Fluid Balance, Sodium and Potassium Flashcards by Daniel Hunt

What % of the body is water?

60%

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what is the ratio of Intracellular fluid to Extracellular fluid?

2:1

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3 areas where extracellular fluid can be?

Intravascular
Interstitial (bathing cells- the largest component of ECF
Transcellular (within epithelial-lined spaces, e.g. CSF, joint fluid, bladder urine, aqueous humour)

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What is Osmolality?

Total number of particles in solution - measured with an osmometer., units = mmol/kg

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What is Osmolarity?

Calculated, measure of solute per liter of solution, units - mmol/l

=2(Na + K) +urea + glucose

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Physiological and Pathological determinants of osmolality/osmolarity in serum/plasma..

Physiological - Na+K+Cl+HCO3+urea+glucose

Pathological = Endogenous (i.e. glucose), Exogenous (ethanol, mannitol)

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What can osmolality be used to diagnose?

SIADH - the normal range for serum osmolality is 275-295mmol/kg

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What is the difference between osmolality and osmolarity known as?

the osmolar gap, and can be useful in metabolic acidosis cases

osmolality and osmolarity should roughly equate

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Normal ranges for Sodium?

135-145 mmol/l

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How is Sodium distributed around the body?

70% is freely exchangeable, the rest complexed in bone

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How are levels of sodium maintained?

Predominantly an extravellular cation, largely maintained by active pumping from ICF>ECF by NA/K ATPase

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Hyponatraemia - Values at which symptoms occur

less than 136 = Nausea and vomiting
less than 131 = confusion
less than 125 = non cardiogenic pulmonary oedema
less than 117 = coma

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Hyponatraemia - treatment?

Treat underlying cause not the hyponatreamia (unless severe

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Hyponatraemia - symptoms?

Symptomatic hyponatraemia is a medical emergency

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What is TURP syndrome?

Hyponatraemia from water absorbed through damaged prostate

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In true hyponatraemia is Osmolality high or low?

Low

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Causes of hypovolaemic hyponatraemia ?

Urinary Sodium greater than 20mmol/l= Renal
- Diuretics, Addison’s, Salt losing nephropathies

Urinary Sodium less than 20mmol/l = Non-Renal
- Vomiting, Diarrhoea, excess sweating, Third space losses (ascites, burns)

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Causes of Euvolaemic hyponatraemia?

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Urinary Sodium >20mmol/l - SIADH, Primary polydipsia, Severe hypothyroidism

Causes of Hypervolaemic hyponatraemia?

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Urinary Sodium >20mmol/l = Renal
- ARF, CRF

Urinary Sodium less than 20mmol/l = Non-Renal
- Cardiac failure, Cirrhosis, Inappropriate IV fluid

Correction of Hyponatraemia, things to be aware of?

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Rapid correction can lead to Central Pontine Myelinolysis (pseudobulbar palsy, paraparesis, locked-in syndrome) therefore aim to increase Na by 1mmol/l per hour

Causes of hyponatreamia post surgery?

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Over hydration with hypotonic IV fluids

Transient increase in ADH due to stress of surgery

Lab criteria for SIADH

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True Hyponatraemia (low serum osmolality)
Clinically euvolaemic
Inappropriately high urine osmolality and increased renal sodium excretion (>20mmol/l) due to decreasing aldosterone levels 
Normal renal, adrenal, thryroid and cardiac function

A diangosis of exclusion

Causes of SIADH

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Malignancy - small cell lung cancer, pancreas, prostate, lymphome (ectopic secretion)
CNS disoders - meningoencephalitis, haemorrhage, abscess
Chest Disease - TB, pneumonia, abscess
Drugs - opiates, SSRIs, carbamazepine

Hypernatraemia - sodium level? symptoms? classification? what ward is it most likely to be seen on?

