Cold injuries: Frostnip, frostbite and cold immersion foot
With rehab we often focus on the dangers of overheating, but cold injuries can be just as big a threat during winter months
By Dr. Ken Lavelle, MD, NREMT-P
Most of us recognize the need for emergency incident rehab in the summer months when the heat and humidity are high. In some ways, performing rehab in the warm months is easier — we can cool with fans and cool water, shade and often just the simple act of sitting with your gear off.
However, rehab in the winter months is much more of a challenge. Inside a burning building, similar conditions to summer can be present so we still have to be prepared for heat-related incidents. But performing rehab in cold weather is difficult without tents, heaters and other extra equipment. We also have additional conditions to be on the lookout for — cold-related injuries. In this column we will look at local cold injuries and then explore hypothermia next time.
Cold injuries have certainly been around since the beginning of time but they have been described more recently from a medical standpoint as a result of military action in the past 200 years. Larrey, who was the military surgeon for Napoleon during the retreat from Moscow in 1812, described his treatment of cold soldiers and how it was not always successful. He recognized that the cycle of "freeze — thaw — freeze" often harmed more than it hurt.
Before we discuss the individual types of injuries, it is important to understand the peripheral circulation — the blood supply to the extremities and skin. This blood supply is made up of many loops of capillaries — very small blood vessels. When the body is warm and would like to dissipate heat, these blood vessels will dilate, to allow more warm blood to come close to relatively cooler air. This is what happens when we appear flushed or red, and this is why it is important to get our bunker gear off when we are trying to cool down.
When the body is cold and it wants to conserve heat, these blood vessels will constrict, which decreases blood flow near the surface. However this also decreases the oxygen supply to these cells. For a short period of time that is not very detrimental. Unlike the cells of the brain that die without oxygen in four to six minutes, skin, muscle and similar cells can survive for hours. Temperatures below freezing can cause other issues that exacerbate the injury, which we will discuss below.
Symptoms frostnip and frostbite
While it is unlikely for the average firefighter to be exposed to these same types of conditions as the Napoleon army, it is not unreasonable for some degree of cold injury to occur at a prolonged incident in sub-freezing temperatures. The most common and fortunately least serious of these is frostnip.
Frostnip is a mild cold injury that many skiers, hunters and others that enjoy the outdoors have experienced. It most likely occurs in the distal extremities where there is decreased bloodflow. Initially there may be some mild pain, pale skin and numbness. There is no permanent tissue damage however and the symptoms all resolve quickly upon rewarming without any lasting symptoms. If there is any redness or swelling (edema), it is mild. The underlying tissues are soft.
Frostnip can be an indication of a more serious pending condition — frostbite. Frostbite represents actual damage to tissues and cells. There are two mechanisms. The first is the formation of ice crystals both inside and outside of the cells. This can cause mechanical damage and cell death. The second method is actually similar to burn injury, where the blood vessels themselves are injured. This can result in worsening of the swelling and even an increase in blood clots in the vessel. The combination of these two mechanisms can cause such severe damage that eventual amputation may be required.
The signs and symptoms of frostbite are initially the same as frostnip. However the symptoms progress to also include worsening clumsiness of the hands (if they are the affected site) and loss of fine motor control. The effects are deeper as well, and the affected skin may appear waxy and firm. Lastly, upon rewarming, the affected area develops more severe pain, burning and electrical shock sensations. Blisters may develop and swelling may be severe.
Is transport necessary?
Obviously the biggest concern to us on the fireground is, how do we tell the difference? How can we know if the firefighter just has mild frostnip and needs to warm up a bit or if they have developed frostbite and require transport to the hospital? The reality is we can''t be completely sure. In the emergency department, how the patient responds over a few hours will tell us what they had, and will steer their disposition — home or stay.
In the field, start with the general assessment we should do of all firefighters — ask them how they feel. Do their feet feel a little numb or do they actually hurt? Are they able to ambulate normally or are they stumbling because their feet won''t do what they want them to do? Are they unable to do simple tasks such as change a nozzle or operate their pack? If they have some of these more severe symptoms, you should at least do a more invasive physical exam, hopefully in a warm environment. Look and feel their hands or feet for the more serious signs as mentioned above. Also consider the time course — frostbite is unlikely at an event of short duration. It is more common at those large multi-alarm fires that last many hours or even days. If you have any doubts, recommend transport for a more complete exam in the hospital.
Treatment of frostbite is simple — protect the extremity. Do not initiate rewarming if there is any chance of a refreeze. For us in a non-wilderness environment, we should splint the extremity with a well-padded splint to prevent fracture or treat fractures that may not be recognized. Do not rub or massage the affected area as this can worsen the mechanical trauma. Do not immerse in water or hold the extremity near the heater — there is a specific way to rewarm the frostbitten area that cannot be done in the field.
Cold immersion foot
A related condition to consider can occur when the temperatures are actually still above freezing — trench foot or cold immersion foot. The term ''trench foot'' came from World War I and was seen among soldiers whose feet were wet and cold for a prolonged period of time. It most commonly occurs with conditions 32 to 59 F.
The cool temperature causes blood vessels to constrict as described above, but no ice crystals form. This constriction limits the amount of oxygen that is supplied to the tissues and cells of the foot, just like in frostbite. A difference is that the skin is also affected by the moisture, which can cause exterior tissue breakdown. This permits the cold temperature to impact the nerves and blood vessels more directly, as the skin is a good protector of these structures.
The firefighter or other individual affected with cold immersion foot may have few symptoms (what they feel). Pain is rare. On exam, the foot is often pale and mottled. There is delayed capillary refill. Symptoms develop upon re-warming — the foot becomes swollen, red and warm, and very painful.
Long-term effects are rare and treatment is aimed at symptomatic relief. Interestingly it is the rewarming that causes the pain and symptoms. As the foot is rewarmed the oxygen demands increase, but the injured blood vessels cannot supply enough. Keeping the extremity cool and then slowly warming over time is the treatment of choice. This is different from frostbite where rapid rewarming (in the hospital) is done.
For us on the fireground, prevention is key. Boots should be well-fitting to prevent local trauma. If staff are operating in a situation where their feet become and stay wet, they should change socks several times a day. This can be difficult as we rarely bring extra socks with us on a regular basis. This condition may be more common in a disaster response or technical rescue rather than a routine fire. If on exam we find skin breakdown or unusual pain or appearance, then hospital evaluation is indicated.
These are just a few of the more common localized (not the whole body) cold injuries that our staff may encounter. It is our job in rehab to both help prevent and to recognize these conditions. Don''t worry, the days are getting longer now so summer is coming!