FRCA Notes

Chronic Obstructive Pulmonary Disease

COPD has yet to be the subject of a CRQ/SAQ.

The curriculum asks us to know how to manage 'common co-existing medical problems including COPD', and 'the different modes of ventilation and the selection of appropriate parameters in COPD'.

Resources

  • COPD is a chronic, progressive inflammatory condition of the airways, lung parenchyma and pulmonary vasculature
  • It is associated with increased rates of intra- and post-operative complications, particularly pulmonary complications
  • Approx. 3 million people in the UK with COPD
  • Diagnosis most common in the 50's
  • Often patients are undiagnosed
  • Almost always associated with smoking, although other conditions can cause similar features e.g. ɑ1-antitrypsin deficiency

  • Smoking is the noxious stimulus leading to COPD
  • Some suggestion that genetic factors (e.g. FAM13A gene variants) can influence development of COPD

  • Chronic inflammation of the central and peripheral airways leads to:
    • Poorly reversible airway narrowing
    • Remodelling of airway smooth muscle
    • Increased number of goblet cells and mucus-secreting glands
  • There are also pulmonary vascular changes, with raised pulmonary pressures

Expiratory airflow limitation

  • Narrow, inflamed airways (obstructive bronchiolitis)
    • Gas trapping and dynamic hyperinflation occur
    • V/Q mismatching arises due to large dead space
    • Altered respiratory muscle mechanics occur owing to the hyperinflated chest

  • Destroyed lung parenchyma (emphysema)
    • Elastin breakdown and loss of alveolar structural integrity impairs gas transfer
    • There is a reduced pulmonary capillary bed area, further worsening V/Q matching

  • Reduced parenchymal support for the small airways

  • The combination of V/Q mismatch, reduced gas transfer and alveolar hypoventilation ultimately leads to respiratory failure

Coalescing pathophysiologies

  • Smoking
  • Malignancies, particularly lung cancer
  • Pulmonary hypertension (33%)
  • Weight loss (50%) from malnutrition, skeletal muscle dysfunction and high energy requirements
  • Cardiovascular disease
  • Polycythaemia
  • Osteoporosis

  • COPD should be considered in:
    • Smokers who are >35yrs of age
    • With symptoms of exertional dyspnoea, chronic cough, regular sputum production or frequent winter bronchitis/wheeze

Spirometry & severity

  • FEV1/FVC <0.7 is diagnostic
  • Reversibility testing is not necessary for diagnosis; COPD should be distinguished from asthma on clinical features

  • No one measure correlates perfectly with true severity in any one individual
  • An assessment should be made using:
    • Spirometry results including FEV1 and TLCO
    • Functional assessment including level of disability, exercise capacity
    • Frequency of exacerbations and degree of dyspnoea
  • However, airflow limitation can be categorised into different severity scales:
Stage FEV (% predicted)
1 (Mild) >80%
2 (Moderate) 50 - 79%
3 (Severe) 30 - 49%
4 (Very severe) <30%
Or FEV1 <50% + respiratory failure

Non-pharmacological

  • Smoking cessation is imperative (even in late disease it will slow the rate of deterioration and prolong time to disability/death)
  • Pulmonary rehabilitation
  • Yearly 'flu and pneumococcal vaccines

Inhaled therapy

  • Long-acting bronchodilators e.g. LAMA or LABA ± ICS
  • Short-acting bronchodilators for relief of dyspnoea and exercise limitations

Oral therapy

  • Maintenance oral steroid therapy may be used in patients with advanced disease, although is typically reserved for exacerbations

  • Oral methylxanthine therapy e.g. theophylline in those with severe disease or who aren't able to use inhalers
    • Narrow therapeutic index and monitoring required to avoid toxicity

  • Oral mucolytics e.g. carbocysteine may be used to aid those with chronic, productive cough

Oxygen therapy

  • LTOT used to reduce PA pressure
  • Provides mortality benefit when used to maintain SpO2 >90% at least 15hrs/day

  • Indicated in those who are no longer smoking with:
    • PaO2 <7.3kPa, or
    • PaO2 <8kPa + polycythaemia/oedema/pulmonary HTN/nocturnal hypoxia

NIV

  • Used to manage respiratory failure from COPD
  • Should be used early in the course of respiratory failure to:
    • Avoid need for invasive ventilation
    • Decrease treatment failure
    • Reduce mortality

