High Frequency Ventillation

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High Frequency Ventillation

  1. 1. Pediatric High Frequency Ventilation: A Clinical Approach Ira M. Cheifetz, MD, FCCM, FAARC Professor of Pediatrics Chief, Pediatric Critical Care Medicine Medical Director, PICU Duke Children’s Hospital
  2. 2. Pediatric ALI and ARDS ♦ HFOV: Arnold study (Crit Care Med, 1994) but control group was pre-ARDS pre-ARDS Network study (i.e., large tidal volume) ♦ HFJV: No data ♦ So, why use HFV in pediatrics? physiology – – pathophysiology – clinical experience
  3. 3. High Frequency Ventilation: A Clinical Approach ♦ Pediatric ALI / ARDS ♦ HFV: Physics and Physiology – HFOV – HFJV ♦ Why? When?
  4. 4. Ventilator Induced Lung Injury Fu, JAP, 1992.
  5. 5. Ventilator Induced Lung Injury Rodents ventilated with three modes: – High Pressure (45 cmH2O), High Volume – Low Pressure (negative pressure ventilator), High Volume – High Pressure (45 cmH2O), Low Volume (strapped chest and abdomen) Dreyfuss, ARRD, 1988.
  6. 6. Ventilator Induced Lung Injury 1.2 1.2 Dry Lung Weight 1 1 HiP-HiV * 0.8 0.8 (ml/kg) LoP-HiV 0.6 0.6 HiP-LoV 0.4 0.4 0.2 0.2 0 0 Dreyfuss, ARRD, 1988.
  7. 7. ARDS: Principles of Management ♦ Maintain a ‘safe’ level of oxygenation ‘safe’ ♦ Maintain adequate O2 delivery O2 – avoid anaerobic metabolism – avoid metabolic acidosis – assess end organ function – monitor ABGs, lactates, MVO2 MVO2 ♦ Prevent 2° complications due to hyperoxia, 2° barotrauma, volutrauma, & biotrauma
  8. 8. High Frequency Ventilation: A Clinical Approach ♦ Pediatric ALI / ARDS ♦ HFV: Physics and Physiology – HFOV – HFJV ♦ Which? Why? When?
  9. 9. HFV: Definition ♦ Tidal volume < dead space volume ♦ Frequency > 150 bpm
  10. 10. CMV vs. HFV CMV HFV rates 0 - 150 150 - 900 tidal vol (ml/kg) 4 - 12 0.1 - 3 0 → 50 alveolar press. 0.1 - 5 (cm H2O)
  11. 11. PIPvent HFV PIPalv MAPalv ΔPvent ΔPalv MAPvent PEEPalv PEEPvent
  12. 12. ARDS ‘Infant’ lung sitting on consolidated lung: ♦ VT of 6 - 10 ml/kg based T on weight ♦ VT may be > 20 ml/kg T based on open lung units
  13. 13. Pulmonary Injury Sequence Froese A, Crit Care Med, 1997 Two injury zones during mechanical ventilation: low lung volume ♦ ventilation tears adhesive surfaces ♦ high lung volume ventilation over- distends resulting in volutrauma
  14. 14. HFV Goals ♦ Establish & maintain adequate FRC normalize lung architecture – improve compliance – – reduced PVR – improve gas exchange ♦ Provide an adequate minute volume while minimizing regional lung over- distension.
  15. 15. Optimizing HFV General Guidelines: ♦ Have a clear concept of how HFV works. ♦ Know determinants of ventilation and oxygenation with your HFV device(s). ♦ Recognize ‘benefits’ of certain strategies vs. ‘risks’ of complications. ♦ Match ventilator strategy to patient’s predominant pathophysiology. ♦ Be prepared to adjust strategy as patient's condition changes.
  16. 16. Reducing the Volume-Cost of Ventilation Each point represents the VT that yielded PCO2 = 40 torr. 2 12 10 Tidal Volume (ml/kg) CMV 8 6 4 HFV anatomic deadspace 2 0 30 60 90 120 180 240 300 360 420 480 540 600 Freq (bpm) Bunnell et al. Am Rev Resp Dis. 1978;117(Part 2):289.
