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Chem Path Year 5 > Sodium and Fluid balance > Flashcards

Sodium and Fluid balance Flashcards

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1
Q

What is Osmolality and what is the Normal Osmolality of blood?

A

Osmolality is the number of solute particles in 1kg of Solvent
-> Normal Range is 275-295mOsmol/kg

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2
Q

Where is AHD released from and what are its 2 actions?

A

ADH - Anti-Diuretic Hormone, is released by the posterior pituitary

V1 (Vasopressin)
-> Acts on vascular smooth muscle and mediates vasoconstriction

V2

  • > Acts on the collecting duct cells on the Kidney
  • > Promotes water retention by inserting Aquaporin-2 channels
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3
Q

What Stimulates ADH release?

A

i) Baroreceptors
- > found in the carotids, atria and aorta
- > identify when there is a low blood volume/pressure
- > Stimulate ADH release

ii) Osmoreceptos
- > found in the hypothalamus
- > identify when the osmalality rises
- > Stimulate ADH release and thirst

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4
Q

What is hyponatraemia? How can it be identified and what is true hyponatraemia?

A

Hyponatraemia is when sodium is below 135mEq/L
It is the commonest electrolyte imbalance in hospitalised patients.
This can be identified by doing a set of U&Es

True Hyponatraemia is when Serum Osmalality is also LOW.
i.e. below 275mOsmol/kg

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5
Q

What are Signs of Low Volume Status?

A

-> Tachycardia
-> Postural Hypotension
-> Dry mucous membranes
-> Reduced Skin Turgor
-> Reduced Urine Output
-> Drowsy/Confused*
This may be a sign of severe hyponatraemia, ESCALATE.
-> Low urine Na+(<20)

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6
Q

What is the most reliable indicator of a hypovolaemic state?

A

Urine Na+ < 20 is MOST reliable of a hypovolaemic state*

  • > i.e. the patient is holding onto their salt in an attempt to retain their fluid
  • Not a useful marker if the patient is on diuretics
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7
Q

What are signs of high volume status?

A
  • > Raised JVP 6-8cm.
  • > Bibasal Crackles
  • > Peripheral Oedema
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8
Q

What are causes of Hypovolaemic Hyponatraemia?

A
  1. Renal – raised urinary sodium;
    - > Diuretic Use
    - > Salt Losing Nephropathy
  2. Extra-Renal – low urinary sodium;
    - > D&V
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9
Q

What are investigations for Hypovolaemic Hyponatraemia?

A

Investigations

  • > Volume Status
  • > Urine Sodium, if > 20 – Renal Cause
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10
Q

What is the management for Hypovolaemic Hyponatraemia?

A

Management

-> Slow volume replacement with 0.9% Saline

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11
Q

What are causes of Euvolaemic Hyponatraemia?

A

Causes

  • > Adrenal Insufficiency
  • > Hypothyroidism
  • > SIADH;
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12
Q

What are investigations for Euvolaemic Hyponatraemia?

A

Investigations

  • > TFT’s
  • > SST (Short Synacthen Test)
  • > Plasma and Urine Osmalality *

SIADH
PLASMA = LOW, URINE(>100) = HIGH.

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13
Q

What is the management for Euvolaemic Hyponatraemia?

A

Management

  • > Fluid Restrict
  • > Treat the underlying cause
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14
Q

What is the first step in the clinical assessment of a patient with hyponatraemia/

A

Clinical Assessment of volume status

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15
Q

How dies D&V cause excess water in hypovolaemic hyponatraemia?

A
  1. Lose BOTH water and sodium from D&V
  2. Baroreceptors detect loss of volume and stimulate ADH
  3. ADH leads to increased water reabsoprtion, not sodium.
  4. Still less water than before (hypovolaemic) and less salt in proportion (hyponatraemic).
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16
Q

What are causes of SIADH?

A

i) CNSi.e. Tumours, bleeds, trauma
ii) Lung pathology i.e. Small Cell Lung Cancer, PE, Pneumothorax, Pneumonnia
iii) Drugs i.e. SSRI, TCA, Opiates, PPI’s, Carbamazepine
iv) Tumours
v) Surgery

Brains, lungs and drugs

17
Q

What are the steps to reach a conclusion of SIADH?

