Sunday, March 23, 2014
Saturday, March 22, 2014
Antifragile but Exposed: A Framework for Understanding Disease that Can Improve Diagnostic Decision Making
Here's an occasional cross-post from Status Iatrogenicus: Antifragile but Exposed: A Framework for Understanding Disease that Can Improve Diagnostic Decision Making
Thursday, March 20, 2014
ProCESS trial of protocol guided therapy for early septic shock. This trial is in essence a multicenter version of the landmark 2001 trial of Early Goal Directed Therapy (EGDT) for severe sepsis by Rivers et al. That trial showed a stunning 16% absolute reduction in mortality in sepsis attributed to the use of a protocol based on physiological goals for hemodynamic management. That absolute reduction in mortality is perhaps the largest for any therapy in critical care medicine. If such a reduction were confirmed, it would make EGDT the single most important therapy in the field. If such reduction cannot be confirmed, there are several reasons why the Rivers results may have been misleading:
- As I have blogged in the case of intensive insulin therapy, Single center studies inflate treatment effects when compared to multicenter studies for reasons that are unclear, but which may be related to bias especially in unblinded studies. (The revelation that Rivers was an investor in one of the devices used in the trial raised additional concerns about bias.)
- Regression to the mean may lead to reduced effect sizes when trials are repeated, especially when the index trial has a very large effect size. In a similar vein, since large absolute mortality reductions are statistically unlikely in critical care medicine, Bayesian inference means that trials reporting large reductions are likely to represent type I statistical errors.
There were other concerns about the Rivers study and how it was later incorporated into practice, but I won't belabor them here. The ProCESS trial randomized about 1350 patients among three groups, one simulating the original Rivers protocol, one to a modified Rivers protocol, and one representing "standard care" that is, care directed by the treating physician without a protocol. The study had 80% power to demonstrate a mortality reduction of 6-7%. Before you read further, please wager, will the trial show any statistically significant differences in outcome that favor EGDT or protocolized care?