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Respiratory Mechanics
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Respiratory Mechanics

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    Respiratory Mechanics Respiratory Mechanics Presentation Transcript

    • 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
    • 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.
    • Case Scenario Time-based capnogram & airway scalars (pressure vs. time and flow vs. time) are:
    • 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
    • Goal: Airway Graphic Analysis ♦ Optimize mechanical ventilation by diagnosing and correcting abnormalities in the interaction between the patient and the ventilator.
    • Airway Scalars Paw (cm H2O) Flow (L/min) Vt (ml)
    • Airway Loops Flow - Volume Pressure - Volume
    • Patient - Ventilator Interactions ♦ Facilitate spontaneous breathing ♦ Optimize patient WOB ♦ Maximize pt-ventilator synchrony – inspiratory synchrony – expiratory synchrony
    • Patient - Ventilator Interactions ♦ Inspiratory synchrony –flow synchrony –trigger synchrony –ETT effects / airleak –avoid overdistention ♦ Expiratory synchrony
    • 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
    • Flow Asynchrony
    • Flow Asynchrony
    • Flow Asynchrony
    • 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
    • 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
    • Patient - Ventilator Interactions ♦ Inspiratory synchrony –flow synchrony –trigger synchrony –ETT effects / airleak –avoid overdistention ♦ Expiratory synchrony
    • 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
    • Trigger Insensitivity
    • Trigger Insensitivity 15
    • 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”)
    • Air Leak
    • Air Leak
    • Autocycling
    • Autocycling
    • Patient - Ventilator Interactions ♦ Inspiratory synchrony –flow synchrony –trigger synchrony –ETT effects / airleak –avoid overdistention ♦ Expiratory synchrony
    • Pulmonary Injury Sequence Froese, CCM, 1997 Froese, CCM, 1997 Two injury zones during mechanical ventilation
    • 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
    • Airway Obstruction – Secretions
    • Airway Obstruction – Secretions
    • Inspiratory Synchrony Optimal inspiratory patient - ventilator synchrony is a function of: ♦inspiratory flow ♦trigger sensitivity ♦ETT effects ♦appropriate lung inflation
    • Patient - Ventilator Interactions ♦ Inspiratory synchrony ♦ Expiratory synchrony –end-expiratory lung volume –premature termination of exhalation & intrinsic PEEP –expiratory resistance
    • End-expiratory Lung Volume ♦ Lung volume prior to inspiration (FRC) ♦ A function of total PEEP and lung compliance Froese, CCM, 1997
    • 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
    • Optimize PEEP dynamic vs. static P-V curve
    • Patient - Ventilator Interactions ♦ Inspiratory synchrony ♦ Expiratory synchrony –end-expiratory lung volume –premature termination of exhalation & intrinsic PEEP –expiratory resistance
    • 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
    • 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
    • Intrinsic PEEP: Treatment ♦ No treatment ♦↑ expiratory time –↓ respiratory rate –↓ inspiratory time –flow cycling of the breath
    • Intrinsic PEEP
    • 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
    • Patient - Ventilator Interactions ♦ Inspiratory synchrony ♦ Expiratory synchrony –end-expiratory lung volume –premature termination of exhalation & intrinsic PEEP –expiratory resistance
    • 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
    • Increased Expiratory Resistance
    • Increased Expiratory Resistance
    • Increased Expiratory Resistance
    • 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
    • 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
    • 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.
    • Case Scenario Time-based capnogram & airway scalars (pressure vs. time and flow vs. time) are:
    • 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