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Objective Optimising the depth and rate of applied chest compressions following out of hospital cardiac arrest is crucial in maintaining end organ perfusion and improving survival. The impedance cardiogram (ICG) measured via defibrillator pads produces a characteristic waveform during chest compressions with the potential to provide feedback on cardiopulmonary resuscitation (CPR) and enhance performance. The objective of this pre-clinical study was to investigate the relationship between mechanical and physiological markers of CPR efficacy in a porcine model and examine the strength of correlation between the ICG amplitude, compression depth and end-tidal CO 2 (ETCO 2 ). Methods Two experiments were performed using 24 swine (12 per experiment). For experiment 1, ventricular fibrillation (VF) was induced and mechanical CPR commenced at varying thrusts (0–60kg) for 2min intervals. Chest compression depth was recorded using a Philips QCPR device with additional recording of invasive physiological parameters: systolic blood pressure, ETCO2, cardiac output and carotid flow. For experiment 2, VF was induced and mechanical CPR commenced at varying depths (0–5cm) for 2min intervals. The ICG was recorded via defibrillator pads attached to the animal's sternum and connected to a Heartsine 500P defibrillator. ICG amplitude, chest compression depth, systolic blood pressure and ETCO 2 were recorded during each cycle. In both experiments the within-animal correlation between the measured parameters was assessed using a mixed effect model. Results In experiment 1 moderate within-animal correlations were observed between physiological parameters and compression depth ( r =0.69–0.77) and thrust ( r =0.66–0.82). A moderate correlation was observed between compression depth and thrust ( r =0.75). In experiment 2 a strong within-animal correlation and moderate overall correlations were observed between ICG amplitude and compression depth ( r =0.89, r =0.79) and ETCO 2 ( r =0.85, r =0.64). Conclusion In this porcine model of induced cardiac arrest moderate within animal correlations were observed between mechanical and physiological markers of chest compression efficacy demonstrating the challenge in utilising a single mechanical metric to quantify chest compression efficacy. ICG amplitude demonstrated strong within animal correlations with compression depth and ETCO 2 suggesting its potential utility to provide CPR feedback in the out of hospital setting to improve performance.

High quality chest compressions (CCs) have been proven to increase patient survival, during cardiac arrest. The impedance cardiogram (ICG) may provide a simple and non-invasive CPR coaching system to improve CC efficacy of minimally trained users. Cardiac arrest was induced in eleven swine. Manual CCs were applied at a fixed depth for two-minute episodes, increasing for each successive episode. Physiological data was recorded at 30s intervals. The primary analysis assessed the relationship between ICG amplitude and CC depth using a 5s analysis window. The secondary analysis compared the ICG amplitude against captured physiological data and CC depth, using a 30s window. The primary analysis yielded a strong Pearson correlation coefficient (95% confidence interval) of 0.90 (0.89, 0.91) between ICG amplitude and CC depth. The secondary analysis produced an overall correlation of 0.92 (0.90, 0.94) between ICG amplitude and CC depth. The within-animal correlation for ICG amplitude and both end-tidal carbon dioxide and systolic blood pressure was 0.94 (0.93, 0.95) and 0.90 (0.88, 0.92) respectively. Our data suggests that the amplitude of ICG is a good predictor of CC efficacy in a porcine model of cardiac arrest, when manual CCs are applied.

Introduction: Studies were conducted to evaluate cardiopulmonary resuscitation (CPR) in a simulated low gravitational field, such as Mars (hypoG), aimed at providing an insight into the performance of terrestrial CPR. Methods: Two studies were conducted to evaluate external chest compressions (ECC) depth and rate, as well as perceived exertion (RPE) and the physiological cost, when 4 sets of 30 ECCs were performed on a standard CPR mannequin for 1.5min during Mars simulation, using terrestrial (1Gz) as control. The first study (n=20; 2005 guidelines) also evaluated the electromyographic (EMG) activity of four muscles (triceps brachii, erector spinae, upper rectus abdominis, pectoralis major). The second study (n=30; 2010 guidelines) included range of elbow flexion, minute ventilation (VE) and peak oxygen consumption (VO2 peak) measurements. HypoG simulation was achieved using a body suspension device (BSD) and a counterweight system. Results: In both studies, subjects successfully performed ECCs at 1Gz and hypoG. In the first study, therewere increases from 1Gz values of 32% (p