Abstract 62: Validating Effectiveness of Ventilation Generated by Chest Compression Alone in the Model Lung.
Introduction: It was recently recommended chest compression only (CCO) cardiopulmonary resuscitation (CPR) by bystanders for adults in cardiac arrest. One of the explanations is that CCO-CPR may generate enough ventilation to match the compromised cardiac output. However, the effectiveness of the ventilation generated by CCO by bystanders has never been determined. A more recent study in intubated patients shows that tidal volumes (Vt) generated by CCO are small (about 41 ml). As the rate of the chest compressions recommended is 100 per min, it appears that the minute ventilation (MV) should be adequate. However, the minute alveolar ventilation is unknown. Considering that the anatomic dead space of an adult is about 150 ml, the ventilation produced by CCO-CPR might be inadequate to match the cardiac output generated by chest compression which is estimated to be about one-third of the normal cardiac output.
Hypothesis: We hypothesize that CCO-CPR does not generate adequate minute alveolar ventilation to match even the compromised cardiac output.
Methods: The study was done in a double chamber model lung. Mechanical ventilation of chamber A (compliance 20ml/cmH2O) allowed spontaneous ventilation of chamber B (compliance 150ml/cmH2O). The residual lung volume of Chamber B was 1634 ml including the volume of the airway, 151 ml. Chamber B was primed with CO2 to establish a pCO2 of 40 mmHg through the entire system. CO2 delivery was then stopped and Chamber A was mechanically ventilated. The pCO2 was measured by 2 separate sensors, one at each end of the airway. The distal sensor opened to the atmosphere. The slopes of pCO2 in the chamber vs. time at various tidal volumes were plotted and compared.
Results: The rate of pCO2 decay and the time required to achieve 50% decay with 500ml Vt x 10 breaths/minute is about 5.3 to 5.8 times faster than with 40ml Vt x 100 breaths/min .
Conclusions: To generate one-third of normal minute alveolar ventilation, the Vt must be at least 80 ml at a frequency of 100 breaths/minute. Since upper airway obstruction and atelectasis is inevitable, CCO-CPR is unlikely to generate sufficient minute alveolar ventilation to match even the compromised cardiac output state.
- © 2010 by American Heart Association, Inc.