14.2 Thoracic Surgery & One-Lung Ventilation Support

14.2 Thoracic Surgery & One-Lung Ventilation Support

Thoracic surgical procedures—including pulmonary resections (pneumonectomy, lobectomy, segmentectomy, wedge resection), video-assisted thoracoscopic surgery (VATS), robotic thoracic procedures, and esophageal surgery—require specialized anesthesia interventions to facilitate surgical exposure and protect healthy lung tissue. Achieving deliberate collapse of the operative lung while maintaining gas exchange through the non-operative lung is known as one-lung ventilation (OLV). Anesthesia technologists must possess a thorough technical mastery of lung isolation devices, fiberoptic bronchoscopy verification techniques, positioning physiology, and the clinical management of acute hypoxemia during thoracic cases.

---

Lateral Decubitus Positioning & V/Q Physiology

Most open thoracotomies and VATS procedures are performed with the patient placed in the lateral decubitus position (operative lung positioned upward [non-dependent], non-operative lung positioned downward [dependent]). The cardiopulmonary consequences of this position differ fundamentally between an awake, spontaneous breathing state and an anesthetized, paralyzed state.

+-----------------------------------------------------------------------------+
|         LATERAL DECUBITUS POSITION: VENTILATION / PERFUSION MISMATCH        |
+-----------------------------------------------------------------------------+

   UPPER (NON-DEPENDENT) LUNG: Operative / Non-Ventilated
   - Receives ~40% of Pulmonary Blood Flow (Low hydrostatic gravity)
   - Under positive pressure ventilation: High Compliance -> Over-ventilated
   - During OLV: Ventilated = 0, Perfused > 0 -> TRUE TRANS-PULMONARY SHUNT!
   =========================================================================
   LOWER (DEPENDENT) LUNG: Non-Operative / Ventilated
   - Receives ~60% of Pulmonary Blood Flow (High hydrostatic gravity)
   - Compressed by: Mediastinum + Abdominal contents pushing up diaphragm
   - Under positive pressure ventilation: Low Compliance -> Prone to Atelectasis

The Awake vs. Anesthetized State

• In the Awake, Spontaneously Breathing Patient: Gravity draws approximately 60% of total pulmonary blood flow to the dependent lung due to hydrostatic pressure gradients. Simultaneously, the dependent diaphragm sits higher in the thoracic cage, placing its muscle fibers on a more advantageous portion of the length-tension curve. Upon contraction, the dependent lung expands efficiently, receiving the majority of ventilation. Thus, ventilation and perfusion are well matched (V/Q ≈ 1.0), and oxygenation is preserved.
• In the Anesthetized, Paralyzed, Mechanically Ventilated Patient: While gravity continues to divert 60% of blood flow to the dependent lung, positive pressure mechanical ventilation redistributes gas unfavorably. The dependent lung experiences reduced compliance because it is physically compressed by the weight of the overlying mediastinum and cephalad displacement of abdominal viscera against the relaxed dependent hemidiaphragm. Consequently, mechanical breaths preferentially divert into the compliant, non-dependent upper lung. This produces a significant ventilation-perfusion (V/Q) mismatch: the upper lung is over-ventilated and under-perfused (wasted dead space), while the lower lung is under-ventilated and over-perfused (physiological shunt).

---

Indications for Lung Separation

Lung isolation is indicated either to protect one lung from the other or to optimize surgical conditions. These indications are traditionally categorized as Absolute or Relative.

---

Double-Lumen Endotracheal Tubes (DLTs)

The Double-Lumen Endotracheal Tube (DLT) (most commonly the Robertshaw design) is the primary workhorse device for lung separation. It consists of two conjoined lumens of unequal length molded into a single rigid polyvinyl chloride (PVC) tube:

1. Tracheal Lumen: Terminates above the carina in the distal trachea; features a clear, high-volume low-pressure (HVLP) tracheal cuff.
2. Bronchial Lumen: Curves and extends past the carina into either the left or right mainstem bronchus; features a distinctive blue, low-volume high-pressure (or HVLP) bronchial cuff.

