Interpreting Arterial Blood Gas Results

Introduction to ABG Interpretation

The British Thoracic Society recommends a systematic, step-by-step analysis of pH, PaCO2, and HCO3- values to determine acid-base status, followed by evaluation of oxygenation parameters 1
The British Journal of Anaesthesia suggests that PaCO2 > 45 mmHg indicates respiratory acidosis 2

The British Thoracic Society recommends assessing PaO2 and checking oxygen saturation (SaO2), with a normal range of >94% in most patients 1
The American Thoracic Society notes that standard pulse oximetry (SpO2) cannot differentiate carboxyhemoglobin, potentially giving falsely normal readings in carbon monoxide poisoning 3

The British Thoracic Society recommends starting NIV in AECOPD when pH < 7.35 and PaCO2 > 6.5 kPa persist despite optimal medical therapy 4

The British Journal of Anaesthesia suggests that sodium bicarbonate therapy should be limited to patients with severe acidosis (arterial pH < 7.1 and base deficit < 10) 2, 5

The British Thoracic Society recommends using the PaO2/FiO2 ratio to assess severity of hypoxemia 6
The British Thoracic Society suggests that in critically ill patients, arterial samples are preferred over capillary samples 1
The British Thoracic Society recommends a target oxygen saturation of 88-92% for patients with COPD and risk of hypercapnic respiratory failure 4, 1
The American Thoracic Society notes that either arterial or venous blood may be used for measuring carboxyhemoglobin levels, as they are similar when CO body stores are in equilibrium 3
The British Thoracic Society recommends using local anesthesia for all ABG specimens except in emergencies 1
The British Thoracic Society suggests that patients undergoing radial ABG should have an Allen's test first to ensure dual blood supply to the hand 7, 8