OVERVIEW

What is hemodialysis?

Hemodialysis is a treatment method that involves removing toxic substances from the blood, including metabolic waste, toxins, and excess water, to maintain normal bodily functions.

Hemodialysis is primarily used for patients with kidney failure and serves as a key treatment for end-stage renal disease (ESRD) patients to sustain life and improve quality of life.

What is dialysis-related hypotension?

Intradialytic hypotension (IDH), also known as dialysis-related hypotension, is a common complication in end-stage renal disease (ESRD) patients undergoing hemodialysis (HD). Currently, there is no universally accepted definition for dialysis-related hypotension.

The Kidney Disease Outcomes Quality Initiative (KDOQI) guidelines and European Best Practice Guidelines define intradialytic hypotension as a systolic blood pressure drop of ≥ 20 mmHg or a mean arterial pressure drop of 10 mmHg, accompanied by clinical symptoms (e.g., headache, weakness, cramps, nausea, vomiting, restlessness, or other hypotension-related symptoms) requiring medical intervention.

Is dialysis-related hypotension common?

Yes.

Symptomatic hypotension occurs in 5%–30% of all dialysis treatments during or immediately after hemodialysis. Some studies suggest the incidence of dialysis-related hypotension may reach 20%–30% in recent years.

Which groups are more prone to dialysis-related hypotension?

Known risk factors for dialysis-related hypotension include: older age, longer dialysis duration, diabetes, lower pre-dialysis blood pressure, female hemodialysis patients, Hispanic ethnicity, higher BMI, and fewer weekly hemodialysis sessions (fewer sessions increase the risk of IDH).

Note: BMI (Body Mass Index) is calculated as weight (kg) divided by height (m) squared.

What are the types of dialysis-related hypotension?

• Based on frequency, dialysis-related hypotension can be classified into episodic hypotension (EH) and chronic sustained hypotension (SH).

• Based on mechanism, it can be divided into stroke volume-dependent hypotension (SVH) and systemic vascular resistance-dependent hypotension (SVRH). This classification is less commonly used in clinical practice and will not be detailed here.

What are the types of dialysis-related hypotension?

• Based on frequency, dialysis-related hypotension can be classified into episodic hypotension (EH) and chronic sustained hypotension (SH).

• Based on mechanism, it can be divided into stroke volume-dependent hypotension (SVH) and systemic vascular resistance-dependent hypotension (SVRH). This classification is less commonly used in clinical practice and will not be detailed here.

SYMPTOMS

What are the clinical manifestations of dialysis-related hypotension?

• Episodic hypotension (EH): Patients with EH usually have normal or elevated baseline blood pressure before dialysis. Blood pressure drops in the later stages of dialysis or after dialysis, specifically manifesting as a systolic blood pressure decrease of more than 30 mmHg or a diastolic blood pressure decrease of more than 20 mmHg. Common symptoms of hypotension may occur, such as dizziness, weakness, pale complexion, muscle cramps, nausea, and vomiting. In severe cases, transient loss of consciousness may occur. Uremic patients with diabetes, left ventricular hypertrophy, or cardiac insufficiency are prone to EH.

• Chronic sustained hypotension (SH): SH mainly refers to a systolic blood pressure that usually does not exceed 100 mmHg during dialysis. Even with a slight increase or acceleration of ultrafiltration, or under normal ultrafiltration conditions, blood pressure may drop slightly with obvious symptoms of hypotension. This generally occurs in patients undergoing long-term maintenance hemodialysis.

CAUSES

What are the causes of dialysis-related hypotension?

• Insufficient effective circulating blood volume: This is the most common cause of dialysis-related hypotension. Errors in estimating dry weight before dialysis lead to excessive planned fluid removal. When ultrafiltration is excessive or too rapid, the ultrafiltration rate exceeds the capillary refill rate, and the vascular contraction response is insufficient, resulting in reduced effective circulating blood volume, decreased cardiac perfusion, and lowered cardiac output, ultimately causing hypotension.

• Reduced peripheral vascular resistance: When effective circulating blood volume decreases, peripheral blood vessels fail to constrict to raise blood pressure, leading to a drop in blood pressure.

• Autonomic dysfunction: More than 50% of patients on maintenance dialysis have autonomic dysfunction, which disrupts the steady-state regulation of blood pressure.

• Cardiovascular disease factors: Conditions such as left ventricular hypertrophy, heart failure, and atherosclerosis can impair cardiovascular responsiveness, weaken defensive mechanisms, and trigger hypotension.

• Dialysate factors: The frequency of dialysis-related hypotension is significantly correlated with dialysate sodium concentration, plasma sodium concentration, and the sodium gradient.

• Other factors: Taking antihypertensive drugs or sedatives before or during dialysis, excessively low dialysate sodium concentration, or excessively high dialysate temperature can all cause vasodilation, reduce peripheral vascular resistance, and induce dialysis-related hypotension.

What are the predisposing factors for dialysis-related hypotension?

Studies indicate that predisposing factors for dialysis-related hypotension include:

• Age > 60 years.
• Comorbidities: Such as heart disease, diabetes, vasculitis, severe anemia, or hypoalbuminemia.
• Eating during hemodialysis.
• High ultrafiltration volume.
• Low-sodium dialysate.
• Acetate-based dialysate.
• Excessively high dialysate temperature.

DIAGNOSIS

How is dialysis-related hypotension clinically diagnosed?

Blood pressure is continuously monitored or measured during dialysis, and diagnosis is generally straightforward based on changes in blood pressure during the procedure.

