Roque, Pedro

Background: During CPR in animals, chest compressions (CC) may produce passive volumes large enough to provide adequate ventilation. In humans, this mechanism may explain why continuous CCs have been associated with improved survival. We quantified the volume of passive ventilation during emergency department (ED) CCs to determine if compression-only CPR (COCPR) provides clinically significant gas exchange during resuscitation. Methods: In an urban ED, continuous flow and volume of air exhaled through an endotracheal tube were measured during the CC phase of manual CPR (between ventilations) with NICO monitors (Philip/Respironics) and recorded using LabView (National Instruments). Gas exchange with CC was quantified using Matlab (Mathworks) as the area under the flow curve (figure). CC quality was measured using accelerometer-based technology (R Series, ZOLL Medical). Results: Eight patients (6 male) aged 37-83 yrs [median age 51 yr (IQR 43-56)] who suffered out-of-hospital cardiac arrest (CA) and were transported and treated with CC in the ED were included. A total of 548 CCs [median depth 1.89 in (IQR=1.66, 2.29), median rate 128 CC/min (IQR=122-134) were analyzed over 30 min of CPR. Median tidal volume per CC was 17.3 mL (IQR=5.9-22.4). This was considerably less than measured dead space in all patients (median 118mL, IQR=93-143), regardless of CC depth. The figure illustrates a typical tracing in which ventilation volume dwarfs any passive ventilation occurring with CC. Conclusion: Late in CA, passive ventilation occurring during CCs appears to produce considerably less gas exchange than calculated dead space. The effectiveness of passive ventilation during early stages of CPR, when chest and lung compliance are greater, remains unknown. However, these findings suggest that the benefits of COCPR strategies may be related to reliably higher CC fraction and/or prevention of the negative effects of hyperventilation rather than from any passive ventilation.