Smoking is associated with improved survival as well as good neurologic outcome in patients treated with therapeutic hypothermia following cardiac arrest, a study found.
Half of smokers survived to hospital discharge with a good neurological outcome compared with only 28% of nonsmokers (P=0.003), according to Jeremy Pollock, MD, of Vanderbilt University in Nashville, Tenn., and colleagues.
The difference remained significant after adjustment for numerous potential confounders, including comorbidities (OR 3.82, 95% CI 1.43-10.24), they reported online in Resuscitation.
"Despite the findings of our study, we do not want the public to take from this that they should go out and start smoking to protect them from a future cardiac arrest," Pollock said in an email to MedPage Today.
"We hope," he said, "this will spur on further thought and discussion in regards to the etiology of the smoker's paradox," a previously observed phenomenon in which smokers are more likely to have an acute coronary syndrome but are less likely to die from an acute myocardial infarction (MI).
The current study is the first to examine the smoker's paradox in the setting of cardiac arrest, where reperfusion injury is similar to that seen in acute MI.
Pollock and colleagues retrospectively examined data from 181 consecutive adult patients who were treated with mild therapeutic hypothermia after a cardiac arrest at Vanderbilt University Medical Center. The events occurred from May 2007 to January 2012. Patients were defined as smokers if their medical record included a note to that effect. All other patients were considered nonsmokers.
Overall, 60% of the patients died in the hospital and 39% were discharged with a good neurological status, defined as a Cerebral Performance Category (CPC) score of 2 or less (no more than moderate disability).
Smokers had a significantly increased likelihood of leaving the hospital with a good neurological status after adjustment for age, initial rhythm, time to the return of spontaneous circulation, bystander cardiopulmonary resuscitation, and time to initiation of therapeutic hypothermia, and after further adjustment for sex and comorbidities using a propensity score.
Smokers also were more likely to have a CPC score of 2 or less at a median follow-up of 3 months (40% versus 19%, P<0.01).
Although the younger age and lower burden of comorbidities among smokers have been proposed as explanations for their improved outcomes from acute coronary syndromes and now cardiac arrest, some studies -- including the current one -- have found the smoker's paradox to remain after adjustment for those factors.
Another possibility -- and one that Pollock and his colleagues hypothesized might explain their findings -- is ischemic conditioning.
"Smoking causes hypoxia in tissue, which may create an ischemic conditioned state, thus attenuating the effects of ischemia and reperfusion caused by cardiac arrest," the researchers explained.
Pollack said that he'd like to design a prospective trial to look at the role of ischemic conditioning during therapeutic hypothermia.
"This would involve inducing ischemic conditioning via a modified blood pressure cuff during therapeutic hypothermia and evaluating change in outcomes," he said.
He and his co-authors acknowledged that the observational design of the study precluded an assessment of causality. Also, the study was limited in that it could not account for all potential confounders, there was no formal assessment of severity of illness, there was a relatively small sample size that might not be generalizable to other populations, and there was possible misclassification of smoking status.
... when I got CV disease. It is now cured... but smoking does not cause or cure Ischematism.