02/12/2025
HYPOTENSION DURING DIALYSIS
Hypotension during intermittent hemodialysis is common, and has been attributed to acute volume shifts, shifts in osmolarity, electrolyte imbalance, temperature changes, altered vasoregulation, and sheer hypovolemia. Intradialytic hypotension (IDH) remains to be a major complication of hemodialysis. It occurs in nearly 25% of dialysis sessions and often requires aggressive resuscitative measures and sometimes premature termination of hemodialysis. It is also a significant independent factor affecting mortality in hemodialysis patients.
Definition:
There is no generally accepted definition of intradialytic hypotension. Kidney Disease Outcomes Quality Initiative (K/DOQI) and European Best Practice Guidelines define intradialytic hypotension as the presence of a decrease in systolic blood pressure > 20mm of Hg or a decrease in mean arterial pressure by 10mm of Hg, which is associated with clinical events and need for nursing interventions.
Pathophysiology:
• Among other factors, the major pathophysiology of these episodes is the removal of large volume of blood water and solutes over a short period of time, overwhelming normal compensatory mechanisms, which include plasma refilling and reduction of venous capacity (due to reduction of pressure transmission to veins). In some patients, a seemingly paradoxical and inappropriate reduction of sympathetic tone may occur, causing reduction of arteriolar resistance, decreased transmission of pressure to veins with corresponding increase in venous capacity. Increased sequestration of blood in veins under conditions of hypovolemia reduces cardiac filling, cardiac output and ultimately blood pressure.
• Hypotensive episodes during hemodialysis in patients with end stage renal disease in absence of inadequate maintenance of the plasma volume, pre-existence of cardiovascular disease, or autonomic nervous system dysfunction are accompanied by increased plasma concentrations of the end-products of nitric oxide metabolism (above the expected levels, based on the reduction of urea).
Risk factors:
• Older age
• Longer dialysis vintage
• Diabetes
• Lower predialysis blood pressure
• Lower albumin
• Female s*x
• Hispanic ethnicity
• Higher body mass index
Causes of intra-dialytic hypotension:
• Major factors that contribute to intradialytic hypotension include:
o Rapid or excessive ultrafiltration
o A rapid reduction in plasma osmolality
o Incorrectly low prescribed target weight
o Autonomic neuropathy
o Diminished cardiac reserve.
• Other contributors to intradialytic hypotension include the intake of antihypertensive medications or the ingestion of a meal immediately before or during dialysis.
• The composition and temperature of the dialysate fluid may contribute to intradialytic hypotension.
o Hypotension has been associated with the use of dialysate acetate, low sodium, high magnesium, and low calcium.
o Dialysate temperature that is higher than body temperature has also been associated with hypotension.
• Other suggested contributors include the release of adenosine during organ ischemia, the increased synthesis of endogenous vasodilators (such as nitric oxide), and inappropriately low plasma vasopressin levels.
Clinical Presentation:
• Occasionally asymptomatic
• Lightheadedness
• Muscle cramps
• Nausea
• Vomiting
• Dyspnea
• Vagal symptoms, including yawning, sighing, and hoarseness, may be observed before the drop in blood pressure is detected.
Acute management:
• Ultrafiltration rate should be decreased or stopped, depending upon the severity of hypotension.
• The patient should be placed in the Trendelenburg position, where the body is laid flat on the back (supine position), with the feet higher than the head by 15 to 30 degrees.
• Intravascular volume should be replaced in cases when blood pressure is not restored after stopping ultrafiltration and repositioning the patient. We give an intravenous fluid bolus of 250 to 500 mL. Intravenous fluid is effective in restoring blood pressure.
• Oxygen should be administered. There is evidence that intradialytic blood oxygen saturation and its variability are associated with intradialytic hypotension. A decrease in central venous oxygen saturation most likely indicates a decline in cardiac output.
• Patients with persistent hypotension despite measures above should be evaluated for evidence of an underlying serious cause.
o This assessment primarily includes a physical examination, including auscultation of heart and lungs, palpation of the abdomen, and examination of the hemodialysis access for evidence of infection.
o An electrocardiogram should be performed.
o Particular concerns include occult sepsis, previously unrecognized cardiac and/or pericardial disease, and gastrointestinal bleeding.
o Rare, serious causes of hypotension on dialysis include hemolysis, reaction to dialyzer, or air embolus. Hemolysis may be suggested by the simultaneous occurrence of symptoms in multiple patients and occasionally port-wine appearance of blood in the venous line. Air embolus may be accompanied by distinctive clinical findings, including characteristic heart sounds.
o Reactions to the dialyzer or machine tubing may be manifested by chest and back pain and by signs of allergic reaction (urticaria, flushing, coughing, sneezing), in addition to hypotension.
• Hypotension that does not respond to saline bolus or is accompanied by symptoms such as fever, chills, chest and/or abdominal pain, or dyspnea suggests a serious cause. Such patients are generally referred to a hospital for more extensive evaluation. Once serious causes have been excluded, further evaluation is directed to the prevention of future episodes.
