Mechanical ventilation during cardiopulmonary resuscitation: influence of positive end-expiratory pressure and head-torso elevation

Background: Efficient ventilation is important during cardiopulmonary resuscitation (CPR). Nevertheless, there is insufficient knowledge on how the patient's position affects ventilatory parameters during mechanically assisted CPR. We studied ventilatory parameters at different positive end-expiratory pressure (PEEP) levels and when using an inspiratory impedance valve (ITD) during horizontal and head-up CPR (HUP-CPR).

Methods: In this human cadaver experimental study, we measured tidal volume (V_T) and pressure during CPR at different randomized PEEP levels (0, 5 or 10 cmH₂O) or with an ITD. CPR was performed, in the following order: horizontal (FLAT), at 18° and then at 35° head-thorax elevation. During the inspiratory phase we measured the net tidal volume (V_T) adjusted to predicted body weight (V_TPBW), reversed airflow (RAF), and maximum and minimum airway pressure (P_max and P_min).

Results: Using ten thawed fresh-frozen cadavers we analyzed the inspiratory phase of 1843 respiratory cycles, 229 without CPR and 1614 with CPR. In a mixed linear model, thoracic position and PEEP significantly impacted V_TPBW (p < 0.001 for each), and the insufflation time, thoracic position and PEEP significantly affected the RAF (p < 0.001 for each) and P_max (p < 0.001). For P_min, only PEEP was significant (p < 0.001). In subgroup analysis, at 35° V_TPBW and P_max were significantly reduced compared with the flat or 18° position.

Conclusion: When using mechanical ventilation during CPR, it seems that the PEEP level and patient position are important determinants of respiratory parameters. Moreover, tidal volume seems to be lower when the thorax is positioned at 35°.