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