Winter has finally arrived in central Wisconsin. I know it’s getting cold because the dog comes back to the porch as soon as he’s finished with his business. No time to dilly dally with smells and rabbit tracks when the thermometer reads 1 degree F.
I’m a paid, on-call first responder for the Plover Fire Department. In less than two minutes I want to be out the door and responding in my personal vehicle to any 9-1-1 emergency in my community — indoors or outdoors. If I’m cold and or shivering on scene, I’m distracted, which may compromise my ability to asses and treat the patient.
As we leave behind winter solstice and begin the march toward longer spring days, remember these things about hypothermia for you and your patients.
Heat Loss Mechanisms
Although “cold weather” is relative to your geography, any temperature below 98.6 degrees F can cause heat loss. I focus on heat loss prevention — my own and the patient’s — when the ambient outdoor temperature is below 50 degrees F. Heat is lost by conduction, convection, radiation, evaporation and respiration.
Radiation is the loss of heat from an area of higher temperature to an area of lower temperature. A patient lying in a ditch is radiating heat into the air around them. Covering the patient with a blanket retains the heat they’re radiating. Heat loss by radiation is the same from all body surface areas. The head doesn’t lose heat faster than other body parts; it’s just uncovered more often. Put a towel over and around your patient’s head as you wheel them from the house/scene to the ambulance to avoid heat loss.
Conduction is the direct transfer of heat from an object of higher temperature to an object of lower temperature. For example, conducts away from an elderly patient to the garage floor where they fell. Move the patient off the floor or add an insulating layer between them and the cold surface to reduce conduction.
Convection is the loss of heat from air or water circulating over the skin. Position yourself or other responders to block a cold wind that might be blowing on the patient.
The evaporation of water from liquid to a vapor requires heat. Sweat is an evaporative heat loss mechanism. If you’re overdressed for the environment, sweating will increase your heat loss, especially if your activity level declines or stops.
Respiration is also a heat-loss mechanism. The vapor you exhale contains warm air that you’re giving away to the world around you. Keep in mind that mouth-to-mask ventilations with your warm breath may be better for the patient than receiving bag-valve mask ventilations in a cold environment, depending on the duration of ventilations, length of time ventilation is required, and ambient air temperature.
A motor vehicle crash patient lying on the pavement on a cold day is in an unsafe scene. They’re rapidly losing heat from conduction, convection and radiation. Rolling the patient directly onto a cold backboard means the patient will continue to conduct heat into the backboard. Immediate actions to increase safety for the patient might include covering the patient with blankets or log-rolling the patient onto a blanket.
Safety takes precedence over other assessment and treatment actions. If a patient has fallen through the ice, they’re extricated before receiving a rapid trauma exam or explaining their SAMPLE history. A patient lying on a cold garage floor has a less obvious, but still significant, safety threat that requires action before assessment and treatment begin.
Heat loss isn’t just a factor of ambient temperature. Wind speed and length of exposure also play a significant role. When it’s cold, minimize outdoor assessment and treatment actions. For example, when a snowmobiler caught his arm on a tree as he sped through the woods. Our response time to his remote location was nearly 30 minutes. When we arrived, he was shivering and stabilizing his obviously broken arm with his own hands. Our first action was to welcome him into our warm ambulance. Once inside, we could begin to assess and treat his arm injury, which included removing and cutting away clothing.
Dress for the Conditions
Our jobs, especially in the winter, often require us to be ready for action in many temperature extremes. To be prepared for a wide variety of environmental conditions it’s best to dress in layers that can be added or removed quickly.
For extended outdoor operations, avoid cotton layers — especially close to your body. Cotton retains moisture and because we still sweat when it’s cold, this can exacerbate heat loss. Instead, choose synthetic layers, such as polypropylene, that “wick” moisture away from the skin and toward outer layers that evaporate the moisture away without significant heat loss.
Several light or mid-weight layers give you more flexibility for a variety of conditions than a single heavy-weight layer. In a 24-hour shift in central Wisconsin, I might experience a 30-40 degrees F temperature change from early morning to midnight. Multiple layers allow me to change and be ready for a variety of conditions.
For your outer layer, choose a wind-resistant and water-resistant or waterproof shell. This reduces heat loss from convection but also minimizes water-compromising insulating layers. New American National Standards Institute (ANSI) guidelines for reflective clothing when working on federally funding roadways went into effect Nov. 24. Your outermost layer must contain specific amounts of reflectivity and high-visibility coloring. A vest that can be worn over any amount of insulation may be most effective.
I carry a pair of mid-weight fleece gloves with me in the winter. They have a rough-grip surface on the palm that helps me secure equipment or the cot. I can even wear these gloves with a pair of nitrile glove as a liner. If the fleece gloves become contaminated, I wash them just like I would my pants or shirt.
Finally, just like your mom always said, wear a hat. It reduces heat loss from convection and radiation. It’s especially effective for emergency responders, like me, who have very little insulation on top.
For more about hypothermia — the good kind — read “The Cold Truth about Spinal Injury.”