Initial Ventilation Modes Quiz

Initial Ventilation Modes

• No single initial mode of invasive mechanical ventilation is ideal for all patients.
• Common initial modes include:
  • Volume-limited assist control ventilation
  • Pressure-limited assist control ventilation
  • Synchronized intermittent mandatory ventilation (SIMV) with pressure support ventilation (SIMV-PSV)
• Pressure support ventilation (PSV) alone is less common as an initial mode but frequently used during weaning.
• Continuous mechanical ventilation (CMV), intermittent mandatory ventilation (IMV), and airway pressure release ventilation (APRV) are not usually initial modes.
• Adaptive support ventilation (ASV) and neurally adjusted ventilatory assist ventilation (NAVA) are investigational modes. High-frequency mechanical ventilation is not recommended for adults.

Ventilation Types (Volume-Limited vs. Pressure-Limited)

• Volume-limited:
  • Breaths can be ventilator-initiated (volume-controlled/volume-cycled [VC]) or patient-initiated (volume-assist [VA]).
  • Delivers a predetermined tidal volume at a set rate, ensuring a minimum minute ventilation.
  • Inspiration ends when the set tidal volume is delivered.
  • Airway pressure depends on airway resistance, lung and chest wall compliance.
  • Used in volume-limited assist control and volume-limited SIMV.
  • Pressure-regulated volume control ventilation (PRVC) is increasingly utilized.
• Pressure-limited:
  • Breaths can be ventilator-initiated (pressure-control/pressure-cycled [PC]) or patient-initiated (pressure-assist [PA]).
  • Flow is determined by a set pressure limit; rate is set.
  • Inspiration ends when the set inspiratory time is reached.
  • Tidal volume varies based on compliance and resistance.
  • A specific minute ventilation cannot be guaranteed.
  • Used in pressure-limited assist control and pressure-limited SIMV.

Pressure Support

• Spontaneous breathing can be supported to a set pressure limit.
• The ventilator provides the driving pressure for each spontaneous breath, determining the maximal airflow.
• Inspiration ends when inspiratory flow reaches a predetermined percentage of its maximum.

Factors Influencing Mode Selection

• Level of Support Needed:
  • Volume- or pressure-limited assist control modes offer more support, minimizing muscle atrophy.
  • Pressure support offers less support and greater patient work of breathing.
  • Severity of respiratory failure impacts support needs.
  • Settings can be adjusted to modify support levels.
• Reason for Ventilation:
  • Patients with acute respiratory distress syndrome (ARDS) often receive low tidal volume ventilation with volume-limited assist control or pressure-limited assist control.
  • Short-term ventilation for airway protection may use SIMV-PSV or PSV.
• Airflow Limitation:
  • Volume-limited modes (e.g., volume-limited assist control, SIMV-PSV) are typical in patients with airflow limitations (COPD, asthma exacerbation).
  • Pressure support or pressure-limited modes (including APRV) are generally avoided.
• Air Leak:
  • Pressure-limited ventilation or SIMV-PSV, or even PSV alone, are preferred for patients with significant air leaks (e.g., pneumothorax).
• Elevated Intracranial Pressure (ICP):
  • Volume-limited modes are frequently used, but pressure-limited modes are sometimes preferred due to theoretical concerns about elevated intrathoracic pressure impacting venous return.
  • No definitive data supports superiority of one mode over the other for ICP management.
• Paralysis/Sedation:
  • PSV is contraindicated in paralyzed or heavily sedated patients. Assist control modes are preferred, ensuring adequate minute ventilation.
• Other Factors:
  • Clinician experience and institutional preferences influence common mode choices.