hypothermic subjects. Therefore, in nonshivering cold subjects, head warming is a viable alternative if torso warming is contraindicated (eg, when performing cardiopulmonary resuscitation or working on open chest wounds).

Comparison of Distal Limb Warming With Fluidotherapy and Warm Water Immersion for Mild Hypothermia Rewarming.

OBJECTIVE: The purpose of the study was to determine the effectiveness of Fluidotherapy rewarming through the distal extremities for mildly hypothermic, vigorously shivering subjects. Fluidotherapy is a dry heat modality in which cellulose particles are suspended by warm air circulation. METHODS: Seven subjects (2 female) were cooled on 3 occasions in 8˚C water for 60 minutes, or to a core temperature of 35°C. They were then dried and rewarmed in a seated position by 1) shivering only; 2) Fluidotherapy applied to the distal extremities (46 ± 1°C, mean ± SD); or 3) water immersion of the distal extremities (44 ± 1°C). The order of rewarming followed a balanced design. Esophageal temperature, skin temperature, heart rate, oxygen consumption, and heat flux were measured. RESULTS: The warm water produced the highest rewarming rate, 6.1°C·h(-1), 95% CI: 5.3-6.9, compared with Fluidotherapy, 2.2°C·h(-1), 95% CI: 1.4-3.0, and shivering only, 2.0°C·h(-1), 95% CI: 1.2-2.8. The Fluidotherapy and warm water conditions increased skin temperature and inhibited shivering heat production, thus reducing metabolic heat production (166 ± 42 W and 181 ± 45 W, respectively), compared with shivering only (322 ± 142 W). Warm water provided a significantly higher net heat gain (398.0 ± 52 W) than shivering only (288.4 ± 115 W). CONCLUSIONS: Fluidotherapy was not as effective as warm water for rewarming mildly hypothermic subjects. Although Fluidotherapy is more portable and technically simpler, it provides a lower rate of rewarming that is similar to shivering only. It does help decrease shivering heat production, lowering energy expenditure and cardiac work, and could be considered in a hospital setting, if convenient.

Comparison of heat donation through the head or torso on mild hypothermia rewarming.

OBJECTIVE: The purpose of the study was to compare the effectiveness of head vs torso warming in rewarming mildly hypothermic, vigorously shivering subjects using a similar source of heat donation. METHODS: Six subjects (1 female) were cooled on 3 occasions in 8 ºC water for 60 minutes or to a core temperature of 35 ºC. They were then dried, insulated, and rewarmed by 1) shivering only; 2) charcoal heater applied to the head; or 3) charcoal heater applied to the torso. The order of rewarming methods followed a balanced design. Esophageal temperature, skin temperature, heart rate, oxygen consumption, and heat flux were measured. RESULTS: There were no significant differences in rewarming rate among the 3 conditions. Torso warming increased skin temperature and inhibited shivering heat production, thus providing similar net heat gain (268 ± 66 W) as did shivering only (355 ± 105 W). Head warming did not inhibit average shivering heat production (290 ± 72 W); it thus provided a greater net heat gain during 35 to 60 minutes of rewarming than did shivering only. CONCLUSIONS: Head warming is as effective as torso warming for rewarming mildly hypothermic victims. Head warming may be the preferred method of rewarming in the field management of hypothermic patients if: 1) extreme conditions in which removal of the insulation and exposure of the torso to the cold is contraindicated; 2) excessive movement is contraindicated (eg, potential spinal injury or severe hypothermia that has a risk of ventricular fibrillation); or 3) if emergency personnel are working on the torso.

Vehicle submersion: a review of the problem, associated risks, and survival information.

BACKGROUND: Of all drownings, 3 to 11% occur in submersed vehicles, yet scientific study of this topic seems limited. METHODS: A search was made of digital medical, drowning, transportation, and rescue databases regarding vehicle submersion drownings. RESULTS: The major risk factors include driving on ice or roadways near water, flooding of roadways or bridges, slippery roads, curved roads, and darkness. A new definition of a Flotation Phase (from water impact until water rises to the bottom of side windows) defines a period when escape is easiest. Since survival probability is highest during this period (generally the first minute)--and then decreases rapidly--cell phones should not be used to call for help because this will only squander the optimal window for survival. It is virtually impossible to open a door until the vehicle is almost completely full of water. Since there is little or no trapped air, this period provides a very low chance of survival. Before exit, children should be released from their restraints. Breaking windows is difficult without a center punch or rescue hammer, which should be visibly mounted within reach of the driver. CONCLUSIONS: Prevention includes installing adequate guardrails, barriers, warning signs, and road markings, or placing roadways at a greater distance from water. Areas at high risk for flooding should have signs and public warning systems for flash flooding should be improved. Public education should also focus on the dangers of driving on flooded roads or bridges, and on ice roads.

