Abstract 1: Derivation of a Novel Hypothermic to Ischemic Ratio as an Indicator for Predicting and Improving Survival from Out of Hospital Cardiac Arrest
Objectives: Therapeutic hypothermia (TH) is recommended by the 2010 AHA guidelines but there is little evidence to guide the duration of therapy required to realize benefit after out-of-hospital cardiac arrest (OOH-CA). We sought to evaluate a novel Hypothermic to Ischemic Ratio (H/I Ratio = total hypothermic time / total ischemic time (TIT)) as a predictor of survival.
Methods: Adult, non-traumatic, OOH-CA patients surviving to hospital admission between January 2008 and January 2011 were included, and structured data including Utstein variables were collected retrospectively. Total hypothermic time was composed of 1) induction interval from ROSC to target temperature (T2T), 2) TH interval, from target temperature until rewarming, and 3) rewarming interval. TIT was measured from pulselessness to ROSC. Backwards stepwise logistic regression was used to fit the most parsimonious models, and odds ratios (OR) were obtained to examine the effects of the predictor variables on survival. The final models were evaluated by Hosmer-Lemeshow and Receiver-Operating Characteristic (ROC) curves.
Results: Overall, 84 patients (49.7%) survived to hospital discharge. The odds of survival for VF were 6.53 times greater than PEA (95% CI 3.28 to 13.01), so separate models were constructed. For VF, longer T2T, shorter TIT, and lower initial patient temperature were significant for predicting survival (R² = 0.41, area under curve = 0.89). H/I Ratio was the most powerful predictor and attained 100% sensitivity at 25:1. For PEA, longer T2T, shorter TIT, and higher initial temperature were significant predictors (R² = 0.45, AUC= 0.91). H/I Ratio was a significant predictor and reached 100% sensitivity at 37:1.
Conclusions: The novel H/I Ratio predicts survival to hospital discharge significantly and suggests that OOH-CA patients may directly benefit from a simple, individualized approach, tailoring total hypothermic time according to presenting rhythm and TIT.
- © 2011 by American Heart Association, Inc.