Effect of paediatric caudal injection volume on optic nerve sheath diameter and regional cerebral oximetry

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Abstract
BACKGROUND: Caudal injections commonly used for neuraxial anaesthesia in children can displace cerebrospinal fluid cranially causing safety concerns in terms of raised intracranial pressure. Optic nerve sheath diameter (ONSD) is a noninvasive surrogate for the measurement of intracranial pressure. Regional cerebral oximetry (CrSO2) can monitor brain oxygenation, which may decrease by a reduction in cerebral flow due to increased intracranial pressure. OBJECTIVES: Comparing how caudal injection volumes of 0.8 and 1.25 ml kg−1 influence ONSD and CrSO2 within the first 30 min after injection. DESIGN: Prospective, randomised and parallel group trial. SETTING: Operating room. PATIENTS: Fifty-eight elective paediatric surgical patients between ages 1 and 7 years old, ASA class I or II, without previous intracranial or ocular pathology and surgery appropriate for single-shot caudal anaesthesia. INTERVENTION: Single-shot caudal anaesthesia with 0.8 ml kg−1 (group L, n = 29) and 1.25 ml kg−1 (group H, n = 29) of 2 mg kg−1 bupivacaine solution. MAIN OUTCOME MEASURES: Optic nerve sheath diameter measured with ultrasonography and regional cerebral oximetry measured by near-infrared spectroscopy before (NIRS), immediately after, 10, 20 and 30 min after the block. RESULTS: Mean ONSD values increased from a baseline of 4.4 ± 0.2 mm to a maximum of 4.5 ± 0.2 mm 20 min after injection in group L and from a baseline of 4.5 ± 0.3 mm to a maximum of 4.8 ± 0.3 mm 10 min after injection in group H. Eight of 29 patients in group H and none in group L had an ONSD increase by more than 10%. Both groups had a reduction of less than 2.5% in CrSO2. CONCLUSION: Caudal injection with 1.25 ml kg−1 increased ONSD, an indirect measurement of ICP, more than 0.8 ml kg−1 and neither volume caused a clinically important reduction in CrSO2. TRIAL REGISTRATION: ClinicalTrials.gov Identifier: NCT04491032

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