Basic life support with four different compression/ventilation ratios in a pig model: The need for ventilation

BackgroundDuring cardiac arrest the paramount goal of basic life support (BLS) is the oxygenation of vital organs. Current recommendations are to combine chest compressions with ventilation in a fixed ratio of 30:2; however the optimum compression/ventilation ratio is still debatable. In our study we compared four different compression/ventilation ratios and documented their effects on the return of spontaneous circulation (ROSC), gas exchange, cerebral tissue oxygenation and haemodynamics in a pig model.MethodsStudy was performed on 32 pigs under general anaesthesia with endotracheal intubation. Arterial and central venous lines were inserted. For continuous cerebral tissue oxygenation a Licox® PtiO2 probe was implanted. After 3 min of cardiac arrest (ventricular fibrillation) animals were randomized to a compression/ventilation-ratio 30:2, 100:5, 100:2 or compressions-only. Subsequently 10 min BLS, Advanced Life Support (ALS) was performed (100%O2, 3 defibrillations, 1 mg adrenaline i.v.). Data were analyzed with 2-factorial ANOVA.ResultsROSC was achieved in 4/8 (30:2), 5/8 (100:5), 2/8 (100:2) and 0/8 (compr-only) pigs. During BLS, PaCO2 increased to 55 mmHg (30:2), 68 mmHg (100:5; p = 0.0001), 66 mmHg (100:2; p = 0.002) and 72 mmHg (compr-only; p < 0.0001). PaO2 decreased to 58 mmg (30:2), 40 mmHg (100:5; p = 0.15), 43 mmHg (100:2; p = 0.04) and 26 mmHg (compr-only; p < 0.0001). PtiO2 baseline values were 12.7, 12.0, 11.1 and 10.0 mmHg and decreased to 8.1 mmHg (30:2), 4.1 mmHg (100:5; p = 0.08), 4.3 mmHg (100:2; p = 0.04), and 4.5 mmHg (compr-only; p = 0.69).ConclusionsDuring BLS, a compression/ventilation-ratio of 100:5 seems to be equivalent to 30:2, while ratios of 100:2 or compressions-only detoriate peripheral arterial oxygenation and reduce the chance for ROSC.