What to do when a patient's oxygen saturation drops?

Management of Dropping Oxygen Saturation

When a patient's oxygen saturation drops, immediately perform a prompt clinical assessment to identify the underlying cause while simultaneously initiating or increasing oxygen therapy to maintain target saturations of 94-98% for most patients or 88-92% for those at risk of hypercapnic respiratory failure. 1

Immediate Response Algorithm

Step 1: Verify the Reading and Assess the Patient

• Check the pulse oximeter placement and function to ensure the reading is accurate and not due to technical error 1
• Perform urgent clinical assessment if saturation falls ≥3% or below the patient's target range 1
• Remember that oxygen treats hypoxaemia, not breathlessness—you must diagnose and treat the underlying cause as a matter of urgency 1

Step 2: Initiate or Increase Oxygen Therapy Based on Severity

For critically ill patients (SpO2 <85%):

• Administer high-concentration oxygen immediately using a reservoir mask at 15 L/min pending reliable oximetry readings 1, 2
• This applies to conditions like cardiac arrest, shock, sepsis, major trauma, or anaphylaxis 1

For moderate hypoxaemia (SpO2 85-93%):

• Start oxygen at 2-6 L/min via nasal cannulae or 5-10 L/min via simple face mask 2
• Target SpO2 of 94-98% for most patients 1, 3
• Target SpO2 of 88-92% for patients at risk of hypercapnic respiratory failure (COPD, morbid obesity, neuromuscular disorders) 1, 3

Step 3: Monitor Response to Therapy

• Reassess oxygen saturation after 5 minutes of starting or changing oxygen therapy 1, 3
• Document the new saturation, delivery device, and flow rate on the observation chart 1
• Continue monitoring: continuously for critically ill patients, four-hourly for stable patients 1, 3

Step 4: Adjust Oxygen Delivery

• Increase oxygen concentration if saturation remains below target after verifying correct equipment function 1
• Use Venturi masks for precise oxygen control in patients requiring specific FiO2 (particularly useful in COPD) 3
• If saturation fails to improve after 5-10 minutes of increased therapy, obtain arterial blood gas measurements 1, 3

Critical Considerations for Specific Patient Populations

Patients at Risk of Hypercapnic Respiratory Failure

• Target 88-92% saturation for patients with COPD, morbid obesity, cystic fibrosis, chest wall deformities, or neuromuscular disorders 1, 3
• Start with 24% Venturi mask at 2-3 L/min or 28% Venturi mask at 4 L/min 1
• Obtain repeat blood gas measurements 30-60 minutes after increasing oxygen to ensure CO2 is not rising 1
• Evidence shows that even in normocapnic COPD patients, maintaining 88-92% targets reduces mortality compared to higher saturations 4

Patients Without Hypercapnic Risk

• Target 94-98% saturation 1, 3
• Pulse oximetry monitoring is sufficient if patient remains clinically stable—repeat blood gases not required 1
• Do not routinely administer oxygen if SpO2 ≥94%, as supplemental oxygen in normoxemic patients may cause harm 2, 5

Common Pitfalls and How to Avoid Them

Pitfall 1: Using Inappropriate Target Ranges

• Never use standard 94-98% targets for all patients—this increases mortality in COPD patients even with normal CO2 levels 4
• The practice of adjusting targets based on CO2 levels is not justified; maintain 88-92% for all patients with COPD regardless of baseline CO2 4

Pitfall 2: Failing to Identify the Underlying Cause

• Oxygen improves oxygenation but does not treat the underlying disease—always investigate why saturation dropped 1
• Assess for pneumonia, pulmonary embolism, heart failure, pneumothorax, mucus plugging, or equipment malfunction 1

Pitfall 3: Inadequate Monitoring After Intervention

• Equilibration occurs within 3.5 minutes when starting oxygen and 4.5 minutes when stopping—much faster than the traditionally taught 20-30 minutes 6
• Reassess at 5 minutes, not 30 minutes, to avoid prolonged hypoxaemia 1, 6

Pitfall 4: Excessive Oxygen in Specific Conditions

• In acute coronary syndromes and stroke, avoid high-concentration oxygen unless required to maintain normal saturation, as hyperoxia may cause vasoconstriction and worsen outcomes 1, 5
• For myocardial infarction, target 94-98% (or 88-92% if hypercapnic risk) rather than routine high-flow oxygen 1

When to Escalate Care

• Request urgent medical review if oxygen requirements increase or saturation remains below target despite appropriate therapy 1
• Consider critical care consultation if flow rates exceed 5 L/min or if patient requires reservoir mask 7
• Obtain arterial blood gas for any patient at risk of hypercapnia who requires increased oxygen, or if clinical concern exists despite adequate saturation 1, 3