Hypotension is low blood pressure. It is diagnosed when the systolic reading (the top or first number in a blood pressure reading) is less than 90mmHg, or 40mmHg less than the patient's usual blood pressure.(1) Maintaining blood pressure while in the standing position depends upon several factors; an adequate amount of blood, no problems for blood to return through the veins to the heart, and properly functioning nervous system.

A serious form of low blood pressure is called orthostatic hypotension. This occurs when one is lying down and gets up too quickly and then feels weak and dizzy from the sudden drop in blood pressure. Orthostatic (also called postural) hypotension can be a very disabling disorder. Patients often lose their job as a result, and often home health support for patients and psychological help for caregivers is essential.

A patient suffering from hypotension should have their current medications reviewed. A number of medications may cause postural hypotension, including diuretics (drugs that remove excess fluid), antihypertensives (medications that lower blood pressure), antidepressants, phenothiazines (drugs for psychiatric disorders), alcohol, narcotics, insulin, barbiturates, and beta-adrenergic and calcium channel blockers (heart drugs). Postprandial hypotension occurs as blood is moved to the abdominal circulation after a meal. Therefore, giving blood pressure lowering medications at meals should be done with caution to make sure that the blood pressure is not already significantly lowered just from eating a meal. Giving medication may lower it further, possibly harming the patient.

The rate of hypotension that happens during or immediately following dialysis ranges from 15 to 50 percent.(2) The cause is usually due to many factors, and includes taking blood pressure medications or food before or during dialysis, severe hypocalcemia (low calcium in the blood), and high amounts of magnesium in the dialysis solution.