How does sevoflurane induction, followed by a ketamine maintenance infusion, affect intraocular pressure? Establishment of an anaesthetic protocol for paediatric glaucoma examinations under anaesthesia

Accurate measurement of intraocular pressure (IOP) is essential in paediatric glaucoma management. Children require serial measurements and examination under anaesthesia (EUA). Most anaesthetic agents reduce IOP, and the ideal time to measure IOP under anaesthesia is questionable.

Study purpose

To determine the effect of sevoflurane induction, followed by intravenous ketamine infusion on IOP, in children undergoing EUA for glaucoma or suspected glaucoma, and to establish the earliest time point at which reliable, repeatable IOP measurements can be obtained under anaesthesia.

Method

A prospective, descriptive study of IOP changes occurring in children requiring EUAs. A standardised anaesthetic protocol: sevoflurane induction, intravenous cannulation, 2 mg/kg intravenous ketamine bolus and 4 mg/kg/hour maintenance for 15 min. IOP measurements (taken supine with a Perkins applanation tonometer) and physiological variables were recorded.

Results

IOPs were measured in 25 children (50 eyes). Twenty-six eyes (52%) were glaucomatous. Mean patient age was 29 months (2–88 months). Physiological variables returned to baseline at 8 min, correlating with recorded sevoflurane elimination. Mean IOP after sevoflurane induction was 3.68 mm Hg lower than with ketamine maintenance at 15 min (95% CI 1.35 to 6.02 mm Hg) (p=0.002). Contrastingly, the difference in IOP between ketamine anaesthesia at 15 min and near wakefulness was 0.28 mm Hg (95% CI –2.23 to 2.79 mm Hg) (p=0.826).

Conclusion

Sevoflurane's IOP-lowering effect is reversed 15 min after the discontinuation of the inhalational gas, if anaesthesia is maintained with an intravenous ketamine infusion. IOP measurements appear to stabilise at this time point until the point of near wakefulness and may reflect awake values.

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