Renal Replacement Therapy

Critical Care Research and Practice Volume 2019, Article ID 6948710, 11 pages

Review Article

in the Critical Care Setting Adeel Rafi Ahmed ,1 Ayanfeoluwa Obilana,2 and David Lappin3

1MB BCh BAO MRCPI MRCP(UK) PGDip (ClinEd), Holder of European Certificate in Nephrology, University Hospital Galway, Galway, Ireland

2MB BCh BAO MRCPI, Specialist Registrar in Nephrology, University Hospital Galway, Galway, Ireland 3MB BCh FRCPI PhD (NUI), Consultant Nephrologist, University Hospital Galway, Galway, Ireland

Correspondence should be addressed to Adeel Rafi Ahmed;

Received 30 March 2019; Accepted 29 May 2019; Published 16 July 2019

Academic Editor: Timothy E. Albertson

Copyright © 2019 Adeel Rafi Ahmed et al. is is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Renal replacement therapy (RRT) is frequently required to manage critically ill patients with acute kidney injury (AKI). ere is limited evidence to support the current practice of RRT in intensive care units (ICUs). Recently published randomized control trials (RCTs) have further questioned our understanding of RRT in critical care. e optimal timing and dosing continues to be debatable; however, current evidence suggests delayed strategy with less intensive dosing when utilising RRT. Various modes of RRT are complementary to each other with no definite benefits to mortality or renal function preservation. Choice of anti- coagulation remains regional citrate anticoagulation in continuous renal replacement therapy (CRRT) with lower bleeding risk when compared with heparin. RRT can be used to support resistant cardiac failure, but evolving therapies such as haemoperfusion are currently not recommended in sepsis.

1. Introduction

Acute kidney injury (AKI) has a significant association with high mortality in critically ill patients [1]. Acute renal re- placement therapy (RRT) provides supportive management for patients with severe AKI and multiorgan failure (MOF). Continuous renal replacement therapy (CRRT), in partic- ular, is utilised for a haemodynamically unstable patient with AKI in an intensive care unit (ICU) setting. is is the standard practice in most ICUs’ in the United Kingdom (UK) and the Republic of Ireland [2]. However, limited consensus exists regarding RRT timing, optimum dosing, modality, and therapeutic efficacy beyond AKI management. In light of emerging data, we look to provide an evidence- based review to address these issues.

2. Timing of RRT

e timing of initiating RRT in critically ill patients with AKI, in the absence of absolute indications, is challenging [3]. ere is a general trend to initiate RRT before a patient develops absolute indications in the ICU setting (Table 1)

[4, 5]. is trend is mostly driven by observational data suggesting that relatively earlier initiation of RRT is asso- ciated with decreased mortality [6–8]. e primary limita- tion is the definition of “early” and “delayed” with investigators using a variety of parameters including bio- chemical markers, like blood urea nitrogen (BUN) and creatinine; clinical markers, like urine output and fluid balance; and the time from onset of developing AKI [9–12].

2.1. Observational Data. Data from the Program to Improve Care in Acute Renal Disease (PICARD) trial, a multicentre observational study of AKI, showed that of the patients who required RRT with no previous chronic kidney disease (CKD), initiation at a lower BUN ≤ 76 mg/dL compared to ≥76mg/dL was associated with lower 14- and 28-day mortality [11, 13]. In another study, investigators used retrospective data to assess a cohort of 130 septic shock patients who required RRT with BUN < 100 mg/dL defined as early RRT and BUN ≥ 100 mg/dL as delayed RRT [14]. e early RRT group had significantly lower mortality at 14, 28, and 365 days compared to delayed RRT.

2 Critical Care Research and Practice

Table 1: Conventional indications for renal replacement therapy.

1.1. Fluid overload resistant to diuretic therapy
1.2. Metabolic acidosis (pH < 7.15) refractory to medical management
1.3. Hyperkalaemia (K > 6.5 mEq/L) refractory to medical management
1.4. Uraemic symptoms or signs (encephalopathy, pericarditis, and bleeding diathesis) Other important indications for RRT
1.5. Poisoning with a dialyzable drug or toxin
1.6. Hyperthermia refractory to regular cooling techniques
1.7. Life-threatening electrolyte derangements in the setting of acute kidney injury 1.8. Progressive azotaemia or oliguria unresponsive to medical management


