What is the preferred anesthesia for an exam under anesthesia in a child with primary congenital glaucoma?

Preferred Anesthesia for Examination Under Anesthesia in Primary Congenital Glaucoma

Ketamine is the preferred anesthetic agent for examination under anesthesia (EUA) in children with primary congenital glaucoma because it provides the most accurate intraocular pressure (IOP) measurements closest to awake values, which is critical for diagnosis and management decisions. 1, 2

Rationale for Ketamine as First-Line Agent

IOP Measurement Accuracy

• Ketamine maintains IOP closest to true awake values, making it essential when accurate pressure measurement determines surgical intervention 2
• Sevoflurane significantly lowers IOP by approximately 28.5% compared to ketamine (mean difference 7.4 mmHg, p<0.001), which can lead to underestimation of disease severity 2
• This IOP-lowering effect of sevoflurane is independent of baseline pressure level, affecting all patients equally 2

Optimal Ketamine Protocol

• Administer ketamine 2 mg/kg intravenous bolus for induction, followed by 4 mg/kg/hour maintenance infusion 1
• Alternative route: intramuscular injection at 5 mg/kg if IV access is challenging 2
• IOP measurements should be taken with a Perkins applanation tonometer in the supine position 1, 2

When Sevoflurane May Be Acceptable

Combined Protocol Approach

• If sevoflurane is used for induction (for ease of mask induction in uncooperative children), wait at least 15 minutes after discontinuation before measuring IOP while maintaining anesthesia with ketamine infusion 1
• At 15 minutes post-sevoflurane discontinuation with ketamine maintenance, IOP measurements stabilize and approximate awake values (mean difference only 0.28 mmHg from near-wakefulness, p=0.826) 1
• Physiological variables return to baseline at 8 minutes, correlating with sevoflurane elimination 1

Critical Timing Considerations

• Never measure IOP immediately after sevoflurane induction - this represents the nadir of IOP reduction (mean 5.6 mmHg in healthy children) 3
• IOP measured during deep sevoflurane anesthesia remains significantly depressed and unreliable for clinical decision-making 3

Complete EUA Protocol Beyond IOP Measurement

Comprehensive Examination Sequence

• Every EUA must include a complete ophthalmic examination, not just IOP measurement 4
• Perform gonioscopy to confirm open angles and assess trabecular meshwork anatomy 5
• Conduct stereoscopic optic nerve examination looking for vertical cup elongation, focal rim thinning (especially superior/inferior poles), disc hemorrhages, and RNFL defects 6
• Examine corneal diameter, clarity, and presence of Haab's striae 5
• Assess anterior chamber depth and lens clarity 4

Additional Diagnostic Procedures

• Consider combining EUA with corneal scraping for culture if infection suspected 4
• Document baseline characteristics before surgical planning 4
• Perform funduscopic examination with indirect ophthalmoscopy after adequate dilation 5

Practical Considerations in Resource-Limited Settings

Alternative Anesthetic Approaches

• In resource-challenged settings where anesthesiologist availability is limited, ketamine administered by trained non-anesthetists may be considered for short procedures like EUA 7
• This approach requires personnel trained in anesthetic resuscitation procedures 7
• Congenital glaucoma represents the most common indication for pediatric EUA (21.3% of cases), making efficient protocols essential 7

Critical Pitfalls to Avoid

Anesthetic Selection Errors

• Do not rely on IOP measurements taken under sevoflurane alone - this will systematically underestimate true IOP and may delay necessary surgical intervention 2
• Avoid propofol-based protocols when accurate IOP measurement is the primary goal, as propofol also significantly reduces IOP 3
• Do not measure IOP during the reversal phase of sevoflurane without ketamine maintenance, as values remain unreliable 3

Measurement Technique

• Ensure measurements are taken supine, as position affects IOP 1
• Take three measurements per eye and use mean values for clinical decisions 2
• Document the exact anesthetic protocol used, as this affects interpretation of serial measurements 1

Monitoring and Safety

Hemodynamic Considerations

• Monitor heart rate and blood pressure throughout the procedure, though these do not directly correlate with IOP changes 3
• Ketamine may cause transient increases in heart rate and blood pressure, which are generally well-tolerated in pediatric patients 1

Age-Specific Factors

• The protocol is effective across the typical age range for congenital glaucoma EUA (mean age 29-55 months in studies) 1, 2
• No correlation exists between IOP changes and patient age, gender, or type of surgery planned 3