NIV/NPPV

Non Invasive Ventilation (NIV)
Noninvasive Positive Pressure Ventilation (NPPV)
Noninvasive Intermittent Positive Pressure Ventilation (NIPPV)
* NPPV is an umbrella term for CPAP and BiPAP, but nowadays some authors pertain to BiPAP when they mention of NPPV. NIPPV is also interchangeable with BiPAP

• application of positive pressure ventilation without intubating or doing tracheostomy
• objectives:
  
  1. improves alveolar ventilation, improves gas exchange, increases tidal volume
  2. improves compliance by reversing microatelectasis
     
  3. rests muscles by decreasing WOB (work of breathing)
  4. CPAP conterbalances inspiratory threshold work related to intrinsic PEEP
• Terms:
  
  • CPAP: continuous Positive Airway Pressure
  • BiPAP: Bilevel PAP
  • IPAP: Inspiratory PAP: positive pressure applied during Inspiration
    
  • EPAP: Expiratory PAP: positive pressure applied during Expiration
    - termed PEEP (positive end-expiratory pressure) if above atmospheric
  • PEEP: alveolar pressure above atmospheric at the end of expiration
    (1) intrinsic or auto PEEP: secondary to incomplete expiration
    (2) extrinsic PEEP: from mechanical ventilator
  • Pressure Support: Delta pressure IPAP-EPAP
  • IPAP Rise time: determines how fast the ventilator will rise from baseline to target IPAP
  • Timed Inspiration: determines the duration of a timed breath. The Rate and the Timed Inspiration are linked so the inspiratory time is never longer than the expiratory time or greater than 3 seconds. If the rate is increased to a value that would exceed a 1:1 ratio, the Timed Inspiration value is automatically reduced to maintain a 1:1 ratio.
    
    
• Types:
  1) CPAP
  
  • delivers constant level of positive pressure throughout respiratory cycle (I and E)
  • does not actively assist during ventilation
  • in acute setting, mainly used for hypoxemic respiratory failure
    (this is used also on OSA: obstructive sleep apnea)
  • improves oxygenation by
    
    1. increasing mean airway pressure
    2. increasing functional residual capacity
    3. opening underventilated and collapsed alveoli, enhacing oxygenation and gas exchange
       
  • decrease WOB (work of breathing) by increasing lung compliance
  • initiated usually between 0-15 cm H2O
    set initially low, then slowly increased to allow adequate oxygenation with as low an FiO2 as possible
  • always check for leaks, as this is can be an impediment to providing adequate support
  
  2) BiPAP
  
  • delivers 2 different pressure levels, one for I and one for E
  • pressure delivered during I is higher than E, thereby providing a degree of assistance during inspiration
  • mainly for ventilatory failure or fatigue
  • aside from benefits of CPAP by providing increased airway pressure during expiration, BiPAP theoretically should further reduce the work of breathing and assist with augmenting ventilation in patients at risk for hypercapnea by given additional inspiratory assist.
  • can be
    (1) time-cycled to deliver a preset inspiratory and expiratory pressure at a controlled rate, or
    (2) flow-cycled to provide added inspiratory pressure when triggered by a patient's negative inspiratory flow. The trigger is similar to invasive mechanical ventilation (decrease in airway pressure or airflow)
  • IPAP: 8-20 cm H2O
    EPAP: 0-15 cm H2O
    
    
• Main uses:
  
  1. COPD (best evidence): BiPAP; Bronchiectasis with hypercapnea
     
  2. Asthma: BiPAP
  3. Acute Cardiogenic Pulmonary Edema (ACPE): CPAP or BiPAP
     - if no hypercapnea, try CPAP between 8-15 cm H2O
     
  4. ALI/ARDS: BiPAP
     - acute diffuse pulmonary infiltrates with PaO2/FiO2 ratio of less than 300 for ALI and less than 200 for ARDS
     
  5. Hypoxemic Respiratory Failure: PaO2 less than 60 or SpO2 less than 90 on high flow
     - if pneumonia is the cause: mixed study
     
  6. Immunosuppressed
     - from solid organ transplantation or hematologic, steroids, chemo, AIDS
     - mortality is high for intubation, so avoided as possible
  7. DNI patients
  8. Weaning from ventilator
     
     
• Selection Criteria
  
  • pH 7.10-7.35 + PaCO2 >45 = acute respiratory acidosis
    - chronic type 2 failure: not for NPPV
    (normal pH, high pCO2, high bicarb)
    - except if acute on chronic:
    (low pH, high pCO2, high bicarb)
  • P/F Ratio: below 200 (ARDS), good for CPAP
    
    
  • RR >24
  • Respiratory distress with
    
    1. Moderate to severe dyspnea
    2. Use of accessory muscles
    3. Abdominal paradox
       
       
• Discontinuation:
  most common cause is patient's intolerance, therefore adequate acclimatization, may put on the mask while preparing for the machine
  
  
• Setting:
  
  • IPAP:
    
    1. High-Low approach, start at 20 then decrement if patient could not tolerate
    2. Low-High approach, start at 8 then increment as tolerated
       
  • EPAP: 4, then increment to 15; higher in ACPE
    
  • Pressure support (delta IPAP-EPAP) could be adjusted to create a higher minute ventilation and thus mitigate hypercapnia
    
  • Titrate FiO2 to aim for SpO2 more than 90%
    
    
  • aim for lower FiO2 as higher FiO2 = lower O2 flow (21% = 240 L/min, 100%=130)
    
  • maintain TV 5 cc/kg
    
  • target is patient more comfortable, improve pH, pCO2, RR
  • 30-60 minutes first review, if still tachypneic or acidemic, intubate sooner
    
    
  • BiPAP Vision
    Modes
    (1) S/T Spontaneous/Time Mode: ventilator delivers pressure support breaths with PEEP. Patient's spontaneous inspiratory effort triggers the ventilator to deliver IPAP. It cycles to EPAP during expiration. If the patient's RR is lower than a prescribed rate, the ventilator triggers a pressure-controlled breath according to the IPAP prescribed. The breath is ventilator-triggered, pressure-limited and time-cycled.
    Need to prescribe:
    
    1. IPAP 4-40
    2. EPAP 4-20
    3. Rate 4-40
    4. Timed inspiration 0.5-3 seconds
    5. IPAP rise time: 0.05, 0.1, 0.2, 0.4 seconds
    6. FiO2 21-100%
       
    
    (2) CPAP
    Need to prescribe
    
    1. CPAP 4-20
    2. FiO2 21-100%
       
    
    
• NPPV failure [Merlani and colleagues] associated with:
  
  • 1. GCS of less than 13 upon ED admission, or
    2. RR >20 after NPPV of an hour, or
    3. pH less than 7.35 after NPPV of an hour
       
       
• Sources:
  
  • Emerg Med Clin N Am 2008; 26:835-847
  • Emerg Med Clin N Am 2003; 21:453-473
• Sample setting: (eg pH less than 7.32, pCO2 >50)
  
  • IPAP at 18, then increment by 2 till 24
  • EPAP at 4
  • delta pressure (pressure support) IPAP-EPAP, always at least 12
  • RR 18
  • FiO2 to keep saturation 92-95%
  • IPAP Rise time: 0.1 sec
  • Timed Insp: 1 sec
    
    
    

External links:
NIV and BiPAP Vision (pdf)
BiPAP Vision checklist and testlist