Arterial Blood Gas Interpretation in Critically Ill Patients

Core Sampling Protocol

In critically ill ICU patients, arterial blood samples from an indwelling arterial catheter should be the first-line approach for ABG analysis, with blood gas analyzers as the default measurement device to ensure accuracy and guide life-sustaining interventions, as recommended by the Critical Care society 1, 2
For patients with invasive vascular monitoring, draw all samples from arterial lines; if temporarily unavailable, use central venous lines; never use capillary finger-stick samples as they are inaccurate in this population, according to the Critical Care Medicine society 3, 1, 4

For ECMO patients, obtain samples from the right radial arterial line, as this best represents cerebral perfusion and helps identify differential oxygenation syndromes, as suggested by the Praxis Medical Insights society 2
For less critically ill patients without invasive monitoring, capillary samples may be acceptable, but arterial puncture with local anesthesia remains preferred, as recommended by the Critical Care society 1, 5

Obtain ABG within 60 minutes of starting oxygen therapy, as recommended by the Praxis Medical Insights society 6
Repeat ABG within 60 minutes of any FiO₂ change, especially in patients at risk for hypercapnic respiratory failure, according to the Thorax society 7, 6
After return of spontaneous circulation post-cardiac arrest, obtain ABG immediately to guide oxygen therapy, as suggested by the Praxis Medical Insights society 2

PaO₂ provides information that pulse oximetry cannot capture, and normal SpO₂ does not exclude significant hypoxemia, acid-base disturbances, or hypercapnia, as recommended by the Praxis Medical Insights society 2, 5, 6
Target SpO₂ of 88-92% in all patients with acute hypercapnic respiratory failure, whether spontaneously breathing or on NIV, according to the Thorax society 7
In patients on supplemental oxygen, ABG is mandatory even with normal saturation, as oxygen masks can hide underlying abnormalities, as suggested by the Praxis Medical Insights society 6

Blood gas analyzers must perform to ±0.4 mmol/L or ±8% above 5 mmol/L for critically ill patients, as recommended by the Critical Care society 1, 6
Point-of-care glucose meters have significant limitations in ICU patients with anemia, hypoxia, shock, or on vasopressors, and arterial blood gas analyzers are more reliable, according to the Critical Care Medicine society 8, 3, 4

Never assume adequate gas exchange based solely on pulse oximetry, as patients can have normal SpO₂ with severe acidosis, hypercapnia, or anemia, as recommended by the Praxis Medical Insights society 2, 5, 6
Never use capillary samples in patients with shock, on vasopressors, or with severe edema, as these produce factitious results that can lead to dangerous treatment errors, according to the Critical Care Medicine society 3, 4

In patients on Non-Invasive Ventilation (NIV), continuous SpO₂ monitoring is essential, but repeated ABG measurement is required to assess PaCO₂ and pH, as recommended by the Thorax society 7
In acute heart failure, ABG helps differentiate cardiac versus pulmonary causes of respiratory distress, and assess effectiveness of CPAP therapy through serial ABG analysis, as suggested by the Praxis Medical Insights society 2
In post-cardiac arrest, immediate ABG after ROSC is mandatory to guide oxygen therapy and avoid hyperoxia, and serial measurements guide ventilator management and assess adequacy of resuscitation, according to the Praxis Medical Insights society 2

In critically ill patients with invasive vascular monitoring, blood gas analyzers using arterial blood samples should be the default method for glucose measurement, as they demonstrate superior accuracy compared to bedside glucometers, particularly in hypoglycemic ranges and hemodynamically unstable patients 9, 10
The minimum accuracy standard for glucose meters in critically ill patients should be 98% of readings within 12.5% of reference standard (or within 0.55 mmol/L for readings <5.5 mmol/L), with remaining 2% within 20% 9, 11
Blood gas analyzers must perform to international standards of ±0.4 mmol/L (or ±8% above 5 mmol/L), which is more stringent than glucose meter requirements 9, 11

For critically ill patients with invasive vascular monitoring, the first-line method for glucose measurement should be a blood gas analyzer using arterial catheter samples 9, 10, 12
For patients without invasive vascular monitoring, glucose meters with capillary samples are acceptable 9, 10

Blood gas analyzers provide simultaneous measurement of multiple parameters alongside glucose, but require the presence of an arterial or central venous catheter 9, 10
Capillary samples with glucose meters are never acceptable for critically ill patients with invasive vascular monitoring 9, 11
Point-of-care glucose meters were not designed for ICU use or to regulate insulin infusions in critically ill patients 13

Blood gas analyzers in ICU settings require routine calibration and quality assurance measures to maintain accuracy standards 12