Abstract P81: Transthoracic Impedance During Real Cardiac Arrest Defibrillation Attempts: Are Stacked-Shocks Appropriate?
Introduction: In 2005, AHA changed recommendations to treat ventricular fibrillation from 3 transthoracic stacked-shocks to 1 shock followed by immediate chest compressions. Prior stacked-shocks were recommended based on low first-shock efficacy of monophasic waveforms and theoretical decrease in TransThoracic Impedance (TTI) following each shock. Recent data shows poor first-shock efficacy of biphasic defibrillation in children. Our objective was to characterize TTI following failed biphasic defibrillation attempts in children during real cardiac arrest, and assess whether a stacked-shock approach is appropriate.
Hypothesis: Transthoracic impedance (TTI) is lower immediately post-shock compared to pre-shock in children ≥8 years during real cardiac arrest. However, the duration of decreased TTI is too short to expect stacked shocks to improve defibrillation success.
Methods: TTI was collected via standard Anterior-Apical defibrillator electrode pads during consecutive in-hospital cardiac arrest defibrillation attempts in children ≥8yrs. TTI (Ohms) was measured continuously, and specifically documented at 0.5 second intervals pre and post-shock. TTI variables analyzed with descriptive summaries/paired t-test.
Results: Analysis yielded 13 evaluable shock events during 5 cardiac arrests (mean age 14.3±5 yrs, weight 47.4±7.3 kg,) between September 2006-May 2009. Compared to pre- shock values (56.6±23.5 Ohms), TTI was significantly lower immediately post-shock at 0.1sec post (55.2±22.2 Ohms, p<0.01), 0.5 sec post (55.4±22.3 Ohms, p<0.01), and 1 sec post (54.3±22.9 vs. p<0.02). No difference was demonstrated by 2 sec post-shock (54.7±23.3 vs. 55.5±24.2 Ohms, p<0.07).
Conclusions: TTI was significantly lower for <2 seconds immediately post-shock, compared to pre-shock, in children during real cardiac arrest. However, TTI reduction quickly dissipates (<2 sec), suggesting limited feasibility and low likelihood that stacked-shocks would improve defibrillation success.