NON-INVASIVE VENTILATION (NIV) 

Effects on Respiratory Mechanics

 Cardiovascular Effects

### Excessive pressure → hypotension

 TYPES / MODES OF NIV

A. CPAP (Continuous Positive Airway Pressure)

 Single continuous pressure throughout respiratory cycle
•Prevents alveolar collapse
Uses
✔ Cardiogenic pulmonary edema
✔ Obstructive sleep apnea
✔ Mild hypoxemic respiratory failure

Standard Starting CPAP

 BiPAP (Bilevel Positive Airway Pressure)

Two pressure levels:

Pressure Support (PS) = IPAP – EPAP

 Advanced Modes (ICU Ventilators)

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

Used mainly in chronic hypercapnic respiratory failure

 INTERFACES USED IN NIV

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

 INDICATIONS 

A. STRONG EVIDENCE / GOLD-STANDARD INDICATIONS

1. Acute Exacerbation of COPD (AECOPD)

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

Guidelines: GOLD, ERS/ATS → Class I recommendation

2. Acute Cardiogenic Pulmonary Edema

Mechanism
• ↓ Preload
• ↓ LV afterload
• Recruits alveoli

B. MODERATE EVIDENCE INDICATIONS

3. Hypoxemic Respiratory Failure (Selected)

• 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

 CHRONIC USE INDICATIONS

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

 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

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

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 ↑

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 

HACOR Score for Predicting NIV Failure

HACOR =

• H → Heart rate
• A → Acidosis (pH)
• C → Consciousness (GCS)
• O → Oxygenation (PaO₂/FiO₂ ratio)
• R → Respiratory rate

 TOTAL SCORE

• Minimum = 0
• Maximum = 26

INTERPRETATION 

 Cut-off ≥5 at 1 hour of NIV is the most commonly used threshold.

 TIMING OF ASSESSMENT 

• Baseline (before NIV)
• After 1 hour of NIV → MOST PREDICTIVE
• Repeat at 12 hours and 24 hours
• HACOR is NOT a replacement for clinical judgment

CLINICAL APPLICATION 

 Indications for using HACOR

• NIV in:
• ARDS
• Pneumonia
• Early COVID hypoxemia
• Immunocompromised patients

 When NOT reliable

• Hypercapnic respiratory failure (e.g., COPD exacerbation)
• Sedated patients (GCS unreliable)
• Hemodynamic instability

 HACOR vs ROX INDEX 

## Delay in intubation ↑ mortality

 COMPLICATIONS OF NIV

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

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)

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)

 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

 DO NOT feed if:

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

B. NIV Factors

High pressures ↑ gastric insufflation & aspiration risk

Route of Feeding on NIV

Oral Feeding (Preferred if feasible)

• Allow small, slow meals Keep head elevated ≥45°.Restart NIV immediately after meals except in aerophagia,Marked gastric distension

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.

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°

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)

Q.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

 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