Abstract Sun101: Physiology of ventilation during flat and head-up cardiopulmonary resuscitation: a multi-model study

Abstract

Background: Ventilation during cardiopulmonary resuscitation may affect cardiac arrest management and outcome. Novel strategies such as head and thorax elevation (HTE) and the use of an impedance threshold device (ITD) have been developed to enhance circulation during CPR. However, the impact of these strategies on ventilation during CPR remains poorly understood. Research Question: To describe and understand the impact on ventilation and lung volumes of horizontal (FLAT) versus HTE positions, with or without ITD use, across multiple experimental models. Methods: This was a cross-over experimental trial conducted using three cardiac arrest models: pigs, Thiel-embalmed cadavers, and thawed fresh-frozen cadavers. Two protocols were applied in randomized order: FLAT and HTE positions, with or without ITD. CPR was standardized with a mechanical suction-cup based chest compression device and volume-controlled ventilation. Primary outcome was the calculation of absolute loss of lung volume (Vloss) below the functional residual capacity during CPR, estimated by measuring the difference between inspiratory tidal volume and expiratory tidal volume for the two consecutive respiratory cycles following interruption of chest compressions for each sequence. We also calculated airway opening pressure (AOP) and respiratory system compliance (Crs), both assessed before CPR initiation. Linear mixed models were used for statistical analysis. Results: Eight pigs and eight cadavers (4 Thiel, 4 fresh-frozen) were included. In the cadaver model, Vloss was 178.13 ± 168.19 in the FLAT position and 84.25 ± 112.87 mL in the HTE (p = 0.74). With ITD, Vloss was 192.75 ± 221.02 mL in the FLAT position and 148.5 ± 187.38 mL in the HTE position (p = 0.95). In the pig model, Vloss was 42.5 ± 31.7 mL in the FLAT position and 38.75 ± 44.77 mL in the HTE (p = 0.74). With ITD, Vloss was 104.62 ± 66.56 mL in the FLAT position and 105.13 ± 62.35 mL in the HTE position (p = 0.84). AOP was significantly lower in HTE vs. FLAT: 5.85 (2.85–10.25) vs. 8.05 (6.38–11.50) cmH2O (p = 0.042). Crs was not significantly different in HTE: 30.91 (21.25–34.44) vs. 26.24 (24.04–30.32) mL/cmH2O (p = 0.197). Conclusions: In the present animal and cadaver models, head and thorax elevation during CPR trends to reduce airway opening pressure and improve loss of lung volume above functional residual capacity. These observations contribute to already reported effect of head and thorax elevation and ITD.