18.2 Anaesthesia for ENT and Laser Airway Surgery, Ophthalmic Surgery, and Laparoscopic and Robotic Surgery
Key Takeaways
In laser airway surgery, use a laser-resistant tracheal tube with a saline-filled cuff, keep the inspired oxygen concentration as low as possible (ideally below 30%), avoid nitrous oxide, and protect the patient's eyes.
The oculocardiac reflex (trigeminal afferent, vagal efferent) causes bradycardia with traction on the extraocular muscles, especially the medial rectus in strabismus surgery; stop the stimulus first, then give atropine or glycopyrrolate if needed.
Normal intraocular pressure is about 10-20 mmHg; suxamethonium, coughing, hypoxia, hypercapnia and pressure on the eye raise it, while most intravenous and volatile anaesthetic agents lower it.
Nitrous oxide must be avoided after intravitreal sulphur hexafluoride or perfluoropropane gas bubbles until the gas has been absorbed, because it expands the bubble and can cause central retinal artery occlusion.
Pneumoperitoneum at 12-15 mmHg raises systemic vascular resistance and mean arterial pressure, reduces FRC and compliance, increases through carbon dioxide absorption, and can cause bradycardia from peritoneal stretch.
18.2 Anaesthesia for ENT and Laser Airway Surgery, Ophthalmic Surgery, and Laparoscopic and Robotic Surgery
Ear, Nose and Throat Surgery
The Shared Airway
ENT surgery often involves the airway itself. Key principles are clear communication with the surgeon, secure tube fixation, protection of the lower airway from blood, and a plan for emergence.
| Technique | Use | Points |
|---|---|---|
| Microlaryngeal tube (small diameter, long, high-volume cuff) | Microlaryngoscopy | Good surgical access; higher resistance |
| Reinforced supraglottic airway | Tonsillectomy, nasal surgery | Avoids intubation; needs surgical cooperation |
| Tubeless techniques: jet ventilation (supraglottic or subglottic) | Laryngeal surgery, stenosis | Requires an unobstructed expiratory path to avoid barotrauma |
| High-flow nasal oxygen with apnoea (THRIVE) | Short laryngeal procedures | Apnoeic oxygenation for limited periods; carbon dioxide rises about 0.15-0.25 kPa/min |
| Tracheostomy under local or general anaesthesia | Obstructing tumours | Plan for awake techniques when the airway is threatened |
Tonsillectomy and Post-Tonsillectomy Bleeding
- Primary haemorrhage occurs within 24 hours; secondary bleeding (often at 5-10 days) is associated with infection.
- Bleeding tonsil: the patient may be hypovolaemic (blood is swallowed), with a full stomach of blood and a difficult view. Resuscitate first, then use rapid sequence induction with two suction devices and a smaller tube than usual, either supine with head-down tilt or in the left lateral head-down position according to the anaesthetist's experience; an experienced anaesthetist should attend.
Laser Surgery
Laser energy can ignite tracheal tubes, drapes and tissue in an oxygen-enriched atmosphere.
- Carbon dioxide lasers (wavelength 10,600 nm) are absorbed by water and penetrate superficially; Nd:YAG lasers (1,064 nm) penetrate deeper and can be transmitted through fibres.
- Use laser-resistant tubes (metal-wrapped or specially coated), fill the cuff with saline (often with methylene blue to show rupture), and place wet swabs around the cuff.
- Keep as low as possible (ideally below 0.3) and avoid nitrous oxide.
- Protect the eyes of the patient and staff with wavelength-specific goggles, and mark the theatre door.
- In an airway fire: stop ventilation and gas flow, remove the tube, pour saline, ventilate with air, then re-intubate and perform bronchoscopy.
Other ENT Considerations
- Nasal surgery: topical vasoconstrictors (for example co-phenylcaine or Moffett's solution) reduce bleeding; a throat pack must be removed at the end (a pack left in place can cause fatal airway obstruction; use a documented check).
- Middle ear surgery: nitrous oxide diffuses into the closed middle ear and can displace grafts; facial nerve monitoring requires avoiding neuromuscular blockade; controlled hypotension improves the surgical field.
- Postoperative nausea and vomiting is common after middle ear and tonsil surgery.
Ophthalmic Surgery
Intraocular Pressure (IOP)
Normal IOP is about 10-20 mmHg. It depends on aqueous humour production and drainage, choroidal blood volume and external pressure on the globe.
| Raises IOP | Lowers IOP |
|---|---|
| Coughing, straining, vomiting | Propofol, thiopental, volatile agents |
| Hypoxia, hypercapnia (choroidal vasodilation) | Hypocapnia |
| Suxamethonium (transient rise of about 5-10 mmHg) | Non-depolarising blockers |
| Laryngoscopy and hypertension | Head-up tilt |
| External pressure from a face mask | Acetazolamide, mannitol |
| Ketamine (variable effect) |
Open Globe (Penetrating Eye) Injury
The risk of a raised IOP is extrusion of the ocular contents, but this must be balanced against aspiration risk in a non-fasted patient. A rapid sequence induction with rocuronium (and sugammadex available) is commonly used; suxamethonium is also acceptable when rapid airway control is the priority, because the clinical risk of vitreous loss is small. Avoid coughing and pressure on the eye.
