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Summa yThe success rate and occurrence of adverse effects are reported in a retrospective study of 650 (99 sacral, 468 lumbar, 76 thoracic and seven cervical) paediatric epidurals performed, mostly (91 %) under light general anaesthesia, by several anaesthetists. Seventeen-gauge Tuohy and 20-gauge (Potts-Coumand@ and Tuohy) needles were used. Anaesthetic solutions used were 1 % lignocaine, 0.5% bupivacaine and a mixture of equal volumes of 0.5% bupivacaine with either 1% lignocaine or 1% etidocaine, all containing 1:200 OOO adrenaline. The epidural space was identified by loss-of-resistance technique (LORT) with normal saline, air or COz. Up to five attempts were occasionally necessary. LORT using fluid resulted in more subarachnoidal penetrations than the LORT using air ( P < 0.05) which was easy and reliable but produced patchy anaesthesia ('painful gaps') in 4.2% of patients. C02-LORT was as easy and reliable as air-LORT and did not result in painful gaps. Lateral and rnid-line insertion routes were equally suitable whatever the level of approach. Twenty-gauge needles, especially Tuohy needles, resulted in significantly less dural punctures in young children. The spread of the local anaesthetic correlated with the volume injected and the height of the epidural approach. Epidural anaesthesia had little haemodynamic effects. Administration of epidural morphine improved the duration of postoperative pain relief but undesirable effects occurred in up to 50% of patients. Low doses of naloxone (2-5 pg-kg-'*h-') counteracted most adverse effects, avoiding urinary retention and delayed apnoea. Anaesthetists and residents without experience in paediatric anaesthesia had a good success rate in performing the techniques (under supervision of an experienced anaesthetist). At the same time, experience in regional anaesthesia would sigruficantly boost the confidence of the anaesthetist in managing such cases. The authors recommend using COZ instead of air in the LORT.

Amide local anaesthetics used for regional anaesthesia in paediatric patients are potent sodium channel blockers with marked stereospecificity, which consistently influences their action, especially their toxic action on the heart. At toxic concentrations, they induce severe arrhythmias with the potential for cardiac arrest. These agents are all bound to serum proteins, mainly to alpha(1)-acid glycoprotein (AAG), but also to human serum albumin. Protein binding ranges from 65% (lidocaine) to more than 95% (bupivacaine, ropivacaine). Because AAG is a major acute phase protein, its concentration rapidly increases when inflammatory processes develop, particularly during the postoperative period. Neonates and infants have a lower AAG concentration in serum as compared with adults; therefore, their free fraction of local anaesthetics is increased accordingly. This has important clinical implications since, at least at steady state, the toxic effects of local anaesthetics are directly related to the free (unbound) drug concentration. After injection into the epidural space, absorption into the bloodstream follows a biphasic process. The buffering properties of the epidural space are important and prevent a rapid rise in concentration. In infants and children, the epidural space seems to protect patients in a similar manner. Moreover, it has been observed that the peak plasma concentration (C(max)) of ropivacaine is delayed in infants and children when compared with adults. The time to C(max) decreases from 90-120 minutes in infants aged less than 6 months to 30 minutes in children aged more than 8 years. This delay in C(max) may also be related to the lower clearance observed in younger patients. Local anaesthetics are metabolised by cytochrome P450 (CYP). The main CYP isoforms involved are CYP3A4 for lidocaine and bupivacaine and CYP1A2 for ropivacaine. CYP3A4 is not mature at birth but is partly replaced by CYP3A7. The intrinsic clearance of bupivacaine is only one-third of that in adults at 1 month of age, and two-thirds at 6 months. CYP1A2 is not fully mature before the age of 3 years. Indeed, the clearance of ropivacaine does not reach its maximum before the age of 5 years. However, at birth this clearance is not as low as expected, and ropivacaine may be used even in younger patients.

Magnetic resonance imaging (MRI) requires long-lasting immobilization that frequently can only be provided by general anesthesia in pediatric patients. Sevoflurane provides adequate anesthesia but many patients experience emergence agitation. Small doses of ketamine and nalbuphine provide moderate sedation but their benefits have subsided at the time of emergence. We hypothesized that delaying their administration until the end of the procedure would prevent emergence agitation without prolonging patient wake-up and discharge times from the postanesthesia care unit. We performed a double-blind study involving 90 patients (aged 6 mo to 8 yr) randomly allocated to 1 of 3 groups receiving either saline (S-group), ketamine (0.25 mg/kg) (K-group), or nalbuphine (0.1 mg/kg) (N-group) at the end of an MRI procedure under sevoflurane anesthesia. We evaluated emergence conditions, sedation/agitation status and completion of discharge criteria at 30 min. The three groups were comparable in age, sex ratio, physical status, and associated medical disorders. Emergence conditions did not differ significantly. There were significantly more agitated children, at all times, in the S-group and more obtunded patients at early times (5 and 10 min) in both K- and N-groups. All patients met discharge criteria at 30 min but significantly more children were awake and quiet in the K-group and still more in the N-group. In conclusion, small doses of ketamine or nalbuphine administered at the end of an MRI procedure under sevoflurane anesthesia reduce emergence agitation without delaying discharge. Nalbuphine provided better results than ketamine.

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