A recently published review in the Journal of Intensive Care outlines the different causes, diagnosis, and management of acute kidney injury in critically ill patients.
Critically ill patients being treated in intensive care units (ICUs) often have several serious medical problems. It is important to ensure that their vital organs are kept functioning to improve their chances of recovery. Acute kidney injury (AKI), previously known as acute renal failure, is a sudden failure of the kidneys which develops over a few hours or days. It is a common complication in ICU patients – it is estimated to occur in over 50% of ICU patients at some point during their critical illness. When the kidneys fail, they are unable to maintain the correct balance of fluid and electrolytes in the body or to excrete waste products. This can damage other body organs such as the lungs, heart, and brain. AKI is linked to high death rates, so it is important to diagnose and treat it early. A recent review paper from Yale School of Medicine (USA) outlined the different causes, diagnosis, and management of AKI in critically ill patients. The review recently appeared in the Journal of Intensive Care.
What Causes Acute Kidney Injury?
Acute kidney injury in critically ill patients can be caused in several different ways:
- Pre-renal AKI:
AKI can result from reduced levels of blood getting to the kidneys where it will be filtered. This is known as pre-renal AKI, as its causes relate to problems before blood gets to the kidneys. The causes of pre-renal AKI include dehydration (vomiting, diarrhea), bleeding (causing low blood pressure), heart failure, and liver failure.
- Renal AKI
AKI can be due to direct damage to the kidney tissues. This is known as renal AKI. The causes include sepsis (severe infection) and certain drugs often used in the ICU that can be toxic to the kidney. For example, these drugs may include some antibiotics such as vancomycin or aminoglycosides.
- Post-renal AKI
If there is a blockage to the urine outflow from the kidneys this can lead to a build-up of pressure in the kidneys, causing AKI. This is known as post-renal AKI.
How is Acute Kidney Injury Diagnosed?
All ICU patients have their kidney function closely monitored by measuring the amount of urine output and the level of electrolytes and waste products in the blood – in particular, the substances urea and creatinine. AKI is diagnosed if there is a sudden rise in creatinine levels over 48 hours. The real challenge is to determine whether AKI is pre-renal, renal, or post-renal and to identify its underlying cause. This is done by careful assessment of various factors including level of hydration, arterial and venous blood pressures, level of urea and creatinine in the blood or urine, excretion of sodium, the concentration of urine, and microscopic examination of urine. These factors have different patterns depending on whether AKI is pre-renal, renal or post-renal
Management of Acute Kidney Injury
Once the cause of acute kidney injury is determined, an appropriate management plan can be made.
- Fluid replacement
In pre-renal AKI, reduced blood volume is corrected by giving the patient intravenous fluids. During fluid replacement, the patient’s urine output and arterial and venous pressures must be carefully monitored to avoid fluid overload. There is some debate as to the best type of replacement fluids to use and further studies are needed to determine which fluids are best for which patients.
- Vasopressors – Drugs to Increase Blood Pressure
Drugs which act to raise arterial blood pressure (vasopressors) can be useful for patients with septic shock and low blood pressure
- Diuretics – Drugs which Increase Urine Output
Some studies have shown that drugs which act on the kidney to increase urine output (known as loop diuretics) can improve the outcome of AKI, although later studies have suggested these drugs are not helpful. Whilst they are not recommended for prevention of AKI in critically ill patients, they may be helpful in the treatment of some patients.
- Renal Replacement Therapy
When kidney function is very limited patients may require support by renal replacement therapy (RRT) until the kidneys recover. RRT includes different forms of dialysis given either intermittently or continuously. Some patients may ultimately require a kidney transplant. The timing of RRT – early vs late – has been investigated in several studies but as yet there is no clear consensus. The decision of when to start RRT is based on clinical judgment regarding the individual patient.
AKI is a serious and common complication seen in critically ill ICU patients. Early accurate diagnosis and treatment can improve outcomes for these patients.
Written by Julie McShane, Medical Writer
Reference: Mohsenin V. Practical approach to detection and management of acute kidney injury in critically ill patient. Journal of Intensive Care (2017) 5:57. Doi:10.1186/s40560-017-0251-y