Disorders of acid-base balance Flashcards
pH =
-log [H+]
Acidosis
disorder to make blood more acidic
Alkalosis
disorder to make blood more alkaline than normal
Acidemia
low blood pH
Alkalaemia
high blood pH
Standard bicarbonate
measures of metabolic component of any acid-base disturbance
Absolute bicarbonate is affected by
respiratory and metabolic components
Standard bicarbonate is standardised as …
pCO2 5.3kPa + temperature 37 degrees celcius
Base excess
quantity of acid required to return pH to normal under standard conditions
Standard base excess corrected to
Hb 50g/L
Base excess in acidosis?
negative
What do we measure: Arterial Blood Gases
pH pO2 pCO2 Standard HCO3- Standard base excess
2 major approaches to interpreting acid-base status
Henderson-Hasselbach Equation
Stewart’s theory
Henderson-Hasselbach equation
- pH = pKa + log([A-]/[HA])
- pH = pKa H2CO3 + log([HCO3-]/[H2CO3])
- pH = 6.1 + log([HCO3-]/0.03 x pCO2)
ESSENTIALLY:
pH = pKa + log [conjugate base]/[acid]
Acidaemia: if pCO2 is increased …
respiratory acidosis
Acidaemia: if pCO2 is increased and [HCO3-] is high
respiratory acidosis with compensatory metabolic alkalosis
Acidaemia: if HCO3- is low
metabolic acidosis
Acidaemia: if HCO3- is low and pCO2 is low
metabolic acidosis with compensatory respiratory alkalosis
Alkalaemia: if pCO2 is low
respiratory alkalosis
Alkalaemia: if pCO2 is low and HCO3- is low
respiratory alkalosis with compensatory metabolic acidosis
Alkalaemia: if HCO3- is high
metabolic alkalosis
Alkalaemia: if HCO3- is high and pCO2 is high
metabolic alkalosis with compensatory respiratory acidosis
Respiratory causes of acidosis
COPD
Asthma
Severe obesity
Hypoventilation
Metabolic causes of acidosis
Hyperkalaemia
Hypoaldosteronism
Diabetic ketoacidosis
Renal failure
Respiratory causes of alkalosis
hyperventilation
Metabolic causes of alkalosis
diarrhoea
vomiting
Strong ion difference
SID = [strong cations] – [strong anions]
cat +
anion -
Anion gap
[Na+]+[K+] - [Cl-] - [HCO3-]
Normal anion gap
10-16
Wide anion gap
Lactic acidosis
Ketoacidosis
Ingestion of acid
Renal failure
Narrow anion gap (e.g. high chloride)
Gastrointestinal HCO3- loss
Renal tubular acidosis
Compensatory mechanisms for metabolic acidosis
Hyperventilation to increase CO2 excretion
Compensatory mechanisms for metabolic alkalosis
Hypoventilation
Renal bicarbonate excretion
Compensatory mechanism of respiratory acidosis
increased renal H+ excretion Bicarbonate retention (but only if chronic)
Compensatory mechanism of respiratory alkalosis
Increased renal bicarbonate loss (if chronic
