Carbon Monoxide Poisoning in the Field

Mechanism & Pathophsiology
Carbon monoxide (CO) is colorless, odorless, tasteless, and initially non-irritating; signs and symptoms of CO poisoning are delayed and often accumulative. CO binds to hemoglobin on red blood cells and is carried as carboxyhemoglobin (COHb) in the blood. Bound CO prevents oxygen uptake by hemoglobin and significantly reduces the blood's oxygen carrying capacity. CO also binds to other molecules in the body and reduces the function of all high oxygen-demand organs (heart, brains, & lungs) even after the CO has been cleared from the blood. In a wilderness environment, CO is typically generated as a byproduct of incomplete fuel combustion in a stove or lantern. Signs and symptoms of CO poisoning vary widely based on exposure level, duration, and the general health and age of an individual.

Moderate amounts of CO exposure at sea level will cause discomfort and may ultimately lead to death; minimal CO exposure at high altitude is potentially fatal. People unacclimatized to high altitude have respiratory rates higher than normal; as a result, CO accumulates faster in their body at altitude than at sea level. Individuals acclimatized to a given altitude have an increased RBC count; as a result, they carry more CO in their blood than unaccilmitized people and there is a significant delay in clearing the accumulated CO once they are removed from the hazardous environment. In both acclimitized and unacclimatized individuals, the decreased pressure at high altitude decreases the amount of oxygen the blood can hold and exacerbates the signs and symptoms, and accelerates the onset of, altitude sickness.

As cold and inclement weather approaches, it's tempting to cook or use a candle or propane lantern inside your shelter, be it made of canvas, nylon, or snow. The smaller the shelter, the faster CO builds. The more insulative the shelter, the faster CO builds. Simmering, using stoves at a low pressure or with a yellow flame, putting a cooking pot in the flame (rather than above it), large diameter pots, low wind, and icing of tent walls (or snow cover), all increase CO production. Kerosene produces more CO than white gas and white gas produces more CO than alcohol.

Prevention

• Avoid cooking or using a lantern inside a tent or snow shelter. Period. Twenty-plus deaths     occur each year from carbon monoxide poisoning in tents and snow shelters.

Assessment

• The patient has a history of using a combustible stove or lantern inside an enclosed tent or snow shelter.
• Exposure to a low concentration of CO yields lightheadedness, confusion, headaches,vertigo, and flu-like signs and symptoms.
• Exposure to higher concentrations of CO or exposure for longer times, causes the patient to develop pink, flushed mucous membranes, an increased pulse rate, decreased BP, cardiac arrhythmia, delirium, hallucinations, dizziness, unsteady gait, confusion, seizures, CNS depression, unresponsiveness, respiratory arrest, and death.
• Long-term neuropsychiatric sequelae are common.
• Oxygen saturation via a pulse oximeter is an unreliable indicator of CO poisoning. 

Field Treatment

• Remove the patient from the toxic environment and place them in a sitting or semi-reclined position in clean air.
• If available, administer oxygen ASAP using a non-rebreather mask.
• Administer rescue breathing (PPV) and CPR as necessary. Respiratory arrest may occur if you are unable to maintain effective blood oxygen levels.
• Begin a Level 2 Evacuation for all awake patients.
• Begin a Level 1 Evacuation for all V P U patients to a hyperbaric center.

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