Acid-base Balance

Question 1

ABG O2 interpretation

Answer 1

Normal oxygenation
-Room air - 10kPa+
-On O2 - 10kPa less than % inspired [O2]

Abnormal
-U10kPa - hypoxic
-U8kPa - RF

Question 2

ABG pH interpretation

Answer 2

Acidotic - U7.35
Normal or compensated - 7.35-7.45
Alkalotic - 7.45+

Does the pCO2 match the pH?
Does the HCO3 match the pH?

Is there compensation? - are pCO2 or HCO3 out of range

Is there a mixed picture?

Question 3

Causes of respiratory acidosis

Answer 3

CO2 retention from poor ventilation
-resp depression (opiates)
-neuromuscular weakness (GBS)
-asthma, COPD
-incorrect mechanical ventilation settings

Question 4

Causes of respiratory alkalosis

Answer 4

Hyperventilation
-anxiety
-pain
-breathing fast to compensate for hypoxia
-PE, PT
-incorrect mechanical ventilation settings

Question 5

Causes of metabolic acidosis

Answer 5

Increased acid prod/ingestion or
Decreased acid excretion or
Increased gastric/renal HCO3 loss

Anion gap can tell you about the possible cause

Question 6

What is base excess

Answer 6

Surrogate marker of metabolic acidosis/alkalosis
-high - primary metabolic alkalosis/compensated resp acidosis
-low - primary metabolic acidosis /compensated respiratory alkalosis

Question 7

Anion gap
-formula
-NAGMA and HAGMA causes

Answer 7

Na - (Cl + HCO3) = 4-12

NAGMA - from HCO3 loss, replaced by CL
-GI/renal HCO3 loss
-Addisons
-Drugs

HAGMA - from increased H
-Lactate
-Ketones
-Urate
-Salicylates, methanol
-Chronic paracetamol

Question 8

Causes of metabolic alkalosis

Answer 8

Decreased H or increased HCO3
-GI/renal acid loss
-milk-alkali syndrome