Management of severe ARDS due to SARS-CoV-2 pneumonia using low-flow extracorporeal CO₂ extraction

Extracorporeal CO₂ extraction (ECCO₂R) is a technique that uses an extracorporeal device to extract excess CO₂ from the blood by passing it through an air exchange membrane using low blood flows and requiring systemic anticoagulation for its use. The main technical difference with extracorporeal membrane oxygenation system (ECMO) is the reduced blood flow (between 300 and 500 ml/min), achieving the elimination of most of the CO₂ produced by metabolism, thanks to the greater solubility of this gas in plasma.

This technique emerged from the need to decouple the oxygenation support from the ventilation support provided by ECMO with the main objective of optimising lung protection during mechanical ventilation (MV) [1]. There is currently no strong evidence regarding the benefit provided by the use of ECCO₂R in this clinical context [2].

We present a series of 8 cases of patients with severe global respiratory failure due to COVID-19, admitted in ICU between December 2020 and May 2021. Regarding patients’ characteristics, we highlight mean values of ICU stay of 45.8 days (± standard deviation 15.8), PaFi of 75.1 (± 10.4) and pH 7.25 (± 0.03), despite endotracheal intubation (ETI) and protective MV with Pplat 29.1 (± 1.61). Prone position was necessary in all cases, both before and after ECCO₂R placement. The mean number of days in prone position prior to ECCO₂R was 3.75 days (± 1.08). Mean number of days from the start of ETI to the start of ECCO₂R was 14.5 days, PaO2/FiO2 of 75.1 and SOFA score 6.6. Transfer to ECMO was not possible in any of the 8 cases, following to the current recommendations of the receiving centres [3].

All cases had positive SARS-CoV-2 polymerase-chain-reaction detection and severe respiratory failure without severe dysfunction of other organs or documented infections.

During ICU admission, selected patients presented persistent hypoxaemia and hypercapnia refractory to lung protective measures (TV 6–8 ml/kg, Pplat < 30) and proning. ECCO₂R support was considered then, preserving the level of lung protection and correcting the expected deterioration of ventilation with worsening respiratory acidosis obtained after achieving an increase in PEEP. Our objectives were also to decrease Pplat in a range of less than 28, to decrease respiratory rate under 25 bpm and to decrease TV (under 7 ml/kg).

Table 1 shows the respiratory status prior to initiation of therapy, and Table 2 shows the results obtained 12–24 h after initiation of the ECCO₂R.

Table 1 Characteristics

Table 2 Data before and after 24-h initiating ECCO₂R

The therapeutic objectives of ProLUNG® (blood flow 400 ml/min and air flow 15 L/min), with a rise in pH (7.32–7.35), were achieved in the first 12 h of treatment. Results are shown in Table 2. Regarding technical complications, thrombocytopenia not induced by heparin was observed in one of the cases, requiring withdrawal of treatment after 5 days.

Regarding the outcome data on the ECCO₂R device, the mean duration of therapy was 5.25 days, with a mean blood flow of 400 ml/min and air flow of 12 lpm. Fifty percentage of the patients survived, with an ICU discharge of 25 days (average value) after disconnection from the ECCO₂R. Case number 8 died within a day after removal of the CO₂ extractor.

These cases, as in previous studies, show us the possible usefulness of applying ECCO₂R based on individual clinical and physiological criteria [4], without development of serious complications, although other known published series report relevant complications [5].

ECCO₂R system could be applied as a tool to optimise the degree of lung protection, essential in patients with severe ARDS. In our experience, ECCO₂R is a simple and feasible therapeutic option for patients with severe respiratory diseases in whom conventional treatment has been maximised. Further studies are needed to strengthen the scientific evidence in this context [6].