Acid Base Balance

Question 1

What is the normal range for plasma pH?

Answer 1

7.35-7.45

Question 2

What are the clinical effects off acidaemia?

Answer 2

Affects enzyme function

K+ movement out of cells -> hyperkalaemia

Question 3

How does acidaemia affect enzyme function?

Answer 3

Denatures them

Question 4

What major affect does hyperkalaemia have?

Answer 4

Increases cardiac excitability causing arrhythmias

Question 5

When does acidaemia become severe?

Answer 5

Below 7.1

Question 6

When does acidaemia become life threatening?

Answer 6

Below 7.0

Question 7

What is the main effect of alkalaemia?

Answer 7

Causes Ca2+ to come out of solution, so free Ca2+ falls

Question 8

What is the effect of alkalaemia induced hypocalcaemia?

Answer 8

Increased neuronal excitability causing parasthesia and tetany

Question 9

What is the mortality rate if pH rises to 7.55?

Answer 9

40%

Question 10

How does the body buffer pH?

Answer 10

With CO2 and HCO3-

Question 11

What is normal arterial CO2?

Answer 11

5.3 kPa

Question 12

What equilibrium is there between CO2 and bicarb in the blood?

Answer 12

CO2 + H2O H+ + HCO3-

Question 13

What physiological process is CO2 determined by in the blood?

Answer 13

Respiration

Question 14

Where are the chemoreceptors than internally control CO2 oncentration in the blood?

Answer 14

Centrally i.e. in the CNS

Question 15

When CO2 is disturbed, what is usually responsible?

Answer 15

Respiratory disease

Question 16

Which organ controls HCO3-?

Answer 16

The kidneys

Question 17

When HCO3- is deranged, what is usually responsible?

Answer 17

Metabolic or renal disease

Question 18

What is the equation for blood pH?

Answer 18

pH= pK + Log([HCO3-]/(pCO2*0.23))

Question 19

Why is pCO2 multiplied by 0.23 in that equation?

Answer 19

Because 23% of blood co2 is dissolved and therefore available to react with the water to create H+

Question 20

Is CO2 dissolved in plasma the main source of HCO3-?

Answer 20

No, it creates a tiny amount. It is made in RBCs and transported to plasma

Question 21

What is HCO3- largely present with in ECF?

Answer 21

Na+ (i.e. it is disociated sodium hydrogen carbonate)

Question 22

How is more HCO3- produced in RBCs?

Answer 22

H+ binds to Hb so the equilibrium of the co2/hco3- equation within the rbc shifts to produce more H+ and HCO3-, which is then exchanged for Cl- in the plasma

Question 23

Why is plasma pH alkaline?

Answer 23

The large concentration of HCO3- stops nearly all the CO2 reacting so very little H+ is produced (as eqm is pushed to the left)

Question 24

What is pK in the equation?

Answer 24

6.1 at body temperature (37 degrees)

Question 25

What Is the normal range for HCO3- in the blood?

Answer 25

22-26 mmol/L

Question 26

In the kidneys, where is most HCO3- saved?

Answer 26

PCT

Question 27

How is HCO3- saved in the PCT?

Answer 27

Na is exchanged for H+. In the lumen, H+ reacts with HCO3- -> CO2 and water which is reabsorbed. Converts back to HCO3- which is transported back to ECF with Na.

Question 28

Where else, apart from the PCT, is HCO3- reabsorbed?

Answer 28

DCT and collecting ducts

Question 29

How is HCO3- reabsorbed in the DCT/CDs?

Answer 29

H+ is actively excreted whilst bound to ammonia nd phosphate, so no CO2 is formed in the lumen. HCO3- in the cell is then transported out into the ECF in exchange for Cl-.

Question 30

Which AA is converted to ammonium in response to low pH?

Answer 30

Glutamine

Question 31

Which ion is H+ exchanged with?

Answer 31

K+

Question 32

What happens to K+ in acidosis?

Answer 32

Hyperkalaemia as more H+ is pumped out so more K+ is retained

Question 33

What happens to K+ in alkalosis?

Answer 33

Hypokalaemia as more H+ is retained so K+ excretion increases in distal nephron

Question 34

What pattern would we see on an ABG of a pt in respiratory acidosis?

Answer 34

High pCO2, Normal HCO3-, Low pH

Question 35

What pattern would we see on an ABG of a pt in respiratory alkalosis?

Answer 35

Low pCO2, Normal HCO3-, rasied pH

Question 36

What if we saw high co2, high hco3- and a normal pH?

Answer 36

Compensated respiratory acidosis

Question 37

How long does compensation take to happen?

Answer 37

Usually 2-3 days

Question 38

What is the anion gap?

Answer 38

Difference measured between cations and anions due to other anions that are not measured

Question 39

When is the anion gap present?

Answer 39

If HCO3- is replaced by other anions, like in metabloic acidosis lactic acid reacts with HCO3- to replace it.

Question 40

How is ventilation stimulated in acidosis?

Answer 40

Peripheral chemoreceptors detect pH drop

Question 41

How is metabolic acidosis compensated?

Answer 41

Increased respiration to blow off CO2

Question 42

Why cant we compensate metabolic alkalosis with respiration?

Answer 42

Can't reduce breathing rate as need to maintain pO2.

Question 43

What conditions cause respiratory acidosis?

Answer 43

COPD, severe asthma, drug overdose, neuromuscular disease

Question 44

What is the difference in chronic conditions?

Answer 44

Respiratory acidosis may be compensated already, so pH is nearer to normal range.

Question 45

When do we see respiratory alkalosis?

Answer 45

Hyperventilation e.g. anxiety/panic attack

Question 46

What conditions cause metabolic acidosis with an anion gap?

Answer 46

DKA, lactic acidosis (exercsising to exhaustion, poor tissue perfusion), and uraemic acidosis in advanced renal failure

Question 47

What conditions cause metabolic acidosis without an anion gap?

Answer 47

Renal tubulr acidosis (rare), or severe/persistent diarrhoea

Question 48

In DKA what happens to K+ and why?

Answer 48

You would expect it to rise, being acidosis, but due to osmotic diuresis, there is a whole body depletion of K= as it is lost in urine

Question 49

What conditions cause metabolic alkalosis?

Answer 49

Severe prolonged vomiting, mechanical drainage of stomach, K+ depletion, mineralocrticoid excess, and certain diuretics such as loop and thiazides.