Carbon monoxide poisoning: high carboxyhemoglobin levels increased the risk of neurological impairment

Clinical bottom line (level 4)

  1. Early neurological impairment in occurs in a third of patients with suspected CO poisoning.
  2. Patients with a Hb CO > 10% were at increased risk of developing neurological impairment (NNF = 3 for 10 days) .
Myers and Britten: Critical Care Medicine 1989; 17 : 139-142
Expires October 2004

The study

Prospective cohort study with unblinded, unobjective outcomes, not adjusted for confounding factors, not validated in an independent set of patients.

Setting: hyperbaric medicine department of trauma hospital, USA

114 patients (aged ?, ?% male) referred with potential carbon monoxide poisoning as a result of fires, or home or industrial exposure to CO.

Excluded if
  • unable to complete psychometric test (comatosed or inability to concentrate)
  • refused to participate



    ?100% followed for 10 days
    Outcomes studied:
  • neurological impairment abnormal psychometric screening battery (developed at test center: not detailed in study) and follow-up by telephone: patients questioned about headaches, dizziness, memory loss, loss of consciousness, irritability, personality changes)

    The evidence

    outcome time to outcome number of patients/total number %
    (95% CI)    		 NNF
    (95% CI)
    neurological impairment 10 days 35/114 31%
    (21% to 40%)    		 3
    (2 to 5)

    prognostic factor for
    neurological impairment     		time to outcome unadjusted RR
    (95% CI)    		 NNF+
    (95% CI)
    HbCO > 10% 10 days 2.70
    (1.41 to 5.19)     		3
    (1 to 13)
    HbCO > 25% 10 days 2.88
    (1.68 to 4.96)     		2
    (1 to 6)

    Comments

    1. HbCO levels and psychometric testing were done at different times following CO exposure, leading to the possibility that neurotoxicity had developed, even though CO levels had normalized.
    2. No description about whether patients had alcohol or drug intoxication, or head injury at the time of psychometric testing.
    3. Psychometic test was not validated in other circumstances: poor reference standard. How does this relate to long-term problems?

    Citation

    1. Myers RA, and Britten JS: Are arterial blood gases of value in treatment decisions for carbon monoxide poisoning?. Critical Care Medicine 1989; 17 : 139-142
    Search Terms: "carbon monoxide," "carbon monoxide poisoning," and "poisoning." in Cochrane and Ovid Medline
    Contributor: Joel Ray, July 1998
    Reviewer: Chris Ball

    Clinical Question.
    Patient carbon monoxide poisoning
    Intervention or Exposure HbCO level
    Outcome neurological impairment