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Less common than hyponatraemia, but usually clinically significant (plasma NA> 148mmol/l)
Symptoms = thirst–> confusion –> seizures + ataxia –> coma
can be classifed based on hydration status
In hospital often iatrogenic, common problem in ITU patients

RAPID CORRECTION CAN LEAD TO CEREBRAL OEDEMA!!!

What causes Hypovolaemic Hypernatraemia?

- GI loss - vomiting, diarrhoea - Skin loss - excess sweating, burins - Renal loss - loop diuretics, Renal disease (impaired concentrating ability), Osmotic diuresis (glucose, mannitol)

What causes Euvolaemic Hypernatraemia?

- Respiratory loss - Tachypnoea - Skin loss - excessive sweating, Fever - Renal loss - Diabetes Insipidus - Misc - No water!

What causes Hypervolaemic Hypernatraemia?

- Mineralocorticoid excess (Conns Syndrome) | - Hypertonic saline

Clinical features of Diabetes Insipidus?

- Hypernatraemia (lethargy, thirst, irritability, confusion, coma, fits) - Clincially euvolaemic - Polyuria and polydipsia - Urine: Plasma olsmolality is less than 2

What are the 2 types of Diabetes Insipidus?

1) Cranial | 2) Nephrogenic

What is Cranial Diabetes Insipidus and what are the causes of it?

``` Lack of/ No ADH causes - Head trauma - Tumour - Surgery ```

What is Nephrogenic Diabetes Insipidus and what are the causes of it?

``` Receptor defect - insensitivity to ADH causes - Inherited - Lithium - Chronic renal failure ```

What test if used to diagnose Diabetes Insipidus?

8hr fluid deprication test

What is a normal result of a 8hr fluid deprication test?

Urine concentration greater than 600mOsmol/kg

What result of a 8hr fluid deprication test would lead you to diagnose Primary Polydipsia?

Urine concentrates 400-600mOsmol/kg

What result of a 8hr fluid deprication test would lead you to diagnose Cranial DI?

Urine concentrates only after giving desmopressin

What result of a 8hr fluid deprication test would lead you to diagnose Nephrogenic DI?

No concentraton of urine after desmopressin

Potassium normal range

3.5-5.5 mmol/l

Potassium - distribution in the body

Predominantly intracellular cation (only 2% is extracellular), maintained by active pumping from EC-> ICF by Na/K ATPase 90% freely exchangeable, the rest bound in RBCs, bone and brain tissue

Hypokalaemia - below what value? causes?

below 3.5mmol/L 1-GI loss- Diarrhea, excess sweat 2-Renal loss - Hyperaldosteronism (Conn's) - due to aldosterones effect on Na/K ATPase in kidneys causing the loss of K via urine and reabsorption of Na and water . - Excess Cortisol (Cushings) - cortisol acts like aldosterone 3-Redistribution into cells - Insulin (increases activity of Na/K ATPase shifting K into cells), Beta-agonists (salbutamol) 4) rare - Hypomagnesesaemia - Mg needed for K processing

Hyperkalaemia - above what value? causes?

>5.5mmol/L Less common than hypokalaemia, but more dangerous Caused by excessive intake (almost always iatrogenic), movement out of cells or decreased excretion

Causes of Hyperkalaemia due to excessive intake?

Oral (fastin) Parenteral (via IV) Stored blood transfusion

Causes of Hyperkalaemia due to Transcellular Movement (ICF>ECF)?

Acidosis Insulin shortage Tissue damage/ catabolic state

Causes of Hyperkalaemia due to Decreased excretion?

``` Acute Renal Failure (oliguric phase) CRF (late) Potassium sparing diuretics (spironolactone) Mineralocorticoid deficiency (Addisons) NSAIDs, ACEi ```

FUN FACT ABOUT POTASSIUM AND H+ IONS...

... H+ and potassium are intimately linked as one moves into the cells one moves out. for every drop in pH of 0.1 there is an increase in K+ of 0.7

Fluid Balance, Sodium and Potassium Flashcards

(44 cards)