High Frequency Oscillation Ventilation

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 AND CONTRA-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 recruitment manoeuvre to 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

References and Links

LITFL

• Paul Young’s ICU Mind Maps
• CCC — High Frequency Ventilation

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