Pressure Controlled Modes

Most commonly used are

• Pressure Control – Assist Control (PC-AC)
• Pressure Control – Synchronized Intermittent Mandatory Ventilation (PC-SIMV)

Breath Characteristics

• Gas is delivered until set Peak inspiratory pressure (Pinsp) is reached
  • Pressure is constant during inspiration resulting in a square pressure waveform
    • How quickly the ventilator achieves the set pressure is determined by the slope setting
    • Constant pressure gives a decelerating pattern of gas flow

• Flow waveform therefore peaks at the start of inspiration and decelerates over time to zero or near zero
  • Shorter Ti may result in smaller TV if the inspiratory flow has not reached zero before cycling to expiration occurs

• Tidal volume varies according to patients lung mechanics and properties of the ventilator circuit

• • Increasing Pinsp on the ventilator will result in a higher TV
  • Increasing lung resistance or reducing lung compliance will result in smaller TV
  • Pinsp should not be set above 30cmH20 due to the risk of inducing lung damage

 
[az_accordion_section] [accordion title=”Pressure Control Assist Control” id=”acc-1″]• What ventilator setting won’t you have to set?
o FiO2
o Tidal Volume [this depends on your other settings and the patient’s respiratory unit mechanics] o Respiratory Rate
o Flow
o Inspiratory time (Ti)
o Pressure
o PEEP

[az_toggle_section] [toggle title=”You tried PC-AC on your patient. What information about your patient does this mode permits you to gain?” id=”tgl-1″] Unlike the VC mode where you could get the Pplat, the resistance and the compliance, this mode only gives you a hint on the compliance of the respiratory unit. In this case, you know that for every 15cmH2O he’s lungs accomodate 340mL of VT. The dynamic compliance (dynamic because done with ongoing flow) is therefore: 340mL/15cmH2O = 23 mL/cmH2O. Dynamic measures are not as reliable as static measures (done when flow is stopped) and therefore, this is just a hint of the actual compliance of your patient, which, as you already know is 35mL/cmH2O. [/toggle] [/az_toggle_section]  
[/accordion] [accordion title=”Pressure Controlled Synchronized intermittent mandatory ventilation (PC-SIMV)” id=”acc-2″]• Equivalent of PC-AC interspersed with Pressure Support (PS)
• Same concepts as VC-SIMV
The ventilator screen would look like this:

 
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