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Electrolytes and Acid-base disorders > Hyponatraemia > Flashcards

Hyponatraemia Flashcards

1
Q

Hyponatraemia may be caused by-?

A

Water excess or sodium depletion

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2
Q

Causes of pseudohyponatraemia

A
  • High blood lipid or protein >>>
    • Hyperlipidaemia (raised serum volume)
    • Hyperproteinaemia (as in myeloma)
  • Taking blood from a drip arm
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3
Q

Why is it important to diagnose pseudohyponatraemia?

A

Because, As the plasma osmolality is normal >>> no treatment is required

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4
Q

Diagnostic tests of hyponatraemia

A
  • Urinary sodium
  • Plasma osmolarity level
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5
Q

Relation between Na (sodium) level and blood glucose level

A

Hyperglycaemia causes hyponatraemia

100mg/dL increase of blood glucose >>> Lower Na level as much as 1.6mEq

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6
Q

Relation between Na salt and blood pressure

A

Adding 6g NaCl salt per day >>> Adds 10mmHg systolic BP

(As such, cutting down 6g NaCl salt/day >>> Lowers systolic BP by 10mmHg)

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7
Q

Normal plasma osmolality (isotonic)

A

275 to 290 mOsm/L (= mOsm/Kg = mmol/Kg)

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8
Q

Hypertonic plasma osmolality

A

>290mOsm/L (= mOsm/Kg = mmol/Kg)

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9
Q

Hypotonic plasma osmolality level

A

<275 mOsm/L (= mOsm/Kg = mmol/Kg)

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10
Q

Classification of hyponatraemia

A

​Classification of hyponatraemia (Na <135mmol/L)

By plasma (=serum) osmolality

  • Hypertonic (plasma osmolality >290)
  • Isotonic (plasma osmolality 275 to 290)
  • Hypotonic (plasma osmolality <275) (Most common)
    • High volume
    • Normal volume
    • Low volume

​​By urinary sodium (Na)

  • Urinary sodium >20mmol/L
    • Na depletion, renal loss (patient often hypovolaemic)
    • Patient often euvolaemic
  • Urinary sodium <20mmol/L
    • Na depletion, extra-renal loss
    • Water excess (patient often hypervolaemic and oedematous)
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11
Q

Hypertonic hyponatraemia >>> Causes

(Na <135mmol/L + plasma osmolality >290mOsm/L)

A
  • Severe hyperglycaemia
    • DKA
    • HHS
  • Hypertonic mannitol
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12
Q

Isotonic hyponatraemia >>> Causes

(Na <135mmol/L + plasma osmolality 275-290mOsm/L)

A
  • Pseudohyponatraemia
    • Hyperlipidaemia (raised serum volume)
    • Taking blood from a drip arm
  • Na free irrigant solutes
    • Hysterectomy
    • TURP (Trans-urethral resection of prostate)
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13
Q

Hypotonic hyponatraemia >>> Classification

(Na <135mmol/L + plasma osmolality <275mOsm/L) >>> Classification

A
  • High volume
  • Normal volume
  • Low volume
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14
Q

Hypotonic hyponatraemia + high ECF volume >>> Causes

(Na <135mmol/L + Plasma osmolality <275mOsm/L + high ECF volume) >>> Causes

A

​Includes interstitial fluid shift

  • CCF (Congestive cardiac failure) >>> oedema
  • Liver Cirrhosis >>> oedema
  • Nephrotic syndrome >>> oedema
  • Renal failure (ARF or CRF) >>> oedema
  • Sepsis
  • Anaphylaxis
  • Pregnancy
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15
Q

