It is the old tip-of-the-iceberg thing: For the 1,000 or more annual deaths in the U.S. from carbon monoxide poisoning, it is estimated that there are 40,000 nonfatal exposures.

The latter are likely underreported, underrecognized and underdiagnosed. As in my November column, the word for carbon monoxide, or CO, is insidious: “working or spreading harmfully in a subtle or stealthy manner, treacherous.”

A motel employee discovered two young women, stumbling, bumbling and mumbling, in midmorning in their room. It was winter, and an ambulance quickly made the 15-mile run to the motel. Smelling no alcohol, the crew presumed the pair were on drugs and transported them to the emergency room, without oxygen. Having had our second cup of coffee and our good eyes open, we recognized them as CO poisoned – the culprit was an in-floor, gas room heater.

Back then, and probably now, almost every patient transported by ambulance receives oxygen. Immediate first aid is simple: remove the victim to normal air and administer oxygen, preferably 100 percent by mask or an airway. As mentioned previously, carbon monoxide has 200 times the affinity for hemoglobin in red blood cells as oxygen, making it difficult and slow to remove.

Levels of more than 40 to 50 percent carboxyhemoglobin (CO plus hemoglobin) can result in brain injury, even death. On normal, room air, it takes four hours or more to clear half the accumulated CO, a four-hour half-life. Half-life on 100 percent oxygen is about one hour, and on hyperbaric oxygen at up to three atmospheres pressure, 20 to 30 minutes.

The worm in the apple is that duration of poisoning, very difficult to guesstimate, is equally as important as carboxyhemoglobin level. Therefore, time is of the essence. The clock ticks as EMS is called, as it travels and spends time at the scene, as it transports, then ER evaluates and the victim is transported to a chamber, usually located in a major city. (There is now one in Farmington.) The hog eating the apple is a major 2009 study, concluding: “No evidence to support use of hyperbaric oxygen for treatment of patients with carbon monoxide poisoning.” However, this is extremely difficult science and because there is no proven harm, hyperbaric oxygen will likely continue to be used.

On a severely cold winter night, a state trooper approached a parked trucker, engine running. The driver reported some nausea and insisted he was OK. The following morning, he was slumped over the steering wheel, motor quit. Both at the scene and in the ER, he had no pulse, blood pressure or respiration. His blood tested positive for CO. Lying on the stretcher with his face on folded arms and legs in the air, he wasn’t just hypothermic (“they’re not dead until warm and dead”), he was frozen solid.

The worm in the apple here, was that our CO test was qualitative (presence of CO), thus limited, not quantitative (the level). But it sure looked like a CO fatality. The autopsy revealed the cause of death to be an acute heart attack in a heavy smoker.

www.alanfraserhouston.com. Dr. Fraser Houston is a retired emergency room physician who worked at area hospitals after moving to Southwest Colorado from New Hampshire in 1990.