High Frequency Oscillatory Ventilation


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High Frequency Oscillatory Ventilation

  1. 1. High Frequency Oscillatory Ventilation<br />PeteyLaohaburanakit, MD, FCCP<br />Critical Care Services<br />Rogue Valley Medical Center<br />
  2. 2. Outline<br />What is HFOV? <br />Ventilator-induced lung injury (VILI)<br />How does HFOV work?<br />Basic concept and gas exchange<br />Oxygenation and ventilation in HFOV<br />Clinical studies<br />Initiation and adjustment<br />Care for patients on HFOV<br />Potential complications<br />
  3. 3. What is HFOV?<br />Not to be confused with high frequency jet ventilation (HFJV), which is rarely used<br />First established use in neonatal ARDS<br />HFOV’s claim to fame is reduction of ventilator-induced lung injury (VILI)<br />
  4. 4.
  5. 5. What is VILI?<br />Two major causes<br />Alveolar distension<br />High plateau pressure<br />Cyclical opening and closing of atelectatic lung<br />Large pressure swing at the alveolar level from large tidal volumes<br />
  6. 6.  V<br /> P<br /> V<br /> P<br /> V<br /> P<br />
  7. 7. Zoneof<br />Overdistension<br />Injury<br />“Safe”<br />Window<br />Volume<br />Zone of<br />Derecruitment<br />and Atelectasis<br />Injury<br />Pressure<br />
  8. 8. Injury<br />Injury<br />
  9. 9.
  10. 10. How does HFOV work?<br />The piston oscillates the lung around a constant mean airway pressure with high frequency<br />The mean airway pressure (Pmaw) is almost always higher than conventional ventilation<br />Small tidal volume with less pressure swing reduces VILI<br />One way to look at it – CPAP with rapid oscillation<br />
  11. 11. CDP<br />“Continuous <br />Distending<br />Pressure”<br />Adjust Valve <br />ET Tube<br />Oscillator<br />Patient<br />BIAS Flow<br />
  12. 12. Pressures at alveolar level<br />
  13. 13.
  14. 14. Gas exchange in HFOV<br />Direct bulk flow<br />Longitudinal (Taylor) dispersion<br />Pendeluft<br />Asymmetric velocity profiles<br />Cardiogenic mixing<br />Molecular diffusion<br />
  15. 15. HFOV and CMV<br />
  16. 16. Decoupling of Ventilation and Oxygenation<br />Controls for oxygenation<br />Pmaw<br />FiO2<br />Alveolar recruitment maneuver<br />Controls for ventilation<br />Amplitude (DP)<br />Hertz<br />Inspiratory time<br />Cuff deflation<br />Permissive hypercapnia<br />
  17. 17.
  18. 18. Oxygenation<br />Primarily controlled by mean airway pressure (Pmaw)<br />Pmaw is a constant pressure used to inflate the lung and hold the alveoli open<br />Since the Pmaw is constant, it reduces the injury that results from cycling the lung open for each breath<br />
  19. 19. x<br />Bias Flow<br />CDP Control Balloon<br />
  20. 20. Ventilation<br />Controlled by the movement of pump/piston mechanism<br />Alveolar ventilation during CMV is defined as f x Vt<br />Alveolar ventilation during HFOV is defined as f x Vt2<br />Changes in volume delivery have the most significant effect on ventilation<br />
  21. 21.
  22. 22.
  23. 23. Regulation of stroke volume<br />The stroke volume will increase if<br />The amplitude increases (higher DP)<br />The frequency decreased (longer cycle time)<br />There is an increase in inspiratory time <br />
  24. 24. Amplitude (DP)<br />The force created by piston movement<br />Dependent on the power setting<br />Results in chest wiggle<br />
  25. 25.
  26. 26. Inspiratory time<br />Controls the time for movement of the piston<br />Increases inspiratory time increases CO2 elimination<br />Increases inspiratory time increases delivered Pmaw<br />
  27. 27.
