Analysis of transthoracic impedance during real cardiac arrest defibrillation attempts in older children and adolescents: are stacked-shocks appropriate?

BACKGROUND: In 2005, the AHA changed the treatment recommendation for shockable rhythms from 3 transthoracic stacked-shocks to a single shock followed by immediate chest compressions. The stacked-shock recommendation was based on low first-shock efficacy of monophasic waveforms and the theoretical decrease in transthoracic impedance (TTI) following each shock. The objective of this study was to characterize TTI following biphasic defibrillation attempts in children ≥ 8 yrs during cardiac arrest to assess whether a stacked-shock approach may be appropriate to improve defibrillation success.
METHODS: TTI (Ohms (Ω)) was collected via standard anterior-apical defibrillator electrode pads during consecutive in-hospital cardiac arrest biphasic defibrillation attempts in children ≥ 8 yrs. Analytic data points for TTI were: 0.1s pre-shock (baseline); post-shock at 0.1, 0.5, 1.0, 1.5, and 2.0 s. TTI variables analyzed with descriptive summaries/paired t-test. p values < 0.05 considered statistically significant after correction for multiple comparisons.
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 and May 2009. Compared to 0.1s pre-shock baseline values (56.8 ± 23.4 Ω), TTI was significantly lower immediately 0.1s post-shock (55.2 ± 22.2 Ω, p = 0.003). Post-shock mean difference from baseline was 1.6 Ω at 0.1s (p = 0.015), 1.4 Ω at 0.5s (p = 0.019) 1.4 Ω at 1.0 s (p = 0.023), 1.1 Ω at 1.5 s (p = 0.028), and 0.95 Ω at 2.0 s (p = 0.096). Time to recharge our clinical defibrillators to standard biphasic shock dose was 2.80 ± 0.05 s.
CONCLUSIONS: During cardiac arrests in children ≥ 8 yrs, TTI decreased after biphasic shocks, but the limited magnitude and duration of TTI changes suggest that stacked-shocks would not improve defibrillation success.