Ventilator Settings

• Peak Inspiratory Pressure (PIP or Ppeak):
  • Is the maximum pressure in the airways:
    • At the end of the inspiratory phase:
      • This valve is often displayed:
        • On the ventilator screen
  • Since this value is generated during a time of airflow:
    • The PIP is a determined by both:
      • Airway resistance and
      • Compliance
  • By convention:
    • All pressures in mechanical ventilation:
      • Are reported in “cm H2O”
        • It is best to target a PIP:
          • Of less than 35 cm H2O
• Plateau Pressure (Pplat):
  • Is the pressure that remains in the alveoli:
    • During the plateau phase:
      • During which there is a:
        • Cessation of air flow, or with a breath-hold
  • To calculate this value:
    • The clinician can push:
      • The “inspiratory hold” button:
        • On the ventilator
  • The plateau pressure:
    • Is effectively the pressure at the alveoli with each mechanical breath, and:
      • Reflects the compliance in the airways:
        • To prevent lung injury:
          • The Pplat should be maintained:
            • At less than 30 cm H2O
• Positive End Expiratory Pressure (PEEP):
  • Is the positive pressure:
    • That remains at the end of exhalation
  • This additional applied positive pressure:
    • Helps prevent atelectasis:
      • By preventing the end-expiratory alveolar collapse
  • PEEP is usually set at:
    • 5 cm H2O or greater:
      • As part of the initial ventilator settings
  • PEEP set by the clinician:
    • Is also known as extrinsic PEEP, or ePEEP:
      • To distinguish it from:
        • The pressure than can arise with air trapping
      • By convention:
        • If not otherwise specified:
          • “PEEP” refers to ePEEP
• Intrinsic PEEP (iPEEP), or auto-PEEP:
  • Is the pressure that remains in the lungs:
    • Due to incomplete exhalation:
      • As can occur in patients with:
        • Obstructive lung diseases
  • This value can be measured by:
    • Holding the “expiratory pause” or “expiratory hold” button on the mechanical ventilator
• Driving pressure (∆P):
  • Is the term that describes the:
    • Pressure changes that occurs during inspiration, and:
      • Is equal to the difference between:
        • The plateau pressure and PEEP (Pplat – PEEP):
          • For example:
            • A patient with a Pplat of 30 cm H2O and a PEEP of 10 cm H20:
              • Would have a driving pressure of 20 cm H2O
                • In other words:
                  • 20 cm H2O would be the pressure that extered to expand the lungs
• Inspiratory time (iTime):
  • Is the time allotted to deliver:
    • The set tidal volume:
      • In volume control settings, or
    • The set pressure:
      • In pressure control settings
• Expiratory Time (eTime):
  • Is the time allotted to fully exhale:
    • The delivered mechanical breath
• I:E ratio, or the inspiratory to expiratory ratio:
  • Is usually expressed as 1:2, 1:3, etc
  • The I:E ratio can be set:
    • Directly, or indirectly on the ventilator by changing the:
      • Inspiratory time
      • The inspiratory flow rate, or
      • The respiratory rate
  • By convention:
    • Decreasing the ratio means:
      • Increasing the expiratory time:
        • For example:
          • 1:3 is a decrease from 1:2:
            • Just like 1/3 is less than 1/2
• Peak inspiratory flow:
  • Is the rate at which the breath is delivered:
    • Expressed in L/min:
      • A common rate is 60 L/min
  • Increasing and decreasing the inspiratory flow:
    • Is a means of indirectly affecting the I:E ratio:
      • A patient with a respiratory rate set at 20, who is not overbreathing:
        • Has three seconds for each complete cycle of breath:
          • If you increase the inspiratory flow:
            • The breath is given faster, and that leaves more time for exhalation:
              • Thus, inspiratory flow indirectly changes the I:E ratio
• Tidal volume (TV or VT):
  • Is the volume of gas:
    • Delivered to the patient with each breath
  • The tidal volume is best expressed in both:
    • Milliliters (ex: 450mL) and
    • Milliliters/kilogram (ex: 6 mL/kg) of predicted body weight
  • Clinicians can choose to set the ventilator:
    • In a volume control mode:
      • Where the tidal volume:
        • Will be constant for each breath
    • In pressure control modes:
      • The pressure is constant:
        • But the tidal volume is an independent variable, and:
          • Will vary slightly with each breath:
            • Regardless:
              • Every mode of ventilation delivers a tidal volume
• Respiratory rate (RR or f, for “frequency”):
  • Is the mandatory number of breaths:
    • Delivered by the ventilator per minute
  • However:
    • It is important to be mindful that:
      • The patient can breathe over this set rate, and therefore:
        • One must report both:
          • Your set RR and
          • The patient’s actual RR
            • Both of these values can found on the ventilator screen
    • In addition:
      • It is important to remember that the RR is a key factor in determining time for exhalation:
        • For example:
          • If a patient has a RR of 10 breaths per minute (bpm):
            • He will have 6 seconds per breath; ((60 seconds/min) / 10 bpm = 6 sec/breath)
          • A RR of 20 bpm:
            • Only allows 3 seconds for the entire respiratory cycle
• Minute ventilation (VĖ, Vė, or MV ):
  • Is the ventilation the patient receives in one minute
  • It is calculated as the:
    • Tidal volume multiplied by the respiratory rate (TV x RR), and:
      • Expressed in liters per minute (L/min)
  • Most healthy adults:
    • Have a baseline minute ventilation of:
      • 4 L/min to 6 L/min
  • But critically ill patients:
    • Such as those attempting to compensate for a metabolic acidosis:
      • May require a minute ventilation of:
        • 12 L/min-15 L/min, or even higher:
          • To meet their demands
• Fraction of inspired oxygen (FiO2):
  • Is a measure of the oxygen delivered by the ventilator during inspiration:
    • Expressed at a percentage
  • Room air contains 21% oxygen
  • A mechanical ventilator:
    • Can deliver varying amounts of oxygen:
      • Up to 100%

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