FRCA Notes

One-Lung Ventilation

This topic features frequently in SBAs and as a part of thoracic CRQs.

The curriculum asks for descriptions of 'the airway management of a patient undergoing one-lung ventilation and anaesthesia'.

Also required is an explanation of 'the changes that occur during one lung ventilation and the strategies to manage these changes'.

Overall good knowledge of the use of double-lumen tubes and endobronchial blockers is required.

Resources

  • One lung ventilation is often used during thoracic surgery where there is a need for one lung to be selectively deflated
  • It typically involves the use of double-lumen endotracheal tubes, or alternatives such as bronchial blockers

Absolute Relative
Tracheo-bronchial disruption
E.g. bronchopleural fistula, bronchial trauma		 Segmental resection | lobectomy | pneumonectomy
Pulmonary infection or haemorrhage
I.e. to avoid-cross contamination		 Pleural surgery
Single lung transplant
Minimally invasive cardiac surgery
Repair of thoracic aortic aneurysm
Oesophageal surgery
Anterior approach to thoracic spine
Bilateral sympathectomies


Prior to anaesthesia

  • In the awake, spontaneously ventilating and upright patient there is relatively good matching of:
    • Ventilation, which is greater in the dependent lung as there is lower transpulmonary pressure owing to gravity
    • Perfusion, which is also greater in the dependent lung due as there is higher hydrostatic pressure owing to gravity
  • This relationship is largely maintained in the semi-supine, supine and lateral positions too

Anaesthesia and PPV

  • FRC is reduced by decreased diaphragmatic tone and altered chest wall mechanics following GA and NMBA
  • FRC encroaches on closing capacity, with the potential for airway closure during tidal ventilation
  • This effect is more pronounced in dependent regions, leading to preferential ventilation of non-dependent lung
  • The application of PPV further increases the preferential ventilation of non-dependent regions

  • There is thus:
    • Preferential ventilation of non-dependent regions
    • Preferential perfusion of dependent regions
    • Consequent low V/Q ratio (V/Q mismatch) in the dependent lung i.e. shunt

  • This is somewhat mitigated by the application of PEEP, which increases FRC and improves ventilation of the dependent lung

Lateral positioning

  • Lateral positioning increases pulmonary blood flow in the dependent lung by approximately 10%
    • When supine there is greater blood flow to the larger right lung (55%) than the smaller left lung (45%)
    • If the patient lies right-side down (i.e. right lung dependent) this changes to 65% and 35% respectively
  • In the awake, spontanously ventilating patient this is largely inconsequential as there is also preferential ventilation of the dependent lung, maintaining V/Q matching

  • In the anaesthetised patient, however, there is preferential ventilation of the non-dependent lung (see above)
    • The non-dependent region receives ~60% of ventilation, while the dependent lung receives ~40%

  • Therefore, for the anaesthetised patient in the lateral position:
    • The dependent lung receives 40% of ventilation but 55-65% of perfusion
    • The non-dependent lung receives 60% of ventilation but 35-45% of perfusion
  • This leads to V/Q mismatching
    • These effects are more pronounced when the left lung is dependent (i.e. lying on left hand side)
    • The effect is also more pronounced when the chest wall is openend

One lung ventilation

  • One-lung ventilation partly re-establishes appropriate V/Q matching in the lateral, anaesthetised patient
  • Deflation of the non-dependent lung to facilitate surgery causes:
    • Ventilation exclusively to the dependent lung
    • Greater perfusion to the dependent lung (~80%), as HPV in the non-dependent lung raises its PVR and reduces pulmonary blood flow by half
  • There is thus better V/Q matching in the dependent lung

  • However, the non-dependent lung experiences essentially zero ventilation but still a degree of blood flow (~20%) despite maximal hypoxic pulmonary vasoconstriction
  • This leads to obligatory intra-pulmonary shunt during one-lung ventilation and risk of hypoxaemia
  • Clamping of the pulmonary artery in the non-dependent lung will near-abolish blood flow to that lung, reducing shunt fraction and improving oxygenation

