Specimen Name Result Units Range
Plasma Sodium 131 mmol/L (135-145)
Potassium 2.1 mmol/L (3.5-5.5)
Chloride 76 mmol/L (100-109)
Bicarbonate 40 mmol/L (22-32)
Urea 36 mmol/L (2.7-7.2)
Creatinine 520 μmol/L (60-110)
ABG pH 7.58 (7.36-7.44)
PaO2 51 mmHg (70-100)
PaCO2 45 mmHg (35-45)
HCO3- 41 mmol/L (21-26)
Urine Sodium 25 mmol/L (> 20)
Chloride 10 mmol/L
Creatinine 32 μmol/L

Infant with vomiting.

What is the acid-base disturbance?

What is the likely cause?
Mixed Metabolic Alkalosis-Acidosis

pH & HCO3- : PCO2 should be 51-58 mmHg → inadequate compensation / associated metabolic acidosis

Pyloric Stenosis:

  • Hypochloraemic, hypokalaemic, metabolic acidosis
  • Hypovolaemia & pre-renal AKI
  • Superimposed lactic acidosis.

 

ABG Correction Factors

  • Metabolic Acidosis:
    • PCO2 : last 2 digits of pH ≥ 7.10
    • HCO3- : for each 10 mmol/L fall → ↓ PCO2 ≈ 12 mmHg
  • Metabolic Alkalosis:
    • PCO2 : last 2 digits of pH ≤ 7.60
    • HCO3- : for each 10 mmol/L rise → ↑ PCO2 ≈ 7 mmHg

 

Hypokalaemic Metabolic Alkalosis
Diuretics (esp. loop agents) - low Na+, Cl- / high urea
Mineralocorticoid excess - normal-high Na+, Cl- / normal urea
Vomiting / Gastric outlet obs. - very low Cl- / low-normal Na+ / high urea
Diarrhoea / laxatives - low Cl- / normal Na+ / high urea
Post massive transfusion - citrate metabolism & acidosis correction