A 23-year-old man is brought to the emergency department by paramedics following a motor vehicle accident. He was an unrestrained passenger in the front seat. Several days after hospitalization, his fluid volume and plasma osmolarity are measured and illustrated in the image below (solid line, normal; dotted line, patient). Which of the following conditions is most likely to cause the findings shown in the image?

Question

A 23-year-old man is brought to the emergency department by paramedics following a motor vehicle accident.  He was an unrestrained passenger in the front seat.  Several days after hospitalization, his fluid volume and plasma osmolarity are measured and illustrated in the image below (solid line, normal; dotted line, patient).  Which of the following conditions is most likely to cause the findings shown in the image?

Quizplus · Accepted Answer

11ec160b_36c4_c8c9_9249_f11930756ab6_MD0001_00 The figure shows the volume of the intracellular (ICF) and extracellular (ECF) fluid compartments (x-axis) and the osmolarity of the fluid in those compartments (y-axis). This patient's recent head trauma is consistent with central diabetes insipidus due to hypothalamic/pituitary damage. The resulting decrease in vasopressin secretion leads to excessive free water excretion by the kidneys, causing hyperosmotic volume contraction. This condition occurs when the loss of free water exceeds the loss of electrolytes, resulting in increased osmolarity and contracted volumes in both the ICF and ECF compartments. Hyperosmotic volume contraction can occur in the setting of diabetes insipidus, decreased fluid intake (dehydration), and with profuse sweating (due to the hypotonic nature of sweat). (Choice A) Acute gastrointestinal hemorrhage (or diarrhea) would cause an isotonic loss of ECF volume, with no effects on osmolarity or ICF volume. This is referred to as isosmotic volume contraction. (Choice B) The lack of aldosterone in adrenal insufficiency causes loss of NaCl with ECF volume depletion (hyposmotic volume contraction). The low osmolarity of the ECF results in shifting of free water into the ICF compartment, causing ICF expansion. (Choice D) Infusion of large amounts of hypertonic saline leads to hypertonic volume expansion. Both the volume and osmolarity of the ECF are increased. The high osmolarity of the ECF leads to shifting of water from the ICF, further increasing the ECF volume. (Choice E) Primary polydipsia (excessive water consumption) and SIADH (inappropriately high vasopressin levels) both cause retention of free water in the body. This leads to expansion of the ICF compartment and a decrease in the osmolarity of both compartments (hyposmotic volume expansion). Expansion of the ECF compartment is limited in these conditions due to compensatory secretion of aldosterone and natriuretic peptides, which help to normalize the extracellular fluid volume. Thus, affected patients are clinically euvolemic. Educational objective: Volume contraction and expansion can be divided into isosmotic, hyposmotic, and hyperosmotic states. Hyperosmotic volume contraction is caused by a loss of free water (with retention of electrolytes). It can occur in patients with diabetes insipidus or as a result of decreased fluid intake/excessive sweating.

A 23-Year-Old Man Is Brought to the Emergency Department by Paramedics