One-Lung Ventilation (OLV)

Definition and Purpose

Indications

Absolute Indications (Lung Isolation - life-threatening if not done)

• Isolation of each lung to prevent contamination: massive hemoptysis, empyema, lung abscess, or bronchopleural fistula
• Unilateral pulmonary lavage (e.g., pulmonary alveolar proteinosis)
• Large bronchopleural fistula - where PPV directed to the diseased side results in inadequate ventilation of the normal lung
• Severe bullous/cystic disease - risk of tension pneumothorax

Relative Indications (Lung Separation - for surgical access)

• Lobectomy, pneumonectomy, segmental resection
• Esophageal surgery
• Thoracic aortic surgery
• Video-assisted thoracoscopic surgery (VATS)
• Minimally invasive cardiac surgery
• Transthoracic spine surgery
• Barash, Clinical Anesthesia, 9e, p. 3173
• Morgan & Mikhail's Clinical Anesthesiology, 7e, p. 1024

Physiology of OLV

The Core Problem: Obligatory Shunt

Two Main Causes of Impaired Oxygenation During OLV

1. Persisting blood flow through the non-ventilated lung - creating a direct shunt
2. Atelectasis in the dependent (ventilated) lung - causing local shunt and low V/Q areas due to lateral position, paralysis, and mediastinal weight

Hypoxic Pulmonary Vasoconstriction (HPV) - The Body's Defense

Factors that INHIBIT HPV (worsen shunting):

• Pulmonary hypertension
• Hypocapnia / respiratory alkalosis
• Increased cardiac output; increased mixed venous PO2
• Hypothermia
• Vasodilators: nitroglycerin, nitroprusside, nitric oxide
• Phosphodiesterase inhibitors (milrinone, enoximone, inamrinone)
• Beta-adrenergic agonists
• Calcium channel blockers
• Volatile (inhalation) anesthetics

Factors that DECREASE blood flow to the VENTILATED lung (indirectly worsen shunting):

• High mean airway pressures (from high PEEP, hyperventilation, or high peak inspiratory pressures)
• Low FiO2 in the ventilated lung (causes HPV in the ventilated lung)
• Vasoconstrictors with greater effect on normoxic than hypoxic vessels
• Intrinsic PEEP from inadequate expiratory times
• Morgan & Mikhail's, 7e, p. 1024-1025
• Miller's Anesthesia, 10e, p. 1321-1322

Techniques for OLV (Lung Separation Devices)

1. Double-Lumen Tube (DLT) - Most Commonly Used

• Has two lumens: one for the trachea, one for a mainstem bronchus
• Left-sided DLT preferred in most cases (safer margin to left upper lobe)
• Right-sided DLT needed for: left pneumonectomy, left mainstem bronchial stenosis, left bronchial trauma
• Confirmation of position is mandatory via fiberoptic bronchoscopy - position can shift with patient movement and surgical traction
• Risk: postoperative hoarseness (44% vs. 17% with bronchial blockers), vocal cord lesions, tracheal/bronchial laceration (rare but serious)
• Advantages: Faster placement, more reliable isolation, allows suction of both lungs, best for lung isolation cases

2. Bronchial Blocker (BB)

• A balloon-tipped catheter passed alongside or through a standard single-lumen tube, directed to the target bronchus under bronchoscopic guidance
• Types: Arndt blocker, Cohen Flex-tip blocker, Fuji Uniblocker, EZ Blocker
• Univent tube: single-lumen tube with an integrated movable endobronchial blocker
• Advantages: Useful in difficult airway, tracheostomy patients, morbidly obese, pediatric patients; avoids tube exchange at end of procedure; lower hoarseness/vocal cord injury rate
• Disadvantages: Slower to place; higher risk of displacement intraoperatively; does not provide a protective seal adequate for lung isolation (blood/pus can bypass the high-pressure balloon); limits suctioning; once deflated, the healthy lung may be contaminated

3. Endobronchial Intubation with Single-Lumen Tube

• Conventional ETT advanced into a mainstem bronchus
• Reserved as a last resort - limited control, no easy switching between lungs

4. Tubeless Techniques

• Used for select VATS procedures
• Avoids intubation entirely; relies on spontaneous ventilation with regional anesthesia

