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Respiratory Mechanics

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Respiratory Mechanics

  1. 1. Airway Graphic Analysis to Optimize Patient-Ventilator Interactions Ira M. Cheifetz, MD, FCCM, FAARC Professor of Pediatrics Chief, Pediatric Critical Care Medical Director, Pediatric ICU Duke Children’s Hospital
  2. 2. Case Scenario ♦ 5 mo (former 27 wk gestation) with CLD admitted with RAD exacerbation & viral pneumonia. ♦ Intubated shortly after admission for impending resp failure. ♦ PC/PS: RR 28, PIP 28, PEEP 7, PS 12 ♦ Sedated with infusions of midazolam & fentanyl. ♦ Infant experiences an acute episode of tachypnea, subcostal retractions, and agitation.
  3. 3. Case Scenario Time-based capnogram & airway scalars (pressure vs. time and flow vs. time) are:
  4. 4. Case Scenario The patient’s acute change in clinical status is most consistent with: a.) worsening bronchospasm b.) pain c.) flow asynchrony d.) trigger insensitivity e.) air trapping
  5. 5. Goal: Airway Graphic Analysis ♦ Optimize mechanical ventilation by diagnosing and correcting abnormalities in the interaction between the patient and the ventilator.
  6. 6. Airway Scalars Paw (cm H2O) Flow (L/min) Vt (ml)
  7. 7. Airway Loops Flow - Volume Pressure - Volume
  8. 8. Patient - Ventilator Interactions ♦ Facilitate spontaneous breathing ♦ Optimize patient WOB ♦ Maximize pt-ventilator synchrony – inspiratory synchrony – expiratory synchrony
  9. 9. Patient - Ventilator Interactions ♦ Inspiratory synchrony –flow synchrony –trigger synchrony –ETT effects / airleak –avoid overdistention ♦ Expiratory synchrony
  10. 10. Flow Synchrony ♦ Flow synchrony is defined as the ideal matching of inspiratory flow of a ventilator breath to the pt's inspiratory demand during assisted or supported ventilation. ♦ Asynchrony: Inadequate inspiratory flow at any point during inspiration causing an increased or irregular pt effort. – leads to increased WOB – “fighting” the ventilator
  11. 11. Flow Asynchrony
  12. 12. Flow Asynchrony
  13. 13. Flow Asynchrony
  14. 14. Optimal Pt - Vent Synchrony ♦ Allows for optimal use of nutritional support – Slutsky, Chest, 1993 ♦ Decreases VILI in neonates – Rosen, Ped Pulm, 1993 ♦ Improves pt comfort and reduces work of breathing – Ramar, Respir Care Clin, 2005
  15. 15. Patient - Ventilator Synchrony ♦ Pt-vent synchrony should be optimized by assessing the pt - ventilator interface before administering sedation. ♦ Increased sedative use in the 1st 24 hrs of ventilation ↑ LOV in pediatric pts with ALI. – Randolph (PALISI Network), JAMA, 2002
  16. 16. Patient - Ventilator Interactions ♦ Inspiratory synchrony –flow synchrony –trigger synchrony –ETT effects / airleak –avoid overdistention ♦ Expiratory synchrony
  17. 17. Trigger Sensitivity ♦ Trigger sensitivity = pt effort required to initiate a ventilator assisted breath ♦ A determinate of pt effort required (WOB) ♦ What affects trigger sensitivity? – pressure vs. flow triggering – proximal vs. distal sensing – ETT leaks / size
  18. 18. Trigger Insensitivity
  19. 19. Trigger Insensitivity 15
  20. 20. Effects of ETT Leaks on Triggering ♦ Problem – ETT leak results in ↓ in airway pressure and/or flow – may be sensed as a patient effort ♦ Result – may initiate a ventilator assisted breath in the absence of a patient effort (“autocycling”)
  21. 21. Air Leak
  22. 22. Air Leak
  23. 23. Autocycling
  24. 24. Autocycling
  25. 25. Patient - Ventilator Interactions ♦ Inspiratory synchrony –flow synchrony –trigger synchrony –ETT effects / airleak –avoid overdistention ♦ Expiratory synchrony
  26. 26. Pulmonary Injury Sequence Froese, CCM, 1997 Froese, CCM, 1997 Two injury zones during mechanical ventilation
  27. 27. Overdistention An ↑ in airway pressure at the end of inspiration without a significant increase in delivered tidal volume – ‘beaking’ at the end of inspiration. C20 / Ctotal < 1.0
