Tag Archives: carbon monoxide

Tox Cards: CO Poisoning

Author: Patrick C. Ng (Chief Resident, San Antonio Military Medical Center) // Edited by: Cynthia Santos, MD (Senior Medical Toxicology Fellow, Emory University School of Medicine), Alex Koyfman, MD (@EMHighAK, EM Attending Physician, UTSW / Parkland Memorial Hospital), and Brit Long, MD (@long_brit, EM Attending Physician, San Antonio Military Medical Center)
Case Presentation:
It is a cold day in the middle of December. A 56 yo female and her 29 yo daughter who is 8 months pregnant present to your ED with a chief complaint of generalized weakness and headache for 2 days. They mention that they think they both caught the flu due to the cold temperatures despite turning their heater on high and using oil lamps for extra heat in their apartment. Their vital signs are normal.
What are the most common signs/symptoms of carbon monoxide (CO) poisoning, and what are the general management plans?

CO poisoning presents with nonspecific symptoms that can be mistaken for other diagnosis such as the flu. Initial treatment includes high-flow supplemental O2. Hyperbaric oxygen therapy (HBOT) may or may not be the “standard of care” (controversial).

  • CO poisoning can be an elusive diagnosis, as non-specific symptoms such as headache, dizziness, nausea, fatigue, and chest pain are non-specific and can be consistent with many other disease processes.(1,2)
  • Key historical clues include people from the same household presenting with symptoms of headache and flu-like symptoms that improve throughout the course of the day (i.e. when patients leave their dwellings for work, school, etc.) and history of exposure to CO sources such as heaters and enclosed garages.(1,2)
  • A co-oximetry is a spectrophotometer that uses many different wavelengths to measure oxygenated hemoglobin (oxyHb), deoxygenated hemoglobin (deoxyHb), as well as carboxyhemoglobin (COHb) and methemoglobin (MetHb) concentrations.(3)
  • The use of greater number of wavelengths in a co-oximeter as compared to a standard pulse oximeter allows the co-oximeter to distinguish between other types of hemoglobin,  whereas a standard pulse oximetry can only distinguish between oxyHb and deoxyHb.(3)
  • Blood COHg levels commonly reaches a level of 10 % in smokers and may even exceed 15 %, as compared with 1 to 3 % in nonsmokers.(2)
  • Standard treatment includes  high-flow O2  via NRB mask (or intubation in severe cases) until symptoms resolve and CO levels return to baseline; pregnant patients should continue for at least 24 hours with fetal wellbeing assessment. Patients also require follow up at 1-2 months for neuropsychiatric assessment.(1,2)
  • Normal half life of Hb-CO is 4-6 hrs with room air oxygen, 40- min with high-flow O2, and 15-30 min with HBOT.(2)
  • Although the indications for HBO are controversial, some recommend HBO for any CO-poisoned patient with mental status change or history of syncope, signs of cardiac ischemia or arrhythmia, history of ischemic heart disease and CO level > 20%, symptoms that do not resolve with normobaric O2 therapy after 4-6 hours, or any pregnant patient with CO > 15%. Coma is generally an undisputed indication for hyperbaric-oxygen therapy.(2)
  • The use of HBO has been reported to reduce the risk of neurological/cognitive sequelae thought to be associated with carbon monoxide poisoning.(4,5)
Main Point:
Carbon monoxide poisoning can be a deadly diagnosis associated with significant morbidity and long-term permanent neurological damage. It can present with very non-specific symptoms. Specific historical clues as well as co-oximetry can help the emergency physician quickly make the diagnosis. High-flow O2 therapy is the initial standard therapy with some advocating HBOT for select severe or at risk cases.
1. Piantadosi CA. Diagnosis and treatment of carbon monoxide poisoning. Respir Care Clin N Am. 1999;5:183-202.
2. Ernst A, Zibrak JD. Carbon Monoxide Poisoning. N Engl J Med 1998;339:1603-1608.
3. Hampson NB. Noninvasive pulse CO-oximetry expedites evaluation and management of patients with carbon monoxide poisoning. Am J Emerg Med. 2012 Nov;30(9):2021-4.

4. Tibbles PM, Perrotta PL. Treatment of carbon monoxide poisoning: a critical review of human outcome studies comparing normobaric oxygen with hyperbaric oxygen. Ann Emerg Med. 1994;24:269-276.
5. Weaver LK, Hopkins RO, Chan KJ, et al. Hyperbaric oxygen for acute carbon monoxide poisoning. N Engl J Med 2002;347:1057–1067