Evaluation and Management of Desaturation

Immediate Technical Verification

The British Thoracic Society recommends verifying the accuracy of the pulse oximeter and oxygen delivery system when a patient desaturates, then urgently assessing for life-threatening causes while simultaneously initiating or escalating oxygen therapy to achieve target saturations based on the patient's risk of hypercapnic respiratory failure 1
The oximeter should be correctly placed and functioning normally with adequate waveform 1
The oxygen delivery device and flow rate should be correct for the prescribed therapy 1
If using a cylinder, verify it contains oxygen and is not empty or near-empty 1
The tubing should be connected to the correct wall outlet (oxygen, not compressed air) 2

For patients without risk of hypercapnic respiratory failure, the target SpO2 is 94-98% 3, 4
If SpO2 is less than 85%, start reservoir mask at 15 L/min immediately, then titrate down once stabilized 4
If SpO2 is 85-93%, use nasal cannulae at 2-6 L/min or simple face mask at 5-10 L/min 3
For patients with risk of hypercapnic respiratory failure, the target SpO2 is 88-92% 3, 5
Start with 24% Venturi mask at 2-3 L/min or 28% Venturi mask at 4 L/min for patients with risk of hypercapnic respiratory failure 6, 5
Alternative: Nasal cannulae at 1-2 L/min for patients with risk of hypercapnic respiratory failure 6, 5

Measure respiratory rate urgently, as tachypnea is more common than cyanosis in hypoxemia 3
Respiratory rate greater than 30 breaths/min requires immediate escalation even with adequate SpO2 5
Record heart rate, as tachycardia with breathlessness may indicate life-threatening cardiopulmonary emergency 5
Measure blood pressure, as hypotension (systolic less than 90 mmHg) indicates critical illness 4
Assess mental status, as confusion and agitation may be presenting features of hypoxemia and/or hypercapnia 3
Calculate physiological track-and-trigger score (e.g., NEWS) 7, 2

Obtain arterial blood gases within 60 minutes in critically ill patients, or in situations such as unexpected or inappropriate fall in SpO2 below 94% 4
Use arterial sample (not capillary/earlobe) for critically ill patients or those with shock/hypotension 4

Observe oxygen saturation for at least 5 minutes after starting or increasing oxygen therapy 9, 1
Recheck at 1 hour if stable 7, 1
Use continuous pulse oximetry for critically ill patients 8
Use four-hourly monitoring for stable patients 9

Urgent clinical review is required if patient requires oxygen therapy to be restarted at higher concentration than before to maintain same target saturation 2, 10
Persistent hypoxemia despite appropriate oxygen therapy requires urgent clinical review 5
pH less than 7.35 with PCO2 greater than 6.0 kPa (respiratory acidosis) requires consideration of non-invasive ventilation 3, 8
Respiratory rate remains greater than 30/min despite oxygen requires urgent clinical review 5
Signs of respiratory fatigue or increased work of breathing require urgent clinical review 8

Transient asymptomatic desaturation does not require correction if patient is otherwise stable and recovering 7, 11
Drive nebulizers with compressed air (not oxygen) if PCO2 elevated or respiratory acidosis present 5
Continue oxygen at 1-2 L/min via nasal prongs during nebulization to prevent desaturation 5
Target saturation 85-88% for patients with paraquat poisoning or bleomycin lung injury 6