Additionally, if a patient reports symptoms such as headache, general weakness, cramps, nausea, vomiting, or restlessness, blood pressure should be measured immediately, as dialysis-related hypotension may be suspected.

What conditions should dialysis-related hypotension be differentiated from?

Many acute complications during dialysis can also present with hypotension. Physicians should note that not all cases of hypotension or reduced circulating blood volume are caused by ultrafiltration and should consider ruling out the following conditions:

• Neurological disorders: Ischemic stroke, intracranial hemorrhage, seizures, dialysis disequilibrium syndrome, etc.;

• Cardiovascular diseases: Heart failure, arrhythmias, acute coronary syndrome, pulmonary embolism, etc.;

• Other conditions: Allergic reactions, gastrointestinal bleeding, etc.

TREATMENT

How to manage dialysis-related hypotension?

Once dialysis-related hypotension occurs, emergency measures should be taken immediately, including: immediately stopping or reducing ultrafiltration, appropriately slowing blood flow, and rapidly replenishing blood volume. Oxygen should also be administered simultaneously.

For patients with severe symptoms, hypertonic saline, hypertonic glucose, or albumin can also be given. Additionally, the patient should be placed in a Trendelenburg position, lying flat with their feet elevated 15–30 degrees above their head.

For severe cases or those unresponsive to the above measures, the underlying cause of hypotension should be actively investigated. Other potential diseases should also be ruled out. Rare but serious causes include hemolysis, dialysis membrane reactions, or air embolism, which should not be overlooked.

What serious consequences can arise if dialysis-related hypotension is not promptly and effectively managed?

Dialysis-related hypotension can lead to ischemia and hypoxia in multiple organs, with the most significant impact on the heart and brain.

Specific consequences include: ischemic brain injury, irreversible ventricular remodeling (left ventricular hypertrophy, atrial enlargement, etc.), arrhythmias, myocardial infarction, heart failure, stroke, vascular calcification, atherosclerosis, and arteriovenous fistula thrombosis.

Although dialysis-related hypotension is closely associated with cardiovascular disease, there is limited research on its relationship with cardiovascular mortality. Whether dialysis-related hypotension is a risk factor for cardiovascular death remains controversial.

Can dialysis-related hypotension recur? How can recurrence be reduced?

Recurrence is common. The following measures can help reduce recurrence and, to some extent, prevent dialysis-related hypotension:

• Reassess target weight (dry weight): In addition to careful history-taking and physical examination, objective methods such as bioimpedance or inferior vena cava diameter measurement can be used to determine dry weight.

• Strictly control interdialytic weight gain: Limiting fluid and salt intake is the most effective way to prevent excessive weight gain. Interdialytic weight gain should be less than 3% of standard body weight.

• Individualized ultrafiltration: For first-time dialysis patients, the elderly, frail, or those using large-surface-area dialyzers, hourly ultrafiltration should not exceed 1% of body weight. Post-dialysis weight should not fall below dry weight.

• Sequential and adjustable sodium dialysis: Low-sodium dialysis increases the risk of hypotension, while high-sodium dialysis may cause thirst. Adjusting dialysate sodium concentration from high to low during dialysis helps maintain stable blood volume.

• Use cool or isothermic dialysis: Cool dialysis improves vascular reactivity and hemodynamic stability, reducing the frequency and severity of intradialytic hypotension (IDH) compared to standard dialysis. Isothermic dialysis maintains constant body temperature throughout dialysis, stabilizing blood pressure in hypotension-prone patients.

• Check dialysate composition: Ensure dialysate calcium concentration ≥ 2.25 mEq/L and magnesium concentration ≥ 1.0 mEq/L.

• Avoid eating during dialysis: Peripheral vascular resistance typically decreases 20–120 minutes after eating, which may lead to a drop in blood pressure.

• Rational use of antihypertensives: Patients prone to dialysis-related hypotension should skip antihypertensive medications on dialysis days. Once-daily medications taken at night are preferable.

• Extend dialysis time: Longer dialysis sessions and/or increased frequency (up to 4 times per week) can effectively prevent or reduce intradialytic hypotension.

• Midodrine: If other measures fail, the selective α-1 adrenergic agonist midodrine can be used. A dose of 2.5–5 mg can be given 15–30 minutes before dialysis. Common side effects include piloerection, urinary retention, supine hypertension (relieved by elevating the head of the bed), paresthesia, and pruritus.

• Correct anemia: Timely anemia correction, including blood transfusions during dialysis for severe cases, can reduce the frequency of dialysis-related hypotension. Erythropoiesis-stimulating agents can be used to achieve target hemoglobin levels.

What is the prognosis for patients with dialysis-related hypotension?

Patients with intradialytic hypotension have higher rates of complications and mortality, particularly those with a minimum systolic blood pressure below 90 mmHg.

DIET & LIFESTYLE

What should high-risk groups for dialysis-related hypotension pay attention to in daily life?

For patients prone to dialysis-related hypotension, dietary control is crucial. Malnourished dialysis patients need to supplement protein and calories while strictly managing weight during dialysis. A low-fat diet with controlled water and salt intake is recommended.

Strictly follow medical instructions during dialysis and avoid eating without permission. Cooperate with blood pressure monitoring and promptly report any discomfort to the doctor.

PREVENTION

Can dialysis-related hypotension be prevented? How to prevent dialysis-related hypotension?

It can be prevented.

For specific prevention methods, refer to the content on recurrence prevention in the "Treatment" section.