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Lung Isolation Devices, Applied Physiology & One-Lung Ventilation

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1. Indications for Lung Separation

Absolute Indications (Life-saving - Lung ISOLATION required)

Relative Indications (Surgical access - Lung SEPARATION sufficient)

• Pneumonectomy, lobectomy, segmentectomy, wedge resection
• Oesophagectomy, thoracic aortic aneurysm, thoracoscopy (VATS)
• Single-lung transplant
• Thoracoscopic spine surgery
• Sleeve resection (requires contralateral DLT - blocker would obstruct anastomosis)

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2. Applied Physiology of One-Lung Ventilation

2a. The Lateral Decubitus Position - Awake vs Anaesthetised

• Dependent lung: better ventilation AND better perfusion (gravity)
• V/Q matching is favourable

• Dependent lung ventilation DECREASES ~15% (diaphragm pushed cephalad, mediastinal weight, atelectasis)
• FRC falls in dependent lung
• Atelectasis averages 5-6% of lung volume, entirely in the dependent lung (vs 6% distributed equally in supine)

• FRC of nondependent lung increases ~10%
• Compliance of the entire respiratory system increases significantly
• If expiration is prolonged, both lungs collapse toward minimal volume

2b. The Obligatory Shunt of OLV

• During two-lung ventilation: Qs/Qt ~10% (5% per lung)
• During OLV: Qs/Qt rises to ~20-35%
• The nondependent lung normally receives ~45% of total pulmonary blood flow
• HPV can reduce this by ~50%, limiting it to ~22-25% of total flow
• Right thoracotomy = larger shunt (right lung is larger, ~10% better perfused)

Miller's 10e: "The essential difference between two-lung ventilation and OLV is that, during OLV, the nonventilated lung has some blood flow and therefore an obligatory shunt, which is not present during two-lung ventilation."

2c. Hypoxic Pulmonary Vasoconstriction (HPV)

• Phase 1 (rapid): Begins immediately, plateaus at 20-30 minutes
• Phase 2 (slow): Begins at ~40 minutes, plateaus after 2 hours
• Offset is also biphasic - pulmonary artery pressures may not return to baseline for several hours after prolonged OLV (clinically relevant during bilateral sequential procedures)
• HPV has a preconditioning effect - response to a second hypoxic challenge is greater than to the first

• Respiratory acidosis (increases HPV in hypoxic lung - but also increases PVR of healthy lung, no net benefit)
• Dexmedetomidine as adjunct to volatile agents improves oxygenation
• TIVA may improve oxygenation vs volatile in select cases (e.g. bleomycin patients)

• Increased CO → elevated PAP → passive pulmonary vasodilation → opposes HPV → worsens Qs/Qt
• Decreased CO → falling venous PO2 → worsens HPV stimulus in dependent lung → variable effect
• Thoracic epidural: no direct HPV effect, but hypotension + fall in CO can indirectly impair oxygenation

2d. Pulmonary Vascular Resistance and Lung Volume

• Lowest at FRC
• Rises with lung volumes ABOVE FRC (small intraalveolar vessels compressed)
• Rises with lung volumes BELOW FRC (large extra-alveolar vessels collapse)
• Goal: keep the ventilated dependent lung as close to its FRC as possible

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3. Lung Isolation Devices

3a. Double-Lumen Tubes (DLTs)

• Robertshaw design (left and right) - the standard disposable DLT in current use
• Left-sided DLT preferred for both left- and right-sided procedures
• Left DLT used successfully in >98% of cases in large series

• Right upper lobe bronchus originates only 1.5-2 cm from the carina - right DLT risks RUL obstruction
• Left mainstem bronchus is longer (~5 cm), providing more margin for safe placement
• Right DLT required when: left pneumonectomy, left sleeve resection, left mainstem tumour, left lung transplant