Left-Sided vs. Right-Sided DLTs

A left-sided DLT is selected in > 90% to 95% of all clinical cases, regardless of whether the surgery is being performed on the right or left lung.

• Anatomy of the Left Mainstem Bronchus: The adult left mainstem bronchus has an average length of 5.0 cm (range 4.5 to 5.5 cm) from the carina to its bifurcation into the left upper and lower lobe bronchi. This extensive length provides a wide, safe "landing zone" where the bronchial cuff can inflate without obstructing any lobar takeoff.
• Anatomy & Hazards of the Right Mainstem Bronchus: The right mainstem bronchus is wider and steeper, but critically, it is exceptionally short: the right upper lobe (RUL) bronchus takeoff originates only 1.5 to 2.5 cm from the carinal bifurcation. A standard circumferential cuff would inevitably occlude the RUL orifice. Therefore, a Right DLT requires a specialized slotted (fenestrated) bronchial cuff.
• The Right DLT Hazard: The ventilation slot of the Right DLT must be positioned millimeter-perfect over the RUL bronchial opening. Even a small rotational or axial displacement can block ventilation to the right upper lobe, triggering massive RUL atelectasis and arterial desaturation. Right DLTs are generally reserved for cases where a left DLT is unsuitable, such as a left mainstem bronchus distorted or compressed by tumor or a thoracic aortic aneurysm, left mainstem bronchus disruption, or some left pneumonectomy and left sleeve resection cases.

+-----------------------------------------------------------------------------+
|                     DLT SIZING AND INTUBATION REFERENCE                     |
+-----------------------------------------------------------------------------+
| Patient Group         | Height Criteria              | DLT French Size      |
+-----------------------+------------------------------+----------------------+
| Small Female          | < 160 cm (5 ft 3 in)         | 35 Fr                |
| Average Female        | ≥ 160 cm (5 ft 3 in)         | 37 Fr                |
| Small Male            | < 170 cm (5 ft 7 in)         | 39 Fr                |
| Average / Large Male  | ≥ 170 cm (5 ft 7 in)         | 41 Fr                |
+-----------------------+------------------------------+----------------------+
| Typical Depth at Teeth| Females: 27 - 29 cm          | Males: 29 - 31 cm    |
+-----------------------+------------------------------+----------------------+

Fiberoptic Bronchoscopy (FOB) Positioning Verification

Height-based sizing is only a starting guide. Studies have found malposition on bronchoscopy in a substantial share (roughly a third or more) of double-lumen tubes that seemed correctly placed by auscultation alone. Direct visualization with a small flexible bronchoscope (sized to fit the tube lumen, commonly about 3.5 to 4 mm outer diameter) is the standard way to confirm placement.

                    FIBEROPTIC BRONCHOSCOPY VERIFICATION STEPS
                                      |
        +-----------------------------+-----------------------------+
        |                                                           |
        v (Down Tracheal Lumen)                                     v (Down Bronchial Lumen)
VIEW CARINAL BIFURCATION                                    VIEW SECONDARY CARINA
- Identify carinal ridge.                                   - Advance into left mainstem bronchus.
- Confirm bronchial limb enters left bronchus.              - Identify left upper lobe (LUL) and
- Verify blue bronchial cuff is visible                       left lower lobe (LLL) orifices.
  JUST BELOW the carina without herniating.                 - Confirm tip does not occlude either
- Herniation occludes right mainstem!                         lobar bronchial takeoff.

Critical Re-Verification Rule: The DLT position must be verified by FOB twice: first immediately after intubation in the supine position, and second after positioning in the lateral decubitus position. Turning the patient stretches the neck and displaces the carina relative to the trachea, frequently dislodging the tube tip cephalad or caudad.

