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.