Lung Isolation

Lung isolation and one-lung ventilation:

Indications

Absolute:

  • Protective isolation
    • Massive haemorrhage
    • Pneumonia
  • Control of distribution of ventilation
    • Massive bullae
    • Bronchopleural fistula
  • Unilateral lung lavage
  • VATS

Relative:

  • Surgical exposure
    • Thoracic aortic aneurysm
    • Pneumonectomy
    • Upper lobectomy
    • Oesophageal surgery
    • Thoracoscopy

Contraindications

Inability to maintain oxygenation on one-lung.

Predictors of hypoxaemia:

  • Patient
    • Preferential perfusion to operative lung
      • Right-sided surgery
      • Previous contralateral resection
      • Contralateral pathology
    • Normal FEV1
    • Chronic vasodilator therapy
    • Poor oxygenation on two lung ventilation
  • Procedure
    • Supine perfusion
    • Volatile anaesthesia >>1 MAC

Anatomy

Equipment

Specific equipment for lung isolation include:

  • Double-lumen ETT
    • Oral
    • Tracheostomy
  • Bronchial blocker
    Subclassified into:
    • Torque-guided
      e.g. Cohen.
    • FOI-guided
      e.g. Arndt, Fuji.
    • Bilateral
      e.g. Easy blocker.
  • Single-lumen ETT
    • Endobronchial tube
    • ETT tube
      Advanced directly.
      • Mostly likely to enter RMB
      • Can be guided with FOI into either bronchus

Double-Lumen ETT

DLTs:

  • Common and versatile
  • Relatively contraindicated in:
    • Poor laryngoscopic airway grades
      Difficult to insert, and extremely challenging to railroad over a bougie or bronchoscope.
    • Aberrant tracheobronchial anatomy
      Potential for significant iatrogenic injury.
  • Come in left- and right-sided variants
    • As the right bronchus intermedius is very short, it is easy to accidentally occlude the right upper lobe with a right-sided DLT
      The side-port on right-sided ports should generally be positioned under bronchoscopic guidance to minimise this risk.
    • In general, a left sided DLT is used for most cases unless:
      • Surgical resection will involve the proximal left main bronchus
      • Aberrant anatomy precludes use of a left-sided DLT
  • Measured in French gauge
    • In general; 41-39Fr is appropriate for males, and 37Fr for females.
    • Depth of DLT insertion: 12cm + 0.1cm per 10cm of patient height

Pros of DLTs:

  • Provide generally good isolation
  • Facilitate easy recruitment and de-recruitment of lung

Cons of DLTs:

  • Large and harder to insert than standard ETTs
  • Smaller internal lumens than standard ETTs
    Require a bronchoscope with a ⩽4mm lumen to instrument a 35 Fr DLT.

Insertion of a left-sided DLT:

  • Place DLT through cords with curve in A-P plane
  • Remove stylet once through cords
  • Rotate DLT 90°
    Anticlockwise for left-sided.
  • Insert DLT until reaching slight resistance
  • Inflate tracheal cuff
  • Confirm ventilation and CO2
  • Evaluate position with bronchoscope
    • Bronchoscope down tracheal lumen
    • Confirm RUL position
    • If RUL unable to be visualised:
      • Shield scope in tracheal lumen
      • Deflate tracheal cuff
      • Slowly withdraw tube until carina visualised
      • Use scope as stylet to advance DLT to desired position
  • Inflate bronchial cuff under vision
    Slight rim of blue cuff should be seen in the LMB.
  • Place bronchoscope down bronchial lumen to ensure left upper lobe bronchus not obstructed

Bronchial Blockers

A low-pressure, high-volume balloon that is inflated to occlude the bronchus. * Key sizes: * 7 Fr for a 6.5 Fr ETT * 9 Fr for a 7.5 Fr ETT

Pros:

  • Preferable in certain situations
    • Difficult intubation
    • High-risk tube exchange
    • Tracheostomy
    • Anatomical abnormalities
      • Endoluminal stricture
  • Selective lobar isolation
    Apply CPAP down internal channel when wire removed.
  • Paediatrics

Cons:

  • Limited control
    • Can’t suction
    • Harder to oxygenate/perform pulmonary toilet
    • Repeated deflation and reinflation is limited
  • ↑ dislodgement
  • Slower:
    • Lung deflation
    • Positioning

Isolation Technique

Isolation can be achieved using:

  • Double lumen ETT
  • Bronchial blocker
  • Endobronchial intubation with a single-lumen ETT

General principles involve:

  • Ventilation with 100% O2
    Aim for maximal denitrogenation; absorption of oxygen will speed up lung collapse.

Isolation with Double-Lumen Tube

Remember to re-check isolation after repositioning the patient

Confirmation of position:

  • Clinical
    • Insert DLT
    • Inflate bronchial cuff
    • Connect circuit directly to bronchial lumen
    • Confirm ventilation on bronchial side, and not on tracheal side
    • Connect circuit to tracheal lumen
    • Inflate tracheal cuff until there is no leak
    • Confirm breath sounds on tracheal side, and not on bronchial side
  • Bronchoscopic
    • Insert DLT
    • Inflate tracheal cuff
    • Confirm tracheal intubation with CO2
    • Bronchoscope down tracheal lumen and identify carina
      Identify trifurcation of RUL if right-sided.
    • Inflate bronchial cuff under vision
      Aim to see narrow rim of blue cuff visible in the main bronchus.
    • If right-sided DLT, pass bronchoscope down bronchial lumen and confirm that the RUL ventilation port is aligned with the RUL bronchus

Isolation:

  • Confirm DLT positioning
  • Clamp DLT proximally on side to be deflated
  • Open DLT to air, distal to the clamp, on the side to be deflated
    • Consider suctioning down open lumen to speed up collapse
  • Confirm ventilation appropriate on remaining lung

Isolation with Bronchial Blocker

  • Turn PEEP to 0cmH2O
  • Insert bronchial blocker
    May be inserted under bronchoscopic guidance or directed blindly.
  • Inflate the bronchial blocker
    This can be performed:
    • At end-expiration (when lung volume is at its minimum)
      This will ↓ the size of the isolated section of lung and therefore the impediment to the surgeon.
    • After waiting until desaturation begins to occur
      In a patient who has been ventilated on 100% oxygen, this will indicate maximal atelectasis in the lung (though may take some time to occur).

