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  • In SIMV mode the ventilator allows two kinds of breath. The first is delivered according to the preset waveform and is the “mandatory breath”. The timing of the start of this breath may be triggered by the patient’s respiratory effort but, if the patient is not making sufficient respiratory effort, is determined by the ventilator. The second is a spontaneous breath. If SIMV is combined with pressure support then the ventilator facilitates this second breath by providing pressure support. This second type of breath is entirely dependent on patient effort. <br /> The graphs illustrate the changes in pressure and flow that occur with first a mandatory breath and then a pressure-supported breath <br />
  • This slide illustrates the breath to breath variation in the duration of time that the pressure support is provided for and the variable inspiratory flow rates. The latter will depend on the degree of patient effort. <br />
  • A great variety of ventilatory modes exist and the number of modes is ever increasing. Clearly it is not possible to cover all these modes in one lecture and therefore I will concentrate on the four modes available on the Servo 900C ventilator, a ventilator that is widely used in intensive care <br />

Icu intro resp Presentation Transcript

  • 1. Absolute Basics of Mechanical Ventilation Dr David Howell Consultant in Intensive Care, Respiratory and Acute Medicine
  • 2. Aims and Objectives • Define Positive Pressure Mechanical Ventilation • Explain Continuous Mandatory Ventilation (CMV) • Explain Synchronised Mandatory Ventilation (SIMV) • Explain Pressure Support Ventilation (PSV) • Explain Basic Ventilator Settings • Not a Talk on Physiology of Mechanical Ventilation
  • 3. What you Encounter
  • 4. Positive Pressure Mechanical Ventilator
  • 5. Lots of Monitors and Knobs to Turn
  • 6. Some are More Complicated than Others
  • 7. Invasive support Advanced Ventilation Tracheostomy Prone Position Nitric Oxide Weaning Standard Ventilation Optimising the Pt for weaning Suctioning Long Term Weaning/Individual plan Weaning Screen/standard protocol Intubation Humidification Wake, Warm & Wean Non-Invasive Ventilation Oxygen Therapy Mask CPAP Non-invasive support Extubation Decannulation
  • 8. NIV vs. Invasive Mechanical Ventilation • NIV is defined as ventilatory support provided via a tight fitting mask or similar interface as opposed to invasive support, which is provided via a laryngeal mask, endotracheal tube or tracheostomy tube. • Tight fitting masks deliver can CPAP, BIPAP or NIV via the mechanical ventilator.
  • 9. Indications for Mechanical Ventilation • The work of breathing usually accounts for 5% of oxygen consumption (V02). • In the critically ill patient this may rise to 30%. • Invasive mechanical ventilation eliminates the metabolic cost of breathing.
  • 10. Indications for Mechanical Ventilation • Inadequate oxygenation (not corrected by supplemental O2 by mask). • Inadequate ventilation (increased PaCO2). • Retention of pulmonary secretions (bronchial toilet). • Airway protection (obtunded patient, depressed gag reflex).
  • 11. Intubation
  • 12. Bare Essentials for Intubation ALSOBLEED 1 Airway: oral Guedel airway to lift tongue off posterior pharynx to facilitate mask ventilation during pre-intubation phase. 2 Liquids: stop feed and aspirate ng tube. 3 Suction: extremely important to avoid pulmonary aspiration. 4 Oxygen: preoxygenate patient and ensure a source of O2 with a delivery mechanism (ambu-bag and mask) is available.
  • 13. Bare Essentials for Intubation ALSOBLEED 5 Bougie: to facilitate tube insertion in more difficult airway. 6 Laryngoscope: have a long and short blade available. 7 Endotracheal tube: for average adult, cuffed oral endotracheal tube 7.0 for women and 8.0 for men. 8 End tidal CO2: to confirm correct position of tube. 9 Drugs: an induction agent, muscle relaxant, sedative are usually required.
  • 14. Principles of Mechanical Ventilation PEEP ET tube Ventilator Tubing Major Airways Alveoli
  • 15. Principles of Mechanical Ventilation • Positive pressure ventilation involves delivering a mechanically generated ‘breath’ to get O2 in and CO2 out. • Gas is pumped in during inspiration (Ti) and the patient passively expires during expiration (Te). • The sum of Ti and Te is the respiratory cycle or ‘breath’.
  • 16. Flow Pressure Principles of Mechanical Ventilation Ti Te Ti Te
  • 17. Principles of Mechanical Ventilation • In the fully ventilated patient, positive pressure breaths are delivered either as preset volume or pressure continuous mandatory breaths (CMV) breaths. • The mechanical ventilator triggers the breath and switches from inspiration to expiration when the preset volume, pressure (or time) is achieved/delivered. • During CMV the patient takes no spontaneous breaths. • CMV is usually used in theatre and in very unwell ICU patients.
  • 18. Principles of Mechanical Ventilation Volume control Pressure control • Tidal volume is preset • Inspiratory Pressure is preset • Usually 500 mls • Usually 15-20 cm H20 • Airway Pressure is Variable • Tidal Volume is Variable
  • 19. Principles of Mechanical Ventilation • Mandatory breaths are delivered during inspiration, to generate a tidal volume (Vt), at a set rate (f), the quotient of which is the minute volume (MV). • Minute Volume = Tidal Volume x frequency • In volume control ventilation, an inspiratory flow rate is also set. • The ratio of the time spent in inspiration:expiration (I:E ratio) is usually 1:2.
