52 in 52 – #20: Pediatric Carbon Monoxide Poisoning: Effects of Hyperbaric Oxygen Therapy on Thiol/Disulfide Balance

Welcome back to the “52 in 52” series. This collection of posts features recently published must-know articles. Our twentieth post looks at hyperbaric oxygen in CO toxicity.

Author: Christiaan van Nispen, MD (Emergency Medicine Physician Resident, San Antonio, TX) and Brannon Inman (Chief Resident, Emergency Medicine Physician, San Antonio, TX) // Reviewed by: Alex Koyfman, MD (@EMHighAK); Brit Long, MD (@long_brit)

Pediatric Carbon Monoxide Poisoning: Effects of Hyperbaric Oxygen Therapy on Thiol/Disulfide Balance

A little background:

Thiols are sulfide groups with various carbon side chains found in biochemical structures such as proteins, homocysteine, and glutathione. Thiols reversibly form disulfide bonds in states of physiologic oxidative stress, such as in the case of carbon monoxide poisoning. As this reaction is reversible, it exists in homeostasis with various thiol/disulfide levels depending on the degree of oxidative stress. This thiol/disulfide homeostasis (TDH) can be measured and used as a surrogate for systemic oxidative stress. The dysregulation of TDH has been implicated in CO poisoning.


What are the effects of hyperbaric versus normobaric oxygen therapy on thiol/disulfide hemostasis in children presenting with carbon monoxide intoxication?

Design: Cross-sectional study at one institution in Turkey




  • 103 total pediatric patients (0-18 years of age) screened for eligibility
  • To be enrolled, patient must be otherwise healthy, on no medications, and have a carboxyhemoglobin level of greater than 10%, and were considered cured once carboxyhemoglobin level dropped below 5%
  • 81 pediatric (0-18 years of age) enrolled
  • Enrollment took place at single medical center in Turkey


  • No randomization; clinical decisions about hyperbaric versus normobaric oxygen therapy were made by treating physicians
  • Unfortunately, little descriptive data about the groups provided (only mean age and gender breakdown)



  • Patients with carboxyhemoglobin level greater than 15% and/or any patient with cardiac or neurological symptoms were started on hyperbaric oxygen therapy at 100% oxygen at 2.4 atmospheres, for 120 minutes



  • Patients with carboxyhemoglobin level greater than 10%, but less than 15%, and without cardiac or neurological symptoms were started on normobaric oxygen therapy (oxygen facemask with reservoir)



  • No statistically significant difference in thiol/disulfide levels in hyperbaric and normobaric oxygen groups
  • Note: thiol/disulfide hemostasis is an antioxidant system in the body; an increase in plasma native thiol and total thiol levels can imply an increased ability to chemically deal with oxidative stress and oxygen free radicals. Carbon monoxide can increase oxidative stress and free radical formation, rendering important the body’s antioxidant ability.

Take Aways:

  • Hyperbaric therapy significantly decreased the levels of plasma native thiols and total thiol levels, and normobaric oxygen therapy did not cause significant changes. Study authors conclude that hyperbaric therapy should therefore be titrated to minimal duration necessary to not excessively drive down antioxidant such as plasma native and total thiol levels.
  • This study deals in exclusively non-patient centered outcomes – levels of antioxidants – with no mention of actual outcomes, other than mentioning all patients in all groups survived; it is unclear whether this change in plasma native and total thiol levels is clinically important.
  • It appears that patients only received normobaric therapy if their carboxyhemoglobin level was less than 15% and not associated with cardiac or neurological compromise, so it is impossible to state if one is superior or even non-inferior to the other group. This study was not randomized; patients who were sick or had high Co-Hb levels went to hyperbaric therapy.
  • Patients were excluded unless they were otherwise in perfect health, i.e., they could not have any chronic disease or use any medications at baseline, which is not realistic to normal patients.
  • Overall, other reasons for being excluded were opaque (the flowchart of the study lists 22 patients as “exclusion,” then additional 7 as “other exclusion criteria”.
  • Based on these data it does not appear that TDH is significantly impacted by hyperbaric therapy, though this may be impacted by the observational nature of the study, sample size, and practice patterns (sick CO poisoned patients go to the dive chamber).

My Take:

Though published in the journal Pediatric Emergency Care and related to an important emergency complaint of carbon monoxide poisoning, it remains unclear to what degree this would impact emergency department management. Respectfully, the study authors’ conclusion that hyperbaric therapy should be used for just the right amount of time to ensure clinical improvement/resolution is somewhat obvious without any of these data, just as any particular therapy for any illness should only be administered for the right amount of time to ensure resolution of that illness.



  1. Bagci Z, Arslan A, Neselioglu S. Pediatric Carbon Monoxide Poisoning: Effects of Hyperbaric Oxygen Therapy on Thiol/Disulfide Balance. Pediatr Emerg Care. 2022;38(3):104-107. Doi: 10.1097/PEC.0000000000002619

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