Amino Acid Requirements in Critically Ill Patients With Acute Kidney Injury
Amino Acid Requirements in Critically Ill Patients With Acute Kidney Injury
Acute kidney injury in critically ill patients is often a complication of an underlying condition such as organ failure, sepsis, or drug therapy. In these patients, stress-induced hypercatabolism results in loss of body cell mass. Unless nutrition support is provided, malnutrition and negative nitrogen balance may ensue. Because of metabolic, fluid, and electrolyte abnormalities, optimization of nutrition to patients with acute kidney injury presents a challenge to the clinician. In patients treated with conventional intermittent hemodialysis, achieving adequate amino acid intake can be limited by azotemia and fluid restriction. With the use of continuous renal replacement therapy (CRRT), however, better control of azotemia and liberalization of fluid intake allow amino acid intake to be maximized to support the patient's metabolic needs. High amino acid doses up to 2.5 g/kg/day in patients treated with CRRT improved nitrogen balance. However, to our knowledge, no studies have correlated increased amino acid intake with improved outcomes in critically ill patients with acute kidney injury. Data from large, prospective, randomized, controlled trials are needed to optimize the dosing of amino acids in critically ill patients with acute kidney injury who are treated with CRRT and to study the safety of high doses and their effects on patient morbidity and survival.
The classic nomenclature "acute renal failure" is being replaced by the more current terminology "acute kidney injury," driven by the Acute Dialysis Quality Initiative (ADQI) group proposal for a consensus definition of acute renal failure. The ADQI consensus definition of acute kidney injury is denoted by the acronym RIFLE, which refers to three stages by increasing severity (risk, injury, failure) based on combined criteria of serum creatinine concentration or glomerular filtration rate and urine output, as well as two outcomes (loss and end-stage kidney disease) in relation to kidney function. In a retrospective study that used the RIFLE classification for the definition of acute kidney injury in the analysis of a database of 41,972 patients from 22 intensive care units (ICUs), patients with risk, injury, and failure had corresponding mortality rates of 20.9%, 45.6%, and 56.8%, respectively. In a multinational, multicenter, prospective, epidemiologic survey of acute kidney injury in ICUs that included a total of 29,269 critically ill patients, 1738 patients (5.9%) developed acute kidney injury sometime during their ICU stay, including 1260 patients (4.3% of critically ill patients or 72.5% of patients with acute kidney injury) who were managed with renal replacement therapy (defined as peritoneal dialysis or any technique of renal support requiring an extracorporeal circuit and an artificial membrane). Hospital and ICU mortality rates in patients with acute kidney injury who were treated with renal replacement therapy were 55% and 64%, respectively.
Malnutrition is common in patients with acute kidney injury and is caused by anorexia, impaired protein metabolism and transport, oxidative stress, metabolic acidosis, nutrient losses through the hemodiafilter, and patient comorbidities. Because acute kidney injury in critically ill patients commonly occurs in the setting of other diseases, nutritional and metabolic changes are the result of underlying conditions such as surgery, trauma, burns, organ failure, and sepsis, rather than acute kidney injury alone. Proper nutrition is aimed at minimizing the effects of hypermetabolism and hypercatabolism and improving patient recovery.
Critically ill patients with acute kidney injury frequently have azotemia and fluid overload, and may not tolerate high fluid removal rates during intermittent hemodialysis over a 3-4-hour period. Patients who are managed with intermittent hemodialysis 3 times/week may need fluid restriction, and the ability to meet their higher amino acid requirements to compensate for hypercatabolism is often hindered by accumulation of nitrogenous waste. Although intermittent hemodialysis 3 times/week is common practice, critically ill patients with acute kidney injury may require more frequent intermittent hemodialysis to achieve metabolic and azotemic control. More frequent intermittent hemodialysis may allow more fluid intake depending on the patient's fluid status and tolerance. However, with continuous renal replacement therapy (CRRT), enhanced nitrogenous waste clearance and liberalization of fluid intake allow increasing amino acid intake to meet the patient's metabolic requirements. The preferred choice of dialysis in hemodynamically unstable patients is CRRT because it allows for slow continuous fluid removal and superior hemodynamic and metabolic control compared with intermittent hemodialysis. There is wide variation with the modalities and types of renal replacement therapies used in hospitals, and available data on amino acid dosing in patients treated with CRRT are limited by study designs.
