Current status of dosing and quantification of acute renal replacement therapy. Part 1: mechanisms and consequences of therapy under-delivery

Clinical outcomes and prognostic factors of mortality in liver cirrhosis patients on continuous renal replacement therapy in two tertiary hospitals in Korea

Background

Data on liver cirrhosis (LC) patients undergoing continuous renal replacement therapy (CRRT) are lacking despite of the dismal prognosis. We therefore evaluated clinical characteristics and predictive factors related to mortality in LC patients undergoing CRRT.

Methods

We performed a retrospective observational study at two tertiary hospitals in Korea. A total of 229 LC patients who underwent CRRT were analyzed. Patients were classified into survivor and non-survivor groups. We used multivariable Cox regression analyses to identify predictive factors of in-hospital mortality.

Results

During a median follow-up of 5 days (interquartile range, 1-19 days), in-hospital mortality rate was 66.4%. In multivariable analysis, the Acute Physiology and Chronic Health Evaluation II (APACHE II) score (hazard ratio [HR], 1.03; 95% confidence interval [CI], 1.01-1.06; p = 0.02), Model for End-Stage Liver Disease (MELD) score (HR, 1.08; 95% CI, 1.04-1.11; p > 0.001), and delivered CRRT dose (HR, 0.95; 95% CI, 0.92-0.98; p = 0.002) were significant risk factors for in-hospital mortality. Patients with a CRRT delivered dose < 25 mL/kg/hr had a higher mortality rate than those with a delivered dose > 35 mL/kg/hr (HR, 3.13; 95% CI, 1.62-6.05; p = 0.001). Subgroup analysis revealed that a CRRT delivered dose > 25 mL/kg/hr was a significant risk factor for in-hospital mortality among LC patients with a MELD score ≥ 30.

Conclusion

High APACHE II score, high MELD score, and low delivered CRRT dose were significant risk factors for in-hospital mortality. CRRT delivered dose impacted mortality significantly, especially in patients with a MELD score ≥ 30.

Dose of Continuous Renal Replacement Therapy in Critically Ill Patients: A Bona Fide Quality Indicator

Acute kidney injury (AKI) is common in critically ill patients, and renal replacement therapy (RRT) constitutes an important aspect of acute management during critical illness. Continuous RRT (CRRT) is frequently utilized in intensive care unit settings, particularly in patients with severe AKI, fluid overload, and hemodynamic instability. The main goal of CRRT is to timely optimize solute control, acid-base, and volume status. Total effluent dose of CRRT is a deliverable that depends on multiple factors and therefore should be systematically monitored (prescribed vs. delivered) and iteratively adjusted in a sustainable mode. In this manuscript, we review current evidence of CRRT dosing and provide recommendations for its implementation as a quality indicator of CRRT delivery.

Elimination of fluconazole during continuous renal replacement therapy. An in vitro assessment

Introduction:

Continuous renal replacement therapy (CRRT) efficiently eliminates fluconazole. However, the routes of elimination were not clarified. Adsorption of fluconazole by filters is a pending question. We studied the elimination of fluconazole in a model mimicking a session of CRRT in humans using the NeckEpur® model. Two filters were studied.

Methods:

The AV1000®-polysulfone filter with the Multifiltrate Pro. Fresenius and the ST150®-polyacrylonitrile filter with the Prismaflex. Baxter-Gambro were studied. Continuous filtration used a flowrate of 2.5 L/h in post-dilution only. Session were made in duplicate. Routes of elimination were assessed using the NeckEpur® model.

Results:

The mean measured initial fluconazole concentration (mean ± SD) for the four sessions in the central compartment (CC) was 14.9 ± 0.2 mg/L. The amount eliminated from the CC at the end of 6 h-session at a 2.5 L/h filtration flowrate for the AV1000®-polysulfone and the ST150®-polyacrylonitrile filters were 90%–93% and 96%–94%, respectively; the clearances from the central compartment (CC) were 2.5–2.6 and 2.4–2.3 L/h, respectively. The means of the instantaneous sieving coefficient were 0.94%–0.91% and 0.99%–0.91%, respectively. The percentages of the amount eliminated from the CC by filtration/adsorption were 100/0%–95/5% and 100/0%–100/0%, respectively.

Conclusion:

Neither the ST150®-polyacrylonitrile nor the AV1000®-polysulfone filters result in any significant adsorption of fluconazole.

