Orthostatic vital signs, also called tilt or postural vital signs, measure blood pressure and pulse rate while patients are sitting, standing or in a supine position, lying face upward. The results of these measurements are used to assess possible volume depletion, such as with blood loss, vomiting, or diarrhea. Physicians use the results to determine if patients need further testing, intravenous fluid replacement therapy, or other forms of treatment.
The technique for taking orthostatic vital signs requires healthcare providers to take two sets of measurements. First, patients go into the supine position for one to three minutes before blood pressure and pulse readings are taken. Patients who are not feeling dizzy and are able to walk on their own can skip the sitting measurement and move right to standing. Those who are brought into a medical facility by ambulance or wheelchair or those suffering from dizziness are placed in a supported sitting position for the second reading. In order to ensure an accurate comparison, the orthostatic vital signs must be taken on the same arm during both measurements.
Typically, when a patient stands up from a supine position, gravity causes the blood to pool in the lower body, which triggers a response in the heart’s receptors. This response causes the blood vessels in the extremities to constrict, the heart rate to increase, and the kidneys to hold onto fluids. These actions force the blood back into the core system that provides circulation to vital organs such as the heart, liver, kidneys and brains. In patients with decreased blood volume, the circulatory system does not have enough blood to create this response.
Experts are in disagreement over exactly what constitutes a significant change in orthostatic vital signs from a supine to a sitting or standing position. The general consensus states that a pulse increase greater than 20 beats per minute or a blood pressure drop greater than 20 millimeters of mercury (MM Hg) may indicate a depleted fluid volume. Typically, physicians are more concerned with the diastolic blood pressure, represented by the bottom number in a blood pressure reading, which measures pressure when the heart is at rest.
Conditions that can cause a loss of fluid volume include recent brain attack such as stroke or aneurism, toxic shock syndrome, heavy alcohol consumption, autonomic disorders, and chronic fatigue syndrome. Prolonged bed rest, diabetes and neurological diseases can also deplete the body’s fluid volume. Some medications may also be responsible for the condition, including diuretics, calcium channel blockers, and monoamine oxidase (MAO) inhibitors.
While orthostatic vital signs can be a useful tool in helping diagnose volume depletion, it is usually followed up with additional testing. Many factors affect blood pressure and pulse rate, so they are not reliable indicators of a specific problem on their own.