Low blood pressure is also known as hypotension. While low blood pressure in adults is a wellness goal, in children, lower-than-normal pressure can be dangerous. Hypotension may occur for a variety of reasons. On one end of the spectrum are relatively mild, reversible causes of hypotension such as dehydration. On the other end of the spectrum are potentially life-threatening reasons for hypotension, such as disease or severe shock.
The Mayo Clinic describes dehydration as the condition that occurs when there is an imbalance between the amount of water a person takes in and the amount of water and fluid the body needs. It is a potentially serious condition that may result from severe diarrhea, fever, or excessive sweating; even exercising on a hot day could cause dehydration. Hypotension--especially orthostatic hypotension--may occur as a result of the dehydration; the decrease in fluid causes a decrease in blood volume and low blood pressure results.
Certain medications can have significant effects on tone of the blood vessels--that is, whether blood vessels are dilated or constricted. For instance, as the name implies, vasodilators such as hydralazine act to dilate the blood vessels. One potential result of such dilation is low blood pressure in children taking these medications. Another example is the calcium channel blocker nifedipine. According to the online pharmacology reference MicroMedex, this medication works by blocking the ability of the calcium ion to pass into certain cells within the heart and blood vessels; this results in dilation of the blood vessels, and could potentially cause low blood pressure in children taking this medication.
According to the medical textbook "Current Diagnosis and Treatment: Emergency Medicine," anemia can be defined as an abnormally low concentration of red blood cells. Within the United States, one of the most common reasons for anemia to occur is iron deficiency; chronic disease may cause anemia. Among the many potential symptoms associated with slowly developing, long-standing anemia, is that of orthostatic hypotension. Orthostatic hypotension refers to low blood pressure that occurs when a person stands up from a sitting position. If anemia develops over a short period of time, low blood pressure--regardless of whether the person is sitting or standing--may be one of the potential indicators that something is wrong.
The adrenal gland is an important organ that is responsible for the release of many hormones that are needed for the body to function normally. Adrenal insufficiency is the general term used to describe the impairment in the production and release of these hormones. In the online medical reference UpToDate, Dr. Patricia Donohoue of the Medical College of Wisconsin reports that in primary adrenal insufficiency, the adrenal gland itself is damaged. One type of primary adrenal insufficiency results in a deficiency of specifically the mineralocorticoid hormones such as aldosterone. Low blood pressure from this type of adrenal insufficiency occurs because there is too little salt--in the form of sodium--in the blood. Children with mineralocorticoid deficiency may have symptoms associated with low blood pressure, such as dizziness.
Shock is the term used to indicate a series of changes in the body that result in a significant decrease in the circulation of blood to the various tissues and organs of the body, leading to decreased oxygen delivery and potentially irreversible damage. Shock may occur for a variety of reasons: severe diarrhea, for instance, can lead to significant loss of fluid from the body and result in hypovolemic shock. A major bacterial infection can lead to a condition known as sepsis, which in turn can cause a type of shock called distributive shock. Regardless of the original cause of the shock, the shock syndrome often follows a certain series of stages. The second of the three stages is known as hypotensive shock; in this stage, the body is no longer able to compensate for the decrease in perfusion and blood pressure starts to fall. Drs. Wendy Pomerantz and Mark Roback, writing in UpToDate, report that children who have lost up to one-third of their circulating blood volume may still have normal blood pressure readings. However, once their blood pressure begins falling, they tend to deteriorate very quickly, so preventing this stage from occurring is the goal.