Question

What is your assessment of a patient acid-base status that has the following ABG values?

pH = 7.3

pCO2 = 40mmHg

HCO3 = 20 meq/L

Answer 1

Answer) The acid-base disorder is METABOLIC ACIDOSIS.

Explanation -

Normal pH is 7.4

Normal pCO2 is 40 mmHg

Normal HCO3- is 24 mEq/L

The given value are

pH - 7.3

pCO2 - 40 mmHg

HCO3- - 20 mEq/L

As the pH levels are decreased, it is acidosis.

pCO2 is a respiratory component as a pCO2 levels are maintained by lungs and the levels are normal.

More the CO2 wash out from the lungs due to alveolar ventilation leads to decrease in pCO2.

Less the CO2 wash out from the lungs leads to increase in pCO2.

HCO3- is a metabolic component as HCO3- reabsorption occurs in kidney and the levels are decreased.

So it is a metabolic acidosis.

Metabolic acidosis - A disorder characterised by a low arterial pH ( a high level of hydrogen ions) and a reduced plasma HCO3- levels.

Causes of metabolic acidosis-

1) Accumulation of ketoacids due to diabetes mellitus

2) Accumulation of lactic acid due to heavy exercise

3) Loss of HCO3- due to severe diarrhoea

4) Ingestion of alcohol, salicytes leads to vomiting, which then leads to loss of HCO3- through vomiting.

Compensation for metabolic acidosis -

1)Respiratory compensation -

Increase in alveolar ventilation leads to decrease in arterial pCO2 (due to CO2 washout), which then leads to decreases formation of H2CO3.

Decrease in H2CO3 leads to decrease in hydrogen levels ( increase in pH).

2) Renal (kidney) compensation-

Renal tubular cells secrete H+ ions into the tubular fluid in exchange for Na+, and for each H+ secreted, one Na+ and one HCO3- are added to the blood.

So it leads to excretion of hydrogen ions and reabsorption of HCO3- ions.