Adverse effects of interrupting precordial compression during cardiopulmonary resuscitation

Objectives: In the current operation of automated external defibrillators, substantial time may be consumed for a ''hands off'' interval during which precordial compression is discontinued to allow for automated rhythm analyses before delivery of the electric countershock. The effects of such a pause on the outcomes of cardiopulmonary resuscitation were investigated. Design: Prospective, randomized, controlled animal study. Setting: Research laboratory. Subjects: Male Sprague Dawley rats. Interventions: Ventricular fibrillation was electrically induced in 25 Sprague-Dawley rats. After 4 mins of untreated ventricular fibrillation, precordial compression was begun and continued for 6 mins. Animals were then randomized to receive an immediate defibrillation shock or the defibrillation attempt was delayed for intervals of 10, 20, 30, or 40 sees. Measurements and Main Results: Immediate defibrillation restored spontaneous circulation in each instance. When defibrillation was delayed for 10 or 20 sees, spontaneous circulation was restored in three of five animals in each group. After a 30-sec delay, spontaneous circulation was restored in only one of five animals (p < .05). No animal was successfully resuscitated after a 40-sec delay (p < .01). With increasing delays, 24- and 48-hr survival rates were correspondingly reduced. Conclusions: During resuscitation from ventricular fibrillation, prolongation of the interval between discontinuation of precordial compression and delivery of the first electric countershock substantially compromises the success of cardiac resuscitation. Accordingly, automated defibrillators are likely to be maximally effective if they are programmed to secure minimal ''hands off'' delay before delivery of the electric countershock.