Observational data examining patients with AKI post cardiac surgery have demonstrated survival benefits with earlier initiation of RRT [10, 12, 15]. Two of the studies used reduced urine output (<100 mL within 8 hours consecutively after surgery, despite furosemide administration) as their criterion for early initiation of CRRT. e attainment of specified BUN, serum creatinine, or potassium thresholds was the trigger for delayed commencement of therapy. e first of these studies examined the outcomes of 64 patients with a high baseline prevalence of class 3 or 4 heart failure and chronic kidney disease (CKD). It reported a survival rate of 78% in the early initiation group, compared with 57% in the delayed initiation group (P < 0.05) [10]. e early ini- tiation group was also found to have had a significantly shorter ICU stay (12.5 versus 8.5 days; P < 0.05), shorter hospital stay (20.9 versus 15.4 days; P < 0.05), and lower rate of multiorgan failure (MOF) (19% versus 29%; P < 0.01). e second study, a retrospective analysis of post-CABG AKI using a historical control group, again showed significantly improved survival (77% versus 45%; P < 0.016), shorter length of ICU stay (12 versus 8 days; P < 0.0001), and shorter length of hospital stay (30 versus 15days) in the early treatment group (12).

e subgroup analysis of Finnish Acute Kidney Injury study (FINNAKI) compared early RRT with RRT once absolute indication(s) occurred [16]. Initiation of RRT, once an absolute indication had developed (delayed initiation), was associated with higher 90-day mortality compared to early RRT.

Observational data regarding innate renal function re- covery based on the timing of initiation of RRT are highly variable with some suggesting no association [17].

2.2. Randomized Control Trial (RCTs). ree RCTs focusing on AKI post cardiopulmonary bypass looked to determine the ideal timing of initiating RRT [18–20]. All the studies were underpowered with a small sample size. In the largest of these with 106 participants, early RRT group was defined as urine output <30 ml/hr for 6 hrs or creatinine clearance <20ml/min and the delayed RRT group when absolute indications develop. No significant difference in 28-day mortality was noted [20].

An Indian RCT involving 208 patients with primarily tropical infections or obstetric complications-related AKI, compared early RRT group (defined as BUN > 70 mg/dL (>23 mmol/L) or serum creatinine > 7 mg/dL (619 micromoles/ l) to delayed RRT (defined as absolute indications) [21]. e

trial included a relatively young population with a mean age of 42years. No significant difference in mortality or renal re- covery was noted.

A Canadian study randomized 101 patients with AKI secondary to hypovolemia or sepsis with urine output <6 ml/kg for 12 hours and serum neutrophil gelatinase- associated lipocalin (NGAL) > 400 ng/mL to early or delayed RRT [22]. e early RRT group was initiated within 12 hours of randomization, while the delayed RRT group was initiated when one of the following indications de- veloped: serum potassium >6 mEq/L, serum bicarbonate <10 mEq/L, or PaO2/FIO2 <200 with evidence of pulmo- nary oedema. All 48 patients assigned to the early group initiated RRT within 12 hours of randomization. irty- three (63%) of 52 patients assigned to the delayed group required RRT, while 25% recovered renal function without the need for any dialysis. ere was no significant differ- ence in mortality or renal outcomes between the early and delayed groups.

e Early Versus Late Initiation of Renal Replacement erapy In Critically Ill Patients With Acute Kidney Injury (ELAIN) trial was a single-centre randomized trial of 231 critically ill patients that tested whether early RRT com- pared to delayed RRT would reduce all-cause mortality at 90 days [23]. Early RRT was defined as starting RRT within 8 hours of fulfilling KDIGO stage 2 AKI and delayed RRT defined as starting RRT within 12 hours of the develop- ment of KDIGO stage 3 AKI or upon an absolute in- dication developing. Ninety-four percent of the participants were postoperative of which 46% were post cardiac surgery. All patients in the early group received RRT, as did 91% of patients in the delayed RRT group. e median difference in time to RRT initiation from ran- domization between the 2 interventions was 21 hours. All patients received continuous veno-venous haemodiafil- tration (CVVHDF). e primary outcome showed an absolute reduction in 90-day mortality of 15.4% in the early RRT group (39.3%) compared to the delayed RRT (54.7%). Early RRT also led to a higher likelihood of di- alysis independence, significantly shorter duration of RRT (9 vs. 25days), and shortening of hospital stay (51 vs. 82 days). However, the study had a low fragility index of 3, which meant 3 additional deaths in the early group would have made the mortality difference insignificant. A po- tential for patient selection, inclusion, and treatment bias exists due to its single centre design.