  28. 28. Airway Obstruction – Secretions
  29. 29. Airway Obstruction – Secretions
  30. 30. Inspiratory Synchrony Optimal inspiratory patient - ventilator synchrony is a function of: ♦inspiratory flow ♦trigger sensitivity ♦ETT effects ♦appropriate lung inflation
  31. 31. Patient - Ventilator Interactions ♦ Inspiratory synchrony ♦ Expiratory synchrony –end-expiratory lung volume –premature termination of exhalation & intrinsic PEEP –expiratory resistance
  32. 32. End-expiratory Lung Volume ♦ Lung volume prior to inspiration (FRC) ♦ A function of total PEEP and lung compliance Froese, CCM, 1997
  33. 33. End-expiratory Lung Volume ♦ If EELV is too low: – lung compliance ↓, Vt ↓, RR ↑ – may result in premature termination of exhalation & intrinsic PEEP – ↑ opening pressure may result in ↑ risk of barotrauma ♦ If EELV is too high: – pulmonary overdistention develops – ↑ risk of volutrauma
  34. 34. Optimize PEEP dynamic vs. static P-V curve
  35. 35. Patient - Ventilator Interactions ♦ Inspiratory synchrony ♦ Expiratory synchrony –end-expiratory lung volume –premature termination of exhalation & intrinsic PEEP –expiratory resistance
  36. 36. Premature Termination of Exhalation ♦ Failure of airway pressure, volume, & exp flow to return to baseline prior to the next vent assisted breath ♦ “Gas trapping” causes intrinsic PEEP
  37. 37. Intrinsic PEEP: Adverse Effects ♦ ↑ WOB ♦ ↑ mean intrathoracic pressure ♦ ↓ cardiac output ♦ ↓ trigger sensitivity ♦ ↓ Vt in pressure limited breath (set PIP) ♦ ↑ PIP in volume limited and pressure control (set ΔP) breaths
  38. 38. Intrinsic PEEP: Treatment ♦ No treatment ♦↑ expiratory time –↓ respiratory rate –↓ inspiratory time –flow cycling of the breath
  39. 39. Intrinsic PEEP
  40. 40. Intrinsic PEEP ♦ Reasons for intrinsic PEEP to occur: –inadequate I:E ratio –↑ respiratory rate –inspiration is time cycled & not responsive to changes in flow ♦ Goal:shorten inspiratory time while maintaining appropriate tidal volume
  41. 41. Patient - Ventilator Interactions ♦ Inspiratory synchrony ♦ Expiratory synchrony –end-expiratory lung volume –premature termination of exhalation & intrinsic PEEP –expiratory resistance
  42. 42. Increased Expiratory Resistance ♦ Obstruction to exhalation caused by: – airway obstruction – ETT occlusion – bronchospasm – blocked expiratory valve ♦ Prolonged expiratory phase causes: – ‘gas trapping’ – ↑ WOB – ↓ trigger sensitivity
  43. 43. Increased Expiratory Resistance
  44. 44. Increased Expiratory Resistance
  45. 45. Increased Expiratory Resistance
  46. 46. Expiratory Synchrony Optimal expiratory patient - ventilator synchrony is a function of: ♦ complete exhalation ♦ an ideal end-expiratory lung volume ♦ elimination of premature termination of exhalation & intrinsic PEEP ♦ minimal expiratory resistance
  47. 47. Airway Graphics to Optimize Patient - Ventilator Interactions ♦ Evaluate airway pressures & tidal volume ♦ Choose appropriate inspiratory flow ♦ Set trigger sensitivity appropriately ♦ Evaluate extent of air leaks ♦ Maintain adequate end-exp. lung volume ♦ Avoid intrinsic PEEP ♦ Minimize expiratory resistance
  48. 48. Case Scenario ♦ 5 mo (former 27 wk gestation) with CLD admitted with RAD exacerbation & viral pneumonia. ♦ Intubated shortly after admission for impending resp failure. ♦ PC/PS: RR 28, PIP 28, PEEP 7, PS 12 ♦ Sedated with infusions of midazolam & fentanyl. ♦ Infant experiences an acute episode of tachypnea, subcostal retractions, and agitation.
  49. 49. Case Scenario Time-based capnogram & airway scalars (pressure vs. time and flow vs. time) are:
  50. 50. Case Scenario The patient’s acute change in clinical status is most consistent with: a.) worsening bronchospasm b.) pain c.) flow asynchrony d.) trigger insensitivity e.) air trapping

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