• Select the largest safe size - less resistance, less cuff pressure needed, less likely to migrate
• Tracheal width on CXR/CT: LMB width ≈ 0.68 × tracheal width
• Average insertion depth (lips): ~28-29 cm for a 170 cm adult, ±1 cm per 10 cm height change
• Ultrasound of trachea can estimate correct DLT size and confirm position

• Tracheal cuff: high-volume, low-pressure - up to 20 mL air
• Bronchial cuff: smaller - checked with 3 mL syringe

1. Insert with bronchial tip facing anteriorly (concave curve up)
2. After passing vocal cords, remove stylet and rotate 90° anticlockwise
3. Advance until resistance is felt (~28-29 cm at lips)
4. Confirm by auscultation + clamping test
5. Mandatory fiberoptic bronchoscopy (FOB) confirmation - visualise:
   • Blue bronchial cuff just below the carina on left
   • No obstruction of left upper lobe orifice
   • Carina visible through the tracheal lumen
6. Recheck position after lateral positioning - tube migration is common

• Airway trauma (particularly with right DLTs - high cuff pressures)
• Malposition (most common - cuff herniation over carina, endobronchial advancement)
• Difficult insertion in patients with small airway/laryngeal pathology

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3b. Bronchial Blockers (BBs)

• No tube exchange needed at end of procedure if postoperative ventilation required
• Preferred with difficult airway - SLT easier to insert than bulky DLT
• Can achieve selective lobar (rather than whole lung) collapse
• Suitable after tracheostomy
• Useful when anatomy makes DLT unsafe (e.g. after tracheal surgery, mediastinoscopy followed by thoracotomy)

• More likely to dislodge intraoperatively than DLT
• Low-pressure cuff - unreliable seal if peak airway pressures >30 cmH2O
• Limited suctioning ability
• Longer time to lung collapse
• Cannot easily apply bilateral independent lung ventilation

• Single-lumen tube with an integrated moveable bronchial blocker housed in a side channel
• Blocker has high-volume, low-pressure balloon
• Directed into mainstem bronchus under FOB guidance
• Ideal for: cases requiring tube change (e.g. mediastinoscopy → thoracotomy), bilateral lung transplant, difficult airway, anticipated prolonged postoperative ventilation
• Can apply CPAP or suction via blocker lumen

Recent meta-analysis (Kumar et al., 2023) comparing left-sided DLT vs EZ-Blocker found no significant difference in oxygenation outcomes during thoracic surgery, though DLTs were faster to position.

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4. Management of One-Lung Ventilation

4a. Confirmation of Correct Position

1. Clinical assessment (chest movement, auscultation, clamping tests)
2. Mandatory FOB verification:
   • Tracheal lumen: visualise carina; blue bronchial cuff just visible below carina on left
   • Left upper lobe orifice must be patent
3. Recheck after turning to lateral position - migration occurs frequently

4b. Ventilator Settings During OLV

• Reduce from two-lung VT to 5-6 mL/kg ideal body weight during OLV
• Larger VTs increase airway pressures and risk VILI
• Lower VTs risk progressive atelectasis

• Keeps FRC near optimal (minimises PVR and maintains V/Q matching)
• Target 5 cmH2O PEEP as a starting point
• In COPD patients with auto-PEEP (4-6 cmH2O average): adding external PEEP has complex effects
  • Low auto-PEEP (<2 cmH2O): external PEEP increases total PEEP usefully
  • High auto-PEEP (>10 cmH2O): adding external PEEP may worsen hyperinflation
• PEEP selective to dependent lung only improves gas exchange; applying bilateral PEEP in lateral position preferentially hyperinflates the nondependent lung

• DP most strongly associated with outcome/mortality (Amato et al., 3562 ARDS patients)
• DP-guided ventilation (titrate PEEP to achieve lowest DP) has been shown to reduce postoperative pneumonia and ARDS vs conventional protective ventilation during thoracic surgery (Park et al., RCT, n=292) - Barash 9e

• PC ventilation: lower peak airway pressures (beneficial after lung transplant, pneumonectomy, with BBs); closely monitor VT as lung compliance changes rapidly
• VC ventilation: guarantees consistent VT delivery
• No oxygenation advantage of PC over VC in most patients (Miller's 10e)

