Patient Encounter Part

The patient presents to clinic several years later and complains that she "feels lousy." She states that she doesn't feel like eating and has lost 9 kg (20 lb) in the last 6 months.

Current Meds: Furosemide 80 mg orally twice daily; metolazone 5 mg orally twice daily; lisinopril 40 mg orally daily; metoprolol 75 mg orally twice daily; insulin glar-gine 30 units subcutaneously at bedtime; insulin lispro subcutaneously per sliding scale with meals; darbepoetin 100 mcg subcutaneously weekly; iron polysaccharide 150 mg orally daily; sevelamer 800 mg orally three times a day with meals; calcitriol 0.25 mcg orally daily; sodium bicarbonate 1,300 mg orally three times a day

ROS: Unremarkable PE:

VS: BP 160/85 mm Hg, P 70 bpm, T 36.8°C (98.2°F), wt 68.2 kg (150 lb)

Chest: RRR, normal Si, S3, and S4 both present; slight pericardial friction rub

Exts: 3+ bilateral lower extremity edema which is present half-way up her calf

Labs: Sodium 142 mEq/L (142 mmol/L); potassium 5.8 mEq/L (5.8 mmol/L); chloride 102 mEq/L (102 mmol/L); carbon dioxide 16 mEq/L (16 mmol/L); BUN 85 mg/ dL (30.35 mmol/L urea); SCr 9.5 mg/dL (840 ^mol/L); glucose 112 mg/dL (6.22 mmol/L); calcium 8.2 mg/dL (2.05 mmol/L); phosphate 5.8 mg/dL (1.87 mmol/L); iPTH 438 pg/mL (438 ng/L or 46.9 pmol/L); WBC 5.3 x 103 cells/mm3 (5.3 x 109/l); RBC 3.2 x 106 cells/mm3 (3.2 x 1012/L); Hgb 9.8 g/dL (98 g/L or 6.08 mmol/L); Hct 29% (0.29); platelets 390 x 103 cells/mm3 (390 x 109/L)

What indications does the patient have for dialysis?

What alternatives for renal replacement therapy exist for the patient?

What are the advantages and disadvantages of each modality for renal replacement?

Three types of membranes used for dialysis are classified by the size of the pores and the ability to remove solutes from the bloodstream.

• Conventional (standard) membranes have small pores, which limit solute removal to relatively small molecules, such as creatinine and urea.

• High-efficiency membranes also have small pores, but have a higher surface area that increases removal of small molecules, such as water, urea, and creatinine from the blood.

Hemodialysis And Urea

FIGURE 26-6. In hemodialysis, the patient's blood is pumped to the dialyzer at a rate of 300 to 600 mL/min. An anticoagulant (usually heparin) is administered to prevent clotting in the dialyzer. The dialyate is pumped at a rate of 500 to 1,000 mL/min through the dialyzer countercurrent to the flow of blood. The rate of fluid removal from the patient is controlled by adjusting the pressure in the dialys-ate compartment. (From Foote EF, Manley HJ. Hemodialysis and peritoneal dialysis. In: DiPiro JT, Talbert RL, Yee GC, et al., eds. Pharmacotherapy: A Pathophysiologic Approach, 7th ed. New York: McGraw-Hill, 2008: 0106, with permission.)

FIGURE 26-6. In hemodialysis, the patient's blood is pumped to the dialyzer at a rate of 300 to 600 mL/min. An anticoagulant (usually heparin) is administered to prevent clotting in the dialyzer. The dialyate is pumped at a rate of 500 to 1,000 mL/min through the dialyzer countercurrent to the flow of blood. The rate of fluid removal from the patient is controlled by adjusting the pressure in the dialys-ate compartment. (From Foote EF, Manley HJ. Hemodialysis and peritoneal dialysis. In: DiPiro JT, Talbert RL, Yee GC, et al., eds. Pharmacotherapy: A Pathophysiologic Approach, 7th ed. New York: McGraw-Hill, 2008: 0106, with permission.)

• High-flux membranes have larger pores that allow for the removal of substances with higher molecular-weight, including some drugs, such as vancomycin, than conventional membranes.

Three primary processes are utilized for the removal of substances from the blood.

• Diffusion is the movement of a solute across the dialyzer membrane from an area of higher concentration (usually the blood) to a lower concentration (usually the dialysate). This process is the primary means for small molecules, such as electrolytes, to be removed from the bloodstream. At times, solutes can be added to the dialysate that are diffused into the bloodstream. Changing the composition of the dialysate allows for control of the amount of electrolytes that are being removed.

• Ultrafiltration is the movement of solvent (plasma water) across the dialyzer membrane by applying hydrostatic or osmotic pressure, and is the primary means for removing water from the bloodstream. Changing the hydrostatic pressure applied to the dialyzer or the osmotic concentration of the dialysate allows for control of the amount of water being removed.

• Convection is the movement of dissolved solutes across the dialyzer membrane by "dragging" the solutes along a pressure gradient with a fluid transport and is the primary means for larger molecules to be removed from the bloodstream, such as urea. Changing the pore size of the dialyzer membrane alters the efficiency of convection and allows for control of the amount of water removed in relation to the amount of solute being removed.

