Acid Base Balance - Pt 2

Question 1

What do respiratory and renal disorders affect?

Answer 1

Resp. = PCO2
Renal = conc. of HCO3-

Question 2

Describe respiratory acidosis

Answer 2

pH has fallen and is due to resp. change
PCO2 is increased
Results from reduced ventilation and retention of CO2

Question 3

What are the acute causes for respiratory acidosis?

Answer 3

Drugs which depress medullary respiratory centres - barbiturates and opiates
Obstructions to major airways

Question 4

What are the chronic causes for respiratory acidosis?

Answer 4

Lung disease - bronchitis, emphysema and asthma
PCO2 increased so increase secretion of H+ and HCO3-
Need to protect pH so increase HCO3-
Generation of new HCO3- but also increased reabsorption

Question 5

What do acid conditions stimulate?

Answer 5

Renal glutaminase - more NH3 produced but it takes time

Question 6

In chronic causes of respiratory acidosis - why does original disturbance not corrected?

Answer 6

Renal compensation for increase HCO3- protects pH but only restoration of ventilation can remove primary disturbance
So BG values are never normalised - kidney maintains high HCO3-

Question 7

Describe respiratory alkalosis

Answer 7

Alkalosis of resp. origin so must be due to fall in PCO2 and can occur through hyperventilation and CO2 blow off

Question 8

What are the acute causes of respiratory alkalosis?

Answer 8

Voluntary hyperventilation, aspirin and first ascent to altitude

Question 9

What are the causes of chronic alkalosis?

Answer 9

Long term residence at altitude so PCO2 below 60mmHg stimulates peripheral chemoreceptors to increase ventilation
Ventilation must be normal to correct disturbance

Question 10

What are alkaline condition dealt with?

Answer 10

HCO3- reabsorption mechanism
If PCO2 drops then less H+ available for excretion so less filtered HCO3- reabsorbed so HCO3- lost in urine

Question 11

Describe metabolic acidosis

Answer 11

Metabolic origin - loss of HCO3-
Decreased HCO3- either from increased buffering or direct loss of HCO3-
PCO2 must be decreased

Question 12

What are the causes of metabolic acidosis?

Answer 12

Increased H+ production - ketoacidosis or lactic acidosis
Failure to excrete dietary load of H+ in renal failure
Loss of HCO3- as in diarrhoea - failure to reabsorb intestinal HCO3-

Question 13

Describe Kussmaul breathing

Answer 13

Degree of hyperventilation - increase depth of breathing so max 30l/min when pH falls to 7
Sign of renal failure or diabetic ketoacidosis

Question 14

What is the problem in metabolic acidosis?

Answer 14

Normally kidneys correct disturbance by restoring HCO3- and getting rid of H+ ions
Source of H+ ions is the carbonic acids from CO2 but resp. compensation lowers PCO2 to protect pH

Question 15

What would complete compensation lead to?

Answer 15

Would remove the drive to correct the original disturbance
Then there is no pressure to correct disturbance - further perturbation may push system too far so compensation may longer not be effective

Question 16

What does decreased PCO2 lead to?

Answer 16

Total amount of H+ secretion by renal tubule will be less than normal but because of plasma HCO3- conc. and filtered HCO3- conc. is reduced

Question 17

What does a reduced plasma HCO3- and filtered HCO3- load mean?

Answer 17

Less total H+ is needed for HCO3- reabsorption and therefore greater proportion is available for excretion to form titratable acid and NH4+
Less H+ secretion = Decreased HCO3- reabsorption and increase new HCO3-

Question 18

What does increase metabolic H+ in body lead to?

Answer 18

Immediate buffering in ECF and then ICF
Resp. compensation within minutes
Renal correction takes longer - to develop response to increase H+ excretion and generates new HCO3-

Question 19

What does respiratory compensation do in metabolic acidosis?

Answer 19

Delays the renal correction but protects the pH

Question 20

Describe metabolic alkalosis

Answer 20

HCO3- must have increased and PCO2 will increase to protect the pH

Question 21

What are the causes of metabolic alkalosis?

Answer 21

Increase H+ ion loss in vomiting
Increase H+ loss in aldosterone excess and liquorice ingestion
Excess administration of HCO3- - renal impairment
Massive blood transfusions

Question 22

How can massive blood transfusions lead to metabolic alkalosis?

Answer 22

Bank blood contains citrate to prevent coagulation which is converted to HCO3- but need 8 units for this

Question 23

What does increased filtered load of HCO3- lead to?

Answer 23

Exceeds the level of H+ secretion to reabsorb it, even in presence of increased PCO2
So excess lost in urine
Resp. delays renal correction but protects the pH

Question 24

What is the summary of respiratory acidosis?

Answer 24

Increase H+ so decreases pH
Primary disturbance is increase PCO2
Compensation is increase HCO3- conc.

Question 25

What is the summary of respiratory alkalosis?

Answer 25

Decrease H+ so increase pH Primary disturbance is decrease PCO2 Compensation is decrease HCO3- conc.

Question 26

What is the summary of metabolic acidosis?

Answer 26

Increase H+ so decrease pH Primary disturbance is decrease HCO3- conc. Compensation is decrease PCO2

Question 27

What is the summary of metabolic alkalosis?

Answer 27

Decrease H+ so increase pH Primary disturbance is increase HCO3- conc. Compensation is increase PCO2

Question 28

What is a decrease in pH caused by?

Answer 28

Decreased HCO3- Increased PCO2

Question 29

What is an increase in pH caused by?

Answer 29

Increased HCO3- Decreased PCO2

Question 30

Does chronic or acute resp. acidosis cause bigger decrease in pH

Answer 30

Acute Because NH3 production takes 4-5 days to turn on and off

Question 31

What can a haemorrhage lead to?

Answer 31

Lactic acidosis

Question 32

What is happening in a patient with metabolic acidosis, respiratory acidosis, and lactic acidosis?

Answer 32

Diabetic ketoacidosis decreases pH Chronic bronchitis decompensates Haemorrhage loss means additional metabolic acidosis Brings pH to brink of survival High acidity causes hyperkalaemia as H+ ions are buffered intracellularly in exchange for K+

Question 33

What would you do for a patient with metabolic and respiratory acidosis?

Answer 33

Insulin (and glucose if non-diabetic) which stimulates cellular uptake of K+ Hyperkalaemia - calcium resonium Ca gluconate IV which increases excitability of heart

Question 34

What does calcium resonium do?

Answer 34

Exchanges Ca2+ ions for K+ ions

Question 35

What happens in a bad case of vomiting - hypovolaemia and metabolc alkalosis?

Answer 35

Loss of NaCl + H2O and HCl Hypovolaemia - stimulates aldosterone to increase distal tubule Na reabsorption In avid Na reabsorption Na is exchanged for H+ PCO2 helps drive H+ secretion and exacerbates metabolic alkalosis

Question 36

What takes precedence between volume and metabolic correction?

Answer 36

Volume

Question 37

What is given in bad case of vomiting - hypovolaemia and metabolic alkalosis?

Answer 37

Give NaCl to restore volume then alkalosis will be corrected

Question 38

What does liquorice contain?

Answer 38

Glycyrrhizic acid which similar to aldosterone - so excess ingestion causes metabolic alkalosis