Anaesthetic Considerations for Strabismus Surgery in Pediatric Patients

1. Patient Population and Preoperative Considerations

• Most strabismus patients are otherwise healthy children, but strabismus incidence is increased in CNS dysfunction: cerebral palsy, meningomyelocele with hydrocephalus.
• Strabismus may be acquired secondary to oculomotor nerve trauma or sensory abnormalities (cataracts, refractive errors).
• Infantile strabismus presents within the first 6 months; these youngest patients carry the highest risk.
• Patients with Down syndrome, prematurity, or metabolic myopathies require tailored evaluation.
• Standard preoperative assessment applies; laboratory testing is not routinely required for healthy children.
• Premedication with oral midazolam facilitates smooth induction and is not associated with significant IOP change.

2. Malignant Hyperthermia (MH) - Critical Consideration

• (Barash's Clinical Anesthesia, 9e, p. 4192)
• (Miller's Anesthesia, 10e, p. 9750)

3. The Oculocardiac Reflex (OCR) - Most Critical Intraoperative Hazard

Mechanism

• Traction on the extraocular muscles (especially medial rectus)
• Pressure on the globe
• Manipulation of conjunctiva, orbital structures, or periosteum

Manifestations

• Most common: sinus bradycardia
• Also: junctional rhythm, ectopic atrial rhythm, AV block, ventricular bigeminy, multifocal PVCs, wandering pacemaker, idioventricular rhythm, asystole, ventricular tachycardia

Incidence

• Reported range: 16% to 82%
• Children have higher vagal tone and therefore a higher incidence than adults
• Hypercapnia, hypoxemia, and shallow anesthetic depth exacerbate the reflex

Prevention

Management When OCR Occurs

1. Ask the surgeon to immediately cease manipulation (first step)
2. Evaluate and correct hypoxia, hypercapnia, inadequate anesthetic depth
3. Heart rate typically returns to baseline within 20 seconds with cessation of stimulus
4. Note: tachyphylaxis occurs - the reflex attenuates with repeated manipulation
5. If bradycardia persists: IV glycopyrrolate 10 mcg/kg or atropine 10-20 mcg/kg
6. Severe/refractory cases: epinephrine may be required

• (Miller's Anesthesia, 10e, pp. 9715-9716)
• (Barash's Clinical Anesthesia, 9e, pp. 4150-4151)

4. Oculorespiratory Reflex (ORR) - Lesser Known

• Not responsive to anticholinergics
• May go unnoticed because of assisted ventilation modes
• A reason to maintain close monitoring of respiratory parameters during strabismus surgery
• (Miller's Anesthesia, 10e, p. 9751)

5. Forced Duction Test (FDT) and Succinylcholine

• Avoid succinylcholine in patients where the ophthalmologist plans to use FDT
• If succinylcholine is used (e.g., for emergency laryngospasm), the FDT must be delayed at least 20 minutes
• In current practice, strabismus surgery in children generally does not require neuromuscular blockade at all
• Succinylcholine in children is reserved for emergencies (laryngospasm)
• (Barash's Clinical Anesthesia, 9e, pp. 4192-4193)

6. Airway Management

• Laryngeal Mask Airway (LMA/SGA) is the preferred airway for strabismus surgery (provided no aspiration risk):
  • Can be inserted without muscle relaxants
  • Causes less hemodynamic perturbation than ETT
  • Less straining/coughing on removal
  • Avoids the succinylcholine/FDT interaction entirely
• Tracheal intubation is reserved for patients at aspiration risk or with specific airway concerns

