When should a pulse oximeter be used to monitor peripheral capillary oxygen saturation and what are the target SpO₂ ranges for healthy adults, patients with chronic hypercapnic respiratory disease (e.g., COPD), and children?

Pulse Oximetry Monitoring: Indications and Target SpO₂ Ranges

Pulse oximetry should be used to continuously or regularly monitor all critically ill patients, those with acute respiratory symptoms, and anyone requiring supplemental oxygen, with target SpO₂ ranges of 94-98% for healthy adults, 88-92% for patients with chronic hypercapnic respiratory disease (COPD, severe obesity, neuromuscular disease), and 94-98% for children without chronic respiratory conditions. 1, 2

When to Use Pulse Oximetry

Mandatory Monitoring Situations

• All critically ill patients require continuous pulse oximetry monitoring 1
• Any patient with acute breathlessness or respiratory symptoms should have SpO₂ measured 1
• Patients receiving supplemental oxygen need ongoing monitoring to titrate therapy 1
• Unexpected fall in SpO₂ below 94% in patients breathing room air warrants immediate assessment and blood gas analysis 1
• Deteriorating oxygen saturation (fall of ≥3%) in patients with previously stable chronic hypoxemia requires monitoring and blood gas measurement 1

Clinical Scenarios Requiring Blood Gas Confirmation

A critical pitfall is relying solely on pulse oximetry. Normal SpO₂ does not exclude serious pathology—patients can have normal oxygen saturation but abnormal pH, elevated PCO₂, or low oxygen content from anemia. 1 Therefore, arterial blood gases are essential in these situations:

• Within 30-60 minutes after initiating oxygen therapy in patients at risk for hypercapnia 1, 2
• Any patient requiring increased oxygen to maintain constant saturation 1
• Patients with risk factors for hypercapnic respiratory failure who develop acute breathlessness or drowsiness 1
• Critically ill patients or those with shock (systolic BP <90 mmHg) require arterial sampling initially 1

Target SpO₂ Ranges by Patient Population

Healthy Adults (No Risk Factors for Hypercapnia)

• Target range: 94-98% 1, 2
• Initiate oxygen when SpO₂ falls below 94% 2, 3
• Start with nasal cannulae at 2-6 L/min or simple face mask at 5-10 L/min 2
• If SpO₂ <85%, use reservoir mask at 15 L/min immediately 2

Patients with Chronic Hypercapnic Respiratory Disease

This includes COPD, bronchiectasis, cystic fibrosis, severe obesity, neuromuscular disease, and chest wall deformities. 1

• Target range: 88-92% 1, 2
• Initiate oxygen when SpO₂ ≤88% 2
• Use controlled low-flow oxygen: 24% Venturi mask at 2-3 L/min, 28% Venturi mask at 4 L/min, or nasal cannulae at 1-2 L/min 1, 2
• May need lower range if acidotic or known to be very sensitive to oxygen therapy 1
• Ideally use "alert cards" to guide therapy based on previous blood gas results 1

Critical adjustment: If blood gases show normal PCO₂ and no history of previous ventilatory support, adjust target to 94-98% 1, 4

Children

• Target range: 94-98% for children without chronic respiratory disease 2
• Same principles apply as for healthy adults 2

Special Populations

Pregnant Women

• Target 94-98% for acute illness, trauma, or sepsis 2
• Target 88-92% if at risk for hypercapnic respiratory failure 2
• Oxygen therapy may be harmful to the fetus if the mother is not hypoxemic 1

Specific Toxicities

• Paraquat poisoning and bleomycin toxicity: Target 85-88% as supplemental oxygen may worsen lung injury 2

Monitoring Algorithm

Step 1: Identify Risk Category

Screen for hypercapnia risk factors: 1, 3

• COPD or fixed airflow obstruction
• Severe obesity (morbid obesity)
• Neuromuscular disease
• Chest wall deformities
• History of previous non-invasive or invasive mechanical ventilation

Step 2: Set Target Range

• No risk factors: 94-98% 1, 2
• Risk factors present: 88-92% 1, 2

Step 3: Initiate Oxygen Based on SpO₂

For patients targeting 94-98%: 2

• SpO₂ 85-94%: Nasal cannulae 2-6 L/min or simple face mask 5-10 L/min
• SpO₂ <85%: Reservoir mask 15 L/min, then titrate down

For patients targeting 88-92%: 1, 2

• Use Venturi masks (24% at 2-3 L/min or 28% at 4 L/min) or nasal cannulae 1-2 L/min
• If respiratory rate >30 breaths/min, increase Venturi mask flow by up to 50% 1

Step 4: Obtain Blood Gases

• Within 30-60 minutes after starting oxygen in hypercapnia-risk patients 1, 2
• Sooner if clinical deterioration occurs 4

Step 5: Adjust Based on Results

• If PCO₂ normal and no history of ventilatory failure, may increase target to 94-98% 1, 4
• If PCO₂ rising or pH abnormal, maintain lower target and consider ventilatory support 1

Critical Pitfalls to Avoid

Do Not Over-Oxygenate

• Maintaining SpO₂ no higher than 96% is recommended to avoid hyperoxemia, which has been associated with increased mortality in a dose-dependent manner 2
• Stop oxygen when upper limit is exceeded (>98% or >92% respectively) 2
• Routine oxygen should not be given to non-hypoxemic patients 2

Recognize Pulse Oximetry Limitations

• All clinical staff must be trained in oximeter use and aware of limitations 1
• Inaccurate readings are more common in patients with dark skin tone—a higher SpO₂ target of 95% may be required in Black patients to ensure adequate oxygenation 5
• Factors affecting accuracy include anemia, peripheral vasoconstriction, and skin discolouration 6
• In COPD exacerbations, pulse oximetry shows only fair agreement with arterial saturation (95% limits of agreement -8.2% to +6.7%), though an SpO₂ of 92% has 100% sensitivity for detecting hypoxia 7

Never Rely Solely on SpO₂

• Normal SpO₂ does not negate the need for blood gas measurements, especially in patients on supplemental oxygen 1
• Pulse oximetry will be normal in patients with normal PO₂ but abnormal pH, PCO₂, or anemia 1

Avoid Sudden Oxygen Cessation

• Sudden oxygen cessation in hypercapnic patients may cause life-threatening rebound hypoxemia 2

Do Not Use Oxygen for Hyperventilation

• Pure hyperventilation from panic attacks does not require oxygen therapy 2
• Paper bag rebreathing should not be used as it may cause dangerous hypoxemia 2