Sedation during spinal anaesthesia in infants

Neuraxial anaesthesia in adults decreases the dose of i.v. or inhalational anaesthetic needed to reach a desired level of sedation. Furthermore, spinal anaesthesia alone has a sedative effect. The mechanism behind this phenomenon is presumed to be decreased afferent stimulation of the reticular activating system after sympatholysis. We hypothesized that this mechanism is equally active in infants undergoing spinal anaesthesia.

In total, 20 unpremedicated former preterm infants underwent surgery under spinal anaesthesia with hyperbaric bupivacaine 0.5% 1 mg kg(-1) with epinephrine 10 microg kg(-1). No additional sedatives or anaesthetics were administered. Sedation was evaluated using the bispectral index (BIS) score and the 95% spectral edge frequency (SEF(95)).

After spinal anaesthesia, mean (SD) BIS began to decrease significantly from baseline 97.0 (1.1) to 83.9 (14.4) after 15 min (P=0.006). BIS decreased further, reaching the lowest values after 30 min [62.2 (14.0); P<0.00001]. Mean (SD) SEF(95) declined from baseline 26.1 (1.8) Hz to 24.3 (3.1) after 5 min (P=0.02) and further to 9.9 (3.8) after 30 min (P<0.00001). Mean arterial pressure also decreased significantly from 66.5 (4.7) mm Hg within 10 min to 56.1 (5.6) after spinal anaesthesia (P=0.0002), while heart rate remained stable.

These results suggest that sedation after spinal anaesthesia in infants is at least as pronounced as in adults. The sedative effect of spinal anaesthesia should be kept in mind when additional sedatives are administered, especially in former preterm infants.