Initiation Strategies for Renal-Replacement erapy in the Intensive Care Unit (AKIKI) trial was a large multicentre

Critical Care Research and Practice


randomized trial of 620 critically ill patients that tested whether delayed RRT compared to early RRT would reduce all-cause 60-day mortality [24]. It involved 31 ICUs from France. Delayed RRT was defined as an absolute indication developing and early RRT as starting RRT within 6 hours of fulfilling KDIGO stage 3 AKI. All the participants were on mechanical ventilation and/or vasopressor support, the majority of whom had septic shock. Ninety-eight percent received RRT in the early group compared to 51% in the delayed group. e median difference in initiating RRT was 57 hrs. e main mode of RRT was intermittent haemo- dialysis (IHD). e primary outcome showed no significant difference in 60-day mortality between early RRT (48.5%) vs delayed RRT (49.7%). In delayed RRT, the number of RRT- free days was greater (19 vs. 17 days), and the occurrence of catheter-related bloodstream infections was lower (5% vs. 10%), compared with the early strategy. ere was no dif- ference in key secondary outcomes including ventilator and vasopressor-free days through day 28, ICU length of stay, hospital length of stay, and dialysis dependence at day 60.

Although AKIKI and ELAIN are the two largest RCTs examining the effect of RRT timing, they were still un- derpowered to detect significant mortality differences between different RRT initiating strategies. ere were some key dif- ferences between the two RCTs, which led to the opposing outcomes. e delayed RRT intervention of ELAIN was similar to the early RRT of AKIKI (AKI KDIGO 3). e ELAIN trial primarily had postoperative patients (94%) with AKI, com- pared to predominantly medical patients with septic shock in AKIKI. e mode of RRT differed as well with CVVHDF used in ELAIN compared to mainly IHD in AKIKI.

e recently published Timing of Renal-Replacement erapy in Patients with Acute Kidney Injury and Sepsis (IDEAL-ICU) trial, a multicentre RCT involving 488 septic patients, found no significant difference in 90-day mortality between early RRT (<12 hrs of Failure stage of RIFLE criteria, comparative to KDIGO stage 3) and delayed RRT (>48 hrs of Failure stage of RIFLE criteria) [25]. IHD was initially used as a mode of RRT in 45% of patients. Median time to RRT in the early compared to the delayed strategy group was 7.6 hrs and 51.5 hrs, respectively. Patients requiring urgent RRT at time of AKI diagnosis were excluded. Twenty-one percent did not require RRT with delayed RRT strategy due to native renal function recovery; however, a higher rate of severe electrolyte abnormalities was noted. e trial was terminated early by the safety monitoring board on the basis of futility, as around 9500 participants per group would have been required to accurately assess the effect of timing of RRT. e study supports the findings of AKIKI trial (Table 2) [24, 26]. All the RCTs thus far on timing of RRT have a high risk of bias for allocation concealment.

Standard vs. Accelerated Initiation of RRT in Acute Kidney Injury trial (STARRT-AKI) is an ongoing multi- centre RCT further evaluating the optimal timing to initiate RRT to have mortality benefits [27].

In conclusion, based on limited evidence, when con- sidering the timing of initiating of RRT in MOF, individual patients physiological reserve based on age, cardiovascular risk factors, pulmonary comorbidities, baseline renal

function, and the trend of inflammatory and renal injury markers should be assessed. A delayed strategy of waiting for 48–72 hrs after progressing to AKI KDIGO 3 or until an absolute indication which arises may be applicable to most medical patients with septic shock [24–26]. Patients with low physiological reserve and AKI may benefit from “early RRT” before absolute indications develop, espe- cially fluid overload [11, 28]. ere may be potential benefits in initiating RRT before absolute indications develop in AKI associated with severe burns or in postoperative patients, particularly after cardiac surgery [23, 29]. Furose- mide stress test (FST) can be used in euvolemic patients with acute tubular necrosis and no underlying CKD, where a bolus of furosemide 1–1.5 mg/kg producing less than 200 ml of urine output over 2hr reflects an increased risk for pro- gression of AKI and RRT requirement [30, 31]. e Acute Disease Quality Initiative (ADQI) workgroup on CRRT recommended initiating RRT when metabolic and fluid de- mands exceed total kidney capacity; however, no specific criteria exist to define excessive demand and low capacity (Table 3) [32]. It is important to note none of the major trials assessing septic shock patients have considered KDIGO stage 2 as an indication for early RRT; thus, further studies are required to conclusively establish early RRT has no benefit in this cohort of patients.

