Mechanical ventilation (main)

Modes

Assist Control (AC)

1. (helps instigated breaths, extra breaths all of set TV)
   1. preset rate and TV
   2. pt able to trigger additional breaths (full assisted tidal volume)
2. spontaneous breathing (above rate) is not allowed
3. beneficial for patients requiring a high minute-ventilation (reduces oxygen consumption and CO2 production of the respiratory muscles)
4. may worsen obstructive airway disease by air trapping or breath stacking

Synchronous Intermittent Mandatory Ventilation (SIMV)

1. senses not to give with breathing if present, extra breaths of pt's TV
2. preset breaths in coordination with the respiratory effort
3. spontaneous breathing allowed between breaths
4. synchronization attempts to limit the barotrauma by not delivering a breath when already maximally inhaled (vs. IMV)
5. for each additional breath triggered by pt, vent delivers variable TV depending on pt effort and condition of lung
6. because of need for pt effort, not recommended for tired or septic pt

Pressure Support (PS)

1. controls via pressure, good if pressures getting too high
2. limits barotrauma and decreases the work of breathing in the spontaneously breathing patient
3. level of pressure set (not TV) to assist spontaneous efforts
4. most ventilators allow back-up respiratory rate (in case of apnea)
5. mode of choice in patients whose respiratory failure is not severe and who have an adequate respiratory drive (improved patient comfort, reduced cardiovascular effects, reduced risk of barotrauma, and improved distribution of gas)

^For the paralyzed patient, there is no difference in minute-ventilation or airway pressures between A/C and SIMV

CPAP

1. needs spont breathing pt
2. not for fatiguing pt
3. no back up rate

Control Mode

1. only in OR
2. machine initiates and delivers breath
3. fixed rate and TV

See Also

• Ventilation (Initial & Changes)
• Ventilation (Weaning)
• Ventilation (Non-Invasive)
• Ventilation (Management)