---

Bronchial Blockers

A Bronchial Blocker is an alternative lung isolation device consisting of a long, thin, flexible catheter (typically 7 to 9 Fr) with an inflatable high-volume low-pressure distal balloon (spherical or elliptical) that is deployed through a standard single-lumen endotracheal tube (SLT).

Major Device Types

1. Arndt Wire-Guided Blocker: Features a dedicated internal nylon guide wire that forms an adjustable loop at the catheter tip. The loop is coupled around a pediatric fiberoptic bronchoscope; as the bronchoscope is steered into the target mainstem bronchus, the blocker is advanced alongside it, after which the wire loop is tightened and withdrawn.
2. Cohen Flexitip Blocker: Features a steerable distal tip controlled by a wheel mechanism at the proximal handle, allowing the clinician to deflect the tip into the left or right mainstem bronchus under direct bronchoscopic vision.
3. Univent Tube: A specialized single-lumen endotracheal tube containing an integrated second lumen that houses a retractable, moveable bronchial blocker.
4. EZ-Blocker: Features a bifurcated, Y-shaped distal tip with two color-coded inflatable balloons that seat naturally across the carina, allowing selective isolation of either mainstem bronchus.

Clinical Indications for Bronchial Blockers

Bronchial blockers are preferred over DLTs in specific high-risk clinical scenarios:

• Difficult Airway: In patients with a known or anticipated difficult airway (limited mouth opening, cervical spine instability, glottic stenosis), intubation with a bulky, rigid DLT (35-41 Fr) carries high morbidity. The airway is secured with a standard 8.0-mm SLT, and a bronchial blocker is placed coaxially.
• Pre-existing Tracheostomy: DLTs cannot be placed through a standard tracheostomy stoma; a bronchial blocker is inserted through a tracheostomy tube.
• Anticipated Postoperative Mechanical Ventilation: If the patient will require ongoing mechanical ventilation in the ICU after surgery, using a bronchial blocker avoids the dangerous step of exchanging a DLT for an SLT in an airway compromised by post-thoracotomy facial and laryngeal edema.
• Pediatric Thoracic Surgery: DLTs are not made in sizes small enough for infants and young children (the smallest widely available DLT is about 26 Fr, suitable only for older children). Bronchial blockers (5 Fr) can isolate lungs in pediatric patients.

---

Hypoxemia During OLV & Hypoxic Pulmonary Vasoconstriction (HPV)

During one-lung ventilation, the operative lung is allowed to collapse while the dependent lung is ventilated. Blood continuing to perfuse the unventilated, collapsed lung creates an obligatory transpulmonary right-to-left shunt (V/Q = 0). Deoxygenated mixed venous blood (PvO₂ ≈ 40 mmHg) mixes with oxygenated blood returning from the dependent lung, lowering arterial oxygen saturation (SpO₂) and PaO₂.

The Protective Role of Hypoxic Pulmonary Vasoconstriction (HPV)

Under normal conditions, Hypoxic Pulmonary Vasoconstriction (HPV) is the body's primary protective reflex against shunt. In response to alveolar hypoxia in the non-ventilated lung, small pulmonary arteries and arterioles constrict. This increases vascular resistance in the operative lung and can reduce its blood flow by roughly half, and redirecting it to the ventilated dependent lung. This intrinsic response substantially limits the transpulmonary shunt.

Factors That Blunt HPV

Anesthesia personnel must avoid pharmacologic agents and physiological states that inhibit HPV:

• Volatile Inhalational Anesthetics: Sevoflurane, desflurane, and isoflurane produce a dose-dependent inhibition of HPV. While concentrations < 1.0 MAC produce minimal blunting, concentrations > 1.0 MAC significantly inhibit arteriolar vasoconstriction, widening the shunt and causing hypoxemia. Many thoracic anesthesiologists deploy Total Intravenous Anesthesia (TIVA) or maintain volatile agents strictly below 1.0 MAC.
• Vasodilator Medications: Direct systemic vasodilators—including sodium nitroprusside, nitroglycerin, hydralazine, calcium channel blockers, and beta-2 agonists—can inhibit hypoxic pulmonary vasoconstriction and worsen oxygenation during OLV.
• Extreme Hemodynamic Variables: Severe hypocapnia, extreme alkalosis, or elevated left atrial/pulmonary artery pressures also blunt HPV.