  17. 17. ∆P is key to controlling PaCO2 ∆P = PIP – PEEP ∆P VT X VCO2 ≈ f x VT For HFV, X = 1.5-2.5
  18. 18. High Frequency Ventilation: A Clinical Approach ♦ Pediatric ALI / ARDS ♦ HFV: Physics and Physiology – HFOV – HFJV ♦ Why? When?
  19. 19. HFOV ♦ Tidal volume < dead space volume ♦ Frequency = 180 - 900 bpm (3 - 15 Hz) ♦ Piston displacement of gas ♦ Active, intermittent exhalation
  20. 20. HFOV Approved in 1991 for neonatal resp failure ♦ – approved for ‘early intervention’ – not classified as a ‘rescue device’ ♦ Approved in 1995 for peds resp failure – no ‘weight limit’ – for selected patients failing CMV (OI > 13 on 2 consecutive ABGs in 6 hrs) ♦ Approved in 2001 for adult ARDS pts – 3100B approved for pts > 35 kg
  21. 21. Ventilator Induced Lung Injury Control animal histology Sugiura, JAP, 1994.
  22. 22. Ventilator Induced Lung Injury CMV animal histology Sugiura, JAP, 1994.
  23. 23. Ventilator Induced Lung Injury HFOV animal histology Sugiura, JAP, 1994.
  24. 24. HFOV: Neonatal Clinical Data RCTs of the 3100A have demonstrated: – ↓ severity of CLD in RDS infants – ↓ cost of hospitalization for RDS – ↓ need for ECMO in eligible candidates – ↓ air leak in severe RDS
  25. 25. Pediatric Clinical Data HFOV 83% survive 11% survive 6% mortality w/o CLD w/ CLD CMV 30% survive 30% survive 40% mortality w/o CLD w/ CLD Arnold, Crit Care Med, 1994
  26. 26. Pediatric Randomized Controlled Trial Arnold, Crit Care Med, 1994
  27. 27. Adult ARDS and HFOV 30 Day Mortality p HFOV CMV % Difference 37% 52% 29% 0.098 MOAT Trial, Am J Respir Crit Care Med, 2002.
  28. 28. Predictors of Outcome: MOAT2 OI = (Paw x FiO2 x 100) / PaO2 2 2 ♦ OI at 16 hrs was the only significant predictor of mortality in a stepwise logistic regression analysis. ♦ OI 15 at 16 hrs → 35% mortality ♦ OI 25 at 16 hrs → 55% mortality MOAT Trial, Am J Respir Crit Care Med, 2002.
  29. 29. Conclusions: MOAT2 ♦ HFOV for treatment of severe ARDS has a 90% predictive value for reducing mortality by 29%. ♦ Trend in ↓ mortality (20%) is recognizable at 6 mos. ♦ Benefits related to chronic lung changes may exist as reflected by the small but extended use of respiratory support in the CMV group. MOAT Trial, Am J Respir Crit Care Med, 2002.
  30. 30. Experience & Data Suggest ♦ Inverse relationship between prior days of CMV & ability to ventilate ♦ > 72 hrs of CMV raised odds of CLD by 25 fold ♦ > 10 days of CMV ↑ risk for mortality ♦ OI > 42 at 48 hours ↑ risk for mortality Arnold, Crit Care Med, 1994. MOAT Trial, Am J Respir Crit Care Med, 2002.
  31. 31. HFOV: Clinical Indications ♦ ALI / ARDS – all ages / weights – OI > 13 on two consecutive ABGs within 6 hours – ‘excessive’ PIP ♦ Air leak syndrome
  32. 32. HFOV: Gas Exchange ♦ Oxygenation and ventilation are decoupled. ♦ PaO2 → Paw and FiO2 PaO2 FiO2 ♦ PaCO2 → amplitude and frequency PaCO2 ♦ Minor exception – % inspiratory time
  33. 33. General Approach to Peds ALI ♦ Rate: based on pt weight and anticipated resonant frequency of the lung.