  • The beneficial effect is less prounounced if one-lung ventilation is employed in the supine position because absence of gravitational effect means preferential perfusion to the ventilated lung is less marked than in the lateral position

Cardiac output

  • Low cardiac output can lead to a reduced SvO2
  • If intrapulmonary shunt is present, the oxygen content of this venous blood may not increase as it passes through the pulmonary circulation
  • Therefore when shunted and non-shunted blood mixes in the left heart, there is a reduced CaO2
  • I.e. for a given shunt fraction, lower cardiac output leads to lower CaO2

  • However, lower cardiac output itself can reduce the shunt fraction and mitigate this effect
  • Conversely, higher cardiac output may increase shunt fraction and exacerbate the issues with low CaO2
  • There is also interplay with factors such as VO2 and haemoglobin concentration

  • Overall, maintaining cardiac output at close to baseline during one-lung ventilation is optimal for CaO2

HPV

  • Maintenance of the hypoxic pulmonary vasoconstriction response in the non-ventilated lung is important for optimising V/Q matching during OLV
  • In general, one should avoid factors known to inhibit HPV:
    • Hypocarbia and alkalosis e.g. excessive minute ventilation
    • Hyperoxia
    • Hypothermia
    • Excessive doses of volatile anaesthetics (although clinically relevant doses of volatile agents do not inhibit HPV)
    • Drugs with (pulmonary) vasodilatory properties such as milrinone, GTN, sodium nitroprusside and β2 agonists

  • One should also avoid high ventilatory pressures, which may increase dependent lung PVR and force blood through the non-dependent lung

  • The goals are to:
    1. Optimise V/Q matching in the ventilated lung
    2. Prevent acute lung injury by using lung-protective ventilation

Optimise V/Q matching

  • Optimise pulmonary blood flow in the ventilated (dependent) lung by:
    • Ensuring complete deflation of the non-ventilated (non-dependent) lung, which increases its PVR and ensures better dependent lung blood flow
    • Avoiding large tidal volumes, as PVR is lowest at FRC
    • Avoiding high PEEP, as PVR is lowest at FRC

Lung-protective ventilation

  • Acute lung injury complicates 4-10% of pulmonary resections and is associated with a high (50-70%) mortality
  • It is due in part to the degree of surgical resection
  • The risk of ventilator-induced acute lung injury can be somewhat mitigated by attempting to reduce:
    • Volutrama, by using smaller tidal volumes and higher respiratory rate
    • Barotrauma, by using pressure control modes, lower PEEP and ensuring lower plateau pressures
    • Atelectotrauma, by individualising PEEP and use of recruitment manoeuvres
    • Oxygen toxicity, by titrating FiO2 appropriately

Overall strategy


Parameter Setting/Target
Ventilator mode Pressure control ventilation
Tidal volume 4-5ml/kg (IBW)
Respiratory rate 15-20 breaths/min
PEEP 3-5cmH2O
Peak pressure <35cmH2O
Plateau pressure <25cmH2O
FiO2 Lowest possible to acheive SpO2 94-98%


  • There are multiple complications of DLT use
  • Hypoxaemia, however, is both a common (incidence ~5%) and readily correctable intra-operative complication during one-lung ventilation

  • Hypoxaemia during one-lung ventilation is defined as an SpO2 ≤90% despite an FiO2 of 1.0
  • It arises due to the obligatory intrapulmonary shunt created during the process of OLV

Risk factors


Patient factors Perioperative factors
Operative lung has a high percentage of
ventilation or perfusion on pre-op. V/Q scan		 Poor PaO2 during two-lung ventilation in lateral position
Chronic lung disease Right sided surgery
Obesity Surgery in supine position (rather than lateral)
Increased age Previous pulmonary resection on dependent lung
Poor pre-operative oxygenation Use of vasodilators

