Ask the Flight Surgeon / By CPT Nathan H. Kwan, M.D.: This month, let’s take a look at cold weather injuries and how they are generally treated and, more importantly, prevented.
With the dropping temperatures of the winter months comes an increased risk of cold weather injuries related to military duties. About 30 cold weather injuries were reported in the military per 100,000 person-years for 2015-2016. Outside of military responsibilities, hobbies like mountaineering, cross-country skiing and other winter sports further increase the risk of injury. Personal risk factors for increased susceptibility to cold injuries include an age greater than 45 years, history of previous cold weather injury, inadequate clothing, exhaustion, dehydration, malnutrition, vibration exposure, and other comorbidities like peripheral vascular disease and anemia. Cold weather injuries can encompass a wide range of insults to the body, including hypothermia, frostbite, and trench foot.
Hypothermia is a potentially dangerous drop in core body temperature below 95°F. It is usually caused by a prolonged exposure to cold. As core temperature drops, hypothermia is further divided into different stages that are marked by a progression of symptoms from shivering to confusion and drowsiness progressing to cessation of shivering and loss of consciousness. Body temperature drops when more heat is lost than is produced. The majority of loss occurs with convection when cold air or water takes heat away from the skin and the lungs expel warm air only to breathe in the cold. Certain medical conditions such as diabetes, hypothyroidism and traumatic injuries as well as some medications may make someone more susceptible to hypothermia. Alcohol consumption, though often and incorrectly touted as a way to beat the cold, actually gives a false perception of warmth and can lead to worsening hypothermia. Even mild hypothermia is a risk to safety of flight with symptoms like sluggishness of thought and muscle movement.
Frostbite, Frostnip, Trench Foot, Chilblains
Frostbite typically occurs in the extremities and is categorized as a freezing cold injury, in which ice crystals form inside cells, causing inflammation, tissue ischemia, and tissue death. Frostbite can be exacerbated by cycles of freezing, thawing, and refreezing. In comparison, frostnip is categorized as a nonfreezing cold injury and describes a pale area skin with reduced sensation (paresthesia). Trench foot, also known as immersion foot, is another nonfreezing cold injury caused by prolonged exposure to cold and dampness and can present with red, swollen and painful feet. Chilblains, also called pernio, are inflammatory skin lesions that are often painful, red/purple in color, and caused by repeated exposure to damp nonfreezing conditions. The pain from these injuries can be distracting or even debilitating and are not compatible with safety of flight.
The emergency management of cold weather injury begins with the initial assessment of the affected person that includes assuring proper support of blood circulation, airway management, and breathing. Next, passive rewarming begins by removing the patient from the cold environment, removing wet clothing, covering the person with blankets or other insulating materials, and maintaining a room temperature of no more than 82°F. Patients should be transported horizontally with minimal muscle exertion.
All of the nonfreezing cold injuries do not result in permanent tissue damage if adequately rewarmed in a timely manner. However, freezing cold injuries like frostbite may require surgical removal of affected tissue depending on the severity. Frostbite areas should be rewarmed in circulated warm water (98.6°F to 102.2°F) with care to avoid striking affected areas against each other or against solid surfaces. However, rewarming should not be attempted if there is high risk of re-exposure to freezing conditions.
Preventive measures include minimizing the modifiable risk factors discussed previously, being aware of weather conditions, and wearing layered clothing that protects the body especially the extremities and digits from cold, wet, and windy conditions. Alcohol consumption, smoking (constricts blood vessels and impairs circulation), and exposure to conductive losses (water, metal surfaces) should be minimized. Footwear should be well fitted; boots should not be too tight as this is a risk factor for trench foot. Frequent changing of socks and other damp clothing reduces the risk for nonfreezing cold injuries. Specialized clothing that wicks away perspiration is also advised.
The Army has an Aeromedical Policy Letter addressing cold injuries. Waivers are necessary for amputations and residual skin damage, including distracting pain, paresthesias, or discoloration. Information required includes a neurological examination and, if needed, an in-flight evaluation to determine if the residual injury interferes with operation of controls. Once a waiver is granted, annual waiver requirements are not normally required unless neurovascular injury was identified.
CPT (Dr.) Nathan H. Kwan is a flight surgeon at the School of Army Aviation Medicine, Fort Rucker, AL.
The views and opinions offered are those of the author and researchers and should not be construed as an official Department of the Army position unless otherwise stated.