NON-INVASIVE VENTILATION (NIV) 

1. DEFINITION

Non-Invasive Ventilation (NIV) is the provision of positive pressure ventilatory support without an artificial airway,

2. PHYSIOLOGICAL PRINCIPLES

A. Effects on Respiratory Mechanics

B. Gas Exchange Effects

• ↑ PaO₂ via alveolar recruitment
• ↓ PaCO₂ via improved minute ventilation
• Improves V/Q matching
• Reduces intrinsic PEEP in COPD

C. Cardiovascular Effects

### Excessive pressure → hypotension

3. TYPES / MODES OF NIV

A. CPAP (Continuous Positive Airway Pressure)

🔹 Single continuous pressure throughout respiratory cycle

Physiology
• Prevents alveolar collapse
• Improves oxygenation
• No ventilatory assistance (no ↑ VT)

Uses
✔ Cardiogenic pulmonary edema
✔ Obstructive sleep apnea
✔ Mild hypoxemic respiratory failure

2️⃣ INITIAL CPAP SETTINGS (STARTING VALUES)

Standard Starting CPAP

3️⃣ HOW TO TITRATE CPAP

A. CPAP PRESSURE TITRATION

Typical Effective Range:
—> 5–10 cm H₂O
—> Maximum: 12–15 cm H₂O (rarely higher)

B. BiPAP (Bilevel Positive Airway Pressure)

Two pressure levels:

Pressure Support (PS) = IPAP – EPAP

C. Advanced Modes (ICU Ventilators)

• PSV-NIV
• NIV-SIMV (rare)
• AVAPS (Average Volume Assured Pressure Support)
• iVAPS

Used mainly in chronic hypercapnic respiratory failure

4. INTERFACES USED IN NIV

—> Helmet NIV increasingly used in ARDS (e.g., COVID)

5. INDICATIONS 

A. STRONG EVIDENCE / GOLD-STANDARD INDICATIONS

1. Acute Exacerbation of COPD (AECOPD)

MOST IMPORTANT INDICATION

Criteria
• pH < 7.35
• PaCO₂ > 45 mmHg
• Moderate–severe dyspnea

Benefits
✔ ↓ Intubation rates
✔ ↓ Mortality
✔ ↓ ICU stay

Guidelines: GOLD, ERS/ATS → Class I recommendation

2. Acute Cardiogenic Pulmonary Edema

• CPAP or BiPAP both effective
• Rapid relief of dyspnea
• ↓ Need for intubation

Mechanism
• ↓ Preload
• ↓ LV afterload
• Recruits alveoli

B. MODERATE EVIDENCE INDICATIONS

3. Hypoxemic Respiratory Failure (Selected)

Examples:
• Pneumonia (carefully selected)
• Early ARDS (PaO₂/FiO₂ > 150)
• Immunocompromised patients

 High failure rates → close monitoring mandatory

4. Post-Extubation Respiratory Failure

• Especially in COPD, CHF
• Prophylactic NIV reduces re-intubation

5. Weaning Facilitation

• Difficult weaning in COPD
• NIV after extubation prevents failure

C. CHRONIC USE INDICATIONS

• Obesity hypoventilation syndrome
• Neuromuscular diseases (ALS, MG, DMD)
• Chest wall deformities
• Stable chronic hypercapnic COPD

6. CONTRAINDICATIONS

A. ABSOLUTE

• Cardiac or respiratory arrest
   Inability to protect airway
   Severe encephalopathy (GCS < 8)
   Active vomiting / GI bleeding
   Facial trauma or surgery
   Uncontrolled agitation

B. RELATIVE

 Hemodynamic instability
 Excessive secretions
 Severe hypoxemia (P/F < 100)
 Recent upper GI surgery

7. INITIATION OF NIV – STEPWISE

A. Patient Selection (MOST IMPORTANT)

Ideal patient:
✔ Awake
✔ Cooperative
✔ Hemodynamically stable
✔ Moderate respiratory distress
✔ Able to clear secretions

B. Initial Settings (BiPAP)

Gradually titrate:
• IPAP ↑ to improve VT & CO₂
• EPAP ↑ for oxygenation

8. MONITORING DURING NIV 

A. Clinical

• RR ↓
• Accessory muscle use ↓
• Dyspnea ↓
• Mental status improves

B. Gas Exchange

ABG at 1–2 hours

Success indicators:
✔ pH ↑
✔ PaCO₂ ↓
✔ PaO₂ ↑

C. Ventilatory Parameters

• Tidal volume
• Leak
• Synchrony
• Patient comfort

9. PREDICTORS OF NIV SUCCESS vs FAILURE

A. Predictors of SUCCESS

✔ pH improves within 1–2 hrs
✔ RR decreases
✔ Patient comfortable
✔ Good mask fit
✔ Stable hemodynamics

B. Predictors of FAILURE (RED FLAGS)

🚩 Worsening hypoxemia
🚩 Rising PaCO₂
🚩 Persistent tachypnea
🚩 Hemodynamic instability
🚩 Reduced consciousness

## Delay in intubation ↑ mortality

10. COMPLICATIONS OF NIV

11. NIV IN ARDS – CONTROVERSIAL BUT IMPORTANT

• NIV failure common in moderate–severe ARDS
• Best outcomes when:
– P/F > 150
– Early initiation
– Helmet NIV preferred

