ABG Interpretation in Complex Medical Conditions

Introduction to ABG Interpretation

The American Thoracic Society recommends that arterial blood gas (ABG) analysis should be performed in critically ill patients to guide oxygen therapy and assess ventilation 2, 3.
The British Thoracic Society suggests that ABG should be obtained within 60 minutes of starting oxygen therapy in patients at risk for hypercapnia, and repeated as necessary to monitor for worsening hypercapnia or acidosis 4, 5.

The British Thoracic Society recommends a target saturation range of 88-92% for patients with COPD or other risk factors for hypercapnic respiratory failure, pending blood gas results 8, 4.
The American College of Chest Physicians suggests that oxygen therapy should be titrated to achieve a target saturation of 94-98% in patients without risk factors for hypercapnia 8.
For patients with carbon monoxide poisoning, the American College of Emergency Physicians recommends giving maximum oxygen via reservoir mask regardless of oximetry readings, as pulse oximetry cannot differentiate between carboxyhaemoglobin and oxyhaemoglobin 8, 5.

The American Thoracic Society recommends that non-invasive ventilation (NIV) should be initiated when pH < 7.35 and PaCO2 > 6.5 kPa persist despite optimal medical therapy in acute hypercapnic respiratory failure 1.
The British Thoracic Society suggests that NIV should be started with CPAP 4-8 cmH2O plus pressure support 10-15 cmH2O, and that target SpO2 should remain 88-92% in hypercapnic respiratory failure 1.

The Society of Critical Care Medicine recommends that ABG measurement should be taken immediately after return of spontaneous circulation (ROSC) following cardiopulmonary resuscitation to guide ongoing oxygen therapy 5.
The American College of Chest Physicians suggests that in peripheral VA-ECMO, ABG should be obtained from the right radial artery to assess cerebral oxygenation, not from the femoral line 7.

The American Thoracic Society recommends that the delta gap calculation should be used to address multiple concurrent metabolic disturbances and clarify interpretation of mixed acid-base conditions 1.
The British Thoracic Society suggests that a P(A-a)O2 gradient ≥20 mmHg should be used for hepatopulmonary syndrome diagnosis in patients aged ≥65 years 1.