Respiratory Systems 8 - Acid-base Regulation Flashcards
List the blood gas composition in the systemic arteries
PaO2 >10kPa
SaO2 >95%
PaCO2 4.7-6.4kPa
List the blood gas composition in the systemic veins
PaO2 5.3kPa
SaO2 ~75%
PaCO2 6.1kPa
Define alkalaemia
Higher than normal pH of the blood
Define acidaemia
Lower than normal pH of the blood
Define alkalosis
Circumstances that will decrease [H+] and increase pH
Define acidosis
Circumstances that will increase [H+] and decrease pH
Explain the relationship between pH and hydrogen ion concentration
As [H+] increases, pH decreases
Where does acid come from?
Mainly respiratory, some metabolic acid (eg. lactic acid)
What is the Sorensen-equation?
Used to calculate pH from proton concentration
pH=-log(10)[H%+]
What is the Henderson equation?
Used to calculate the dissociation constant
πΎ=([H+][π»πΆπ3β])/([πΆπ2][H2O])
What is the Henderson-Hasslebalch equation?
ππ»=ππΎ+πππ(10 ) ([π»πΆπ3β])/([πΆπ2])
Describe the compensatory mechanisms for when acidosis or alkalosis occur.
- Changes in ventilation stimulates a rapid compensatory response
- Changes in H+ retention/secretion at the kidneys stimulates a slow compensatory response
Describe the stages in interpretation procedure when acidosis or alkalosis oxxur
- Type of imbalance
- Aetiology
- Compensaton?
- Oxygenation?
What is the optimum pH?
7.4
Describe how uncompensated respiratory acidosis affects pH
- CO2 increases in alveoli, so less CO2 moves out the blood and therefore pH decreases
How is acidosis corrected in the acute phase?
- CO2 combines with water to form bicarbonate which moves out of the erythrocyte by AE1 transporter.
- This pushes the bicarbonate ion concentration up in the plasma, so the bicarbonate will react with H+ to make hydrogen bicarbonate
How is acidosis corrected in the chronic phase?
Increasing bicarbonate reabsorption in the kidneys to return the pH to normal
What is seen in the blood composition following partially compensated respiratory acidosis?
- pH will still be slightly low
- PCO2 will be high
Base excess will be high as there is more bicarbonate than expected from CO2
What is seen in the blood composition of a patient with fully compensated respiratory acidosis?
- pH is normal
- PCO2 is high
- Base excess is high
What would happen to blood compensation in uncompensated respiratory alkalosis?
- PCO2 down
- High pH
- Normal base excess
How is uncompensated respiratory alkalosis compensated?
- No acute phase
- Reduced bicarbonate reabsorbed and increased excretion
- Increased dissociation of bicarbonic acid
What is the blood composition in partially compensated respiratory alkalosis?
High pH
Low pCO2
Low base excess
What is the blood composition in fully compensated respiratory alkalosis?
- Normal pH
- Low CO2
- Low base excess
What is the blood composition in uncompensated metabolic acidosis?
- Low pH
- Normal CO2
- Low base excess
What is the blood composition in partially compensated metabolic acidosis?
- Low pH
- Low CO2
- Low base excess
What is the blood composition in fully compensated metabolic acidosis?
- Normal pH
- Low CO2
- Low base excess
What is the blood composition in uncompensated metabolic alkalosis?
- High pH
- Normal CO2
- High base excess
What is the blood composition in partially compensated metabolic alkalosis?
- High pH
- High PCO2
- High base excess
What is the blood composition in fully compensated metabolic alkalosis?
- Normal pH
- High PCO2
- High base excess
What causes metabolic acidosis?
Diarrhoea (losing HCO3- and gaining H+)
What causes metabolic alkalosis?
Vomiting (losing H+ and gaining HCO3-)
What is type 1 respiratory failure?
- A low level of oxygen in the blood, with a normal or low level of CO2
- Caused by failure of oxygenation
What is type 2 respiratory failure?
- Caused by inadequate alveolar ventilation
- Both oxygen and CO2 are affected
- Low oxygen and high CO2