4c. Recruitment Manoeuvres (RMs)

• Goal: open atelectatic zones in dependent lung then maintain patency with PEEP ("open lung" strategy)
• Methods: sustained inflation 35-40 cmH2O for 30-40 seconds OR stepwise PEEP increases by 5 cmH2O q5 breaths to final PEEP of 20 cmH2O (plateau ~40 cmH2O)
• Caveats during lung resection:
  • Overpressure may leak past bronchial cuff onto bronchial stump/anastomosis
  • Impeded venous return worsens hypoxia by reducing ventilated-lung blood flow
  • Stepwise approaches preferred over abrupt sustained inflation

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5. Prediction and Treatment of Hypoxaemia During OLV

5a. Predictors of Hypoxaemia

5b. Nadir of Desaturation

• Most patients reach their lowest SpO2 within the first 10-20 minutes of OLV, stabilising as HPV increases over the next 1-2 hours
• Majority who desaturate do so quickly within 10 minutes

5c. Treatment Algorithm - Hypoxaemia During OLV

• Resume two-lung ventilation immediately (open bronchial cuff/deflate blocker)

1. Confirm FiO2 = 1.0
2. Check DLT/BB position with FOB (displacement is the commonest cause)
3. Ensure optimal cardiac output; reduce volatile anaesthetic to <1 MAC
4. Apply PEEP 5 cmH2O to the ventilated lung (with recruitment manoeuvre first)
5. Apnoeic oxygen insufflation to the non-ventilated lung (2-10 L/min O2 via catheter)
6. CPAP 1-2 cmH2O to the non-ventilated lung (first recruit it; this is the most effective single manoeuvre for refractory hypoxaemia)
7. Partial ventilation of non-ventilated lung:
   • Intermittent positive-pressure ventilation (negotiate with surgeon)
   • Selective lobar collapse (BB in most affected lobe)
   • Small VT ventilation
8. Pharmacological: consider inhaled NO, inhaled almitrine (limited availability), reduce/stop vasodilators
9. Mechanical restriction of blood flow to non-ventilated lung (surgical ligation of PA during pneumonectomy dramatically improves PaO2)
10. ECMO (last resort)

Miller's 10e: "Hypoxemia during one-lung ventilation responds readily to treatment in the vast majority of cases."

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6. Lung Separation in the Difficult Airway

• Recognised difficult airway: Awake fibreoptic intubation with DLT or SLT (then exchange to DLT via tube exchanger or direct bronchial blocker via SLT)
• Unanticipated difficult airway: Same strategy after SLT secured
• DLT is bulky with large external diameter - limited FOB manoeuvring distance
• Tube exchangers: 11 Fr fits through 35-41 Fr DLTs; 14 Fr does NOT fit through 35 Fr DLT
• Never advance tube exchanger against resistance (risk of tracheal/bronchial laceration)
• Always use laryngoscopy when passing tube over an airway guide

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7. Anaesthetic Choice

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8. Recent Evidence

• Kumar et al., 2023 (Meta-analysis, PMID 37347963) - Left DLT vs EZ-Blocker: no significant oxygenation difference; DLTs positioned faster
• Samara et al., 2024 (Review, PMID 39764824) - Updates in lung isolation techniques (Best Pract Res Clin Anaesthesiol)
• Zajac et al., 2025 (Review, PMID 40619184) - Intraoperative ventilation in thoracic surgery (Thorac Surg Clin)
• Amato et al. (NEJM) - Driving pressure most strongly associated with survival in mechanically ventilated patients

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Quick Reference Summary

INDICATIONS         DLT = lung ISOLATION (contamination, fistula, lavage)
                    DLT or BB = lung SEPARATION (surgical access)

DLT SIZING          Women <1.6m → 35Fr   | >1.6m → 37Fr
                    Men   <1.7m → 39Fr   | >1.7m → 41Fr
                    Left-sided DLT preferred in nearly all cases

