HFOV uses small, rapid lung oscillations to reduce ventilator-induced lung injury compared to conventional mechanical ventilation. It works by maintaining constant mean airway pressure and small tidal volumes to avoid alveolar overdistension and collapse. Several early studies found HFOV improved oxygenation compared to CMV for ARDS, but larger trials found no significant difference in mortality. Proper patient selection, early initiation, and careful titration of pressures and settings are key to optimize outcomes with HFOV.

1. High Frequency Oscillatory VentilationPeteyLaohaburanakit, MD, FCCPCritical Care ServicesRogue Valley Medical Center

2. OutlineWhat is HFOV? Ventilator-induced lung injury (VILI)How does HFOV work?Basic concept and gas exchangeOxygenation and ventilation in HFOVClinical studiesInitiation and adjustmentCare for patients on HFOVPotential complications

3. What is HFOV?Not to be confused with high frequency jet ventilation (HFJV), which is rarely usedFirst established use in neonatal ARDSHFOV’s claim to fame is reduction of ventilator-induced lung injury (VILI)

5. What is VILI?Two major causesAlveolar distensionHigh plateau pressureCyclical opening and closing of atelectatic lungLarge pressure swing at the alveolar level from large tidal volumes

6.  V P V P V P

7. ZoneofOverdistensionInjury“Safe”WindowVolumeZone ofDerecruitmentand AtelectasisInjuryPressure

8. InjuryInjury

10. How does HFOV work?The piston oscillates the lung around a constant mean airway pressure with high frequencyThe mean airway pressure (Pmaw) is almost always higher than conventional ventilationSmall tidal volume with less pressure swing reduces VILIOne way to look at it – CPAP with rapid oscillation

11. CDP“Continuous DistendingPressure”Adjust Valve ET TubeOscillatorPatientBIAS Flow

12. Pressures at alveolar level

14. Gas exchange in HFOVDirect bulk flowLongitudinal (Taylor) dispersionPendeluftAsymmetric velocity profilesCardiogenic mixingMolecular diffusion

15. HFOV and CMV

16. Decoupling of Ventilation and OxygenationControls for oxygenationPmawFiO2Alveolar recruitment maneuverControls for ventilationAmplitude (DP)HertzInspiratory timeCuff deflationPermissive hypercapnia

18. OxygenationPrimarily controlled by mean airway pressure (Pmaw)Pmaw is a constant pressure used to inflate the lung and hold the alveoli openSince the Pmaw is constant, it reduces the injury that results from cycling the lung open for each breath

19. xBias FlowCDP Control Balloon

20. VentilationControlled by the movement of pump/piston mechanismAlveolar ventilation during CMV is defined as f x VtAlveolar ventilation during HFOV is defined as f x Vt2Changes in volume delivery have the most significant effect on ventilation

23. Regulation of stroke volumeThe stroke volume will increase ifThe 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 movementDependent on the power settingResults in chest wiggle

26. Inspiratory timeControls the time for movement of the pistonIncreases inspiratory time increases CO2 eliminationIncreases inspiratory time increases delivered Pmaw

28. PaO2PaCO2

29. Clinical DataPilot studiesMehta S et al. Crit Care Med 2001Derdak S et al. Am J RespirCrit Care Med 2002Multicenter oscillatory ventilation for ARDS trial (MOAT)OSCILLATE – Canadian clinical trials group

30. Pilot StudiesHFOV was as effective as CMV for ARDSHFOV patients reached oxygenation goals earlierEarly implementation was associated with better outcomesCMV groups were not ventilated with ARDS Network protocol*

31. MOAT Study - Design13 university-affiliated medical centers, recruitment 1997-2000Eligibility: age >= 16 on mechanical ventilationPaO2/FiO2 < 200 while on PEEP >= 10Bilateral pulmonary infiltrates on CXRNo evidence of left atrialhypertension

32. MOAT Study - DesignExclusion:Weight < 35 KgSevere COPD or asthmaIntractable shockSevere airleakNonpulmonary terminal diagnosisFiO2 > 0.80 for more than 2 days

33. MOAT Study - ResultsN=148Mean age 50APACHE II score 22PaO2/FiO2 ratio 112Oxygenation index (OI) 25Mean duration on mechanical ventilation prior to HFOV 2.8 days

34. MOAT Study -ResultsA : Mean airwaypressureB : P/F ratioC : OxygenationIndexD : PaCO2

35. MOAT Study - Results

36. MOAT Study – OI for prognosis

37. MOAT Study - CriticismsNot powered to evaluate mortality (would need n=199)Control group did not comply with ARDS Network standardsHigher Vt (8 ml/kg measured wt, 10.6 ml/kg ideal wt)Peak Paw 38 cm H2O at 48 hours