  • 20. Principles of Mechanical Ventilation Pressure Control Breath Flow Pressure Volume Control Breath Ti Te Ti Te
  • 21. Principles of Mechanical Ventilation • Mechanically ventilated patients usually receive positive end-expiratory pressure (PEEP), to overcome the loss of physiological PEEP provided by the larynx and vocal cords. • PEEP is delivered throughout the respiratory cycle and is synonymous to CPAP, but in the intubated patient. • Standard PEEP setting is 5 cm H20. • Sedation is often required to prevent ventilator-patient asynchrony.
  • 22. Basic Settings on the Ventilator • Tidal Volume Pressure controlled breath (15-20 cm H20) Volume controlled breath (500 mls) • Rate (frequency) (10-12 breaths/minute) • Positive end expiratory pressure (PEEP) (5 cm H20) • FiO2 (0.21-1) • Peak airway pressure (PAP)
  • 23. Principles of Mechanical Ventilation • Why is the peak airway pressure (PAP) important? • Ventilator Induced Lung Injury (VILI). • Mechanical ventilation is injurious to the lung. • Aim PAP< 35 cm H20.
  • 24. Principles of Mechanical Ventilation Volume Breath Pressure Breath Flow Pressure 35 cm H20 Ti Te Ti Te
  • 25. Pneumothorax
  • 26. Principles of Mechanical Ventilation Don’t forget that the peak airway pressure will also include the PEEP that is added
  • 27. Principles of Mechanical Ventilation • Once stabilised on CMV, the level of ventilatory support may be reduced (weaning). • This can be done by providing a mixture of synchronised intermittent mandatory breaths (SIMV) and spontaneously triggered pressure supported breaths (PSV).
  • 28. Principles of Mechanical Ventilation • Ventilator assisted breaths are synchronized with the patient’s breathing to prevent the possibility of a mechanical breath on top of a spontaneous breath. • However, the patient’s attempt at a breath would not be enough to generate an adequate tidal volume on its own, hence the term ‘pressure support’.
  • 29. Principles of Mechanical Ventilation • Pressure support is only delivered during inspiration and the patient’s attempt at breathing triggers the breath rather than the ventilator. • A standard level of pressure support delivered in inspiration is 20 cm H20
  • 30. SIMV and Pressure Support Ventilation Ventilator Patient
  • 31. Principles of Mechanical Ventilation • As patients improve, mandatory breaths are withdrawn and receive pressure-supported breaths alone. • Finally, as tidal volumes improve, the level of pressure support is reduced and then withdrawn so patients breathe spontaneously with PEEP alone. • Extubation can now be contemplated. • Spontaneous modes of breathing should always be encouraged as respiratory muscle function is maintained
  • 32. Pressure Support Ventilation Patient Patient
  • 33. Successful Weaning and Extubation • To succeed, the initiating cause of respiratory failure, sepsis, fluid and electrolyte imbalance and nutritional status should all be treated or optimised. • Failure to wean is associated with: • Ongoing high V02. • Muscle fatigue. • Inadequate drive. • Inadequate cardiac reserve.
  • 34. Successful Weaning and Extubation • Weaning screens exist to help select patients for extubation. • In the unsupported patient, if f/Vt is >100, extubation is likely to be unsuccessful. • There is some evidence to support extubation to NIV, particularly in patients with COPD.
  • 35. Basic Ventilatory Modes: Summary • Continuous Mandatory Ventilation (CMV) Pressure control Volume control No spontaneous breathing Ventilator triggers breath • Synchronised intermittent mandatory ventilation (SIMV)/Pressure Support Ventilation (PSV) Pressure control (SIMV) Volume control (SIMV) Some spontaneous breathing is allowed (PSV) Mixture of ventilator and patient triggered breaths
  • 36. Basic Ventilatory Modes: Summary • Pressure Support Ventilation (PSV) Spontaneous breathing with inspiratory support All patient triggered breaths • PEEP/CPAP (5 cm H20) Entirely spontaneous breathing Consider extubation
  • 37. Basic Ventilatory Modes: Summary CMV PSV PEEP SIMV PSV Mandatory Overlap Spontaneous
  • 38. Standard Ventilator Settings MORITE Mode O2 Respiratory Rate Inspiratory Action Inspiratory Time Expiratory Action
  • 39. Standard Ventilator Settings MORITE Mode CMV, Volume Control O2 0.5 (50% 02) Respiratory Rate 12/minute Inspiratory Action Set Vt at 500 mls Inspiratory Time Set I:E ratio 1:2 Expiratory Action Set PEEP at 5 cm H20 Be Aware PAP ≤35 cm H2O
  • 40. Spontaneously Ventilating Patient Failing Conventional Therapy Consider CPAP on Ward Optimise NIV on ICU BIPAP Patient Position Humidification BIPAP on Ward Patient Requiring Basic Invasive Mechanical Ventilation CMV (VCV or PCV) Escalation IMV (VCV or PCV) PSV PEEP/CPAP De-escalation