Relative low flow extra corporeal CO2-removal in ards patients: A pilot study

Abstract

Introduction Mechanical ventilation (MV) of patients with Acute Respiratory Distress Syndrome (ARDS) should be performed with a lung protective strategy, since this is associated with better clinical outcomes. Lung protective MV contains the lowering of the plateau pressure (PPLAT) and the tidal volume (VT). Physician’s choice for lung protective MV can be hindered by the consequence of decreased CO2 clearance, i.e. respiratory acidosis. Veno-venous extracorporeal CO2-removal (ECCO2-R) is a recent therapy allowing extracorporeal CO2 clearance and normalisation of pH. Objectives The aim of this pilot study was to evaluate whether ECCO2-R using relative low blood flow was able to treat respiratory acidosis in ARDS patients treated with lung protective MV, so that further reduction of PPLAT and VT was feasible. Methods This is a single centre trial in which patients who met the Berlin definition of ARDS with a PaO2/FiO2 < 150mmHg and who had respiratory acidosis were included. The first 2 hours of therapy blood flow was 300ml/min, after which it was increased to 400ml/min. During the ECCO2-R we aimed at lowering PPLAT and VT. For every patient we used the Abylcap® device (Bellco, Italy) with either the Lynda® machine (8 patients) or the Amplya™ (1 patient). Every patient was heparinized to prevent clotting of the circuit and oxygenator. During the complete study period, ventilator settings and results of blood gases were recorded. Data are reported as median [interquartile range] or n (%). Results We included 9 patients, 4 female, with a median age of 50 y [22.8, 66.5]. All patients showed a decrease of pCO2 after 2 hours of treatment with median reduction of 28.2% [11.6, 31.0; p = 0.008]; five patients (56%) had a decrease in pCO2 of more than 20%. The median reduction in PPLAT after 5 days (D5) of treatment was 8.5cmH2O (5.3, 12.5; p = 0.012). Median reduction in VT at D5 was 1.52ml/kg predicted body weight (0.65, 1.85; p = 0.017). In all patients pH could be corrected to normal range values with an increase of median pH from 7.17 (7.11, 7.21) at inclusion to 7.42 (7.40,7.44) (p = 0.012) at D5. ECCO2-R was hemodynamically well tolerated. Three patients needed a blood transfusion because of bleeding. Two patients needed a circuit renewal earlier than scheduled because of clotting of the circuit or oxygenator, both patients were treated with the Lynda® machine. Conclusions In patients with moderate ARDS, veno-venous ECCO2-R using relative low blood flow is a promising extracorporeal technique allowing removal of CO2, thus allowing MV with lower PPLAT and VT. An explanation for the inter-patient variation in efficiency of CO2 removal could not be found in our patient cohort.