Support with veno-venous extracorporeal membrane oxygenation (VV-ECMO) can be considered for patients with severe (combined) hypoxemia and hypercapnia. By adjusting sweep gas flow (SGF), blood oxygenation and correction of partial pressure of arterial carbon dioxide (PaCO2) can be achieved instantly (1), which enables lung protective ventilation. Although VV-ECMO has been shown to improve outcomes in acute respiratory distress syndrome (ARDS) (2), severe morbidity and mortality remain high (3). One contributing factor may be the deleterious effect of instantaneous and large magnitude PaCO2-correction during the initiation of VV-ECMO, as it has been associated with neurological complications (4).
Physiologically, PaCO2-removal raises cerebrospinal fluid (CSF) pH (4), causing contraction of perivascular smooth muscle cells and decreased cerebral blood flow (CBF). However, in longstanding respiratory acidosis, CBF would have partially
normalized together with CSF pH due to metabolic compensation, despite persisting hypercapnia. In these instances, rapidly correcting PaCO2, while disregarding pH, could result in the overcorrection of otherwise near-normal CBF, which might be detrimental for the brain.
This study aims to explore whether arterial pH is a better predictor of changes in CBFV, than PaCO2, and potentially useful as guide for managing CBF during the initiation of VV-ECMO. Therefore, we monitored changes in cerebral blood flow velocity (CBFV), as surrogate of CBF, in relation to the correction of arterial pH and PaCO2 during the initiation of VV-ECMO.