What to evaluate and manage in a patient with desaturation (decreased oxygen saturation)?

Evaluation and Management of Desaturation

When a patient desaturates, immediately verify the accuracy of the pulse oximeter and oxygen delivery system, then urgently assess 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

Immediate Technical Verification

Before assuming true desaturation, confirm:

• Oximeter is correctly placed and functioning normally with adequate waveform 1
• Oxygen delivery device and flow rate are correct for the prescribed therapy 1
• If using a cylinder, verify it contains oxygen (check labeling) and is not empty or near-empty 1
• Tubing is connected to the correct wall outlet (oxygen, not compressed air) 1

Initial Oxygen Therapy Adjustment

For Patients WITHOUT Risk of Hypercapnic Respiratory Failure

• Target SpO2: 94-98% 1
• If SpO2 <85%: Start reservoir mask at 15 L/min immediately, then titrate down once stabilized 1, 2
• If SpO2 85-93%: Use nasal cannulae at 2-6 L/min or simple face mask at 5-10 L/min 1, 2

For Patients WITH Risk of Hypercapnic Respiratory Failure

Risk factors include: severe/moderate COPD (especially with prior respiratory failure or on long-term oxygen), severe chest wall/spinal disease, neuromuscular disease, severe obesity, cystic fibrosis, bronchiectasis 1

• Target SpO2: 88-92% (or level stated on alert card) 1, 2
• Start with 24% Venturi mask at 2-3 L/min or 28% Venturi mask at 4 L/min 1, 2
• Alternative: Nasal cannulae at 1-2 L/min 1, 2
• Do NOT exceed FiO2 28% until arterial blood gases are known 2

Critical Clinical Assessment

Vital Signs and Physical Examination

• Measure respiratory rate urgently - tachypnea is more common than cyanosis in hypoxemia 1
• Respiratory rate >30 breaths/min requires immediate escalation even with adequate SpO2 2
• Record heart rate - tachycardia with breathlessness may indicate life-threatening cardiopulmonary emergency 2
• Measure blood pressure - hypotension (systolic <90 mmHg) indicates critical illness 1
• Assess mental status - confusion and agitation may be presenting features of hypoxemia and/or hypercapnia 1
• Calculate physiological track-and-trigger score (e.g., NEWS) 1

Arterial Blood Gas Analysis

Obtain arterial blood gases within 60 minutes in the following situations: 1, 2

• All critically ill patients 1
• Unexpected or inappropriate fall in SpO2 below 94% 1
• Deteriorating oxygen saturation (fall of ≥3%) in previously stable chronic hypoxemia 1
• Patients requiring increased FiO2 to maintain constant saturation 1
• Any patient with risk factors for hypercapnic respiratory failure who develops acute breathlessness, drowsiness, or other features of CO2 retention 1
• Suspected metabolic conditions (diabetic ketoacidosis, renal failure) 1

For critically ill patients or those with shock/hypotension, use arterial sample (not capillary/earlobe) 1

Specific Causes to Evaluate

Equipment-Related Issues

• Endobronchial intubation (accounts for nearly 20% of desaturations under anesthesia) 3
• Disconnection or malfunction of oxygen delivery system 1
• Empty oxygen cylinder 1

Pulmonary Causes

• Underlying lung disease exacerbation 3
• Excessive secretions or mucus plugging 1, 3
• Pneumothorax (especially if chest tube present) 4
• Pulmonary edema 1
• Pneumonia or aspiration 1

Cardiovascular Causes

• Acute coronary syndrome - obtain 12-lead ECG urgently 2
• Arrhythmias 2
• Pulmonary embolism 1

Airway Causes

• Bronchospasm 1
• Upper airway obstruction 1

Monitoring After Oxygen Adjustment

• Observe oxygen saturation for at least 5 minutes after starting or increasing oxygen therapy 1
• Recheck at 1 hour if stable 1
• Continuous pulse oximetry for critically ill patients 4
• Four-hourly monitoring for stable patients 1

When to Escalate Care

Urgent clinical review is required if: 1

• Patient requires oxygen therapy to be restarted at higher concentration than before to maintain same target saturation 1
• Persistent hypoxemia despite appropriate oxygen therapy 2
• pH <7.35 with PCO2 >6.0 kPa (respiratory acidosis) - consider non-invasive ventilation 1, 4
• pH <7.26 predicts poor outcome and requires NIV consideration 2
• Respiratory rate remains >30/min despite oxygen 2
• Signs of respiratory fatigue or increased work of breathing 4

Special Considerations

Transient Asymptomatic Desaturation

• Does not require correction if patient is otherwise stable and recovering 1
• Common after minor exertion or due to mucus plugging in recovering patients 1

Oxygen-Driven Nebulizers

• Drive nebulizers with compressed air (not oxygen) if PCO2 elevated or respiratory acidosis present 2
• Continue oxygen at 1-2 L/min via nasal prongs during nebulization to prevent desaturation 2

Conditions Where Oxygen May Be Harmful

• Paraquat poisoning or bleomycin lung injury - target saturation 85-88% 1
• Non-hypoxemic patients with stroke or myocardial infarction 1