Carbon monoxide poisoning: hyperbaric oxygen delivery prevented delayed neurologic sequelae.

Clinical bottom line (level 1b)

  1. Patients with carbon monoxide poisoning who had hyperbaric oxygen compared with normobaric oxygen, had less delayed neurological sequelae after 4 weeks (NNT = 4 at 4 weeks) .
  2. Patients with delayed neurological sequelae recovered within a month, and many continued normal daily activity in the meantime.
  3. This single study is more optimistic in its estimate of effect than further studies and a recent meta-analysis.
Thom et al: Annals of Emergency Medicine 1995; 25: 474-480
Expires July 2003

The study

Unblinded concealed randomised trial without intention-to-treat
Setting: hyperbaric centre, university hospital, USA

65 patients (aged mean 37 years, 52% male) referred from emergency departments with a history of acute exposure to combustion products, with an increased CO haemoglobin (mean ~22%) and symptoms of carbon monoxide poisoning

Excluded if
  • history of unconsciousness
  • cardiac compromise (chest pain or ischaemic changes on ECG)


    • Control Group: (n = 32, 30 analysed): normobaric 100% oxygen by mask until all symptoms resolved.
    Experimental Group: (n = 33, 30 analysed): hyperbaric 100% oxygen at 2.8 atmospheres for 30 minutes, followed by 2.0 atmospheres for 90 minutes.
    Therapy was started within 6 hours of the original carbon monoxide poisoning
    93% followed for 4 weeks

    The evidence

    Outcome Time to outcome CEREERRRR
    (95% CI)    		ARR
    (95% CI)    		NNT
    (95% CI)
    delayed neuropsychologic sequelae 4 weeks 7
    (23.3%)    		 0
    (0.00%)    		 100%
    (% to %)    		 23.3%
    (8.20% to 38.5%)    		 4
    (3 to 12)

  • Delayed neurological sequelae continued for a mean of 41 +/- 8 days. 4/7 patients were able to carry on with their daily activities.

    • Comments

    1. A Cochrane review of this subject showed no effect of hyperbaric oxygen.
    2. Subjective end-point and tester's influence on patients' neuropsychiatric performance combined with lack of blinding makes results much less certain.
    3. Benefits appear minor considering expense and difficulties of using hyperbaric oxygen.

    Citation

    1. Thom SR, Taber RL, Mendiguren II, et al: Delayed neuropsychologic sequelae after carbon monoxide poisoning: prevention by treatment with hyperbaric oxygen. Annals of Emergency Medicine 1995; 25: 474-480
    Search Terms: carbon monoxide, carbon monoxide poisoning and poisoning in Cochrane and Ovid Medline
    Contributor: Joel Ray and Chris Ball, July 2000
    Reviewer: David L. Simel

    Clinical Question.
    Patient CO poisoning
    Intervention or Exposure hyperbaric oxygen
    Comparison normobaric oxygen
    Outcome neurological sequelae