Estimation of renal function immediately after cessation of continuous renal replacement therapy at the ICU

Estimating glomerular filtration (eGFR) after Continuous Renal Replacement Therapy (CRRT) is important to guide drug dosing and to assess the need to re-initiate CRRT. Standard eGFR equations cannot be applied as these patients neither have steady-state serum creatinine concentration nor average muscle mass. In this study we evaluate the combination of dynamic renal function with CT-scan based correction for aberrant muscle mass to estimate renal function immediately after CRRT cessation. We prospectively included 31 patients admitted to an academic intensive care unit (ICU) with a total of 37 CRRT cessations and measured serum creatinine before cessation (T1), directly (T2) and 5 h (T3) after cessation and the following two days when eGFR stabilized (T4, T5). We used the dynamic creatinine clearance calculation (D3C) equation to calculate eGFR (D3C_GFR) and creatinine clearance (D3C_creat) between T2-T3. D3C_creat was corrected for aberrant muscle mass when a CT-scan was available using the CRAFT equation. We compared D3C_GFR to stabilized CKD-EPI at T5 and D3C_Creat to 4-h urinary creatinine clearance (4-h uCrCl) between T2-T3. We retrospectively validated these results in a larger retrospective cohort (NICE database; 1856 patients, 2064 cessations). The D3C_GFR was comparable to observed stabilized CKD-EPI at T5 in the prospective cohort (MPE = - 1.6 ml/min/1.73 m², p30 = 76%) and in the retrospective NICE-database (MPE = 3.2 ml/min/1.73 m², p30 = 80%). In the prospective cohort, the D3C_Creat had poor accuracy compared to 4-h uCrCl (MPE = 17 ml/min/1.73 m², p30 = 24%). In a subset of patients (n = 13) where CT-scans were available, combination of CRAFT and D3C_Creat improved bias and accuracy (MPE = 8 ml/min/1.73 m², RMSE = 18 ml/min/1.73 m²) versus D3C_Creat alone (MPE = 18 ml/min/1.73 m², RMSE = 32 ml/min/1.73 m²). The D3C_GFR improves assessment of eGFR in ICU patients immediately after CRRT cessation. Although the D3C_Creat had poor association with underlying creatinine clearance, inclusion of CT derived biometric parameters in the dynamic renal function algorithm further improved the performance, stressing the role of muscle mass integration into renal function equations in critically ill patients.