Pharmacology for Dentistry

General Anaesthetics 65

SEVOFLURANE

This is also a new compound and un-
dergoing clinical trial. It is noninflammable,
non-irritant agent. It produces more rapid
induction and termination of anaesthesia
than observed with other inhalational
agents. The respiratory and circulatory ef-
fects of sevoflurane resemble those of
isoflurane.

INTRAVENOUS ANAESTHETICS

Intravenous anaesthetics are mainly used for
rapid induction of anaesthesia, which is then
maintained by an inhalational agent. They
also serve to reduce the amount of mainte-
nance anaesthetics.

In this section the agents having anaes-
thetic properties will be discussed. More de-
tails of each class of drug and their uses in
other circumstances are presented elsewhere.

BARBITURATES

THIOPENTONE SODIUM

It is an ultra short acting thiobarbiturate. The
sodium salts are highly soluble in water
yielding a very alkaline solution (pH 10.5 to
11), which must be prepared freshly before
injection. Induction is generally smooth and
takes approximately 10 to 30 seconds.

Thiopentone sodium is usually given as
92.5 percent solution, initially 100 to 150 mg
over 10-15 seconds and repeated if necessary
depending upon the patient’s response after
20-30 seconds. On repeated administration
the extracerebral sites are gradually filled up
and lower doses produces anaesthesia
which lasts longer.

Because of its poor analgesic property,

the painful procedures should not be car-

ried out under its influence unless an opioid

or nitrous oxide has been given.

Thiopentone depresses respiration tran-

siently. Blood pressure falls immediately

after injection but recovers rapidly. It does

not sensitize the myocardium to adrenaline.

Thiopentone also has been sometimes

used for rapid control of convulsions.

Adverse effects include laryngospasm,

which occurs generally when respiratory

secretions or other irritants are present. Shiv-

ering and delirium may occur during recov-

ery. Postoperative pain induces restlessness.

Nausea and vomiting are uncommon. It can

precipitate acute intermittent porphyria in

susceptible individuals.

METHOHEXITONE SODIUM

It is preferred to thiopentone sodium for

short procedures and out patients due to its

rapid recovery. It is approximately three

times more potent than thiopentone sodium

with quicker and briefer action.

The only disadvantages associated with

its use are that induction is less smooth, rest-

lessness is more common, as is coughing and

hiccup.

NON-BARBITURATE INTRAVENOUS

ANAESTHETICS

PROPANIDID

It is an oily liquid eugenol derivative and

less potent than thiopentone. It is a very

short acting intravenous anaesthetic and

specially used for very short outpatient op-

erations and dental procedures.