OLV PHYSIOLOGY      Obligatory shunt from non-ventilated lung (~20-35% Qs/Qt)
                    HPV reduces nondependent lung blood flow by ~50%
                    HPV = biphasic (rapid 0-30min + slow 40min-2h)
                    HPV inhibited by: vasodilators, high-dose volatiles, N2O

OLV SETTINGS        VT 5-6 mL/kg IBW | PEEP 5 cmH2O | FiO2 1.0
                    Minimise driving pressure | Recheck tube position with FOB

HYPOXAEMIA Rx       1. Resume two-lung ventilation if severe
(stepwise)          2. FiO2 1.0 + FOB tube check
                    3. Optimise CO, reduce volatiles <1MAC
                    4. PEEP to ventilated lung
                    5. Apnoeic O2 to non-ventilated lung
                    6. CPAP 1-2cmH2O to non-ventilated lung (most effective)

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Addendum: Dorsch & Dorsch - Understanding Anesthesia Equipment (5th edition)

Note: Dorsch & Dorsch's Understanding Anesthesia Equipment (5th ed., Lippincott Williams & Wilkins) is not currently in the textbook library. The following section is drawn from my training knowledge of this reference text, supplemented by Morgan & Mikhail's Clinical Anesthesiology 7e (which is available in the library). Content attributed to Dorsch & Dorsch below reflects the canonical descriptions from that work.

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Dorsch & Dorsch - Equipment-Focused Notes on Lung Isolation Devices

D&D Chapter Context

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1. Double-Lumen Tubes - Construction & Design (Dorsch & Dorsch)

Basic Structure (all DLTs)

• Two parallel lumens of unequal length, fused together along their lengths
• Bronchial (longer) lumen: enters the mainstem bronchus; has the endobronchial cuff
• Tracheal (shorter) lumen: terminates in the trachea above the carina; has the tracheal cuff
• Two cuffs: one endobronchial (small, high-pressure if over-inflated), one endotracheal (high-volume, low-pressure)
• Colour coding: bronchial cuff pilot balloon and connector = blue; tracheal = clear/white (universal convention)
• Tubes made of PVC (polyvinylchloride); disposable; radiopaque stripe along length
• Pre-formed curvature to direct the bronchial tip into the desired bronchus

Robertshaw Design (the modern standard)

• Original Robertshaw (1962): red rubber, reusable, D-shaped lumens
• Modern disposable versions (Mallinckrodt, Rusch, Portex, Sheridan): PVC, single-use
• D-shaped lumens (one D + one reverse-D back to back) give larger cross-sectional area than two circular lumens - less resistance to airflow
• Bronchial tip is angled/curved to enter the appropriate bronchus

Left-Sided DLT - Anatomy

• Bronchial lumen curved to enter left mainstem bronchus
• Left mainstem bronchus is ~5 cm from carina to upper lobe takeoff - provides adequate safety margin for cuff placement without obstructing left upper lobe (LUL)
• Endobronchial cuff, when properly positioned, sits just distal to the carina in the left mainstem; inflating it ~1-2 mL provides isolation

Right-Sided DLT - Special Design Requirements

• Right-sided DLTs incorporate a lateral slot/Murphy eye (ventilation slot or "RUL portal") in the bronchial cuff or just distal to it to allow RUL ventilation
• The slot must be aligned with the RUL orifice - the most technically demanding aspect of right DLT placement
• Modified cuff designs (e.g. Bronchocath right, Rusch right):
  • Some use an asymmetric or slotted cuff with the slot positioned for RUL orifice alignment
  • The Mallinckrodt Bronchocath right has a slot within the endobronchial cuff
• Right DLT alignment is confirmed by FOB: endobronchial lumen FOB should show RUL orifice aligned with the slot
• Even with ideal positioning, right DLT malposition is far more common than with left DLTs - hence the strong preference for left DLTs in most cases

Sizes Available (all manufacturers)

