Fluid& electrolyte balance

Question 1

What proportion of our body weight is made up of total body water

Answer 1

• 60% of ideal body weight for men

- 50-55% of ideal body weight for women

Question 2

What is TBW made up of

Answer 2

• 2/3= intracellular fluid

- 1/3= extracellular fluid

Question 3

What is intracellular fluid made up of?

Answer 3

• 75% interstitial fluid

- 25% plasma

Question 4

What is the blood volume for females and males respectively?

Answer 4

• 65ml/kg (females)

- 75ml/kg (males)

Question 5

What are insensible losses?

Answer 5

• We can’t detect/sense how much we’re losing

- e.g skin &lungs

Question 6

What generates the differences between electrolyte distribution between the ECF&ICF?

Answer 6

The Na+/k+ pump

Question 7

What can we always be certain of in terms of ions in any fluid?

Answer 7

In any fluid the total cations=total anions

Question 8

What is the total Na in the body made up of?

Answer 8

• 25% non exchangeable (in tissues such as bone)- slow turnover
• 75% exchangeable- ECF
• Normal range in plasma is 135-145mmol/L-reflects body water content
• sodium consumption variable 110-220mmol/day
• Approx 5-10mmol loss in sweat& faeces, most regulated by kidneys

Question 9

How is sodium excretion regulated by?

Answer 9

• Renin-angiotensin-aldosterone
• Natriuretic peptides
• Intrinsic renal mechanisms

Question 10

How is dehydration/ increased osmolarity monitored/ controlled

Answer 10

Via the ADH system

Question 11

Is the collecting duct permeable to water?

Answer 11

-If ADH is present, the collecting duct is highly permeable to water

Question 12

In the case of fluid overload, how is this detected?

Answer 12

• Atrial natriuretic peptide( ANP) is released when the atria are stretched
• Brain/ B-type natriuretic peptide is released when the ventricles are stretched
• Detected in the heart

Question 13

What effect do the natriuretic peptides have on the afferent and efferent arterioles to the glomerulus

Answer 13

• Dilate the afferent arteriole to the glomerulus

- constrict the efferent arteriole

Question 14

What effect do the natriuretic peptides have?

Answer 14

1. ) cause vasodilation & this decreases blood pressure
2. ) Decrease renin which decreases ang II & aldo; this subsequently increases GFR leading to natriuresis& diuresis
3. ) Increase GFR leading to decreased renin & allows for natriuresis and diuresis

Question 15

When and why do we prescribe IV fluids?

Answer 15

1. ) MAINTENANCE: To maintain euvolaemia when oral intake is reduced e.g being NBM,nauseated,vomiting or diarrhoea
2. ) REPLACEMENT: previous/ongoing or predictable future losses such as Diaorrhea and vomitting, drains, urine, sweat,3rd spacing,burns , surgery, polyuria
3. ) RESUSCITATION: Reapidly restore intravascular compartment e.g following haemorrhage,marked dehydration, vasodilation, shock

Question 16

What are the symptoms & clinical signs of someone with hypovolemia?

Answer 16

• Symptoms: GI losses, thirst,lethargy,postural dizziness,reduced urine volume, confusion
• Clinical signs: Pulse=fast&weak; BP postural drop >20mmHg or low BP; loss of skin turgor;sunken eyes;dry mucous membranes

Question 17

What are the symptoms & clinical signs of someone with hypervolemia?

Answer 17

• Symptoms: breathlessness,peripheral oedema,weight gain, abdominal bloating, confusion
• Clinical signs: Pulse can be fast,bounding; BP can be high, can be low; skin turgor generally maintained; can have peripheral oedema; JVP can be elevated; can have ascites

Question 18

Which fluids can we use for resuscitation?

Answer 18

• 0.9% NaCl
• Balanced crystalloid solutions, such as Hartmann’s solution
• Colloids

Question 19

Which fluids can we use for maintenance of blood volume?

Answer 19

• 5% glucose

- Glucose& saline solutions, such as 0.18% saline in 4% glucose

Question 20

What is hyponatraemia?

Answer 20

Na<135mmol/L

-Low na in the blood

Question 21

How can we classify hyponatraemia?