Escape from a submersible vehicle simulator wearing different thermoprotective flotation clothing.

BACKGROUND: Winter road workers, who drive heavy vehicles on ice-covered waterways, are at risk for ice failure and subsequent drowning in frigid water. Some workers who are recommended to wear thermoprotective flotation clothing are concerned that buoyancy or bulk may impede underwater exit. METHODS: Using a simulator, 10 volunteers (2 women) compared everyday winter clothing (Control), a flotation Jacket and Overall, and an inflated inflatable personal flotation device (Inflated Vest). On each study day, all clothing conditions were tested in either Cool (20 degrees C) or Cold (8 degrees C) water conditions using a randomized balance design. After each trial, subjective ratings for thermal sensation and exit tasks along with exit task times were determined. RESULTS: Exit task times were unaffected by clothing or water conditions. Compared to Control, the Inflated Vest was rated with higher exit task difficulty and impedance, while the Jacket and Overall were not (ratings for exit task difficulty and impedance in cold water were: Control, 'a little' and 'none'; Jacket, 'a little' and 'a little'; Overall, 'a little' and 'moderate'; and Inflated Vest, 'moderate' and 'moderate - a lot'). Finally, there was a training effect, with total exit times improving by 20% from trials 1-8 (12.3 to 9.8 s). CONCLUSIONS: Results suggest that, compared to Control clothing, flotation Jackets and Overalls do not increase exit time or impede exit during egress from a submerged vehicle while providing thermoprotection and buoyancy in 20 degrees C and 8 degrees C water. The Inflated Vest created the most perceived exit impedance in comparison to Control.

Clothing buoyancy and underwater horizontal swim distance after exiting a submersed vehicle simulator.

BACKGROUND: Winter road workers, who drive heavy vehicles over ice-covered waterways, are at risk for ice failure, vehicle submersion, and subsequent drowning in frigid water. Although some jurisdictions require these workers to wear flotation clothing, there are concerns that, following an underwater exit in fast-moving water, increased clothing buoyancy may reduce ability to swim against the current to safely return to the ice opening. METHODS: Using a simulator in a swimming pool (3.7 m deep, 28 degrees C), 11 volunteers (5 women) were submersed 8 times each to test the effects from both an Upright and an Inverted position of a normal nonflotation winter jacket (Control), a flotation Jacket, a flotation Overall, and a personal inflatable vest which was inflated (Inflated Vest) on underwater horizontal swim distance. Subjects also rated exit difficulty and impedance, psychological stress, and thermal comfort. RESULTS: Compared to Control, Jacket, and Overall, the Inflated Vest generally increased exit difficulty, escape impedance, and psychological stress, while greatly decreasing the ability to swim horizontally underwater before reaching the surface (Control, 6.1 m; Jacket, 5.0 m; Overall, 3.4 m; and Inflated Vest only 1.4 m). Swim distance with the Overall was also significantly shorter than Control, but not Jacket. DISCUSSION: Flotation clothing (either Jackets or Overalls) is recommended for vehicle travel on ice because they do not impede underwater exit from a vehicle and allow significant horizontal underwater swim distance. An inflatable vest is not recommended because inappropriate premature inflation could increase exit impedance and decreased underwater swim distance.

Exit strategies and safety concerns for machinery occupants following ice failure and submersion.

BACKGROUND: Of all drownings, 5 to 11% occur in submerged vehicles. Winter road workers are at high risk for vehicle submersion because they drive heavy vehicles over ice. METHODS: A crane was used for repeated occupied and unoccupied submersions of a 5-ton truck/snow plow (N = 25) and a 1-ton truck/snow plow (N = 23); some data were compared to those from our previous study on passenger vehicles (Aviat Space Environ Med 2010; 81:779-84). RESULTS: The 1-ton truck sank faster than an intact car, while the 5-ton truck sank within 4 s. Four subjects could escape through the windows, doors, or roof hatch when the 1-ton truck was on the surface or submerged. Hatch exit took 2-3 times longer than windows/doors. Because the 5-ton truck sank so quickly, there was no opportunity to escape while on the surface. With windows open, exit through the window, door, or roof hatch could only occur after the cab was full of water. With windows closed, rapid pressure buildup imploded the windshield. Bulk and buoyancy of thermoprotective flotation clothing did not impede exit in any scenario. One to three 200-L sealed containers mounted to the front of the 1-ton truck increased the Floating Phase by approximately 20-40 s each. CONCLUSIONS: Results suggest that a heavy vehicle will sink before surface exit is possible. Occupants would, therefore, be forced to breath-hold and make an underwater exit through a window, door, or roof hatch. Front-mounted external flotation devices on a light truck increased floating time and the possibility of exit while still on the surface.

