A dehydrated patient may experience an orthostatic BP change when standing. By how many millimeters of mercury can systolic BP drop?

A dehydrated patient may experience an orthostatic BP change when standing. By how many millimeters of mercury can systolic BP drop?

• A. 5 to 10 mmHg
• B. 10 to 15 mmHg
• C. 20 to 25 mmHg
• D. 30 to 40 mmHg

Answer: (B)

When standing, gravity pulls blood into the legs, and in someone who is dehydrated there is already less circulating volume to begin with. The heart can’t fully compensate quickly, so a modest drop in systolic blood pressure occurs. A drop of about 10–15 mmHg is a common amount seen with volume depletion and can produce symptoms like lightheadedness in older adults. Larger drops, around 20 mmHg or more, would meet the usual diagnostic threshold for orthostatic hypotension, but the scenario highlights the typical, milder change that dehydration can cause. So the best choice is the 10–15 mmHg range. The other options represent either too small a change to explain symptoms or a drop large enough to be considered a more definite orthostatic diagnosis.

When standing, gravity pulls blood into the legs, and in someone who is dehydrated there is already less circulating volume to begin with. The heart can’t fully compensate quickly, so a modest drop in systolic blood pressure occurs. A drop of about 10–15 mmHg is a common amount seen with volume depletion and can produce symptoms like lightheadedness in older adults. Larger drops, around 20 mmHg or more, would meet the usual diagnostic threshold for orthostatic hypotension, but the scenario highlights the typical, milder change that dehydration can cause. So the best choice is the 10–15 mmHg range. The other options represent either too small a change to explain symptoms or a drop large enough to be considered a more definite orthostatic diagnosis.