What is Intermittent Positive Pressure Ventilation (IPPV)?

Intermittent Positive Pressure Ventilation (IPPV)

IPPV is a mode of mechanical ventilation that delivers positive pressure breaths to assist or control ventilation, providing an increased tidal volume for patients with various respiratory conditions.

Definition and Mechanism

IPPV refers to a form of mechanical ventilation where positive pressure is applied to the airway during inspiration, followed by passive exhalation. This creates a pressure gradient that:

• Delivers a controlled volume or pressure of gas to the lungs
• Increases tidal volume beyond what the patient can achieve independently
• Assists or replaces the work of breathing
• Improves gas exchange by enhancing alveolar ventilation

Types and Modes of IPPV

IPPV can be delivered in several modes:

1. Controlled Mechanical Ventilation (CMV):

   • Machine delivers all breaths at a set rate and volume/pressure
   • Patient has no control over breathing pattern
   • Used when patient is unable to initiate breaths

2. Spontaneous Mode (S):

   • Patient triggers and controls all breaths
   • Device provides pressure support during inspiration
   • No backup rate provided

3. Spontaneous-Timed Mode (ST):

   • Patient can trigger breaths, but a backup rate ensures minimum ventilation
   • Recommended by the American Academy of Sleep Medicine over purely spontaneous mode 1
   • Backup rate typically set 2-4 breaths below patient's spontaneous rate

4. Timed Mode (T):

   • Machine delivers breaths at a set rate with fixed inspiratory time
   • Patient has no control over breathing pattern
   • Rarely used except in patients unable to synchronize with the device 2

Delivery Methods

IPPV can be delivered through:

1. Invasive methods:

   • Endotracheal intubation
   • Tracheostomy

2. Non-invasive methods (NIV/NPPV):

   • Nasal mask
   • Oronasal (full face) mask
   • Mouthpiece
   • Nasal pillows

Key Parameters and Settings

When setting up IPPV, particularly in non-invasive form (BiPAP), the following parameters are adjusted:

• IPAP (Inspiratory Positive Airway Pressure): Typically 8-12 cmH2O initially 1
• EPAP (Expiratory Positive Airway Pressure): Typically 3-5 cmH2O initially 1
• Backup Rate: Set slightly below patient's spontaneous rate 1
• Inspiratory Time: 30-40% of respiratory cycle 1
• Rise Time: Transition speed from EPAP to IPAP
  • Shorter (100-400 ms) for obstructive disease
  • Longer (300-600 ms) for restrictive disease 1

Clinical Applications

IPPV is indicated for:

1. Acute respiratory failure:

   • COPD exacerbations with respiratory acidosis (pH <7.35) 1
   • Acute cardiogenic pulmonary edema
   • Hypercapnic respiratory failure from neuromuscular disorders 1

2. Chronic respiratory conditions:

   • Chest wall deformities (kyphoscoliosis)
   • Neuromuscular disorders
   • Central hypoventilation syndromes

3. Special situations:

   • Severe bronchospasm unresponsive to standard therapy 3
   • Management of atelectasis that hasn't improved with simpler therapies 3

Contraindications

IPPV is contraindicated in:

• Hemodynamic instability
• Severe bleeding
• Pneumothorax
• Severely depressed mental status
• Copious secretions
• Facial trauma/anatomical abnormalities preventing mask seal 1

Advantages and Limitations

Advantages:

• Improves gas exchange
• Reduces work of breathing
• Can prevent intubation in appropriate cases
• Reduces ICU length of stay when used appropriately 1

Limitations:

• Effects are short-lived (approximately 1 hour) 3
• May cause barotrauma if pressures are too high
• Potential for ventilator-associated pneumonia with invasive IPPV
• Mask discomfort and skin breakdown with non-invasive IPPV

Monitoring and Adjustment

Proper monitoring during IPPV includes:

• Continuous oxygen saturation (target 88-92%)
• Repeat blood gas measurements within 1-2 hours of initiation
• Respiratory rate and pattern
• Patient comfort and synchrony with the ventilator 1

Historical Context

IPPV has been a mainstay of respiratory support for decades, though its applications have evolved. While early widespread use has diminished as simpler alternatives have emerged for some conditions, it remains essential for managing acute and chronic respiratory failure 3, 4.

Common Pitfalls and Considerations

1. Inadequate pressure settings: Ensure IPAP is progressively increased to reach 20-30 cmH2O within 10-30 minutes in severe cases 1

2. Poor mask fit: Can lead to excessive leaks and reduced effectiveness

3. Insufficient monitoring: Failure to monitor blood gases may result in undetected hypoventilation or hyperventilation

4. Inappropriate mode selection: Using spontaneous mode without backup rate in patients with central hypoventilation or weak respiratory drive

5. Aspiration risk: Elevate head of bed to reduce aspiration risk, especially in patients receiving nutrition 1

IPPV remains a cornerstone therapy for managing respiratory failure, though its specific application should be guided by the underlying condition, patient characteristics, and clinical response.