Hypotonic hyponatraemia + normal ECF volume >>> Causes

(Na <135mmol/L + Plasma osmolality <275mOsm/L + normal ECF volume) >>> Causes

A

Limited interstitial fluid shift

  • SIADH (following are the causes of SIADH)
    • ​Malignancy (Mass lesions)
      • Small cell lung cancer (SCLC)
      • Pancreatic cancer, prostatic cancer
    • CNS disorders/Neurological (all relate to bleeding)
      • Stroke
      • Haemorrhage (subarachnoid, subdural)
      • Meningitis, Encephalitis, Abscess
      • Surgery
      • Trauma
    • ​Pulmonary infections
      • ​TB
      • Pneumonia
    • ​Other pulmonary causes
      • Acute respiratory failure
      • Positive-pressure ventilation
    • Drugs
      • Sulfonylureas (e.g. Chlorpropamide)
      • SSRIs
        • ​Citalopram,Escitalopram,Fluoxetine,Paroxetine,Sertraline
      • TCA, antipsychotics, neuroleptics
      • Carbamazepine, Na-valproate
      • Cyclophosphamide
      • Cisplatin
      • Vinca alkaloids (Vincristine, Vinblastine)
      • Ecstasy (MDMA)
      • Desmopressin (A Tx of DI)
    • Others: Porphyrias (e.g. AIP)
  • ​​Hypothyroidism
  • Secondary adrenal insufficiency
  • Carcinomas
  • Decreased intake of solutes
    • Beer potomania
    • Tea-and-toast diet
  • Primary polydipsia
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16
Q

Hypotonic hyponatraemia + Low ECF volume >>> Causes

(Na <135mmol/L + Plasma osmolality <275mOsm/L + low ECF volume) >>> Causes

A
  • Cerebral salt wasting
    • Haemorrhage
    • Surgery
    • Trauma
  • Hypokalaemia (K <3.5mmol/L)
  • Renal Na loss (Urinary Na>20mmol/L)
    • Diuretic agents: Loop diuretics, Thiazides, Indapamide, Amiloride etc.
    • Osmotic diuretics: Mannitol, urea, glucose etc.
    • Addison’s disease (Primary adrenal insufficiency)
    • Salt wasting neprhopathy
    • Lithium
    • Bicarbonaturia
    • Ketonuria
  • Extra-renal Na loss (Urinary Na<20mmol/L)
    • Diarrhoea
    • Vomiting
    • Blood loss
    • Excessive sweating
    • Fluid sequestration ‘3rd space’
      • Bowel obstruction
      • Peritonitis
      • Pancreatitis
      • Muscle trauma
      • Burns
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17
Q

Hyponatraemia (Serum Na <135mmol/L) + Urinary Na >20mmol/L

A

Na depletion, renal loss (patient often hypovolaemic)/ dehydrated

  • Diuretic agents: Loop diuretics, Thiazides, Indapamide, Amiloride etc.
  • Osmotic diuretics: Mannitol, glucose, urea etc.
  • Diuretic stage of renal failure
  • Acute tubular necrosis of ARF (urinary Na >40mmol/L)
  • Addison’s disease (Adrenal insufficiency)

Patient often euvolaemic

  • SIADH (urine osmolarity >100mOsm/L or mmol/Kg (often >500) > with all its causes
  • Hypothyroidism
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18
Q

Hyponatreamia (Serum Na <135mmol/L) + Urinary Na <20mmol/L >>> Causes

A

Na depletion, extra-renal cause

  • Dirrhoea
  • Vomiting
  • Sweating
  • Burns
  • Adenoma of rectum

​Water excess (patient is often hypervolaemic + oedematous)

  • Secondary hyperaldosteronism
    • ​​CCF, Cirrhosis (both >> oedema)
    • Liver cirrhosis
    • Nephrotic syndrome
  • ​Low GFR: Renal failure + volume overload (=oedema)
  • IV dextrose
  • Psychogenic polydipsia

​Pre-renal uraemia of ARF has urine Na <20mmol/L

19
Q

Hyponatraemia >>> Approach to diagnosis (finding the cause)

A
  • In hyponatraemia >>> check urinary Na
  • If urinary Na >20mmol/L >>>
    • Check if hypovolaemic or Na depletion by renal loss ​(See relevent causes)
    • OR euvolaemia ​(See relevent causes)
  • ​If urinay Na <20mmol/L >>>
    • ​Check if hypovolaemic or Na depletion by extra-renal loss ​(See relevent causes)
    • OR hypervolaemia (See relevent causes)
20
Q

SIADH is characterised by - ?

