Potassium and pH

Question 1

Role of potassium

Answer 1

key determinant of resting membrane potential

Question 2

ENaC/ROMK channel function

Answer 2

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

Question 3

K+ excretion is dependent on:

Answer 3

Plasma K+ concentration

Aldosterone

Question 4

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

Answer 4

Maintaining the difference in electrolyte concentration between the ICF and ECF

Question 5

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

Answer 5

beta adrenergic stimuli and thyroxine

Question 6

Adrenaline effect on potassium

Answer 6

Adrenaline lowers plasma K+

Question 7

Main causes of low K+:

Answer 7

Reduced intake (unlikely)
Renal losses
Intracellular shift

Question 8

Causes of IC shift of low K+

Answer 8

Glucose load
Adrenaline
Alkalosis

Question 9

Renal losses can cause low K+:

Answer 9

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

Question 10

What happens after glucose is ingested and enters the blood?

Answer 10

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

Question 11

Most common cause of low K+

Answer 11

Diarrhoea + Vomiting

Question 12

Overview of causes of high plasma K+:

Answer 12

Increased intake (unlikely)
Renal retention
Intracellular shift

Question 13

Causes of renal retention of K+

Answer 13

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

Question 14

Causes of IC shift of high K+

Answer 14

Insulin deficiency
Acidosis
Exercise
Cell lysis

Question 15

How does acidosis cause high K+?

Answer 15

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+

Question 16

Main issue with high K+

Answer 16

Abnormal ECG

Question 17

ECG abnormalities with hyperkalaemia:

Answer 17

Tented T waves
Loss of P waves
Broad QRS
BRADYCARDIA

Question 18

Treatment of Hyperkalaemia

Answer 18

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

Question 19

Calcium Chloride as hyperkalaemia treatment mechanism of action

Answer 19

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

Question 20

50% glucose as hyperkalaemia treatment mechanism of action

Answer 20

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

Question 21

Sodium bicarbonate as hyperkalaemia treatment mechanism of action

Answer 21

This works if your patient is not fluid overloaded

This also affects the movement of potassium between ECF and ICF

Question 22

Consequences of changes in pH:

Answer 22

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

Question 23

What is HCO3- controlled by?

Answer 23

Kidneys

Question 24

What is total CO2 controlled by?

Answer 24

Lungs

Question 25

What occurs if you breathe faster

Answer 25

pCO2 decreases --> respiratory alkalosis

Question 26

What occurs if you breathe slower

Answer 26

pCO2 increases --> respiratory acidosis

Question 27

What happens if someone has lobar pneumonia?

Answer 27

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

Question 28

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

Answer 28

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

Question 29

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

Answer 29

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

Question 30

Oxygen and CO2 levels in focal lung disorders

Answer 30

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

Question 31

What causes type 1 respiratory failure

Answer 31

caused by FOCAL lung disorders Pneumonia Pulmonary embolism

Question 32

Blood gases in Type 1 respiratory failure

Answer 32

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

Question 33

What can also cause Respiratory alkalosis?1.

Answer 33

hyperventilation

Question 34

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

Answer 34

Because the whole lung is not functioning properly

Question 35

CAUSES of Type 2 Respiratory Failure:

Answer 35

``` Airways disease (mainly COPD) Pulmonary fibrosis ```

Question 36

Blood gases in Type 2 respiratory failure?

Answer 36

``` pO2 = LOW pCO2 = HIGH ```

Question 37

Common causes of metabolic acidosis

Answer 37

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

Question 38

Changes in other acids that cause metabolic acidosis

Answer 38

Lactic Acid | Ketoacids

Question 39

What is the anion gap?

Answer 39

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

Question 40

Anion gap range

Answer 40

12 +/- 4

Question 41

Anions that aren't measured:

Answer 41

Phosphate Proteins Specific metabolic acid

Question 42

Common causes of metabolic alkalosis:

Answer 42

Diuretics Mineralocorticoid excess Vomiting

Question 43

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

Answer 43

Metabolic acidosis

Question 44

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

Answer 44

Metabolic alkalosis

Question 45

Diarrhoea - more likely to cause acidosis/alkalosis?

Answer 45

Acidosis

Question 46

Vomiting - more likely to cause acidosis/alkalosis?

Answer 46

Alkalosis

Question 47

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

Answer 47

Renal tubular disease | Urinary diversion

Question 48

Conditions that cause acidosis but do NOT alter plasma K+

Answer 48

Ketones Lactate Poisons

Question 49

Causes of Ketoacidosis

Answer 49

Diabetic Ketoacidosis (most common) Starvation Alcoholics

Question 50

Causes of Lactic Acidosis

Answer 50

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

Question 51

Low pH leads to:

Answer 51

Breathlessness | Causes strong respiratory drive

Question 52

High pH leads to:

Answer 52

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

Question 53

Compensation for metabolic acidosis

Answer 53

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

Question 54

Compensation for respiratory acidosis

Answer 54

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