Carbon Monoxide Toxicity Clinical Presentation
- Author: Guy N Shochat, MD; Chief Editor: Asim Tarabar, MD more...
Misdiagnosis of carbon monoxide (CO) toxicity commonly occurs because of the vagueness and broad spectrum of complaints; symptoms often are attributed to a viral illness. Specifically inquiring about possible exposures when considering the diagnosis is important (see Background and Causes).
For nonfatal nonintentional non–fire-related exposures, the most common symptom was headache (37%) followed by dizziness (18%) and nausea (17%). However, any of the following symptoms should alert suspicion in the winter months, especially when the patient has a history compatible with CO exposure and when more than one patient in a group or household presents with similar complaints:
Malaise, flulike symptoms, fatigue
Dyspnea on exertion
Chest pain, palpitations
Nausea, vomiting, diarrhea
Dizziness, weakness, confusion
Visual disturbance, syncope, seizure
Fecal and urinary incontinence
Memory and gait disturbances
Bizarre neurologic symptoms, coma
Chronic exposure also produces the above symptoms; however, patients with chronic CO exposure may present with loss of dentition, gradual-onset neuropsychiatric symptoms, or, simply, recent impairment of cognitive ability.
Physical examination is of limited value. Inhalation injury or burns should always alert the clinician to the possibility of CO exposure.
Vital signs may include the following:
Hypertension or hypotension
Marked tachypnea (rare; severe intoxication often associated with mild or no tachypnea)
Although so-called cherry-red skin has traditionally been considered a sign of CO poisoning (ie, "When you're cherry red, you're dead"), it is in fact rare. Pallor is present more often
Ophthalmologic findings include the following:
Flame-shaped retinal hemorrhages
Bright red retinal veins (a sensitive early sign)
Noncardiogenic pulmonary edema
Neurologic and/or neuropsychiatric findings may include the following;
Memory disturbance (most common), including retrograde and anterograde amnesia with amnestic confabulatory states
Emotional lability, impaired judgment, and decreased cognitive ability
Stupor, coma, gait disturbance, movement disorders, and rigidity
Brisk reflexes, apraxia, agnosia, tic disorders, hearing and vestibular dysfunction, blindness, psychosis
Long-term exposures or severe acute exposures frequently result in long-term neuropsychiatric sequelae. Additionally, some individuals develop delayed neuropsychiatric symptoms, often after severe intoxications associated with coma.
After recovery from the initial incident, patients present several days to weeks later with neuropsychiatric symptoms such as those just described. Two thirds of patients eventually recover completely.
See the list below:
Most unintentional fatalities occur in stationary vehicles from preventable causes such as malfunctioning exhaust systems, inadequately ventilated passenger compartments, operation in an enclosed space, and utilization of auxiliary fuel-burning heaters inside a car or camper.
Most unintentional automobile-related CO deaths in garages have occurred despite open garage doors or windows, demonstrating the inadequacy of passive ventilation in such situations.
Colorado state datafrom 1986-1991 revealed that leading sources of 1149 unintentional nonfatal CO poisonings were residential furnaces (40%), automobile exhaust (24%), and fires (12%); however, furnaces were responsible for onlly 10% of fatal poisonings 
In the setting of structure fires, CO presents greater risk than thermal injury or oxygen deprivation, both for firefighters and victims 
In most developing countries, cooking or heating is often done with unvented cookstoves, wood, charcoal, animal dung, or agricultural waste, wwhich has been linked with elevated HbCO levels
Boats and houseboats represent a significant and underappreciated source of exposure, with multiple case reports and studies 
Anderson AR, Centers for Disease Control and Prevention (CDC). Top five chemicals resulting in injuries from acute chemical incidents—Hazardous Substances Emergency Events Surveillance, nine states, 1999-2008. MMWR Suppl. 2015 Apr 10. 64 (2):39-46. [Medline].
Hampson NB, Piantadosi CA, Thom SR, Weaver LK. Practice recommendations in the diagnosis, management, and prevention of carbon monoxide poisoning. Am J Respir Crit Care Med. 2012 Dec 1. 186 (11):1095-101. [Medline]. [Full Text].
Hampson NB, Dunn SL. Carbon Monoxide Poisoning from Portable Electrical Generators. J Emerg Med. 2015 Aug. 49 (2):125-9. [Medline].
