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Invasive Mechanical Ventilation

Invasive Mechanical Ventilation. Ventilate is derived from Latin word “ventus” meaning wind. Mask based device. Negative pressure ventilators “The Iron Lung”. Why ventilate?. Improve oxygenation Increase/maintain minute ventilation and help CO 2 clearance Decrease work of breathing

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Invasive Mechanical Ventilation

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  1. Invasive Mechanical Ventilation Kishore P. Critical care conference

  2. Ventilate is derived from Latin word “ventus” meaning wind Kishore P. Critical Care Conference

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

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

  5. Common indications for ventilation • Hypoxemic respiratory failure – 66% • Acute exacerbation of COPD – 13% • Neuromuscular disorders - 10% • Coma - 10% Data from Americas and Europe Kishore P. Critical Care Conference Am. J. Respir. Crit. Care Med., Volume 161, Number 5, May 2000, 1450-1458

  6. 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

  7. 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

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

  9. Modes of ventilationVolume controlled • Machine delivers a set volume irrespective of the pressure generated within the system • Adv. - predefined minute volume is guaranteed • Disadv. - changes in mechanical properties of lungs (resistance or compliance) can lead to high pressures - Patient is unable to adjust breathing pattern to changes in ventilatory demand Kishore P. Critical Care Conference

  10. 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

  11. TV, inspiratory flow, I:E ratio Tidal volume Airway pressure Peak inspiratory pressure, inspiratory time, Maximum inspiratory pressure Tidal volume Volume control Pressure control Settings Constant Variable Kishore P. Critical Care Conference

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

  13. Continuous mandatory ventilation (CMV) • Also known as controlled mechanical ventilation • Rate, I:E ratio, volume determined entirely by machine and cannot be altered by patient effort • Used in paralyzed patients only Kishore P.

  14. Intermittent mandatory ventilation (IMV) • Patient is allowed to take spontaneous breaths in between preset timed ventilator breaths • The ventilator does not offer any assistance to the spontaneous breaths • Stacking of breaths may occur Kishore P.

  15. Assist control (A/C) • In addition to a preset number of mandatory breaths, the ventilator delivers additional full breaths whenever the patient has a spontaneous respiratory effort • Sensitivity of trigger important Kishore P.

  16. Synchronized intermittent mandatory ventilation (SIMV) • The ventilator attempts to synchronize the set number of mandatory breaths with the patients respiratory efforts • The ventilator waits for a patient effort during a sensitive peroid before every breath. In its absence, it gives a controlled breath • Spontaneous breaths outside of this sensitive period are unsupported • Commonly used mode Kishore P.

  17. Pressure support • Delivers a breath to a preset airway pressure when the patient makes an inspiratory effort • Cycles into expiration when inspiratory flow falls toward end of inspiration • Used along with SIMV • Useful for weaning Kishore P.

  18. Newer modes • Hype • Add to cost • No reliable evidence for better outcomes in terms of mortality, duration of ventilation Kishore P.

  19. Adaptive support ventilation (ASV) • A weight based minimum minute ventilation is set. • the machine decides how to achieve that MV with the least work of breathing-fixes an appropriate TV and rate • Decreases the need for frequent reassessment and changes in ventilator settings • No outcome difference Kishore P.

  20. Proportional assist ventilation (PAV) • Useful weaning mode • The proportion of work of breathing to be contributed by the ventilator is set • Each breath gets a different degree of support from the ventilator depending on patient effort. • Theoretically smooth offloading Kishore P.

  21. Others • Airway pressure release ventilation (APRV) • Pressure controlled inverse ratio ventilation Kishore P.

  22. Patient system interaction CPAP +PEEP Spontaneous SIMV IMV Controlled MV Assisted-pressure support Assist control

  23. One of the key goals of mechanical ventilation is to decrease work of breathing • Improper ventilator settings can however increase work of breathing, increasing patient distress and worsening hemodynamics and metabolic parameters Kishore P. Critical Care Conference

  24. Remember • Ventilation is not an end in itself, it is only a form of organ support • The nuances of ventilation should not take away from the primary goal of treating the underlying condition Kishore P. Critical Care Conference

  25. Who’s Watching the Patient? Pierson, IN: Tobin, Principles and Practice of Critical Care Monitoring Kishore P.

  26. Default settings • TV-6-8ml/kg • Rate – 15/min • FiO2 – 100% • PEEP – 5cmH2O • Pressure support – 15cmH2O • Ti – 1.0 sec • Pramp – 50msec Kishore P. Critical care conference

  27. Monitor and re-adjust • FiO2- • based on PaO2 and SpO2. maintain PaO2 60-90mmHg • Aim to reduce FiO2 below 60% • PEEP- • based on PaO2 and SpO2. • Aim to reduce FiO2 below 60%. • Can increase rapidly but can be reduced very gradually Kishore P. Critical care conference

  28. Monitor and re-adjust • Rate – • To keep CO2 in normal range-30 to 50 mmHg • Exceptions: ↑ICP, acute phase of MACD • Pressure support – • Spontaneous breaths should have at least 80% of set TV • Tidal volume – • Adjust so that peak pressure < 30cm H2O • Ti – • clinical and graphical synchrony • Pramp – • increase only in obstructed airways Kishore P. Critical care conference

  29. Adjuncts • Tracheobronchial hygiene • Sedation and analgesia • Stress ulcer prophylaxis • DVT prophylaxis • Eye care Kishore P. Critical care conference

  30. Considerations while buying a new ventilator • Advanced modes are expensive-do you really need them • Must have NIV • Cost must include humidifier, nebulizer, compressor • Find out cost of replacables-flow sensors • Service back up • Try out for a week in the ICU-hands on • Bargain, bargain, bargain.. Kishore P. Critical care conference

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