Mechanical Ventilation

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  1. Mandatory breath
    • Set sequence that delivers a pre-defined breath...machine controls timing (when inhalation starts) and size (when inhalation stops)
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    • Control: (independent variable)
    • -Volume
    • Control the flow for a target amount of time
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    • -Pressure
    • Control the pressure for a target amount of time
    • **Pressure control is especially good for stiff lungs: won't overdistend the alveoli
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    • -Dual: control pressure but adjust by computer. "Pressure regulated volume control"
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  2. Components of ventilator
    • -Air pump
    • -Inhalation valve solenoid  - reduces (controls) the pressure on inspiration
    • - Exhale valve solenoid - safety mechanism (release valve) for if the pt coughs or obstructs

    • All controlled by a microprocessor
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  3. Volutrauma
    • Trauma to the alveoli caused by over-distension (or pressures >>> physiologic)
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    • Avoid over-distension by:
    • -Tidal volume around 6ml/kg
    • -PIP less than 30cm/H2O (peak inspiratory pressure)

    Those who get lower VT have improved survival and discharge status
  4. Breathing patterns
    • Continuous mandatory ventilation (aka assist control)
    • Intermittent mandatory ventilation
    • No mandatory ventilation (PEEP, CPAP, etc.)
  5. Intermittent Mandatory Ventilation
    • Set length of breath
    • Set number of breaths/minute (respiratory rate)
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  6. Continuous Mandatory Ventilation
    (assist control)
    Ventilator responds to stimulus from patient (i.e. they begin to take breath) by giving a mandatory breath

    • *Back up rate set as a safeguard (minimum number of respirations per minute) in case pt doesn't give stimulus
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  7. No mandatory ventilation
    • PEEP
    • Positive end expiratory pressure
    • -"Floor" pressure - independent of pt's breathing attempt
    • -Often combined with supported breaths (extra pressure when ventilator senses pt's effort)Image Upload 9

    CPAP - continuous positive airway pressure without the supported breaths

    • Indications:
    • -The addition of positive pressure can help maintain open alveoli...
    • ARDS - adult respiratory distress syndrome
    • -thought to be a process of decreased surfactant production
    • -smaller lungs with fewer gas-exchange alveoli
    • -fewer inflating alveoli
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    PEEP: increases the pressure to keep some of the "bad" alveoli open

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  8. Principles of Ventilation
    • -Hysteresis -
    • different volumes for the same pressure depending on whether the lung is being
    • loaded or unloaded (inflating or deflating)
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    • -LaPlace's law
    • pressure within the alveoli is dependent upon the surface tension and the radius of the alveoli

    • Pressure = (2 x surface tension)/radius
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Card Set
Mechanical Ventilation
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