Prevention of recurrent episodes:
• Patients who have recurrent episodes of intradialytic hypotension should be carefully evaluated and preventive strategies put in place. Subsequent evaluation and intervention depend upon patient response to initial measures.
• First-line approach: The first-line approach includes reassessing the target weight, avoiding food intake during dialysis, withholding antihypertensive agents prior to dialysis, and limiting interdialytic sodium intake to reduce ultrafiltration requirements.
o Reassess target weight – We reassess the prescription target weight. The optimal target weight is often determined empirically by trial and error ("probing"). Using a trial-and-error approach, the target weight is set just above the weight at which unacceptable symptoms, such as cramping, nausea, and vomiting, or hypotension occur. Future episodes of intradialytic hypotension may be prevented in some patients by increasing the target weight.
o Avoid food during dialysis – We ask patients who are prone to intradialytic hypotension to avoid food during dialysis. Peripheral vascular resistance generally drops 20 to 120 minutes after the ingestion of food, which may cause a decrease in blood pressure.
o Withhold antihypertensive agents – Patients who are prone to intradialytic hypotension should withhold antihypertensive agents prior to dialysis. Among such patients, we avoid prescribing blood pressure medications that need to be taken twice (or more) daily. Whenever possible, we prefer medications that can be given once daily and then ask patients to take the dose at night.
o Limit interdialytic sodium intake – We ask patients who are prone to intradialytic hypotension to limit sodium (salt) intake, which results in a reduction in fluid intake. Excessive sodium intake results in thirst and larger extracellular volume gain that must be removed by ultrafiltration. Since the dialysis time for each session is generally fixed, the ultrafiltration rate must be increased to attain target weight by the end of the individual session. We generally ask patients to limit sodium intake to 1 to 2 grams per day; this amount of sodium is equivalent to 2.5 and 5 grams of salt, respectively, or roughly one-half and one teaspoon of salt, respectively.
o Review dialysate composition – We generally make sure that dialysate calcium and magnesium are ≥2.25 mEq/L and ≥1.0 mEq/L, respectively. Low-dialysate calcium and magnesium have been associated with intradialytic hypotension.
o Increase urine output – Among patients with residual urine output, we attempt to augment urine output with oral diuretic administration. Use of loop diuretics has been associated with lower interdialytic weight gain and lower rates of intradialytic hypotension among hemodialysis patients.
• Second-line approach: The second-line approach includes a cardiac evaluation, the use of cool dialysate, and an increase in dialysis time and/or frequency.
o Assess primary cardiac factors – We perform a careful assessment for primary cardiac factors that may promote the development of intradialytic hypotension. The risk of intradialytic hypotension is increased in patients with heart failure, cardiomegaly, or ischemic heart disease. A pericardial effusion should be excluded with an echocardiogram.
o Use of cool dialysate – If primary cardiac factors are not present on evaluation, we use cool-temperature dialysis. Cool-temperature dialysis has been shown to increase hemodynamic stability. If employing a fixed reduction, we reduce the dialysate temperature to 0.5 to 1.0o C below the patient’s body temperature (as monitored by tympanic thermometer). This may lower the body temperature up to approximately 1ºC. This change is generally well tolerated, although some patients develop unacceptable side effects such as chilling or cramping.
o Increasing dialysis time – If the above measures fail to sufficiently decrease the frequency of intradialytic hypotension, we increase the dialysis time. This may be done by increasing the time per session or by adding an additional treatment per week. Increasing the time and/or frequency of hemodialysis may be effective in preventing or reducing intradialytic hypotension.
• Third-line approach: If other treatment options fail to prevent intradialytic hypotension, we use a third-line approach, which includes giving midodrine and/or switching the patient to other forms of dialysis.
o Midodrine – If all other measures fail to decrease the frequency of intradialytic hypotension, we use the selective alpha-1 adrenergic agonist, midodrine. Among patients with autonomic neuropathy and possibly other patients with severe hemodialysis hypotension not responsive to the above measures, midodrine may be effective and well tolerated. We generally give 2.5 to 5 mg, 15 to 30 minutes prior to dialysis. In cases where hypotension occurs later in the hemodialysis treatment, we utilize split dosing, with an initial dose given 30 minutes prior to dialysis and a second dose given halfway through treatment (at least three hours after the first dose).
o Change to other modes of dialysis – Changing from standard, thrice-weekly, in-center hemodialysis to other modes of dialysis, such as peritoneal dialysis, daily dialysis, hemodiafiltration (HDF; if available), or nocturnal hemodialysis, may be an option for patients who have chronic, debilitating intradialytic hypotension. HDF may mitigate intradialytic hypotension.
• Other treatments — In addition to the measures listed above, the correction of anemia to target levels with erythropoiesis-stimulating agents may decrease the frequency of intradialytic hypotension by improving cardiac function.
(Ref: uptodate.com+ncbi.nlm.nih.gov/books)