My car is sinking: automobile submersion, lessons in vehicle escape.

INTRODUCTION: In North America approximately 400 individuals per year die in submersed vehicles, accounting for 5-11% of all drownings. About half of people surveyed would let the vehicle fill with water before attempting exit. METHODS: We used a crane and two passenger vehicles of the same make, model, and year-one with passenger compartment intact (I) and one with holes (H) in the floor (area approximately 2200 cm2)--to conduct occupied and unoccupied submersions. RESULTS: Three phases of submersion were identified: 1) FLOATING, vehicles floated for 15 s (H) to 63 s (I) before the water reached the bottom of the side windows; 2) SINKING, the subsequent period until the vehicle is completely under water, but before it fills completely; and 3) SUBMERGED, the vehicle was full of water and several feet below the surface. Total time to submersion was 150 s for I but only 37 s for H. Opening the door to exit Vehicle I decreased submersion time from 150 to 30 s. Even the most difficult exit strategy attempted (three men and a child manikin through one window) was quickly performed from Vehicle I (only 51 s). During one exit attempt, initiated during the sinking phase, it was impossible to open the doors or windows until the vehicle was completely full of water. CONCLUSIONS: A vehicle is most easily exited during the initial Floating Phase. We suggest the following escape procedure: SEATBELT(s) unfastened; WINDOWS open; CHILDREN released from restraints and brought close to an adult; and OUT, children should exit first.

Skin Cooling on Breath-Hold Duration and Predicted Emergency Air Supply Duration During Immersion.

PURPOSE: This study was intended to determine the effect of skin cooling on breath-hold duration and predicted emergency air supply duration during immersion.METHODS: While wearing a helicopter transport suit with a dive mask, 12 subjects (29 ± 10 yr, 78 ± 14 kg, 177 ± 7 cm, 2 women) were studied in 8 and 20°C water. Subjects performed a maximum breath-hold, then breathed for 90 s (through a mouthpiece connected to room air) in five skin-exposure conditions. The first trial was out of water for Control (suit zipped, hood on, mask off). Four submersion conditions included exposure of the: Partial Face (hood and mask on); Face (hood on, mask off); Head (hood and mask off); and Whole Body (suit unzipped, hood and mask off).RESULTS: Decreasing temperature and increasing skin exposure reduced breath-hold time (to as low as 10 ± 4 s), generally increased minute ventilation (up to 40 ± 15 L · min-1), and decreased predicted endurance time (PET) of a 55-L helicopter underwater emergency breathing apparatus. In 8°C water, PET decreased from 2 min 39 s (Partial Face) to 1 min 11 s (Whole Body).CONCLUSION: The most significant factor increasing breath-hold and predicted survival time was zipping up the suit. Face masks and suit hoods increased thermal comfort. Therefore, wearing the suits zipped with hoods on and, if possible, donning the dive mask prior to crashing, may increase survivability. The results have important applications for the education and preparation of helicopter occupants. Thermal protective suits and dive masks should be provided.Madu VC, Carnahan H, Brown R, Ennis K-A, Tymko KS, Hurrie DMG, McDonald GK, Cornish SM, Giesbrecht GG. Skin cooling on breath-hold duration and predicted emergency air supply duration during immersion. Aerosp Med Hum Perform. 2020; 91(7):578-585.

Public knowledge, attitudes and practices of vehicle submersion incidents: a pilot study.

INTRODUCTION: Vehicle submersions account for up to 10% of all drownings in high-income countries. Reports indicate that occupants may be conscious and functional, but possibly making incorrect decisions for self-rescue leading to drowning. This study investigated current public knowledge, attitudes and practices regarding vehicle submersion incidents and to determine if individuals, who are aware of educational efforts regarding vehicle submersions, indicated better responses. METHOD: A knowledge, attitude and practice (KAP) survey was developed based on previous findings and guidelines from Operation ALIVE (Automobile submersion: Lessons In Vehicle Escape) for vehicle submersion incidents. RESULTS: The majority of respondents (87%) had knowledge of vehicle submersions from the media, but they were not aware (94%) of an effective self-rescue protocol. Respondents felt they had low risk of involvement in a vehicle submersion, and that the chance of survival was likely. Most respondents selected a "successful" initial action for escape; however, other responses indicate the chances of completing a successful self-rescue sequence was less likely. Only 45% of respondents were "aware" of Operation ALIVE educational initiatives, and this awareness did not generally produce better responses. CONCLUSIONS: Public understanding of vehicle submersion incidents is low and current public education efforts have not increased awareness in the severity or the urgency for performing self-rescue in this scenario. Simply increasing public knowledge of "SWOC" ("SEATBELTS" off, "WINDOWS" open, "OUT" immediately, "CHILDREN" first) would help to decrease the high fatality rate associated with this type of road traffic accident.