66 - 70 Physiology SBAs for the Primary FRCA
Question 66
You have been asked to review a patient on intensive care who has been declared dead by neurological criteria, and is listed for organ retrieval. You note the patient's urine output has been over 400 ml/hour for the last six hours.
Which of the following would you most likely see for this patient?
- High serum osmolality, high urine sodium, low urine osmolality
- High serum osmolality, low urine sodium, high urine osmolality
- Low serum osmolality, low urine sodium, low urine osmolality
- High serum osmolality, low urine sodium, low urine osmolality
- Low serum osmolality, high urine sodium, high urine osmolality
Answer
- High serum osmolality, low urine sodium, low urine osmolality
This is a classic history of cranial diabetes insipidus. Intracranial pathology leads to hypothalamic failure and inability to produce antidiuretic hormone.
- No ADH means the kidney struggles to retain water
- This means lots of water is lost to the urine, but sodium is relatively well retained
- This means the osmolality of the blood increases, and that of the urine decreases, along with the sodium content (insipid means weak or tasteless)
The treatment is desmopressin or arginine vasopressin to encourage fluid retention, and please don't taste your patient's urine.