Acid Base Flashcards
What is normal blood pH range?
7.35 - 7.45
What impact does COPD have on acid base?
Leads to chronic respiratory acidosis due to the build up of CO2
These people can be in two categories:
pink puffers = very breathless as they are sensitive to this CO2
blue bloaters = no longer breathless, CO2 levels become the driver to breathe so caution when ventilating
What does aspirin do to acid base?
Mixed metabolic acidosis + respiratory alkalosis
Very low Co2 and low bicarb
What causes the resp alkalosis in the mixed acidosis + alkalosis in aspirin overdose?
Due to hyperventilation as aspirin is a salicylate which stimulates resp centres
What is metabolic alkalosis?
High pH = Low H+ ions
Normal CO2 but
High HCO3-
Hypokalaemia
What causes metabolic alkalosis?
H+ loss through vomiting/pyloric stenosis
Hypokalaemia (vomiting, diarrhoea, diuretics, conns)
ingestion of bicarb = antacids
How to compensate for metabolic alkalosis?
Reduced ventilation = hypoventilation
to increase the pCO2
What results will be expected in compensated metabolic alkalosis?
Normal pH
High CO2
High bicarb
What is metabolic acidosis?
Low pH
with normal pCO2 but
LOW HCO3-
What are the causes of metabolic acidosis?
Increased production of H+ = DKA, Lactic acidosis (sepsis, metformin overdose)
Decreased excretion - renal tubular acidosis
Bicarbonate loss - intestinal fistula, diarrhoea, laxative abuse
How to compensate for metabolic acidosis?
Laboured breathing = hyperventilation to reduce CO2 levels atleast
What does compensated metabolic acidosis look like?
Normal pH
Low pCO2
Low bicarb
What is respiratory alkalosis?
High pH
Low pCO2 driving the alkalosis
Normal Bicarb
Causes of respiratory alkalosis?
Hyperventilation e.g. anxiety, hypoglycaemia, salicylates
Assisted ventilation
Urea cycle disorders
What does metformin overdose do to acid base?
Causes lactic acidosis which results in metabolic acidosis
Why does alkalosis sometimes cause tetany?
Alkalosis decreases free ionised calcium which can cause symptoms of tetany and carpopedal spasm (hypocalcaemia)
How does your body compensate for respiratory alkalosis?
Kidneys retain H+ and decrease production of Bicarb
What does compensated respiratory alkalosis look like?
Normal pH
Low CO2
low Bicarb
Both respiratory alkalosis and metabolic acidosis when compensated for look like:
Low bicarb, low CO2
- How to differentiate?
If the pCO₂ was initially low, it’s respiratory alkalosis.
If the HCO₃⁻ was initially low, it’s metabolic acidosis.
What is Respiratory acidosis?
Low pH
Driven by HIGH pCO2
Normal bircab
What causes respiratory acidosis?
Hypoventilation = asthma attach, anaesthesia, opiate overdose, raised ICP
Lung problems e.g. COPD, emphysema, pneumonia, PE, ARDS
How to compensate for respiratory acidosis?
Renal retention of bicarbonate ions
What does compensated respiratory acidosis look like?
Normal pH
High CO2
High bicarb
Both metabolic alkalosis and respiratory acidosis when compensated for present with
Normal pH, high CO2, high Bicarb
how to know what acid base imbalance occured?
If the HCO₃⁻ was initially high, it’s metabolic alkalosis.
If the pCO₂ was initially high, it’s respiratory acidosis.