Surgical intervention

  • Lung volume reduction surgery is an essentially palliative treatment - see above-linked BJA Education article for specifics
  • Lung transplant

  • Increased risk of hospitalisation vs. general population
  • Increased mortality on ICU if they contract VAP , even if not suffering an IECOPD
  • Worse long-term survival post-operatively, owing to:
    • Increased rate of pulmonary complications
    • COPD being a risk factor for hypoxia requiring post-operative intubation, itself an independent predictor of 30-day mortality

Perioperative management of the patient with COPD


History and examination

  • COPD severity
  • Exercise tolerance
  • Frequency of exacerbations and recent steroids/antibiotics
  • Previous hospital admissions inc. need for NIV/I&V
  • Associated comorbidities

Investigations

  • Bloods: FBC, U&E, LFT inc. albumin, clotting
  • Baseline ABG may be indicated
  • ECG: evidence of concomitant IHD or right heart strain
  • TTE: right heart strain ± cor pulmonale
  • CXR is not mandatory but should be considered if there is recent deterioration in symptoms (i.e. is there infection or malignancy?)
  • Up to date spirometry
  • Functional capacity assessments e.g. 6 minute walk test

Risk assessment

  • Pre-operative albumin <35g/dL ± poor nutritional status associated with poor outcome in thoracic surgery

  • Poor prognostic markers:
    • Declining exercise tolerance
    • Low BMI ± significant weight loss
    • >2 hospital admissions per year

Optimisation

  • Encourage smoking cessation, regardless of the interval before surgery, which may include nicotine replacement therapy
  • Consider pre-operative physiotherapy if large sputum load
  • Prehabilitaiton
  • Consider booking HDU bed

Monitoring and access

  • AAGBI
  • Low threhsold for arterial line as higher risk of haemodynamic compromise and respiratory complications

Anaesthetic technique

  • GA, particularly I&V and IPPV, is associated with adverse outcomes

    • Associations with GA in COPD
    Laryngospasm
    Bronchospasm
    Cardiovascular instability
    Barotrauma
    Hypoxia
    ↑ rate post-op. pulmonary complications

  • A regional technique may therefore be beneficial, with reduced risk of post-operative pulmonary complications
  • However:
    • Not all surgeries amenable to RA
    • Patients may not be able to lie flat intra-operatively
    • Complications of the block (e.g. phrenic nerve anaesthesia following interscalene BPB) may be riskier than GA

Ventilatory management

  • Issues from mechanical ventilation arise mostly due to increase intrathoracic pressure when using PPV
  • The limited expiratory flow rate (because of airway narrowing) results in breath stacking/gas trapping, dynamic hyperinflation and generation of PEEPi
  • This risks barotrauma, volutrauma and hypercarbia

  • Signs of gas trapping include:
    • Non-plateauing capnograph trace
    • Upsloping end of capnography trace ('shark's fin')
    • Expiratory flow (or flow-volume loop) not reaching zero before next breath
    • Measurement of PEEPi
    • Disconnecting the circuit, which will cause a rise in ETCO2 and BP as the intrathoracic volume is decompressed

  • The increase intrathoracic pressure also:
    • Decreased venous return
    • Raises PA pressure, causing raised PVR and right heart strain

  • These issues can be somewhat mitigated using a similar ventilatory strategy to those with asthma:
Setting/target Goal
Endotracheal tube As large as fits
Mode Volume control (constant flow decreases Ppeak)
Respiratory rate Low e.g. start at 10 - 12 breaths/min
Tidal volume 4 - 8ml/kg
FiO2 Sufficient for sats >92%
I:E ratio Prolonged i.e. 1:4 or even more
Tinsp Reduced, by increasing inspiratory flow rate and using non-distensible tubing
PEEP ≤5cmH2O
Pplat ≤35cmH2O
pH >7.20

Care bundle

  • Normothermia using warming techniques
  • Prophylactic antibiotics as per local policy
  • VTE prophylaxis
  • Multi-modal analgesia avoiding long-acting opioids
  • Multi-modal anti-emetics

  • Optimise prior to extubation with:
    • Full reversal of NMBA
    • Adequate oxygenation
    • Normothermia
    • Consider peri-extubation bronchodilators
  • Consider extubating to NIV if significant concern

  • Close monitoring for post-operative respiratory failure and pneumonia
  • Consider HDU setting
  • Early chest physiotherapy, saline nebulisers