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Micro Laryngeal Surgery (MLS) and Anaesthesia

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1. DEFINITION AND OVERVIEW

• Morgan & Mikhail define it as: "laryngoscopy aided by an operating microscope"
• Introduced clinically by Oskar Kleinsasser, who adapted the microscope to direct laryngoscopy to allow fine manipulation of the vocal folds

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2. INDICATIONS

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3. SURGICAL ANATOMY - VOCAL FOLD LAYERS

Surgical principle: Preserve the SLP and vocal ligament at all costs. Violation of the vocal ligament leads to scarring and permanent voice impairment.

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4. EQUIPMENT AND SETUP

A. Patient Positioning

• Boyce-Jackson position: Flexion at the cervico-thoracic junction + extension at the atlanto-occipital joint ("sniffing position")
• This aligns the oral, pharyngeal, and laryngeal axes to allow direct line-of-sight to the larynx
• A shoulder roll may be used to aid extension
• External laryngeal counter-pressure (by assistant fingers or tape) may improve visualization in difficult cases

B. Laryngoscopes

• Multiple sizes and styles must be available (anterior-lipped, distending types)
• Rigid laryngoscope is suspended using a fulcrum suspension bar attached to the operating table - this leaves both surgeon's hands free for bimanual microsurgery
• Different blade lengths/widths allow access to anterior commissure, posterior glottis, and subglottis

C. Operating Microscope

• Focal length typically 400 mm for adult laryngoscopy
• Provides 6-40x magnification
• CO2 laser may be coupled directly to the microscope (micromanipulator)

D. Instruments

• Bouchayer forceps (atraumatic soft tissue microlaryngeal forceps) - most commonly used
• Curved and straight scissors, microforceps, microelevators, suctions
• Cold steel instruments vs. laser
• Principle: fine, sharp, and well-maintained instruments only - trauma beyond necessary = scarring = worse voice

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5. ANAESTHESIA FOR MICRO LARYNGEAL SURGERY

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ANAESTHETIC GOALS (Morgan & Mikhail)

┌─────────────────────────────────────────────────────────┐
│           KEY ANAESTHETIC GOALS IN MLS                  │
├─────────────────────────────────────────────────────────┤
│ 1. IMMOBILE SURGICAL FIELD                              │
│    → Profound neuromuscular blockade                    │
│                                                         │
│ 2. MASSETER MUSCLE RELAXATION                           │
│    → For introduction of suspension laryngoscope        │
│                                                         │
│ 3. ADEQUATE OXYGENATION AND VENTILATION                 │
│    → Without obstructing surgical field                 │
│                                                         │
│ 4. CARDIOVASCULAR STABILITY                             │
│    → Despite rapidly varying stimulation                │
│                                                         │
│ 5. RAPID RECOVERY                                       │
│    → Outpatient/day-case procedure typically            │
└─────────────────────────────────────────────────────────┘

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5A. PREOPERATIVE ASSESSMENT

• Nature of airway problem: voice disorder, stridor, hemoptysis, dysphagia
• Likely diagnosis: papillomas, tracheal stenosis, tumors, vocal cord dysfunction, foreign body
• Can the patient be mask-ventilated? (can we rescue if intubation fails?)
• Can the patient be intubated by conventional/video laryngoscopy?

• Flow-volume loop (especially in subglottic/tracheal stenosis)
• CT/MRI of neck and chest (tumor extent, tracheal narrowing)
• Review of indirect laryngoscopy or flexible nasopharyngoscopy findings

• Mallampati score, mouth opening, neck extension, thyromental distance
• Previous anaesthetic history, especially any difficult intubation records

• AVOID sedatives in patients with threatening upper airway obstruction
• Glycopyrrolate 0.2-0.3 mg IM (1 hour pre-op): reduces secretions, improves airway visualization, more effective than IV route

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5B. INDUCTION OF ANAESTHESIA

FLOW: Preoperative Assessment → Plan Airway Strategy → Induce
                                        ↓
                    Is airway potentially difficult?
                         ↙              ↘
                       YES               NO
                        ↓                ↓
          Awake FOB / Tracheostomy    Standard IV induction
          under local anaesthesia     Propofol + Fentanyl/Remifentanil
                                      + NMB (succinylcholine or rocuronium)