3. Optimal Dosing of CRRT

e rationale behind very high effluent flow rate (>60 ml/kg/ hr) was driven by limited evidence suggesting that removal of inflammatory mediators would improve homeostasis in septic patients. Specific to CRRT in septic AKI, initially small, short- duration RCTs suggested that high effluent flow rate reduced vasopressor requirements, thus improving haemodynamic stability [33–35]. Initial data suggested survival benefit with relatively higher effluent flow rate (>35 ml/kg/hr) [36, 37]. e IVOIRE study consisting of 137 patients with septic shock- associated AKI compared an effluent flow rate of 70 ml/kg/hr with 35 ml/kg/hr. ere was no significant difference in va- sopressor requirement and 28-day mortality between the two groups [38]. A recent Cochrane review (2017) also concluded that there was no mortality benefit with the use of high-volume haemofiltration (HVHF) compared to standard therapy in AKI secondary to septic shock [39].

However, the discussion is incomplete without men- tioning two landmark trials, the VA/NIH Acute Renal Failure Trial Network (ATN) study and the Randomized Evaluation of Normal versus Augmented Level (RENAL) Replacement erapy Study [40, 41]. ese trials compared HVHF versus standard therapy. e ATN study, consisting of 1124 patients, defined high-intensity RRT as IHD or sustained low-efficiency dialysis (SLED) 6 times per week in haemodynamically stable patients, or CVVHDF at an ef- fluent flow rate of 35 mL/kg per hour in haemodynamically unstable patients. Standard intensity treatment was defined as three IHD treatment sessions per week or CVVHDF at 20mL/kg per hour, respectively. is study found that higher-intensity treatment was not associated with reduced mortality, improved renal recovery, or reduced rate of


Design Setting


(i) Main inclusion criteria

(i) Main exclusion criteria

(ii) No. Of patients

Baseline characteristics

(i) SOFA score (early vs delayed) (i) APACHE II score (early vs delayed)
Intervention-early RRT

Control-delayed RRT

RRT requirement in delayed group (%)

Method of RRT

Primary outcome

(i) Mortality in early vs delayed RRT
(ii) P value
Secondary outcome

(i) Duration of RRT early vs delayed (median days)
(ii) Ongoing requirement for RRT


Critical Care Research and Practice Table 2: Early versus Delayed RRT strategy: a comparison of ELAIN, AKIKI, and IDEAL-ICU studies.

ELAIN (23)

Single centre Predominantly postoperative patients; 47% post cardiac surgery.

(i) KDIGO stage 2
(ii) NGAL>150 mg/ml
(iii) Critical illness including at least one of severe sepsis/ vasopressor support/refractory fluid overload/SOFA score >2.

Preexisting renal disease eGFR <30 ml/min/1.73m2

15.6 vs 16
30.6 vs 32.7
<8 hrs of AKI KDIGO 2

<12 hrs of AKI KDIGO 3 or absolute indication

AKIKI (24)

RCT Multicentre (31 ICUs)

Predominantly medical patients with septic shock

(i) KDIGO stage 3 (Cr>354micromol/L or anuria for >12 hrs or urine output<0.3 ml/kg/hr for 24 hrs) (i) Critical illness (mechanical ventilation or vasopressor)

Preexisting renal disease CrCl < 30 ml/min/1.73m2 620

10.9 vs 10.8 Not available (NA)

<6 hrs of AKI KDIGO 3 Absolute indications (urea >40 mg/dl, K+>6 mmol/l, pH < 7.15, acute pulmonary oedema, oliguria/anuria >72 hrs)


RCT Multicentre (29 ICUs)

Patients with septic shock

(i) Failure stage of RIFLE criteria: Oliguria (urine output <0.3 ml per kilogram of body weight per hour for ≥24 hours), Anuria for 12 hours or more, or a serum creatinine level 3 times the baseline level or ≥4 mg per deciliter (≥350 μmol per litre) (ii) Septic shock <48 hrs of commencing vasopressor support
End-stage renal disease and obstructive nephropathy 488

12.2 vs 12.4


<12 hrs of failure stage of RIFLE

>48 hrs of failure stage of RIFLE criteria or absolute indications developing

91 51 62


At 90 days: 39.3% vs 54.7% 0.03

9 vs 25
At 90days: 13% vs 15%

Early RRT compared with delayedinitiationofRRT reduced mortality over the first 90 days.

