Ammonia is a natural waste product generated within the body. Elevated levels can become harmful, especially when the body’s natural processing systems are overwhelmed. This article explains how dialysis removes ammonia from the bloodstream.
Understanding Ammonia and Its Impact
Ammonia, a nitrogen-containing compound, forms primarily from the breakdown of amino acids and other nitrogenous compounds, including protein metabolism. Intestinal bacteria also produce ammonia through urease action on urea. The body converts this ammonia into a less toxic substance called urea via the urea cycle, mainly in the liver. Kidneys then excrete urea in urine.
If the liver’s urea cycle is impaired or ammonia production is excessively high, ammonia can accumulate in the blood. Even slightly elevated concentrations, called hyperammonemia, are toxic to the central nervous system. This neurotoxicity can cause confusion, disorientation, excessive sleepiness, and difficulty concentrating. In severe cases, high ammonia levels can lead to brain swelling, seizures, coma, and be fatal.
How Dialysis Functions
Dialysis serves as an artificial kidney, stepping in when the body’s own kidneys are unable to effectively remove waste products and excess fluid from the blood. The process involves circulating a patient’s blood, either outside or within the body, exposing it to a special cleaning solution called dialysate. A semipermeable membrane separates the blood from the dialysate, allowing certain substances to pass through.
Dialysis primarily removes waste through diffusion, where solutes move from high concentration in the blood to low concentration in the dialysate. Convection also occurs when fluid is removed from the blood, carrying dissolved solutes. This artificial filtration system helps restore the balance of electrolytes and fluids.
Ammonia Removal Through Dialysis
Dialysis is effective at removing ammonia from the bloodstream. Ammonia is a small molecule with a low molecular weight, making it amenable to removal by dialytic techniques. Dialysis clears ammonia primarily through diffusion, moving it from the patient’s blood across the semipermeable membrane into the ammonia-free dialysate.
Ammonia removal efficiency is influenced by blood flow rate, dialysate flow rate, and dialyzer membrane surface area. Higher blood and dialysate flow rates lead to more rapid ammonia clearance. Hemodialysis, which filters blood outside the body, is more rapid and efficient for acute ammonia levels than peritoneal dialysis, which uses the abdominal lining. This is due to hemodialysis’s higher blood flow and larger effective surface area.
When Dialysis is Used for Ammonia
Dialysis treats high ammonia levels when the body’s natural detoxification pathways are overwhelmed. This often occurs in acute liver failure, where the liver is too damaged to convert ammonia to urea effectively. It is also used in certain inborn errors of metabolism, genetic conditions affecting urea cycle enzymes.
This intervention is reserved for severe, life-threatening hyperammonemia, especially when other medical therapies, such as medications to reduce ammonia production or enhance its excretion, are insufficient or too slow. Hemodialysis is often the preferred method for rapid ammonia reduction in acute scenarios. While medical management supports the body’s own systems, dialysis provides a direct and swift method of removing the substance from circulation.