NIV, BiPAP, and CPAP Guide

Non-invasive ventilation (NIV) delivers positive pressure respiratory support without the need for endotracheal intubation or a tracheostomy. It interfaces with the patient through a mask — typically full-face, nasal, or total-face — allowing spontaneously breathing patients to receive ventilatory assistance while avoiding the risks of invasive mechanical ventilation.

NIV has become one of the most important tools in respiratory therapy and critical care medicine. When applied appropriately, it reduces the need for intubation, decreases ICU length of stay, and improves outcomes in select patient populations. The two primary modalities of NIV used in clinical practice are CPAP and BiPAP.

The respiratory therapist plays a central role in initiating, managing, and titrating NIV — from interface selection and fitting to pressure adjustments and patient monitoring. Understanding the physiologic basis and clinical applications of each modality is essential for safe, effective use.

CPAP delivers a single, continuous level of positive airway pressure throughout the entire respiratory cycle — both inspiration and expiration. It does not provide any additional inspiratory pressure support above the set baseline. The patient performs all of the work of breathing; CPAP simply maintains the airways at a higher-than-atmospheric pressure throughout the cycle.

How CPAP Works

The physiologic effect of CPAP is to increase functional residual capacity (FRC) — the volume of gas remaining in the lungs at end-expiration. This recruits collapsed or partially collapsed alveoli, improves V/Q matching, reduces intrapulmonary shunt, and decreases the work of breathing by preventing alveolar collapse with each breath.

Primary Clinical Indications for CPAP

• • Obstructive sleep apnea (OSA) — first-line therapy
• • Cardiogenic pulmonary edema — reduces preload and afterload while improving oxygenation
• • Mild hypoxemic respiratory failure without significant hypercarbia
• • Post-extubation support in select patients
• • Weaning from invasive mechanical ventilation

Typical CPAP Settings

BiPAP delivers two distinct levels of positive pressure: a higher inspiratory positive airway pressure (IPAP) and a lower expiratory positive airway pressure (EPAP). The difference between IPAP and EPAP (called pressure support) augments the patient's tidal volume during inspiration, reducing the work of breathing and enhancing ventilation.

How BiPAP Works

During inspiration, the machine delivers higher pressure (IPAP) to assist the breath. During expiration, pressure drops to the lower EPAP level to prevent alveolar collapse and maintain oxygenation. The pressure support provided (IPAP minus EPAP) assists ventilation by augmenting tidal volumes and reducing respiratory muscle load.

Because BiPAP provides active ventilatory support, it is particularly effective in patients with hypercapnic respiratory failure — those who are retaining CO₂ and need help eliminating it.

Primary Clinical Indications for BiPAP

• • COPD exacerbation with hypercapnia and respiratory acidosis (pH 7.25–7.35)
• • Acute hypercapnic respiratory failure from any cause
• • Acute cardiogenic pulmonary edema (when CPAP is insufficient)
• • Obesity hypoventilation syndrome
• • Neuromuscular diseases with chronic ventilatory failure
• • Post-extubation support in high-risk patients

Typical BiPAP Starting Settings

While both modalities use positive airway pressure through a non-invasive interface, they serve different physiologic needs and are indicated in different clinical scenarios.

Proper patient selection is critical to the success of NIV. Patients who are alert, cooperative, and able to protect their airway are the best candidates. NIV should not be used as a substitute for intubation in patients who are rapidly deteriorating or who meet criteria for immediate intubation.

Absolute Contraindications to NIV

• • Respiratory arrest or cardiac arrest
• • Severely impaired consciousness (GCS ≤ 8 in most cases)
• • Inability to protect airway or high aspiration risk
• • Uncooperative or agitated patient
• • Facial trauma or surgery precluding mask use
• • Recent upper GI surgery or esophageal anastomosis
• • Undrained pneumothorax

Relative Contraindications

• • Excessive secretions not manageable by patient
• • Hemodynamic instability requiring vasopressors
• • Claustrophobia or poor patient tolerance
• • Severe metabolic acidosis (pH < 7.25 — consider intubation)

The success of NIV is heavily influenced by interface selection and proper fitting. The interface is the connection between the patient and the ventilator circuit — a poor fit leads to excessive leak, reduced efficacy, patient discomfort, and skin breakdown.

Oronasal (full-face) masks covering both the nose and mouth are most commonly used for acute NIV in the hospital setting because they accommodate patients who mouth-breathe and provide a better seal during respiratory distress. Nasal masks and nasal pillows are preferred for chronic home use (e.g., sleep apnea) due to improved comfort.

Total-face masks covering the entire face are used when conventional masks cause skin breakdown or in patients with facial irregularities. Helmet interfaces are used in some centers for extended NIV in ARDS, though they require specialized ventilator circuits.

After initiating NIV, ongoing monitoring by the respiratory therapist is essential. Assess the patient within 30–60 minutes of initiation and document response. Key monitoring parameters include:

• • SpO₂: Target ≥92–95% (88–92% in COPD to avoid hypercapnia worsening)
• • Respiratory rate: Should decrease toward 12–20 breaths/min
• • Work of breathing: Accessory muscle use should decrease
• • Patient synchrony: Assess for patient-ventilator dyssynchrony
• • Exhaled tidal volume: Target 6–8 mL/kg ideal body weight
• • ABG: Repeat at 1–2 hours post-initiation to assess pH and PaCO₂ trend

If the patient is not improving within 1–2 hours of adequate NIV trial — worsening pH, rising PaCO₂, declining consciousness, or hemodynamic instability — escalation to invasive mechanical ventilation should be considered promptly.