Review #1.4

• Airway pressures monitored during mechanical ventilation

  • Peak Inspiratory Pressure
  • Mean Airway Pressure
  • Plateau Pressure
  • PEEP
• Peak Inspiratory Pressure (PIP)


  Highest proximal airway pressure reached during inspiration
• PIP during VC AC or VC SIMV mode

  • Varies due to lung compliance, thoracic compliance, airway resistance and vent settings
• PIP during PC AC or PC SIMV mode

  PIP is set
• Mean Airway Pressure


  Average pressure within airway during mechanical ventilation
• Mean Airway Pressure is defined by

  PIP, Ti, Te, PEEP
• How Mean Airway Pressure will increase

  Increase in PIP, PEEP, and Ti with respect to TRCT
• How Mean Airway Pressure will decrease

  Decrease in PEEP, PIP and Ti with respect to TRCT
• Increasing a patient's Mean Airway Pressure

  There will be a reduction in venous return and may impair cardiac output
• Plateau Pressure


  Static measurement done by performing a 1 sec inspiratory hold at end of inspiration of mechanical breath
• To obtain the plateau pressure

  1 sec inspiratory hold
• Decrease in lung compliance

  Increases plateau pressure (ARDS)
• Increase in lung compliance

  Decrease plateau pressure (COPD)
• To avoid alveolar overdistention

  Smaller tidal volumes, maintain low Pplateau (less than 30 CM H20), use pressure- limited ventilation
• PEEP


  Provides baseline pressure throughout inspiration and expiration while on ventilator
• What PEEP can do

  • Can prevent end-expiratory alveolar collapse, increase FRC, and improves arterial oxygenation
• Typical PEEP level set 5cmH20
• Autopeep


  Intrinsic PEEP, incomplete emptying of the lungs which may occur during the expiratory phase
• Autopeep can cause


  Alveolar overdistention, increases pts trigger work, raise ICP levels, and increase the likelihood of barotrauma and VALI
• To assess autopeep on the ventilator

  Expiratory hold .5 to 2 seconds
• Compliance


  How easily the lung and thorax expand
• Normal compliance range 60-100 ml/cmh2o
• Dynamic compliance


  Measurement of lung expansion during breathing. Vt over PIP - PEEP
• Static compliance


  Lungs ability to stretch when lungs are not in motion. Vt over Pplateau - PEEP
• Conditions that increase lung compliance

  • COPD
  • Emphysema
• Conditions that decrease lung compliance

  • Atelectasis
  • Pneumonia
  • Pulmonary edema
  • ARDS
  • Pulmonary fibrosis
• Elastance


  Resistance of the lungs and thorax to inflate
• When compliance increases


  Elastance decreases
• When compliance decreases


  Elastance increases
• Elastic recoil


  Tendency of the lungs to deflate following inflation
• Airway resistance formula


  Raw= (PIP-Pplat) / inspiratory flow
• If airway resistance increases

  Ventilatory workload increases
• If airway resistance decreases

  Ventilatory workload decreases
• Issues that can cause an increase in Airway Resistance

  • Bronchoconstriction
  • Secretions
  • Airway swelling
  • Foreign body
• Diseases that can cause an increase in airway resistance

  • Asthma
  • Cystic fibrosis
  • COPD
  • Restrictive lung disease with coexisting non-parenchymal lung disease
• High Ppeak, Normal Pplat

  Resistance Problem
• High Peak, High Pplat


  Compliance Problem
• Elevated Baseline


  PEEP Problem