• Propofol 1.5-2.5 mg/kg IV (smooth, antiemetic, good for TIVA)
• Fentanyl or Remifentanil (short-acting opioids preferred for rapid recovery)
• Succinylcholine 1-2 mg/kg (rapid onset, short duration - useful for initial laryngoscopy check)
• OR Rocuronium 1.2 mg/kg with sugammadex reversal (reversed even from profound block with 16 mg/kg)

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5C. AIRWAY MANAGEMENT - METHODS OF VENTILATION

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METHOD 1: MICROLARYNGEAL ENDOTRACHEAL TUBE (MLT) - Most Common

┌─────────────────────────────────────────────────────────────┐
│              MICROLARYNGEAL TUBE (MLT)                      │
├────────────────────────────┬────────────────────────────────┤
│ Size: 4.0 / 5.0 / 6.0 mm  │ Same length as adult ETT       │
│ Cuff: HIGH-VOLUME,         │ Disproportionately large cuff  │
│       LOW-PRESSURE         │ Stiff, kink-resistant          │
├────────────────────────────┴────────────────────────────────┤
│ ADVANTAGES:                                                 │
│  ✓ Protects against aspiration                              │
│  ✓ Allows inhalational agents + ETCO2 monitoring            │
│  ✓ Conventional positive-pressure ventilation               │
│  ✓ Secure airway                                            │
├─────────────────────────────────────────────────────────────┤
│ DISADVANTAGES:                                              │
│  ✗ Occupies posterior glottis and vocal cords               │
│  ✗ Obstructs surgical access to posterior commissure        │
│  ✗ Cannot assess true cord mobility                         │
└─────────────────────────────────────────────────────────────┘

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METHOD 2: JET VENTILATION - Field-Clear Technique

• Inspiration: 1-2 seconds of high-pressure O2 jet
• Expiration: 4-6 seconds - passive, must be allowed to complete
• Chest wall movement must be monitored to prevent air trapping
• ETCO2 is unreliable (constant dilution of alveolar gases) - arterial blood gas may be needed

• 80-300 cycles/minute
• Very small tidal volumes
• Minimal movement of vocal cords - ideal for precise microsurgery
• Requires TIVA (total intravenous anaesthesia) - no inhalational agents possible

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METHOD 3: INTERMITTENT APNEA TECHNIQUE

CYCLE:
Pre-oxygenate → Ventilate via mask or ETT
        ↓
   Remove tube / withdraw
        ↓
   Surgeon operates (2-3 min apnea window)
        ↓
  SpO2 monitored continuously
        ↓
   Desaturation → Re-ventilate
        ↓
   Repeat cycle

• Duration of apnea guided by pulse oximetry (usually 2-3 min)
• Risks: Hypoventilation, hypercarbia, failure to re-establish airway, aspiration
• Suitable for short procedures and diagnostic laryngoscopy

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METHOD 4: SPONTANEOUS VENTILATION WITH VOLATILE AGENT

• Used mainly in pediatric MLS (diagnostic MLB - microlaryngoscopy and bronchoscopy)
• Sevoflurane via nasopharyngeal tube or oropharyngeal tube at corner of mouth
• Advantage: Dynamic assessment of laryngeal movements possible (cord palsy, malacia)
• Disadvantage: Less control, slower deepening, OR pollution
• Cannot assess dynamic function if paralyzed

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SUMMARY TABLE - VENTILATION METHODS

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5D. MAINTENANCE OF ANAESTHESIA

• Jet ventilation is used (no circuit connection)
• Laser surgery (reduces risk of airway fire)
• Day-case requirement

• Propofol infusion (TCI or weight-based, 4-12 mg/kg/hr): smooth, antiemetic
• Remifentanil infusion (0.05-0.5 mcg/kg/min): preferred in MLS because:
  • Procedure is intensely stimulating during laryngoscopy
  • But causes minimal postoperative discomfort (short procedure)
  • Titration of longer-acting opioids is difficult in this context
• Dexmedetomidine: useful adjunct for hemodynamic stability

• Profound NMB maintained throughout (immobile field essential)
• Options:
  • Rocuronium (1.2 mg/kg) + sugammadex reversal at end - has largely replaced succinylcholine infusion
  • Succinylcholine infusion (historical): still an option but largely obsolete now
  • Intermittent intermediate-acting NMBs (cisatracurium, vecuronium): for longer procedures

