Open Eye Surgery - Anaesthetic Considerations

The Core Problem: Two Competing Priorities

1. Protect airway / prevent aspiration (especially in trauma with full stomach)
2. Prevent any rise in intraocular pressure (IOP) that could expel intraocular contents - vitreous, lens, iris, or haemorrhage

Physiology of IOP - What the Anaesthetist Controls

• Barash's Clinical Anesthesia 9e, Table 49-1; Miller's Anesthesia 10e, Chapter 65

The Oculocardiac Reflex (OCR)

• Also known as the trigeminovagal reflex (Aschner-Dagnini, 1908)
• Triggered by: traction on extraocular muscles, pressure on globe, conjunctival or orbital traction, retrobulbar block performance, ocular trauma
• Afferent: ciliary nerves → ciliary ganglion → ophthalmic division of CN V → Gasserian ganglion → trigeminal sensory nucleus
• Efferent: vagal motor nucleus → heart → bradycardia, AV block, ventricular ectopy, asystole
• Medial rectus traction is the most potent trigger; response attenuates with repeated stimulation
• More frequent in children (especially strabismus surgery) than adults
• Exacerbated by hypoxia, hypercapnia, deep opioid use (fentanyl, alfentanil, remifentanil), and light anaesthesia

Management of OCR

1. Ask surgeon to cease stimulation immediately
2. Check for and treat hypoxia, hypercapnia, light anaesthesia
3. If arrhythmia persists: IV glycopyrrolate 0.1–0.2 mg (paediatric: 10 mcg/kg) or atropine 10–20 mcg/kg
4. Rarely, epinephrine for refractory severe bradycardia or asystole
5. Prophylaxis: anticholinergic premedication (atropine/glycopyrrolate), retrobulbar block (not uniformly effective), adequate anaesthetic depth

• Miller's Anesthesia 10e

The "Open-Eye, Full-Stomach" Dilemma

The Succinylcholine Controversy

Succinylcholine may be used when its benefits (rapid onset, best intubating conditions, brief duration in a cannot-intubate scenario) outweigh theoretical risk. Coughing, straining, and suboptimal intubation raise IOP far more than succinylcholine itself.

Preferred RSI Approach: Rocuronium + Sugammadex

• Rocuronium 1.2 mg/kg IV provides rapid-onset RSI conditions
• Verify complete NMB with quantitative nerve stimulator before laryngoscopy (attempting laryngoscopy before full block onset causes coughing/straining = catastrophic IOP rise)
• Reverse with sugammadex - this previously cited disadvantage (prolonged duration) is now largely eliminated
• Smooth emergence is achieved with well-timed opioids to prevent coughing/bucking at extubation

Attenuation strategies (none perfectly reliable):

• Pre-treatment with defasciculating dose of non-depolarising NMB (partial protection)
• IV lidocaine 1.5 mg/kg (some evidence for blunting haemodynamic response)
• Acetazolamide, beta-blockers, narcotics (variable efficacy)
• Barash's Clinical Anesthesia 9e; Miller's Anesthesia 10e

Regional Anaesthesia in Open Globe?

Considerations in the ELDERLY

Comorbidities

• Diabetes mellitus, hypertension, CAD, COPD, renal insufficiency are common
• Reduced functional reserve means less physiological buffer to any haemodynamic perturbation
• Polypharmacy is the rule: ophthalmic beta-blockers (timolol), alpha-agonists (brimonidine), pilocarpine, acetazolamide all have systemic effects

Ophthalmic Drug Interactions in the Elderly

MAC (Monitored Anaesthesia Care) in the Elderly

• Avoid deep sedation / polypharmacy: high-dose opioids + benzodiazepines + hypnotics in the geriatric patient risk respiratory depression, airway obstruction, hypotension, CNS aberrations, and prolonged recovery - "all the disadvantages of GA without the controllability"
• Dexmedetomidine has an extended elimination half-life in the elderly - single bolus early in the procedure allows adequate clearance
• Patients must remain sufficiently responsive to commands (movement = major cause of eye injury and medicolegal liability)
• CO2 accumulation under drapes is an underappreciated hazard - ensure adequate ventilation about the face; supplemental O2 can delay detection of hypoventilation
• Maintain adequate warmth: shivering during delicate eye surgery is dangerous and stresses the heart in CAD patients
• Avoid combining supplemental O2 + electrocautery (oculoplastic surgery) → risk of surgical fire (accounts for ~1/3 of MAC closed claims for facial surgery)
• Undersedation is equally dangerous: tachycardia and hypertension (especially in coronary disease) must be avoided

