Critical Care - Renal Replacement Therapy

Renal replacement therapy or R RT is a treatment that replaces certain functions of the kidneys such as fluid and electrolyte balance, acid base regulation and excretion of nitrogenous waste products and toxins.

R RT is indicated in conditions where kidney function is impaired or absent, including acute kidney injury and endstage renal disease.

But it can also be used to treat other temporary serious conditions like electrolyte imbalances, fluid overload poisoning or drug overdose.

R RT can be done continuously over many hours or days like in continuous renal replacement therapy or CRR T or intermittently like in hemodialysis or peritoneal dialysis also known as PD.

Ok. So to perform renal replacement therapy, an access site is necessary to gain entry to the body.

In hemodialysis, access to the bloodstream will vary depending on the type of therapy and whether renal replacement therapy is needed temporarily or on a long term basis.

Starting with temporary renal replacement therapy. Vascular access can be obtained through a percutaneous catheter within a large central vein such as the internal jugular vein or the femoral vein.

This temporary vascular access can be used immediately after placement. So it's often used in conditions that require emergency renal replacement therapy.

For long term hemodialysis access, an arteriovenous or AV fistula can be created during this process. An artery and a vein are surgically connected.

Most commonly joining the radial artery and cephalic vein in the arm. This causes the vein to become arterialized, meaning it enlarges and develops thicker walls so it can withstand higher pressure and flow of blood and it allows for the insertion of a large bore needle to obtain arterial blood.

This maturing process takes several weeks. Another type of access is an A V graft which also involves connecting an artery and a vein but is done using a synthetic tube.

The graft will also take weeks to mature before it's ready for use. The final type of renal replacement therapy access is for peritoneal dialysis which is obtained by surgically inserting a catheter directly into the peritoneal cavity.

Now, there are two main mechanisms that make renal replacement therapy possible. First, diffusion is the process where nitrogenous waste products and other solutes are removed from the body as they move from a greater concentration across a semipermeable membrane to a lesser concentration until the two solutions have the same concentration of solutes.

On the other hand, ultrafiltration primarily involves fluid and certain low molecular weight particles like electrolytes moving across a semipermeable membrane using an osmotic gradient.

OK. Now, let's review the types of renal replacement therapy to understand diffusion and ultrafiltration and action.

Hemodialysis is performed using a dialysis machine. In acute care settings, outpatient centers or in the home.

During therapy, the patient's blood travels from their access site through one tubule and enters the dialyzer sometimes called a hemofilter, which is the blood filtering component of the machine that essentially acts as an artificial kidney.

The dialyzer has two compartments separated by a semipermeable membrane. The patient's blood enters on one side and the other side contains the dialysate, which is a type of solution that creates the pressure gradient that makes diffusion and ultrafiltration happen as blood moves through the dialyzer cellular components and proteins stay within the blood.

While excess fluid electrolytes and nitrogenous wastes like urea and creatinine move into the dialysate solution on the other side of the semipermeable membrane.

Once the blood passes through the dialyzer, a second tubule returns the filtered blood from the dialyzer back to the patient and the used dialysate is discarded.

Now, fluids and electrolytes typically shift somewhat quickly during hemodialysis which usually takes 3 to 4 hours. So patients who are hemodynamically unstable may not be able to tolerate intermittent hemodialysis.

Instead, these patients will undergo crrt which slows the process of fluid and solute removal. So the shifts in blood composition occur more gradually, usually over 24 hours.

Another type of dialysis is peritoneal dialysis, which uses the peritoneal membrane which surrounds the abdominal cavity and lines the abdominal organs as the semipermeable membrane through which diffusion and ultrafiltration occurs during peritoneal dialysis dialysate is infused by gravity through a catheter that's placed into the abdominal cavity.

The dialysate dwells in the peritoneal space for about 4 to 6 hours depending on the patient's individual needs. During this time, toxins and excess fluid and electrolytes are filtered through the peritoneal membrane and drawn into the dialysate.

Afterwards, the dialysate is drained and disposed like hemodialysis and crrt peritoneal dialysis can be performed in acute care settings but is more often performed by the patient at home.

Ok. So when caring for your patient on renal replacement therapy, goals of care include preparing them for treatment and monitoring for complications related to therapy.

Begin by checking baseline, laboratory results including electrolytes and renal studies such as B UN and creatinine measure vital signs, record baseline weight, calculate intake and output ratio to determine fluid status, assess for edema and auscultate.

Heart and lung sounds. Also be sure to consult the pharmacist to determine which medications should be held or rescheduled.

For example, water soluble medications are often administered after treatment to avoid them being dialyzed out of the patient's blood if ordered, also administer the prescribed anticoagulants to prevent the formation of blood clots, which can happen as blood interacts with the artificial surfaces within the dialysis machine.

Next, examine their access site. Look for signs of skin breakdown and infection like swelling, redness or drainage.

For those with venous access devices, check for perfusion distal to the site by assessing skin color temperature capillary refill and pulses.

For patients with an AV fistula or graft determine patency by auscultating for a bru or a whooshing sound and palpating for a thrill or a vibration felt by the fingers then monitor for complications during renal replacement therapy.

Complications include those caused by fluid and electrolyte shifts like nausea, vomiting, cramping, hypotension or cardiac arrhythmias also watch for dialysis disequilibrium syndrome, which can happen due to sudden shifts in B UN and creatinine levels causing symptoms like headache, altered level of consciousness and seizures.

For patients undergoing peritoneal dialysis, assess for discomfort related to abdominal expansion during dwell time. After renal replacement therapy is complete.

Ensure the access site is flushed per protocol and monitor for bleeding drainage or swelling. Next, take another set of vital signs, check their weight, calculate fluid intake and output balance and review post dialysis.

Laboratory test results as ordered, be sure to monitor for delayed complications including hypovolemia, electrolyte imbalance or infection.

In addition, after peritoneal dialysis, examine the drained dialysate for a cloudy color indicating infection. All right.

As a quick recap renal replacement therapy or R RT is a process that removes nitrogenous waste products, toxins and excess fluid and electrolytes from the bloodstream.

It's typically indicated for patients with acute kidney injury or endstage kidney disease but can also be used in other conditions.

Common types of R RT include intermittent or continuous hemodialysis and peritoneal dialysis. Nursing considerations when caring for a patient receiving R RT include preparing them for treatment and monitoring for complications related to therapy.