Carbon monoxide poisoning: early hyperbaric O2 was better than normobaric O2 at preventing headache and pulmonary oedema.

Clinical bottom line (level 1b)

  1. Patients with carbon monoxide poisoning who received hyperbaric oxygen had less pulmonary oedema or headache after 12 hours (NNT = 3 at 12 hours) compared with normobaric oxygen.
  2. Patients on hyperbaric oxygen had a lower carboxyhaemoglobin level after two hours, but not after 12 hours compared with patients on normobaric oxygen.
Ducasse et al: Undersea Hyperbaric Medicine 1995; 22: 9-15
Expires July 2003

The study

Unblinded ?concealed randomised trial without intention-to-treat
Setting: hyperbaric medical centre, France

26 patients (aged range 18 to 70 years, 54% male) hospitalised for moderate carbon monoxide poisoning (mean HbCO level 24%).

Excluded if
  • CO poisoning >12 hours age
  • pregnant
  • Glasgow Coma Score <12
  • elapsed time between discovery and hospitalisation >2 hours


    • Note:
  • All 26 patients had a Glasgow Coma Scale score greater than 14/15 at time of admission to hospital, although 17 had initially lost consciousness prior to arrival.


    • Control Group: (n = 13, 13 analysed): normobaric oxygen at 100% for 6 hours, then at 50% for 6 hours. Treatment was started at a mean time of 53 minutes from rescue.
    Experimental Group: (n = 13, 13 analysed): hyperbaric oxygenation at 2.5 atm for 2 hours, then normobaric 100% oxygen fro 4 hours, then 50% normobaric oxygen for 6 hours. Treatment started at a mean time of 53 minutes from rescue

    100% followed for 12 hours

    The evidence

    Outcome Time to outcome CEREERRRR
    (95% CI)    		ARR
    (95% CI)    		NNT
    (95% CI)
    pulmonary oedema or headache 12 hours 5
    (38.5%)    		 0
    (0.00%)    		 100%
    (% to %)    		 38.5%
    (12.0% to 64.9%)    		 3
    (2 to 8)

    Outcome Control Group
    (SD)    		 Experimental Group
    (SD)    		 Mean Difference
    (95% CI)
    HbCO level (%) 6.4
    (4.5)     		1.9
    (1.2)     		4.5
    (1.8 to 7.2)
    HbCO level (%) 1.2
    (0.2)     		1.2
    (0.6)     		0.0
    (-0.36 to 0.36)

    Comments

    1. This is a very small trial, without blinding or pre-specified outcomes. the only 'hard' clinical outcomes were assessed at 12 hours following therapy, and were based on a non-standardised clinical examination. It is questionable whether the two reported adverse outcomes (pulmonary oedema and headache) were simply selected from a myriad of other non-significant outcomes, raising the possibility of spurious findings. Without long-term assessment, it remains unclear whether these short-term outcomes are important.

    Citation

    1. Ducasse JL, Celsis P, Vergnes JPM: Non-comatose patients with acute carbon monoxide poisoning: hyperbaric or normobaric oxygenation?. Undersea Hyperbaric Medicine 1995; 22: 9-15
    Search Terms: carbon monoxide, carbon monoxide poisoning and poisoning in Cochrane and Ovid Medline
    Contributor: Joel Ray and Chris Ball, July 2000
    Reviewer:

    Clinical Question.
    Patient CO poisoning
    Intervention or Exposure hyperbaric oxygen
    Comparison normobaric oxygen
    Outcome pulmonary oedema or headache