- Chris Nickson
OVERVIEW
High Frequency Oscillation Ventilation (HFOV) is an unconventional form of mechanical ventilation that maintains lung recruitment, avoids overdistention, and does not rely on bulk flow for oxygenation and ventilation
HFOV is essentially a vibrating CPAP machine
Antony Tobin
DESCRIPTION
- small tidal volumes (1-4mL/kg)
- delivered at high frequencies (3-15 Hz) with an oscillatory pump
- maintains constant lung recruitment
- aims to prevent lung injury from overdistention and loss of recruitment (atelectrauma)
MECHANISM OF GAS EXCHANGE
TV is less than dead space -> normal bulk flow inadequate -> but gas delivery into the system still undergoes gas exchange by a number of proposed mechanisms (PAT the Cool Cat):
- Pendelluft mixing = mixing of gas between lung units due to impedance differences
- Augmented diffusion = gas mixing within the alveolar units
- Taylor dispersion = dispersion of molecules beyond the bulk flow front
- Coaxial flow patterns = net flow through the centre of the airway on way down, then on outside of airway on way up
- Cardiogenic mixing = agitation of surrounding lung tissue with molecular diffusion
INDICATIONS ANDCONTRA-INDICATIONS
Indications
- oxygenation failure: requiring an FiO2 > 0.7 and PEEP >14 cmH20
- ventilation failure: pH < 7.25 with VT 6mL/kg and plateau pressure > 30cmH20
- ARDS/ALI in primary treatment or rescue in failed oxygenation with conventional ventilation
- part of trial
- children and adults
Contra-indications
- alternative means of treating respiratory failure available and preferred (e.g. ECMO)
- severe airflow obstruction
- intracranial hypertension
VENTILATION PRINCIPLES
Targets
- pH > 7.25
- utilise highest possible frequency to minimise tidal volume (only decrease for CO2 control if amplitude of oscillations maximal)
- SpO2 > 88% or PaO2 55mmHg (decreases oxygen toxicity)
Factors determining PaO2
- mean airway pressure
- FiO2
Factors determining PaCO2
- amplitude of oscillations (delta P) (“power”)
- frequency of oscillations (Hz)
- inspiratory time
- cuff leak
These factors can be independently adjusted
Typical Initial settings in adults
- Bias flow 40 L/min
- Inspiratory time 33%
- mPaw 34 cm H2O
- FIO2 1.0
- Amplitude (delta P) 90 cm H2O.
- Initial frequency based on most recent arterial blood gas:
pH <7.10 = 4 Hz
pH 7.10–7.19 = 5 Hz
pH 7.20–7.35 = 6 Hz
pH >7.35 = 7 Hz
After initial HFOV settings are established, perform an initial recruitment maneuver and oxygen/mPaw adjustment as per protocol (see Fessler et al, 2007)
PROS AND CONS OF HFOV
Advantages
- decreases VILI
- dissociation between oxygenation and carbon dioxide clearance
- mobilisation of secretions
Disadvantages
- derecruitment once ceased
- requirement for heavy sedation and paralysis
- higher risk of hemodynamic instability due to high mean airway pressure
- requires active humidification
- no evidence of benefit, and higher mortality in adult ARDS in one important RCT (OSCILLATE)
EVIDENCE
Evidence summary
- HFOV found to cause harm or have no benefit in the 2 best RCTs in adult ARDS patients
- previous studies compared HFOV to outdated ventilation strategies
- Unclear if lack of benefit is due HFOV per se or the protocols used, patient selection or need for increased sedation and paralysis
- As ARDS is a heterogeneous lung disease from differing causes, there may be some patient subgroups that might be helped (e.g. patients with homogeneous, recruitable lung) while others are harmed — but we don’t know if this is true!
