Pediatric emergency medicine trisk 1511 1511
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posture. Symptoms of orthostatic hypotension consist of lightheadedness,
syncope or presyncope, vision changes, headaches, palpitations, tremulousness,
and diaphoresis and are ameliorated by recumbent position. The causes include
volume depletion (e.g., hemorrhage or dehydration), febrile illness, pregnancy,
anemia, eating disorders, and use of medications such as diuretics, vasodilators,
or calcium channel blockers. Symptoms typically abate upon treatment of the
primary cause. In some patients, recurrent orthostatic symptoms may occur in the
absence of true orthostatic hypotension, and may be associated with an excessive
increase in heart rate during upright positioning. This condition is known as
postural orthostatic tachycardia syndrome (POTS). It is a clinical syndrome
usually characterized by (1) frequent symptoms that occur with standing, such as
lightheadedness, blurred vision, palpitations, tremor, generalized weakness,
exercise intolerance, and fatigue; (2) an increase in heart rate of ≥30 beats per
minute (bpm) when moving from a recumbent to a standing position (or ≥40 bpm
in individuals 12 to 19 years of age); and (3) the absence of orthostatic
hypotension (as defined by >20 mm Hg drop in systolic BP). There are two forms
of POTS, and both forms are observed more often in females than males. In the
first and more common type, persistent tachycardia, associated with fatigue,
exercise intolerance, and palpitations, is present while the patient assumes an
upright position. This condition may occur after a viral illness, trauma, or surgery.
The second or central form of POTS is often associated with migraines, tremor,
and excessive sweating. Presyncope is a more common symptom than syncope in
patients with POTS; however, POTS and vasovagal syncope are not mutually
exclusive. The clinician should make careful use of the history and physical
examination to distinguish between patients with suspected POTS and those with
other disorders. The anxiety and somatic hypervigilance sometimes attributed to
patients with POTS may be associated with other disorders such as migraine or
mood disorders. Similarly, fatigue and weakness could be signs of another
systemic illness.
Dysautonomia
In rare cases, a child may exhibit an inadequate vasoconstriction in response to
postural changes that would normally demand sympathetic nervous system
activation. In such patients, the heart rate may not increase appropriately with
standing, and BP may be labile, leading to syncope.
Drugs and Toxins
Medications that decrease cardiac output, such as barbiturates and tricyclic
antidepressants, may cause syncope. Recreational drugs such as cocaine, alcohol,
