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Mechanical Ventilaton

Mechanical Ventilaton. Ramon Garza III, M.D. Indications. Airway instability Most surgical patients or trauma Primary Respirator Failure Mostly medical i.e. ARDS, CHF, COPD. Basic Principles. Facilitate Gas exchange for oxygen delivery to tissues Ventilation for removal of carbon dioxide

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Mechanical Ventilaton

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  1. Mechanical Ventilaton Ramon Garza III, M.D.

  2. Indications • Airway instability • Most surgical patients or trauma • Primary Respirator Failure • Mostly medical i.e. ARDS, CHF, COPD

  3. Basic Principles • Facilitate Gas exchange for oxygen delivery to tissues • Ventilation for removal of carbon dioxide • Minimize detrimental effects

  4. Ventilation vs Oxygenation • Ventilation= CO2 gas exchange • Oxygenation= equilibrium of oxygen tension gradient between alveoli and oxygen in blood

  5. Ventilation • Minute Ventilation (VE)= total gas exhaled per minute • VE= Tidal Volume x Respiratory Rate

  6. Ventilation • Goal of mechanical ventilation is maintaining normal pCO2 • Dead space ventilation can inhibit elimination of CO2

  7. Oxygenation • Oxygen tension between alveoli and capillaries favors oxygen transfer to blood • Most important factor is V/Q matching

  8. Oxygenation • Evaluation of Oxygenation by A-a gradient • A-a gradient= PAO2-PaO2 • Normal PaO2= 90mmHg • Normal A-a gradient= (Age+10)/4 • P/F ratio is useful to evaluate degree of hypoxemia • Normal PaO2/FiO2= 90mmHg/0.21=500

  9. Oxygenation • Improve oxygenation by increasing FiO2 or by adjusting mean airway pressure • Minute ventilation does NOT change oxygenation *except in extremely low ventilation

  10. Mechanical Ventilation • 3 Variables • Trigger • Limit • Cycle • Modes and settings are varying combinations of these 3 variables

  11. Trigger • Signal that tells ventilator to give a breath • Signal comes from Pt • Change in flow w/in circuit • Change in pressure w/in circuit • Time trigger • If pt does not initiate breath w/in allotted time->machine will give breath

  12. Limit Variable • Maximal set inspiratory flow or pressure • How much “breath” they are going to take • Volume control vs Pressure control Volume= flow x time

  13. Cycle • Factor that terminates inspiratory cycle • Time • Flow • Pressure • Volume

  14. Specific Types of Ventilation

  15. Pressure Support • Simplest form of pressure limited ventilation • Pt breathing + ventilator support until target pressure • Passive exhalation

  16. Pressure Control • Differs from pressure support b/c inspiratory time is set by ventilator • Can be used in Assist Control or in SIMV • Drawback is when lungs have decreased compliance-> Lower Tidal Volume

  17. Intermittent Mechanical Ventilation • Only a set number of breaths are supported • Can be synchronized to pt’s inspiratory efforts • Pt breaths above set number are not supported • Most common ventilator mode you will see is SIMV

  18. Mechanical Ventilation in Respiratory Failure • After 30min stabilization period check ABG and adjust vent • Use pulse oximetry as a guide for adjusting FiO2 and PEEP

  19. Oxygenation • Goal of mechanical ventilation is normal pCO2 and oxygen delivery to tissues • pO2 of 60mmHg = 90% saturation and is adequate for O2 delivery to tissues

  20. How to increase PaO2? • Increase FiO2 • Does not work if intrapulmonary shunt present • Prolonged high FiO2 can be detrimental to pulmonary function

  21. How to increase PaO2? • Change patient to an upright position • Increase mean airway pressure • Increase PEEP to improve FRC • Improves V/Q mismatching • Have to balance increasing PEEP to improve oxygenation and risk of decreasing preload *Goal of ventilation is maximize oxygen delivery to tissues

  22. Management of Ventilator • Initial settings depend on patient • Otherwise healthy post op pt • FiO2 30% • PEEP 5cm H2O • Multiply injured trauma pt • FiO2 100% • PEEP of 15cm H2O

  23. Mechanical Ventilation • Check ABG early (w/in 30min) • If sats decrease -> • Suction • Check ABG • CXR to confirm tube placement, assess lungs, check for pneumo • Pt may need w/u for PE, MI, etc

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