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

Background: During 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. Methods: Study 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 (R) PtiO(2) 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%O-2, 3 defibrillations, 1 mg adrenaline i.v.). Data were analyzed with 2-factorial ANOVA. Results: ROSC 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). PtiO(2) 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). Conclusions: During 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. (C) 2009 Elsevier Ireland Ltd. All rights reserved.