Ventilator Modes

• Assist Control (AC):
  • Is a commonly used mode of ventilation:
    • Is one of the safest modes of ventilation:
      • In the Emergency Department
  • Patients receive:
    • The same breath, with the same parameters:
      • As set by the clinician, with every breath
    • They may take additional breaths, or over-breathe:
      • But every breath:
        • Will deliver the same set parameters
    • Assist control can be:
      • Volume-targeted:
        • Volume control, AC/VC:
          • Where the clinician sets a desired volume, or
      • Pressure-targeted:
        • Pressure control, AC/PC:
          • Where the clinician selects a desired pressure
• Synchronized Intermittent Mandatory Ventilation (SIMV):
  • Is a type of intermittent mandatory ventilation, or IMV
  • The set parameters are similar to those in AC, and the settings can be:
    • Volume controlled (SIMV-VC) or
    • Pressure controlled (SIMV-PC)
  • Similar to AC:
    • Each mandatory breath in SIMV:
      • Will deliver the identical set parameters:
        • However, with additional spontaneous breaths:
          • The patient will only receive pressure support or CPAP:
            • For example:
              • In SIMV-VC we can set a TV, and as long as the patient is not breathing spontaneously:
                • Each delivered mechanical breath will achieve this tidal volume
              • However, spontaneous breaths in this mode of ventilation:
                • Will have more variable tidal volumes:
                  • Based on patient and airway factors
• Pressure Regulated Volume Control (PRVC):
  • Is a type of assist-control (AC):
    • That combines the best attributes of:
      • Volume control and
      • Pressure control
  • The clinician selects:
    • A desired tidal volume:
      • The ventilator gives that tidal volume with each breath:
        • At the lowest possible pressure:
          • If the pressure gets too high and reaches a predefined maximum level:
            • The ventilator will stop the air flow and cycle into the exhalation phase:
              • To prevent excessive airway pressure and resulting lung injury
  • In this mode of ventilation:
    • The pressure target is adjusted:
      • Based on lung compliance:
        • To help achieve the set tidal volume
• Pressure Support:
  • Is a partial support mode of ventilation:
    • In which the patient receives a constant pressure (the PEEP):
      • As well as a supplemental, “supporting” pressure:
        • When the ventilator breath is triggered
  • In this mode:
    • The clinicians can set the PEEP and
    • The additional desired pressure over the PEEP
      • However:
        • The peak inspiratory airflow, the respiratory rate, and the tidal volume:
          • Are all dependent variables:
            • Determined by the patient’s effort
          • The patient triggers every breath, and when the patient stops exerting effort:
          • The ventilator stops administering the driving pressure, or the desired pressure over PEEP:
            • Therefore, patients placed on this mode of ventilation:
              • Must be able to take spontaneous breaths
• Non-invasive positive pressure ventilation (NIPPV):
  • Refers to two non-invasive modes of ventilation:
    • In which the patient’s airway is not secured with an endotracheal tube:
      • Rather, these modes of ventilation are delivered through:
        • A tight-fitting facemask or nasal prongs
  • There are several indications, and clear contraindications to these modes of ventilation:
    • Both CPAP and BPAP are non-invasive modes of ventilation
• Continuous Positive Airway Pressure (CPAP):
  • Is a partial support mode of ventilation:
    • In which the patient received a constant airway pressure throughout the respiratory cycle
  • The peak inspiratory airflow, respiratory rate, and tidal volume are:
    • All dependent variables and determined by the patient’s effort:
      • Therefore:
        • The patient must be awake, minimally sedated, and able to take spontaneous breaths during this mode of ventilation
• Bilevel Positive Airway Pressure (BPAP or BiPAP):
  • Is a partial support mode of ventilation:
    • In which the patient receives two levels of airway pressure throughout the respiratory cycle:
      • A high inspiratory pressure (iPAP):
        • Is similar to the peak airway pressure setting
      • The lower expiratory pressure (ePAP):
        • Similar to PEEP:
          • Is clinically apparent at the end of expiration and helps maintain alveolar distention
  • The patient must be awake, minimally sedated, and able to take spontaneous breaths during this mode of ventilation
• Unconventional Modes of Ventilation:
  • There are other modes of ventilation occasionally used in specific circumstances in ICUs, including:
    • Airway Pressure Release Ventilation (APRV):
      • Also referred to as:
        • Bi-Level or Bi-vent
    • High-frequency Oscillatory Ventilation
    • Proportional Assist Ventilation (PAV), and
    • Neurally Adjusted Ventilator Assist (NAVA)
      • But these modes are not appropriate in the ED without expert consultation

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