What are the indications for rescue BiPAP (Bilevel Positive Airway Pressure) and CPAP (Continuous Positive Airway Pressure)?

Indications for Rescue BiPAP and CPAP

Both BiPAP and CPAP should be used for acute cardiogenic pulmonary edema, while BiPAP is specifically indicated for hypercapnic respiratory failure (pH <7.35) in COPD exacerbations, and CPAP is preferred for hypoxemic respiratory failure without hypercapnia. 1

Primary Indications by Clinical Scenario

Cardiogenic Pulmonary Edema

• Either BiPAP or CPAP is strongly recommended for patients with acute respiratory failure due to cardiogenic pulmonary edema who remain hypoxic despite maximal medical treatment 1
• Both modalities decrease mortality (RR 0.80) and reduce intubation rates (RR 0.60) with moderate certainty of evidence 1
• CPAP offers advantages of simpler technology, easier synchronization, and potentially less expensive equipment 1
• BiPAP should be reserved for patients in whom CPAP is unsuccessful in the cardiogenic pulmonary edema setting 1
• Pre-hospital CPAP or BiPAP is conditionally recommended and decreases intubation rates (RR 0.31) 1

Important caveat: BiPAP may increase myocardial infarction risk in acute heart failure patients (71% vs 31% with CPAP in one study), though evidence certainty is very low 1, 2

COPD Exacerbations with Hypercapnic Respiratory Failure

• BiPAP should be considered when respiratory acidosis (pH <7.35, H+ >45 nmol/L) persists despite maximum medical treatment on controlled oxygen therapy 1
• This represents a strong indication with high-quality evidence (Grade A recommendation) 1
• BiPAP is specifically indicated for type 2 respiratory failure with elevated PaCO₂ 2
• Blood gases should be repeated at 30-60 minutes after initiating BiPAP to check for rising PCO₂ or falling pH 3

Post-Operative Respiratory Failure

• NIV (BiPAP or CPAP) is conditionally recommended for post-operative acute respiratory failure, particularly after thoracic or abdominal surgery 1
• NIV reduces mortality (RR 0.28), intubation rates (RR 0.27), and nosocomial pneumonia (RR 0.20) in post-operative patients 1
• CPAP specifically decreased re-intubation rates from 10% to 1% after abdominal surgery in patients who developed hypoxemia immediately after extubation 1
• Surgical complications such as anastomotic leak or intra-abdominal sepsis must be addressed before initiating NIV 1

Hypoxemic Respiratory Failure (Community-Acquired Pneumonia, Early ARDS)

• A trial of NIV may be offered only in highly selected cooperative patients with isolated respiratory failure, managed by experienced teams in ICU settings 1
• Evidence shows reduced intubation rates (RR 0.75) but not mortality benefit, with low certainty of evidence 1
• Many patients with acute pneumonia and hypoxemia resistant to high-flow oxygen will require intubation; trials of CPAP or NIV should only occur in HDU or ICU settings 1
• BiPAP has lower success rates for type 1 (hypoxemic) respiratory failure compared to CPAP, with risk ratio 2.6 times higher for failure 2

Neuromuscular Disease and Chest Wall Deformity

• BiPAP is indicated for acute or acute-on-chronic hypercapnic respiratory failure due to chest wall deformity or neuromuscular disease 1
• BiPAP is specifically recommended for patients with neuromuscular disorders affecting respiratory function, particularly those requiring backup rate support 2
• This represents a Grade C recommendation based on consistent evidence 1

Obesity Hypoventilation Syndrome

• BiPAP is indicated for patients with obesity hypoventilation syndrome (BMI >30 kg/m² with daytime hypercapnia) 2
• BiPAP effectively reduces nocturnal CO₂ retention in hypoventilatory respiratory failure 4

Clinical Decision Algorithm

When to Choose BiPAP Over CPAP:

1. Presence of hypercapnia with respiratory acidosis (pH <7.35) 1, 3
2. CPAP failure in cardiogenic pulmonary edema 1
3. Patient intolerance of high CPAP pressures (>15 cm H₂O) 2, 3
4. Neuromuscular disease requiring backup rate support 2
5. Decompensated obstructive sleep apnea with respiratory acidosis 1

When to Choose CPAP:

1. Cardiogenic pulmonary edema as first-line therapy 1
2. Hypoxemic respiratory failure without hypercapnia 1
3. Chest wall trauma with hypoxia despite adequate analgesia and high-flow oxygen 1
4. Post-operative hypoxemia without respiratory symptoms 1

Initial Settings and Monitoring

BiPAP Settings:

• Minimum starting IPAP: 8 cm H₂O; minimum starting EPAP: 4 cm H₂O 2, 3
• Typical pressure differential: 4-6 cm H₂O (minimum 4 cm H₂O, maximum 10 cm H₂O) 2, 3
• For reducing work of breathing: IPAP 14-20 cm H₂O, EPAP 4-8 cm H₂O 3

Monitoring Requirements:

• Reassess early after starting NIV and intubate promptly if not improving 1
• Do not delay intubation if BiPAP fails to improve clinical status within 1-2 hours 2
• Monitor SpO₂ continuously, targeting 90-96% (or ≥92% in some guidelines) 2
• Repeat blood gases at 30-60 minutes after initiating BiPAP in hypercapnic patients 3
• Monitor blood pressure regularly, as NIV can reduce blood pressure and should be used cautiously in hypotensive patients 2, 3

Absolute Contraindications

NIV should not be used in the following situations: 1

• Recent facial or upper airway surgery
• Facial burns or trauma
• Fixed upper airway obstruction
• Active vomiting
• Inability to protect the airway
• Copious respiratory secretions
• Life-threatening hypoxemia
• Severe confusion/agitation
• Recent upper gastrointestinal surgery
• Bowel obstruction

Critical Pitfalls to Avoid

• Patient selection is paramount: NIV should only be attempted in cooperative patients without contraindications such as abnormal mental status, shock, or multiorgan failure 1
• Experienced team requirement: NIV for hypoxemic respiratory failure should only be managed by experienced clinical teams with close ICU monitoring 1
• Early intubation decision: A decision about tracheal intubation should be made before commencing NIV and documented in case notes 1
• Excessive secretions: BiPAP effectiveness is limited in bronchiectasis due to excessive secretions; it should not be used routinely 1
• Asthma: NIV should not be used routinely in acute asthma 1
• Chest wall trauma monitoring: Patients with chest wall trauma treated with CPAP or NIV should be monitored in ICU due to pneumothorax risk 1