7. Postoperative Nausea and Vomiting (PONV) - Major Problem

Eberhart's 4-Point Risk Score for POV in Children

PONV Prevention Strategy

• For high risk (≥2 risk factors) - which includes essentially all strabismus patients:
  • Dexamethasone 0.1-0.2 mg/kg at start of procedure
  • Ondansetron 0.1 mg/kg toward the end of the case
  • Propofol infusion at subhypnotic dose + antiemetic combination
• For 4 risk factors (maximal risk):
  • Avoid nitrous oxide and volatile inhalational agents
  • Implement TIVA with propofol
• Other agents: NK1 antagonist aprepitant (oral preop or IV); droperidol (0.075 mg/kg at induction is effective but limited by FDA black box warning for QTc prolongation)
• Note: TIVA/propofol reduces POV but is associated with a higher incidence of OCR and bradycardia - a trade-off that must be managed
• (Miller's Anesthesia, 10e, pp. 9750-9751)
• (Barash's Clinical Anesthesia, 9e, pp. 4193-4194)

8. Anesthetic Agents - Key Interactions Summary

9. Associated Systemic Conditions to Screen For

• Cerebral palsy / CNS dysfunction: altered pharmacodynamics, aspiration risk, positioning issues
• Meningomyelocele with hydrocephalus: latex allergy protocol, VP shunt considerations
• Down syndrome: atlantoaxial instability, subglottic stenosis, congenital heart disease
• Neuromuscular disorders (e.g., myopathies): heightened MH susceptibility, avoid succinylcholine broadly

10. Quick Reference - Key "Do Not Miss" Points

1. MH susceptibility is theoretically increased - be prepared
2. OCR will happen - anticipate it, have anticholinergics drawn and ready
3. Avoid succinylcholine if FDT is planned intraoperatively
4. LMA is the airway of choice (no muscle relaxant needed)
5. Aggressive PONV prophylaxis is mandatory (dual/triple therapy for most)
6. TIVA vs inhalational is a deliberate trade-off (less PONV vs more OCR)
7. Opioid-sparing where possible (less OCR, less PONV)
8. Watch for the oculorespiratory reflex - it won't respond to atropine

Anaesthetic Management for Elderly Cataract Surgery

1. Preoperative Evaluation

No Routine Testing

Conditions Requiring Optimization Before Proceeding

Key Elderly-Specific History Points

• Systemic ophthalmic drug effects: Timolol (beta-blocker drops) can cause bradycardia, bronchospasm; phenylephrine drops (10%) contain 5 mg per drop - cardiovascular effects in elderly. Acetazolamide causes fluid/electrolyte disturbance. Echothiophate iodide (phosphodiesterase inhibitor) prolongs succinylcholine effect.
• Alpha-1 antagonists (tamsulosin, silodosin): Cause Intraoperative Floppy Iris Syndrome (IFIS) - triad of poor pupil dilation, floppy iris, iris prolapse - persists >1 year after stopping; anesthesiologist must inform the surgeon.
• Anticoagulants/antiplatelets: Safe to continue warfarin (if INR within range) and antiplatelet agents for cataract surgery. Risk of retrobulbar hemorrhage with needle blocks in anticoagulated patients favors topical or sub-Tenon technique.
• Previous intraocular gas bubble (SF6, C3F8): Must avoid nitrous oxide (causes expansion of bubble).
• High myopia (axial length >25 mm): Increased risk of globe perforation with needle blocks - favor sub-Tenon or topical technique.
• Positioning ability: Patient must lie flat (supine) for the duration. Cervical/lumbar spine disease, severe GORD, heart failure, and claustrophobia require special planning.
• Cognitive status: Dementia or inability to cooperate precludes topical anesthesia and may require general anesthesia.

2. Anesthesia Options for Cataract Surgery

Comparison Overview

3. Orbital Block Techniques

Needle positions for retrobulbar (intraconal) and peribulbar (extraconal) blocks - Miller's Anesthesia, 10e