Anticoagulation, delivered dose and outcomes in CRRT: The program to improve care in acute renal disease (PICARD)

Delivered dialysis dose by continuous renal replacement therapies (CRRT) depends on circuit efficacy, which is influenced in part by the anticoagulation strategy. We evaluated the association of anticoagulation strategy used on solute clearance efficacy, circuit longevity, bleeding complications, and mortality. We analyzed data from 1740 sessions 24 h in length among 244 critically ill patients, with at least 48 h on CRRT. Regional citrate, heparin, or saline flushes was variably used to prevent or attenuate filter clotting. We calculated delivered dose using the standardized Kt/Vurea . We monitored filter efficacy by calculating effluent urea nitrogen/blood urea nitrogen ratios. Filter longevity was significantly higher with citrate (median 48, interquartile range [IQR] 20.3-75.0 hours) than with heparin (5.9, IQR 8.5-27.0 hours) or no anticoagulation (17.5, IQR 9.5-32 hours, P < 0.0001). Delivered dose was highest in treatments where citrate was employed. Bleeding complications were similar across the three groups (P = 0.25). Compared with no anticoagulation, odds of death was higher with the heparin use (odds ratio [OR] 1.82, 95% confidence interval [CI] 1.02-3.32; P = 0.033), but not with citrate (OR 1.02 95% CI 0.54-1.96; P = 0.53). Relative to heparin or no anticoagulation, the use of regional citrate for anticoagulation in CRRT was associated with significantly prolonged filter life and increased filter efficacy with respect to delivered dialysis dose. Rates of bleeding complications, transfusions, and mortality were similar across the three groups. While these and other data suggest that citrate anticoagulation may offer superior technical performance than heparin or no anticoagulation, adequately powered clinical trials comparing alternative anticoagulation strategies should be performed to evaluate overall safety and efficacy.

Actually delivered dose of continuous renal replacement therapy is underestimated in hemofiltration

Dose determination in continuous renal replacement therapy (CRRT) is controversial. Most clinical trials use effluent flow rate as a surrogate of the dose. However, such definition may overestimate actually delivered dose due to declining filter function. The current study aimed to determine the difference between prescribed and delivered clearance and its association with transmembrane pressure. Hemofiltration was done in a mixed pre- and postdilution mode. Creatinine concentrations in serum and effluent fluid were measured simultaneously at 4, 10, 16, 28, 40, 52, and 64 hours for an individual hemofilter. Prescribed clearance (K) was estimated as the effluent flow rate corrected for predilution, and delivered clearance (Kx) was estimated using the ratio of serum and effluent creatinine. A total of 60 patients involving 248 filters were included in our analysis. The mean filter life span was 37.7 hours (standard deviation: 17.6). K overestimated Kx by 9.3% (95% confidence interval: -4.4% to 32.3%). The differences between K and Kx increased progressively over time. Transmembrane pressure was significantly correlated to the reduction with a Spearman's rho of 0.44 (p < 0.001). K significantly overestimates Kx during CRRT, and the difference increases progressively over time. Filters are recommended to be changed at 48-72 hours on a routine basis.

Toward the optimal dose metric in continuous renal replacement therapy

PURPOSE

There is no consensus on the optimal method to measure delivered dialysis dose in patients with acute kidney injury (AKI). The use of direct dialysate-side quantification of dose in preference to the use of formal blood-based urea kinetic modeling and simplified blood urea nitrogen (BUN) methods has been recommended for dose assessment in critically-ill patients with AKI. We evaluate six different blood-side and dialysate-side methods for dose quantification.

METHODS

We examined data from 52 critically-ill patients with AKI requiring dialysis. All patients were treated with pre-dilution CVVHDF and regional citrate anticoagulation. Delivered dose was calculated using blood-side and dialysis-side kinetics. Filter function was assessed during the entire course of therapy by calculating BUN to dialysis fluid urea nitrogen (FUN) ratios q/12 hours.

RESULTS

Median daily treatment time was 1,413 min (1,260-1,440). The median observed effluent volume per treatment was 2,355 mL/h (2,060-2,863) (p<0.001). Urea mass removal rate was 13.0 ± 7.6 mg/min. Both EKR (r²=0.250; p<0.001) and KD (r²=0.409; p<0.001) showed a good correlation with actual solute removal. EKR and KD presented a decline in their values that was related to the decrease in filter function assessed by the FUN/BUN ratio.

CONCLUSIONS

Effluent rate (mL/kg/h) can only empirically provide an estimated of dose in CRRT. For clinical practice, we recommend that the delivered dose should be measured and expressed as KD. EKR also constitutes a good method for dose comparisons over time and across modalities.

Effluent volume and dialysis dose in CRRT: time for reappraisal

The results of several studies assessing dialysis dose have dampened the enthusiasm of clinicians for considering dialysis dose as a modifiable factor influencing outcomes in patients with acute kidney injury. Powerful evidence from two large, multicenter trials indicates that increasing the dialysis dose, measured as hourly effluent volume, has no benefit in continuous renal replacement therapy (CRRT). However, some important operational characteristics that affect delivered dose were not evaluated. Effluent volume does not correspond to the actual delivered dose, as a decline in filter efficacy reduces solute removal during therapy. We believe that providing accurate parameters of delivered dose could improve the delivery of a prescribed dose and refine the assessment of the effect of dose on outcomes in critically ill patients treated with CRRT.

Solute clearance in CRRT: prescribed dose versus actual delivered dose

BACKGROUND

Substantial efforts have been made toward defining the dose threshold of continuous renal replacement therapy (CRRT) associated with improved survival in critically ill patients with acute kidney injury. Published studies have used prescribed effluent rates, expressed as total effluent volume (TEV) per weight and unit time (mL/kg/h), as a surrogate for dose. The purpose of this study was to compare differences in CRRT dose based on prescribed effluent rate, measured TEV and direct measurement of urea and creatinine clearance.

