C H A P T E R 2 7
General and local anaesthetic agents
417
A
naesthetics
are drugs that are used to cause complete
or partial loss of sensation. The anaesthetics can be sub-
divided into general and local anaesthetics, depending
on their site of action. General anaesthetics are central
nervous system (CNS) depressants used to produce loss
of pain sensation and consciousness. Local anaesthetics
are drugs used to cause loss of pain sensation and feeling
in a designated area of the body without the systemic
effects associated with severe CNS depression. This
chapter discusses various general and local anaesthetics.
Box 27.1 highlights information about using anaesthet-
ics with various age groups.
GENERAL ANAESTHESIA
General anaesthesia
involves the administration of a
combination of several different general anaesthetic
agents to achieve the following goals:
analgesia
, or
loss of pain perception;
unconsciousness
, or loss of
awareness of one’s surroundings; and
amnesia
, or ina-
bility to recall what took place. Ideally, the drugs are
combined to achieve the best effects with the fewest
adverse effects. In addition, general anaesthesia also
blocks the body reflexes. Blockage of autonomic reflexes
prevents involuntary reflex response to body injury
that might compromise a person’s cardiac, respiratory,
gastrointestinal (GI) and immune status. Blockage of
muscle reflexes prevents jerking movements that might
interfere with the success of the surgical procedure.
Risk factors associated with general anaesthesia
Widespread CNS depression, which is not without risks,
occurs with general anaesthesia. In addition, all other
body systems are affected. Because of the wide systemic
effects, people must be evaluated for factors that may
increase their risk. These factors include the following:
•
CNS factors
: Underlying neurological disease
(e.g. epilepsy, stroke, myasthenia gravis) that presents
BOX 27.1
Drug therapy across the lifespan
Anaesthetic agents
CHILDREN
Children are at greater risk for complications after
anaesthesia—laryngospasm, bronchospasm, aspiration
and even death.They require very careful monitoring and
support, and the anaesthetist needs to be very skilled at
calculating dosage and balance during the procedure.
Propofol is widely used for diagnostic tests and short
procedures in children older than 3 years of age because
of its rapid onset and metabolism and generally smooth
recovery. Sevoflurane has a minimal impact on intracranial
pressure and allows a very rapid induction and recovery
with minimal sympathetic reaction. It is still quite
expensive, however, which may limit its use.The dosage
of anaesthetics may need to be higher in children, and that
factor will be considered by the anaesthetist.
Care after general anaesthesia should include support
and reassurance; assessment of the child for any skin
breakdown related to immobility, and safety precautions
until full recovery has occurred.
Local anaesthetics are used in children in much the
same way that they are used in adults.
Bupivacaine does not have established doses for
children younger than 12 years of age. Benzocaine should
not be used in children younger than 1 year of age.
When topically applying a local anaesthetic, it is
important to remember that there is greater risk of
systemic absorption and toxicity with infants.
Tight nappies can act like occlusive dressings and
increase systemic absorption. Children need to be
cautioned not to bite themselves when receiving dental
anaesthesia.
ADULTS
Adults require a considerable amount of teaching and
support when receiving anaesthetics, including what will
happen, what they will feel, how it will feel when they
recover and the approximate time to recovery.
Adults should be monitored closely until fully
recovered from general anaesthetics and should
be cautioned to prevent injury when receiving local
anaesthetics. It is important to remember to reassure and
talk to adults who may be aware of their surroundings yet
unable to speak.
PREGNANCY AND BREASTFEEDING
Most of the general anaesthetics are not recommended
for use during pregnancy because of the potential risk
to the fetus. Short-onset and local anaesthetics are
frequently used at delivery. Use of a regional or other local
anaesthetic is usually preferred if surgery is needed during
pregnancy. During breastfeeding, it is recommended that
the mother wait 4 to 6 hours to feed the baby after the
anaesthetic is used.
OLDER ADULTS
Older people are more likely to experience the adverse
effects associated with these drugs, including central
nervous system, cardiovascular and dermatological
effects.Thinner skin and the possibility of decreased
perfusion to the skin makes them especially susceptible to
skin breakdown during immobility. Because older people
often also have renal or hepatic impairment, they are
also more likely to have toxic levels of the drug related to
changes in metabolism and excretion.The older person
should have safety measures in effect, such as siderails,
a call bell and assistance to ambulate; special efforts to
provide skin care to prevent skin breakdown are especially
important with older skin.The older person may require
longer monitoring and regular orienting and reassuring.
After general anaesthesia, it is very important to promote
vigorous deep breathing and coughing to decrease the risk
of pneumonia.
