Blood pressure is measured as systolic -- the pressure as the heart contracts -- over diastolic -- the pressure as the heart muscle relaxes. A normal blood pressure reading for most adults is lower than 120/80. Low blood pressure, or hypotension, according to MayoClinic.com, is a reading of 90/60 or less. There are many causes of low blood pressure, and some can become life-threatening.
Dehydration
Dehydration occurs as the amount of fluid required by the body is lost and not replaced. Causes of dehydration include not drinking enough water or fluids, excessive sweating or urine output and illnesses such as diarrhea and vomiting. When dehydration becomes severe, it is a life-threatening emergency.
Symptoms of dehydration include dry mouth, low blood pressure, rapid heart rate and reduced or no urine output. Risk factors for developing low blood pressure from dehydration include sick infants and children, prolonged bed rest and anyone with extreme heat exposure.
Treatment goals for low blood pressure caused by dehydration are to replace fluids by mouth or by intravenous feeding to restore the balance of fluid intake and output.
Eating
Symptoms of dizziness or lightheadedness following a meal can indicate a condition known as postprandial hypotension, or low blood pressure after eating. According to Merck.com postprandial hypotension affects up to one-third of the elderly.
The digestive process requires a lot of blood flow, which requires the heart to pump more efficiently. Conditions that can increase the risk of postprandial hypotension include taking high blood pressure medications before meals and disorders such as Parkinson's disease and diabetes.
Treatment goals for postprandial hypotension include reducing the dosage of high blood pressure medicine before meals, eating smaller meals that are low in carbohydrates and lying down after eating.
Anaphylaxis
Anaphylaxis is a potentially life-threatening allergic reaction to allergens such as insect bites, medications or food. Symptoms of anaphylaxis can involve the respiratory system with difficulty breathing; the gastrointestinal tract with nausea and vomiting; and the cardiovascular system with rapid pulse and low blood pressure.
The risk for anaphylaxis is increased in people with a history of any type of allergic reaction, reports the University of Maryland Medical Center. Treatment goals include airway support, fluids and medications to restore the blood pressure to normal.
Getting Up Quickly
Low blood pressure that occurs upon standing up quickly is known as orthostatic hypotension. Possible causes include being elderly, medications, pregnancy, diabetes, immobility and dehydration.
Factors associated with orthostatic hypotension, according to MayoClinic.com, include people over the age of 65, medications such as diuretics and heart medications, getting too hot and crossing the legs at the knee.
