The impact of head and thorax elevation on respiratory mechanics during cardiopulmonary resuscitation: a multi-model study.

BACKGROUND: The impact on ventilation of head and thorax elevation (HTE) and the use of an impedance threshold device (ITD) during cardiopulmonary resuscitation (CPR) remains poorly understood. The aim was to describe the impact on ventilation and absolute lung volumes of HTE vs. horizontal (FLAT) positions, with or without ITD use, across multiple cardiac arrest experimental models. METHODS: This was a cross-over experimental trial conducted using three models: pigs, Thiel-embalmed cadavers, and thawed fresh-frozen cadavers. Two protocols were applied in a 1:1 randomized order: FLAT and HTE positions first, with or without ITD. Primary outcome was the calculation of absolute loss of lung volume (Vloss) below the functional residual capacity. Airway opening pressure (AOP) and respiratory system compliance (Crs) were also calculated, 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 linear mixed model, there was a significant difference for Vloss for FLAT vs. HTE (p = 0.05) with an estimate of 43.9 mL (95%CI: 1.41; 86.4), while no significant difference was observed comparing ITD vs. no-ITD (p = 0.28) with an estimate of 23.6 mL (95%CI: -18.9; 66.1). In cadavers, AOP was not significantly different: HTE: 5.9 (2.9-10.3) vs. FLAT: 8.1 (6.4-11.5) cmH2O (p = 0.07). Crs was not significantly different: HTE: 30.9 (21.3-34.4) vs. FLAT: 26.2 (24.0-30.3) mL/cmH2O (p = 0.2). CONCLUSIONS: In this multi-model study, HTE during CPR limits loss of lung volume below functional residual capacity.