97% and a specificity of 96% for blood loss >630 mL). This change (as well as severe posturaldizziness, s may last 12–72 hours if IV fluids are not administered.
The second most helpful finding is postural dizziness so severe to stop the test. This has the same sensitivity and specificity as tachycardia. Mild postural dizziness, instead, has no value. Hypotension of any degree while standing has little value unless associated with dizziness. In fact, an orthostatic drop in systolic BP >20 mmHg unassociated with dizziness can occur in one third of patients >65 years old and 10% of younger subjects, with or without hypovolemia.
Supine hypotension (systolic BP <95 mmHg) and tachycardia (>100/min) may be absent, even in
patients with blood losses >1 L. Hence, although quite specific for hypovolemia when present, supine
hypotension and tachycardia have low sensitivity; they are present in one tenth of patients with
moderate blood loss and in one third with severe blood loss. Paradoxically, blood-loss patients may
even present with bradycardia as a result of a vagal reflex.
Note that bedside maneuvers have been primarily studied in patients with blood loss. They have not been
as extensively evaluated for hypovolemia from vomiting, diarrhea, or decreased oral intake.