# Intubate early if no rapid improvement

12. WHEN TO INTUBATE (DO NOT DELAY)

Immediate intubation if:
• Cardiac arrest
• Severe hypoxemia
• Airway compromise
• NIV failure at 1–2 hrs

🔹How to WEANING FROM NON-INVASIVE VENTILATION (NIV)

1️⃣ WHEN TO CONSIDER NIV WEANING (READINESS CRITERIA)

A. Clinical Stability

✔ Awake, alert, cooperative
✔ Hemodynamically stable (no/inotrope minimal)
✔ RR ≤ 25/min
✔ No severe accessory muscle use
✔ Minimal dyspnea (Borg ≤ 3)

B. Gas Exchange Targets

C. Ventilator Settings (Low Support)

2️⃣ NIV WEANING STRATEGIES (IMPORTANT FOR EXAMS)

🔹 Strategy 1: Gradual Reduction of NIV Duration (Most Common)

Principle: Increase spontaneous breathing time off NIV

✔ Preferred in COPD, AHF, hypercapnic failure

🔹 Strategy 2: Gradual Reduction of NIV Pressure Support

Stepwise decrease in IPAP

✔ Useful in pressure-dependent patients

Feeding a Patient on Non-Invasive Ventilation (NIV)

Core Principles

• NIV ≠ absolute contraindication to enteral feeding
• Aim to maintain nutrition without increasing aspiration risk or NIV failure

1. Assess Before Feeding (Mandatory)

A. Patient Factors

 DO NOT feed if:

• GCS < 13
• Active vomiting
• Copious secretions
• Severe hypoxemia or hypercapnic encephalopathy

B. NIV Factors

High pressures ↑ gastric insufflation & aspiration risk

2. Route of Feeding on NIV

A. Oral Feeding (Preferred if feasible)

Best option when patient is stable

How to do it

• Temporarily remove mask
• Feed small, frequent meals
• Restart NIV immediately after meals

Why NIV is needed immediately after meals

Pathophysiology

After meals:

• ↑ Oxygen consumption
• ↑ CO₂ production
• ↑ Diaphragmatic splinting due to gastric distension
• ↑ Work of breathing

 High-risk patients (COPD, OHS, neuromuscular disease) may decompensate rapidly if NIV is delayed.

How to do it safely 

1. Pause NIV briefly for oral intake
2. Allow small, slow meals
3. Keep head elevated ≥45°
4. Reapply NIV immediately after swallowing is complete
5. Start with previous settings, reassess comfort and leaks

When should you NOT restart NIV immediately?

👉 In these cases:

• Delay NIV briefly
• Decompress stomach (NGT if needed)
• Resume NIV once safe

Indications

• Mild–moderate respiratory failure
• Intermittent NIV (e.g., COPD exacerbation)

Limitations

• Fatigue
• Inadequate calorie intake

B. Enteral Feeding (Most ICU Patients)

1️⃣ Nasogastric Tube (NGT)

Most commonly used

Problems

• Mask leak around tube
• Gastric distension
• Aspiration risk

Risk reduction

• Use fine-bore (8–10 Fr) NGT
• Prefer continuous feeding
• Elevate head end 30–45°
• Monitor gastric residual volumes (GRV)

2️⃣ Post-Pyloric Feeding (Nasojejunal) – BEST for High Risk

Preferred when available

Indications

• High aspiration risk
• Poor gastric emptying
• High NIV pressures
• Recurrent feed intolerance

– ESPEN & SCCM recommend post-pyloric feeding if NIV > 48 h(always recheck current recommendations)

C. Parenteral Nutrition (PN)

NOT first line

Indications

• Unable to tolerate enteral feeding
• Severe aspiration risk
• Persistent NIV intolerance to feeding

How NIV decreases afterload

1️⃣ Key Concept: What Is LV Afterload?

LV afterload ≈ LV transmural systolic pressure

LV afterload=PLV −Pintrathoracic

Where:

• PLV = intracavitary LV systolic pressure
• Pintrathoracic ≈ pleural pressure

 It is the pressure the LV must generate to eject blood

2️⃣ NIV Increases Intrathoracic Pressure

• CPAP / EPAP → positive pressure throughout respiratory cycle
• IPAP (in BiPAP) → intermittent higher positive pressure during inspiration

3️⃣ How Increased Intrathoracic Pressure ↓ LV Afterload

🔹 A. Reduction in LV Transmural Pressure

LV transmural pressure=PLV −Ppleural

When NIV increases pleural pressure:

• External pressure on LV rises
• LV does not need to generate as high intracavitary pressure
• → Afterload decreases

🔹 B. Reduction in Aortic Transmural Pressure

• Aorta lies within thorax
• Increased intrathoracic pressure:
• Raises external pressure on aorta
• ↓ Aortic wall tension

Wall stress∝2hPtransmural ×r

Thus:

• ↓ pressure gradient between LV and aorta
• ↓ resistance to LV ejection

7️⃣ CPAP vs BiPAP – Afterload Effect

👉 Both reduce afterload via EPAP component

 GUIDELINES REFERENCED

• ERS/ATS NIV Guidelines
• GOLD COPD Guidelines
• Surviving Sepsis Campaign
• Harrison’s Principles of Internal Medicine
• NEJM / Intensive Care Medicine reviews