• 28 Fr, 32 Fr, 35 Fr, 37 Fr, 39 Fr, 41 Fr
• 28 Fr and 32 Fr: for smaller adults and adolescents
• Internal lumen diameters: 5.0-6.0 mm per lumen (for 39-41 Fr)

Cuff Characteristics (Dorsch & Dorsch emphasis)

• Tracheal cuff: High-volume, low-pressure (HVLP); up to 15-20 mL; resting volume ~10 mL at seal pressure
• Bronchial cuff: SMALLER volume; just 1-3 mL sufficient for seal in most adults - over-inflation causes endobronchial mucosal ischaemia and bronchial rupture
  • Critical teaching point from D&D: "The bronchial cuff should be inflated with the minimum volume required to achieve a seal" - just-seal technique
  • Peak airway pressure should not exceed 30 cmH2O to prevent gas leaking past the bronchial cuff
• Cuff pressure monitoring: Recommended for bronchial cuff especially; no standardised threshold but generally <25-30 cmH2O
• Nitrous oxide diffusion: N2O diffuses into PVC cuffs over time, increasing cuff pressure - important consideration during long cases; monitor and adjust

Connector System

• Y-piece adapter at the proximal end connects both lumens to the breathing circuit
• Individual clamps (Tuohy-Borst type or simple rubber clamps) on each limb allow selective ventilation or lung collapse
• Cross-connection fittings allow independent ventilatory circuits to each lumen (e.g. for differential PEEP)

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2. Confirmation of DLT Position - The Auscultation Protocol (Morgan & Mikhail / D&D)

• Breath sounds heard bilaterally = tube is likely in trachea

• Left thoracotomy (left DLT): breath sounds should disappear on LEFT
• If sounds disappear on right → tube is in right bronchus (too far right) or tube too deep

• Inflate bronchial cuff (~2 mL)
• Ventilate via bronchial lumen only
• Sounds should be heard on ipsilateral side only

1. Tube too distal (bronchial tip too far in): Both lumens in the bronchus - clamping tracheal lumen silences both lungs
2. Tube too proximal (not far enough): Bronchial lumen tip still in trachea - no isolation achieved
3. Wrong bronchus: Left DLT in right bronchus (less common given the anatomical angle)

• The carina
• The bronchial lumen entering the left mainstem bronchus
• The top of the blue bronchial cuff just visible below the carina (not herniating above it)
• Left upper lobe orifice visible and unobstructed

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3. Bronchial Blockers - Equipment Details (Dorsch & Dorsch)

General Construction

• Flexible catheter with a distal high-volume, low-pressure balloon cuff
• Central lumen (1.4-2.0 mm depending on device): allows lung deflation (slow), O2 insufflation, or CPAP application
• Radiopaque marker at tip for CXR verification
• Proximal multiport adapter: one port for balloon inflation, one for the central lumen, one for passage of the airway tube

The Arndt Endobronchial Blocker

• Available in 5 Fr (paediatric), 7 Fr, and 9 Fr
• Unique feature: A wire loop at the distal tip - the FOB is threaded through this loop, and the blocker is "railroaded" into position as the bronchoscope is advanced into the target bronchus
• Wire loop is then retracted (straightening the tip) to allow ventilation/suction through the central lumen
• 9 Fr: requires ETT ≥8 mm; central lumen 1.4 mm
• 5 Fr: requires ETT ≥4.5 mm; suitable for children ≥2 years
• Disadvantage: The blocker is not directly visualised during insertion (only the FOB tip is seen)

Cohen Endobronchial Blocker (9 Fr)

• Unique feature: A rotating wheel at the proximal end deflects the tip in one plane (left or right) - allows directed placement without needing the FOB as a rail
• Still requires FOB for confirmation
• Central lumen 1.8 mm; Murphy eye present
• Requires ETT ≥8 mm
• More expensive than Arndt

Fuji Uniblocker (9 Fr)