A

Hyponatraemia secondary to the dilutional effects of excessive water retention

21
Q

SIADH >>> Mechanism

A

Due to inappropriate ADH secretion >>> excessive water retention >>> dilutional effects >>> hyponatraemia (low Na conc.) >>> low plasma osmolality + high urine osmolality + elevated urine sodium (above 20 mmol/L)

(Free water excretion is likely to be reduced)

22
Q

SIADH >>> Findings

A
  • Na conc. in blood: <135mmol/L
  • Urine Na: >20 mmol/L
  • Plasma osmolarity: <275 mOsm/kg
  • Urine osmolarity: >100 mOsm/kg (often >500mmol/kg)
23
Q

SIADH >>> Causes

A
  • Malignancy (Mass lesions)
    • Small cell lung cancer (SCLC)
    • Pancreatic cancer, prostatic cancer
  • CNS disorders/Neurological (all relate to bleeding)
    • Stroke
    • Haemorrhage (subarachnoid, subdural)
    • Meningitis, Encephalitis, Abscess
    • Surgery
    • Trauma
  • ​Pulmonary infections
    • ​TB
    • Pneumonia
  • ​Other pulmonary causes
    • Acute respiratory failure
    • Positive-pressure ventilation (PPV)
  • Drugs
    • Sulfonylureas (e.g. Chlorpropamide)
    • SSRIs
    • ​Citalopram, Escitalopram, Fluoxetine, Paroxetine, Sertraline
    • TCA, antipsychotics, neuroleptics
    • Carbamazepine, Na-valproate
    • Cyclophosphamide
    • Cisplatin
    • Vinca alkaloids (Vincristine, Vinblastine)
    • Ecstasy (MDMA)
    • Desmopressin (A Tx of DI)
  • Others: Porphyrias (e.g. AIP)
24
Q

SIADH >>> Dx Criteria

A
  • Hyponatraemia (Na <135mEq/L)
  • ​Urine Na >20mEq/L
  • Plasma/serum osmolarity is decreased (<270mOsm/kg)
  • Urine osmolarity is greater than that of serum osmolarity (inappropriately high urine osmolarity >100mOsm/L)
  • No clinical evidence of oedema (fluid overload) or dehydration [Patient is euvolaemic]
  • Normal adrenal, normal renal, normal thyroid function [adrenal insufficiency, renal failure, and thyroid disorder are excluded]
25
Q

SIADH >>> other diagnosting points

(also to check these, after main Dx criteria)

A
  • Suppression of RAS (Renin Angiotensin System)
  • No equal concentration of ANP (atrial natriuretic peptide)
  • Maintained hypervolemia
  • Normal serum creatinine
  • Normal acid base and K balance
  • ↓BUN
  • ↓Uric acid
  • ↓Albumin
26
Q

SIADH >>> Association

A

AIP (Acute intermittent Porphyria)

27
Q

SIADH >>> Management

A
  • Fluid restriction
  • Slow correction of Na
    • Rapid correction >>> precipitates central pontine myelinolysis
  • DOC: Demeclocycline
    • M/A: reduces the responsiveness of the collecting tubule cells to ADH
    • S/E: Nephrogenic DI
  • ADH (vasopressin) receptor antagonists (have been developed recently);

Also Lithium can do so >> so, sometimes used as a treatment of SIADH >>> S/E: Nephrogenic DI

28
Q

Why do we need to slowly correct the hyponatraemia in SIADH management?

A

Because rapid correction precipitates central pontine myelinolysis

29
Q

Demeclocycline >>> Mechanism

A

It reduces the responsiveness of the collecting tubule cells to ADH

30
Q

Demeclocycline >>> Side effect

A

Nephrogenic Diabetes insipidus

31
Q

How are SIADH & Diabetes insipidus related regarding cause & treatment?

