Of 154 patients admitted to our ICU with COVID-19 disease, 47 (30.5%) required RRT. Of these, 26 were transferred from other hospitals. Comparison was made against a contemporaneous cohort of consecutive non-COVID-19 critically ill patients who required RRT in ICU during the course of the preceding year. Of the 44 non-COVID-19 patients that required RRT, 8 had end-stage renal disease (ESRD) and were excluded, leaving 36 non-COVID-19 patients in the final analysis. Among non-COVID-19 patients, the primary aetiology of AKI included sepsis (47.2%), hypovolaemia (5.5%), post- major surgery (8.3%), post- cardiac arrest (8.3%) and other causes (30.6%) (Supplementary Table 1).
There were no significant between-group differences in gender, body mass index (BMI), time from hospital admission to ICU admission, and proportions of patients with hypertension and diabetes mellitus (Table 1). Non-COVID-19, patients were older, more likely to have chronic kidney disease (CKD), and had a higher serum creatinine on hospital admission. Censored for patients without CKD, the between-group difference in admission serum creatinine remained significant (Table 1).
A greater proportion of COVID-19 patients with required invasive mechanical ventilation (IMV) (100% vs 75%; p<0.001) and vasopressors (100% vs. 86%); p=0.008). Although time from hospital admission to requiring IMV was similar, the median time from IMV requirement to RRT requirement was a week longer in COVID-19 patients (Table 1).
RRT initiation, clearance, and discontinuation
No inter-group differences were seen in cumulative fluid balance, urine output in the preceding 24 hours, pH, potassium, serum creatinine or urea on initiation of RRT (p>0.05) (Supplementary Table 2). Non-COVID-19 patients had markedly higher values of PaO2:FiO2 ratio, arterial lactate and base deficit, and a lower serum bicarbonate (Figure 1, Supplementary Table 2).
Initiation of RRT achieved significant reductions in daily fluid balance in both groups, with COVID-19 patients achieving a greater net negative fluid balance (Figure 2; Supplementary Table 3). However, despite the reduction in fluid balance, there was no improvement in PaO2:FiO2 ratio in either group (p=0.797), with a persistently lower PaO2:FiO2 ratio in COVID-19 patients (p<0.001). The degree of metabolic acidosis remained significantly less severe in COVID-19 patients despite a lower CVVHF exchange rate, and serum creatinine values remaining higher. The more profound degree of overall acidosis (arterial pH) in COVID-19 patients was related to a respiratory acidosis and therefore remained unchanged following initiation of RRT.
Anticoagulation and thrombosis
The overall incidences of filter clotting and blood transfusion requirements were higher in COVID-19 patients (Supplementary Table 4). All non-COVID-19 patients received citrate regional anticoagulation.
Twenty-seven of the 47 (57%) COVID-19 patients requiring acute RRT were diagnosed with a venous thromboembolic event (VTE), all of whom received therapeutic low molecular weight heparin (LMWH). In addition, seven patients received regional citrate anticoagulation. Of the 20 patients without any evidence of VTE during admission, 17 were initiated on citrate anticoagulation with prophylactic LMWH while 3 patients were initiated on RRT with therapeutic anticoagulation with LMWH without citrate. Nineteen patients switched from regional citrate anticoagulation to systemic LMWH anticoagulation or vice versa depending on citrate availability. The 20 COVID-19 patients without diagnosed VTE had a similar incidence of filter clotting compared to the 27 patients with VTE. There was also no difference in the incidence of circuit clotting between days on citrate and days on LMWH.
Hospital mortality was similar between patients with and without COVID-19 (60% vs. 68%; p=0.508) (Table 2). Among survivors, the duration of RRT, IMV, ICU stay and time from RRT cessation to hospital discharge was greater among COVID-19 patients. On hospital discharge, serum creatinine was significantly lower among patients with COVID-19 (Figure 3), excluding one patient with COVID-19 who was referred for ongoing RRT. Censored for patients without CKD, hospital discharge serum creatinine was comparable to patients without COVID (Table 2).