C H A P T E R 2 7
General and local anaesthetic agents
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Induction
Induction
is the period from the beginning of anaes-
thesia until stage 3, or surgical anaesthesia, is reached.
The danger period for many people during induction is
stage 2 because of the systemic stimulation that occurs.
Often a rapid-acting anaesthetic is used to move quickly
through this phase and into stage 3. NMJ blockers may
be used during induction to facilitate intubation, which
is necessary to support the person with mechanical ven-
tilation during anaesthesia (see Chapter 28).
Maintenance
Maintenance is the period from stage 3 until the surgical
procedure is complete. A slower, more predictable
anaesthetic, such as a gas anaesthetic, may be used to
maintain the anaesthesia once the person is in stage 3.
Recovery
Recovery is the period from discontinuation of the
anaesthetic until the person has regained conscious-
ness, movement and the ability to communicate. During
recovery, the person requires continuous monitoring
for any adverse effects of the drugs used and to ensure
support of the person’s vital functions as necessary.
■■
General anaesthesia produces analgesia, amnesia and
unconsciousness.
■■
General anaesthesia places the person at risk for
problems because of its extensive CNS depression and
widespread effects on other body systems.
■■
Balanced anaesthesia involves the administration of
several drugs rather than a single drug to achieve
analgesia, muscle relaxation, unconsciousness and
amnesia.
■■
Induction of anaesthesia is the period ranging from
administration of the anaesthetic to the point of
surgical anaesthesia.
GENERAL ANAESTHETIC AGENTS
Several different types of drugs are used as general
anaesthetics. These include barbiturate and non-
barbiturate anaesthetics, gas anaesthetics and volatile
liquids. See Table 27.1 for a list of general anaesthetic
agents along with the anticipated adverse effects of these
drugs.
B
arbiturate anaesthetics
The barbiturate anaesthetics (Table 27.1) are intra
venous drugs used to induce rapid anaesthesia, which
is then maintained with an inhaled drug. The available
drug in this group is thiopentone (
Pentothal
).
KEY POINTS
Therapeutic actions and indications
Thiopentone is a barbiturate that is used for induction
of anaesthesia, particularly in intravenous anaesthetics.
Because it has no analgesic properties, the person may
need additional analgesics after surgery.
Pharmacokinetics
Thiopentone has a very rapid onset of action, usually
within 10 to 30 seconds, and an ultra-short recovery
period of 5 to 8 minutes. Induction is generally smooth
and rapid, but dose-related cardiovascular and respira-
tory depression can occur. Awakening from a moderate
dose of thiopentone is rapid because the drug redis-
tributes into other tissues, particularly fat. However,
metabolism is slow and sedative effects can persist for
24 hours. Repeated doses have a cumulative effect and
recovery is much slower.
Contraindications and cautions
The drug should not be used until the anaesthetist and
staff are ready and equipped for intubation and respira-
tory support
because of the rapid onset and because the
drug can cause respiratory depression and apnoea.
The
drug should not be used during pregnancy or breast-
feeding unless the benefit clearly outweighs the potential
risk to the fetus or neonate
because of the CNS depres-
sive effects of this drug. This drug is lipophilic and can
be rapidly absorbed through the placental barrier.
Adverse effects
The adverse effects associated with this drug are related
to the suppression of the CNS with decreased pulse,
hypotension, suppressed respirations and decreased
GI activity. Nausea and vomiting after recovery are
common.
Prototype summary: Thiopentone
Indications:
Induction of anaesthesia, maintenance
of anaesthesia; induction of a hypnotic state.
Actions:
Depresses the CNS to produce hypnosis and
anaesthesia without analgesia.
Pharmacokinetics:
Route
Onset
Duration
IV
1 min
20–30 mins
T
1/2
:
3 to 8 hours; metabolised in the liver, excreted
in the urine.
Adverse effects:
Emergence delirium, headache,
restlessness, anxiety, cardiovascular depression,
respiratory depression, apnoea, salivation, hiccups,
skin rashes.
