The following arterial blood gas and biochemistry results are from a patient with cardiac and respiratory disease and recent profuse vomiting.
|Parameter||Patient value||Normal range|
|pH||7.5||7.35 – 7.45|
|PaO2||58.0 mmHg (7.6 kPa)|
|PaCO2||47* mmHg (6.2 kPa)||35 – 45 (4.6 – 6.0)|
|HCO3||34.8* mmol/l||22 – 27|
|Base Excess||10.2*||-2.0 – +2.0|
|Sodium||137 mmol/l||135 – 145|
|Potassium||2.5* mmol/l||3.5 – 5.0|
|Chloride||92* mmol/l||95 – 105|
a) Describe the acid-base disturbance(s)
b) List the potential causes of the acid-base abnormalities in this patient
Metabolic alkalosis with respiratory compensation
Vomiting from gastric outlet obstruction
Post hypercapnoeic alkalosis
This question is a fairly straightforward ABG interpretation exercise.
I could add nothing more to these answers. The question plainly states there has been profuse vomiting.
Let us dissect these results systematically.
- The A-a gradient is high:
PAO2 = (0.4 × 713) - (47 × 1.25) = 155.05
Thus, A-a = (155.05 - 58) = 97.05mmHg.
- There is alkalaemia
- The PaCO2 is compensatory
- The SBE is 10.2, suggesting a metabolic alkalosis
- The respiratory compensation is reasonable - the expected PaCO2(0.7 × 34.8) + 20 = 44.36mmHg, which is within +/- 5mmHg of the recorded value
- The anion gap is normal: (137) - (92 + 34) = 11, or 13.5 when calculated with potassium
Thus, this patient has a metabolic alkalosis - likely due to vomiting. A diagnostic approach to metabolic alkalosis is offered elsewhere, and goes through this in some detail. In brief, potenial causes include the following:
- Gastric losses by vomiting or drainage
- loop diuretics
- posthypercapneic state (chronic compensatory renal loss)
- Primary hyperaldosteronism
- Mineralocorticoid oversupplementation
- Licorice (glycyrrhizic acid)
- β-lactam antibiotics
- Liddle syndrome
- Severe hypertension
- Bartter and Gitelman syndromes
- Laxative abuse
- Clay ingestion
- Recovery from starvation
- Hypercalcemia of malignancy
- Milk-alkali syndrome
Khanna, Apurv, and Neil A. Kurtzman. "Metabolic alkalosis." J NEPHROL 2006; 19 (suppl 9): S86-S96
Tripathy, Swagata. "Extreme metabolic alkalosis in intensive care." Indian journal of critical care medicine: peer-reviewed, official publication of Indian Society of Critical Care Medicine 13.4 (2009): 217.
Galla, John H. "Metabolic alkalosis." Journal of the American Society of Nephrology 11.2 (2000): 369-375.