Vascular Access

Long-term permanent access to the bloodstream is a key component of HD. There are three primary techniques used to obtain permanent vascular access in patients receiving HD, including arteriovenous fistulas (AVF), arteriovenous grafts (AVG) and catheters. An AVF is the preferred access method because it has the longest survival rate and the fewest complications.65 An AVF is made by creating an anastomosis between an artery and a vein, usually in the forearm of the nondominant arm (Fig. 26-7). An AVG results in a similar access site, but uses a synthetic graft, usually made of poly-tetrafluoroethylene, to connect the artery and vein in the forearm (Fig. 26-7). The advantages of the AVG is that it is able to be used within 2 to 3 weeks, compared to 2 to 3 months for an AVF. However, AVGs are complicated by stenosis, thrombosis, and infections, which lead to a shorter survival time of the graft. Double-lumen venous catheters, placed in the femoral, subclavian, or jugular vein, are often used as temporary access while waiting for the AVF or AVG to mature. The catheters are tunneled beneath the skin to an exit site to reduce the risk of infection. Venous catheters can also be used as permanent access in patients in whom arteriovenous access cannot be established.

Complications of Hemodialysis

Complications associated with HD include hypotension, muscle cramping, thrombosis, and infection.

Hypotension

Hypotension is the most common complication seen during hemodialysis. It has been reported to occur with approximately 10% to 30% of dialysis sessions, but may be as frequent as 50% of sessions in some patients.66

Pathophysiology. Hypotension associated with hemodia-lysis manifests as a symptomatic sudden drop of more than 30 mm Hg in mean arterial or systolic pressure or a systolic pressure drop to less than 90 mm Hg during the dialysis session. The primary cause is fluid removal from the bloodstream. Ultrafiltration removes fluid from the plasma, which promotes redistribution of fluids from extracellular spaces into the plasma. However, decreased serum albumin levels and removal of solutes from the bloodstream decrease the osmotic pressure of the plasma relative to the extracellular spaces, slowing redistribution during hemodialysis.67 The decreased plasma volume causes hypotension. Other factors that can contribute to hypotension include antihypertensive medications prior to HD, a target "dry weight" (the target weight after HD session is complete) that is too low, diastolic or autonomic dysfunction, low dialysate calcium or sodium, high dialysate temperature, or ingesting meals prior to HD.

Fistula For Dialysis

FIGURE 26-7. The predominant types of vascular access for chronic dialysis patients are (A) the arteriovenous fistula and (B) the synthetic arteriovenous forearm graft. The first primary arteriovenous fistula is usually created by the surgical anastamosis of the cephalic vein with the radial artery. The flow of blood from the higher-pressure arterial system results in hypertrophy of the vein. The most common AV graft (depicted in green) is between the brachial artery and the basilic or cephalic vein. The flow of blood may be diminished in the radial and ulnar arteries because it preferentially flows into the low pressure graft. (From Foote EF, Manley HJ. Hemodialysis and peritoneal dialysis. In: DiPiro JT, Talbert RL, Yee GC, et al., eds. Pharmacotherapy: A Pathophysiologic Approach, 7th ed. New York: McGraw-Hill, 2008: 0106, with permission.)

FIGURE 26-7. The predominant types of vascular access for chronic dialysis patients are (A) the arteriovenous fistula and (B) the synthetic arteriovenous forearm graft. The first primary arteriovenous fistula is usually created by the surgical anastamosis of the cephalic vein with the radial artery. The flow of blood from the higher-pressure arterial system results in hypertrophy of the vein. The most common AV graft (depicted in green) is between the brachial artery and the basilic or cephalic vein. The flow of blood may be diminished in the radial and ulnar arteries because it preferentially flows into the low pressure graft. (From Foote EF, Manley HJ. Hemodialysis and peritoneal dialysis. In: DiPiro JT, Talbert RL, Yee GC, et al., eds. Pharmacotherapy: A Pathophysiologic Approach, 7th ed. New York: McGraw-Hill, 2008: 0106, with permission.)

Risk factors that may increase the potential for hypotension include elderly age, diabetes, autonomic neuropathy, uremia, and cardiac disease.66 The symptoms associated with hypotension during dialysis include dizziness, nausea, vomiting, sweating, and chest pain.

Treatment. Nonpharmacologic management of acute hypotension that occurs during dialysis involves placing the patient in the Trendelenburg position (with the head lower than the feet) and decreasing the ultrafiltration rate. Pharmacologic management of acute hypotension during dialysis includes administration of normal saline (100-200 mL), hypertonic saline (23.4%, 10-20 mL), or mannitol (12.5 g) to restore intravascular volume.

Preventive measures for patients who may be prone to hypotension include accurate determination of the "dry weight" and maintaining a constant ultrafiltration rate. Midodrine is an a-adrenergic agonist that is effective in reducing hypotension in patients with autonomic dysfunction that is taken with each dialysis session or as chronic therapy. Midodrine can be administered at doses of 2.5 to 10 mg prior to HD or 5 mg twice daily for chronic hypotension. Side effects of midodrine include pruritus and paresthesias.

Diabetes 2

Diabetes 2

Diabetes is a disease that affects the way your body uses food. Normally, your body converts sugars, starches and other foods into a form of sugar called glucose. Your body uses glucose for fuel. The cells receive the glucose through the bloodstream. They then use insulin a hormone made by the pancreas to absorb the glucose, convert it into energy, and either use it or store it for later use. Learn more...

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