• Standard: SpO2, ETCO2, ECG, NIBP
• Train-of-four (TOF) monitor to guide NMB depth
• Arterial line during jet ventilation (for ABG if needed)

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5E. CARDIOVASCULAR STABILITY

1. Patients often have significant cardiovascular comorbidities (elderly, smokers, alcohol users)
2. The procedure alternates between intense laryngoscopic stimulation and periods of minimal stimulation

• Modest baseline anaesthesia (don't try to keep constant deep anaesthesia)
• Supplement with short-acting agents during intense stimulation:
  • IV bolus propofol or remifentanil
  • Esmolol for sudden hypertension/tachycardia
• Nerve blocks (less commonly): glossopharyngeal nerve + superior laryngeal nerve block to blunt cardiovascular response

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6. LASER SURGERY CONSIDERATIONS

Types of Lasers Used

Laser Hazards and Precautions

┌───────────────────────────────────────────────────────────────┐
│                    LASER SAFETY CHECKLIST                     │
├───────────────────────────────────────────────────────────────┤
│  PERSONNEL PROTECTION                                         │
│  ✓ Wavelength-specific laser eye protection for ALL staff     │
│  ✓ Patient's eyes taped shut + moist eye pads                 │
│  ✓ OSHA-compliant respiratory filter masks (laser plume)      │
│  ✓ OR windows covered, laser-in-use signage on door           │
│                                                               │
│  AIRWAY FIRE PREVENTION (Most Critical!)                      │
│  ✓ FiO2 < 30% (if tolerated) - N2 or air as diluent          │
│  ✓ Avoid N2O (supports combustion)                            │
│  ✓ Use laser-resistant ETT (if tube in field)                 │
│  ✓ Cuff inflated with SALINE (not air) - double-cuff tubes    │
│  ✓ No dry cotton or flammable materials near laser            │
│  ✓ Jet ventilation eliminates tube fire risk entirely         │
└───────────────────────────────────────────────────────────────┘

Laser-Resistant ETT Options

• Double-cuffed metal tubes (Hunsaker, Mallinckrodt, Laserguard): distal cuff provides backup if proximal cuff fails
• Metallic tape wrapping of standard tubes is suboptimal - no FDA approval, no cuff protection

Airway Fire Protocol

AIRWAY FIRE RESPONSE:
  1. Stop ventilation IMMEDIATELY
  2. Remove endotracheal tube from airway
  3. Disconnect circuit from anaesthesia machine; turn OFF O2
  4. Submerge burning tube in water
  5. Ventilate with face mask; re-intubate
  6. Bronchoscopy to assess airway damage
  7. Serial chest X-rays + ABG
  8. Consider bronchial lavage + IV steroids

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7. POSTOPERATIVE CARE

• Deep extubation is controversial - risk of laryngospasm
• Awake extubation preferred: ensure NMB fully reversed (TOF ratio >0.9), spontaneous breathing, responsive
• Have difficult airway trolley immediately available

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8. SPECIAL CONSIDERATIONS

A. Difficult Airway / Cannot Intubate Scenario

CANNOT INTUBATE / DIFFICULT AIRWAY ALGORITHM IN MLS:
                    ↓
    Pre-op: Identify risk factors
         (stridor, tumor, prior RT, obesity)
                    ↓
    Awake Flexible Fibreoptic Intubation (AFOI)
         under topical anaesthesia + sedation
                    ↓
    If AFOI fails OR expected severe obstruction:
         Awake tracheostomy under local anaesthesia
                    ↓
    Note: Even tracheostomy does NOT prevent
    intra-op obstruction from surgical manipulation
    or hemorrhage

B. Recurrent Respiratory Papillomatosis (RRP)

• Multiple surgeries required (debulking, not curative)
• Microdebrider or KTP laser via MLS
• Anaesthetic challenge: papillomas can shed and obstruct airway
• Prefer jet ventilation or smallest possible MLT
• Antiviral adjuvants: intralesional cidofovir, bevacizumab

C. Pediatric MLS

• Diagnostic MLB (microlaryngoscopy + bronchoscopy): spontaneous ventilation with sevoflurane preferred for dynamic assessment
• Subglottic jet ventilation impractical and risky for children (barotrauma, air trapping)
• LMA useful if flexible fibreoptic tracheobronchoscopy planned and child difficult to intubate (e.g., mandibular hypoplasia)
• Smaller instruments, greater care with positioning

