Case- 1
A 30 yr old woman, fractured her skull in an
accident. She had no major injuries, no significant blood loss and her
cardiovascular system was stable. She was unconscious for 2 days after the
accident. On the 4th day of her admission to hospital, she was noted
to be producing large volumes of urine and complaining of thirst.
Biochemical findings were:
Na+ K+ Cl-
HCO3- Urea Creatinine Glucose
150 3.6 106
25 5.5 mmol/L 80 μmol/L 5.4 mmol/L
Serum osmolality =
310 mmol/kg
Urine osmolality = 110 mmol/kg
Urine volume = 8L/ day
Solution:-
One can make a confident diagnosis of central diabetes insipidus from the history of head trauma and the observation that she was producing large volumes of urine and complaining of thirst. Her blood glucose level excludes diabetes mellitus as a cause of her polyuria and her hypernatraemia accounts for her thirst. In normal circumstances a serum sodium concentration of 150 mmol/L will stimulate AVP production and cause the urine to be maximally concentrated. This patient’s urinemis, therefore, inappropriately dilute. It would be unnecessary and even dangerous to attempt to perform a water deprivation test on this patient. Note that her serum urea is not increased. This reflects her high urine flow-rate despite her significant water depletion.
Cases 2
A 31 year old woman was admitted to a surgical ward with
a 2 day history of abdominal pain and
vomiting. Her BP was 110/65 mmHg and her pulse 88 beats per minute and regular.
A provisional diagnosis of intestinal obstruction was made.
On admission, tests showed:
Na+ K+ Cl- HCO3- Urea Creatinine
128 6.1 92
18 10.8 mmol/L 180μmol/L
She was given 1.5 L of 0.9% saline intravenously, overnight
and the following morning her symptoms had resolved. Her serum sodium had
increased to 134mmol/L and her serum potassium had fallen to 4.8 mmol/L. On
reviewing her history, she had been unwell for a number of months with weight
loss and anorexia. She had noted to be pigmented. Her cortisol levels were less
than 60nmol/L
Solution:-
This presentation is classical of acute adrenal failure with characteristic symptoms, physical findings and electrolyte pattern. The diagnosis is confirmed by the Synacthen test. On presentation, this woman was sodium depleted with pre-renal uraemia. As her ECF was expanded with 0.9%
sodium chloride, this improved her glomerular filtration rate, which is sufficient, even in the absence of aldosterone, to correct the hyperkalaemia by increasing her urinary potassium excretion. The reduction in this patient’s blood volume will stimulate vasopressin secretion, giving rise to the hyponatraemia. The sodium chloride infusion by restoring her blood volume will inhibit AVP secretion, enabling her to correct the hyponatraemia.
