Progressive Care Nursing Certification (PCCN) Practice Exam

What is the primary cause of dehydration in hyperosmolar hyperglycemic syndrome (HHS)?

1. Lack of anti-diuretic hormone (ADH)

2. Inability of the kidneys to concentrate urine

3. Nausea and vomiting

4. Osmotic diuresis from very high blood glucose

The correct answer is: Osmotic diuresis from very high blood glucose

In hyperosmolar hyperglycemic syndrome (HHS), the primary cause of dehydration is osmotic diuresis that occurs due to very high blood glucose levels. In this condition, the blood glucose becomes significantly elevated, often exceeding 600 mg/dL, leading to an increase in plasma osmolarity. As a result, osmotic pressure pulls water out of the cells and into the bloodstream, which causes excess glucose to spill into the urine. This elevated glucose level creates a high osmotic load in the renal tubules, prompting the kidneys to excrete more water along with the glucose in an attempt to eliminate the excess. This process significantly increases urine output, leading to dehydration as the body loses large amounts of fluid. The lack of adequate hydration can further complicate the overall metabolic state of the patient, as the loss of fluid contributes to the concentration of electrolytes and can lead to a state of cellular dehydration, exacerbating hyperglycemic conditions. The other choices identify factors that may contribute to the overall clinical picture in different contexts but do not directly address the fundamental mechanism of dehydration in HHS.