• Unique feature: A pre-formed fixed angle bend at the distal end
• No active steering mechanism; relies on rotation of the catheter to direct it
• Requires FOB for confirmation of position
• Central lumen 2 mm (largest of all blockers - marginally better for suctioning)
• No Murphy eye

EZ-Blocker (7 Fr)

• Unique feature: A bifurcated Y-shaped distal end - two separate limbs that straddle the carina, one entering each mainstem bronchus
• Can be deployed without FOB guidance (Y straddles carina by design) and then the desired lobe is selectively blocked by inflating the appropriate arm's cuff
• Provides bilateral blocking capability without repositioning
• Requires ETT ≥8 mm
• No central lumen capable of suctioning - the lumens are too narrow
• Less suitable for selective lobar blocking

Balloon Characteristics (all blockers)

• High-volume, low-pressure spherical or elliptical cuff
• Inflation volume: 4-8 mL for 9 Fr; less for 5-7 Fr
• Cuff pressure must remain below 25 cmH2O to avoid mucosal ischaemia
• Critical: Peak airway pressure must be kept below 30 cmH2O or gas will bypass the cuff and break the seal

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4. The Univent Tube - Equipment Detail (Dorsch & Dorsch)

• Single lumen PVC endotracheal tube with a small anterior channel (3.5-4 mm diameter) running along the inner wall of the main tube
• The bronchial blocker catheter (7.5 Fr) sits inside this channel and can be advanced 8 cm beyond the tip of the main tube
• Tube sizes available: 3.5-9.0 mm internal diameter (most comprehensive paediatric-adult range of any lung isolation device)
  • 3.5 mm (paediatric) → 9.0 mm (large adult)
• The blocker has a high-volume, low-pressure spherical cuff (inflated with 3-8 mL)
• Central lumen of blocker: 2 mm - allows CPAP application, O2 insufflation, or slow suctioning
• Locking mechanism: A clamp at the proximal end of the channel locks the blocker in position once placed
• Tube is stiffer than standard ETTs due to the side channel - intubation may need a different laryngoscope technique
• Available in both oral and nasal versions

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5. Endobronchial (Single-Lumen) Tubes for OLV

• Gordon-Green tube / Macintosh-Leatherdale tube (historical): single-lumen endobronchial tubes designed to be advanced into the mainstem bronchus for OLV
• Largely superseded by DLTs and blockers
• Still occasionally used in paediatric thoracic anaesthesia where DLTs are too large
• In children, an appropriately sized standard ETT can be advanced into the mainstem bronchus under FOB guidance

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6. Fibreoptic Bronchoscope - The Essential Companion Tool

• Outer diameter ≤4 mm to pass through 35 Fr DLT lumen (internal diameter ~5 mm)
• Standard 4.0-4.2 mm FOB fits comfortably through 37-41 Fr DLT lumens
• For 5 Fr Arndt blocker: a 2.2 mm ultra-thin bronchoscope is required

• Carina in midfield
• Blue bronchial cuff just visible below carina in left mainstem
• Cuff not herniating above the carina
• Right mainstem bronchus unobstructed

• RUL orifice aligned with the ventilation slot/Murphy eye
• Bronchial lumen tip pointed toward right middle/lower lobe

• Initial placement
• Turning to lateral decubitus
• Any change in position
• After significant haemodynamic events or if unexplained increase in airway pressure

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7. Summary Comparison Table - All Lung Isolation Devices

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8. Paediatric Lung Isolation - Dorsch & Dorsch Emphasis

1. 5 Fr Arndt Blocker via ETT ≥4.5 mm - suitable from ~2 years
2. Univent tube (3.5-6.0 mm ID versions) - from ~6 years (10-20 kg)
3. Selective endobronchial intubation with standard age-appropriate ETT advanced into the mainstem bronchus under FOB guidance
4. Fogarty embolectomy catheter (3-4 Fr) used as improvised bronchial blocker - historical, still occasionally used
5. Cook paediatric bronchial blocker set (dedicated paediatric system)

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9. Common Equipment-Related Complications

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