LAUSR

NEW FINDINGS Several studies report progressive hypoxemia once extracorporeal carbon dioxide removal is started in patients with hypercapnic respiratory failure, possibly due to an altered respiratory quotient. In this quality control report we show that the respiratory quotient is only altered minimally when extracorporeal carbon dioxide removal is started, and that the progressive hypoxemia is rather due to an increase of shunt. ABSTRACT The use of extracorporeal carbon dioxide removal (ECCO2 R) has been proposed in patients with Acute Respiratory Distress Syndrome to achieve lung-protective ventilation and in patients with selective hypercapnic respiratory failure. However, several studies report progressive hypoxemia as expressed by a need to increase the inspired oxygen fraction to maintain adequate oxygenation or by a decrease in PaO2 /FiO2 ratio once ECCO2 R is started. We present a case of a patient who was admitted to the intensive care unit for a COVID-19 pneumonia and was intubated for hypercapnic respiratory insufficiency. ECCO2 R was started and the patient subsequently developed progressive hypoxemia. To test whether the hypoxemia was due to the ECCO2 R blood samples were taken in different settings: A) "no ECCO2 R": blood flow 150 ml/min with a ECCO2 R gas flow of 0 l/min, and B) "with ECCO2 R": blood flow 400 ml/min with gasflow 12 l/min. We measured PaO2 , PA O2 , PaO2 /FiO2 ratio, DA-aO2, PaCO2 and the respiratory quotient by indirect calorimetry in each setting. Respiratory quotient was 0,60 without ECCO2 R and 0,57 with ECCO2 R. The PA O2 was 220,4 mmHg without ECCO2 R and raised to 240,3 mmHg with ECCO2 R and the PaO2 /FiO2 ratio decreased from 177 to 171. Our study showed only a minimal change in respiratory quotient when ECCO2 R was started. We were the first to directly measure the respiratory quotient before and after the initiation of ECCO2 R in a patient with hypercapnic respiratory failure. This article is protected by copyright. All rights reserved.