Abstract Body: Introduction
Adding active chest lift above anatomic neutral position during the decompression phase of the compression-decompression cycle of cardiopulmonary resuscitation (CPR) decrease intrathoracic pressure with the effect of refilling the heart and may improve blood flow. A novel mechanical device providing active compression-decompression CPR (ACD-CPR) could improve hemodynamic proxy variables for blood flow. Our goal was to document whether we achieved better hemodynamic effect of a mechanical ACD-CPR device (LUCAS 2 ACD, Intervention), compared to standard mechanical chest compressions (LUCAS 2, Control).

Methods
In this prospective block randomized out-of-hospital clinical CPR study we included non-traumatic cardiac arrest patients >18 years old, anterior-posterior chest diameter 170-273 mm, and treated by Oslo’s anesthesiologist-manned rapid response car. Exclusion criteria were pregnancy, imprisonment, or previous chest surgery. Comparisons of Control versus Intervention devices were based on: maximum End Tidal CO₂ (p_MTCO₂), invasive arterial blood pressure (Systolic and Mean Arterial Pressure, SAP and MAP, respectively), and cerebral oximetry (SctO₂). Both devices deliver a chest compression rate of 102 min^-1, and depth 5.3 cm. The Intervention device lifts the chest 3.0 cm above its neutral position during decompression. Analyses were done with non-linear regression with a generalized additive mixed model (GAMM) and presented as mean (standard deviation (SD)) [95% confidence interval [CI]], p≤.05 was considered statistically significant.

Results
We included 109 Control and 101 Intervention patients with comparable baseline characteristics (sex, cardiac arrest site, witnessed or not, bystander CPR or not, initial cardiac rhythm, cause of arrest, time intervals). GAMM analysis for the first 5, 10, and 30 min after inclusion are presented in Table 1. The Intervention device generated significantly higher p_MTCO₂, SAP, MAP at 5, 10 and 30 min, while SctO₂ was significantly higher during the first 5 and 10 min compared to Control. Fig. 1 and 2 illustrate 30 min continuous values of Control and Intervention patients for p_MTCO₂ and SAP, respectively.

Conclusions
The Intervention device generated significantly higher p_MTCO₂, SAP, MAP at 5, 10 and 30 min, while SctO₂ was higher during the first 5 and 10 min compared to Control. To investigate whether these improved proxy values of hemodynamics also improve clinical outcome, further studies are needed.