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Mechanical Ventilation 101

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  1. Mechanical Ventilation 101 Dr Paul Healey ICU Fellow John Hunter Hospital Newcastle

  2. Outline • What is mechanical ventilation ? • History of mechanical ventilation. • Why do we mechanically ventilate patients ? • Modes of mechanical ventilation ? • Setting the ventilator • Trouble shooting ventilation • Refractory Hypoxaemia • When to extubate the patient ?

  3. Mechanical ventilation • Is a method to mechanically assist or replace spontaneous ventilation. • Is a supportive therapy. • Two main divisions of mechanical ventilation • Negative pressure ventilation • Positive pressure ventilation

  4. Polio epidemic – Copenhagen 1952

  5. Positive pressure ventilation

  6. Mechanical ventilation Positive pressure ventilation • Non-invasive ventilation (NIV) modes: • Continuous Positive Airways Pressure (CPAP) • Bi-level Positive Airways Pressure (BiPAP) • Invasive positive pressure ventilation (IPPV) modes: • Volume Control Ventilation (VCV) • Pressure Control Ventilation (PCV) • Pressure Support Ventilation (PSV)

  7. Case study • Mr CS – 75 year old male, weighs 80kg. • Background • IHD, Ex-smoker 20 years ago, Type II DM, AF. • Day 4 post Hartmans procedure for colorectal cancer, severe abdominal pain and fever. Anastamotic leak on CT scan. Commenced on IV Tazocin. • Taken to OT and had extensive washout of abdomen and stoma formed. Abdomen is closed. • Currently ventilated in OT on FiO2 50% PCV-VG 14 x 480mL, with PEEP of 6cmH2O. • Vital signs: HR 115, BP 110/50 on 0.2mcg/kg/min of Noradrenaline, SaO2 96%, temperature 38.8 degrees. • Last ABG: pH 7.32, PaO2 92mmHg, PaCO2 35mmHg, Lactate 2.2mmol/l and BE -5.3mmol/l • What is the reason for mechanically ventilating this patient ?? • What are the risks of mechanical ventilation ??

  8. Why do we mechanically ventilate patients ? • Indications for mechanical ventilation • Impaired level of consciousness • Potential airway compromise • Respiratory failure • Hypoxaemic • Hypercapnoeic • Work of breathing and fatigue • Cardiac failure

  9. Risks of mechanical ventilation 1. Respiratory Complications • Infection • Ventilator Associated Events • Ventilator Induced Lung Injury (VILI) • Barotrauma • Volutrauma • Atelectotrauma • Gas trapping and intrinsic PEEP • Oxygen toxicity 2. Non-respiratory complications • Haemodynamic compromise • Raised ICP • Reduced urine output

  10. Modes of ventilation

  11. Modes of invasive ventilation Nomenclature • Triggering – what initiates a breath • Ventilator • Patient • Inspiration • Volume • Pressure • Cycling – what determines change from inspiration to expiration • Volume • Time • Flow • Exhalation • Passive process due to lung elastic recoil

  12. Modes of ventilation • Classification based on patient triggering: 1. Mandatory ventilation modes 2. Spontaneous ventilation modes 3. Adaptive ventilation modes

  13. Modes of ventilation 1. Mandatory ventilation modes • Volume control ventilation (VCV) • Pressure control ventilation (PCV) • Synchronised Intermittent Mandatory Ventilation (SIMV)

  14. Ventilator waveforms

  15. Volume Control Ventilation

  16. Modes of ventilation 1. Mandatory modes • Volume control ventilation • All breaths given are the same preset volume • Advantages • Relatively simple to set • Guaranteed minute ventilation • Rests respiratory muscles • Disadvantages • Historically, no patient triggering • Ventilator-patient dysynchrony • Reduced lung compliance will result in increased pressures and potential barotrauma

  17. PCV

  18. Modes of ventilation 1. Mandatory modes • Pressure control ventilation • All breaths have same preset inspiratory pressure and time • Advantages • Simple to set • Avoids high inspiratory pressures • Rests respiratory muscles • Disadvantages • Historically, no patient triggering • Change in lung compliance results in change in tidal volumes • No guaranteed minute ventilation

  19. SIMV

  20. SIMV

  21. Modes of ventilation 1. Mandatory modes • SIMV - Mandatory VCV or PCV with triggered PSV • Advantages • Better patient-ventilator synchrony • Guaranteed minute ventilation • Allows patient triggering and possible weaning • Disadvantages - More complicated mode with multiple settings

