Principles of Thoracic Anaesthesia

This covers general considerations for thoracic anaesthesia, with the exception of principles (including management of hypoxia) under one-lung ventilation.

Key considerations:

• Pre-operative optimisation

  • Smoking cessation
  • Exercise
    • Secretion clearance
  • Optimise lungs
    • Bronchodilators
    • Steroids
    • Antibiotics
  • Secretions
    • Chest physiotherapy
    • Spirometry

• Indication

  • Tumour
    • Mass effect
      Mediastinal mass:
      • Lymphomas
        Rapidly growing - may cause rapid compression.
      • Germ cell-tumours
      • Thymus
      • Thyroid goitres
    • Metabolic
    • Metastases
    • Medication
  • Bullectomy
  • LVRS
  • Transplant

• Respiratory assessment
  Prediction of post-operative pulmonary function is vital to:

• Confirm suitability
  Stratify to:

  • Curative-intent
  • Defined limits of resection

• Ventilator weaning and post-operative disposition
  Dependent on PPO FEV₁:

  • ⩾40%
    Extubate in operating room.
  • 30-40%
    Consider extubation.
  • ⩽30%
    
    • Staged weaning
    • Consider thoracic epidural

• Analgesia plan

  • Use of regional anaesthesia

Preoperative Assessment

Should include:

• Normal history and examination
  • Key comorbidities:
    • Chronic lung disease
    • Smoking history
    • Functional capacity
    • Cardiac comorbidities
  • Acute disease process:
    • Bronchospasm
    • Infection
    • Obstruction.collapse
    • Mass effect
  • Treatment effects
    • Chemotherapy
    • Radiotherapy
• Detailed airway assessment
  Insertion of a DLT is more difficult than SLT.

Assessment of Pulmonary Function

• Ability to tolerate:
  • Resection
  • One-lung ventilation
• Broadly speaking, resection is appropriate if:
  • FEV₁ ⩾1.5L for lobectomy
  • FEV₁ ⩾2.0L or 80% predicted for pneumonectomy

The “3-legged” stool of respiratory assessment evaluates a patients ability to tolerate removal of an anatomically resectable lung cancer. Many approaches have been described; institutional practice will vary depending on the availability of more advanced investigations (e.g. CPET) testing. This is one approach:

• Perform Spirometry
  FEV₁ and DLCO are:
  • ⩾60% of predicted
    Proceed to surgery.
  • <60% of predicted
    • Estimate predicted postoperative lung function
      FEV₁ and DLCO are:
      • ⩾40% of predicted
        Proceed to surgery.
      • <40% of predicted
        Perform CPET testing
        
        • Not always available, and not always performed
        • As measured by CPET, or surrogate
        • VO₂ max >15mL/kg/min
          Can proceed to surgery. Most useful predictor of outcome. Indicated by:
          • Stair climb ⩾2 flights
          • 6 minute walk test ⩾610m
          • Exercise SpO₂ <4%)
        • VO₂ max
          • ⩾10mL/kg/min
            May, in certain circumstances, proceed to surgery.
          • <10mL/kg/min
            Discuss alternatives.

Predicted Post-Operative Function Estimation

Predicting post-operative function:

• Estimates the proportion of lung function lost by resection
  • Assumes that all lung segments contribute equally to function
    Usually not the case as diseased units will inherently perform less well.
• Performed for both FEV₁ and DLCO
  Calculated as \[PPO FEV_1 = Preoperative \ FEV_1 \times {Number \ of \ segments \ initially - Number \ of segments \ resected \over Number \ of \ segments \ initially}\]
  • Normal is 19 segments

Risk Stratification

Elevated risk seen with:

• Abnormal blood gases
  Historically used, but convey ↑ risk if:
  • PaO₂ >60mmHg
  • PaCO₂ <45mmHg
• VO₂max <15mL/kg/min have very high morbidity and mortality
  • VO₂max >20mL/kg/min have few respiratory complications

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References

1. Gould G, Pearce A. Assessment of suitability for lung resection. Contin Educ Anaesth Crit Care Pain. 2006 Jun 1;6(3):97–100.