Measuring end-tidal carbon dioxide (ET CO2 ) is a practical non-invasive method for detecting pulmonary blood flow, reflecting cardiac output and thereby the quality of CPR. It has also been shown to rise before clinically detectable return of spontaneous circulation (ROSC).
Passive leg raising (PLR) increases venous return and may therefore augment cardiac output and in a cardiac arrest this may be reflected by an elevation in ETCO2.
A Swedish observational study of 126 patients with out of hospital cardiac arrest due to a likely cardiac aetiology underwent tracheal intubation with standardised ventilation and chest compressions (either manually or using the LUCAS device, as part of larger study of mechanical chest compressions according to a cluster design). Patients were stratified to receive either PLR to 20 degrees or no PLR. ETCO2 was measured during CPR, either for 15min, or until the detection of ROSC.

During PLR, an increase in ETCO2 was found in all 44 patients who received PLR within 15s (p=0.003), 45s (p = 0.002) and 75 s (p = 0.0001). Survival to hospital discharge was 7% among patients with PLR and 1% among those without PLR (p = 0.12). Among patients experiencing ROSC (60 of 126), there was a marked increase in ETCO2 1 min before the detection of a palpable pulse.
Passive leg raising during cardiopulmonary resuscitation in out-of-hospital cardiac arrest—Does it improve circulation and outcome?
Resuscitation. 2010 Dec;81(12):1615-20