Combined extracorporeal CO2 removal and renal replacement therapy in a pregnant patient with COVID-19: a case report


Background. Pregnant women are at high risk of Coronavirus disease 2019 (COVID-19) complications, including acute respiratory distress syndrome. Currently, one of the cornerstones in the treatment of this condition is lung-protective ventilation (LPV) with low tidal volumes. However, the occurrence of hypercapnia may limit this ventilatory strategy. So, different extracorporeal CO2 removal (ECCO2R) procedures have been developed. ECCO2R comprises a variety of techniques, including low-flow and high-flow systems, that may be performed with dedicated devices or combined with continuous renal replacement therapy (CRRT).
Case description. Here, we report a unique case of a pregnant patient affected by COVID-19 who required extracorporeal support for multiorgan failure. While on LPV, because of the concomitant hypercapnia and acute kidney injury, the patient was treated with an ECCO2R membrane inserted in series after a hemofilter in a CRRT platform. This combined treatment reducing hypercapnia allowed LPV maintenance at the same time while providing kidney replacement and ensuring maternal and fetal hemodynamic stability. Adverse effects consisted of minor bleeding episodes due to the anticoagulation required to maintain the extracorporeal circuit patency. The patient’s pulmonary and kidney function progressively recovered, permitting the withdrawal of any extracorporeal treatment. At the 25th gestational week, the patient underwent spontaneous premature vaginal delivery because of placental abruption. She gave birth to an 800-gram female baby, who three days later died because of multiorgan failure related to extreme prematurity.
Conclusions. This case supports using ECCO2R-CRRT combined treatment as a suitable approach in the management of complex conditions, such as pregnancy, even in the case of severe COVID-19.

Keywords: pregnancy, COVID-19, lung-protective ventilation, hypercapnia, CO2 removal, acute kidney injury, continuous renal replacement therapy


Pulmonary involvement in Coronavirus disease 2019 (COVID-19) is highly heterogeneous, with clinical presentation ranging from asymptomatic forms to acute respiratory distress syndrome (ARDS) [1]. This heterogenicity may be explained by demographic factors, history of comorbidities, distinctive genetic background, and pharmacological treatments [2].

Among the different populations of COVID-19 patients, pregnant women deserve specific attention. Indeed, these patients, due to immunological and cardiorespiratory changes occurring in pregnancy, are at risk of the more severe complications of the disease, including ARDS [3, 4].

Most patients with ARDS require mechanical ventilation (MV), and in some cases also extracorporeal respiratory support (ECLS) [5].

These therapies encompass extracorporeal membrane oxygenation (ECMO) and the extracorporeal carbon dioxide removal system (ECCO2R). Briefly, ECMO takes over the gas exchange function of the lungs ensuring full oxygenation and CO2 removal, while ECCO2R is a CO2 removal system that does not affect oxygenation, and whose principal aim is consenting to lung protection (Table 1). 

La visualizzazione dell’intero documento è riservata a Soci attivi, devi essere registrato e aver eseguito la Login con utente e password.

Acetate-free Biofiltration: CO2-free treatment for hemodialysis patients with hypercapnia


In bicarbonate-dialysis the dialysate is acid, thus allowing salts to remain in their soluble form, as a result of the chemical reaction of bicarbonate with any acid that yields carbon dioxide (CO2). The residual anion, commonly acetate or more rarely citrate, reaches the patients’ bloodstream. CO2 also spreads to the patients and ventilation needs therefore to be increased to avoid hypercapnia. In addition, during on-line haemodiafiltration in post-dilution mode, the dialysate – in the form of infusate – carries CO2 (and acetate) to the patient, bypassing the filtering membrane. On the contrary, in Acetate-Free Biofiltration (AFB) the dialysate is free of acid and, uniquely, is also a CO2-free bath. Despite the infusion of bicarbonate in post-dilution mode, the blood coming back from the extracorporeal circuit does not carry any burden of CO2. As a result, AFB is the recommended renal replacement therapy for patients affected by lung disease and those with CO2 retention (respiratory acidosis). Patients with some degree of ventilatory dysfunction may in fact experience acute hypercapnia (acidosis by dialysate) at the beginning of the treatment if bicarbonate-dialysis or on-line HDF is performed (and regardless of whether acetate-containing or citrate-containing bath is employed). Acidosis by dialysate is characterized by respiratory symptoms first and by haemodynamic instability later, which make it look very similar to acetate intolerance. To discriminate between these two conditions, blood gas analysis is mandatory. The presence of hypercapnia can be revealed by using the Very Simple Formula (expected pCO2 = bicarbonate + 15), thus identifying those patients that may take the most advantage of AFB.


KEYWORDS: acetate-free biofiltration, carbon dioxide, hypercapnia

Sorry, this entry is only available in Italian.

Dalla acetato-dialisi alla dialisi acetato-free

All’inizio degli anni ’80 venne proposta, quale alternativa alla predominante acetato-dialisi, una nuova tecnica dialitica, chiamata acetate-free biofiltration (AFB), caratterizzata da un dialisato completamente privo di tamponi [13]. Grandi quantità di acetato (>30 mmol/L) rendevano mal tollerati i trattamenti ma la sostituzione di questo tampone con il bicarbonato, oltre ad essere tecnicamente complessa, comportava la precipitazione di sali di calcio e di magnesio ed aumentava il rischio di contaminazione batterica. 

La visualizzazione dell’intero documento è riservata a Soci attivi, devi essere registrato e aver eseguito la Login con utente e password.