A 30-year-old woman with a 1-week history of severe diarrhea feels dizzy when she stands up. Blood pressure (while supine) is 112/76 mm Hg with a pulse of 88/min; blood pressure (while standing) is 80/60 mm Hg with a pulse of 120/min. In addition to controlling her diarrhea, the most appropriate initial therapy is intravenous administration of which of the following?
Desmopressin
5% Dextrose in water
Fresh frozen plasma
0.9% Saline
Methoxamine
Correct answer
0.9% Saline
Explanation:
This patient is exhibiting signs and symptoms of orthostatic (postural) hypotension in the setting of decreased intravascular volume secondary to prolonged diarrhea. Orthostatic hypotension is diagnosed when, within 2-5 minutes of standing, one or more of the following are present: (1) 20mmHg or more fall in systolic pressure; (2) 10mmHg or more fall in diastolic pressure; (3) symptoms of cerebral hypoperfusion. There are many etiologies of orthostatic hypotension which include decreased intravascular volume, autonomic insufficiency, alcohol, medications, and aging. The patient’s prolonged diarrhea has left her in a volume depleted state, causing the apparent signs and symptoms. The best initial therapy for this patient is to replete her intravascular volume with intravenous fluids that are as similar to her plasma as possible. The patient has lost both water and electrolytes in her diarrhea, both of which need to be replaced. Of the answer choices 0.9% Saline (choice D) both resembles plasma the most and is cost- effective. 0.9% Saline is also known as normal saline and is comprised of 154mEq of sodium and 154mEq of chloride.
Desmopressin (choice A) is a synthetic arginine vasopressin analogue that has antidiuretic effects. It can be used to treat patients with central diabetes insipidus. This patient most likely has high levels of ADH in her volume deplete state and would benefit more with IV hydration.
5% Dextrose in water (choice B) is a type of IV fluid; however, it is not as physiologically similar to plasma as 0.9% Saline. 5% dextrose in water is essentially water with dextrose without any electrolytes. Furthermore, as the dextrose will be rapidly metabolized, the water supplied distributes across both the extracellular and intracellular fluid compartments. This leads to a reduced amount of intravascular volume repletion relative to supplying saline.
Fresh frozen plasma (choice C) is a blood product with strict indications, only given to patients to replace clotting factors, not to correct volume status.
Methoxamine (choice E) is an alpha-1-adrenergic receptor agonist that induces vasoconstriction. This patient would benefit more from correcting volume status with IV fluids than with a vasoconstrictor.