38. OSCILLATE StudyCanadian Clinical Trials GroupThe OSCILLation in ARDS Treated EarlyGoal N = 94Completed in December 2008

39. HFOV for ARDSWhen to consider?The earlier the betterFiO2 >= 0.60, PEEP >= 10 with P/F ratio < 200Plateau pressure > 30Oxygenation index (OI) > 24OI = (FiO2 x 100) x Pmaw / PaO2Failed ARDS Net protocol

40. Key to successPatient selectionTiming of initiationEarly application provides protection and reduces risks of further lung damageRescue with HFOV may or may not improve mortalityThe later HFOV is started the less chance of survival

41. Initial settingsRecruitment maneuverPmaw 5 cmH2O above CMV PmawFiO2 1.0Frequency 5-6 HertzPower 40, adjust for good chest wiggleInspiratory time at 33%Set bias flow at > 25 lpm, go higher if needed

42. Ventilator Strategies - GoalsNormalize lung volumeMinimize pressure change at alveolar levelWean FiO2 to a safe level firstPhysiological targetsSaO2 between 88% and 93%Delay weaning Pmaw until FiO2 < 0.5pH > 7.25PaCO2 in the range of 45-70 mmHg

43. Oxygenation StrategiesInitial Pmaw 5 cm > CMV PmawIncrease Pmaw until you are able to decrease FiO2 to 60% with SaO2 of 90%Avoid hyperinflation – CXROptimize preload, myocardial functionMean arterial pressure > 75 mmHg

44. Adjusting the settingsHypercapniaIncrease DPDecrease frequencyIncrease inspiratory timeDeflate the cuffHypocapniaIncrease frequencyDecrease DP

45. Bedside MonitoringChest wiggle factorChest X-rayArterial blood gas

46. Chest wiggle factor (CWF)Wiggling from clavicles to mid-thighsMonitor at initiation and closely thereafterReassess after any position changeAbsent or diminished CWFAirway or ET tube obstructionAsymmetrical CWFOne-lung intubationPneumothoraxUnilateral mucous plug

47. Chest X-rayFirst CXR at 1 hour, no later than 4 hoursChest inflation to 10-12th ribsGet CXR if unsure whether is patient is hyperinflated or derecruitedDo not stop the piston or disconnect the patient from HFOV for CXRThe purpose of CXR is to assess lung inflation while the patient is on HFOV

48. Physical ExamHeart soundsStop the piston, listen to the heart sound quickly, re-start the pistonBreath soundsCannot be heard with HFOVIntensity of sound produced by the piston should be equal throughoutIf not, get CXR

49. Patient careSuctioningIndicated by decreased or absent CWF, decrease in SaO2 or increase in PaCO2Every time the patient is disconnected from HFOV, the lung is de-recruitedClosed suction catheter may mitigate de-recruitment, DP may need adjustment to compensate for attenuation of DP due to right angle adapterMay require temporary increase in Pmaw

50. Patient CareBronchodilator therapyRarely needed because HFOV is relatively contraindicated in active airflow obstructionOnly few ones with active bronchospasmAdministered via baggingIV Terbutaline for patients who do not tolerate disconnections

51. Patient CareHumidificationTraditional heated humidifierHeated wire humidifierCircuitLonger, flexible circuit allows patient positioning to prevent skin breakdown

52. Patient CarePositioningAvoid disconnectionAfter change of position, observe chest wiggle, SpO2 and PtcCO2Check ET tube positionReadjust HFOV parameters as needed

53. Patient CareSedationPatient often needs to be heavily sedated to avoid spontaneous breathingSpontaneous breathing leads to unstable, fluctatingPmawParalytics have become less popular

54. Weaning from HFOVWean FiO2 for SaO2 > 90%Once FiO2 is < 0.60, recheck CXRIf CXR shows appropriate inflation, begin decreasing Pmaw in 2-3 cmH2O incrementsWean DP in 5 cmH2O increments for PaCO2Once the optimal frequency is found, leave it alone

55. Transition to CMVStable PmawTolerates positioning and nursing careStable blood gasesResolution of original lung pathologySwitch to PCV Vt6 ml/kgPEEP, PC and i-time adjusted to Pmaw comparable to the HFOV-generated Pmaw

56. HFOV FailureFailure criteriaInability to decrease FiO2 by 10% within 24 hoursInability to improve ventilation or maintain ventilation with (PaCO2 < 80 or pH > 7.25)

57. Potential ComplicationsHypotensionIV fluid boluses until CVP or PCWP increased by 5-10 mmHgVasopressors in refractory casesPneumothoraxProgressive hypotension and desaturationDiminished or absent CWFDiminished chest auscultation

58. Potential ComplicationsEndotracheal tube obstructionRise in PaCO2 in otherwise stable patientInability to pass suction catheter