McKenna's Pharmacology for Nursing, 2e

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C H A P T E R 2 7 General and local anaesthetic agents

run to and from the region in which the loss of pain sen- sation or muscle paralysis is desired. These blocks are not performed in the surgical field, but at some distance from the field. They involve a greater area with potential for more adverse effects. Several types of nerve blocks are possible: • Peripheral nerve block: blockage of the sensory and motor aspects of a particular nerve for relief of pain or for diagnostic purposes. • Central nerve block: injection of anaesthetic into the roots of the nerves in the spinal cord. • Epidural anaesthesia: injection of the drug into the epidural space where the nerves emerge from the spinal cord. • Caudal block: injection of anaesthetic into the sacral canal, below the epidural area. • Spinal anaesthesia: injection of anaesthetic into the spinal subarachnoid space. Intravenous regional local anaesthesia Intravenous regional local anaesthesia involves carefully draining all of the blood from the person’s arm or leg, securing a tourniquet to prevent the anaesthetic from

entering the general circulation, and then injecting the anaesthetic into the vein of the arm or leg. This tech- nique is used for very specific surgical procedures.

LOCAL ANAESTHETIC AGENTS Local anaesthetic agents (Table 27.2) are used primar- ily to prevent the person from feeling pain for varying periods of time after the agents have been adminis- tered in the peripheral nervous system. In increasing concentrations, local anaesthetics can also cause loss of the following sensations (in this sequence): tempera- ture, touch, proprioception (position sense) and skeletal muscle tone. If these other aspects of nerve function are progressively lost, recovery occurs in the reverse order of the loss. The local anaesthetics are very powerful nerve blockers, and it is very important that their effects be limited to a particular area of the body. They should not be absorbed systemically. Systemic absorption could produce toxic effects on the nervous system and the heart (e.g. severe CNS depression, cardiac arrhythmias).

TABLE 27.2

DRUGS IN FOCUS Local anaesthetic agents

Special considerations

Drug name

Onset

Duration

Administration

Esters amethocaine (Minims Amethocaine Eye Drops) benzocaine (Cepacaine, Cepacol) Amides bupivacaine (Marcain)

10–20 seconds 10–20 minutes Eye

Eye should be protected from rubbing or contamination

1 minute

30–60 minutes Skin, mucous membranes Avoid tight bandages with skin preparation

5–20 minutes 2–7 hours

Local, epidural, dental, caudal, subarachnoid, sympathetic, retrobulbar

Do not use Bier Block— deaths have occurred

cinchocaine (Proctosedyl, Rectinol, Scheriproct)

<15 minutes

3–4 hours

Skin, mucous membranes Monitor for local reactions

levobupivacaine (Chirocaine)

8–20 minutes

7–10 hours

Local nerve block, epidural

Use cautiously in individuals with cardiovascular conditions Short acting, preferred for short procedures; danger if absorbed systemically Advise person to take care with hot drinks Advise people not to bite themselves Avoid rapid infusion; offers good pain management postop and OB

5–15 minutes

30–90 minutes Caudal, epidural, spinal cervical, dental, skin, mucous membrane, topical patch

lignocaine (EMLA, Xylocaine, Ziagel)

mepivacaine (Scandonest)

5–10 minutes

0.5 hours

Dental procedures

prilocaine (Citanest)

1–15 minutes

0.5–3 hours

Nerve block, dental

ropivacaine (Naropin)

1–5 minutes

2–6 hours

Nerve block, epidural, caudal