Arterial Blood Gases & Acid Base Regulation Flashcards
What should be in equilibrium with pCO2 (theoretical)?
Bicarbonate
What is FMetHb?
ferritin NOT ferrous in the haem- molecule that is unable to bind O2
What does acidosis correct?
alkalaemia
What does hyperventilation result in?
increased CO2 clearance
What are the 4 key aspects found from an ABG?
- what is the type of imbalance?
- what is the aetiology of imbalance?
- any homeostatic compensation?
- oxygenation?
How to assess compensation?
- both values should change
- only one indicates it is UNcompensated
- changes in pH suggest partial compensation
What is base excess?
the difference between the actual bicarbonate and the expected bicarbonate
How do you calculate pH?
-log10[H+]
How do you calculate [H+]?
10^-pH
What is an acid?
Proton donor
What is a base?
- proton acceptors
- anionic (-ive) molecules
What proportion of acid is respiratory (CO2) or metabolic (lactic, HCl…)?
about 95:5
What does alkalosis correct?
acidaemia
What can cause a rapid compensation?
- respiratory compensation
- changes in ventilation change CO2 ventilation, altering pH
What can cause a slow compensation?
- metabolic compensation
- Changes in HCO3- and H+ retention/secretion in the kidneys, lead to changes in pH
How long does slow consumption take?
up to days
What is acidosis/alkalosis?
conditions that cause a change in pH
What is alkalaemia/acidaemia?
whether pH is above/below 7.35-7.45.
What are the different types of imbalance?
- acidosis
- alkalosis
- normal
What are the different aetiologies of an imbalance?
- respiratory (acidosis/alkalosis)
- metabolic (acidosis/alkalosis)
- mixed (respiratory and metabolic)
- nroaml
What are the different forms of homeostatic compensation?
- uncompensated
- partially compensated
- fully compensated
What are the different forms of oxygenation?
- Hypoxaemia
- Normoxaemia
- Hyperoxaemia
How do you differentiate between respiratory and metabolic causes?
look at the CO2 level
What would indicate compensation?
- changes in PaO2 and PaCO2
- changes in pH (if not normal, partial)
What do changes in base excess indicate?
decrease if in respiratory alkalosis - for compensation (or vice versa)
What is a normal PaCO2?
4.7-6.4 kPa
What is a normal base excess?
-2 to 2
What is a normal PaO2?
10-13.5kPa
What can indicate partial compensation?
changes in PaCO2 or base excess that would help with alkalosis/acidosis but abnormal pH
What is seen in uncompensated respiratory acidosis?
- low pH
- high PaCO2
- normal BE
What is seen in partially compensated respiratory acidosis?
- low pH
- high PaCO2
- high BE
What is seen in fully compensated respiratory acidosis?
- normal pH
- high PaCO2
- high BE
What is seen in uncompensated respiratory alkalosis?
- high pH
- low PCO2
- normal BE
What is seen in partially compensated respiratory alkalosis?
- high pH
- low PCO2
- low BE
What is seen in fully compensated respiratory alkalosis?
- normal pH
- low PCO2
- low BE
What is seen in uncompensated metabolic acidosis?
- low pH
- normal PaCO2
- low BE
What is seen in partially compensated metabolic acidosis?
- low pH
- low PaCO2
- low BE
What is seen in fully compensated metabolic acidosis?
- normal pH
- low PaCO2
- low BE
What is seen in uncompensated metabolic alkalosis?
- high pH
- normal PCO2
- high BE
What is seen in partially compensated metabolic alkalosis?
- high pH
- high PCO2
- high BE
What is seen in fully compensated metabolic alkalosis?
- normal pH
- high PCO2
- high BE
What mechanism is used to compensate for respiratory acidosis?
chronic: increased HCO3- retention
What can cause respiratory acidosis?
- insufficient removal of CO2 from lungs
- COPD, asthma, OSA, hypoventilation
What can cause respiratory alkalosis?
hyperventilation
What mechanism is used to compensate for respiratory alkalosis?
chronic phase: reduced HCO3- retention/reabsorption
What can cause metabolic acidosis?
- increased acid production (diabetic ketoacidosis)
- loss of bicarbonate (diarrhoea)
- reduced acid secretion (kidney disease)
What mechanism is used to compensate for metabolic acidosis?
hyperventilation
What can cause metabolic alkalosis?
- vomiting (loss of gastric secretions)
- diuretics
- antacid abuse
- H+ losing/HCO3- gaining conditions
What mechanism is used to compensate for metabolic alkalosis?
hypoventilation
What is the respiratory acid?
Carbonic acid from carbon dioxide
What are the metabolic acids?
- lactic acid
- hydrochloric acid
- keto acids
What is the metabolic base?
Bicarbonate
