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

Abstract

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 venti- lation on pulmonary gas exchange in anaesthetized patients performed with a ventilation/compression ratio of 2:15 com- pared to 5:50. Methods: Forty patients scheduled for elective cardiac surgery received general anesthesia (Propofol/Sufentanil/ Rocu- ronium). 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 venti- lation 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/comp- ression ratios of 2:15 and 5:50 enable an adequate oxygenation and stable acid base balance.