Abstract
Introduction: Compression-induced ventilation may aid gas exchange during CPR. We hypothesized that the amount of gas moving in and out of the lungs depends on chest compression depth. Methods: VF was induced in five female, anesthetized and intubated pigs of about 30 kg. After 30 seconds of non-intervention time, chest compressions were started and maintained at a rate of 100 compressions per minute. Every two minutes chest compression depth was altered, resulting in 14 minutes of CPR with a depth sequence of 4 cm, 3 cm, 4 cm, 5 cm, 5.5 cm, 5 cm and 4 cm. Ventilations were performed manually with a bag-valve device 10 times per minute during continuous chest compressions by a dedicated expert. Airway flow was measured at the end of the endotracheal tube. Compression-induced ventilation was determined from the periods between the manual ventilations. The average compression-induced minute ventilation volume was determined over the last minute of each two minute period of CPR at each specific chest compression depth. Results: The compression-induced ventilation volume in the first period of CPR at 4 cm of depth was 1.6 ± 0.9 L/min (about 4% of total ventilation volume). The figure shows how the compression-induced ventilation volume decreases with increasing chest compression depth, relative to this initial value. CPR with a chest compression depth of 4 cm was performed three times in each pig, and the corresponding compression-induced ventilation volumes decreased with time. This suggested that there might be just a time effect (e.g. atelectasis). However, the final compression depth of 4 cm resulted in larger compression-induced ventilation volumes than the preceding 5 cm and 5.5 cm compression depths, indicating that the decreased volume over time could not purely be a time effect, but must also be an effect of the depth. Conclusion: In conclusion, compression-induced ventilation volume appears to decrease with deeper chest compressions as well as with prolonged CPR.
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