A
  1. No hypovolaemia
  2. No hypothyroidism
  3. No adrenal insufficiency
  4. Reduced plasma osmolality
  5. Increased urine osmolality (>100)
18
Q

What are causes of Hypervolaemic Hyponatraemia?

A

Causes

  • > Cardiac Failure
  • > Cirrhosis
  • > Renal Failure
19
Q

What are the investigations for Hypervolaemic Hyponatraemia?

A

Investigations

?Hypervolaemic Clinical Signs

20
Q

What is the treatment for Hypervolaemic Hyponatraemia?

A

Treatment

  • > Fluid Restriction
  • > Treat the cause
21
Q

What are signs of Severe Hyponatraemia and how do you manage this?

A

Reduced GCS, Seizures,

Seek Expert Help
-> Hypertonic 3% Saline

22
Q

How does hypothyroidism cause hyponatraemia?

A
  1. Decreased TFT’s lead to decreased contractility of the heart.
  2. Decreased blood pressure as a result detected by baroreceptors
  3. Lead to ADH release and water reabsorption but not sodium
23
Q

What is the most important point to remember while correcting hyponatraemia?

A
  1. Serum Na must not be corrected >8-10 mmol/L in the first 24hrs
  2. Risk of osmotic demyelination/Central Pontine Myelinolysis (quadriplegia, dysarthria, dysphagia, seizures, coma, death)
24
Q

What are the drugs used to treat SIADH?

A

If water restriction is insufficient:

  1. Demeclocycline (Reduce response to ADH)
  2. Tolvaptan (V2 Receptor Antagonist)

Fluid Restriction + Salt Tablets + Furesomide

25
Q

What are causes of hypernatraemia?

A

Caused by UNREPLACED FLUID LOSS

i) GI Losses
ii) Sweat Losses
iii) Renal Losses (Osmotic Diuresis (i.e. Diabetes Mellitus, Diabetes Insipidus)

26
Q

What is the management of hypernatraemia?

A
  • > 5% Dextrose (This is basically water and will replace the fluid without increasing Sodium* i.e. NaCl Saline)
  • 0.9% NaCl may be indicated initially to treat the extracellular fluid loss (in hypovolaemic patient)

4-6hourly Na+ measurements.

27
Q

What is diabetes insipidus and what are the two types?

A

Diabetes Insipidus -> Reduced Effect of ADH on the Collecting Ducts of the Kidney

  • > inability to concentrate urine therefore a lot of water lost
  • > if this water loss is unreplaced, can cause Hypernatraemia

Central (Lack of ADH Production)

  • > Pituitary Surgery
  • > Irradiation
  • > Trauma to Base of Skull

Nephrogenic (Resistance to ADH)

  • > Hypercalcaemia
  • > Hypokalaemic
  • > Medications i.e. Lithium
  • > Sickle Cell
28
Q

What are the investigations for Diabetes insipidus?

A

Investigations

  • Serum Glucose (exclude DM)
  • Serum Potassium (Low K+ can cause DI)
  • Serum Calcium (High Ca2+ can cause DI)
  • Plasma and Urine Osmolality (Nephrogenic Vs Central)

Fluid Deprivation Test
-Plasma and Urine Osmalality measures every hour for 8 hours when fluid restricted

29
Q

How can a fluid deprivation test differentiate between central and nephrogenic DI?

A
  • Urine Osmalality should remain low in DI
  • > GIve DDAVP, if Urine Osmalality rises by >45%, Central DI; If not Nephrogenic

In Cranial DI the urine osmolality would be expected to rise to >600 mOsmol/kg

30
Q

What are the effects of diabetes mellitus on serum sodium?

A

Variable
Hyperglycaemia initially draws water out of cells -> Hyponatraemia.

OR

Hyperglycaemia then leads to Osmotic Diuresis -> Hypernatraemia.

31
Q

How does cirrhosis result in hyponatraemia?

A
  1. Cirrhosis patients produce more NO
  2. NO causes vasodilation
  3. Vasodilation leads to decreased blood pressure
  4. Baroreceptors thereore stimulate ADH release and cause water reabsorption - dilutes sodium

Chem Path Year 5 (6 decks)

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