Role of ventilation in acid-base balance

Question 1

Define pH

Answer 1

pH = -log[H⁺]

Question 2

Role of bicarbonate buffering system?

Answer 2

enables excess H⁺ converted to H2O + CO2 so it can be removed by increasing ventilation

Question 3

What happens when pH increases?

Answer 3

hypoventilation to increase PaCO2, yield more H⁺

Question 4

Eg of buffer?

Answer 4

weak acid H2CO3 + conjugate base HCO3⁻

Question 5

What happens when pH decreases?

Answer 5

hyperventilation to decrease PaCO2, so less H⁺

Question 6

What happens if HCO3⁻ increased?

Answer 6

decrease in H⁺, increase pH

Question 7

What’s the Henderson-Hasselbach equation?

Answer 7

pH ∝ log[HCO3⁻]/PaCO2

Question 8

How does the kidney regulate HCO3⁻?

Answer 8

regulates reabsorption/excretion of glomerular filtrate (days)

Question 9

How do the lungs regulate PaCO2?

Answer 9

regulates ventilation (mins-hrs)

Question 10

What’s blood pH determined by?

Answer 10

ratio of HCO3: PaCO2

Question 11

Define Ka

Answer 11

eq constant for dissociation of acid in water, ratio ionised: unionised species so degree to which an acid’s able to donate H+ generating acidity
Ka= [H⁺][A⁻]/[HA]

Question 12

How can signs of respiratory + metabolic distress can be diagnosed + interpreted ?

Answer 12

analysis of ABG + pH

Question 13

What’s [H2CO3] in blood is determined by?

Answer 13

PaCO2, CO2 solubility, a constant : 0.226 mM/kPa

Question 14

eg of diff intracellular buffers?

Answer 14

Phosphate buffer system
AA / proteins
Hb

Question 15

eg of diff extracellular buffers?

Answer 15

Bicarbonate buffer system
Plasma proteins (eg albumin)

Question 16

Define acidosis + alkalosis

Answer 16

pH < 7.35

pH > 7.45

Question 17

Diff types of acidosis + cause?

Answer 17

respiratory acidosis - high CO2

metabolic acidosis - low HCO3⁻

Question 18

Diff types of alkalosis + cause?

Answer 18

respiratory alkalosis - low CO2

metabolic alkalosis - high HCO3⁻

Question 19

Diff causes of acidosis?

Answer 19

Hypercapnia (hypoventilation)
↑ Lactic acid (spesis)
↑ Ketone bodies (diabetes)
↓ Kidney acid excretion (renal failure)
↓HCO3- reabsorption (renal acidosis)
Diarrhoea (loss of HCO3- from gut)

Question 20

Symptoms of acidosis?

Answer 20

Tachypnoea
Muscular weakness
Headache
Confusion, Coma
Cardiac arrhythmia
Hyperkalaemia

Question 21

What are the diff compensatory mechanisms for acidosis?

Answer 21

Hyperventilation (↓PaCO2, respiratory compensation)

↓ HCO3- excretion (renal compensation)

Question 22

Diff causes of alkalosis?

Answer 22

Hypocapnia (hyperventilation)
Vomiting (loss of H+ in HCl)
↑ kidney acid excretion (diuretics)
↑ alkalotic agent consumption (antacids, NaHCO3)

Question 23

Symptoms of alkalosis?

Answer 23

Bradypnoea
Muscular weakness, cramps, tetany
Headache, Nausea
Lightheadedness, confusion, coma
Cardiac arrhythmia
Hypokalaemia

Question 24

What are the diff compensatory mechanisms for alkalosis?

Answer 24

Hypoventilation (↑PaCO2, respiratory compensation)

↑ HCO3- excretion (renal compensation)

Question 25

What’s acidosis-induced hyperkalaemia + symptoms?

Answer 25

K+ accumulation in serum due to increase in blood,extracellular [H+] so no H+ conc gradient for K+ influx
cardiac arrhythmia + muscle weakness

Question 26

How cells exchange H+ for K+?

Answer 26

-H+ efflux, Na+ influx - relies on H+ conc gradient
-Na+ efflux, K+ influx
net effect = K+ influx, H+ efflux

Question 27

What’s alkalosis-induced vasoconstriction + symptoms?

Answer 27

-Hyperventilation = ↓PaCO2 +↓H+ –> high pH
-vasoconstriction of cerebral arteries
-↓ cerebral blood flow
headache, lightheadedness, confusion, seizures

Question 28

What’s CO2 effect on blood vessels?

Answer 28

CO2 (via H+) acts as vasodilator (cerebral arteries sensitive)