Carbon monoxide poisoning: hyperbaric therapy offered no benefit over 100% oxygen in conscious patients.

Clinical bottom line (level 1b)

  1. Most patients presenting with carbon monoxide poisoning had a headache or felt dizzy.
  2. Two thirds of patients with CO poisoning and no initial loss of consciousness made a full recovery at one month. None died or suffered neurological sequelae.
  3. Hyperbaric oxygen was no better than 100% normobaric oxygen for these patients.
  4. 5% of patients who lost consciousness died or had neurological signs at one month. The role of hyperbaric oxygen for these patients was unclear.
Raphael et al: Lancet 1989; : 414-418
Expires July 2003

The study

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

629 patients (aged mean 36 years, 54% female) accidental carbon monoxide poisoning at home (diagnosed by carboxyhaemoglobin level > 5% in non-smokers or >10% in smokers)

Excluded if
  • admitted >12 hours after exposure
  • <15 years old
  • multiple intoxications (eg. CO poisoning with drug poisoning or exposure to another toxic gas as may be encountered in fires)
  • pregnancy
  • contraindication to hyperbaric oxygen
  • non-feasibility of hyperbaric oxygen
  • difficulty in classifying patients


    • Control Group: (n = 311, 273 analysed): patients were divided into two groups: (a) no initial loss of consciousness- normobaric 100% oxygen for 6 hours (n=170; 148 analysed); (b) initial loss of consciousness consisting either of a loss for a few seconds or coma (defined as inability to be roused by rescuers)- 100% oxygen for 4 hours, with two sessions of hyperbaric oxygen 2-12 hours apart (n=141; 125 analysed)
    Experimental Group: (n = 318, 286 analysed): (a) no loss of consciousness- hyperbaric oxygen for 2 hours (total of one hour at 2 atm), then normobaric oxygen for 4 hours (n=173; 159 analysed); (b) no loss of consciousness- hyperbaric oxygen for 2 hours, then normobaric oxygen for 4 hours (n=145; 127 analysed)

    89% followed for 30 days

    The evidence

    no loss of consciousness
    Outcome Time to outcome CEREERRRR
    (95% CI)    		ARR
    (95% CI)    		NNT
    (95% CI)
    recovery 30 days 98
    (66.2%)    		 108
    (67.9%)    		 -3%
    (-20% to 12%)    		 -1.71%
    (-12.2% to 8.81%)    		 59
    (NNT = 8 to infinity;
    NNH = 11 to infinity)

    loss of consciousness
    Outcome Time to outcome CEREERRRR
    (95% CI)    		ARR
    (95% CI)    		NNT
    (95% CI)
    recovery 30 days 65
    (52.0%)    		 68
    (53.5%)    		 -3%
    (-30% to 18%)    		 -1.54%
    (-13.9% to 10.8%)    		 65
    (NNT = 7 to infinity;
    NNH = 9 to infinity)
    death or serious sequelae 30 days 6
    (4.80%)    		 5
    (3.94%)    		 18%
    (-162% to 74%)    		 0.86%
    (-4.19% to 5.91%)    		 120
    (NNT = 17 to infinity;
    NNH = 24 to infinity)

  • No patient with loss of consciousness died or had neurological signs after one month (95% CI: 0.0 to 0.97%).
  • Clinical finding, % (95% CI):
    • headache- 84% (81% to 87%)
    • dizziness and/or muscle weakness- 78% (75% to 81%)
    • gastrointestinal dysfunction- 53% (49% to 56%)
    • loss of consciousness- 34% (30% to 37%)
    • coma- 13% (10% to 16%)
    • seizures- 2.9% (1.6% to 4.2%)

    • Comments

    1. Do patients who lose consciousness need hyperbaric oxygen at all? Another study is required to compare hyperbaric or normobaric oxygen in these patients.

    Citation

    1. Raphael JC, Elkharrat D, Jars-Guincestre MC, et al: Trial of normobaric and hyperbaric oxygen for acute carbon monoxide intoxication. Lancet 1989; : 414-418
    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 death