Acute Kidney Injury and Kidney Replacement Therapy in the Critically Ill Patient

Historically, KRT has been offered when a patient fulfills at least one of the AEIOUs: severe Acidosis,

Electrolyte abnormalities (eg, hyperkalemia), Intoxication), refractory volume Overload, or symptomatic

Uremia. The multicenter BICAR-ICU study showed that randomization to sodium bicarbonate

administration for a pH of 7.2 or less and PCO2 of 45 mm Hg or less, rather than no therapy, failed

to improve all-cause mortality or death in ICU patients. However, of note, patients in the bicarbonate

group had a significantly lower rate of new dialysis initiation, suggesting this temporizing measure

had a secondary benefit and decreased dialysis initiation for acidemia or hyperkalemia while kidneys

spontaneously improved.

No consensus exists on the optimal timing of KRT. It is unclear whether KRT should be initiated

when a patient reaches KDIGO stage III or potentially earlier to avoid complications associated with

metabolic/fluid derangements. Several recent randomized controlled trials regarding KRT timing have

been published with disparate results. These include the ELAIN and AKIKI trials published in 2016, the

IDEAL-ICU trial published in 2018, and the STARRT-AKI trial published in 2020.

STARRT-AKI: Multicenter, multinational trial of 2927 individuals with stage 2 or 3 AKI who

received either “accelerated KRT,” meaning therapy was initiated within 12 hours of meeting

eligibility criteria, or “standard KRT,” meaning therapy was not initiated unless the patient fulfilled

a conventional indication (analogous to the AEIOU indications mentioned earlier). Clinicians

needed to attest to equipoise in the decision to initiate KRT before the patient could be enrolled.

For the primary end point of all-cause mortality at 90 days, there was no difference between groups

(44% in each group). Only two-thirds of the patients in the standard KRT group ultimately required

dialysis, whereas 97% of the patients in the accelerated KRT group received dialysis. There were

more adverse events in the accelerated KRT group.

At this point, although the findings of these trials somewhat vary, it appears that there is no consistent,

reproducible advantage to beginning KRT early in a patient’s course as opposed to waiting until

stage 3 AKI with an urgent indication.

The practice of KRT discontinuation is non-standardized but typically occurs when the precipitant is

improved or resolved (e.g., sepsis controlled) and patients can satisfactorily maintain their fluid and

solute balance without extracorporeal support.

Modalities are classified according to duration as intermittent KRT, prolonged intermittent KRT, or

continuous KRT.

semipermeable membrane by convection, diffusion, or both.

Convection uses the concept of “solute drag” and can remove both small- (less than 500-1000

Da) and middle- (less than 10,000 Da) molecular-weight solutes. Solute removal occurs when the

transmembrane pressure drives water and solute across a semipermeable membrane. This process

involves adding replacement fluid (pre- and/or post-filter) to replace the excess volume that is being

removed and replenish the desired electrolytes. Pre-filter replacement fluid may improve filter life

and deter circuit clotting. Post-filter replacement fluid may improve solute clearance efficiency

because of the hemoconcentration of blood entering the dialyzer.

Diffusion is the movement of solutes from an area of higher solute concentration to an area of

lower concentration. A concentration gradient is produced by running an electrolyte solution (i.e.,

dialysate fluid with a flow rate of 17–40 mL/minute) countercurrent to the flow of blood. Small-

molecular-weight solutes (less than 500 Da) are cleared efficiently.