The Nature of Carbon Monoxide

  • Carbon monoxide is a gas produced by incomplete combustion.
  • Carbon monoxide is a colorless, odorless, tasteless, and non-irritating to human senses.
  • It is undetectable by humans without the aid of special devices.
  • It does not cause any of your senses to activate until you are already experiencing the symptoms of damage from exposure.
  • The presence of carbon monoxide in the blood decreases the oxygen transport capability of the cardiovascular system.
  • Carbon monoxide damages tissues though several mechanisms, including hypoxia (CO binds to iron molecules within hemoglobin, interfering with oxygen delivery to tissues); neurochemical changes resulting in abnormal function and cellular death; and acceleration of apoptosis (premature, programmed cellular death) in hippocampus of the brain.
  • 500 parts per million is a lethal mixture for most exposed humans over a period of several hours.
  • The threshold limit value allowed by the U.S. Environmental Protection Agency and the World Health Organization for outside air is 9 ppm.
  • Many federal and local governmental agencies have adopted a 9 ppm threshold for immediate remedial action.
  • Like any toxin, the damage caused by carbon monoxide is a function of time and dose.
  • Portions of the brain are irreversibly lost following CO poisoning through atrophy and cell death. Unconsciousness or change in conscious state are not necessary for this to occur.
  • The principal elements of damage from CO poisoning include:
    • Fatigue, tiredness, weakness, sleepiness, and sleep disturbance;
    • Persistent neurological symptoms involving clumsiness, and large and small muscle control;
    • Elements of memory problems (word-finding, losing things, places), impaired attention-concentration, impaired self-initiation and self-monitoring, problems with sorting-organizing, multi-tasking, slowed speed of mental processing and problems in making decisions and working in an “intellectual” job.
    • Persistent affective/emotional problems involving decreased self-esteem and self-confidence, increased general anxiety, less easy-going nature and greater irritability, mood changes involving depression, a perceived worsening of life due to CO poisoning.
  • The half life of carboxyhemoglobin is 4 to 5 hours. Within one day, the COHb level in the blood will be at or near background no matter how high it was to start with. The half life of COHb when breathing 100% oxygen is around 50 to 70 minutes. The half life of COHb with hyperbaric oxygen is 20 minutes.
  • Victims see general practitioners, neurologists, interns, cardiologists – not the health professionals most helpful in the diagnosis, testing, and management of people with carbon monoxide poisoning.
  • Neuropsychologists are the gold standard for assessing carbon monoxide-induced brain damage because the majority of lasting health effects occur in the cognitive memory and affective-emotional arenas.
  • It is not understood why some individuals recover well, while others have long-lasting impairments.
  • 15% to 49% of individuals diagnosed with carbon monoxide poisoning will develop cognitive sequelae.
  • The brain damage is irreversible.
  • As patients with brain injury age, they are at risk for early cognitive decline and Alzheimer’s disease.
  • Cognitive therapy for these problems does not exist. Treatment should be directed to helping the patient cope and adapt to their disabilities.

Helffenstein, “Neuropsychological Evaluation of the Carbon Monoxide-Poisoned Patient” (2000).

  • Carboxyhemoglobin levels do not correspond to other symptoms of CO poisoning nor do they correlate with subsequent residual deficits.
  • The Carbon Monoxide Neuropsychological Screening Battery has been developed for Emergency Room evaluations. In addition to general orientation, it includes Digit Span, Trail Making, Digit Symbol, Aphasia Screening, and Block Design.
  • The greater the length of retrograde or post-traumatic amnesia, the greater the likelihood of permanent cognitive impairment.
  • Developing a sensitivity to a variety of substances is quite common; e.g., car exhaust, smoke (cigarettes or cigar), pain, gas fumes from spray cans, heavy colognes, products containing formaldehyde, and herbicides/pesticides.
  • The most common areas of deficit are executive functioning, attention and concentration, memory functioning, visual-perceptual abilities, and processing speed.

Helffenstein, “Neurocognitive and Neurobehavioral Sequelae of Chronic Carbon Monoxide Poisoning: A Retrospective Study and Case Presentation”

  • As with any toxin, there are three components in determining the severity of the exposure. These include the level or amount of toxin the individual is exposed to, the frequency of exposure, and the duration of each exposure.
  • Penney notes that the misdiagnosis rate in cases of chronic CO poisoning is very high because, “It almost invariably presents with too many disparate, seemingly unrelated and for the most part, nonspecific symptoms”.
  • Hartman case study disclosed house plants died and silverware turned black quickly.
  • The blood brain barrier is more permeable in the frontal and temporal regions, which would result in more uptake of CO into these regions. In addition, the frontal and temporal regions of the brain are less able to compensate for a hypoxic event.
  • Individuals who have sustained chronic exposure to CO will often experience multiple persisting symptoms in multiple systems. As a result, this population would be at risk for obtaining elevated FBS scores simply because they are honestly reporting their persisting symptoms on the MMPI-2.
  • The Pearson Assessment website suggests that raw scores above 23 on the FBS should “raise concerns” about the validity of self-reported symptoms and that raw scores above 28 should raise “very significant concerns” about the validity of self-reported symptoms. Of the 19 participants in the study, only 7 had FBS scores of 23 or less. Three had FBS scores ranging from 23 to 27 and 9 had FBS scores of 28 or greater. The average FBS score was 26.2.