Answer 21

1. ) Hypovolaemia
2. )Euvolaemia: urine Na>30mmol/L
3. )Hypervolaemia urine Na <25mmol/L and in chronic kidney disease urine Na>30mmol/L

Question 22

What is SIADH?

Answer 22

syndrome of inappropriate ADH secretion

Question 23

What are the signs& symptoms of hyponatraemia?

Answer 23

Presence of symptoms related to severity

• MILD hyponatremia(130-135mmol/L) = asymptomatic
• MODERATE hyponatraemia(121-129mmol/L)=cramps,weakness,nausea
• SEVERE hyponatraemia(,120mmol/L)= lethargy, headache,confusion
• SEVERE& RAPIDLY EVOLVING hyponatraemia= seizures, coma,respiratory arrest

Osmotic gradient between ECF& ICF within the brain

• Water moves into cells
• Raised intracranial pressure due to oedema-Neurological symptoms

Question 24

How can we treat hyponatraemia?

Answer 24

• Hypovolemia: correct volume depletion e.g 0.9% saline
• Euvolaemia: underlying cause, fluid restriction
• Hypervolaemia: underlyng cause, fluid restriction (vasopressin receptor antagonists)
• Aggressive therapy used if the symptoms are severe and there has been acute hyponatraemia for less than 24hours

Question 25

What is the risk associated with rapid correction of low Na?

Answer 25

-Risk of central pontine myelinosis( a neurological disorder caused by severe damage of the myelin sheath of nerve cells in the pons; may be iatrogenically induced

Question 26

What is hypernatraemia & what are the symptoms ?

Answer 26

- Na >145mmol/L - Results from: net water loss, hypertonic Na gain - Increase in plasma toxicity pulls water out of cells, resulting in a decrease in intracellular volume - severe if Na>158mmol/L - Symptoms: thirst,anorexia,weakness,stupor,seizures,coma

Question 27

How can we classify hypernatraemia?

Answer 27

- Un-replaced water loss | - Sodium overload

Question 28

How can we treat hypernatraemia?

Answer 28

1. ) Chronic hypernatraemia: - Treat underlying cause - Use of hypotonic fluid e.g 5% dextrose given slowly - Lower Na by max of 10mmol/L per day - always reassess 2. ) Acute therapy/emergency - Hypotomic fluid - Lower Na by 1-2mmol/L/h to restore normal Na levels within 24h - Because acute, increase in the plasma Na can lead to irreversible neurologic injury--- needs expert help

Question 29

What is hypokalaemia?

Answer 29

- K<3.5mmol/L - K enters the body via oral intake or IV, largely stored in the cells, excreted in urine - Results from : decreased K intake; increased entry into cells; increased losses (GI/urine) - Manifestations are proportionate to severity... 1. ) Muscle weakness; usually when <2.5mmol/L-progresses from lower extremities 2. ) ECG changes &arrhythmias 3. ) Chronic: renal abnormalities; impaired concentrating ability, raise BP

Question 30

What ECG changes may be present in hypokalaemia?

Answer 30

- Flat T wave - U waves - ST depression - PR interval prolonged - Prolonged QT intervals

Question 31

How can we treat hypokalaemia?

Answer 31

- Correct Mg levels - K replacement- oral vs IV - If IV max 10-20mmol/hr and cardiac monitoring

Question 32

What is hyperkalaemia?

Answer 32

k>5.5mmol/L | -Classified as 1.) increased release from cells 2.) reduced urinary excretion

Question 33

What are the symptoms of hyperkalaemia?

Answer 33

- Paraesthesiae - Muscle weakeness-paralysis - arrhymias

Question 34

What ECG changes may result from hyperkalaemia?

Answer 34

- Tall peaked T waves - shortened QT interval - PR interval lengthening - QRS widening - P waves disappear- sine waves

Question 35

How can we treat hyperkalaemia?

Answer 35

- IV calcium gluconate- antagonise membrane action of high K - IV insulin with glucose- drive K into cells - Remove K from the body(consider loop diuretics, haemodialysis& haemofiltration) - Other therapies to drive K into cells: sodium bicarbonate, Beta agonists