Question 19

College answer

a)    What pre-operative respiratory assessments would be helpful to assess his risks for the surgery and post-operative course?  
•    CXR and ABG’s 
•    FEV 1 and diffusing capacity for carbon monoxide (DLCO) 
•    Calculated predicted postoperative (PPO) FEV 1 and PPO DLCO  
•    6-minute walk test 
 
b)    Outline your management for this patient with regard to: 
i. Post-operative Analgesia: Multimodal approach to analgesia 
•    Satisfactory analgesia can be achieved with i.v. opioids; however, their beneficial effects might be counterbalanced by the risk of respiratory depression, mild attenuation of the cough reflex, and diaphragm elevation due to bowel distension. 
•    The Opioid-sparing effect of a Regional techniques and avoidance of possible side effects of systemic analgesics may be advantageous in increasing tidal volume and vital capacity, and improving diaphragm activity- Epidural, Para vertebral analgesia, Intrathecal and intercostal block. 
•    Nonsteroidal anti-inflammatory drugs, especially Ketorolac may be used to supplement opioid analgesia. These drugs work synergistically with opioids and have no respiratory depressive effects. Disadvantages include platelet and renal dysfunction. Concern over renal dysfunction in patients in whom restrictive fluid administration is the norm means NSAID’s are often avoided. 
•    Ketamine, gabanoids 
•    Paracetamol at recommended doses, along with rescue doses of Tramadol, may be proposed as a valid analgesic regimen 
 
iii. Post-operative fluid management 
•    Patients routinely extubated post op and may need minimal iv fluids 
•    Potential risk of postoperative lung injury with liberal fluid administration. 
 
c)  
Give a differential diagnosis for his deterioration?  
•    Surgical Complication: 

• Haemothorax
• Pneumothorax 
• Prolonged air leak/Bronchopulmonary fistula 

•    Infectious causes

•  Aspiration pneumonia
• Hospital acquired pneumonia  
• Empyema 

•    Other complication: 

• Atelectasis
• Pulmonary oedema
• PE 

 
Outline how you would manage his ventilation 
Mechanical ventilation may increase the risk of bronchial stump disruption, bronchopleural fistula, persistent air leakage, and pulmonary infection. 
•    Protective ventilatory settings with small tidal volumes (Vts) and positive end-expiratory pressure (PEEP) should be applied to reduce the risk of ventilator-induced lung injury 
•    Prolonged mechanical ventilation may be associated with a significant risk for pneumonia every effort should be made to promote fast weaning from invasive airways. 
•    Acceptable rather than normal ABG targets 
•    Single lung ventilation may be required if there is a bronchopulmonary fistula 
 

Discussion

Pre-operative assessment for the patient undergoing pneumonectomy: based on UpToDate, the 2013 ACCP clinical practice guidelines and the 2001 BTS guidelines 

• Spirometry: FEV₁ of less than 80% of predicted suggests that there will be complications
• Actual diffusing capacity: DLCO of less than 80% of expected also predicts complications
• Post-operative FEV1 (calculated):  post-op FEV₁ of less than 30% of predicted is associated with increased risk of mortality
• Post-operative DLCO (calculated): post-op DLCO of less than 30% of predicted is associated with increased risk of mortality
• Arterial O₂ and CO₂ are abbreviated as "ABG" in the college answer but in fact these parameters ae not particularly useful (for example, because of improved V\Q matching the arterial O₂ may actually improve post pneumonectomy, making it a pointless preoperative risk marker).
• Exercise testing can be performed for the marginal patients. This can take the shape of stair-climbing, the "shuttle test", integrated cardiopulmonary exercise testing (which measures VO₂) and the "six minute walk test" mentioned in the CICM model answer. 

Post-operative management:

Analgesia

• Analgesia needs to be sophisticated and multimodal:
  • Regional block (paravertebral seems to be favoured over thoracic epidural- Powell et al, 2011)
  • Opiates
  • Opiate-sparing agents (eg. NSAIDs and paracetamol)
  • Addition of ketamine and neuropathic pain management agents (gabapentin, tricyclic antidepressants, etc) could have an advantage

Fluid management

• Fluid management needs to reflect the changes in the pulmonary circulation:
  • The right heart has suddenly increased afterload by 50-60%
  • The pulmonary veins have suddenly increased pressure by 50-60%
  • Increased pressure can cause capillary damage, increasing their leakyness
  • The overall upshot of all these is a propensity to pulmonary oedema
  • The management recommendation is to keep their fluid balance neutral or negative as much as possible

Causes of early deterioration with haemodynamic instability and dyspnoea:

• Vascular causes
  • Myocardial infarction
  • Pulmonary embolism
• Infectious causes
  • Hospital-acquired pneumonia
  • Post-pneumonectomy empyema
  • Sputum plug
• Drug-related causes
  • Epidural analgesia overdose
  • Epidural haematoma complications
  • Excess opiates
• Surgical complications
  • Bleeding complications (haemothorax)
  • Bronchial stump breakdown (pneumothorax)
  • Bronchopleural fistula
  • Chylothorax (thoracic duct injury)

"Outline how you would manage his ventilation" is a strangely worded question, as the answer would be strongly dependent on what the causes of the respiratory failure is. Let us try to answer this as if it did not matter why the patient was being ventilated. The basic principles (from Lytle et al, 2008) would be:

• Smaller tidal volumes: 
• Lower positive pressure: avoid bronchial stump barotrauma; minimise PEEP.
• Rapid weaning and early extubation: most studies have found a significantly increased risk of BPF if ventilation continues (Toufektzian et al, 2015)
• NIV appears to be associated with fewer complications