On paediatric regional anaesthesia : The use of paravertebral blockade, aspects on plasma protein binding, and systemic toxicity of local anaesthetics

Abstract

Paediatric regional anaesthesia has gained widespread popularity during recent yearsbecause of an excellent potential for intra- and postoperative pain relief and reduction of thesurgically induced stress response. The aim of the present thesis was to adapt and develop thetechnique of paravertebral blockade (PVB) for the safe use in paediatric patients and also toinvestigate aspects on plasma protein binding and toxicity of local anaesthetic drugs whichmight be of importance in the special settings of paediatric anaesthesia. The optimal landmarks for puncture of the thoracic paravertebral space (PVS) was derivedfrom computed tomography and clinical measurements and were found to correlate well withpatient weight (r = 0.94-0.95). The lateral distance from the spinous process and the depthfrom the skin to the PVS can be calculated from the equations: lateral distance (mm) = 0.12kg + 10.2 and depth (mm) = 0.53 kg + 21.2. Retrospective data indicate that the PVB iscapable of providing similar postoperative pain relief in children undergoing renal surgery withan unilateral incision compared to lumbar epidural blocks. In a prospective multi-centre studythe failure rate and complications associated with PVB were studied in a mixed population ofadult and paediatric patients and PVB was found comparable in these aspects to otherestablished alternative regional techniques. Plasma concentrations of lidocaine after bolusinjection (5 mg . kg-1 ) and subsequent infusion (2.5 mg .kg-1 h-1 ) of lidocaine with adrenalineinto the PVS were found to be well below the levels associated with side effects or toxicity. In vitro studies of the effects of hypothermia and haemodilution on the plasma proteinbinding (PPB) of lidocaine, assessed by ultrafiltration, were carried out on blood collectedfrom healthy, medication free, adult volunteers. A significant reduction in PPB could beobserved between 37 and 24 ¡C but a further decrease in temperature did not cause anyaddition reduction in PPB. Even moderate degrees of dilution of the plasma phase of the bloodwill cause a decrease in PPB but the PPB was not found to be affected by changes inhaemotocrit. In order to confirm a clinical impression of side effects or even early signs ofcentral nervous system toxicity in ex-premature infants undergoing awake caudal anaesthesia,unblinded assessments of behavioural changes before and twenty minutes after the performanceof a caudal block with bupivacaine (3.1 mg . kg-1) were compared with blinded evaluations ofsimultaneously performed EEG recordings. An integrated evaluation of the findings supportthe occurrence of systemic side effects and signs of early CNS toxicity at plasma concentra-tions of bupivacaine within the 0.56-1.62 . mg ml-1 range.The current thesis delineate the use of paravertebral blockade in paediatric patients and hasalso elucidated some aspects of plasma protein binding and toxicity of local anaesthetic drugsthat are of special interest in paediatric regional anaesthesia.Key words: Anesthesia, regional, paravertebral; Children, infants; Local anesthetics,bupivacaine, lidocaine; Pharmacokinetics; Plasma protein binding; Side effects; Toxicity.PA Lönnqvist: On paediatric regional anaesthesia: The use of paravertebral blockade, aspectson plasma protein binding, and systemic toxicity of local anaesthetics. Stockholm 1996.ISBN 91-628-1974-7