Leaning during chest compressions impairs cardiac output and left ventricular myocardial blood flow in piglet cardiac arrest

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Abstract
Objective: Complete recoil of the chest wall between chest compressions during cardiopulmonary resuscitation is recommended, because incomplete chest wall recoil from leaning may decrease venous return and thereby decrease blood flow. We evaluated the hemodynamic effect of 10% or 20% lean during piglet cardiopulmonary resuscitation. Design: Prospective, sequential, controlled experimental animal investigation. Setting: University research laboratory. Subjects: Domestic piglets. Interventions: After induction of ventricular fibrillation, cardiopulmonary resuscitation was provided to ten piglets (10.7 ± 1.2 kg) for 18 mins as six 3-min epochs with no lean, 10% lean, or 20% lean to maintain aortic systolic pressure of 80–90 mm Hg. Because the mean force to attain 80–90 mm Hg was 18 kg in preliminary studies, the equivalent of 10% and 20% lean was provided by use of 1.8- and 3.6-kg weights on the chest. Measurements and Main Results: Using a linear mixed-effect regression model to control for changes in cardiopulmonary resuscitation hemodynamics over time, mean right atrial diastolic pressure was 9 ± 0.6 mm Hg with no lean, 10 ± 0.3 mm Hg with 10% lean (p < .01), and 13 ± 0.3 mm Hg with 20% lean (p < .01), resulting in decreased coronary perfusion pressure with leaning. Microsphere-determined cardiac index and left ventricular myocardial blood flow were lower with 10% and 20% leaning throughout the 18 mins of cardiopulmonary resuscitation. Mean cardiac index decreased from 1.9 ± 0.2 L · M−2 · min−1 with no leaning to 1.6 ± 0.1 L · M−2 · min−1 with 10% leaning, and 1.4 ± 0.2 L · M−2 · min−1 with 20% leaning (p < .05). The myocardial blood flow decreased from 39 ± 7 mL · min−1 · 100 g−1 with no lean to 30 ± 6 mL · min−1 · 100 g−1 with 10% leaning and 26 ± 6 mL · min−1 · 100 g−1 with 20% leaning (p < .05). Conclusions: Leaning of 10% to 20% (i.e., 1.8–3.6 kg) during cardiopulmonary resuscitation substantially decreased coronary perfusion pressure, cardiac index, and myocardial blood flow.