Hyper- vs Normobaric Oxygen Therapy To Reduce Mortality in Carbon Monoxide Poisoning

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50,000 cases of carbon monoxide exposure annually in the US result in 1000 to 2000 accidental deaths.
50,000 cases of carbon monoxide exposure annually in the US result in 1000 to 2000 accidental deaths.

Hyperbaric oxygen therapy (HBOT) was associated with lower mortality rates up to 4 years after treatment of carbon monoxide poisoning (COP), compared with the standard of 100% normobaric oxygen delivered via a non-rebreathing mask or endotracheal intubation, according to a recent study published in Chest.1 The mortality rate was even lower in patients who were treated repeatedly, especially patients younger than 20 and patients who had acute respiratory failure at the time of treatment.

Carbon monoxide poisoning is a significant public health issue resulting in large numbers of accidental deaths and suicides every year. Estimates from the United States showed that 50,000 cases of carbon monoxide (CO) exposure annually result in 1000 to 2000 accidental deaths.1 In Taiwan, the incidence of suicide by COP increased 25-fold between 1999 and 2009.2 A previous study by Huang, et al3 found significantly faster dissociation of CO from carboxyhemoglobin (COHb) with HBOT, and a reduction in half-life nearly 4 times that of normobaric oxygen by mask (23 minutes vs up to 80 minutes), suggesting an HBOT benefit in all patients with COP.3

In the current study, the researchers, led by How-Ran Guo, MD, MPH, ScD, of the department of environmental and occupational health at the National Cheng Kung University in Tainan, Taiwan, assembled a cohort of 25,737 patients with COP registered in the National Poisoning Database (NPD) between 1999 and 2012. Of those patients, 18,459 were treated with standard therapies (mean age: 36.4±17.1; P <.001); 7278 received HBOT (mean age: 34.6±14.7; P <.001). The patients receiving HBOT were more likely to have developed COP as a result of a suicide attempt and had higher rates of acute respiratory and renal failure, but were less like to have drug poisoning.

The majority of patients who received HBOT were treated more than once over the course of the initial 1-month period following COP; 38.18% had 2 to 5 treatments and 30.31% had more than 5 treatments, compared with 31.51% who were treated only once. Mortality rates decreased significantly with increasing administrations; adjusted hazard ratio (aHR) was 0.79 (95% CI, 0.64-0.95) for 2 to 5 sessions and 0.81 (95% CI, 0.67-0.99) for more than 5 sessions, compared with single treatments.

“The mortality risk was particularly higher in the first month after COP…but remained significantly higher for a year,” the researchers noted. “The brain and heart, which have high metabolic rates and are the most vital organs for survival, are most susceptible to hypoxia, and this is the mechanism through which COP causes mortality.”

Dr Guo and colleagues also reported that longer term immunological and inflammatory damage could occur independent of hypoxia to multiple organ systems, resulting in death later on.4-6 The impact of HBOT on reducing mortality persisted for 4 years after treatment.1

“In addition to HBOT, we identified older age, male sex, lower monthly income, underlying comorbidities…and concomitant suicide and acute respiratory failure [as] independent mortality predictors [in patients with COP],” Dr Gao and colleagues concluded.

Study Limitations

  • Data on socioeconomic variables — including lifestyle factors, smoking, and body mass index (BMI) — were not available via the NPD; the investigators adjusted for major underlying comorbidities, which may have minimized the confounding effect
  • HBOT protocols were not standardized
  • The NPD does not include data regarding the level of COP
  • This study may not be generalizable to other countries due to differences in race, culture, and treatment protocols


  1. Huang CC, Ho CH, Chen YC, et al. Hyperbaric oxygen therapy is associated with lower short- and long-term mortality in patients with carbon monoxide poisoning. Chest. 2017;17:30723-30727. doi:10.1016/j.chest.2017.03.049
  2. Pan YJ, Liao SC, Lee MB. Suicide by charcoal burning in Taiwan, 1995-2006. J Affect Disord. 2010;120(1-3):254-257. doi:10.1016/j.jad.2009.04.003
  3. Huang CC, Chung MH, Weng SF, et al. Long-term prognosis of patients with carbon monoxide poisoning: a nationwide cohort study. PLoS One. 2014;9(8):e105503. doi:10.1371/journal.pone.0105503.
  4. Ernst A, Zibrak JD. Carbon monoxide poisoning. N Engl J Med. 1998;339:1603-1608. doi: 10.1056/NEJM199811263392206
  5. Weaver LK. Carbon monoxide poisoning. N Engl J Med. 2009;360:1217-1225. doi: 10.1056/NEJMcp0808891
  6. 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;186(11):1095-1101. doi:10.1164/rccm.201207-1284CI 

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