Positioning

• Arthritis and orthopaedic deformities require meticulous padding and positioning
• Patients with spinal deformity may not tolerate prolonged supine position
• Ensure patient is warm and comfortable before draping

Preoperative Evaluation

• ECG monitoring is mandatory (OCR risk, existing arrhythmias)
• Pulse oximetry + capnography (ETCO2) essential
• Screen for anticoagulation (warfarin, DOACs) - relevant to regional block haematoma risk

Considerations in PAEDIATRICS

Procedures Common in Children

• Strabismus repair (most common paediatric ophthalmic surgery)
• Retinopathy of prematurity (ROP) treatment - laser or cryotherapy in premature neonates
• Congenital cataract / glaucoma
• Eye examination under anaesthesia (EUA)
• Nasolacrimal duct probing

Oculocardiac Reflex - Paediatric Emphasis

• Medial rectus traction is the highest-risk manoeuvre
• Choi et al. reported that ketamine induction was associated with lower OCR incidence compared to propofol in children
• Anticholinergic premedication (atropine 20 mcg/kg IM or IV; glycopyrrolate 10 mcg/kg) reduces but does not eliminate incidence
• Avoid fentanyl/alfentanil/remifentanil as sole agents - opioids potentiate OCR
• Hypercapnia and hypoxia markedly exacerbate OCR - maintain normoventilation and adequate oxygenation

Strabismus Surgery - Additional Issues

• Oculogastric reflex: nausea and vomiting are extremely common (up to 50–80% without prophylaxis) - use multimodal antiemetics (ondansetron + dexamethasone); limit opioids
• Forced duction testing: surgeon may ask for testing before and after muscle adjustment - ensure adequate depth
• Malignant hyperthermia (MH): strabismus surgery has a known (though debated) association with MH susceptibility. Have dantrolene immediately available
• Succinylcholine in strabismus: avoid if MH suspected; also affects forced duction test results

Retinopathy of Prematurity (ROP)

• Often ex-premature neonates with bronchopulmonary dysplasia, corrected or uncorrected congenital heart disease, anaemia
• Risk of post-anaesthetic apnoea (especially if postconceptual age <60 weeks) - requires postoperative apnoea monitoring; caffeine may be used prophylactically
• Avoid high FiO2 (contributes to ROP progression) - use minimum O2 to maintain SpO2 90–95% in prematures

Induction Considerations

• Inhalational induction (sevoflurane) is typically used
• Ketamine (IV or IM) is useful when IV access is difficult; note it can mildly raise IOP (though data are debated)
• Propofol is safe and lowers IOP but requires IV access
• LMA is acceptable for many routine procedures (EUA, squint surgery); endotracheal intubation preferred for open globe, longer procedures, or risk of OCR/full-stomach

General Paediatric Principles

• Pre-operative fasting applies (standard nil-by-mouth times)
• Parental presence at induction reduces distress
• Dexmedetomidine (intranasal 1-2 mcg/kg) can provide anxiolysis without respiratory depression
• Temperature maintenance is critical (neonates and infants have poor thermoregulation)
• PONV prophylaxis is mandatory in all paediatric strabismus cases

Nitrous Oxide and Intravitreal Gas - A Universal Contraindication

• N2O has a much higher blood-gas partition coefficient than SF6/C3F8 → rapidly diffuses into the bubble → dramatic IOP rise → potential retinal ischaemia
• On discontinuation, the reverse occurs: bubble collapses rapidly
• N2O must be stopped at least 15 minutes before intravitreal gas injection, and avoided for weeks in patients who have received long-acting gases (C3F8 persists for up to 8–10 weeks)

Summary Table: Open Eye Anaesthesia by Population

• Barash, Cullen & Stoelting's Clinical Anesthesia 9e, Chapter 49 (Ophthalmic Anesthesia)
• Miller's Anesthesia 10e, Chapter 65 (Ophthalmic Anesthesia)