METHODS

We analyzed data that had been prospectively collected on 200 patients enrolled in a randomized trial comparing survival with a prescribed effluent rate of 20 mL/kg/h (standard dose) to 35 mL/kg/h (high dose) using pre-dilution continuous venovenous hemodiafiltration (CVVHDF). Filters were changed every 72 h. Blood urea nitrogen (BUN), serum creatinine (SCr), effluent urea nitrogen (EUN) and effluent creatinine (ECr) were collected daily. Actual delivered dose was calculated as: (EUN/BUN)*TEV for urea and (ECr/SCr)*TEV for creatinine. Data were available for 165 patients.

RESULTS

In both groups, prescribed dose differed significantly from the measured TEV dose (P < 0.001). In the standard dose group, there was no difference between the measured TEV dose and actual delivered urea and creatinine clearances. However, in the high-dose group, measured TEV dose differed significantly from delivered urea clearance by 7.1% (P < 0.001) and creatinine clearance by 13.9% (P < 0.001).

CONCLUSIONS

Dose based on prescribed effluent rate or measured TEV is a poor substitute for actual CVVHDF creatinine and urea clearance.

Assessing and delivering dialysis dose in acute kidney injury

Assessing and delivering dialysis dose in acute kidney injury (AKI) has emerged as an important issue in the management of critically ill patients. There is ongoing debate on how dose of dialysis should be expressed and measured. Most studies have focused on clearance of small molecules (blood urea nitrogen) as a marker of delivered dose and for establishing dose-outcome relationships. Recent evidence has shown that other markers may also be important to consider, as acid-base balance and fluid overload have emerged as important factors contributing to outcomes. In this review, we provide an evaluation of current approaches to prescribing and delivering dialysis dose in AKI, identify gaps in practice and propose an integrated approach to optimize dose delivery in dialysis with a goal to improve outcomes.

Effluent volume in continuous renal replacement therapy overestimates the delivered dose of dialysis

BACKGROUND AND OBJECTIVES

Studies examining dose of continuous renal replacement therapy (CRRT) and outcomes have yielded conflicting results. Most studies considered the prescribed dose as the effluent rate represented by ml/kg per hour and reported this volume as a surrogate of solute removal. Because filter fouling can reduce the efficacy of solute clearance, the actual delivered dose may be substantially lower than the observed effluent rate.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

Data were examined from 52 critically ill patients with acute kidney injury (AKI) requiring dialysis. All patients were treated with predilution continuous venovenous hemodiafiltration (CVVHDF) and regional citrate anticoagulation. Filter performance was monitored during the entire course of therapy by measuring blood urea nitrogen (BUN) and dialysis fluid urea nitrogen (FUN) at initiation and every 12 hours. Filter efficacy was assessed by calculating FUN/BUN ratios every 12 hours of filter use. Prescribed urea clearance (K, ml/min) was determined from the effluent rate. Actual delivered urea clearance was determined using dialysis-side measurements.

RESULTS

Median daily treatment time was 1413 minutes (1260 to 1440) with a total effluent volume of 46.4 ± 17.4 L and urea mass removal of 13.0 ± 7.6 mg/min. Prescribed clearance overestimated the actual delivered clearance by 23.8%. This gap between prescribed and delivered clearance was related to the decrease in filter function assessed by the FUN/BUN ratio.

CONCLUSIONS

Effluent volume significantly overestimates delivered dose of small solutes in CRRT. To assess adequacy of CRRT, solute clearance should be measured rather than estimated by the effluent volume.

Disease severity adversely affects delivery of dialysis in acute renal failure

BACKGROUND/AIMS

Methods of intermittent hemodialysis (IHD) dose quantification in acute renal failure (ARF) are not well defined. This observational study was designed to evaluate the impact of disease activity on delivered single pool Kt/V(urea) in ARF patients.

METHODS

100 patients with severe ARF (acute intrinsic renal disease in 18 patients, nephrotoxic acute tubular necrosis in 38 patients, and septic ARF in 44 patients) were analyzed during four consecutive sessions of IHD, performed for 3.5-5 h every other day or daily. Target IHD dose was a single pool Kt/V(urea) of 1.2 or more per dialysis session for all patients. Prescribed Kt/V(urea) was calculated from desired dialyzer clearance (K), desired treatment time (t) and anthropometric estimates for urea distribution volume (V). The desired clearance (K) was estimated from prescribed blood flow rate and manufacturer's charts of in vivo data obtained in maintenance dialysis patients. Delivered single pool Kt/V(urea) was calculated using the Daugirdas equation.

RESULTS

None of the patients had prescription failure of the target dose. The delivered IHD doses were substantially lower than the prescribed Kt/V values, particularly in ARF patients with sepsis/septic shock. Stratification according to disease severity revealed that all patients with isolated ARF, but none with 3 or more organ failures and none who needed vasopressive support received the target dose.

CONCLUSION

Prescription of target IHD dose by single pool Kt/V(urea) resulted in suboptimal dialysis dose delivery in critically ill patients. Numerous patient-related and treatment-immanent factors acting in concert reduced the delivered dose.