  22. PSV

  23. Modes of ventilation 2. Spontaneous ventilation modes • Pressure support ventilation • Provides a set inspiratory and expiratory pressure during patient initiated breathing • Inspiration ends when inspiratory flow falls to a preset level (usually 25%) • Advantages • Maintains full spontaneous ventilation • Better ventilator-patient synchrony • Weaning mode of ventilation • Disadvantages • Historically no back-up ventilation • Changes in patient effort and lung compliance effect tidal volumes

  24. PRVC

  25. Mechanical ventilation 3. Adaptive ventilation modes • Assist • Pressure regulated volume control • PCV - VG

  26. Case study • Mr CS – 75 year old male, weighs 80kg. • Background • IHD, Ex-smoker 20 years ago, Type II DM, AF. • Day 4 post Hartmans procedure for colorectal cancer, severe abdominal pain and fever. Anastamotic leak on CT scan. Commenced on IV Tazocin. • Taken to OT and had extensive washout of abdomen and stoma formed. Abdomen is closed. • Currently ventilated in OT on FiO2 50% PCV-VG 14 x 480mL, with PEEP of 6cmH2O. • Vital signs: HR 115, BP 110/50 on 0.2mcg/kg/min of Noradrenaline, SaO2 96%, temperature 38.8 degrees. • Last ABG: pH 7.32, PaO2 82mmHg, PaCO2 35mmHg, Lactate 2.2mmol/l and BE -5.3mmol/l • How are you going to set the ventilator ?? • What other information would you want to know ??

  27. Setting the ventilator • FiO2 • Mode • Triggering • Tidal volume • Inspiratory pressure • PEEP • Respiratory rate • Inspiratory time • I:E ratio • Inspiratory flow • Alarm settings • Peak pressure • PEEP • Minute ventilation

  28. How to set a ventilator • FiO2 • Begin at 100% and wean as quickly as able to < 60% • Mode • Volume controlled ventilation • Set tidal volume 6 – 8 mL/kg • Pressure controlled ventilation • Set inspiratory pressure 10 – 20 cmH2O • Triggering • Flow triggering : 1 – 5 L/min • Pressure triggering: -0.5 to -2.0 cmH2o • Inspiratory pressure (Plateau) • Aim < 30 cmH2O. • VCV or SIMV = plateau pressure • PCV = Sum of PEEP and Inspiratory pressure • PEEP • Start with 5-10 cmH20 • Respiratory rate • Start at 10 – 12 breaths per minute • Inspiratory time • Normal 0.8 – 1.3 seconds • I:E ratio • Normally 1:2 • Increase in obstructive airways disease (COPD/Asthma) • Inspiratory flow • 40 – 60 L/min

  29. Case study • Mr CS – 75 year old male, weighs 80kg. • Background • IHD, Ex-smoker 20 years ago, Type II DM, AF. • Day 4 post Hartmans procedure for colorectal cancer, severe abdominal pain and fever. Anastamotic leak on CT scan. Commenced on IV Tazocin. • Taken to OT and had extensive washout of abdomen and stoma formed. Abdomen is closed. • Currently ventilated in OT on FiO2 50% PCV-VG 14 x 480mL, with PEEP of 6cmH2O. • Vital signs: HR 115, BP 110/50 on 0.2mcg/kg/min of Noradrenaline, SaO2 96%, temperature 38.8 degrees. • Last ABG: pH 7.32, PaO2 82mmHg, PaCO2 35mmHg, Lactate 2.2mmol/l and BE -5.3mmol/l • How are you going to set the ventilator ?? • What other information would you want to know ??

  30. Setting the ventilator • FiO2 • Mode • Triggering • Tidal volume • Inspiratory pressure • PEEP • Respiratory rate • Inspiratory time • I:E ratio • Inspiratory flow • Alarm settings • Peak pressure • PEEP • Minute ventilation

  31. What is the evidence ??

  32. Ventilation modes - evidence • A single RCT and 3 observational trials • There were no statistically significant differences in mortality, oxygenation, or work of breathing • PCV • lower peak airway pressures • a more homogeneous gas distribution (less regional alveolar over distension) • improved patient-ventilator synchrony • earlier liberation from mechanical ventilation than volume-limited ventilation • VCV • it can guarantee a constant tidal volume, ensuring a minimum minute ventilation

  33. Evidence for ventilation

  34. Evidence for ventilation

  35. Evidence for ventilation –FACCT trial