Pneumonectomy, One-Lung Ventilation (OLV) and Anaesthesia

1. Overview

2. Physiology of OLV

• The collapsed lung continues to be perfused but is no longer ventilated, creating a right-to-left intrapulmonary shunt of 20-30%, which widens the A-a O2 gradient and can cause hypoxemia (Morgan and Mikhail's Clinical Anesthesiology, 7e, p. 1024).
• Hypoxic pulmonary vasoconstriction (HPV) partially compensates by diverting blood flow away from the collapsed lung. HPV is inhibited by pulmonary hypertension, hypocapnia/alkalosis, high mixed venous PO2, hypothermia, vasodilators (nitroglycerin, nitroprusside, nitric oxide), phosphodiesterase inhibitors, beta-agonists, calcium channel blockers, and volatile anesthetics.
• Factors that instead increase flow to the collapsed lung (worsening shunt) include high mean airway pressure in the ventilated lung (high PEEP, hyperventilation, high peak pressures), low FiO2 causing HPV in the ventilated lung, and intrinsic PEEP.
• In the lateral decubitus position, gravity favors perfusion and ventilation to the dependent lung; in the awake, spontaneously breathing patient this produces good V/Q matching, but once the chest is opened, mediastinal shift and paradoxical breathing can occur, sometimes requiring emergent conversion to positive-pressure ventilation (Barash's Clinical Anesthesia, 9e, p. 3165-3166).

3. Techniques for Lung Isolation

1. Double-lumen tube (DLT) - most commonly used
2. Single-lumen tube plus a bronchial blocker
3. Single-lumen tube advanced into a mainstem bronchus
4. "Tubeless" techniques for VATS

4. Ventilator Management During OLV

• FiO2: often 1.0 for safety margin against hypoxemia, though this risks absorption atelectasis; some centers use lower FiO2 (0.5-0.8) with pressure-controlled ventilation once isolation is stable (Barash p. 3201-3202; Morgan p. 1046).
• Tidal volume: lung-protective strategy of 4-6 mL/kg predicted/ideal body weight (older practice of using two-lung tidal volumes is now discouraged) - this reduces inflammatory cytokine release and postoperative respiratory failure risk (Miller's, p. 7255; Morgan, p. 1024).
• Airway pressures: keep plateau pressure <25 cmH2O and peak pressure <35 cmH2O.
• PEEP to the dependent lung and recruitment maneuvers prevent atelectasis and derecruitment, especially since very low tidal volumes (<3 mL/kg/lung) can themselves cause atelectasis and hypoxemia.
• Permissive hypercapnia is acceptable if oxygenation and minute ventilation are otherwise reasonable.
• CPAP to the nondependent (operative) lung (5-10 cmH2O) is the single most effective maneuver to raise PaO2 during hypoxemia, keeping alveoli patent for passive oxygen uptake without fully reinflating the lung (Barash, p. 3201).

5. Managing Intraoperative Hypoxemia

1. Confirm/re-check DLT or blocker position (fiberoptic bronchoscopy) - it may shift with surgical traction.
2. Increase FiO2 to 1.0.
3. Recruitment maneuvers on the ventilated lung.
4. Apply adequate (not excessive) PEEP to the dependent lung.
5. Apply CPAP or blow-by oxygen to the operative lung (used cautiously during VATS since lung inflation obscures the surgical field).
6. As a last resort, the surgeon can clamp the pulmonary artery to the collapsed lung.

6. Pneumonectomy-Specific Anaesthetic Considerations

• Monitoring: large-bore IV access (for potential transfusion), invasive arterial line for continuous BP and blood gas sampling, and central venous access to guide fluid therapy and administer vasopressors (Miller's, p. 7254).
• Right ventricular effects: pneumonectomy raises pulmonary artery pressure and vascular resistance, increasing RV afterload; the RV may dilate with reduced function immediately postoperatively.
• Fluid management: strict restriction is recommended. Excess intraoperative fluid (>3 L in the first 24 hours), right-sided pneumonectomy, and high urine output are risk factors for postpneumonectomy pulmonary edema / acute lung injury (ALI) - a complication with only ~4% incidence but 30-50% mortality when it occurs. Inotropes/vasopressors may be used instead of fluid boluses to support hemodynamics.
• Tidal volume: 5-6 mL/kg ideal body weight recommended specifically for pneumonectomy patients; median VT >8 mL/kg was associated with higher postoperative respiratory failure risk, while <6 mL/kg was protective.
• Postpneumonectomy space management: no universal consensus - some surgeons leave no drain, others use a balanced drainage system with high/low-pressure relief valves to keep the mediastinum midline; aggressive suction on an empty hemithorax can cause mediastinal shift and hemodynamic collapse. A chest X-ray is mandatory on arrival in PACU/ICU to check mediastinal position.
• Emergence: the operative lung is reinflated gradually to a peak pressure <30 cmH2O at case end to protect the bronchial staple line; clamping the dependent lumen during reinflation prevents overdistention of the dependent lung.
• ABG monitoring: intermittent arterial blood gases are more reliable than end-tidal CO2, since OLV increases dead space and creates an unpredictable arterial-to-end-tidal CO2 gradient.

7. Recent Evidence (supplementary)