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Invasive Mechanical Ventilation

Invasive Mechanical Ventilation. D. Sara Salarian , . Why ventilate?. Improve oxygenation Increase/maintain minute ventilation and help CO 2 clearance Decrease work of breathing Protect airway. Mask based device. Negative pressure ventilators “The Iron Lung”.

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Invasive Mechanical Ventilation

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  1. Invasive Mechanical Ventilation D. Sara Salarian,

  2. Why ventilate? • Improve oxygenation • Increase/maintain minute ventilation and help CO2 clearance • Decrease work of breathing • Protect airway Kishore P. Critical Care Conference

  3. Mask based device Negative pressure ventilators “The Iron Lung”

  4. Origins of mechanical ventilation The era of intensive care medicine began with positive-pressure ventilation • Negative-pressure ventilators (“iron lungs”) • Non-invasive ventilation first used in Boston Children’s Hospital in 1928 • Used extensively during polio outbreaks in 1940s – 1950s • Positive-pressure ventilators • Invasive ventilation first used at Massachusetts General Hospital in 1955 • Now the modern standard of mechanical ventilation The iron lung created negative pressure in abdomen as well as the chest, decreasing cardiac output. Iron lung polio ward at Rancho Los Amigos Hospital in 1953.

  5. Modes of Mechanical Ventilation • Spontaneous/Controlled/Dual • Controlled Mechanical Ventilation (CMV) • Assist Control (AC)/Volume Control (VC) • Intermittent Mandatory Ventilation (SIMV) • Pressure Control (PCV) • Pressure Support Ventilation (PSV)

  6. Patient system interaction CPAP +PEEP Spontaneous SIMV IMV Kishore P. Critical Care Conference Controlled MV Assisted-pressure support Assist control

  7. Breath Types • Spontaneous Breath • Inspiration is both initiated and terminated by the patient. • Mandatory Breath • Inspiration is either initiated or terminated by the ventilator. < >

  8. Breath Patterns • Continuous Mandatory Ventilation • CMV • All breaths mandatory • Intermittent Mandatory Ventilation • IMV or SIMV • Mandatory and spontaneous breaths • Continuous SpontaneousVentilation • All breaths spontaneous < >

  9. Phase Variables • TRIGGERstarts inspiration • Example: pressure drop when patient sucks in • LIMITpreset inspiratory value • Example: preset maximum inspiratory flow • CYCLEstops inspiration • Example: preset inspiratory time < >

  10. VOLUME-CYCLED VENTILATION • the controlled variables of tidal volume and inspiratory flow determine airway pressure and inspiratory time • Variations in airway resistance or lung compliance alter airway pressures but do not affect minute ventilation • There are three methods of initiating the inspiratory phase in volume-cycled mechanical ventilators: controlled, assist-control, and intermittent mandatory ventilation (IMV)

  11. Modes of ventilationPressure controlled • Ventilator applies a predefined target pressure to the airway during inspiration • Adv. - decreased risk of barotrauma • Disadv. - with decreasing compliance or increasing resistance, tidal volume and minute ventilation fall Kishore P. Critical Care Conference

  12. Comparison chart

  13. MODES OF PPV

  14. Controlled mechanical ventilation (CMV) • minute ventilation is completely dependent upon the rate and tidal volume set on the ventilator. Any respiratory efforts made by the patient do not contribute to minute ventilation • Controlled ventilation is the required ventilatory mode in patients who are making no respiratory effort (eg, spinal cord injury or drug overdose and those who have been subjected to pharmacologic paralysis).

  15. Controlled Mechanical Ventilation • Advantages: rests muscles of respiration • Disadvantages: requires sedation/neuro-muscular blockade, potential adverse hemodynamic effects

  16. Time-Cycled Flow (L/min) Set PC level Pressure (cm H2O) Volume (ml) Controlled Mode (Pressure-Targeted Ventilation) Time Triggered, Pressure Limited, Time Cycled Ventilation Time (sec)

  17. Pressure Control Ventilation C = VT / PC Flow (L/min) Set PC level Pressure (cm H2O) Cl Cl Volume (ml) Time (sec)

  18. Controlled Mode Volume Targeted Flow (L/min) Pressure (cm H2O) Volume (ml) Time (sec)

  19. ASSIST-CONTROL MECHANICAL VENTILATION • In the assist-control (A/C) mode, the ventilator senses an inspiratory effort by the patient and responds by delivering a preset tidal volume. Every inspiratory effort that satisfies the ventilator's demand valve trigger threshold initiates delivery of the preset tidal volume • Patient work is therefore required to trigger the ventilator and continues during inspiration • A control mode back-up rate is set on the ventilator to prevent hypoventilation

  20. Assist-Control Ventilation • Volume or time-cycled breaths + minimal ventilator rate • Additional breaths delivered with inspiratory effort • Order: AC Vt 500, RR12, 100% FiO2, 5 PEEP