- HFOV should not be a routine part of the management of ARDS patients, but is still an option for refractory ARDS patients (in the absence of ECMO)
Cochrance Systematic Review (published prior to OSCAR and OSCILLATE)
- meta-analysis in ALI and ARDS patients
- 8 RCTs, n= 419 patients
- reviewed HFOV vs conventional MV as initial strategy rather than as a rescue treatment for refractory hypoxaemia
- in HFOV group
-> PF ratios higher at 24 hour intervals through improving mean airway pressure
-> mortality significantly reduced at 30 days
-> less likely to fail
-> no effect on duration of MV
-> not associated with an increase in adverse events - Commentary and criticisms:
— results of OSCAR and OSCILLATE were not included
— based on only a small number of patients
OSCAR trial 2013
- non-blinded intention-to-treat MC RCT
- 795 patients
- HFOV versus usual care control group
- outcomes:
-> all cause mortality at 28 days was 41.7% vs 41.1% (P=0.85 chi-square test) - Commentary and criticisms:
— less hemodynamic compromise, lower airway pressures than OSCILLATE and more protocol variation, possibly due to physician judgement limiting the harm from HFOV settings
— HFOV groups received more sedatives and muscle relaxants - Conclusion: no mortality difference at 1 month
OSCILLATE trial 2013
- non-blinded intention-to-treat MCRCT
- 548 new-onset, moderate-to-severe ARDS patients
- HFOV vs low TV high PEEP controlled ventilation strategy
- outcomes:
-> 47% vs 35% in-hospital mortality (RR 1.33, 95% CI 1.09 to 1.64)
-> were given more midazolam, more NMBs, more vasopressors - Commentary and criticisms:
— stopped early due to harm from HFOV
— HFOV strategy had high mean airway pressures – would a lower mean airway pressure strategy make a difference?
—groups similar at baseline, both had baseline recruitmentmanoeuvreto improve lung homogeneity - Conclusion: Increased mortality in ARDS patients treated with HFOV
HIFI study 1989
- RCT
- no benefit from HFOV in respiratory distress of premature infants and increased adverse effects (pneumoperitoneum, IVH, periventrivular leukomalacia)
VIDEOS
Demonstration of HFOV
Lecture on HFOV basics
References and Links
CCC Ventilation Series
Modes: Adaptive Support Ventilation (ASV), Airway Pressure Release Ventilation (APRV), High Frequency Oscillation Ventilation (HFOV), High Frequency Ventilation (HFV), Modes of ventilation, Non-Invasive Ventilation (NIV), Spontaneous breathing and mechanical ventilation
Conditions: Acute Respiratory Distress Syndrome (ARDS), ARDS Definitions, ARDS Literature Summaries, Asthma, Bronchopleural Fistula, Burns, Oxygenation and Ventilation, COPD, Haemoptysis, Improving Oxygenation in ARDS, NIV and Asthma, NIV and the Critically Ill, Ventilator Induced Lung Injury (VILI), Volutrauma
Strategies: ARDSnet Ventilation, Open lung approach, Oxygen Saturation Targets, Protective Lung Ventilation, Recruitment manoeuvres in ARDS, Sedation pauses, Selective Lung Ventilation
Adjuncts: Adjunctive Respiratory Therapies, ECMO Overview, Heliox, Neuromuscular blockade in ARDS, Prone positioning and Mechanical Ventilation
Situations: Cuff leak, Difficulty weaning, High Airway Pressures, Post-Intubation Care, Post-intubation hypoxia
Troubleshooting: Autotriggering of the ventilator, High airway and alveolar pressures / pressure alarm, Ventilator Dyssynchrony
Investigation / Indices: A-a gradient, Capnography and waveforms, Electrical Impedance Tomography, Indices that predict difficult weaning, PaO2/FiO2 Ratio (PF), Transpulmonary pressure (TPP)
Extubation: Cuff Leak Test, Extubation Assessment in ED, Extubation Assessment in ICU, NIV for weaning, Post-Extubation Stridor, Spontaneous breathing trial, Unplanned extubation, Weaning from mechanical ventilation
Core Knowledge: Basics of Mechanical Ventilation, Driving Pressure, Dynamic pressure-volume loops, flow versus time graph, flow volume loops, Indications and complications, Intrinsic PEEP (autoPEEP), Oxygen Haemoglobin Dissociation Curve, Positive End Expiratory Pressure (PEEP), Pulmonary Mechanics, Pressure Vs Time Graph, Pressure vs Volume Loop, Setting up a ventilator, Ventilator waveform analysis, Volume vs time graph
Equipment: Capnography and CO2 Detector, Heat and Moisture Exchanger (HME), Ideal helicopter ventilator, Wet Circuit
MISC: Sedation in ICU, Ventilation literature summaries
LITFL
- Paul Young’s ICU Mind Maps
Review articles and commentaries
- Bouchut JC, Godard J, Claris O. High-frequency oscillatory ventilation. Anesthesiology. 2004 Apr;100(4):1007-12. PMID: 15087640.