Multiple modalities: >50% initially on IHD

At 60 days: 48.5% vs 49.7% 0.79


At 60days: 2% vs 5%

No significant difference in mortality between an early and delayedstrategyfortheinitiation of RRT therapy. A delayed strategy averted the need for RRT in a large number of patients.

Multiple modalities: 45% initially on IHD

At 90 days: 58% vs 54% 0.38

4 vs 2
At 90days: 2% vs 3%

No significant difference in 90- daymortalitybetweenearlyand strategy of RRT among septic shock patients.

nonrenal organ failure when compared with less intensive therapy [40]. It also showed significantly more hypotensive episodes requiring vasopressor support and hypo- phosphatemia in the high-intensity group.

e RENAL study, to date, is the most comprehensive work on the subject of CRRT dosing. 1508 patients were randomly assigned to high-intensity treatment (40 ml/kg/hr) or lower intensity treatment (25 ml/kg/hr). Mode of CRRT was CVVHDF in both groups. Higher intensity of CRRT did not reduce the mortality at 90 days and the rate of dialysis dependence or improve haemodynamic profile but was

associated with significantly higher rates of hypo- phosphatemia [41].

In conclusion, high effluent flow rates do not affect mortality but are associated with greater electrolyte dis- turbances, nursing requirements, nutritional demands, and difficulty in maintaining therapeutic drug doses. e current evidence suggests performing CRRT at a minimum delivered dose of effluent flow rate of 20–25 ml/kg/hr (thus prescribing >25 ml/kg/hr to account for treatment interruptions) [40– 42]. Further larger trials require regarding optimal CRRT dosing in septic shock patients (Figure 1).

Critical Care Research and Practice 5 Table 3: 17th Acute Disease Quality Initiative (ADQI) consensus on patient selection and timing of CRRT (2016) [32].

Consensus statement 1.1: Acute RRT should be considered when metabolic and fluid demands exceed total kidney capacity
Consensus statement 1.2: Demand for kidney function is determined by nonrenal comorbidities, the severity of the acute disease, and solute and fluid burden.
Consensus statement 1.3: Total kidney function is measured using a variety of different methods. Changes in kidney function and duration of kidney dysfunction can be anticipated by markers of kidney damage.
Consensus statement 1.4: e demand-capacity imbalance is dynamic and should be evaluated regularly
Consensus statement 1.5: For patients requiring multiple types of organ support, decisions about initiating or withholding RRT should be considered together with other therapies
Consensus statement 1.6: Once the decision to initiate RRT has been made, the therapy should be started as soon as possible, typically within less than 3 h.
Consensus statement 2.1: Selection of RRT modality depends on the capability/availability of the technology, its inherited risks, and the current needs of the patient
Consensus statement 2.2: Continuous types of RRT are recommended in situations where shifts in fluid balance and metabolic fluctuations are poorly tolerated. Intermittent and prolonged intermittent types of RRT have a role in situations where rehabilitation or mobilisation is the priority, and fluid and metabolic fluctuations can be tolerated
Consensus statement 2.3: Availability of technologies is determined by local regulations, local resources, including staff and their training/ experience and laboratory support, and financial constraints. e choice of technologies that should be made available must balance these issues.
Consensus statement 3.1: In situations where other extracorporeal therapies are required, continuous RRT is recommended and integrated systems are preferred over parallel systems.
Consensus statement 4.1: Transition of modalities should be considered if the demand-capacity imbalance or treatment priorities have changed and can be met better by an alternative technique.
Consensus statement 5.1: RRT should be discontinued if kidney function has recovered sufficiently to reduce the demand-capacity imbalance (current and expected) to acceptable levels or the overall goals of treatment have changed.
Consensus statement 5.2: To determine sustained recovery of kidney function, we recommend monitoring of urine output and SCr during RRT.
Consensus statement 5.3: For patients requiring multiple types of organ support, decisions about withdrawing RRT should be considered together with other therapies


ml/kg/hr 15 20

25 30 35 40 45

CRRT dose



25 = 40 RENAL study

= 35 Tolwa


= 35 ATN study

ni et al.

