Blood Gas
Pulse oximetry
Arterial (ABG)
Capillary (CBG)
Venous (VBG)
Acidosis v alkalosis
acidaemia v alkalaemia
respiratory v metabolic
compensated v uncompensated (Acute v chronic + simple v mixed as below)
Respiratory compensation begins within 30 minutes and is complete within 12 to 24 hours (no lag if metabolic process is slow)
Anion gap = (Na +K) – (Cl + HCO3)
differentiates type of metabolic acidosis
Normal anion gap = the unmeasured anions (Ca, Mg, Po4, Albumin...)
Albumin contributes most
Phosphate also significant
normal AG = 0.2 x [albumin] (g/L) + 1.5 x [phosphate] (mmol/L)
normal is lab depended usually range is ~2-10 = normal
Causes:
High (increased acid production)
base excess
chloride
Arterial (ABG)
Capillary (CBG)
Venous (VBG)
Acidosis v alkalosis
acidaemia v alkalaemia
respiratory v metabolic
compensated v uncompensated (Acute v chronic + simple v mixed as below)
Respiratory compensation begins within 30 minutes and is complete within 12 to 24 hours (no lag if metabolic process is slow)
- Met Acid: HCO3 drop 1 mmo/L > PCO2 drop 1.2 mmHg (OR PCO2 should be similar to the decimal digits of the arterial pH)
- Met Alk: HCO3 rise 1 mmol/L > PCO2 rise 0.7 mmHg
- Resp Acid: CO2 rise 10 mmHg > HCO3 rise 1 meq/L (4 meq/L in chronic i.e. >5d)
- Resp Alk: PCO2 drop 10 mmHg > HCO3 drop 2 meq/L (4meq/L in chronic i.e. >5d)
Anion gap = (Na +K) – (Cl + HCO3)
differentiates type of metabolic acidosis
Normal anion gap = the unmeasured anions (Ca, Mg, Po4, Albumin...)
Albumin contributes most
Phosphate also significant
normal AG = 0.2 x [albumin] (g/L) + 1.5 x [phosphate] (mmol/L)
normal is lab depended usually range is ~2-10 = normal
Causes:
High (increased acid production)
- Uremia
- Ketoacidosis (DKA, stavation)
- Lactic acidosis
- Aspirin overdose (salicylate)
- Diarrhoea, distal stoma loss
- Renal tubular acidosis (hyperchloraemic normal GFR)
base excess
chloride