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The judgment and awareness of how much of a particular therapeutic procedure should be, and actually it is, delivered is essential for a good medical practice. However, recent surveys have shown a disappointingly low number of physicians that report being aware of, or calculating, RRT dose in AKI.774
Although widely used for evaluation of RRT in CKD, Kt/V urea has important limitations as a tool for RRT dosing in AKI. AKI patients are metabolically unstable, with variations in urea generation. In addition, their urea volume of distribution appears to exceed the patient’s total body-water volume.775 Different ways to measure Kt/V obtained significantly different results in AKI patients.776 In the same way, the selection of a target serum urea level as an indicator of dialysis dose is highly arbitrary, as serum urea is influenced by several extrarenal factors, such as ethnicity, age, gender, nutrition, presence of liver disease, sepsis, muscle injury, drugs, etc.
Several clinical investigations have shown that the actual delivered dose of RRT in AKI patients is frequently smaller than the prescribed dose, and even smaller than the recommended minimum for CKD patients.771,773,776–778 Impediments to adequate dose delivery were hemodynamic instability, patient size, access problems, technical problems, need for patient transportation, and early filter clotting.
Trials studying dose in CRRT have used the amount of effluent volume normalized by the patient’s weight and procedure time as a parameter for dose evaluation. However, the actual effluent flow will be influenced by interruptions of CRRT, and effluent flow will exceed actual dose with use of predilution or with reductions in membrane permeability during the treatment. In summary, it is essential to check very carefully if the prescribed RRT dose is really being delivered to AKI patients. Increasing filter size, dialysis time, blood flow rate, dialysate flow rate, and/or effluent flow rate should be considered in case of dose inadequacy.
In determining a prescription of RRT it is mandatory to consider parameters other than small-solute clearance, such as patients’ fluid balance, acid-base and electrolyte homeostasis, and nutrition, among others, as possible components of an optimal RRT dose. In fact, positive fluid balance appears to be an independent risk factor for mortality in AKI patients.83
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