Intraconal block with the orbital muscle cone - Barash's Clinical Anesthesia, 9e

A. Retrobulbar (Intraconal) Block

• Needle position: Inside the muscular cone (intraconal), behind the globe
• Technique: With globe in primary gaze, a 3-cm, 23-27 gauge needle is placed at the junction of the inferior and lateral walls of the orbit just above the inferior orbital rim. Advanced parallel to the orbit floor (~10-degree elevation) for ~15 mm past the equator, then redirected medially and slightly upward toward the pupil-macula axis. 2-5 mL local anesthetic injected.
• Onset: Rapid (5-10 min)
• Provides: Dense analgesia + profound akinesia of all extraocular muscles (note: superior oblique is outside the cone and may not be fully blocked)
• Advantages: Quicker onset, less chemosis than peribulbar
• Complications:
  • Retrobulbar hemorrhage (~1%): venous (usually self-limiting) vs arterial (can threaten vision - may require lateral canthotomy)
  • Globe perforation: risk higher with high myopia (axial length >25 mm) and inexperienced operators; devastating prognosis if delayed diagnosis
  • Brainstem anesthesia: retrograde tracking of LA along the optic nerve sheath into subarachnoid space - presents with aphasia, confusion, apnea, cardiac arrest, loss of consciousness; management is supportive
  • Intra-arterial injection: retrograde to ICA → CNS excitation, seizures
  • Optic nerve damage

B. Peribulbar (Extraconal) Block

• Needle position: Outside the muscular cone, anterior to equator of the globe
• Technique: A 3-cm, 23-gauge needle at the junction of the middle and lateral thirds of the lower lid, directed vertically backwards parallel to the orbit floor. Classic technique uses two injections (inferotemporal + superonasal). Larger volume (5-10 mL) needed vs retrobulbar.
• Advantages over retrobulbar:
  • Needle does not pass through the muscle cone → lower risk of optic nerve injury and direct muscle trauma
  • No retrobulbar hemorrhage (needle stays anterior)
  • Preferred in the United States since the mid-1990s
• Disadvantages:
  • Slower onset (slower diffusion across the cone septae)
  • Incomplete akinesia more common
  • Greater volume injected → greater IOP rise initially (5-10 mmHg, falls to below baseline within 5 min)
  • More chemosis

C. Sub-Tenon (Episcleral) Block

• Technique: After topical anesthesia, a small incision is made in the conjunctiva and Tenon's capsule (usually inferonasal quadrant) with fine scissors. A blunt cannula is guided through the opening and local anesthetic (typically 3-5 mL) is infused into the episcleral space. LA spreads into the posterior orbit.
• Advantages:
  • No sharp needle in the posterior orbit - significantly reduced risk of globe perforation, especially in high myopia
  • Excellent option for anticoagulated patients (risk of significant hemorrhage is very low)
  • Rapid onset of analgesia
  • Preferred in the UK and New Zealand
• Disadvantages:
  • Requires conjunctival incision (surgeon or skilled anesthesiologist)
  • Chemosis, conjunctival bleeding common (cosmetically minor)
  • Akinesia may be incomplete (especially with small-volume techniques)
• Complications: Globe perforation (with longer metallic cannulae), hemorrhage, rectus muscle trauma, postoperative strabismus, orbital cellulitis, brainstem anesthesia (rare)
• Note: Sub-Tenon block is the preferred choice in anticoagulated elderly and in high myopia.

D. Topical Anesthesia (TA)

• Agents: 0.5% tetracaine drops, 0.75% bupivacaine drops, 2% lidocaine drops/gel, or lidocaine gel (gels provide higher anterior chamber concentration)
• Supplement: Intracameral injection of 0.1-0.2 mL 1% preservative-free lidocaine into the anterior chamber ("sugarcaine" = lidocaine + bisulfite-free epinephrine)
• Advantages:
  • No injection → no risk of retrobulbar hemorrhage or globe perforation
  • Ideal for anticoagulated patients, monocular patients (avoids prolonged amaurosis)
  • Most widely used technique for routine cataract surgery in cooperative patients
• Limitations:
  • No akinesia - requires full patient cooperation and ability to fixate
  • Contraindications: Dementia, inability to communicate, photophobia, active infection, dense cataract requiring significant iris manipulation, large scleral incisions anticipated
  • Some discomfort - may need IV analgesic supplementation
  • Analgesia dissipates with constant irrigation

E. Facial Nerve Block (Adjunct)

• Motor innervation of orbicularis oculi is outside the orbital cone, so retrobulbar/peribulbar blocks do not prevent lid squeezing.
• Facial nerve blocks (van Lint technique at orbital rim, or O'Brien technique at the mandibular condyle) provide lid akinesia.
• Less frequently used with peribulbar technique (which partially obtunds the orbicularis) and not needed with topical anesthesia if patient is cooperative.