9 or 20 = 48 Bouman et al.

25 < 44 Saudan et al.

20 < 35 or 45 Ronco et al.


Figure 1: Summary of evidence investigating CRRT dosing(ml/kg/hr). Red box: supporting high effluent flow rate. Green box: supporting lower effluent flow rate.

4. Modality of RRT

High-quality data directly comparing between CRRT and IHD is lacking due to preferential use of CRRT in hae- modynamically unstable patients and lack of CRRT avail- ability in all centres. Current evidence base suggests that

CRRT offers no definite benefits to mortality or preservation of renal function when compared to IHD [43, 44].

CRRT, developed in Germany in the 1970s, is generally the preferred choice of RRT in haemodynamically unstable patients due to the potential advantage of more controlled fluid and solute removal, which maintains physiological


Critical Care Research and Practice

stability, particularly mean arterial pressure [45–47]. Fluid accumulation is an independent risk factor for poor prog- nosis in MOF, and CRRT has been shown to be superior at overall fluid removal compared to IHD [13]. Sustained low- efficiency dialysis (SLED) has comparable haemodynamic outcomes and can be considered in MOF [48].

CRRT is associated with a smaller increase in intracranial pressure (ICP) compared to IHD. us, it is the preferred option in liver failure awaiting transplantation and acute brain injury, conditions that predispose to cerebral oedema [49–51].

Patients with AKI associated with hypercatabolic states such as severe burns, rhabdomyolysis, posttrauma, or tu- mour lysis syndrome may benefit from CRRT, as these conditions tend to have more severe haemodynamic in- stability, metabolic acidosis and fluid overload [29, 52].

IHD is considered the first-line therapy in situations requiring rapid correction of electrolytes (hyperkalaemia), urgent fluid removal, and poisoning.

Overall CRRT, IHD, and SLED are complementary modalities, and their use is based on individual patient condition, availability of nursing staff, equipment, and other resources. Multiple modalities can be used on the same patient. In our practice, we continue to use CRRT in hae- modynamically unstable patients in the ICU setting fol- lowing which we transition them to IHD, once vasopressor support is no longer required (Table 4).

5. Extracorporeal Blood Purification beyond AKI in Sepsis

It is widely believed that CRRT removes, or alters the production of, inflammatory mediators and thereby might restore immune homeostasis. Adsorption of inflammatory mediators onto the surface of haemofilters plays a com- plementary role to simple convection in this process [53, 54]. However, it must be noted that haemofiltration may cause the removal of both proinflammatory and anti-in- flammatory cytokines [54]. High cut off (HCO) membranes and high effluent flow rate have been combined with CRRT for cytokine removal in septic patients [55, 56]. Current evidence, however, does not support the routine use of HCO membrane or high effluent flow rate and larger RCTs are required to elucidate any renal or mortality benefits [39]. Haemoperfusion therapy has been considered in septic shock to reduce inflammatory mediators and improve haemodynamic stability. However, the EUPHRATES trial, a multicentre RCT, demonstrated no mortality benefits of using polymyxin B haemoperfusion therapy in septic shock associated with high endotoxin levels. us, haemoperfusion in septic shock is currently not recommended [57].

6. RRT and Organ Support

In the intensive care setting, AKI occurs in a high percentage of patients with ARDS, cardiogenic shock, and fulminant hepatic failure. Experience using CRRT in the management of these patients has generated interest in whether this in- tervention can improve outcomes even in patients without

AKI, that is, whether CRRT has a supportive role in the management of heart, lung, or liver failure.

6.1.RRTinHeartFailure. eUNLOADtrialcomparedthe safety and efficacy of early ultrafiltration (UF) versus standard diuretic therapy in patients presenting with decompensated heart failure (HF). Early UF produced greater fluid and weight loss at 48 hrs with reduced reho- spitalization, number of hospital days, and unscheduled clinic visits at 90-day follow-up. Serum creatinine was similar in both groups [58]. e CARRESS-HF trial also looked at safety and efficacy of UF compared to a stepped pharmacological approach based on a targeted urine output (UO) of 3–5 L/day [59]. Intravenous diuretics, thiazide-like diuretics (metolazone), inotropic agents, left ventricular assist device (LVAD), and UF crossover were all used in a stepped-up approach to achieve desired UO. e stepped pharmacological therapy showed superiority to UF in terms of preservation of renal function, lower adverse events, and similar weight loss at 96 hrs. A smaller RCT demonstrated a lower rehospitalization rate at 1 year when UF was used as the primary modality to manage decompensated heart failure [60].

