This brief article bubbled back up to the surface the other day, with a colleague claiming an “NNT of 5” for mortality for antibiotic prophylaxis following cardiac arrest. An NNT of 5 is excellent, mortality is a bad thing – so why aren’t we doing this?
This is a retrospective review of 138 patients resuscitated from OHCA and admitted to a British ICU, all receiving therapeutic hypothermia, stratified by receipt of antibiotics within 7 days of the ICU stay. Mortality was 56.6% in those receiving antibiotics and 75.3% for those not receiving antibiotics, thus the independent association with antibiotics use and survival with an NNT of 5.
This is, unfortunately, an egregious example of an abstract exaggerating and misleading from the correct conclusion, including the authors own results and discussion. Any mortality difference between groups occurred in the first 3 days following admission – thus, immortal time bias, as those patients who could receive antibiotics were, by definition, those who lived long enough to receive them. This fact is ultimately reflected in the presented results, in which the Cox proportional hazards model identified no significant predictive effect of antibiotics on survival. However, the authors – particularly in the abstract – focus on the superficial mortality observation, and inappropriately promote the potential value of prophylactic antibiotic use. This supposed NNT of 5 is nonsense, and ought never have been published.
Don’t just read the abstract!
Also, editors of Resuscitation, don’t let authors write such abstracts!
“Early antibiotics improve survival following out-of hospital cardiac arrest”
emlitofnote will be on holiday hiatus until December 29th. Cheers!
Ryan,
Yes, antibiotics after OHCA has been getting some traction. Possibly (in part) due to the publicity given in the July 2014 EMRAP paper chase. A paper was presented that claimed 38% of all patients are bacteremic! The conclusions was that it would reasonable to hang antibiotics.
(Paper Chase 1: Antibiotics for Cardiac Arrest!
Sanjay Arora MD and Michael Menchine MD. Coba V et al. The incidence and significance of bacteremia in out of hospital cardiac arrest. Resuscitation. 2014
Feb;85(2):196-202. PMID: 24128800. In short: patients who are presenting with an out of hospital cardiac arrest should probably be getting antibiotics.)
This all seems quite reasonable if you would like to ignore the fact that this was not an RCT and the vast majority of these had to be false positives. We struggle to get good quality blood cultures under ideal circumstances. What about blood cultures during a arrest?
I guess the hypothesis has been raised. It doesn't sound like it would be difficult to actually perform an RCT on this and get some real data.
Brian
Yeah, that paper is a total bit of nonsense. As you say, drawing blood cultures on the mostly dead is probably challenging. However, a lot of the positive cultures are gram-negatives – which sounds about right, for someone who has been in a state of hypoperfusion for an extended period of time with necrosis and likely breakdown of the natural immune barriers.
I'm sure some subset benefits from antibiotics – but certainly not as a non-selected intervention with an NNT of 5.