Carbon Monoxide (CO) Concentration

Reference Ranges
Carbon Monoxide (CO)
Adult ( > 16y) < 2.00

Carbon Monoxide (CO) Concentration

As many symptoms of carbon monoxide poisoning also occur with many other types of poisonings and infections (such as the flu), the diagnosis is often difficult.[47][62] A history of potential carbon monoxide exposure, such as being exposed to a residential fire, may suggest poisoning, but the diagnosis is confirmed by measuring the levels of carbon monoxide in the blood. This can be determined by measuring the amount of carboxyhemoglobin compared to the amount of hemoglobin in the blood.[17] Carbon monoxide is produced naturally by the body as a byproduct of converting protoporphyrin into bilirubin. This carbon monoxide also combines with hemoglobin to make carbooxyhemoglobin, but not at toxic levels.[17] The ratio of carboxyhemoglobin to hemoglobin molecules in an average person who may be up to 5%, although cigarette smokers who smoke two packs/day may have levels up to 9%.[63]

Serious toxicity occurs with the carboxyhemoglobin to hemoglobin ratio above 25%, and the risk of fatality is high with levels over 70%. Still, no consistent dose response relationship has been found between carboxyhemoglobin levels and clinical effects.[16] Carboxyhemoglobin levels are more guides to exposure levels than guides to effects, as they do not reliably predict clinical course of action or short- or long-term consequences.[64] Persons poisoned who come to medical facilities a relatively long time after exposure to carbon monoxide may have normal or only slightly elevated levels of carboxyhemoglobin, but still have significant symptoms as levels of carboxyhemoglobin may be well past their peak.[65] For late arriving patients a normal carboxyhemoglobin level does not rule out poisoning.[66] A CO-oximeter is used to determine carboxyhemoglobin levels.[67][68] Pulse CO-oximeters estimate carboxyhemoglobin with a non-invasive finger clip similar to a pulse oximeter.[69] The use of a pulse oximeter is not effective in the diagnosis of carbon monoxide poisoning as patients suffering from carbon monoxide poisoning may have a normal oxygen saturation level on a pulse oximeter.[70] This is due to the carboxyhemoglobin being misrepresented as oxyhemoglobin.[71]

Differential diagnosis

There are many conditions to be considered in the differential diagnosis of carbon monoxide poisoning.[7][22] The earliest symptoms, especially from low level exposures, are often non-specific and readily confused with other illnesses, typically flu-like viral syndromes, depression, chronic fatigue syndrome, chest pain, and migraine or other headaches.[72] Carbon monoxide has been called a “great mimicker” due to the presentation of poisoning being diverse and nonspecific.[7] Other conditions included in the differential diagnosis include acute respiratory distress syndrome, altitude sickness, lactic acidosis, diabetic ketoacidosis, meningitis, methemoglobinemia, or opioid or toxic alcohol poisoning

References

  1. ^ Myers RA, Britten JS (February 1989). "Are arterial blood gases of value in treatment decisions for carbon monoxide poisoning?". Critical Care Medicine 17 (2): 139–142. PMID 2644066. 
  2. ^ Keleş A, Demircan A, Kurtoğlu G (June 2008). "Carbon monoxide poisoning: how many patients do we miss?". European Journal of Emergency Medicine: Official Journal of the European Society for Emergency Medicine 15 (3): 154–157. doi:10.1097/MEJ.0b013e3282efd519. PMID 18460956. 
  3. ^ Rodkey FL, Hill TA, Pitts LL, Robertson RF (August 1979). "Spectrophotometric measurement of carboxyhemoglobin and methemoglobin in blood". Clinical Chemistry 25 (8): 1388–1393. PMID 455674. http://www.clinchem.org/cgi/pmidlookup?view=long&pmid=455674. Retrieved 2009-07-17. 
  4. ^ Rees PJ, Chilvers C, Clark TJ (January 1980). "Evaluation of methods used to estimate inhaled dose of carbon monoxide". Thorax 35 (1): 47–51. doi:10.1136/thx.35.1.47. PMID 7361284. PMC 471219. http://thorax.bmj.com/cgi/pmidlookup?view=long&pmid=7361284. 
  5. ^ Coulange M, Barthelemy A, Hug F, Thierry AL, De Haro L (March 2008). "Reliability of new pulse CO-oximeter in victims of carbon monoxide poisoning". Undersea & Hyperbaric Medicine 35 (2): 107–111. PMID 18500075. http://archive.rubicon-foundation.org/8084. 
  6. ^ Vegfors M, Lennmarken C (May 1991). "Carboxyhaemoglobinaemia and pulse oximetry". British Journal of Anaesthesia 66 (5): 625–626. doi:10.1093/bja/66.5.625. PMID 2031826. 
  7. ^ Barker SJ, Tremper KK (May 1987). "The effect of carbon monoxide inhalation on pulse oximetry and transcutaneous PO2". Anesthesiology 66 (5): 677–679. PMID 3578881. 
  8. ^ Ilano AL, Raffin TA (Jan 1990). "Management of carbon monoxide poisoning" (Free full text). Chest 97 (1): 165–9. doi:10.1378/chest.97.1.165. PMID 2403894
GT:0.068