Continuous Renal Replacement Therapy-
Most ECMO patients were also rapidly started on continuous renal replacement therapy (CRRT) for precise volume management and the potential added benefit of cytokine removal. High flow pre-filter replacement fluid was maintained at 6 liters to remove cytokines through convective clearance. (Table 4) Maintaining a replacement fluid rate at 6 liters required significant nursing time. Attempting to pull CRRT from the ECMO circuit post oxygenator and return to the ECMO circuit post pump/pre-oxygenator created an additional challenge of maintaining high CRRT blood flowrates due to the CRRT return pressure. This was remedied by returning the CRRT circuit blood directly to the venous drainage line (pre-pump) of the ECMO circuit (Figure 4). High flow CRRT was performed under an investigational protocol, as there is a dearth of good evidence that cytokine removal impacts outcomes (13). Due to the prothrombotic nature of the Covid-19 patients, regional citrate anticoagulation was utilized for the CRRT circuits even though all patients were concurrently systemically anticoagulated.
Patients were placed on a regional citrate protocol unless they had evidence of hepatic dysfunction. If the CRRT circuit clotted repeatedly despite therapeutic levels of heparin and citrate, patients were transitioned to the bivalirudin anticoagulation strategy. The indications for CRRT were volume removal or acute kidney injury, and due to the limited supply of replacement fluid, the duration of high flow clearance was truncated for many patients. The levels of inflammatory markers predictably decreased, and CRRT was discontinued in patients with recovering renal function once the excess fluid had been removed or adequate fluid removal was achievable with loop diuretic infusions.