  21. Assist-Control Ventilation • Advantages: reduced work of breathing; allows patient to modify minute ventilation • Disadvantages: potential adverse hemodynamic effects or inappropriate hyperventilation

  22. INTERMITTENT MANDATORY VENTILATION • With intermittent mandatory ventilation (IMV), the degree of ventilatory support is determined by the selected IMV rate. At regular intervals, the ventilator delivers a breath based upon a preset tidal volume and rate. In addition, the patient is allowed to breathe spontaneously through the ventilator circuit at a tidal volume and rate determined according to need and capacity. • Most present day ventilators synchronize the intermittent ventilator breaths with inspiratory effort by the patient, a modality termed synchronized IMV or SIMV. However, this modification requires a trigger modality

  23. Synchronized Intermittent Mandatory Ventilation (SIMV) • Potential advantages • More comfortable for some patients • Less hemodynamic effects • Potential disadvantages • Increased work of breathing

  24. SIMV(Volume-Targeted Ventilation) Flow (L/m) Pressure (cm H2O) Volume (mL) Spontaneous Breaths

  25. Flow (L/min) Pressure (cm H2O) Volume (ml) SIMV + PS (Pressure-Targeted Ventilation) Time-Cycled Flow-Cycled Set PC level Set PS level Time (sec) PS Breath

  26. PRESSURE SUPPORT VENTILATION • Pressure support ventilation (PSV) is flow-cycled in that, once triggered by a demand valve, the preset pressure is sustained until the inspiratory flow tapers, usually to 25 percent of its maximal value [22]. PSV tends to be a comfortable ventilatory modality because the patient has greater control over ventilator cycling and flow rates. Close monitoring is required whenever PSV is used alone because neither tidal volume nor minute ventilation is guaranteed. PSV can be added during full or partial support with SIMV to overcome endotracheal tube and ventilator circuitry resistance encountered during spontaneous breaths

  27. Pressure-Support Ventilation • Pressure assist during spontaneous inspiration with flow-cycled breath • Pressure assist continues until inspiratory effort decreases • Delivered tidal volume dependent on inspiratory effort and resistance/compliance of lung/thorax Order: PS 10, PEEP 0, 50% FiO2

  28. Pressure-Support Ventilation • Potential advantages • Patient comfort • Decreased work of breathing • May enhance patient-ventilator synchrony • Used with SIMV to support spontaneous breaths

  29. Pressure-Support Ventilation • Potential disadvantages • Variable tidal volume if pulmonary resistance/compliance changes rapidly • If sole mode of ventilation, apnea alarm mode may be only backup • Gas leak from circuit may interfere with cycling

  30. Flow Cycling CPAP level CPAP + PSV Flow (L/m) Set PS level Pressure (cm H2O) Volume (mL) Time (sec)

  31. VENTILATOR SETTINGS • Ventilatory support requires consideration of trigger mode and sensitivity, respiratory rate, tidal volume, flow rate, flow pattern, and the fraction of inspired oxygen (FiO2).

  32. Ventilator Settings • Mode • Rate • Volume (VT) • Pressure • FIO2 • PEEP • I:E

  33. Key concepts • Determinants of CO2 clearance - Ventilator factors * Rate * Tidal volume * Anatomical dead space - Patient factors * Physiological dead space * CO2 production Alveolar minute ventilation Kishore P. Critical Care Conference

  34. Key concepts • Determinants of Oxygenation - Ventilator factors: * FiO2 ( fraction of oxygen in inspired air) * Mean airway pressure * PEEP ( positive end expiratory pressure) - Patient factors * V/Q (ventilation/ perfusion) mismatch * Shunt * Diffusion defect * Reduced mixed venous oxygen Kishore P. Critical Care Conference

  35. Adjust FiO2 and PEEP according to PaO2 and SpO2 • Adjust TV and rate according to PCO2 and pH Kishore P. Critical Care Conference

  36. POSITIVE END-EXPIRATORY PRESSURE • PEEP: an elevation in alveolar pressure above atmospheric pressure at the end of exhalation • Extrinsic PEEP (ePEEP): applied through a mechanical ventilator ACV without PEEP ACV with PEEP

  37. Auto-PEEP Detection viathe Flow Waveform Normal -------------------------------------------------------- Flow does not return to zero - Auto-PEEP

  38. Air Trapping Auto-PEEP Normal Patient Air Trapping Inspiration Time (sec) Flow (L/min) } Expiration

  39. Flow-Volume Loop Inspiration PIFR Volume (ml) FRC VT Flow (L/min) PEFR Expiration

  40. Air Trapping Inspiration Flow (L/min) Does not return to baseline Volume (ml) Normal Abnormal Expiration

  41. Air Leak Inspiration Flow (L/min) Volume (ml) Air Leak in mL Normal Abnormal Expiration

  42. Airway Secretions/Water in the Circuit Inspiration Flow (L/min) Origins Volume (ml) Normal Abnormal Expiration

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