UNFINISHED Acid Base Balance 2

Question 1

What aspects of acid base balance control are the renal and respiratory systems responsible for?

Answer 1

• Renal: determines [HCO3]

- Respiratory: determines PCO2

Question 2

How does the renal system respond to increased PCO2 that can be a result of lung disease or drugs (barbituates / opiates)?

Answer 2

• Needs to protect pH, so need to increase [HCO3]
• Renal glutaminase will work better under acidic conditions, and increased PCO2 increases the ability of the kidneys to secrete H+ and reabsorb HCO3

Question 3

How would the PCO2 and [HCO3] of a patient with reduced ventilation compare to a healthy patient? What about their pH?

Answer 3

PCO2 and [HCO3] would be high
- PCO2 high due to the lung disorder causing reduced ventilation, [HCO3] high due to the kidneys attempt to account for the reduced ventilation

• As long as there is no underlying kidney pathology the pH will be within normal range (perhaps a tad low)

Question 4

What are some causes of respiratory alkalosis? (increased ventilation / decreased PCO2)

Answer 4

• Altitude
• Aspirin
• Hyperventilation

Question 5

How do the kidneys account for decreased PCO2 (respiratory alkalosis)??

Answer 5

Lower PCO2 means less H+ for excretion, this means less H+ to facilitate HCO3 reabsorption - so H+ is retained and HCO3 is excreted

Question 6

What characterizes metabolic acidosis in terms of PCO2 & [HCO3]?

Answer 6

Metabolic acidosis is characterized by decreased [HCO3]

• Either due to buffering of H+ or direct loss of HCO3

Question 7

What are some causes of metabolic acidosis?

Answer 7

• Increased H+ production as in ketoacidosis / lactic acidosis
• Failure to excrete the normal dietary load of H+ as in renal failure
• Loss of HCO3 as in diarrhoea

Question 8

What is Kussmaul breathing? What is it a sign of?

Answer 8

• It is deep, laboured breathing that increases the volume of breath from around 5-6L/min to 30L/min.
• It is a means of increasing ventilation in response to acidosis (resp. compensation for metabolic acidosis)
• Sign of DKA and renal failure (serious)

Question 9

Metabolic acidosis causes the resp. system to increase ventilation, which reduced PCO2. Since PCO2 is the main drive for H+ ion excretion, how is this accounted for?

Answer 9

• In metabolic acidosis the bicarbonate levels are reduced, so less bicarc. is filtered and so less H+ is required to reabsorb the filtered bicarb.
• This leaves excess H+ to be used by the titratable acidity and ammonium excretion mechanisms, which create new bicarb. while secreting H+
• The very low HCO3 means the low H+ is still enough

Question 10

How quickly does the body recover from metabolic alkalosis?

Answer 10

• Resp. system responds within minutes to protect the pH, not a fix though just a compensation
• Renal glutaminase takes 4-5 days to reach max. function, as HCO3 rises the resp. compensation slowly decreases until eventually all excess H+ is excreted