acid/base

Question 1

renal acid/base regulation

Answer 1

acidosis = increased H+ secretion from nephron and therefore reabsorption of HCO3-

alkalosis = reduced secretion of H+ from nephron and reduced reabsorption of HCO3-

Question 2

difference between stimuli of O2 and CO2 to ventilate

Answer 2

PaO2 is a nonlinear stimulus to ventilation

PaCO2 is a linear, potent stimulus to ventilation

Question 3

respiratory regulation and receptors

Answer 3

• arterial Pco2 and pH are sensed by chemoreceptors in brain and aortic and carotid bodies
• increased Pco2 and reduced pH stimulate ventilatory drive and vice versa (central receptors)
• hypoxia also acts as a potent stimulus for ventilatory drive (peripheral chemoreceptors)

Question 4

bicarbonate reabsorption by the kidney

Answer 4

• directly related to PaCO2
• inversely related to plasma levels of plasma (K+) and (Cl-)
• increased by increased plasma levels of adrenal corticosteroids e.g. cushing’s disease

Question 5

give the arterial blood samples for metabolic alkalosis with respiratory compensation

Answer 5

high pH
high Pco2
high HCO3-
+ve BE

Question 6

give the arterial blood samples for metabolic acidosis with respiratory compensation

Answer 6

low pH
low Pco2
low HCO3-
-ve BE

Question 7

give the arterial blood samples for mixed respiratory acidosis and metabolic acidosis

Answer 7

low pH
high Pco2
low HCO3-
-ve BE

Question 8

alveolar gas equation and what it shows

Answer 8

PAO2 = 150 - (PACO2 / 0.8) + 2

larger A-a gradient due to impaired diffusion

Question 9

how do you differentiate metabolic acidosis causes

Answer 9

• in acidosis with mixed acid, protons are buffered by HCO3-
• where anion of fixed acid generated is Cl (diarrhoea, renal dysfunction)
  AG = Na - (↑↑Cl + ↓↓HCO3-) = normal
• where anion of fixed acid generated is not Cl (DKA, lactic acidosis)
  AG = Na — (Cl + ↓↓HCO3-) = ↑AG

Question 10

when is HCO3 excreted by the kidney

Answer 10

when plasma bicarbonate is >24mmols/L