Healthcare and Medicine Reference
In-Depth Information
to take steps to avoid intravascular injection
Box 4.1 Example of a maximum safe dose calculation
to seek effects of accidental intravascular injection by continu-
ally asking the patient for symptoms of early toxicity during
The agent and concentration should be chosen according to the
proposed site of injection, volume of solution likely to be required,
and the duration of anaesthesia required. Maximum safe doses for
the commonly used agents are given in Table 4.1. An example of a
maximum safe dose calculation is given in Box 4.1.
A 75-kg man requires infi ltration anaesthesia to suture a clean
laceration to the forearm.
Option 1
Bupivacaine is chosen as the agent to provide prolonged
post-procedure anaesthesia. Maximum safe dose of plain
2 mg/kg
150 mg
0.5% bupivacaine contains 0.5 g (500 mg) of drug per 100 mL.
75 kg
Therefore a 10-mL ampoule of 0.5% bupivacaine contains 50 mg.
Maximum safe volume of 0.5% bupivacaine
Step-by-step guide: local anaesthetic infi ltration
30 mL
Give a full explanation to the patient in appropriate terms
and ensure they consent to the procedure.
Set up your trolley (Box 4.2).
Option 2
Lidocaine is chosen to provide a quick onset of action. Maximum
safe dose of plain lidocaine:
4 mg/kg
Prepare your trolley as a sterile fi eld. Wear a plastic
disposable apron and non-sterile gloves, and take alcohol
hand rub with you.
75kg = 300 mg
1% lidocaine contains 1 g (1000 mg) of drug per 100 mL.
Therefore a 10-mL ampoule of 1% lidocaine contains 100 mg.
Maximum safe volume of 1% lidocaine
30 mL
Ensure that the patient has no history of adverse reaction to
local anaesthetic.
Calculate and do not exceed the maximum safe dose of your
Box 4.2 Equipment for local anaesthesia
chosen agent.
Position the patient comfortably, with the area to be infi ltrated
Cleaning solution (2% chlorhexidine in 70% isopropyl alcohol
on a secure surface.
Ensure that the fi eld is adequately lit, adopt universal precau-
10-mL syringe
tions, and set a sterile fi eld.
Adequately clean the skin with an appropriate antiseptic solu-
Green (21G) needle for drawing up local anaesthetic from
Orange (25G) or blue (23G) needle for infi ltration
tion (e.g. 2% chlorhexidine in 70% alcohol) and allow to dry.
Using a 25G (orange) or 23G (blue) needle, enter the skin at an
Second 21G needle if deeper infi ltration will be required
angle of approximately 45°.
As soon as the needle is subcutaneous, ensure that blood cannot
be aspirated. Without moving the needle, push on the plunger
to infi ltrate with approximately 0.5-2 mL of local anaesthetic.
Ask the patient if they have any tingling or numbness around
aspect (Figure 4.2). 1% lidocaine is a suitable choice of agent and
will provide anaesthesia for 1-2 hours.
Using a 25G (orange) needle, enter the dorsal aspect of the web
the mouth, or are feeling light-headed or dizzy.
Advance the needle subcutaneously, avoiding superfi cial veins,
space, close to the phalanx on one side.
Advance until the tip of the needle is just above the palmar
until the tip is at the edge of the wheal just created.
Aspirate once more before injecting further solution.
aspect of the web space.
Aspirate to ensure the absence of blood, then inject 1-2 mL of
Repeat steps 7-10 until the skin area is fully infi ltrated, or the
maximum safe dose has been reached.
If deeper anaesthesia is required (for example for chest drain
solution to block the palmar (volar) nerve.
Withdraw the needle until just under the dorsal skin.
insertion), now insert the needle into deeper tissues through
the subcutaneous wheal and repeat steps 7-11 until infi ltration
is complete.
Document the agent, concentration and volume used and any
Aspirate to ensure the absence of blood, then inject a further
1 mL of solution to block the dorsal nerve.
Ask the patient if they have any tingling or numbness around
the mouth, or are feeling light-headed or dizzy.
Repeat steps 6-11 for the opposite side of the digit.
complications. Allow time for the local anaesthetic to work
before attempting further procedures.
If toxicity is suspected at any time, discontinue injection and
Document the procedure in the notes.
assess using an ABCDE approach.
Topical local anaesthesia
Two topical local anaesthetic agents are in common use: EMLA®
and Ametop®. EMLA (eutectic mixture of local anaesthetics)
contains 2.5% lidocaine and 2.5% prilocaine; Ametop contains 4%
tetracaine. Some systemic absorption may occur with these agents,
and maximum safe doses should be observed.
Step-by-step guide: digital ring block
Set up your trolley and perform steps 1-5 as for subcutaneous infi l-
tration. There are four digital nerves per digit, one on each side
toward the fl exor aspect and one on each side toward the extensor
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