In light of the above results, we broadly agree with the recommendations of American College of Cardiology (ACC) that UF is a reasonable therapeutic modality in refractory heart failure not responding to medical management [61].

6.2. RRT in Acute Respiratory Distress Syndrome. Acute re- spiratory distress syndrome (ARDS) is seen in up to 15% of ICU admission with sepsis being the most common cause [62]. e FACCT trial demonstrated that a conservative fluid management strategy was associated with a reduction in mechanical ventilation and RRT requirement . A post hoc analysis of the same trial showed a decrease in AKI incidence with a conservative fluid strategy [64]. A few small studies have shown reduced ventilatory re- quirements and improvement in oxygenation with use of CRRT in ARDS [65, 66]. A small study of 53 patients showed the benefit of initiating CRRT within 12 hrs of developing ARDS compared to after 48 hrs [65]. However, in a post hoc analysis of the AKIKI trial, a subgroup of patients with ARDS or sepsis and AKI KDIGO 3 showed no difference in ventilator-free days and 60-day mortality [26]. Early renal recovery was also seen with delayed RRT.

In the presence of positive fluid balance and ARDS, CRRT may be considered to reduce extravascular lung volume and more readily support a conservative fluid management strategy.

6.3. RRT in Liver Failure. Application of blood purification strategies to humans with liver failure has mainly occurred in trial settings and is not yet common practice. Experi- mental approaches have included haemodiabsorption and the molecular adsorbent recirculating system (MARS) [67]. Small studies using these techniques in the management of hepatic failure showed benefit in patients with acute-on- chronic hepatic failure, hepatorenal syndrome (HRS), and

Critical Care Research and Practice


Table 4: Comparison of various RRT modalities.


Cost Duration

Haemodynamic instability Compatible with extracorporeal life support
In raised intracranial pressure


Serum concentration of renally cleared drugs

Vascular access

Compatible with supporting large volume infusions (antibiotics, nutrition, etc.)


24 hrs (though achieves 16 hrs on avg.)
Most compatible


Usually no change Predilution can be utilised to maintain circuit

Least fluctuation

Nontunnelled or tunnelled catheter

Most compatible

Not compatible—would need to be discontinued.


4 hrs daily /alternate days

Least suitable No Increases Can be omitted

Major fluctuations

AV fistula or nontunnelled or tunnelled catheter



6–12 hrs daily /alternate days

Can increase Can be omitted

Some fluctuation

AV fistula or nontunnelled or tunnelled catheter

Would need to be daily and longer sessions

of bleeding. e available options are regional heparin anticoagulation (RHA) and regional citrate anticoagulation (RCA).

RCA is the preferred modality of anticoagulation in CRRT as recommended in the KDIGO guidelines [42]. Evidence from RCTs suggests lower bleeding rates, reduced cost, and longer haemofilter survival, but similar overall mortality when compared to systemic anticoagulation (heparin-based) [72–74]. Citrate binds to calcium (and magnesium) impairing calcium-dependent procoagulants. Citrate-Calcium complexes are partially removed in the effluent and the rest metabolized in the liver, where they are converted to bicarbonate in 1:3 ratio, while calcium is released [75]. Calcium reinfusion via a central line is re- quired to replace lost calcium. Two different preparations of RCA are mainly in use, 4% trisodium citrate or anticoag- ulant citrate dextrose form A using various protocols. RCA is technically more difficult to perform than systemic anti- coagulation with UFH and can lead to hypocalcaemia, hypomagnesaemia, hypernatraemia, metabolic alkalosis (in preserved liver function), and high anion gap metabolic acidosis (in liver dysfunction). It is thus relatively contra- indicated in acute liver injury and cardiogenic shock with significant lactic acidosis [75].

RHA involves prefilter infusion of UFH and neutrali- zation with protamine infusion postfilter. RHA is rarely used in practice and carries a higher risk of anaphylactoid re- action, hypotension, leucopenia, thrombocytopenia sec- ondary to protamine, and a shorter haemofilter survival compared to RCA [76].

