Recruitment

A recruitment manoeuvre is a sustained, transient ↑ in airway pressure above normal tidal ventilation pressure, and sustained beyond a normal inspiratory time, which aims to open collapsed alveoli and small airways so they are able to participate in gas exchange.

Indications

Hypoxaemia with evidence of recruitable lung:

  • Clinical suggestion of collapse
    • Post-intubation
    • Post-bronchoscopy
  • Radiographically recruitable lung
    Evidence of volume loss implying collapse rather than consolidation.
  • PEEP-responsive ARDS
    How to identify this subgroup remains unclear.

Contraindications

  • High risk of barotrauma:
    • Bullous lung disease
    • Previous PTHx
    • Current PTHx
  • CVS instability

Principles

Lung parenchyma collapses in a heterogenous fashion. Alveoli:

  • Open when pressure exceeds the critical opening pressure
  • Collapse when pressure falls below critical closing pressure
    • Critical closing pressure is less than the critical opening pressure
      Application of PEEP above the critical closing pressure keeps alveoli open.
  • Will tend to distribute pressure first to well-aerated lung
    This may lead to over-distention of healthy lung, prior to recruitment of lung units with poor compliance

Recruitment manoeuvres:

  • Are cheap
  • Have been shown to improve:
    • Oxygenation
    • Gas exchange
    • Inflammatory markers
  • Are described with a wide variety of techniques:
    • 30cmH2O for 30-60s
      Safe, moderately effective.
    • 40cmH2O for 40s
    • Pip at 50cmH2O, aiming PEEP above the upper inflection point on the pressure-volume loop
    • Titration of Pip up to 40cmH2O
    • Staircase recruitment

No recruitment strategy has been shown to be superior.

P-V Loop

Staircase Recruitment

Practice

Appropriate in carefully selected patients. Considerations:

  • High chance of recruitable lung
  • Low risk of harm
  • Recruitment strategy
    • I have found 30cmH2O for 60s or 40cmH2O for 40s, abandoning if hypotension or hypoxia result, to be safe and effective
    • My experience with staircase recruitment is that it causes significant haemodynamic instability without much additional benefit in oxygenation

Complications

Risks relate to significant ↑ airway pressure:

  • Requires sedation/paralysis
  • Barotrauma
    • Pneumothorax
    • Pneumomediastinum
    • Cyclic atelectasis
      Re-collapse after cessation of recruitment.
  • Cardiovascular instability
    • ↑↑ RV afterload
    • ↓ VR

Key Studies

  • ART (2017)
    • ~1000 adults with moderate-severe ARDS requiring mechanical ventilation, without high risk of barotrauma or escalating vasoactive requirements
    • Multicentre (120!), unblinded, allocation concealed, block randomised trial
    • Open lung vs. control
      • Open lung
        • PCV with driving pressure of 15cmH2O
        • Muscle relaxation applied
        • Staircase recruitment up to PEEP of 45cmH2O
        • PEEP down-titrated in 3cmH2O increments, with measurement of static compliance at leach level
          Level with highest lung compliance noted.
        • Further recruitment at PEEP 45cmH2O of PEEP
        • New PEEP set to level at maximal compliance + 2cmH2O
      • Control
        • Conventional ARDSnet ventilation
      • Both groups managed with VCV at 6mL/kg with safe lung ventilation
      • Refractory hypoxaemia managed with proning, iNO, or VV ECMO
      • Pressure support attempted once PEEP <14cmH2O
    • ↑ Mortality in open lung group (55.3% vs 49.3%, p=0.04)
    • Secondary outcomes showed the open lung group had ↑ 6 month mortality, ↓ ventilator free days, and more pneumothoraces requiring drainage
    • Compliance in open lung group did not significantly ↑ following recruitment
    • Recruitment manoeuvre had to be abandoned in 15% due to hypotension or hypoxia
    • Most patients only had one recruitment manoeuvre
    • Indiscriminate aggressive recruitment manoeuvres are harmful in moderate-severe ARDS, but this does not rule out benefit in select subgroups

References

  1. Writing Group for the Alveolar Recruitment for Acute Respiratory Distress Syndrome Trial (ART) Investigators. Effect of Lung Recruitment and Titrated Positive End-Expiratory Pressure (PEEP) vs Low PEEP on Mortality in Patients With Acute Respiratory Distress Syndrome: A Randomized Clinical Trial. JAMA. 2017;318(14):1335-1345. doi:10.1001/jama.2017.14171
  2. Cavalcanti AB, Amato MBP, de Carvalho CRR. Should the ART trial change our practice? J Thorac Dis. 2018;10(3):E224-E226. doi:10.21037/jtd.2018.02.25
  3. Hess DR. Recruitment Maneuvers and PEEP Titration. Respiratory Care. 2015;60(11):1688-1704. doi:10.4187/respcare.04409