6

Question 1

WHat is the most abundant intracellular cation?

Answer 1

Potassium

Question 2

What is the range of normal serum potassium?

Answer 2

3.5-5.5 mmol/L

Question 3

What problems may occur if serum potassium is outside the normal range?

Answer 3

Will cause nerve dysfunction and cardiac arrest

Question 4

What two system excrete potassium and how much do they secrete?

Answer 4

• kidneys excrete 80% K+

- bowel excretes 20%

Question 5

Why is it important to maintain a relatively low extracellular [K+]?

Answer 5

-to maintain the steep K+ ion gradient of excitable and non-excitable cells

Question 6

WHat metabolic disturbances can occur if you have extremely low ECF [K+]?

Answer 6

• inability of kidney to form concentrated urine
• tendency to develop metabolic alkalosis; and, closely related to this acid base disturbance
• a striking enhancement of renal ammonium excretion

Question 7

What is the normal range for intracellular [K+]?

Answer 7

130-140mmol/L

Question 8

How will an ECG show different stages of hyperkalaemia?

Answer 8

• > 6.0 mmol/L: tall T wave
• > 7.5 Mmol/L: long PR interval, wide QRS duration, tall T wave
• > 9.0 mmol/L: absent P wave, sinusoidal wave

Question 9

What problems can occur at the different stages of hypokalaemia?

Answer 9

2.5-3 mmol/L: AF, muscle weakness, muscle cramps, constipation
<2.5 mmol/L: increasing weakness, cardiac conduction abnormalities, cardiac arrest

Question 10

When giving diuretic drugs to promote diuresis, why is it more effective to give a combination of 2 diuretics?

Answer 10

• synergistic effect
• one nephron segment can compensate for altered sodium reabsorption at another nephron segment; therefore, blocking multiple nephron sites significantly enhances efficacy

Question 11

Where in the nephron is majority of K+ filtered out?

Answer 11

At glomerulus and PCT

Question 12

What hormone stimulates potassium secretion into the lumen?

Answer 12

Aldosterone

Question 13

What does spironolactone do?

Answer 13

Stops K+ from being excreted which causes serum [K+] to increase

Question 14

In what instance will carbonic anhydrase inhibitors be used as a treatment?

Answer 14

• Glaucoma to reduce the formation of aqueous humour

- also in some unusual types of infantile epilepsy

Question 15

On which areas of the nephron do diuretics act on?

Answer 15

• thick ascending loop of Henle
• early DCT
• CT and ducts

Question 16

What are some causes of hyperkalaemia?

Answer 16

Lack of excretion

• ACE inhibitors
• aldosterone deficiency

Release from cells

• acidosis
• cellular breakdown: ischaemia, toxins, chemo, rhabdomyolysis

Excess administration

• potassium containing fluids or medications
• blood transfusion

Question 17

How can we treat hyperkalaemia?

Answer 17

Immediate

• insulin: shifts K+ into cells, lasts 6 hours
• salbutamol: same action as insulin, lasts 6 hours
• calcium stabilizes cardiac membrane potential

Later

• low potassium diet
• calcium resonium to bind potassium in gut
• stop offending medications
• furosemide: enhances potassium loss in urine

Question 18

What are some causes of hypokalaemia?

Answer 18

• potassium entering cells: insulin, alkalosis, beta 2 agonists
• extra renal losses: diarrhoea, laxatives
• decreased intake
• renal losses: diuretics, renal tubular acidosis, DKA
• increase GI loss: vomiting, diarrhoea
• magnesium deficiency

Question 19

How can we treat hypokalaemia?

Answer 19

• treat cause
• give potassium replacement
• oral: bananas, orange, Sando-K
• IV: saline +40mmol KCl, Dextrose +40mmol KCl, Central concentrated KCl
• potassium sparing diuretics: spironolactone, amilorides, etc.

Question 20

What 3 things predominantly increase 3Na/2K ATPASE activity?

Answer 20

• K+ concentration in plasma
• insulin
• noradrenaline effect on B2-adrenoceptors

Question 21

What things inhibit Na/K ATPase activity?

Answer 21

• digitalis

- chronic disease (heart failure, CKD)

Question 22

In what ways is potassium excreted?

Answer 22

• kidney

- small amounts lost in faeces and sweat

Question 23

Whereabouts in the nephron is potassium reabsorbed?

Answer 23

• 65 to 70% reabsorbed in PCT

- 20 to 25% reabsorbed in thick ascending loop

Question 24

How can hyperkalaemia and hypokalaemia symptoms affect the membrane potential?

Answer 24

• low serum K+ leads to bigger K+ gradient between intracellular and extracellular compartment
• depolarisation leads to increased excitability (risk of arrhythmia)
• high serum K+ leads to smaller K+ gradient
• decreased membrane excitability (risk of cardiac arrhythmias)
• risk of symptoms depends on both degree and rapidity of change

Question 25

Why is it hard to treat babies and elderly for infection?

Answer 25

• babies have 75% TBW so too much fluid

- elderly have 50% TBW, ability to hold on to water and not excrete is poor

Question 26

What are some differences between hypernatremia and hyponatremia?

Answer 26

Hypernatremia

• cell shrinkage
• confusion/seizures

Hyponatremia

• cell swelling
• cerebral oedema
• headache/seizures

Question 27

What is a 1000mL 5% dextrose solution used for?

Answer 27

• used when fluids are lost from body and need carbohydrates
• contains 50g/L glucose
• osmolarity = 278 mOsm/kg
• glucose is taken up by cells rapidly
• hyperglycemia will occur if infusion rate is quicker than uptake and metabolism
• H2O reduces osmolarity of all compartments

Question 28

What is a 1000mL 0.9% saline solution used for?

Answer 28

• needed to replenish sodium levels
• contains 154mmol Na+ and 154mmol Cl-
• osmolarity= 308mOsm/kg
• Na+ remains in the ECF, no change in osmolarity

Question 29

What is 1000mL Hartmann’s solution used for?

Answer 29

• used for replacing fluids and electrolytes in those who have low blood volume or low BP
• contains 131mmol Na, 111mmol Cl, 5mmol K+, 2mmol Ca, and 29mmol lactate
• osmolarity = 280mOsm/kg
• majority retained in the extracellular space as osmolarity maintained with effective osmoles sodium, potassium and calcium

Question 30

Why would a patient need IV fluids?

Answer 30

• nil by mouth
• malfunctioning GI tract
• dehydration
• fluid losses
• abnormal electrolytes

Always ask yourself:

• whether a pt. Needs IV fluids
• whether you need to do anything to try and stop fluid loss

Question 31

How do you determine which IV fluid to give?

Answer 31

• What does the patient need as maintenance?
• give maintenance fluids if unable to take orally
• has the patient lost any additional fluids?
• what are they losing?
• just replace as close to that as possible

Question 32

What do maintaineance fluids do?

Answer 32

Replace standard daily losses

Question 33

How do we determine the amount of fluids to give?

Answer 33

• look at size and age of pt and make relative measurements
• older: give more
• younger: give less
• decide which fluids you want to give for 24 hours