Carbon monoxide is an invisible odorless gas that is a byproduct of burning fuels including auto emissions, lawnmowers, fireplaces, furnaces and other natural gas appliances such as water heaters. Natural sources include forest fires and a small amount from the breakdown of heme in the body. Smoking increases CO levels and smokers have increased CO levels to between 5% and 9%, but heavy smokers can have levels up to 15% in the blood. In the indoor environment, smokers become net contributors to ambient CO levels. CO can build up in the air inside and reach dangerous levels if there is not proper ventilation or the burning is occurring in a small, confined space.
Some lesser-known sources of CO include "incomplete combustion and inadequate ventilation of domestic
natural gas, indoor burning of charcoal for barbecues, propane gas
cylinders (forklift trucks), petrol powered generators, and methylene
chloride exposure from spray paint (hepatic conversion to CO)". Carbon monoxide monitors can be placed near potential sources to alert you if there is a leak. Many travel experts recommend bringing a carbon monoxide monitor with you when you travel because regulations vary from place to place and are not always fully enforced anyway.
"COHB decreases with a half life of approximately 320 minutes in air. However this half life is further decreased to 80 minutes if 100% oxygen is given to the patient." Symptoms of carbon monoxide poisoning include headache, dizziness, fatigue, poor tolerance for exercise, weakness, chest pain (also called angina), nausea, vomiting, and confusion. Acute exposure can lead to confusion, seizure, loss of consciousness, and even death. The presence of additional stressors, such as low temperatures may increase the effects of CO. A number of studies have found even small changes in ambient CO levels correlating with cardiac complications and death "levels of CO commonly found in urban outdoor air may induce arrhythmia, angina, and sudden death in people with heart disease." as well as a statistically significant increase in Myocardial Infarction in patients with increased chronic exposure to CO.
"To make the diagnosis, a blood test with access to a co-oximeter, to measure carboxyhaemoglobin (COHB) levels is required." If a person survives the exposure they may have long-term damage to the brain. The symptoms of brain injury from carbon monoxide resemble those of brain injury from other sources and can include headaches, dizziness, and difficulties with sleep, mood, balance, vision, movement, memory, and other cognitive problems. Symptoms may be present right away or can be delayed. Injury to the brain from acute exposure can often be seen on MRI scans soon after the exposure occurred.
Carbon monoxide exposure can lead to brain injury in several ways. It can cause hypoxia, a state in which the brain does not receive adequate levels of oxygen, because carbon monoxide binds to the hemoglobin in the bloodstream which limits the amount of oxygen that can be transported to the cells in the brain. If cells don't receive enough oxygen they are not able to produce enough energy to function properly and can even die, particularly in the brain region called the hippocampus which is important for memory. Carbon monoxide can also cause injury to the brain from inflammation, from damaging certain proteins that surround neurons, and from causing iron to be released into the brain which is toxic to brain cells. In some cases, treatment with Hyperbaric Oxygen Therapy can reverse some of this damage.
Carbon monoxide poisoning mimicking gastroenteritis
Revenge of the barbecue grill. Carbon monoxide poisoning
Occult carbon monoxide poisoning in patients with neurologic illness
"We conclude that unrecognized carbon monoxide poisoning occurs in a
small but important fraction of patients with wintertime neurologic
illness and can be identified by a characteristic risk factor profile."
Chronic and occult carbon monoxide poisoning: we don’t know what we’re missing
"There is a strong possibility that low level exposure to CO is
responsible for widespread and significant morbidity, however the
clinical syndrome produced is often overlooked because of a range of
presentations, obscure symptoms, and a lack of awareness of the problem. In the USA, comparatively small changes in ambient levels of CO as a
result of pollution have been shown to affect rates of presentation to
emergency departments with various complaints."
"“Occult CO poisoning” is used to indicate those cases of CO poisoning that may never come to the attention of a medical practitioner. In most cases, this is as a result of chronic CO poisoning and most frequently the patient will not even ask for a medical opinion. Occasionally acute poisoning as a result of exposure to high concentrations of gas may remain occult, and although the patient presents to a medical practitioner—the diagnosis is missed (at least until the patient re-attends, often with cohabitees with similar symptoms). Occasionally, deaths have occurred."
"Pyramid of disease: CO poisoning can be looked upon as a “disease” with a pyramid of presentation—the tip of the iceberg is overt acute poisoning, while the base is occult, low level exposure. A difficult question to answer is: how big is the base? Even ambient levels of CO in the atmosphere as a result of pollution cause changes in the hospitalization and mortality rates of patients with certain diseases."
"At levels of COHB greater than 10% patients with pre-existing cardiac disease experience increased severity and duration of angina and if levels rise above 15% they are at increased risk of myocardial infarction. If a patient has had an acute myocardial infarction, the threshold for ventricular fibrillation can be reduced to 9% COHB. Patients with severe chronic bronchitis or emphysema experience a significant reduction in the walking distance when breathing air after exposure to CO and intermittent claudication occurs with less provocation in patients with low levels of COHB. Even in normal subjects a COHB concentration as little as 4.4% has been shown to limit work capacity and maximal oxygen consumption."
"In patients with acute poisoning, 30% or more may experience delayed onset of neuropsychiatric symptoms. Symptoms include cognitive and personality changes, dementia, psychosis, parkinsonism, amnesia, depression, and incontinence. There is also good evidence that apparently minor low level acute and chronic exposure causes varying degrees of neuropsychological impairment. It is postulated that CO causes lipid peroxidation of neurological tissues. Early hyperbaric oxygen therapy decreases the extent of lipid peroxidation and this would explain the decreased incidence of neuropsychiatric sequelae after hyperbaric treatment. The regions of the brain most frequently involved include the globus pallidus and deep white matter.
Epidemiological bases for the current ambient carbon monoxide standards
Systematic review and meta-analysis of studies between short-term exposure to ambient carbon monoxide and non-accidental, cardiovascular, and respiratory mortality in China
"Our meta-analysis demonstrated that exposure to ambient CO was positive
with risk of deaths from all non-accidental causes, total
cardiovascular, and respiratory diseases. Based on these findings,
tougher intervention policies and initiatives to reduce the health
effects of CO exposure should be established."
Chronic and occult carbon monoxide poisoning: we don’t know what we’re missing
Carbon monoxide poisoning mimicking gastroenteritis.
