Acute kidney injury (renal failure) requiring dialysis is a common reason for admission to the intensive care unit and a common complication seen in patients in ICU for other conditions. It is a life-threatening condition with high mortality. Dialysis is a method for performing the filtration tasks of the kidneys artificially. It involves removing excess fluid, solutes and waste products.
Indications for Acute Dialysis
The mnemonic AEIOU can be used to remember the indications for acute dialysis in patients with a severe acute kidney injury:
- A – Acidosis (severe and not responding to treatment)
- E – Electrolyte abnormalities (treatment-resistant hyperkalaemia)
- I – Intoxication (overdose of certain medications)
- O – Oedema (severe and unresponsive pulmonary oedema)
- U – Uraemia symptoms such as seizures or reduced consciousness
Options
There are two options for dialysis in patients with renal failure:
- Peritoneal dialysis (rarely used in acute renal failure)
- Haemodialysis
Peritoneal dialysis is very rarely used in acute kidney injury and is generally limited to use in patients with chronic kidney disease.
Haemodialysis
With haemodialysis, patients have their blood filtered by a haemodialysis machine. Blood is taken out of the body, through the dialysis machine, then pumped back into the body. Inside the dialysis machine, the blood passes along a series of semipermeable membranes. Solutes filter out of the blood, across the membrane and into a fluid called dialysate. The concentration gradient between the blood and the dialysate fluid causes water and solutes to diffuse out of the blood and across the membrane.
Haemodialysis requires good access to an abundant blood supply. This can be done in the acute setting with a Vas Cath (central venous catheter). Two lumens are required on the catheter, one to remove the blood and one to put the blood back in. Anticoagulation with citrate or heparin is necessary to prevent blood clotting in the machine and during the process.
The amount of water and solutes removed from the blood can be controlled depending on the patient’s clinical condition and reason for dialysis.
There are two options for haemodialysis:
- Continuous renal replacement therapy (CRRT)
- Intermittent haemodialysis (IHD)
Continuous renal replacement therapy involves continuously performing dialysis 24 hours a day. Most patients requiring haemodialysis in ICU will be on CRRT.
Intermittent haemodialysis involves running the machine and performing dialysis for set periods, for example, 3-12 hours, before taking a break from dialysis.
Last updated August 2021