Chest compressions during ventilation in out-of-hospital cardiac arrest cause reversed airflow.

Aim: During cardiopulmonary resuscitation, once the patient is intubated, compressions and ventilations are performed simultaneously. Chest compressions during the inspiratory phase of ventilation may force air out of the lungs, causing so-called "reversed airflow", which may lead to ineffective ventilation. The purpose of this study is to determine the occurrence of this phenomenon and to quantify the volume of reversed airflow.

Methods: Observational study. During manual ventilation of intubated patients receiving chest compressions, the pressure gradient over the endotracheal tube was measured using two air-filled catheters connected to a custom-made portable device. Chest compression data were measured using an accelerometer on a Zoll E- series defibrillator. All data are reported as mean (standard deviation; range).

Results: Twenty-five patients and a total of 368 ventilations were studied, on average 15 (6; 10-30) per patient. The mean tidal volume, minute volume and ventilation rate were respectively 690 ml (160; 240-1260), 10.5 l/min (4.8; 4.4-22.1) and 18/min (6; 6-35). Reversed airflow was observed in 21/25 patients (84%) and in 65% of all ventilations, with on average two episodes per ventilation. Fifty-five percent of the chest compressions during the inspiratory phase of the ventilation generated reversed airflow. The mean volume of the reversed airflow was 96 ml per episode (52; 12-364).

Conclusion: Chest compressions during ventilation in intubated patients generated reversed airflow in most patients. There was wide variation in the number of episodes and volume of the reversed airflow between patients. The effect of this phenomenon on the efficacy of ventilation during resuscitation and on outcome needs further investigation.