Sat27November0556PM 5

A 78-year-old woman presents to the Emergency department with a change in her mental state over the past few weeks. She has a medical history of hypertension and hypothyroidism. Medication includes hydrochlorothiazide, aspirin, ramipril and levothyroxine.

On physical examination, she has decreased skin turgor, orthostatic hypotension and is disorientated in time and place. There are no focal neurological signs.

Initial biochemical tests are as follows:

Na 111 mmol/L (135-145)

K 4.1 mmol/L (3.5-5.1)

Cl 105 mmol/L (99-101)

Bic 29 mmo/L (22-29)

Urea 16.4 mmol/L (1.7-8.3)

Creatinine 100 µmol/L (44-80)

Glucose 13.5 mmol/L (3.5-5.5)

Plasma osmolality 278 mOsm/kg

Urinary osmolality 450 mOsm/kg

Hb 148 g/L (115-145)

Hct 0.52 (0.37-0.47)

Which one of the following options is the most appropriate initial clinical action?

(Please select 1 option)

Change antihypertensive medication

Intravenous infusion of hypertonic saline

Intravenous loop diuretic

Intravenous infusion of isotonic saline Correct

Restrict water

Explanation

This patient has a significant hyponatraemia. It is sufficiently low to give rise to clinical manifestations.

The symptoms and signs of hyponatraemia are mainly neurological and are related both to the severity and in particular to the rapidity of onset of the change in the plasma sodium concentration. Patients may also have symptoms related to concurrent volume depletion and to possible underlying neurologic disorders that predispose to the electrolyte abnormality.

125 - 130 mmol/L - Nausea and malaise

115 - 125 mmol/L - Headache, lethargy, seizures and coma

<120 mmol/L - Up to 11% present with coma.

The combination of a thiazide diuretic and ramipril is the most likely cause of this patient's symptomatic hyponatraemia. The patient has hypovolaemic hyponatraemia that is best treated with isotonic saline. The plasma sodium should not be corrected too quickly. For that reason, hypertonic saline would not be recommended in this patient.

Hypovolaemic hyponatraemia:

Administer isotonic saline to patients who are hypovolaemic to replace the contracted intravascular volume (thereby treating the cause of vasopressin release). Patients with hypovolaemia secondary to diuretics may also need potassium repletion, which, like sodium, is osmotically active. Correction of volume repletion turns off the stimulus to ADH secretion, so a large water diuresis may ensue, leading to a more rapid correction of hyponatraemia than desired. If so, hypotonic fluid such as D5/½ normal saline may need to be administered.

Hypervolaemic hyponatraemia:

Patients with hypervolaemic hyponatraemia should be managed with fluid restriction, plus loop diuretics, and correction of the underlying condition. The use of a V2 receptor antagonist may be considered.

Answer Statistics

1

4%

2

37%

3

1%

4

50%

5

10%

Times answered: 266