Session 5

Question 1

Explain depolarisation

Answer 1

If extracellular K+ rises, resting membrane potential is decreased

Na+ ions in

Question 2

Explain repolarisation

Answer 2

If extracellular k+ falls, resting membrane potential is increased (hyperpolarised)

K+ ions out

Question 3

ECG trace in hypokalaemia

Answer 3

Peaked P wave
Prolonged PR
ST depression
Shallow T wave
Prominent U wave

Question 4

ECG trace in hyperkalaemia

Answer 4

Wide, flat P wave
prolonged PR
Decreased R wave amplitude
Widened QRS
Depressed ST segment
Tall, peaked T wave

Question 5

Intra and Extra cellular concentrations of K+

Answer 5

Intra- 130-140 mEq/L
Extra- 3.5-5.5 mEq/L (due to Na+Ka+ATPase)

Question 6

Distribution of body water

Answer 6

60% fluids (40% solids)

In 60% = 1/3 ECF, 2/3 ICF

In 1/3 ECF = 75% interstitial fluid, 25% plasma

Question 7

How do the intercalated cells control pH of blood

Answer 7

Acidosis: secrete H+ into tubule, reabsorb K+ and HCO3- into blood

Alkalosis: secrete K+ and HCO3- into tubule, reabsorb H+ into blood

Question 8

Clinical features of hyperkalaemia

Answer 8

Can be asymptomatic
Muscle weakness, cardiac arrhythmis (impacts nerve conduction)

Question 9

Hyperkalaemia can result from

Answer 9

Lack of excretion - (kidneys failing, AKI/CKD, potassium sparing diuretics, ACE inhibitor, aldosterone problem)

Release from cells- acidosis, lysis

Excess administration- too much fluids, medications

Question 10

When is emergency treatment of hyperkalaemia needed

Answer 10

When there is more than 6.5mlmol/L or ECG changes

Question 11

Emergency treatment of hyperkalaemia

Answer 11

Calcium gluconate- Ca2+ stabilises the myocardium, preventing arrhythmias

Insulin- drives K+ into cells to lower plasma concentrations, given with glucose to avoid hypoglycaemia

Calcium resonium- removes K+ by binding to it and increasing excretion. Only way to remove K+ without renal replacement therapy

Question 12

Clinical effects of hypokalaemia

Answer 12

Muscle weakness, cramps and tetany (starts in lower extremities)

Vasoconstriction and cardiac arrhythmias

Impaired ADH action causing thirst, polyuria and no concentration of urine

Metabolic alkalosis due to increase in intracellular H+ concentration

Question 13

Long term control of hyperkalaemia

Answer 13

Low potassium diet
Stop offending medications
Furosemide- enhances potassium loss in urine
Dialysis?

Question 14

Causes of hypokalaemia

Answer 14

Reduced dietary intake (anorexia nervosa)
Increased entry into cells (alkalosis or noradrenaline release due to stress perhaps)
Increased GI losses
Increased urine loss

Question 15

Treatment for hypokalaemia

Answer 15

Treat cause- diuretics, diarrhoea, poor oral intake

Give replacement:
Oral- banana, orange, Sando-K
IV- add KCL to IV bags
Potassium sparing diuretics= spironolactone, amiloride

Question 16

K+ too high or low will cause

Answer 16

Nerve dysfunction and cardiac arrest

Question 17

Excretion of K+

Answer 17

Kidneys excrete 80% of K+, bowel 20%

Question 18

Insulin will decrease k+ for appprox

Answer 18

6 hours

Question 19

What is osmolality

Answer 19

Particles of solute per kg of solvent

Question 20

What is osmolarity

Answer 20

Particles of solute per litre of solution

Question 21

What is tonicity

Answer 21

Effective osmotic pressure gradient of two solutions separated by a semi permeable membrane

Question 22

Differences in movement between intracellular and extracellular

Answer 22

Intracellular: potassium is major cation, Cell membrane limits transport

Extracellular: Sodium is major cation, concentration gradients allow movement

Question 23

What is the TBW of a newborn baby

Answer 23

75%

Question 24

What is TBW in elderly

Answer 24

45%

Question 25

Why do patients need fluids

Answer 25

Nil by mouth Malfunctioning gastro-intestinal tract Dehydration Fluid losses Abnormal electrolytes

Question 26

What to think about when giving fluids

Answer 26

Maintenance fluids- day to day requirements Has patient lost any additional fluids

Question 27

What happens when you give dextrose

Answer 27

Glucose taken up by cells rapidly (intracellular), H20 reduces osmolarity of all compartments equally

Question 28

Movement of ions between spaces

Answer 28

Extracellular: Na+ can move between interstitial and intravascular (plasma and interstitium) Na+ K+ ATPase allows transport of Na+ out of intracellular space and K+ in

Question 29

What happens when you give saline

Answer 29

Na+ remains in ECF, no change in osmolarity (no drive to move intracellular)

Question 30

What happens when you give Hartman’s

Answer 30

Majority retained in extracellular space as osmolarity maintained with effective osmoles sodium, potassium and calcium

Question 31

What happens when you give dextrose and saline

Answer 31

H20 reduces osmolarity of all compartments Saline remains in ECF Dextrose drawn into ICF

Question 32

Why are maintained requirements different in hospital patients

Answer 32

Vasopressin (ADH) differences (drugs, pain, nausea, low ECV) Generally not sweating much RAAS, catecholamines, reduced caloric expenditure (stress response)

Question 33

NICE guidelines for fluids

Answer 33

25-30ml/kg/day of water 1 mmol/kg/day of potassium, sodium and chloride 50-110g/day of glucose to limit starvation ketosis

Question 34

What happens when you give a patient saline that isn’t needed

Answer 34

Expanded ECF

Question 35

What happens when a patient drinks too much water

Answer 35

Water expands ECF Dilutes ECF (osmolarity decreased) Water moves from ECF to ICF due to difference in osmolarity until new eq. Reached

Question 36

What happens to the fluid volumes of a bleeding person

Answer 36

Losing volume from ECF

Question 37

What happens to fluid volumes in a patient vomiting

Answer 37

ECF decreases Osmolarity increases as more dehydrated Water moves from ICF to ECF

Question 38

What happens to the fluid volumes of someone who drinks salt water in large volume

Answer 38

ECF volume increases Osmolarity increases Water moves from ICF to ECF

Question 39

What would you give a 96kg man who is NBM

Answer 39

1 x Hartman’s 2 x 5% dextrose (+40 mmol KCL)

Question 40

What would you give a 65kg person who is NBM

Answer 40

2L 0.18 NaCl, 4% dextrose with KCL added to the bags

Question 41

What would you give a 65kg person who is vomiting

Answer 41

1L saline, 2L 5% dextrose with KCL added So saline can go ECF and dextrose can go ICF