7.3. Systematic Anticoagulation. UFH infusion remains the most widely used anticoagulant, despite being a second- line option (when RCA contraindicated) as per KDIGO guidelines and available evidence suggesting that RCA is

IHD : intermittent haemodialysis; SLED : sustained low-efficiency dialysis; CRRT : continuous renal replacement therapy.

Most compatible

Could be compatible if done at night/rest time

even fulminant hepatic failure. In the absence of more robust evidence to confirm these findings, no recom- mendation can be given to support their routine use in clinical practice [68]. ere is no evidence to suggest that RRT increases long-term survival in HRS without liver transplantation. us, CRRT should only be utilised if a reversible element to liver failure exists or the patient is listed for liver transplantation [69].

7. Anticoagulation in RRT

Extracorporeal circuit clotting is a major issue with CRRT primarily due to the accumulation of proteins in a process called concentration polarization. Significant loss of thera- peutic time occurs in replacing clotted haemofilters, which diminishes the efficacy of the treatment. us, anti- coagulation needs to be individualized for each patient.

Anticoagulation options for CRRT can be divided into four categories.

7.1. Anticoagulation Free. Anticoagulation-free RRT should be considered the first line in patients with a high risk of bleeding, such as severe thrombocytopenia, liver dysfunction, coagulation disorder, or any other contraindication to regional anticoagulation (citrate). Haemofilter survival can be pro- longed by diminishing haemoconcentration within the filter through predilution replacement fluid, maintaining a filtration fraction percentage of <20% and achieving relatively high blood flow rates (200–300 ml/min) [70, 71]. Patients on therapeutic anticoagulation for another indication (e.g., atrial fibrillation) do not require additional anticoagulation for CRRT.

7.2. Regional Anticoagulation. is technique allows pro- longed haemofilter life without systemic anticoagulation; thus, it can be utilised in patients with moderate to high risk


Critical Care Research and Practice

superior in haemofilter survival and bleeding risk [42, 74]. Long-term experience, reversibility with protamine, and ease of use maintain its popularity [77]. Heparin-induced thrombocytopenia (HIT) is a complication that can develop within five to ten days of heparin use which requires im- mediate discontinuation of heparin (discussed further be- low) [78]. e aim is to maintain activated partial thromboplastin time (aPTT) between 40 and 45 seconds [79].

Low-molecular heparin (LMWH) has the potential ad- vantage of lower bleeding and HIT risk when compared to UFH. However, the experience with its use is limited and requires serial factor Xa monitoring. Limited data from RCTs suggest that LMWH has higher bleeding incidence when compared to RCA, but similar to UFH [80, 81]. Haemofilter survival with LMWH anticoagulation may be slightly superior to UFH [81].

7.4. Anticoagulation in Special Situations and Other Agents.

Immune-mediated HIT (type 2) is a complication seen with the use of heparin. It is a prothrombotic condition and usually requires systemic anticoagulation on CRRT. Management options include non-heparin-based antico- agulants such as argatroban, lepirudin, and danaparoid [82–86]. Argatroban has hepatic metabolism and may be preferred in AKI. Epoprostenol (prostacyclin) is also a viable option; however, its use in MOF is limited due to a significant risk of hypotension, increasing intracranial pressures and relatively short haemofilter survival [87, 88]. Prostacyclin has a heparin sparing effect and may have a role in centres which utilize UFH as the primary mode of anticoagulation [89].

8. Conclusion

e role of RRT in the ICU is primarily to support renal dysfunction with MOF. e strategies to employ it are dy- namic and evolving. e optimal time to commence RRT remains a topic of literature debate, surgical patients may benefit from early initiation of therapy, whilst septic patients with MOF may benefit from a delayed strategy. CRRT is considered the first line when managing critically ill patients with haemodynamic instability, although no definitive evi- dence is available to suggest mortality benefits or renal function preservation when compared to IHD. RRT is a potential therapeutic option when managing resistant con- gestive heart failure; however, other therapies like haemo- perfusion in sepsis have proven ineffective. RCA has comparatively lower bleeding risk compared to heparin-based therapy and remains the choice of anticoagulant in CRRT.

Conflicts of Interest

e authors declare no potential conflicts of interest.

Authors’ Contributions

All authors equally contributed to this paper with concep- tion and design of the study, literature review and analysis,

drafting and critical revision and editing, and final approval of the final version.


e authors thank Muniza Manshad Satti, MBBS MRCPI MSc (Clinical Research), National University of Ireland Galway.


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