  34. 34. Tidal Volume Delivery Chest Wall Plethysmography 2.5 2.5 chest excursion chest excursion 2 2 60% He 1.5 1.5 1 1 O2/N2 22 0.5 0.5 0 0 2 4 6 8 10 12 14 16 2 4 6 8 10 12 14 16 Hz Hz
  35. 35. General Approach to Peds ALI ♦ Rate: based on pt weight and anticipated resonant frequency of the lung. ♦ Paw: titrate to ideal lung volume and, thus, optimal oxygenation. ♦ Amplitude: titrate for desired ventilation; permissive hypercapnia. ♦ % inspiratory time: generally 33%
  36. 36. A Clinical Caution…. If amplitude is ≥ 3 times Paw, PEEP generated by HFOV is ≤ 0. Paw Amp Hz PEEP 15 50 5 0 15 50 6 0 15 50 7 0 Bass et al; in progress.
  37. 37. High Frequency Ventilation: A Clinical Approach ♦ Pediatric ALI / ARDS ♦ HFV: Physics and Physiology – HFOV – HFJV ♦ Why? When?
  38. 38. HFJV ♦ Tidal volume < dead space volume ♦ Frequency = 240 - 480 bpm ♦ ‘Jet’ pulse of gas ♦ Passive, continuous exhalation ♦ FDA approved in 1988
  39. 39. Flow Streaming Reduces Effective Dead Space Inspired gas jets into the airways at high velocity but low pressure. CO 2 CO2 Gas swirls down the airways, splitting at bifurcations, seeking path of least resistance in the center of the airways. The train of tiny tidal volume pockets moves high pO2 gas close to alveoli, while CO2 is compressed against airway walls.
  40. 40. Exhalation During HFJV CO 2 Exhaled gas swirls out CO 2 CO 2 around the incoming gas, CO 2 sweeping the CO2-rich CO2 deadspace gas out along the airway walls. CO 2 This action may help remove excess secretions and debris.
  41. 41. HFJV: Clinical Indications ♦ Neonatal lung injury and air leak syndrome – FDA approved ♦ Peds ALI / ARDS – not FDA approved ♦ Need for improved CO2 elimination CO2 – ALI + bronchospasm (i.e. bronchiolitis + pneumonitis) – ALI with significant pulm hypertension – RV dysfunction / passive pulm blood flow ♦ Note: weight limitation – based on pathophys
  42. 42. Proximal Air Leak Courtesy of Dave Platt, Bunnell Inc.
  43. 43. High Frequency Ventilation: A Clinical Approach ♦ Pediatric ALI / ARDS ♦ HFV: Physics and Physiology – HFOV – HFJV ♦ Why? When?
  44. 44. HFOV ♦ Advantages ability to generate high mean pressures while – limiting peak pressures works for all size and age pts (3100 A / B) – FDA approved for peds ALI / ARDS – air leak syndrome – ♦ Disadvantages less efficient exhalation: intermittent, active – increased need for sedation and NMB – no indication of VT delivery or lung volume – T
  45. 45. Pediatric Options for HFV Early intervention vs. Rescue therapy Why wait to start HFV??
  46. 46. Pediatric HFV ♦ HFV is capable of recruiting & protecting ♦ the acutely injured lung presumably better than CMV. ♦ Time to intervention is a critical factor in ♦ determining the outcome of patients managed with HFV.
  47. 47. Optimizing HFV General Guidelines: ♦ Have a clear concept of how HFV works. ♦ Know determinants of ‘ventilation’ and oxygenation with your HFV device(s). ♦ Recognize ‘benefits’ of certain settings vs. ‘risks’ of complications. ♦ Match ventilator strategy to patient’s predominant pathophysiology. ♦ Be prepared to adjust strategy as patient condition changes.
  48. 48. Pediatric ALI and ARDS ♦ HFV: Why use it? – Physiology, pathophysiology, clinical experience, and some data. ♦ CMV Modes: – No data support any mode over another. – Literature does support low tidal volume ventilation. (ARDS Network, NEJM, 2000) – HFV is the ultimate in low tidal volume ventilation.

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