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Objective Our intent was to evolve a prognosticator that would predict the likelihood that an electrical shock would restore a perfusing rhythm. Such a prognosticator was to be based on conventional electrocardiographic signals but without constraints caused by artifacts resulting from precordial compression. The adverse effects of “hands off” intervals for rhythm analyses would therefore be minimized. Such a prognosticator was further intended to reduce the number of electrical shocks and the total energy delivered and thereby minimize postresuscitation myocardial dysfunction. Design Observational study. Subjects Medical research laboratory of a university-affiliated research and educational institute. Subjects Domestic pigs. Interventions Ventricular fibrillation was induced in an established porcine model of cardiac arrest. Recordings of scalar lead 2 over the frequency range of 4–48 Hz were utilized. The area under the curve representing the amplitude and frequency was defined as the amplitude spectrum area (AMSA). Measurements and Main Results A derivation group of 55 animals yielded a threshold value of AMSA that uniformly predicted successful resuscitation. A separate group of 10 animals, a validation group, confirmed that an AMSA value of 21 mV·Hz predicted restoration of perfusing rhythm after 7 of 8 electrical shocks and failure of electrical conversion in 21 of 23 electrical shocks, yielding sensitivity and specificity of about 90%. The negative predictive value of AMSA was 95% and statistically equivalent to that of coronary perfusion pressure, mean amplitude, and median frequency. The positive predictive value that would prompt continuation of cardiopulmonary resuscitation without interruption for an unsuccessful defibrillation attempt was greatly improved with AMSA (78%) as compared with coronary perfusion pressure (42%), mean amplitude (32%), and median frequency (29%). Conclusion AMSA has the potential for guiding more optimal timing of defibrillation without adverse interruption of cardiopulmonary resuscitation or the delivery of unsuccessful high energy electrical shocks that contribute to postresuscitation myocardial injury.

To document the relationships between cardiac index and end-tidal carbon dioxide tension (PetCO2 during diverse low-flow states of circulatory shock.Randomized, prospective, controlled studies on animal models of hemorrhagic, septic, and cardiogenic shock.University-affiliated research laboratory.Sixteen anesthetized domestic pigs weighing 35-45 kg.Hemorrhagic shock was induced in five pigs by bleeding followed by reinfusion of shed blood. Septic shock was induced in five pigs by infusion of live Escherichia coli. Cardiogenic shock followed an interval of global myocardial ischemia after inducing and reversing ventricular fibrillation in six pigs.PetCO2 was continuously measured. Cardiac index was measured intermittently by using conventional thermodilution techniques. Cardiac index was correlated with PetCO2 by polynomial regression and Bland-Altman analyses. PetCO2 was highly correlated with cardiac index during hemorrhagic shock (r2 = .69, p.01), septic shock (r2 = .65, p.01), and cardiogenic shock (r2 = .81, p.01). PetCO2 predicted thermodilution cardiac index with bias of -11+/-27 (+/-2 SD) mL/min/kg during hemorrhagic shock, 1.3+/-20.4 (+/- 2 SD) mL/min/kg during septic shock, and -1+/-12 (+/-2 SD) mL/min/kg during cardiogenic shock.Cardiac output and PetCO2 were highly related in diverse experimental models of circulatory shock in which cardiac output was reduced by40% of baseline values. Therefore, measurement of PetCO2 is a noninvasive alternative for continuous assessment of cardiac output during low-flow circulatory shock states of diverse causes.

Objective: The objective of this study was to measure stroke volumes produced by precordial compression during cardiopulmonary resuscitation and to quantitate relationships of stroke volume to measurements of end-tidal carbon dioxide. Design: A prospective, observational animal study. Setting: Medical research laboratory in a university-affiliated research and educational foundation. Subjects: Domestic pigs. Interventions: Eighteen anesthetized male, domestic pigs weighing between 40 and 45 kg were investigated. Ventricular fibrillation was electrically induced and continued for intervals ranging from 4 to 10 mins. Precordial compression was maintained at 80 per minute together with mechanical ventilation after endotracheal intubation. Measurements and Main Results: Stroke volumes were measured with the aid of transesophageal echocardiographic imaging. End-tidal carbon dioxide was quantitated with conventional capnography. Baseline values of thermodilution cardiac output were highly correlated with echocardiographic measurements (r = .92). The stroke volume index produced by precordial compression averaged 0.45 mL/kg or approximately 37% of the average prearrest value of 1.22 mUkg. The end-tidal carbon dioxide was highly predictive of stroke volume index (r = .88, p

Objectives: To identify a method for predicting the success or failure of a defibrillatory shock such as to avoid potentially detrimental interruptions of cardiopulmonary resuscitation (CPR). Such a method would also guide more optimal programming of automated external defibrillators. Design: Prospective, observational animal study. Setting: Medical research laboratory in a university-affiliated research and educational foundation. Subjects: Domestic pigs. Interventions: Ventricular fibrillation (VF) was electrically induced in 66 domestic pigs. After an interval of between 3 and 5 mins of untreated VF, precordial compression was begun. Electrocardiographic lead 2 was monitored and artifacts produced during precordial compression were removed by digital filtering. Measurements and Main Results: In the derivation study, electrical defibrillation restored spontaneous circulation in 30 of the 66 animals. Successfully resuscitated animals had significantly greater coronary perfusion pressure, maximum VF amplitude, mean VF amplitude, and dominant VF frequency. No animals were resuscitated if the coronary perfusion pressure was