BASED ON CONCENTRATION gradients across a semipermeable membrane, hemodialysis replaces two of the major functions of failing kidneys: removing excess fluid from the body and cleaning the blood by removing excess electrolytes and metabolic waste. If, for example, the concentration of a small molecular weight solute such as creatinine is higher on one side of the membrane than on the other, the solute will diffuse across the membrane from an area of higher concentration to an area of lower concentration. Similarly, if fluid pressure is higher on one side of the membrane than on the other, fluid will flow across the membrane from an area of higher pressure to an area of lower pressure.
Hemodialysis is a complex procedure requiring advanced technology and careful supervision from educated nurses and technicians. This is particularly true in a hospital, where patients are less stable and more prone to complications than they might be in an outpatient dialysis center.
In this article, review the causes and manifestations of one of the most common complications of hemodialysis: dialysis hypotension (also called intradialytic hypotension). Also, learn interventions you can use to prevent and treat dialysis hypotension while your patient is on hemodialysis.
Why hemodialysis may lead to dialysis hypotension
Dialysis hypotension occurs in as many as 25% of hemodialysis treatments and affects half of all hemodialysis patients.1,2 It limits the dose of dialysis, diminishes any remaining renal function, and contributes to the patient's chronic cardiovascular and cognitive decline.1,2
The primary cause of dialysis hypotension is fluid removal.3 If fluid is removed too quickly or if too much is removed overall, blood volume drops and the body responds. Most people can tolerate losing up to 25% of their blood volume, but dialysis patients are much less tolerant of volume loss.4 Because they're typically older adults with other health problems, such as heart disease or diabetes, most dialysis patients have blunted cardiovascular and neurologic responses to changes in fluid volume, leaving them especially vulnerable to dialysis hypotension.3 (See Who's at risk?) Dialysis increases body temperature, causing vasodilation, which exacerbates hypotension.
Recognizing signs and symptoms
Dialysis hypotension is defined as a decrease in systolic BP by more than 20 mm Hg or a decrease in mean arterial pressure by 10 mm Hg associated with the following signs and symptoms:
- abdominal discomfort
- muscle cramps
- dizziness or fainting
These can be easy to miss in a patient who's already debilitated, and restlessness may seem like a normal response to undergoing dialysis for several hours. Always look for subtle changes in your patient's appearance and behavior that may suggest dialysis hypotension.
Prevention and intervention
Many dialysis patients have had a "dry weight" determined for them. This is set at the weight below which unacceptable signs and symptoms, such as cramping, nausea, vomiting, or hypotension, occur.5 In an outpatient setting, patients are normally weighed before their hemodialysis treatment to see how much fluid they need to lose to get back to their dry weight.
Determining a healthy patient's dry weight is helpful in preventing excess loss of fluid volume and dialysis hypotension, but it may not be right for a hospitalized patient because the dry weight can rapidly change when he becomes acutely ill, loses muscle or other tissue mass, or is anorexic.6 Weigh your patient daily and note the reported dry weight, but avoid using it as a gold standard while the patient is hospitalized.
Advise your patient to maintain any sodium and fluid restrictions, refrain from taking antihypertensive medications and long-acting vasodilators before the scheduled dialysis (as ordered), and avoid eating just before or during dialysis.7
Increasing blood osmolality is another common strategy for preventing dialysis hypotension.1 This can be done with I.V. hypertonic saline, mannitol, or albumin, or by increasing the dialysis solution's sodium content. These methods are especially helpful with patients who have uremia. In these patients, the quick removal of metabolic waste from the blood can lower the osmolality so much that fluid shifts away from blood into the tissues, which contributes to blood volume loss.3 Raising blood osmolality has some drawbacks, however, because it also stimulates thirst and weight gain between dialysis treatments.
Another approach to avoid dialysis hypotension is to cool the dialysis solution down to 95.9° F (35.5° C) to stimulate the patient's sympathetic nervous system.1 This constricts blood vessels, increases the heart rate, and improves cardiac contractility—all of which help prevent hypotension by increasing cardiac output. Some patients notice the temperature change and may shiver or complain of feeling cold.1 Maintaining body temperature at the patient's predialysis temperature can help prevent adverse reactions.7
Devices to monitor intradialytic changes in blood volume have been advocated to minimize dialysis hypotension based on the concept that the likelihood of developing hypotension will always occur at roughly the same reduction of blood volume; however, most studies haven't found a close relationship between individual changes in blood volume and occurrence of hypotension. Blood volume monitoring can be an effective tool when it's incorporated into a biofeedback system where dialysate conductivity and ultrafiltration rate are constantly adjusted on the basis of input from the measured change in blood volume. It's designed to guide the reduction in blood volume along a preset individual trajectory to avoid sudden reductions that can cause hypotension. This technique reduces the frequency of hypotensive episodes and provides greater stability of BP during and after the procedure.5
Once dialysis hypotension begins, early intervention is key. You can stop its progression by positioning the patient flat or in the Trendelenburg position, giving a 200-mL bolus of 0.9% sodium chloride, and turning down the rate of fluid loss.8 If problems continue, consider these interventions:
- Exclude a nondialysis-related cause such as cardiac ischemia, pericardial effusion, or infection.
- Individualize the dialysis prescription with an accurate setting of the dry weight.
- Increase the osmolality and cool the dialysis solution.
- Maximize cardiac performance with an inflatable abdominal band to improve venous return to the heart.
You may find that your patient doesn't respond and isn't stable enough for regular hemodialysis. If so, have the treatment stopped and call the patient's nephrologist, who may order continuous renal replacement therapy. Used mostly in ICUs, this is a slower, gentler hemodialysis that's much easier for an unstable patient to tolerate.
As your hospitalized patient's nurse, you're privy to a comprehensive view of the patient's health that the dialysis staff may not have. Collaborate with them to make sure your patient is safe and comfortable.
Who's at risk?7
Patients with the following conditions should be evaluated carefully for the risk of developing dialysis hypotension.
- diabetic chronic kidney disease (stage 5)
- cardiovascular disease
- poor nutritional status and hypoalbuminemia
- uremic neuropathy or autonomic dysfunction
- severe anemia
- predialysis systolic BP of <100 mm Hg
- age 65 or over
1. Dheehan S, Henrich WL. Preventing dialysis hypotension: a comparison of usual protective maneuvers. Kidney Int
2. Santoro A, Mancini E, Basile C, et al. Sodium volume controlled hemodialysis in hypotension-prone patients: a randomized, multicenter controlled trial. Kidney Int.
3. Kitamura M, Saito A. Dialysis hypotension: a review of recent studies of 4 causative factors. Nephrology
4. van der Sande FM, Kooman JP, Leunissen KM. Intradialytic hypotension—new concepts on an old problem. Nephrol Dial Transplant
5. Palmer BF, Henrich WL. Recent advances in the prevention and management of intradialytic hypotension. J Am Nephrol
6. Levin NW, Folden T, Zhu F, Ronco C.. Dry weight determination. In: Ronco C., series ed, La Greca G, vol ed. Contributions to Nephrology: Vol. 137. Hemodialysis Technology
. Basel, Switzerland: Karger; 2002:272–278.
7. National Kidney Foundation. KDOQI clinical practice guidelines for cardiovascular disease in dialysis patients
8. Hemametrics. Hypovolemia