2. Disorders Of Sodium Balance

Question 1

Explain plasma toxicity.

Answer 1

Sodium is a clue for plasma toxicity
ADH regulates osmolality via changes in urine water content
- Kidney reacts by retaining water and producing small amount of concentrated urine
- Retained water goes back to body and not excreted out

Question 2

Define hyponatremia.

Answer 2

Hyponatremia: sodium < 135 mEq/L

Question 3

What is the management of hyponatremia? (Symptomatic vs Asymptomatic)
(3)

Answer 3

1. Uncompensated, severe symptoms: 3% saline bolus 150ml over 20 mins + nephrology consult
2. Uncompensated, mild symptoms: monitored trial of 0.9% saline + nephrology consult
3. Compensated, asymptomatic: water restriction, treat volume disorder (CCF, volume depletion), increase solute intake (dietician)
   —> Meds: loop diuretics + NaCl, urea (not recommended), Demeclocycline (in palliative cases = NSCLC)

Question 4

Define hypernatremia.

Describe the pathophysiology of hypernatremia and it’s clinical presentation.

Answer 4

Hypernatremia: sodium > 145 mEq/L

PATHOPHYSIOLOGY
1. Water excretion > water outake
2. 2 step process:
—> Generation: gain of sodium, loss of water
—> Maintenance: inability to ingest water

CLINICAL PRESENTATION

1. Fluid deprivation: patients can’t perceive, response, or communicate their thirst
2. Elderly or cognitively impaired patients

Question 5

What is SAIDH?

What causes it?
5

Answer 5

1. MDMA: ecstasy
2. Neurological: meningitis, tumours, trauma, SAH
3. Pulmonary disease: lung cancer, TB
4. Stress: pain, vomiting, post-surg
5. Medication: antipsychotics, SSRI, sulfonylureas (1st gen), Pitocin / Oxytocin, narcotics, Cyclophsophamide

Question 6

Describe cause and effects of volume depletion.

What is daily salt water intake?
What is max and min urine volume?

Answer 6

1. Delivery of water to diluting segments of nephron
2. Functional diluting segments
3. Collecting tubule impermeable to water (lack of ADH)

• Drink 14L/day
• Ability to excrete water depends on:
  1) Properly functioning ADH axis
  2) Total solute intake

Normal solute intake: 10mOsm/kg/day —> 700 mOsms for 70kg person

• Min urine vol: 500 mls
• Max urine vol: 800 - 2000mls

Question 7

How do you calculate free water deficit?

Answer 7

Rise in Na proportional to weight loss due to water

(Na level - 140) / 140 x kg x 0.5

Kg x 0.5 = estimate of total body water

Question 8

Review cases on notes

6

Answer 8

6 cases