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Flashcards in Potassium and pH Deck (54):
1

Role of potassium

key determinant of resting membrane potential

2

ENaC/ROMK channel function

Na+ comes in and K+ goes out
So it is important in regulating K+ elimination
Aldosterone activates these channels and inserts them into the membrane

3

K+ excretion is dependent on:

Plasma K+ concentration
Aldosterone

4

What is Na+/K+ pump is responsible for?

Maintaining the difference in electrolyte concentration between the ICF and ECF

5

What can Na+/K+ pump activity be influenced by?

beta adrenergic stimuli and thyroxine

6

Adrenaline effect on potassium

Adrenaline lowers plasma K+

7

Main causes of low K+:

Reduced intake (unlikely)
Renal losses
Intracellular shift

8

Causes of IC shift of low K+

Glucose load
Adrenaline
Alkalosis

9

Renal losses can cause low K+:

Mineralocorticoid excess (e.g. Conn's syndrome)
Renal tubular disorder
Diuretics

10

What happens after glucose is ingested and enters the blood?

Stimulates a release of insulin, which drives K+ into cells

11

Most common cause of low K+

Diarrhoea + Vomiting

12

Overview of causes of high plasma K+:

Increased intake (unlikely)
Renal retention
Intracellular shift

13

Causes of renal retention of K+

Mineralocorticoid deficiency (Addison's disease)
ACE inhibitors
Renal failure
Potassium sparing diuretics (e.g. spironolactone)

14

Causes of IC shift of high K+

Insulin deficiency
Acidosis
Exercise
Cell lysis

15

How does acidosis cause high K+?

When you're acidotic, the H+ ions compete with the K+ ions so when you are acidotic you don't get as good activity of that pump leading to high plasma K+

16

Main issue with high K+

Abnormal ECG

17

ECG abnormalities with hyperkalaemia:

Tented T waves
Loss of P waves
Broad QRS
BRADYCARDIA

18

Treatment of Hyperkalaemia

Calcium Chloride (IV)
50% Glucose
Sodium Bicarbonate (NaHCO3)

19

Calcium Chloride as hyperkalaemia treatment mechanism of action

NO EFFECT on plasma potassium but it does reduce the effect of potassium on cardiac excitability and limits the ECG changes
It fixes the bradycardia
In other words, it makes your heart resistant to the effects of hyperkalaemia

20

50% glucose as hyperkalaemia treatment mechanism of action

As that glucose is taken up by cells, there is a shift of potassium from the ECF to the ICF
It will lower plasma K+ within half an hour and it will last for about 4-6 hours - the K+ will eventually leak back out again but it does buy you time

21

Sodium bicarbonate as hyperkalaemia treatment mechanism of action

This works if your patient is not fluid overloaded
This also affects the movement of potassium between ECF and ICF

22

Consequences of changes in pH:

Impaired ventricular function
Arrhythmias, lower fibrillation threshold
Vasodilation, catecholamine release
Impaired oxygen delivery
Bronchoconstriction
Reduced hepatic/renal blood flow
Impaired consciousness
Respiratory muscle fatigue
Protein catabolism
Insulin resistance

23

What is HCO3- controlled by?

Kidneys

24

What is total CO2 controlled by?

Lungs

25

What occurs if you breathe faster

pCO2 decreases --> respiratory alkalosis

26

What occurs if you breathe slower

pCO2 increases --> respiratory acidosis

27

What happens if someone has lobar pneumonia?

The blood that goes to the bit that has pneumonia will NOT become fully saturated
The blood that goes to the normal parts of the lungs will be fully saturated
Lowers the oxygen content of the blood

28

What happens to blood going to damaged part of lung in lobar pneumonia

Blood going to the damaged region will not have its CO2 removed so the blood coming away from this part of the lung will have a higher CO2 concentration

29

What happens to blood going to healthy parts of lung in lobar pneumonia

The good regions of the lung will have abnormally LOW CO2 because you're breathing a bit faster and removing more CO2

30

Oxygen and CO2 levels in focal lung disorders

With FOCAL lung disorders, the oxygen will go down BUT the CO2 will not increase

31

What causes type 1 respiratory failure

caused by FOCAL lung disorders
Pneumonia
Pulmonary embolism

32

Blood gases in Type 1 respiratory failure

Oxygen = LOW (< 8 kPa)
CO2 = NORMAL or LOW

33

What can also cause Respiratory alkalosis?1.

hyperventilation

34

Why is there an abnormality of BOTH oxygen and CO2 in Type 2 respiratory failure?

Because the whole lung is not functioning properly

35

CAUSES of Type 2 Respiratory Failure:

Airways disease (mainly COPD)
Pulmonary fibrosis

36

Blood gases in Type 2 respiratory failure?

pO2 = LOW
pCO2 = HIGH

37

Common causes of metabolic acidosis

Renal failure
Mineralocorticoid deficiency
Diarrhoea
These causes are also associated with a HIGH CHLORIDE

38

Changes in other acids that cause metabolic acidosis

Lactic Acid
Ketoacids

39

What is the anion gap?

When the amount of Na+ (cation) should equal the amount of the total anions (Cl- and HCO3-) but there are some protein based anions that are not measured so there is always a little bit of a gap

40

Anion gap range

12 +/- 4

41

Anions that aren't measured:

Phosphate
Proteins
Specific metabolic acid

42

Common causes of metabolic alkalosis:

Diuretics
Mineralocorticoid excess
Vomiting

43

Things that cause high K+ tend to cause which acidosis/alkalosis?

Metabolic acidosis

44

Things that case low K+ tend to cause which acidosis/alkalosis?

Metabolic alkalosis

45

Diarrhoea - more likely to cause acidosis/alkalosis?

Acidosis

46

Vomiting - more likely to cause acidosis/alkalosis?

Alkalosis

47

Unusual disorders that cause metabolic acidosis that are associated with a low K

Renal tubular disease
Urinary diversion

48

Conditions that cause acidosis but do NOT alter plasma K+

Ketones
Lactate
Poisons

49

Causes of Ketoacidosis

Diabetic Ketoacidosis (most common)
Starvation
Alcoholics

50

Causes of Lactic Acidosis

Occurs mainly when there is a lack of tissue perfusion (tissue hypoxia causes anaerobic respiration)
Shock
Liver failure
Short bowel

51

Low pH leads to:

Breathlessness
Causes strong respiratory drive

52

High pH leads to:

Cramps/tetany
Because pH affects calcium ionisation and that affects muscle excitability

53

Compensation for metabolic acidosis

Breathing faster - this lowers CO2 and restores the pH - this change occurs FAST

54

Compensation for respiratory acidosis

Develop a metabolic alkalosis to compensate - changing bicarbonate reabsorption release - this change occurs SLOWLY