  28. 28. PaO2<br />PaCO2<br />
  29. 29. Clinical Data<br />Pilot studies<br />Mehta S et al. Crit Care Med 2001<br />Derdak S et al. Am J RespirCrit Care Med 2002<br />Multicenter oscillatory ventilation for ARDS trial (MOAT)<br />OSCILLATE – Canadian clinical trials group<br />
  30. 30. Pilot Studies<br />HFOV was as effective as CMV for ARDS<br />HFOV patients reached oxygenation goals earlier<br />Early implementation was associated with better outcomes<br />CMV groups were not ventilated with ARDS Network protocol*<br />
  31. 31. MOAT Study - Design<br />13 university-affiliated medical centers, recruitment 1997-2000<br />Eligibility: <br />age &gt;= 16 on mechanical ventilation<br />PaO2/FiO2 &lt; 200 while on PEEP &gt;= 10<br />Bilateral pulmonary infiltrates on CXR<br />No evidence of left atrialhypertension<br />
  32. 32. MOAT Study - Design<br />Exclusion:<br />Weight &lt; 35 Kg<br />Severe COPD or asthma<br />Intractable shock<br />Severe airleak<br />Nonpulmonary terminal diagnosis<br />FiO2 &gt; 0.80 for more than 2 days<br />
  33. 33. MOAT Study - Results<br />N=148<br />Mean age 50<br />APACHE II score 22<br />PaO2/FiO2 ratio 112<br />Oxygenation index (OI) 25<br />Mean duration on mechanical ventilation prior to HFOV 2.8 days<br />
  34. 34. MOAT Study -Results<br />A : Mean airway<br />pressure<br />B : P/F ratio<br />C : Oxygenation<br />Index<br />D : PaCO2<br />
  35. 35. MOAT Study - Results<br />
  36. 36. MOAT Study – OI for prognosis<br />
  37. 37. MOAT Study - Criticisms<br />Not powered to evaluate mortality (would need n=199)<br />Control group did not comply with ARDS Network standards<br />Higher Vt (8 ml/kg measured wt, 10.6 ml/kg ideal wt)<br />Peak Paw 38 cm H2O at 48 hours<br />
  38. 38. OSCILLATE Study<br />Canadian Clinical Trials Group<br />The OSCILLation in ARDS Treated Early<br />Goal N = 94<br />Completed in December 2008<br />
  39. 39. HFOV for ARDS<br />When to consider?<br />The earlier the better<br />FiO2 &gt;= 0.60, PEEP &gt;= 10 with P/F ratio &lt; 200<br />Plateau pressure &gt; 30<br />Oxygenation index (OI) &gt; 24<br />OI = (FiO2 x 100) x Pmaw / PaO2<br />Failed ARDS Net protocol<br />
  40. 40. Key to success<br />Patient selection<br />Timing of initiation<br />Early application provides protection and reduces risks of further lung damage<br />Rescue with HFOV may or may not improve mortality<br />The later HFOV is started the less chance of survival<br />
  41. 41. Initial settings<br />Recruitment maneuver<br />Pmaw 5 cmH2O above CMV Pmaw<br />FiO2 1.0<br />Frequency 5-6 Hertz<br />Power 40, adjust for good chest wiggle<br />Inspiratory time at 33%<br />Set bias flow at &gt; 25 lpm, go higher if needed<br />
  42. 42. Ventilator Strategies - Goals<br />Normalize lung volume<br />Minimize pressure change at alveolar level<br />Wean FiO2 to a safe level first<br />Physiological targets<br />SaO2 between 88% and 93%<br />Delay weaning Pmaw until FiO2 &lt; 0.5<br />pH &gt; 7.25<br />PaCO2 in the range of 45-70 mmHg<br />
  43. 43. Oxygenation Strategies<br />Initial Pmaw 5 cm &gt; CMV Pmaw<br />Increase Pmaw until you are able to decrease FiO2 to 60% with SaO2 of 90%<br />Avoid hyperinflation – CXR<br />Optimize preload, myocardial function<br />Mean arterial pressure &gt; 75 mmHg<br />
  44. 44. Adjusting the settings<br />Hypercapnia<br />Increase DP<br />Decrease frequency<br />Increase inspiratory time<br />Deflate the cuff<br />Hypocapnia<br />Increase frequency<br />Decrease DP<br />