• Barash, 9e, p. 3173-3194
• Morgan & Mikhail's, 7e, p. 1025

Management of OLV: Ventilation Strategy

Tidal Volume

• Old practice: 10 mL/kg (same as two-lung ventilation) - raised PaO2 by recruiting atelectatic regions but caused ventilator-induced lung injury
• Current recommendation: 4-6 mL/kg ideal body weight - lung-protective strategy
• Tidal volumes < 3 mL/kg per lung may paradoxically cause derecruitment, atelectasis, and hypoxemia

FiO2

• Start with FiO2 1.0 in patients at risk; a lower FiO2 of 50-80% is preferred when possible
• High FiO2 carries risk of oxygen toxicity and absorption atelectasis

Ventilatory Pressures

• Plateau pressure < 25 cm H2O
• Peak airway pressure < 35 cm H2O
• Pressure-controlled ventilation may reduce peak pressures and improve gas distribution

PEEP

• PEEP to the ventilated (dependent) lung maintains it near FRC and prevents atelectasis
• PEEP must be individualized - excessive PEEP raises airway pressures, compresses alveolar vessels, and can redistribute blood flow toward the non-ventilated lung, worsening oxygenation
• Titrate PEEP to optimal compliance

Pre-OLV: Denitrogenation

• Before collapsing the non-ventilated lung, ventilate it with 100% oxygen to wash out nitrogen
• Nitrogen has low blood-gas solubility and delays collapse (especially problematic in emphysema and at start of VATS)
• Nitrous oxide accelerates collapse further but is generally avoided in thoracic cases (risk of bullae)

Recruitment Maneuvers

• Perform a recruitment maneuver to the dependent lung immediately after initiating OLV (hold at 20 cmH2O for 15-20 seconds)
• Counteracts atelectasis that accumulates during the pre-OLV two-lung phase

Permissive Hypercapnia

• Acceptable in patients with elevated CO2 despite adequate SpO2 and reasonable minute ventilation
• Hypercarbia slightly increases HPV but the net benefit is minimal and can raise PAP in the ventilated lung

Reinflation

• At end of procedure: reinflate operative lung gradually to peak inspiratory pressure < 30 cm H2O to avoid disrupting staple lines
• Miller's Anesthesia, 10e, p. 7189-7204
• Morgan & Mikhail's, 7e, p. 1046

Management of Hypoxemia During OLV

• Almitrine (IV pulmonary vasoconstrictor) - potentiates HPV, reduces shunt flow to non-ventilated lung; most effective when combined with inhaled NO
• Inhaled NO - vasodilates ventilated regions, improving V/Q; minimal effect alone but synergistic with almitrine
• Inhaled NO alone has little benefit

• Miller's Anesthesia, 10e, p. 7191
• Morgan & Mikhail's, 7e, p. 1046-1047

Acute Lung Injury (ALI) After OLV

• Overall incidence: 2.5% of all lung resections
• After pneumonectomy: 7.9%
• When ALI occurs: ~40% mortality or major morbidity

Monitoring During OLV

• Pulse oximetry - continuous SpO2 monitoring is essential
• Arterial blood gas - periodic ABG for PaO2 and PaCO2
• End-tidal CO2 - useful as a trend but underestimates PaCO2 due to increased dead space; the A-ET CO2 gradient is unpredictable during OLV

Special Situations

Summary Points

1. OLV creates an obligatory shunt (20-30%) from persistent perfusion of the non-ventilated lung
2. HPV is the main defense - inhibited by volatiles, vasodilators, and alkalosis
3. DLT is the gold standard for most cases; bronchial blocker preferred in difficult airway and tracheostomy
4. Fiberoptic confirmation of DLT/BB position is mandatory
5. Lung-protective ventilation: 4-6 mL/kg TV, low pressures, individualized PEEP
6. Acceptable SpO2 ≥ 90% during OLV; treat stepwise if hypoxemia occurs
7. ALI is the primary modern concern: protective ventilation strategy reduces risk

• Miller's Anesthesia, 10e | Morgan & Mikhail's Clinical Anesthesiology, 7e | Barash, Clinical Anesthesia, 9e