Aetiology


Failure of gas delivery Impediment to gas flow Other deranged physiology
Anaesthetic machine issue Malposition of DLT/BB Inadequate CO e.g. haemorrhage, acute cardiac failure
Breathing circuit disconnected Sputum/blood obstructing lumen Failure of non-ventilated lung collapse
Bronchospasm Atelectasis of ventilated lung
Air trapping
Dynamic hyperinflation		 Inadequate ventilation of lung
Coughing or moving PE or gas embolism
Pneumothorax

Prevention

  • Lung-protective ventilatory strategy (see above)
  • Avoid factors inhibiting HPV (see above)
  • Avoid excessive fluids
  • Maintain cardiac output
  • Suction airway of non-ventilated lung to aid lung collapse

Management - malposition

  • The commonest cause of hypoxaemia is malposition of the lung isolation device
  • Management thereof is by:
    • Asking the surgeon to stop
    • Checking the position of the device bronchoscopically
    • Correcting position as necessary
    • Ensuring adequate depth of anaesthesia to prevent coughing/moving

Management - everything else

  • Management for hypoxaemia not due to malposition depends somewhat on the cause

  • Optimising oxygenation of the ventilated lung
    • Increase FiO2 to 1.0
    • Apply, or increase, PEEP to the ventilated lung, acknowledging this may counterintuitively impair DO2 by reducing cardiac output and exacerbating shunt
    • Perform recruitment manoeuvres to reverse atelectasis
    • Suction airways using bronchoscope to reduce sputum-induced atelectasis
    • Treat bronchospasm (if present)

  • Improving oxygenation/perfusion in the non-ventilated lung
    • Apply 2-10cmH2O CPAP to the non-ventilated lung
    • Apply 2-10L/min 100% oxygen to the non-ventilated lung
    • Inhaled epoprostenol or nitric oxide can decrease PVR in the non-ventilated lung

  • Optimise overall V/Q matching by impairing oxygenation/perfusion in the non-ventilated lung
    • Suction of the non-ventilated lung to encourage collapse
    • TIVA anaesthetic to mitigate any volatile-induced inhibition of HPV
    • Early ligation/clamping of the ipsilateral pulmonary artery during pneumonectomy (but not lobectomy)

  • Optimise DO2
    • Ensure adequate cardiac output
    • Raise MAP with vasopressors
    • Ensure adequate volume replacement
    • Optimise haemoglobin concentration i.e. blood transfusion

  • Intermittent two-lung ventilation
  • Abandon OLV and use two-lung ventilation strategy

VATS

  • VATS may be performed with the operative lung positive to atmospheric pressure
  • This is achieved by insufflating carbon dioxide into the pleural space of the operative lung
  • Carbon dioxide insufflation can result in hypercarbia, high airway pressure, mediastinal shift and hypoxaemia
  • Management is as above but with caution over using PEEP in the non-dependent lung, which can obscure the surgical field
  • If required, apply only 2cmH2O CPAP to the non-ventilated lung

RATS

  • Robotic-assisted thoracoscopic surgery is increasingly used with evidence of positive impacts on blood loss, scarring and duration of hospital stay
  • Issues include:
    • CO2 insufflation as with VATS
    • Limited airway access because of the robot, which impairs ability to rapidly correct malpositioning
    • Increased technical difficulty in applying a pulmonary artery clamp if necessary
  • RATS should be abandoned if there is significant, refractory hypoxaemia

Bilateral procedures

  • Examples include resection of mediastinal masses and bilateral sympathectomies
  • Often performed supine, which increases the prevalence of significant hypoxaemia during one-lung ventilation

Bleomycin chemotherapy

  • Chemotherapeutic agent which causes pulmonary toxicity in up to 10% of patients
  • Said toxicity is polyfactorial but increased by the use of high fractions of inspired oxygen
  • The risk of oxygen-induced pulmonary toxicity following bleomycin therapy is lifelong
  • Target saturations are 85-88%