Selective Lobar Isolation with Bronchial Blocker

  • This technique allows isolation of one particular area of lung whilst maintaining gas exchange in the remaining lung
    Isolation of the RUL or RML/RLL is easiest to perform.
  • Place DLT and isolate the operative/injured lung
  • Place bronchial blocker into the non-ventilated lung and inflate the blocker
  • Apply CPAP:
    Initially 5-10cmH2O until recruited, then ↓ to 2-5cmH2O.
    • Down bronchial blocker
      Can be performed by removing loop from Arndt blocker.
    • To DLT lumen

Lung Isolation in the Difficult Airway

Options include:

  • Awake FOI with DLT
  • Awake FOI with SLT and BB
  • Awake FOI with SLT and airway exchange
    Requires a catheter at least 70cm long.
  • Asleep DLT with combined VL and bronchoscopy

Tracheostomy:

  • Remove and insert DLT
    Certain DLTs made for this purpose.
  • Leave in and insert BB

Surgical Considerations

Surgical technique will affect rate and adequacy of lung collapse:

  • Airtight seal with thoracoscopic ports will reduce pneumothorax development
  • Suctioning will re-expand lung

Ventilatory Technique

  • Priority is to avoid hypoxia
    Typically aim SpO2 > 90%.
    • Maintain FRC in ventilated lung
  • Maximise PVR in the independent/operative/deflated lung
  • Minimise PVR in the dependent/ventilated lung

General Approach:

  • Optimise FRC of the dependent lung
    Occurs at lower than usual volumes due to paralysis, lateral position, and the weight of the mediastinum.
    • Any shunt in ventilated lung is poorly tolerated
  • Avoid impediments to hypoxic pulmonary vasoconstriction in ventilated lung
    • Hypocapnoea
    • Vasodilators
    • Excessive volatile
  • Begin at:
    • FiO2 of 1.0
      Aim to down-titrate to 0.5-0.8.
    • VT of 5ml/kg
    • 5-10cmH2 of PEEP
      Consider ZEEP in the severe COAD patient.
  • Targeting:
    • Pplat < 25cmH2O
    • PaCO2 ~35mmHg
      Permissive hypercapnoea acceptable;

Responding to Hypoxaemia

PaO2 falls rapidly initially, with a nadir at 20-30 minutes. Will tend to improve as HPV ↑.

Critical hypoxaemia:

  • May occur with:
    • Rapid decline
    • Major comorbidity
    • Haemodynamic instability
  • Recruit operative lung until stabilised/help arrived
    • ↑ FiO2
    • Two-lung ventilation
      If SpO2 <88-85%.
    • CPAP

Identify and treat common causes:

  • Basics first
    Check the tube and check the patient:
    • Failure of isolation
      • Bronchoscopy
    • Obstruction
      • Suction
  • Derecruitment
    • Recruitment maneuvre 30-40cmH2O, noting a drop in CO, BP, and SpO2 will transiently follow.
      • Arterial line useful if recruiting longer than 10-20s
    • PEEP titration
      Typically up to 10cmH2O - noting that excessive PEEP will worsen PVR.
  • Low DO2
    • Ensure Hb adequate
    • Consider inotropes
    • Fall in CO
      • Mediastinal pressure by surgeon
  • Shunt through operative lung
    Likely cause of hypoxia when other factors are optimised. Consider:
    • Oxygen to operative lung
      Delivery of low-flow (e.g. 2L/min) O2 down a suction catheter.
      • Catheter can be placed under bronchoscopic guidance to minimise effect on surgical exposure
    • CPAP to operative lung
      May interfere with surgical exposure depending on amount of CPAP applied and proximity of operative site to hilum.
      • 2cmH2O nearly always tolerated
      • 9cmH2O begins to impinge
    • Pulmonary vasodilators to ventilated lung
      Not appropriate as rescue therapy.
      • iNO at 20ppm is effective only when combined with a vasoconstrictor
      • Inhaled PGE1 at 10ng/kg/min
    • Intermittent two-lung ventilation
      May significantly hamper surgical access and prolong operating time.
    • Clamp PA of operative lung
      Technically difficult for surgeons to accomplish and not risk-free; they are usually reluctant to do this but it is very helpful if the vessels are exposed (e.g. in pneumonectomy).

Complications

Complications of one-lung ventilation include:

  • Hypoxia due to shunt
  • Acute Lung Injury
    ~2-5% incidence.

References

  1. Lohser J. Managing Hypoxemia During Minimally Invasive Thoracic Surgery. Anesthesiology Clinics. 2012;30(4):683-697.
  2. Collins SR, Titus BJ, Campos JH, Blank RS. Lung Isolation in the Patient With a Difficult Airway. Anesth Analg. 2018 Jun;126(6):1968–78.