DR. S.V. SINGH, OMBUDSPERSON - E-mail ID: ombudsperson@santosh.ac.in

The most predominant complication of COVID 19 is arterial hypoxaemia thereby affecting lung compliance., requiring  mechanical ventilation due to which they are placed in a ventilator.Acid base imbalance is frequent association with patients suffering from serious viral illness and COVID being one such dreaded disease. To monitor acid base balance of patient ABG is a routine investigation which is carried out.

ABG provides us information regarding patients oxygenation, ventilation adequacy and acid base levels. Patients of COVID 19  may develop acute respiratory distress, and CT chest is an effective tool to identify lung lesions in COVID19 pneumonia, however it cannot be repeatedly done to monitor those lung lesions as there is risk of radiological exposure.

In research by Shang etal it was confirmed that ABG values correlated with the presence and morphology of  CT lesions and it can be done repeatedly for regular monitoring of critically ill patients. Thus ABG is a rapid, cheaper and a widely used investigation and a valuable tool for preliminary prognostic assessment of patients with SARSCOV2 infection.

Components of ABG



Arterial blood




80-100mm of Hg

O2 saturation



35-45 mm of Hg




-2 TO +2


Indications of ABG

  • Prime indication is both acute and chronic respiratory failure
  • Any condition causing severe metabolic acidosis like Cardiac failure, Kidney failure, Liver failure, severe diabetic ketoacidosis, hyperosmolar non ketotic Coma
  • Multiorgan Failure
  • Sepsis

Interpretation of ABG

  1. Blood pH – Higher values indicate alkalosis and lower values indicates acidosis and normal values indicates either normal,mixed defect or compensatory defect
  2. PaCO2 – identifies whether it is a respiratory problem or not. High PaCO2 with an acidosis indicates respiratory problem, lower or normal PaCO2 points towards compensation
  3. HCO3 – If bicarbonate fits with Ph it suggests a primary metabolic issue,if not it indicates  compensation
  4. Check for any compensation like low PaCO2 in severe metabolic acidosis
  5. Anion gap -this  is particularly useful in metabolic acidosis. The sum of cations is greater than anions (10-18mmol/L ,known as anion gap. Metabolic acidosis leads to raised anion gap
  6. O2 levels provides information of whether hypoxaemia present or not.


Thus, ABG is a routinely done investigation in Central lab, Santosh Hospitals to monitor critical patients and in also in cases of COVID patients who are having severe hypoxaemia due to lung lesions .It yields a more precise measure of gaseous exchange. With knowledge of PaO2.PaCO2 and FiO2(in intubated patients), the alveolar to arterial oxygen gradient can be rapidly calculated ,which is of great value in monitoring intubated patients.