---

Stepwise Algorithm for Refractory Hypoxemia During OLV

When arterial oxygen saturation declines (SpO₂ < 90–92%) during one-lung ventilation, the anesthesia team must execute a structured, standardized troubleshooting algorithm.

+-----------------------------------------------------------------------------+
|                 STEPWISE MANAGEMENT ALGORITHM FOR OLV HYPOXEMIA             |
+-----------------------------------------------------------------------------+
                                      |
                                      v
  STEP 1: MAXIMIZE INSPIRED OXYGEN (FiO2 1.0)
  - Deliver 100% O2 immediately; verify circuit integrity and analyzer.
                                      |
                                      v
  STEP 2: BRONCHOSCOPIC VERIFICATION OF TUBE POSITION
  - Insert pediatric fiberoptic bronchoscope down tracheal and bronchial lumens.
  - RULE OUT MALPOSITION: Bronchial cuff herniation over carina or dislodgement
    is the most frequent cause of acute intraoperative hypoxemia!
                                      |
                                      v
  STEP 3: APPLY CPAP (5 - 10 cmH2O) TO NON-DEPENDENT (OPERATIVE) LUNG
  - HIGHLY EFFECTIVE MANEUVER: Deliver low-pressure continuous O2 to collapsed lung.
  - Maintains minimal alveolar patency for oxygen uptake without expanding lung
    enough to obscure the surgical field (may still hinder VATS). Reduces shunt.
                                      |
                                      v
  STEP 4: APPLY PEEP (5 cmH2O) TO DEPENDENT (VENTILATED) LUNG
  - Recruits atelectatic alveoli in dependent lung, increasing FRC.
  - CAUTION: Avoid excessive PEEP (> 8-10 cmH2O); high PEEP increases dependent
    pulmonary vascular resistance, diverting blood BACK to the non-ventilated lung!
                                      |
                                      v
  STEP 5: ALVEOLAR RECRUITMENT MANEUVER TO DEPENDENT LUNG
  - Perform a sustained-inflation recruitment maneuver to re-expand alveoli.
                                      |
                                      v
  STEP 6: RESUME INTERMITTENT TWO-LUNG VENTILATION
  - If hypoxemia is refractory, inform the surgeon and re-expand the operative lung.
  - In pneumonectomy, the surgeon can clamp the pulmonary artery early to abolish shunt.

The order of Steps 3 through 5 varies among references. During VATS, many teams recruit the ventilated lung and add PEEP before CPAP, because CPAP can partially reinflate the operative lung and hinder the surgeon's view.

Equipment Checklist for the Anesthesia Technologist

To ensure flawless support during thoracic surgical cases, the anesthesia technologist should have the following equipment prepared and tested prior to patient arrival:

1. DLTs & Stylets: Left-sided DLTs in sizes 35, 37, 39, and 41 Fr, paired with malleable stylets lubricated and pre-shaped with a hockey-stick curve.
2. Fiberoptic Bronchoscope Tower: Pediatric video bronchoscope (outer diameter ≤ 3.8 mm), light source, anti-fog solution, suction adapter, and silicone lubricant.
3. Airway Adapters & CPAP Valves: Y-piece swivel connectors, right-angle catheter mounts, DLT clamp forceps, and a dedicated CPAP delivery system (e.g., a disposable CPAP valve supplied by a separate oxygen flowmeter) capable of delivering 5 to 10 cmH₂O of oxygen to the operative lung.
4. Bronchial Blocker Kit: Wire-guided or Cohen flexitip blockers, multi-port endoscopy swivel adapters, and single-lumen ETTs (sizes 7.5 to 8.5 mm ID).