Workplace Safety and Health Topic:Carbon Monoxide (CO) Dangers in Boating. Centers for Disease Control and Prevention. Available at http://www.cdc.gov/niosh/topics/coboating/. August 16, 2013; Accessed: May 5, 2016.
Hawkes AP, McCammon JB, Hoffman RE. Indoor use of concrete saws and other gas-powered equipment. Analysis of reported carbon monoxide poisoning cases in Colorado. J Occup Environ Med. 1998 Jan. 40(1):49-54. [Medline].
Nager EC, O'Connor RE. Carbon monoxide poisoning from spray paint inhalation. Acad Emerg Med. 1998 Jan. 5(1):84-6. [Medline].
Suner S, Jay G. Carbon monoxide has direct toxicity on the myocardium distinct from effects of hypoxia in an ex vivo rat heart model. Acad Emerg Med. 2008 Jan. 15(1):59-65. [Medline].
Sircar K, Clower J, Shin MK, Bailey C, King M, Yip F. Carbon monoxide poisoning deaths in the United States, 1999 to 2012. Am J Emerg Med. 2015 Sep. 33 (9):1140-5. [Medline].
Mowry JB, Spyker DA, Brooks DE, McMillan N, Schauben JL. 2014 Annual Report of the American Association of Poison Control Centers' National Poison Data System (NPDS): 32nd Annual Report. Clin Toxicol (Phila). 2015. 53 (10):962-1147. [Medline]. [Full Text].
Routley VH, Ozanne-Smith J. The impact of catalytic converters on motor vehicle exhaust gas suicides. Med J Aust. 1998 Jan 19. 168(2):65-7. [Medline].
QuickStats: Average Annual Number of Deaths and Death Rates from Unintentional, Non–Fire-Related Carbon Monoxide Poisoning,*† by Sex and Age Group — United States, 1999–2010. MMWR Morb Mortal Wkly Rep. Available at http://www.cdc.gov/mmwr/preview/mmwrhtml/mm6303a6.htm?s_cid=mm6303a6_e. Accessed: September 30, 2014.
Wrenn K, Conners GP. Carbon monoxide poisoning during ice storms: a tale of two cities. J Emerg Med. 1997 Jul-Aug. 15(4):465-7. [Medline].
Centers for Disease Control and Prevention (CDC). Notes from the field: carbon monoxide exposures reported to poison centers and related to hurricane Sandy - Northeastern United States, 2012. MMWR Morb Mortal Wkly Rep. 2012 Nov 9. 61 (44):905. [Medline]. [Full Text].
Cook M, Simon PA, Hoffman RE. Unintentional carbon monoxide poisoning in Colorado, 1986 through 1991. Am J Public Health. 1995 Jul. 85 (7):988-90. [Medline].
Cone DC, MacMillan D, Parwani V, Van Gelder C. Threats to life in residential structure fires. Prehosp Emerg Care. 2008 Jul-Sep. 12(3):297-301. [Medline].
Hampson NB. Noninvasive pulse CO-oximetry expedites evaluation and management of patients with carbon monoxide poisoning. Am J Emerg Med. 2012 May 23. [Medline].
Perrone J, Hoffman RS. Falsely elevated carboxyhemoglobin levels secondary to fetal hemoglobin. Acad Emerg Med. 1996 Mar. 3(3):287-9. [Medline].
Cha YS, Kim H, Hwang SO, Kim JY, Kim YK, Choi EH, et al. Incidence and patterns of cardiomyopathy in carbon monoxide-poisoned patients with myocardial injury. Clin Toxicol (Phila). 2016 Apr 11. 1-7. [Medline].
Henry CR, Satran D, Lindgren B, Adkinson C, Nicholson CI, Henry TD. Myocardial injury and long-term mortality following moderate to severe carbon monoxide poisoning. JAMA. 2006 Jan 25. 295(4):398-402. [Medline].
Damlapinar R, Arikan FI, Sahin S, Dallar Y. Lactate Level Is More Significant Than Carboxihemoglobin Level in Determining Prognosis of Carbon Monoxide Intoxication of Childhood. Pediatr Emerg Care. 2015 Jul 14. 37 (1):1-7. [Medline].
So GM, Kosofsky BE, Southern JF. Acute hydrocephalus following carbon monoxide poisoning. Pediatr Neurol. 1997 Oct. 17(3):270-3. [Medline].
Chin W, Jacoby L, Simon O, Talati N, Wegrzyn G, Jacoby R, et al. Hyperbaric programs in the United States: Locations and capabilities of treating decompression sickness, arterial gas embolisms, and acute carbon monoxide poisoning: survey results. Undersea Hyperb Med. 2016 Jan-Feb. 43 (1):29-43. [Medline].