Abstract and Introduction
Abstract
Acute kidney injury in critically ill patients is often a complication of an underlying condition such as organ failure, sepsis, or drug therapy. In these patients, stress-induced hypercatabolism results in loss of body cell mass. Unless nutrition support is provided, malnutrition and negative nitrogen balance may ensue. Because of metabolic, fluid, and electrolyte abnormalities, optimization of nutrition to patients with acute kidney injury presents a challenge to the clinician. In patients treated with conventional intermittent hemodialysis, achieving adequate amino acid intake can be limited by azotemia and fluid restriction. With the use of continuous renal replacement therapy (CRRT), however, better control of azotemia and liberalization of fluid intake allow amino acid intake to be maximized to support the patient's metabolic needs. High amino acid doses up to 2.5 g/kg/day in patients treated with CRRT improved nitrogen balance. However, to our knowledge, no studies have correlated increased amino acid intake with improved outcomes in critically ill patients with acute kidney injury. Data from large, prospective, randomized, controlled trials are needed to optimize the dosing of amino acids in critically ill patients with acute kidney injury who are treated with CRRT and to study the safety of high doses and their effects on patient morbidity and survival.
Introduction
The classic nomenclature "acute renal failure" is being replaced by the more current terminology "acute kidney injury," driven by the Acute Dialysis Quality Initiative (ADQI) group proposal for a consensus definition of acute renal failure. The ADQI consensus definition of acute kidney injury is denoted by the acronym RIFLE, which refers to three stages by increasing severity (risk, injury, failure) based on combined criteria of serum creatinine concentration or glomerular filtration rate and urine output, as well as two outcomes (loss and end-stage kidney disease) in relation to kidney function. In a retrospective study that used the RIFLE classification for the definition of acute kidney injury in the analysis of a database of 41,972 patients from 22 intensive care units (ICUs), patients with risk, injury, and failure had corresponding mortality rates of 20.9%, 45.6%, and 56.8%, respectively. In a multinational, multicenter, prospective, epidemiologic survey of acute kidney injury in ICUs that included a total of 29,269 critically ill patients, 1738 patients (5.9%) developed acute kidney injury sometime during their ICU stay, including 1260 patients (4.3% of critically ill patients or 72.5% of patients with acute kidney injury) who were managed with renal replacement therapy (defined as peritoneal dialysis or any technique of renal support requiring an extracorporeal circuit and an artificial membrane). Hospital and ICU mortality rates in patients with acute kidney injury who were treated with renal replacement therapy were 55% and 64%, respectively.
Malnutrition is common in patients with acute kidney injury and is caused by anorexia, impaired protein metabolism and transport, oxidative stress, metabolic acidosis, nutrient losses through the hemodiafilter, and patient comorbidities. Because acute kidney injury in critically ill patients commonly occurs in the setting of other diseases, nutritional and metabolic changes are the result of underlying conditions such as surgery, trauma, burns, organ failure, and sepsis, rather than acute kidney injury alone. Proper nutrition is aimed at minimizing the effects of hypermetabolism and hypercatabolism and improving patient recovery.
Critically ill patients with acute kidney injury frequently have azotemia and fluid overload, and may not tolerate high fluid removal rates during intermittent hemodialysis over a 3-4-hour period. Patients who are managed with intermittent hemodialysis 3 times/week may need fluid restriction, and the ability to meet their higher amino acid requirements to compensate for hypercatabolism is often hindered by accumulation of nitrogenous waste. Although intermittent hemodialysis 3 times/week is common practice, critically ill patients with acute kidney injury may require more frequent intermittent hemodialysis to achieve metabolic and azotemic control. More frequent intermittent hemodialysis may allow more fluid intake depending on the patient's fluid status and tolerance. However, with continuous renal replacement therapy (CRRT), enhanced nitrogenous waste clearance and liberalization of fluid intake allow increasing amino acid intake to meet the patient's metabolic requirements. The preferred choice of dialysis in hemodynamically unstable patients is CRRT because it allows for slow continuous fluid removal and superior hemodynamic and metabolic control compared with intermittent hemodialysis. There is wide variation with the modalities and types of renal replacement therapies used in hospitals, and available data on amino acid dosing in patients treated with CRRT are limited by study designs.
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