- Ferguson ND, Slutsky AS. Point: High-frequency ventilation is the optimal physiological approach to ventilate ARDS patients. J Appl Physiol. 2008 Apr;104(4):1230-1. PMID: 18048584. [Free Fulltext]
- Fessler HE, Derdak S, Ferguson ND, Hager DN, Kacmarek RM, Thompson BT, Brower RG. A protocol for high-frequency oscillatory ventilation in adults: results from a roundtable discussion. Crit Care Med. 2007 Jul;35(7):1649-54. PubMed PMID: 17522576. [Free Fulltext pdf]
- Malhotra A, Drazen JM. High-frequency oscillatory ventilation on shaky ground. N Engl J Med. 2013 Feb 28;368(9):863-5. doi: 10.1056/NEJMe1300103. Epub 2013 Jan 22. PubMed PMID: 23339640.
Trial and systematic reviews
- Sud S, Sud M, Friedrich JO, Wunsch H, Meade MO, Ferguson ND, Adhikari NK. High-frequency ventilation versus conventional ventilation for treatment of acute lung injury and acute respiratory distress syndrome. Cochrane Database Syst Rev. 2013 Feb 28;2:CD004085. doi: 10.1002/14651858.CD004085.pub3. Review. PubMed PMID: 23450549. [Free Fulltext]
- Ferguson ND, Cook DJ, Guyatt GH, Mehta S, Hand L, Austin P, Zhou Q, Matte A, Walter SD, Lamontagne F, Granton JT, Arabi YM, Arroliga AC, Stewart TE, Slutsky AS, Meade MO; the OSCILLATE Trial Investigators and the Canadian Critical Care Trials Group. High-Frequency Oscillation in Early Acute Respiratory Distress Syndrome. N Engl J Med. 2013 Jan 22. [Epub ahead of print] PubMed PMID: 23339639. [Free Fulltext]
- The HIFI Study Group.High-frequency oscillatory ventilation compared with conventional mechanical ventilation in the treatment of respiratory failure in preterm infants. N Engl J Med. 1989 Jan 12;320(2):88-93. PubMed PMID: 2643039.
- Young D, Lamb SE, Shah S, MacKenzie I, Tunnicliffe W, Lall R, Rowan K, Cuthbertson BH; OSCAR Study Group. High-frequency oscillation for acute respiratory distress syndrome. N Engl J Med. 2013 Feb 28;368(9):806-13. doi: 10.1056/NEJMoa1215716. Epub 2013 Jan 22. PubMed PMID: 23339638. [Free Fulltext]
Social media and web resources
- ICN Podcast — 35. Antony Tobin on HFOV
Critical Care
Compendium
more CCC…
Chris Nickson
Chris is an Intensivist and ECMO specialist at theAlfred ICU in Melbourne. He is also a Clinical Adjunct Associate Professor at Monash University.He is a co-founder of theAustralia and New Zealand Clinician Educator Network(ANZCEN) and is the Lead for theANZCEN Clinician Educator Incubatorprogramme. He is on the Board of Directors for theIntensive Care Foundationand is a First Part Examiner for theCollege of Intensive Care Medicine. He is an internationally recognised Clinician Educator with a passion for helping clinicians learn and for improving the clinical performance of individuals and collectives.
After finishing his medical degree at the University of Auckland, he continued post-graduate training in New Zealand as well as Australia’s Northern Territory, Perth and Melbourne. He has completed fellowship training in both intensive care medicine and emergency medicine, as well as post-graduate training in biochemistry, clinical toxicology, clinical epidemiology, and health professional education.
He is actively involved in in using translational simulation to improve patient care and the design of processes and systems at Alfred Health. He coordinates the Alfred ICU’s education and simulation programmes and runs the unit’s educationwebsite,INTENSIVE. He created the ‘Critically Ill Airway’ course and teaches on numerous courses around the world. He is one of the founders of theFOAMmovement (Free Open-Access Medical education) and is co-creator oflitfl.com,theRAGE podcast, theResuscitologycourse, and theSMACCconference.
His one great achievement is being the father of three amazing children.
OnTwitter, he is@precordialthump.
| INTENSIVE | RAGE | Resuscitology | SMACC
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