Strabismus pediatric patients anaesthetic considerations

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strabismus surgery pediatric anesthesia complications

I now have comprehensive information from both Miller's Anesthesia (10e) and Barash's Clinical Anesthesia (9e). Let me compile the full answer.

Anaesthetic Considerations for Strabismus Surgery in Pediatric Patients

Strabismus surgery is the most common pediatric ophthalmic operation performed in the United States. Approximately 3% of the population has strabismus (misalignment of the visual axes), and the surgery involves recession (weakening a muscle by moving its insertion) or resection (strengthening a muscle by removing a short strip) of extraocular muscles. While most patients are healthy children, a significant subset has associated neurological conditions or syndromes.

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

Strabismus (and ptosis) patients are thought to have an increased incidence of malignant hyperthermia susceptibility. This is consistent with the broader observation that MH-susceptible individuals often have localized skeletal muscle weakness or musculoskeletal abnormalities. Although recent studies have challenged this belief, the theoretical risk must be taken seriously.

Practical implication: Anesthesiologists should be cognizant of this risk and maintain a low threshold for MH vigilance - have dantrolene immediately available, monitor temperature, capnography, and be alert to unexplained tachycardia or increased CO2.

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

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

Mechanism

The OCR (trigeminovagal reflex) is triggered by:

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

Afferent limb: ciliary nerves → ciliary ganglion → ophthalmic division of trigeminal nerve (V1) → Gasserian ganglion → trigeminal sensory nucleus
Efferent limb: motor nucleus of vagus nerve → heart (reduced HR and contractility)

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

Method	Notes
IM anticholinergics (premedication)	Ineffective for prophylaxis
IV atropine (0.02 mg/kg) just before surgery	May reduce incidence in pediatric strabismus surgery - but carries risk of arrhythmias itself
IV glycopyrrolate (0.01 mg/kg)	Associated with less tachycardia than atropine; preferred by some
Ketamine induction	Reported lowest OCR incidence vs propofol (Choi et al.)
Retrobulbar block	Blocks afferent limb but not uniformly effective; carries its own risks
Opioids (fentanyl, alfentanil, remifentanil)	May contribute to OCR - use cautiously
Avoid hypercapnia/hypoxia	Critical; optimize ventilation
Adequate anesthetic depth	Shallow anesthesia exacerbates OCR

Management When OCR Occurs

Ask the surgeon to immediately cease manipulation (first step)
Evaluate and correct hypoxia, hypercapnia, inadequate anesthetic depth
Heart rate typically returns to baseline within 20 seconds with cessation of stimulus
Note: tachyphylaxis occurs - the reflex attenuates with repeated manipulation
If bradycardia persists: IV glycopyrrolate 10 mcg/kg or atropine 10-20 mcg/kg
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

A lesser-known companion reflex: extraocular muscle traction also causes bradypnea and respiratory pauses. The afferent limb is the same as OCR but the efferent limb is not fully established. Importantly:

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

The forced duction test (FDT) is an intraoperative maneuver where the surgeon grasps the sclera and moves the eye into each field of gaze to determine whether strabismus is due to muscle paresis or a restrictive force - this informs the surgical plan.

Problem with succinylcholine: Succinylcholine causes prolonged contracture of extraocular muscles, falsely elevating force needed to rotate the globe and giving an abnormal (misleading) FDT. This elevation persists for 15-20 minutes after administration (even though skeletal paralysis resolves in <5 minutes and IOP rise is transient).

Recommendations:

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

Strabismus surgery is an independent risk factor for postoperative vomiting (POV) in children, with a historical incidence exceeding 50%.

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

Risk Factor	Points
Age > 3 years	1
Surgery duration > 30 minutes	1
History of POV (patient/sibling/parent)	1
Strabismus surgery	1

Predicted POV risk: 2 factors = 30%, 3 factors = 55%, 4 factors = 70%

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

Agent	Effect Relevant to Strabismus
Succinylcholine	Falsely elevates FDT for 20+ min; avoid if FDT planned
Ketamine	Lowest OCR incidence on induction; minimal IOP effect
Propofol (TIVA)	Reduces POV; increases OCR/bradycardia risk
Opioids (fentanyl, alfentanil, remifentanil)	May augment OCR
Nitrous oxide	Avoid in high-risk POV patients
Volatile agents	Dose-related IOP reduction; avoid in max-risk POV
Atropine IV	Reduces OCR but can itself cause arrhythmias
Glycopyrrolate IV	Preferred anticholinergic; less tachycardia

9. Associated Systemic Conditions to Screen For

Because strabismus has a higher incidence in certain populations, preoperative screening matters:

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

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

Sources: Miller's Anesthesia, 2-Volume Set, 10e (pp. 9708-9751) | Barash, Cullen, and Stoelting's Clinical Anesthesia, 9e (pp. 4131-4194)

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