Acid- base abnormality

Question 1

What is meant by “acid-base abnormality”?

Answer 1

Conditions characterised by changes in the concentration of hydrogen ions or bicarbonate, leading to changes in the arterial blood pH.

Question 2

What are the different causes of acid- base abnormality?

Answer 2

1. Metabolic Acidosis
   - Normal Anion Gap (6-16 mmol/L) ⇒ diarrhoea, renal tubular acidosis, addison disease (hyperkalaemia = acidosis), acetazolamide, acute gastroenteritis
   - Raised Anion Gap (>16 mmol/L) ⇒ lactic acidosis (eg. sepsis, metformin), diabetic ketoacidosis, uraemia, alcohol (metabolic ketoacidosis with normal or low glucose - think alcohol), Tricyclic antidepressant overdose, Aspirin overdose
2. Metabolic Alkalosis ( loss of H+ or gain of HCO3-) ⇒ vomiting, diuretics, hyperaldosteronism + Cushing’s (hypokalaemia = alkalosis), secretory villous adenoma
3. Respiratory Acidosis (hypoventilation) ⇒ airway obstruction, COPD, opioids/sedatives, weakening of respiratory muscles
4. Respiratory Alkalosis (hyperventilation) ⇒ anxiety/panic attack, PE, hypoxia (eg. due to high altitude), aspirin OD (in early stages)
5. Anxiety/Panic Attack ⇒ hyperventilation leading to respiratory alkalosis, this causes hypocalcaemia which can then cause tingling in lips and fingers.

Question 3

What are the presenting symptoms/ signs of acid- base abnormality?

Answer 3

rapid breathing, fatigue, and confusion.

Question 4

What investigations are used to diganose/ monitor acid- base abnormality?

Answer 4

1. Arterial Blood Gas
   a. Evaluate Blood pH ⇒ <7.35 (acidosis) or >7.45 (alkalosis)
   b. Evaluate pCO2 ⇒ if pH and CO2 change in opposite direction = respiratory disorder. If pH and CO2 change in same direction = metabolic disorder.
   c. Evaluate HCO3- ⇒ high = metabolic alkalosis or compensated respiratory acidosis. Low = metabolic acidosis or compensated respiratory alkalosis.
   Base Excess ⇒ >+3 indicates metabolic alkalosis. <-3 indicates metabolic acidosis.
   - ROME ⇒ Respiratory = Opposite (CO2). Metabolic = Equal (HCO3-)
   - Anion Gap = ([Na+] + [K+]) - ([Cl] + [HCO3]) 

Question 5

How is acid-base abnormality managed?

Answer 5

1. Respiratory Acidosis & Alkalosis → treat underlying cause
2. Metabolic Acidosis → IV Sodium Bicarbonate
3. Metabolic Alkalosis → Acetazolamide (carbonic anhydrase inhibiting diuretic)