The Oculocardiac Reflex
Traction on the extraocular muscles (especially the medial rectus in strabismus surgery), pressure on the globe or orbital injection triggers bradycardia, arrhythmias or even asystole.
- Afferent: ophthalmic division of the trigeminal nerve via the ciliary ganglion.
- Efferent: vagus nerve.
- Management: stop the surgical stimulus first; then give atropine or glycopyrrolate if bradycardia persists. The reflex fatigues with repeated traction. Children are particularly susceptible.
Regional Anaesthesia for Eye Surgery
| Block | Features | Risks |
|---|---|---|
| Topical | Cataract surgery | No akinesia |
| Sub-Tenon's | Blunt cannula under Tenon's capsule | Chemosis, subconjunctival haemorrhage; serious complications rare |
| Peribulbar | Needle outside the muscle cone | Globe perforation (especially axial length above 26 mm in myopia), haemorrhage |
| Retrobulbar | Needle inside the muscle cone | Brainstem anaesthesia (injection along the optic nerve sheath into the subarachnoid space), retrobulbar haemorrhage, globe perforation |
Brainstem anaesthesia after retrobulbar block presents within minutes with confusion, apnoea, contralateral blindness or cardiovascular instability; treat with ventilatory and circulatory support until it wears off.
Intraocular Gases and Ophthalmic Drugs
- Sulphur hexafluoride (SF6) and perfluoropropane (C3F8) gas bubbles expand if nitrous oxide is given; avoid nitrous oxide until the gas has been absorbed (about 2 weeks for SF6 and 6-8 weeks for C3F8; patients wear a warning wristband).
- Echothiophate (an anticholinesterase eye drop, now rare) prolongs suxamethonium.
- Timolol drops can cause bradycardia and bronchospasm.
- Acetazolamide causes metabolic acidosis and hypokalaemia.
- Phenylephrine drops (10%) can cause hypertension.
Laparoscopic and Robotic Surgery
Physiological Effects of Pneumoperitoneum
Carbon dioxide is used because it is non-flammable and very soluble (reducing embolism risk). Intra-abdominal pressure is usually kept at 12-15 mmHg.
| System | Effect |
|---|---|
| Cardiovascular | Raised systemic vascular resistance and mean arterial pressure; cardiac output often falls initially; venous return falls at higher pressures; vagal bradycardia or asystole during insufflation |
| Respiratory | Cephalad diaphragm displacement, reduced FRC and compliance, atelectasis, raised airway pressure; endobronchial intubation as the carina moves upward |
| Carbon dioxide absorption | Raises and end-tidal carbon dioxide; minute ventilation must increase by about 15-25% |
| Renal | Reduced renal blood flow and urine output |
| Cerebral and ocular | Raised intracranial and intraocular pressure, especially with steep head-down tilt |
Positioning
- Steep Trendelenburg (for example 30-45° in robotic prostatectomy) increases venous pressure in the head, causes facial and airway oedema, raises intraocular pressure and may cause the patient to slide; limit duration and protect pressure points.
- Reverse Trendelenburg (upper abdominal surgery) reduces venous return.
Complications
- Carbon dioxide embolism: sudden fall in end-tidal carbon dioxide, hypotension, a "mill-wheel" murmur; stop insufflation, release the pneumoperitoneum, give 100% oxygen, place in left lateral head-down position, aspirate through a central line if present.
- Subcutaneous emphysema and pneumothorax or pneumomediastinum from tracking of gas (especially in hiatus hernia surgery), causing a rising end-tidal carbon dioxide.
- Vascular and visceral injury during trocar insertion.
- Shoulder tip pain from residual gas irritating the diaphragm.
During strabismus surgery in a child, the heart rate falls abruptly from 110 to 45 beats/min as the surgeon pulls on the medial rectus muscle. What is the first action?
Give adrenaline 10 micrograms/kg intravenously immediately
Ask the surgeon to stop traction on the muscle
Deepen anaesthesia with a bolus of propofol
Start external cardiac pacing
A patient had vitreoretinal surgery with a perfluoropropane (C3F8) gas bubble 2 weeks ago and now needs an emergency appendicectomy. What is the most important anaesthetic precaution?
Avoid suxamethonium because it permanently raises intraocular pressure
Give acetazolamide to shrink the gas bubble before induction
Avoid nitrous oxide, which would expand the bubble and could occlude the retinal artery
Use a high inspired oxygen concentration of 100% throughout to speed absorption of the bubble
Which physiological change typically accompanies carbon dioxide pneumoperitoneum at 15 mmHg in a healthy patient?
A fall in systemic vascular resistance and a rise in functional residual capacity
Reduced end-tidal carbon dioxide because carbon dioxide is poorly soluble in blood
Improved renal blood flow because of raised abdominal pressure
Raised SVR and MAP, reduced FRC and a rising
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