Carbon Monoxide Poisoning

Murray, UT (3/18/2009) – Last month’s mass evacuation of a Ogden, Utah, sink-manufacturing plant due to carbon monoxide poisoning that seriously sickened nearly 50 workers and exposed others to dangerously high levels of carbon monoxide, is the latest high-profile case of carbon monoxide poisoning in Utah.

The number of reported cases of carbon monoxide poisonings in the United State is increasing – last year more than 50,000 people were treated in emergency rooms for CO poisoning – and the numbers continue to grow.

In one of the most comprehensive reports on the physiological effects of carbon monoxide poisoning on victims, Lindell Weaver, MD, medical director of the Hyperbaric Medicine Center at Intermountain Medical Center, writes about the significant health problems victims can face immediately and years down the road in this week’s issue of The New England Journal of Medicine.

Among Dr. Weaver’s key findings and recommendations:

• Evidence shows that CO poisoning causes inflammation, as well as hypoxia, and this inflammation may explain much of what can be seen in patients with long-term cognitive problems. Patients commonly have neuro-psychological disorders after carbon monoxide poisoning. In one randomized trial, 46 percent of poisoned patients treated with regular oxygen had cognitive problems six weeks after poisoning, and 45 percent had associated problems. Associated disorders include gait and motor disturbances, peripheral neuropathy, hearing loss and vestibular abnormalities, and dementia and psychosis, which can be permanent.
• Inflammation caused by carbon monoxide results in tissue injury. Whether anti-inflammatory therapy or the use of other neuro-protective interventions, such as induced hypothermia, could improve outcomes after poisoning is unknown.
• Carbon monoxide poisoning can exacerbate angina and cause cardiac injury, even in persons with normal coronary arteries. Therefore, Dr. Weaver recommends that all poisoned patients should undergo a cardiovascular investigation, including electrocardiography and measurement of cardiac enzymes. If cardiac injury is present, a cardiology consultation should be performed.
• Patients with carbon monoxide poisoning should be followed medically after discharge, which often does not happen. The extent and rate of recovery after poisoning are variable, and recovery is often complicated by the development of associated problems that can persist or develop weeks after poisoning. Many of these can be permanent.
• Dr. Weaver suggests that patients with disorders resulting from their exposure should have their symptoms treated through cognitive, psychiatric, vocational, speech, occupational, and physical rehabilitation, although data on the effects of these interventions in patients with carbon monoxide–related disorders are unknown. Patients with persistent headaches may benefit from evaluation by a specialist.
• Although carbon monoxide poisoning can cause myriad neurological and neuro-psychological problems, the incidence of disorders after carbon monoxide poisoning is not clearly known. Prospective studies of patients treated with regular oxygen showed that 34 percent reported symptoms such as headaches or memory problems at four weeks after exposure and 46 percent had neuro-psychological problems six weeks later.
• In patients without a history of carbon monoxide poisoning, abnormalities found on neuro-imaging that are consistent with those reported after carbon monoxide poisoning showed an increased risk of early cognitive decline. It is unknown whether patients with carbon monoxide poisoning who have such abnormalities are also at increased risk for early cognitive decline or Alzheimer’s disease.
• A CO poisoning patient’s initial condition does not predict later outcomes with certainty, but particular variables known at the time of poisoning are predictive of risks for subsequent problems. In one study, patients who were 36 years of age or older or who had been exposed to carbon monoxide for at least 24 hours, who did not receive hyperbaric oxygen, or who had other abnormalities upon hospital admission, had an increased risk of cognitive disorders at six weeks as compared with those without these characteristics.
• Patients with dizziness before hospital admission or headaches at the time of admission had an increased risk of neurological problems one month after poisoning. Given the role of inflammation in carbon monoxide, associated injury levels of inflammatory markers might predict the risk of related disorders, but this possibility requires further study.
• Nearly 20 percent of CO poisoning patients had cognitive problems and 37 percent had abnormal neurological evaluations approximately six years after poisoning.
• Responses to carbon monoxide exposures are variable. Exposed children often become symptomatic earlier, and recover faster, than similarly exposed adults, because of their lesser blood volume and increased minute ventilation per unit of body mass as compared with adults. Prospective studies of children exposed to carbon monoxide have reported variable rates of disorders.

The unborn fetus is highly susceptible to the adverse effects of carbon monoxide. The period required to eliminate carbon monoxide is prolonged for fetal blood as compared with adult blood, and maternal poisoning and hypoxemia contribute to fetal hypoxia. Fetal mortality exceeds 50 percent in cases of severe poisonings. Dr. Weaver says hyperbaric-oxygen therapy should be considered in women with acute carbon monoxide poisoning, including pregnant women, and in particular if the fetus shows signs of distress.