What are the causes and management of a fall in oxygen saturation (SpO2)?

Causes and Management of Falling SpO2 Levels

A fall in oxygen saturation (SpO2) requires immediate assessment of potential causes and appropriate management based on the patient's condition, with supplemental oxygen therapy titrated to maintain target SpO2 ranges of 94-98% for most patients and 88-92% for those at risk of hypercapnic respiratory failure. 1, 2

Common Causes of Falling SpO2

• Respiratory causes: Airway obstruction, bronchiolitis, COPD exacerbation, pneumonia, and pulmonary edema 1
• Cardiovascular causes: Heart failure and pulmonary embolism 1
• Risk factors in infants: Age less than 12 weeks, history of prematurity, and underlying cardiopulmonary disease 1
• Technical factors: Inaccurate pulse oximeter readings due to poor perfusion, motion artifact, or probe misplacement 2

Initial Assessment

• Verify reading accuracy and assess respiratory rate, work of breathing, and heart rate 1, 2
• Check for signs of severe respiratory distress (increased work of breathing, use of accessory muscles, nasal flaring) 1
• Identify patients at risk for hypercapnic respiratory failure, including those with:
  • Moderate to severe COPD
  • Severe chest wall or spinal disease
  • Neuromuscular disease
  • Severe obesity
  • Cystic fibrosis or bronchiectasis 2, 3

Management Algorithm

Step 1: Immediate Interventions

• Clear airway secretions if present 2
• Position patient appropriately to optimize breathing 2
• Administer supplemental oxygen based on patient risk profile:
  • For most patients: Target SpO2 94-98% 3, 1
  • For patients at risk of hypercapnic respiratory failure: Target SpO2 88-92% 3, 1

Step 2: Oxygen Delivery Device Selection

• For patients with SpO2 below 85% (not at risk of hypercapnic failure): Start with reservoir mask at 15 L/min 3
• For moderate hypoxemia: Use nasal cannulae (1-6 L/min) or simple face mask (5-10 L/min) 3
• Adjust flow rate to maintain target SpO2 range 3, 2

Step 3: Diagnostic Evaluation

• Obtain arterial or arterialised blood gases in the following situations:
  • All critically ill patients
  • Unexpected or inappropriate fall in SpO2 below 94%
  • Deteriorating oxygen saturation (fall of ≥3%) in previously stable chronic hypoxemia
  • Patients requiring increased FiO2 to maintain constant oxygen saturation
  • Patients at risk for hypercapnic respiratory failure who develop acute symptoms
  • Patients with metabolic conditions (e.g., diabetic ketoacidosis)
  • Unexpected changes in vital signs 3

Step 4: Advanced Interventions Based on Cause

• For COPD exacerbations or cardiogenic pulmonary edema: Consider non-invasive ventilation (NIV) 1
• For severe respiratory distress or failure: Consider endotracheal intubation and mechanical ventilation 1
• For pulmonary edema: Administer diuretics and address underlying arrhythmias if present 1

Special Considerations

• Premature infants and those with heart/lung disease: Maintain SpO2 ≥90% with close monitoring during oxygen therapy and weaning 1, 2
• Patients with paraquat poisoning or bleomycin lung injury: Target lower SpO2 of 85-88% as higher oxygen levels may be harmful 2
• Patients with fever, acidosis, or hemoglobinopathies: May require higher SpO2 targets due to shifts in the oxyhemoglobin dissociation curve 2
• Risk of hyperoxia: Be cautious with oxygen administration when SpO2 >95%, especially in patients on low-flow devices without clear respiratory compromise 4, 5

Monitoring and Follow-up

• Continuously monitor SpO2 after initiating oxygen therapy 2
• Increase Venturi mask flow by up to 50% if respiratory rate exceeds 30 breaths/min 3
• The requirement for increased oxygen concentration indicates need for urgent clinical reassessment 3
• Consider arterial blood gas measurement for accurate assessment of pH and PCO2, especially in critically ill patients 3, 6

Prevention

• Avoid exposure to passive smoking 1
• Encourage breastfeeding to prevent bronchiolitis in infants 1
• Implement targeted oxygenation protocols to avoid both hypoxemia and hyperoxemia 7