Abstract Introduction Acute right ventricular (RV) failure is common in critically ill patients and is associated with poor outcomes. Mechanical ventilation (MV) in patients with RV failure is challenging and lacks supporting evidence. Permissive hypercapnia may offer physiological benefits, allowing a reduction in intrathoracic pressures, thereby mitigating the impact of MV on RV function. Although hypercapnia is associated with increased pulmonary vascular resistance (PVR), it remains unclear whether this results from hypercapnia itself or the accompanying respiratory acidosis. We hypothesised that permissive hypercapnia may be beneficial in RV failure; buffering acidosis enabled assessment of the separate effects of hypercapnia and acidaemia. Methods Prospective, randomized crossover preclinical study in ovine models of acute severe RV failure induced by either 1) pulmonary artery banding to rapidly increase RV afterload, targeting an RV systolic pressure 50 mmHg or 2) myocardial injury through direct injections of 96% ethanol into the RV free wall, targeting an RV ejection fraction 35%. Sheep were ventilated for 30 minutes with different settings as reported in Table 1. Briefly, following baseline assessment, permissive hypercapnia and buffered permissive hypercapnia were sequentially applied. A Swan-Ganz catheter was used to monitor systemic and pulmonary haemodynamics. Mechanical Power (MP) was computed according to previous formula1. The primary outcome was RV ejection fraction computed through a pressure-volume (PV) loop. Secondary outcomes were biventricular PV loop; cardiac and lung ultrasound; respiratory mechanics; lung, heart and kidney histology. Results We report preliminary results from one experiment in which a sheep underwent pulmonary artery banding. Across the baseline, permissive hypercapnia, and buffered permissive hypercapnia timepoints, mechanical power was 29, 11, and 14 J/min, respectively. The right ventricular ejection fraction was 37%, 35%, and 42%, while pulmonary vascular resistance was 8.8, 8.2, and 6.3 Wood units. Cardiac output measured 3.5, 4.4, and 4.4 L/min, with corresponding stroke volumes of 36, 37, and 45 mL. Conclusions To the best of our knowledge, this is the first assessment of buffered permissive hypercapnia in a model of RV dysfunction. Preliminary findings indicate that buffering respiratory acidosis improves RV performance and permits ventilation at low mechanical power. 1. Gattinoni L. et al, Intensive Care Med. 2016;42(10):1567-75 This abstract is funded by: The Prince Charles Hospital Foundation
Baccoli et al. (Fri,) studied this question.