Dietetic classification of AKI
From a nutritional point of view patients can be divided into two groups:
- Patients with AKI in the non-catabolic state
- Patients with AKI in the catabolic state
Within nutritional assessment is important to assess the presence of a catabolic state. There is no universal definition of how to identify the degree of catabolism, however, the following factors should be considered: the underlying condition, clinical status, objective measurements of inflammatory markers, biochemistry and clinical observation.
AKI in the non-catabolic state
Typically, patients with pre-renal or post-renal injuries present in a non-catabolic state. Common causes of AKI in a non-catabolic state include dehydration, certain medications and urinary obstruction. Generally, these patients are stable and where required any renal replacement therapy (RRT) will usually be provided by conventional haemodialysis (HD). Although they could have any stage of AKI, these are likely to be predominantly patients with stage 1 and 2 AKI. Oral diet alone, or the addition of nutritionally-dense supplementary sip feeds will frequently be sufficient to meet the patients’ needs; if not artificial nutrition support should be established.
AKI in the catabolic state
Typically, patients with an intra-renal injury present in a catabolic state. Causes of AKI in a catabolic state include sepsis, acidosis and trauma. Patients often have multi-organ failure and are likely to be managed on an intensive care unit. Although they could have any stage of AKI, these are likely to be predominantly patients with stage 2 and 3 AKI. AKI is seen in approximately 50% patients on ICU (Hostle et al, 2015), of whom 5-10% will require continuous renal replacement therapy (CRRT) (Tandukar and Palevsky 2019).
PEW is often present in this group of patients and is associated with poorer patient outcomes in terms of length of hospital stay, complications and mortality rates (Fiaccadori et al, 2021). Protein turnover rates are increased resulting in negative nitrogen balance. Nitrogen requirements are increased above normal and are influenced by the mode of RRT undertaken. Nutrition support can only improve protein and energy balance and possibly protein synthesis but cannot suppress critical illness -induced catabolism (Ostermann et al, 2019).
Patients will usually require artificial nutrition support, particularly if intubated and sedated. Wherever possible, this should be provided via the enteral route (Singer et al, 2019). Standard formulae can be used, but nutritionally-dense feeds with or without reduced electrolyte content are useful where the control of fluid balance and/or serum phosphate and potassium levels are raised.