Check oxygen saturation with a pulse oximeter
Look for low SpO2, often below 94%
Watch for shortness of breath that seems mild compared with the low oxygen level
Observe rapid breathing
Notice unusual fatigue or weakness
Check for confusion, restlessness, or anxiety
Look for bluish lips or fingertips
Monitor heart rate for tachycardia
Assess for difficulty speaking full sentences
Watch for signs of silent deterioration despite minimal complaints
Confirm with arterial blood gas testing if available
Seek urgent medical evaluation if oxygen levels are low