Healthcare and Medicine Reference
In-Depth Information
Local Anaesthesia and Safe Sedation
Ron Daniels
Heart of England NHS Foundation Trust, Birmingham, UK
reassuring to the patient, it is at best unsatisfactory and at worst
an assault.
This chapter covers aspects of local anaesthesia and sedation
relevant to the practical procedures described in this topic. Specifi c
agents in common use are described: this is not intended to be an
exhaustive list. You should identify the policies and practices in use
in your organisation, and familiarise yourself with which drugs and
agents are available and where.
By the end of this chapter, you should:
be able to describe the indications for local anaesthesia and
be able to determine an appropriate agent for sedation and
for local anaesthesia in an individual patient
have an understanding of the modes of action and doses of
these agents
know the principles behind safe administration of single-agent
Local anaesthesia
Defi nition
Local anaesthesia is defi ned by a loss of sensation in the immediate
area of the body where the agent has been administered. Effective
local anaesthesia requires the blocking of transmission of pain by
both A
conscious sedation
be able to plan safe local anaesthesia including ring block
be able to recognise and treat complications of local anaesthesia
and sedation.
(fast myelinated, 'sharp' pain) and C (slow unmyelinated,
dull/throbbing pain) nerve fi bres.
Local anaesthetic agents are used by anaesthetists and other expe-
rienced practitioners for both peripheral and central nerve blocks,
examples being femoral nerve block and spinal (subarachnoid)
block, respectively. Less commonly now, regional intravenous block-
ade (Biers' block) of limbs may be performed. These are specialist
techniques outside the scope of this topic. This chapter introduces
some commonly used local anaesthetic agents, and describes their
safe use in local infi ltration and in performing a digital ring block.
Most of the practical procedures described in this topic are potentially
unpleasant for the patient, and a number may be painful. For some
procedures, local anaesthesia and sedation will only occasionally
be necessary in the adult patient (for example, peripheral venous
cannulation with a small-bore cannula). For others, local anaesthe-
sia will routinely be required (e.g. chest drain insertion). Cultural
and individual factors may make sedation desirable for some
patients undergoing more uncomfortable procedures.
The importance of appropriate discussion with the patient
before a procedure and ongoing reassurance during it cannot be
underestimated. For lengthier and more uncomfortable proce-
dures, it is good practice to have a colleague available to hold the
patient's hand and provide reassurance. Managing the patient's
expectations of the procedure, being frank about the severity and
duration of any likely discomfort, and explaining the reasons for
performing it can minimise or negate any requirement for sedation
and analgesia.
A practitioner must ensure that sedation is never administered
to a patient simply to reduce the need for this basic communica-
tion. Whilst it is undoubtedly easier to practice without continually
Local anaesthetic agents
There are two principal groups of local anaesthetics - the esters
(such as cocaine) and the more commonly used amides (lidocaine,
bupivacaine, prilocaine). Agents differ in their potency, time to
onset and duration of action according to physical properties
including their lipid solubility, tendency toward protein binding
and pKa (the pH at which equal proportions of ionised and non-
ionised drug are present).
Local anaesthetics work by diffusing across the myelin sheath or
neuron membrane in their non-ionised form. More lipid-soluble
agents are more potent because more of the drug can cross into
the neurone. Local anaesthetics then ionise inside the neurone, to
block sodium channels from the inside (Figure 4.1). The rapidity
of this process, and thus the onset of action, is determined by their
pKa. The closer the pKa to physiological pH, the faster the onset.
More highly protein-bound drugs will bind more strongly and have
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