Cyanide, the heart, and hydroxocobalamin
May 22, 2010, 2:44 pm
Cyanide Poisoning and Cardiac Disorders: 161 Cases. Fortin JL et al. J Emerg Med May 2010;38:467-476,
This manufacturer-sponsored, multicenter retrospective study reviewed cases of patients with smoke inhalation or cyanide ingestion who received early hydroxocobalamin in the field, before arriving at hospital. The study period was from January 1995 to July 2008. The authors paid special attention to the cardiovascular effects and complications of possible cyanide exposure.
There were 161 patients analyzed, 135 (84%) of whom had cardiac abnormalities on the initial EKG or monitor tracing. These included: asystole (58), ventricular fibrillation (3), myocardial ischemia (5), supraventricular tachycardia (56), and ventricular tachycardia (1). Five patients with cardiac arrest survived without neurological sequelae after treatment.
The authors try to torture the data every which way to establish an inference far outside of their stated goal. They state without qualification in their discussion: “Early administration of [hydroxocobalamin] seems to be an essential factor to improve outcome in the case of cardiac arrest.” There are two major things wrong with this statement:
1) This study was not designed — nor could it possibly be used — to support such a conclusion. It was not randomized, there was no control group, and confounding factors were not considered or discussed. For example, all these patients must have been receiving high-dose oxygen at the same time they were receiving the antidote. Couldn’t concomitant treatment of carbon monoxide toxicity (with oxygen) just as easily account for the survivors.
2) The authors reveal — but do not emphasize — that all (or most — it’s not clear from the paper) of the five neurologically intact survivors who had initial cardiac arrest regained spontaneous cardiac activity before hydroxocobalamin was administered.
Although I have been a proponent of hydroxocobalamin as a cyanide antidote for theortetical reasons, I have to admit that this paper makes me less enthusiastic about the drug — given it’s high acquisition cost. A reasonable summary of the paper could be:
A retrospective review of patients with suspected cyanide toxicity over 13.5 years in 4 major cities found that only five patients with cardiac arrest who received prehospital hydroxocobalamin survived to hospital discharge, and all of these regained spontaneous cardiac activity before receiving the antidote.
Of course, it is possible that these patients, or others in the study, received other patient-oriented benefits from hydroxocobalamin. But this study certainly doesn’t look for or demonstrate such benefits.