Hypoxaemia during one lung ventilation

Question 1

Absolute indications for one-lung ventilation

Answer 1

• Video-assisted thoracoscopic surgery
• To protect the healthy lung from: infection, haemorrhage, lung lavage
• To control ventilation to one lung because of: unilateral bullae, bronchopleural fistula, major bronchial disruption or trauma

Question 2

Relative indications for one-lung ventilation

Answer 2

• Lobectomy
• Pleural surgery
• Minimally invasive cardiac surgery
• Thoracic aortic aneurysm surgery
• Lung volume reduction
• Oesophageal surgery
• Mediastinal mass reduction
• Bilateral sympathectomies

Question 3

Factors affecting V/Q matching during one-lung ventilation

Answer 3

• Lateral position
• Position of mediastinum
• Pulmonary vasoconstriction
• PEEP
• Cardiac output

Question 4

Timings of hypoxic pulmonary vasoconstriction during one-lung ventilation

Answer 4

• Occurs within a few seconds and plateaus at 20-30mins
• Second phase occurs around 40 mins and plateaus at 2 hours
• Typically develops at a threshold PaO2 of 11.3kPa and reaches a max at 8.7kPa

Question 5

Factors that inhibit hypoxic pulmonary vasoconstriction

Answer 5

• Inhalational volatile anaesthetics
• B2-adrenergic drugs: adrenaline and dobutamine
• Phosphodiesterase inhibitors: milrinone
• IV vasodilators: GTN, SNP
• Alkylosis
• Hypocapnia
• Surgical manipulation of the lung
• Sepsis
• COPD
• Pregnancy

Question 6

Lung protective ventilation when on one-lung ventilation

Answer 6

• Pressure control modes with a decelerating flow pattern
• TV 4-5ml/kg pred body weight
• Peak pressures <25cmH2O
• Relatively low PEEP with frequent recruitment manoeuvres

Question 7

RFx for hypoxaemia one-lung ventilation

Answer 7

Patient factors
- COPD
- Obesity
- Increased age
- Hypoxia before surgery

Anaesthetic and Surgical factors
- Previous pulmonary resection on ventilated lung
- Right-sided lung surgery
- OLV in the supine position
- Use of high dose volatiles or vasodilators intra-op

Question 8

Prevention of hypoxia during one-lung ventilation

Answer 8

• Maintain normal CO
• Avoid anaemia
• Avoid IV vasodilators
• Use OLV lung protective ventilation

Question 9

Causes of abrupt severe hypoxia during one-lung ventilation

Answer 9

• Major haemorrhage
• Tension PTX in ventilated lung
• Malposition of double-lumen tube
• Gas embolism
• Acute RV failure or PE

Question 10

Bleomycin and pulmonary toxicity

Answer 10

• Chemotherapy agent used in the treatment of germ cell tumours, lymphomas and gynae cancers
• Can cause pulmonary toxicity
• Further hyperoxia following this can worsen pulmonary fibrosis
• SpO2 should be maintained at 85-90%

Question 11

Management of hypoxaemia on one lung ventilation

Answer 11

• Increase FiO2 to 1.0
• Switch to manual ventilation to assess that the circuit is intact and gives idea of lung compliance
• Increase the minute volume
• Check DLT position with a bronchoscope
• Suction
• Ensure adequate CO- vasopressors/ fluids
• Apply PEEP to ventilated lung - with caution this may reduce perfusion and worsen shunt
• Fill the FRC of the non-ventilated lung with O2- suction catheter into non-ventilated lung connected to O2
• Apply PEEP with CPAP circuit to non-ventilated lung
• Intermittent dual lung ventilation
• Clamping of the pulmonary artery to the non-ventilated lung- only an option in pneumonectomy