Acid base regulation****** Flashcards
Define Alkalaemia
Refers to high-than-normal pH of blood
Define Acidaemia
Refers to lower-than-normal pH of blood
Define Alkalosis
Describes circumstances that will decrease [H+] and increase pH
Define Acidosis
Describes circumstances that will increase [H+] and decrease pH
What is the equilibrium equation?
H2O + CO2 -H2CO3 H+ + HCO3-
What is the Pitts and swan experiment and what did they find out?
Dog is anaesthetised. Baseline blood is drawn and it was pH= 7.44.
Dog was injected with 14 molar acid and they expected pH to be 2.5 and so dog to die but it didn’t
what does Pitts and Swan experiment show?
The blood has an ENORMOUS buffering capacity that can react almost IMMEDIATELY to imbalances
What are the 2 sources of acid?
- Respiratory acid: CO2
- Metabolic acid: pyruvic acid, lactic acid, all other acids that are not CO2
what is the ratio which the acids are produced?
Respiratory acid: metabolic acid
100: 1
What is sorensen
equation?
To calculate pH from proton concentration (or vice versa)
𝑝𝐻=−Log10[H+]
What is henderson equation?
To calculate the dissociation constant (Ka)
K= [H+][HCO3-]/ [CO2][H2O]
what is Henderson-Hasselbalch equation
Combines the above equations
pH= pK + Log10 [HCO3-]/[CO2]
What is the normal pH for arterial blood
7.40
What is the normal pH for venous blood
7.36
What is the normal CO2 flux?
For every 100 mL of blood that goes through the systemic capillaries, 4mL of CO2 is added.
therefore:
4 mL/dL/min
What is the cardiac output in Litres?
5L
What is the basic partial pressure of oxygen guidelines?
Basic guidelines for PaO2
> 10 kPa is normal
8-10 kPa is mild hypoxaemia
6-8 is moderate hypoxaemia
<6 kPa is severe hypoxaemia
What can we tell from an ABG?
Is a low blood pH acidosis or acidaemia? [H+] only? You’d better convert! Is the PaCO2 normal, high or low? This is assessing the respiratory component Is the BE excess high or low? This is assessing the metabolic component Is the patient hypoxaemic? No, mildly, moderately or severely?
what are the compensatory mechanisms?
- Changes in ventilation can stimulate a RAPID compensatory response to change CO2 elimination and therefore alter pH
- Changes in HCO3- and H+ retention/secretion in the kidneys can stimulate a SLOW compensatory response to increase/decrease pH
What does an acidosis and an alkalosis need?
An acidosis will need an alkalosis to correct
An alkalosis will need an acidosis to correct
What causes a rise/fall in base excess?
A rise in base excess is due to:
- an increase in renal excretion of acid, ingestion/administration of a base or loss of acid from vomiting.
- The result is a metabolic alkalosis.
A fall in base excess is due to:
- the overproduction of metabolic acids, the ingestion of acid, a reduction/failure of acid excretion by the kidney or excessive loss of alkali from intestines with diarrhoea.
- The result is a metabolic acidosis