D. Transoral Laser Microsurgery (TLM) for Laryngeal Cancer

• CO2 laser via suspension MLS for T1/T2 glottic carcinoma
• Excellent oncologic outcomes, voice preservation
• TIVA + jet ventilation is ideal (no flammable tube in field)
• Close coordination between anaesthetist and surgeon for "laser on/off" periods

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9. COMPLICATIONS OF MLS

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10. COMPLETE FLOW CHART: ANAESTHETIC MANAGEMENT OF MLS

PATIENT REFERRED FOR MICROLARYNGEAL SURGERY
              ↓
┌─────────────────────────────────┐
│   PRE-OPERATIVE ASSESSMENT      │
│  • Airway: MP, TMD, extension   │
│  • Pathology: stridor? stenosis?│
│  • Imaging: CT, flow-volume     │
│  • Comorbidities, medications   │
│  • Previous anaesthesia records │
└──────────────┬──────────────────┘
               ↓
    CAN AIRWAY BE SECURED SAFELY?
         ↙              ↘
       YES               NO / UNCERTAIN
        ↓                     ↓
IV Induction         AWAKE FOB / Tracheostomy
Propofol +           under local anaesthesia
Remifentanil +
Rocuronium 1.2 mg/kg
        ↓
AIRWAY SECURED - SELECT VENTILATION METHOD:
         ↓
  ┌──────────────────────────────────┐
  │ ANTERIOR/MID CORD LESION?        │
  │  → Microlaryngeal Tube (MLT)     │
  │    4-6 mm, high-vol/low-P cuff   │
  │    Conventional IPPV             │
  └──────────────────────────────────┘
  ┌──────────────────────────────────┐
  │ POSTERIOR GLOTTIS/CORDS/         │
  │ LASER SURGERY?                   │
  │  → Jet Ventilation               │
  │    (Supraglottic via scope port  │
  │     or Subglottic via cannula)   │
  │    TIVA MANDATORY                │
  │    ETCO2 unreliable - ABG PRN    │
  └──────────────────────────────────┘
  ┌──────────────────────────────────┐
  │ SHORT DIAGNOSTIC PROCEDURE?      │
  │  → Intermittent Apnea            │
  │    SpO2 guided, 2-3 min windows  │
  └──────────────────────────────────┘
  ┌──────────────────────────────────┐
  │ PEDIATRIC / DYNAMIC ASSESSMENT?  │
  │  → Spontaneous Ventilation       │
  │    Sevoflurane via NP tube       │
  └──────────────────────────────────┘
               ↓
     MAINTENANCE (TIVA preferred)
     Propofol + Remifentanil infusion
     Profound NMB maintained
     TOF monitoring
               ↓
   IS LASER BEING USED?
         ↙           ↘
       YES             NO
        ↓               ↓
  FiO2 <30%       Standard monitoring
  Avoid N2O        continues
  Laser-safe ETT
  Saline-filled cuff
  Eye protection all
  Laser plume suction
               ↓
     CARDIOVASCULAR STABILITY
     Baseline moderate anaesthesia
     Bolus propofol/remifentanil during
     intense stimulation
     Esmolol for hypertension/tachycardia
               ↓
  END OF PROCEDURE
  Reverse NMB (Sugammadex 16 mg/kg
  from deep block if rocuronium)
  TOF ratio > 0.9
  Awake extubation preferred
               ↓
  POST-OPERATIVE CARE
  SpO2 monitoring, voice rest
  Steroids if edema expected
  Day-case discharge criteria met

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QUICK REFERENCE SUMMARY

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• Morgan & Mikhail's Clinical Anesthesiology, 7e, Chapter 37 (ENT Anaesthesia, Endoscopy section) - comprehensive anaesthetic management
• Scott-Brown's Otorhinolaryngology Head & Neck Surgery, Chapter 67 (Phonosurgery/MLS technique and anatomy)
• Scott-Brown's Vol 2 (Pediatric MLS, jet ventilation)
• Cummings Otolaryngology HNS (remifentanil in suspension laryngoscopy)
• KJ Lee's Essential Otolaryngology (indications - vocal fold polyps, cysts, subglottic cysts)