Does a Ventilation/Compression Ratio of 5:50 Alter Gas Exchange in Basic Life Support? A Simulation in a BLS-Model of Patients Undergoing General Anesthesia

Background: The goal of Basic Life Support is the oxygenation of vital organs during cardiac arrest. Therefore, chest compressions are combined with ventilation in a fixed ratio. This study investigated the influence of bag/mask ventilation on pulmonary gas exchange in anaesthetized patients performed with a ventilation/compression ratio of 2:15 compared to 5:50. Methods: Forty patients scheduled for elective cardiac surgery received general anesthesia (Propofol/Sufentanil/ Rocuronium). Upon loss of consciousness bag/mask ventilation was started (15l/min O2 with reservoir bag) over a six minute period using either 2 ventilations every 9 seconds (simulated ventilation/compression ratio 2:15) or 5 ventilations every 30 seconds (simulated ventilation/compression ratio 5:50). Arterial blood gas sampling was performed at beginning of ventilation and after six minutes. Data were analyzed with 2-factorial ANOVA. Results: Arterial PO2 increased in both groups during the ventilation with pure oxygen (PaO2: 2:15 group: 259 mmHg [0 min], 369 mmHg [6 min]; 5:50 group: 277 mmHg [0 min], 363 mmHg [6 min]; n.s.). Arterial pCO2 also increased (PaCO2: 2:15 group: 47 mmHg [0min], 48 mmHg [6min]; 5:50 group: 47 mmHg [0min], 52 mmHg [6min], P=0,018). Consequently, pH decreased in both groups (pH: 2:15 group; 7,37 [0min], 7,36[6min]; 5:50 group: 7,38 [0min], 7,34 [6min], P=0,02). There was no critical decrease of SpO2 at any time. Conclusions: In the anesthetized patient with spontaneous circulation bag/mask ventilation simulating ventilation/compression ratios of 2:15 and 5:50 enable an adequate oxygenation and stable acid base balance.