  45. 45. Bedside Monitoring<br />Chest wiggle factor<br />Chest X-ray<br />Arterial blood gas<br />
  46. 46. Chest wiggle factor (CWF)<br />Wiggling from clavicles to mid-thighs<br />Monitor at initiation and closely thereafter<br />Reassess after any position change<br />Absent or diminished CWF<br />Airway or ET tube obstruction<br />Asymmetrical CWF<br />One-lung intubation<br />Pneumothorax<br />Unilateral mucous plug<br />
  47. 47. Chest X-ray<br />First CXR at 1 hour, no later than 4 hours<br />Chest inflation to 10-12th ribs<br />Get CXR if unsure whether is patient is hyperinflated or derecruited<br />Do not stop the piston or disconnect the patient from HFOV for CXR<br />The purpose of CXR is to assess lung inflation while the patient is on HFOV<br />
  48. 48. Physical Exam<br />Heart sounds<br />Stop the piston, listen to the heart sound quickly, re-start the piston<br />Breath sounds<br />Cannot be heard with HFOV<br />Intensity of sound produced by the piston should be equal throughout<br />If not, get CXR<br />
  49. 49. Patient care<br />Suctioning<br />Indicated by decreased or absent CWF, decrease in SaO2 or increase in PaCO2<br />Every time the patient is disconnected from HFOV, the lung is de-recruited<br />Closed suction catheter may mitigate de-recruitment, DP may need adjustment to compensate for attenuation of DP due to right angle adapter<br />May require temporary increase in Pmaw<br />
  50. 50. Patient Care<br />Bronchodilator therapy<br />Rarely needed because HFOV is relatively contraindicated in active airflow obstruction<br />Only few ones with active bronchospasm<br />Administered via bagging<br />IV Terbutaline for patients who do not tolerate disconnections<br />
  51. 51. Patient Care<br />Humidification<br />Traditional heated humidifier<br />Heated wire humidifier<br />Circuit<br />Longer, flexible circuit allows patient positioning to prevent skin breakdown<br />
  52. 52. Patient Care<br />Positioning<br />Avoid disconnection<br />After change of position, observe chest wiggle, SpO2 and PtcCO2<br />Check ET tube position<br />Readjust HFOV parameters as needed<br />
  53. 53. Patient Care<br />Sedation<br />Patient often needs to be heavily sedated to avoid spontaneous breathing<br />Spontaneous breathing leads to unstable, fluctatingPmaw<br />Paralytics have become less popular<br />
  54. 54. Weaning from HFOV<br />Wean FiO2 for SaO2 &gt; 90%<br />Once FiO2 is &lt; 0.60, recheck CXR<br />If CXR shows appropriate inflation, begin decreasing Pmaw in 2-3 cmH2O increments<br />Wean DP in 5 cmH2O increments for PaCO2<br />Once the optimal frequency is found, leave it alone<br />
  55. 55. Transition to CMV<br />Stable Pmaw<br />Tolerates positioning and nursing care<br />Stable blood gases<br />Resolution of original lung pathology<br />Switch to PCV <br />Vt6 ml/kg<br />PEEP, PC and i-time adjusted to Pmaw comparable to the HFOV-generated Pmaw<br />
  56. 56. HFOV Failure<br />Failure criteria<br />Inability to decrease FiO2 by 10% within 24 hours<br />Inability to improve ventilation or maintain ventilation with (PaCO2 &lt; 80 or pH &gt; 7.25)<br />
  57. 57. Potential Complications<br />Hypotension<br />IV fluid boluses until CVP or PCWP increased by 5-10 mmHg<br />Vasopressors in refractory cases<br />Pneumothorax<br />Progressive hypotension and desaturation<br />Diminished or absent CWF<br />Diminished chest auscultation<br />
  58. 58. Potential Complications<br />Endotracheal tube obstruction<br />Rise in PaCO2 in otherwise stable patient<br />Inability to pass suction catheter<br />