4. Local Anesthetic Choice and Adjuvants

5. Monitored Anesthesia Care (MAC) - Sedation Strategy

For Topical Anesthesia Cases

• Most patients want sedation even with topical anesthesia.
• Midazolam: Primary anxiolytic; side effects of oversedation, paradoxical reaction, postoperative delirium and memory deficit are particularly concerning in the elderly
• Remimazolam: Newer FDA-approved benzodiazepine with rapid onset/metabolism - promising for elderly cognitive safety; further study needed
• Low-dose propofol + short-acting opioid: Reasonable alternatives
• Dexmedetomidine: Effective sedation with minimal respiratory depression and analgesia; however causes bradycardia, hypotension, and prolonged recovery - use case by case
• Ketamine: NOT appropriate - dysphoric and hallucinogenic properties
• Avoid oversedation: Sudden awakening under drapes leads to disorienting movement - potentially catastrophic for an open eye

For Orbital Block Cases (MAC During Block Placement)

• 6 parts 10 mg/mL propofol + 2 parts alfentanil (or fentanyl) + 2 parts 1% lidocaine in a single syringe
• Titrated by age and weight; produces OAA/S level 3 sedation within 30-90 seconds
• Provides excellent analgesia + sedation + hemodynamic stability with minimal airway need
• Sedation maintained at OAA/S 3 (comfortable, follows commands, remains still)
• After the block, an orbital block provides 2-6 hours of postoperative analgesia - reduces PACU analgesic requirements

6. Elderly-Specific Anesthetic Considerations

7. IOP Considerations

• Inhalational agents cause dose-related reductions in IOP (favorable for intraocular surgery)
• Increases in IOP occur with: laryngoscopy/intubation (favor LMA), coughing/straining (30-40 mmHg rise), hypoxia, hypercapnia, prone position, forceful lid squeeze (up to 70 mmHg)
• Orbital blocks initially increase IOP by 5-10 mmHg (peribulbar more than retrobulbar due to larger volume), falling below baseline within 5 minutes
• Gentle ocular massage or Honan balloon (30 mmHg for 10 min) applied after the block helps reduce IOP before incision

8. General Anesthesia - When Indicated and Approach

• Uncooperative/demented patients
• Unable to remain still (tremor, movement disorder, severe anxiety/claustrophobia)
• Very young children (n/a for elderly cataract)
• Complex, prolonged procedures

• LMA preferred over endotracheal tube: less IOP rise on insertion/removal, less coughing and straining at emergence
• Smooth induction and emergence are paramount to avoid IOP spikes
• Emergence techniques: deep extubation, IV lidocaine 1.5 mg/kg, dexmedetomidine 0.25-1 mcg/kg 15 min before emergence, opioids
• TIVA with propofol preferred in elderly with cognitive vulnerability to reduce POCD risk

9. Postoperative Considerations

• Cataract surgery is a day-case procedure; most patients bypass Phase 1 PACU if regional technique was used
• PONV prophylaxis: lower risk than with GA; regional anesthesia avoids this problem
• Postoperative analgesia: orbital block provides 2-6 hours of excellent pain control post-cataract; topical anesthesia provides less
• Cognitive: monitor for emergence delirium and POCD, especially in older patients who received heavy sedation or GA
• Wrong-site surgery prevention: Time-out and site marking are particularly important - laterality errors in ophthalmic surgery are a recognized medico-legal risk