It is often difficult to assess the success of caudal epidural block in children under general anaesthesia. We hypothesized that increase in lower limb perfusion index after caudal anaesthesia indicates a successful block and aimed to study changes in lower limb perfusion index after caudal block in children under general anaesthesia.

This prospective observational study was conducted in children aged 2–12 years. The primary outcome was changes in lower limb perfusion index for 20 min after caudal block. Secondary outcomes included upper limb perfusion index at the same times, differences in lower and upper limb perfusion index, haemodynamic parameters and the correlation of perfusion index with heart rate and blood pressure.

After caudal block, lower limb perfusion index increased within 1 min (31.28 %), was 100 % higher at 5 min and reached a maximum (153.18 %) increase at 15 min. The maximum increase in upper limb perfusion index was 35.13 %. There was a fall in heart rate (8.79 %), systolic blood pressure (8.77 %), diastolic blood pressure (14.16) and mean arterial pressure (11.43 %) which were maximum at 20 min. We found a positive correlation, r = 0.97, p = .001, between perfusion index and heart rate and perfusion index and diastolic blood pressure, r = 0.82, p = .043.

There were significant and immediate increases in lower limb perfusion index after successful caudal block. Haemodynamic changes were less marked and delayed. Perfusion index was found to be an objective, sensitive and early indicator of successful caudal block in children under general anaesthesia.