A
  • Lithium & Demeclocyline cause nephrogenic DI ; But they treat SIADH
  • Desmopression treat Nephrogenic DI ; But it causes SIADH
  • Diabetes insipidus itself is a cause of “hypernatraemia”
32
Q

Drug causes of SIADH

A
  • Sulfonylureas (e.g. Chlorpropamide)
  • SSRIs
    • ​Citalopram, Escitalopram, Fluoxetine, Paroxetine, Sertraline
  • TCA, antipsychotics, neuroleptics
  • Carbamazepine, Na-valproate
  • Cyclophosphamide
  • Cisplatin
  • Vinca alkaloids (Vincristine, Vinblastine)
  • Ecstasy (MDMA)
  • Desmopressin (A Tx of DI)
33
Q

Drug causes of hyponatraemia

A

By the mechanism of SIADH + reduced urinary Na reabsorption + high urinary Na excretion >20mmol/L + normovolaemia (normal ECF volume)

  • Sulfonylureas (e.g. Chlorpropamide)
  • SSRIs
    • ​Citalopram, Escitalopram, Fluoxetine, Paroxetine, Sertraline
    • TCA, antipsychotics, neuroleptics
  • Carbamazepine, Na-valproate
  • Cyclophosphamide
  • Cisplatin
  • Vinca alkaloids (Vincristine, Vinblastine)
  • Ecstasy (MDMA)
  • Desmopressin (A Tx of DI)

NOT by mechanism of SIADH + BUT by reduced urinary Na reabsorption + high urinary Na excretion >20mmol/L + hypovolaemia (low ECF volume)

  • Diuretic agents: Loop diuretics, Thiazides, Indapamide, Amiloride etc.
  • Osmotic diuretics: Mannitol, glucose, urea etc.
  • Lithium
34
Q

What is Beer potomania?

A
  • A recognized cause of hyponatraemia in alcohol misusers
  • Findings: “osmolar gap” due to presence of osmotically active “ethanol” in the blood
  • Tx: the electrolyte imbalance normally corrects itself with cessation of alcohol.
35
Q

Ascites and hyponatraemia - any relation?

A
  • Patients with CLD and ascites >>> often “hyponatraemia” (difficult to manage)
  • Diuretic therapy for the management of ascites often contributes to the hyponatraemia.
36
Q

Patient with ascites (CLD) with hyponatraemia >>> Management?

A

British society of gastroenterology guidelines suggest >>>

  • If serum Na ≤120 mmol/L >>>
    • Stop diuretic therapy
    • Volume expansion (with colloid or normal saline)
  • If serum Na 121 to 125 mmol/L >>>
    • Check Sr. creatinine >>> if normal >>> may continue diuretic therapy (but reduce the dose) (so that > if necessary, we can stop it)
  • If serum Na 126-135 mmol/L >>>
    • No specific intervention
    • Only careful monitoring
  • If serum Na is normal + but sr. creatinine is rising (high) >>>
    • Stop diuretic therapy
    • Volume expansion (with colloid or normal saline)
  • When to give fluid restriction >>>
    • Only in them who are >>>
      • Clinically euvolaemic + not on diuretics + severe hyponatraemia + normal serum creatinine
37
Q

ADH >>> chemical nature

A

A nona-peptide (nona = 9)

38
Q

ADH is manufactured in - ?

A

Supra-optic (SO) and paraventricular (PV) nuclei of the hypothalamus

39
Q

ADH is released (secreted) from - ?

A

Posterior pituitary

40
Q

ADH: Mechanism of action

A
  • It acts on the collecting ducts >>> improves water permeability >>> hence, water retention
  • It inserts aquaporin-2 channels in the collecting ducts of the kidneys >>> promotes water reabsorption
41
Q

ADH >>> site of action

A

collecting ducts

42
Q

ADH secretion is potentiated (increased) by - ?

A
  • Sulfonylureas (e.g. Chlorpropamide)
  • SSRIs
    • ​Citalopram, Escitalopram, Fluoxetine, Paroxetine, Sertraline
  • TCA, antipsychotics, neuroleptics
  • Carbamazepine, Na-valproate
  • Cyclophosphamide
  • Cisplatin
  • Vinca alkaloids (Vincristine, Vinblastine)
  • Ecstasy (MDMA)
  • Desmopressin (A Tx of DI)

​(All the drug causes of SIADH)

43
Q

ADH secretion is inhibited by - ?

A

Ethanol

Electrolytes and Acid-base disorders (18 decks)

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