Buckley NA, Isbister GK, Stokes B, Juurlink DN. Hyperbaric oxygen for carbon monoxide poisoning : a systematic review and critical analysis of the evidence. Toxicol Rev. 2005. 24(2):75-92. [Medline].
Buckley NA, Juurlink DN, Isbister G, Bennett MH, Lavonas EJ. Hyperbaric oxygen for carbon monoxide poisoning. Cochrane Database Syst Rev. 2011 Apr 13. 4:CD002041. [Medline].
Turner M, Esaw M, Clark RJ. Carbon monoxide poisoning treated with hyperbaric oxygen: metabolic acidosis as a predictor of treatment requirements. J Accid Emerg Med. 1999 Mar. 16 (2):96-8. [Medline].
Sloan EP, Murphy DG, Hart R, Cooper MA, Turnbull T, Barreca RS, et al. Complications and protocol considerations in carbon monoxide-poisoned patients who require hyperbaric oxygen therapy: report from a ten-year experience. Ann Emerg Med. 1989 Jun. 18 (6):629-34. [Medline].
Lai CY, Huang YW, Tseng CH, Lin CL, Sung FC, Kao CH. Patients With Carbon Monoxide Poisoning and Subsequent Dementia: A Population-Based Cohort Study. Medicine (Baltimore). 2016 Jan. 95 (1):e2418. [Medline].
Lai CY, Chou MC, Lin CL, Kao CH. Increased risk of Parkinson disease in patients with carbon monoxide intoxication: a population-based cohort study. Medicine (Baltimore). 2015 May. 94 (19):e869. [Medline].
Krenzelok EP, Roth R, Full R. Carbon monoxide ... the silent killer with an audible solution. Am J Emerg Med. 1996 Sep. 14(5):484-6. [Medline].
Hampson NB, Piantadosi CA, Thom SR, Weaver LK. Practice recommendations in the diagnosis, management, and prevention of carbon monoxide poisoning. Am J Respir Crit Care Med. 2012 Dec 1. 186(11):1095-101. [Medline].
Bourtros AR, Hoyt JL. Management of carbon monoxide poisoning in the absence of hyperbaric oxygenation chamber. Crit Care Med. 1976 May-Jun. 4(3):144-7. [Medline].
Bozeman WP, Myers RA, Barish RA. Confirmation of the pulse oximetry gap in carbon monoxide poisoning. Ann Emerg Med. 1997 Nov. 30(5):608-11. [Medline].
Dogan N, Savrun A, Levent S, Günaydin G, Celik G, Akküçük H, et al. Can initial lactate levels predict the severity of unintentional carbon monoxide poisoning?. Hum Exp Toxicol. 2014 Jun 27. [Medline].
Inagaki T, Ishino H, Seno H, Umegae N, Aoyama T. A long-term follow-up study of serial magnetic resonance images in patients with delayed encephalopathy after acute carbon monoxide poisoning. Psychiatry Clin Neurosci. 1997 Dec. 51(6):421-3. [Medline].
Jones JS, Lagasse J, Zimmerman G. Computed tomographic findings after acute carbon monoxide poisoning. Am J Emerg Med. 1994 Jul. 12(4):448-51. [Medline].
Leem JH, Kaplan BM, Shim YK, et al. Exposures to air pollutants during pregnancy and preterm delivery. Environ Health Perspect. 2006 Jun. 114(6):905-10. [Medline].
Raub JA, Benignus VA. Carbon monoxide and the nervous system. Neurosci Biobehav Rev. 2002 Dec. 26(8):925-40. [Medline].
Reisdorff EJ, Wiegenstein JG. Carbon monoxide poisoning. Tintinalli JE, et al, eds. Emergency Medicine: A Comprehensive Study Guide. 4th ed. New York, NY: McGraw-Hill; 1996. 914-9.
Suner S, Partridge R, Sucov A, et al. Non-invasive pulse CO-oximetry screening in the emergency department identifies occult carbon monoxide toxicity. J Emerg Med. 2008 May. 34(4):441-50. [Medline].
Van Hoesen K. Hyperbaric oxygen therapy. Rosen P, et al, eds. Emergency Medicine: Concepts and Clinical Practice. 2nd ed. St. Louis, Mo: Mosby-Year Book; 1998. 1032-42.