Maximum PaO2 with 100% Oxygen

Physiological Range on 100% Oxygen

When breathing 100% oxygen, PaO2 can reach extremely high levels—typically 350-500 mm Hg or higher—but an oxygen saturation of 100% may correspond to a PaO2 anywhere between 80 and 500 mm Hg, making saturation alone an unreliable indicator of actual arterial oxygen tension 1, 2
In clinical studies of post-cardiac arrest patients ventilated with 100% oxygen, mean PaO2 values reached 345±174 mm Hg (range approximately 343-500 mm Hg) at 60 minutes after return of spontaneous circulation 2, 3, 4
Animal studies demonstrate that 100% oxygen can generate PaO2 values of 250-450 mm Hg during the first 10-60 minutes of ventilation 3, 4

Hyperoxia (PaO2 >350 mm Hg) is associated with increased brain lipid peroxidation, metabolic dysfunction, neurodegeneration, and worse neurological outcomes in post-cardiac arrest patients 3, 4
In cardiac arrest models, PaO2 of 250-350 mm Hg during reperfusion resulted in worse cardiac function compared to PaO2 of 40-90 mm Hg 3, 4
A pulse oximetry reading of 100% saturation is dangerously misleading because it cannot distinguish between a safe PaO2 of 80 mm Hg and a potentially harmful PaO2 of 500 mm Hg 1, 2

For most critically ill patients, target oxygen saturation should be 94-98%, which typically corresponds to PaO2 of approximately 60-100 mm Hg 5
In patients at risk of hypercapnic respiratory failure, target 88-92% saturation 5
After return of spontaneous circulation, titrate FiO2 to the minimum concentration needed to achieve arterial oxyhemoglobin saturation ≥94%, avoiding routine use of 100% oxygen beyond initial resuscitation, as recommended by the American Heart Association with a Class I, Level of Evidence C recommendation 1, 2

Carbon monoxide poisoning is the only common scenario where targeting 100% saturation and using 100% oxygen is appropriate, regardless of oximetry readings 5
During active CPR and immediate post-arrest period, 100% oxygen via reservoir mask at 15 L/min is appropriate until reliable oximetry monitoring is established 5, 6

Once a patient is stabilized, arterial blood gas measurement is essential when saturation is 100% to determine actual PaO2 and guide appropriate FiO2 weaning 1, 2

Hyperoxia (oxygen levels above normal) causes direct tissue injury through oxygen-derived free radicals, increased brain lipid peroxidation, metabolic dysfunction, and neurodegeneration in patients on 100% oxygen, according to the American Heart Association 7
The American Heart Association recommends avoiding routine 100% oxygen beyond initial stabilization, with a Class I recommendation to titrate FiO2 to maintain SpO2 ≥94% in patients with significant hyperoxia 8, 7

Reduce FiO2 from 1.0 to 0.4-0.5 immediately in patients with significant hyperoxia, as recommended by the American College of Cardiology 8, 7
Target SpO2 94-98% or PaO2 75-100 mmHg in patients with hyperoxia, and decrease FiO2 by 0.1 increments if PaO2 remains >100 mmHg 8, 7

Maintain lung-protective ventilation with plateau pressure <30 cmH2O while adjusting FiO2 in patients with ARDS or acute lung injury, as recommended by the American Thoracic Society 9, 10
Use PEEP titration guided by FiO2 requirements per ARDSnet protocol in patients with ARDS or acute lung injury 10
Consider prone positioning if PaO2/FiO2 ratio falls below 150 mmHg after FiO2 reduction in patients with ARDS or acute lung injury 9, 10
Permissive hypercapnia is acceptable if pH >7.20 to maintain lung protection in patients with ARDS or acute lung injury 10

Use pulse oximetry for continuous monitoring once SpO2 is <100% in patients with hyperoxia, as recommended by the American Heart Association 8, 7
Once stable at target SpO2, pulse oximetry alone is adequate for ongoing monitoring in patients with hyperoxia 8, 7