Articles: anesthetics.
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A number of obstetric fatalities related to epidural anaesthesia have been reported recently. In each case catheter or needle misplacement had resulted in a lethal intrathecal or intravascular injection. In this review these cases and a number of other similar but nonfatal reports are examined. ⋯ A detailed test dose protocol is recommended, which will safely warn of epidural catheter and needle misplacement in the most effective manner possible. If the protocol is used, accidental subarachnoid and intravascular injections can be reduced to a minimum, but they will still occur. It is emphasised that these complications should not cause fatalities if trained personnel and adequate resuscitation facilities are available.
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The most important clinical properties of local anaesthetic agents are potency, onset, duration of action and relative blockade of sensory and motor fibres. These qualities are related primarily to the physicochemical properties of the various compounds. ⋯ In general, the local anaesthetics for infiltration, peripheral nerve blockade, and extradural anaesthesia can be classified into three groups: agents of low potency and short duration, for example procaine and chloroprocaine; agents of moderate potency and duration, for example lignocaine, mepivacaine and prilocaine; and agents of high potency and long duration, for example amethocaine, bupivacaine and etidocaine. These local anaesthetics also vary in terms of onset: chloroprocaine, lignocaine, mepivacaine, prilocaine and etidocaine have a rapid onset, while procaine, amethocaine and bupivacaine are characterized by a longer latency period.
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In general, the cardiovascular system is more resistant to the toxic actions of local anaesthetics than is the central nervous system. However, if sufficient doses and blood levels of local anaesthetics are achieved, signs of profound cardiovascular depression may be observed. Differences exist between local anaesthetics in terms of their relative potential for cardiotoxicity. ⋯ However, large dosages of chloroprocaine solutions administered intrathecally have been associated with prolonged sensory-motor deficits in a few patients due probably to the low pH and presence of sodium bisulfite in the chloroprocaine solutions. In general, the incidence of toxic reactions to local anaesthetic agents is extremely low. However, as with any class of pharmacological agents, local anaesthetics may cause severe toxic reactions, due usually to the improper use of these drugs.