Randomized clinical trial in carbon monoxide poisoning needed

Carbon monoxide poisoning

Carbon monoxide (CO) poisoning is common and frequently unrecognized since the signs and symptoms are relatively nonspecific. CO poisoning causes tissue hypoxia. Additionally, various animal studies have demonstrated that CO interferes with myoglobin, P450, and other enzyme function; causes lipid peroxidation through neutrophil activation; produces oxidative stress manifested by peroxynitrate deposition in endothelium; binds to cytochrome aa3, disrupting intracellular oxygen utilization; can cause neuroexcitotoxicity; and contributes to hippocampal cellular death through apoptosis. Emergency treatment for CO poisoning is 100% oxygen. Hyperbaric oxygen therapy (HBO2) is accepted in CO poisoning, although data from randomized clinical trials regarding the efficacy of HBO2 in CO poisoning is conflicting. CO poisoning, even when treated with supplemental oxygen can leave the patient with permanent neurocognitive or affective problems. Unfortunately, there appears to be no marker or constellation of signs or symptoms at presentation that predicts long-term outcome following CO poisoning. Given the neurocognitive sequelae following CO poisoning, increased awareness and prevention of CO poisoning is imperative.

Hyperbaric or normobaric oxygen for acute carbon monoxide poisoning: a randomised controlled clinical trial

OBJECTIVE

To assess neurological sequelae in patients with all grades of carbon monoxide (CO) poisoning after treatment with hyperbaric oxygen (HBO) and normobaric oxygen (NBO).

DESIGN

Randomised controlled double-blind trial, including an extended series of neuropsychological tests and sham treatments in a multiplace hyperbaric chamber for patients treated with NBO.

SETTING

The multiplace hyperbaric chamber at the Alfred Hospital, a university-attached quarternary referral centre in Melbourne providing the only hyperbaric service in the State of Victoria.

PATIENTS

All patients referred with CO poisoning between 1 September 1993 and 30 December 1995, irrespective of severity of poisoning. Pregnant women, children, burns victims and those refusing consent were excluded.

INTERVENTION

Daily 100-minute treatments with 100% oxygen in a hyperbaric chamber--60 minutes at 2.8 atmospheres absolute for the HBO group and at 1.0 atmosphere absolute for the NBO group--for three days (or for six days for patients who were clinically abnormal or had poor neuropsychological outcome after three treatments). Both groups received continuous high flow oxygen between treatments.

MAIN OUTCOME MEASURES

Neuropsychological performance at completion of treatment, and at one month where possible.

RESULTS

More patients in the HBO group required additional treatments (28% v. 15%, P = 0.01 for all patients; 35% v. 13%, P = 0.001 for severely poisoned patients). HBO patients had a worse outcome in the learning test at completion of treatment (P = 0.01 for all patients; P = 0.005 for severely poisoned patients) and a greater number of abnormal test results at completion of treatment (P = 0.02 for all patients; P = 0.008 for severely poisoned patients). A greater percentage of severely poisoned patients in the HBO group had a poor outcome at completion of treatment (P = 0.03). Delayed neurological sequelae were restricted to HBO patients (P = 0.03). No outcome measure was worse in the NBO group.

CONCLUSION

In this trial, in which both groups received high doses of oxygen, HBO therapy did not benefit, and may have worsened, the outcome. We cannot recommend its use in CO poisoning.

Environmental emergencies

This article reviews the pearls and pitfalls of high-altitude sickness, decompression sickness, and barotrauma; new findings relevant to the near-drowning patient; continued controversies on hyperbaric oxygen for carbon monoxide poisoning; pitfalls in hypothermia management; and updates on the management of venomous snakebites.