Modifiable factors associated with improved cardiac arrest survival in a multicenter basic life support/defibrillation system: OPALS study phase I results

Study objectives: This study was conducted to identify modifiable factors a ssociated with survival for prehospital cardiac arrest in a large, multicen ter EMS system with basic life support/defibrillation (BLS-D) level of care . Methods: This observational cohort study constitutes Phase I of the 3-phase Ontario Prehospital advanced life Support (OPALS) Study. Included were all adults who had cardiac arrest before EMS arrival in 21 urban/suburban comm unities that operate under the jurisdiction of 1 ambulance services branch, have 911 telephone service, and provide ambulance defibrillation but no pr ehospital advanced life support (ALS). Central dispatch and ambulance recor ds were reviewed according to the Utstein guidelines. Associations between multiple patient and EMS factors and survival to discharge were assessed by univariate then stepwise logistic regression analyses. Results: From January 1, 1991, to January 31, 1995, 5,335 eligible patients were treated. Of these, 46.8% of cardiac arrests were witnessed by citizen s, 14.5% received bystander CPR, 25.6% received CPR by fire or police, and 38.2% had an initial rhythm of ventricular fibrillation/ventricular tachyca rdia (VF/VT). The mean interval from call received to vehicle stopped was 6 .7 minutes. Survival was 3.5% overall and 8.8% for VP/VT. Multivariate anal ysis found the following factors to be independently associated with surviv al (odds ratio with 95% confidence intervals): age .81 (.73, .89), bystande r-witnessed arrest 4.05 (2.78, 5.90), bystander CPR 2.98 (2.07, 4.29), CPR by fire or police 2.20 (1.46, 3.31), and response interval call received to vehicle stopped .76 (.71, .82). Conclusion: This represents the largest multicenter BLS-D study of prehospi tal cardiac arrest yet conducted and clearly indicates that patient surviva l may be improved by optimization of EMS response intervals, bystander CPR, as well as first-responder CPR by fire or police.