chapt 5

• Full ventilatory support (FVS)


  Ventilator provides all the energy necessary to maintain effective alveolar ventilation
• Partial ventilatory support (PVS)

  Degree of mechanical ventilation where set machine rates are lower than 6 breaths/min and the patient participates in the work of breathing
• Ventilator modes for PVS

  • Intermittent mandatory ventilation (IMV)
  • Pressure support ventilation (PSV)
  • Volume support
  • Proportional assist ventilation (PAV)
  • Mandatory minute volume (MMV)
• Mandatory breaths


  • Ventilator controls the timing, the tidal volume, or the inspiratory pressure
• Spontaneous breaths


  • Patient controls the timing and the tidal volume
• Assisted breaths


  • Ventilator does part of the work of breathing for the patient
• Volume control ventilation


  Volume selected is constant and independent of what happens to pressure when the patient's lung characteristics change
• In volume control ventilation, inspiratory flow is above the x-axis and expiratory flow is below the x-axis
• In volume control ventilation, with reduced compliance, inspiratory pressure increases and with increased compliance, inspiratory pressure decreases
• Pressure control ventilation


  Pressure is the control variable, and volume varies based on the patient's lung characteristics
• In pressure control ventilation, inspiratory flow is above the x-axis and expiratory flow is below the x-axis
• In pressure control ventilation, with reduced compliance, tidal volume decreases and with increased compliance, tidal volume increases
• Continuous mandatory ventilation (CMV)


  • Ventilator delivers a mandatory breath on a preset schedule, regardless of the patient's respiratory effort
• Intermittent mandatory ventilation (IMV)

  • Ventilator delivers a mandatory breath at a preset rate, but the patient can breathe spontaneously between mandatory breaths
• Continuous spontaneous ventilation (CSV)


  • Patient breathes spontaneously at all times, with no mandatory breaths delivered by the ventilator
• Assisted breath


  If the airway pressure rises above baseline during inspiration, the breath is assisted
• Pressure support mode


  The clinician sets the target pressure but the patient initiates the breath (patient triggered). The ventilator delivers the set pressure above baseline pressure to assist the patient's breathing effort.
• Control variable


  The independent variable that will be used to establish gas flow to the patient. In volume control ventilation, the volume selected is constant and independent of what happens to pressure. In pressure control ventilation, the pressure remains constant, but volume delivery changes as lung characteristics change.
• Volume control ventilation


  • Guarantees a specific volume delivery and volume of expired gas (VE), regardless of changes in lung compliance and resistance or patient effort
  • The goal is to maintain a certain level of PaCO2
• Disadvantages of volume control ventilation

  • Can cause the peak and alveolar pressures to rise, leading to alveolar overdistention when the lung condition worsens
  • The delivery of flow is fixed on some ventilators and may not match patient demand
  • If the sensitivity level is not set appropriately for the patient, it can make it more difficult for the patient to trigger inspiration
• Pressure control ventilation


  • Allows the clinician to set a maximum pressure, which reduces the risk of overdistention of the lungs by limiting the amount of positive pressure applied to the lung
  • Delivers a decelerating flow pattern during inspiration, which has been suggested to spare more normal areas of the lungs from overinflation
  • May be more comfortable for patients who can breathe spontaneously
• Disadvantages of pressure control ventilation

  • Volume delivery varies as the patient's lung characteristics change
  • Clinicians are less familiar with pressure control ventilation
  • VT and VE decrease when lung characteristics deteriorate
• Clinical studies comparing pressure control ventilation with volume control ventilation are divided over which method is superior
• Breath delivery timing or sequence

  1. Continuous mandatory ventilation (CMV)

  2. Intermittent mechanical ventilation (IMV)

  3. Continuous spontaneous ventilation
• Continuous mandatory ventilation (CMV)


  Either time- or patient-triggered breaths are mandatory breaths; the patient is not generating any spontaneous breaths
• Intermittent mechanical ventilation (IMV)

  The patient receives a set number of mandatory breaths each minute, but is also allowed to breathe spontaneous breaths between mandatory breaths
• Continuous spontaneous ventilation


  All breaths are spontaneous and are therefore patient triggered. These spontaneous breaths may be assisted (e.g., pressure support ventilation) or unassisted (e.g., CPAP)
• Modes of ventilation are often identified using abbreviations (e.g., VC-CMV, PC-IMV, VS, PSV, and MMV)
• The control panel of a ventilator has a dial or touch pad that allows the practitioner to select a particular mode
• There is considerable variability in the way manufacturers name modes, therefore the terminology can be confusing
• Time (sec)


  0
• Time (sec)


  20
• Time (sec)


  65
• CHAPTER 5 Selecting the Ventilator and the Mode
• Modes of ventilation


  Identified using abbreviations (e.g., VC-CMV, PC-IMV, VS, PSV, and MMV)
• Physicians, therapists, or manufacturers who develop modes of ventilation often create these terms
• Considerable variability exists in the way manufacturers name modes; therefore the terminology can be confusing
• Five basic modes of ventilation

  • VC-CMV
  • PC-CMV
  • VC-IMV
  • PC-IMV
  • CSV
• Spontaneous modes of ventilation commonly used in the ICU

  • Bilevel positive airway pressure (PAP)
  • Dual-control modes
  • Mandatory minute ventilation (MMV)
  • Airway pressure release ventilation (APRV)
  • Proportional assist ventilation (PAV)
• Intermittent positive pressure breathing (IPPV)


  Continuous mechanical support of breathing in an apneic patient; every breath was mandatory