General Anaesthetics 63one of the first substances to be employed
for general anaesthesia. It is a potent agent
and produces full anaesthesia when inhaled
in low concentration. A concentration of 10
to 15% in the inspired air is usually required
for induction. It produces prolonged and
unpleasant induction with salivation and
marked respiratory secretions. For this at-
ropine must be given prior to anaesthesia
for inhibition of these secretions.
Respiration and blood pressure are gen-
erally well maintained because of reflex
stimulation and high sympathetic tone.
Because of its slow induction and recov-
ery, irritant property and other disadvan-
tages ether is rarely used these days and may
be occasionally used as a supplement to ni-
trous oxide-oxygen mixture in children.
TRICHLOROETHYLENE
It is a clear, colourless liquid with a char-
acteristic odour but a blue dye is added for
distinction from chloroform. It is a potent
analgesic with a rapid onset of action but
muscular relaxation with this agent is inad-
equate. Induction and recovery are slow.
It may produce tachypnoea and brady-
cardia and sensitizes the myocardium to
adrenaline and cardiac arrhythmias can oc-
cur probably due to hypoxic release of
adrenaline.
Now-a-days, it is occasionally used in
obstetrics, burns dressings etc. as a self
medication analgesic.
HALOTHANE
It is a volatile liquid, non-irritant and
non-inflammable. It is most widely used
volatile anaesthetic due to its smooth and
rapid induction. It inhibits laryngeal and
pharyngeal reflexes in upper planes of sur-
gical anaesthesia.
Halothane causes relatively greater de-
pression of respiration. It inhibits intesti-
nal and uterine contractions. Cardiac out-
put is also reduced by 20 to 50 percent when
anaesthesia is induced by inspiration of ha-
lothane at 0.8 to 1.2 percent concentration,
which is necessary for surgical anaesthesia.
Heart rate is slowed during anaesthesia,
tachyarrhythmias may also occur in the
presence of halothane.
Halothane causes dose-dependent re-
ductions of renal blood flow and glomeru-
lar filtration rate as a result of fall in blood
pressure.
Hepatitis occurs in susceptible individu-
als with repeated use.
It causes decrease in uterine muscle tone.
Elimination of halothane may continue
for 24 to 48 hours after prolonged adminis-
tration. Recovery is smooth and reasonably
quick. It is currently one of the most popu-
lar anaesthetic used due to its non-irritant,
non-inflammable, pleasant and rapid action.ENFLURANE
It is a clear, colourless, noninflammable
liquid with a mild, sweet odour and consid-
ered to be a useful alternative to halothane.
Induction of anaesthesia, appropriate for
surgery may be achieved within 10 minutes
after approximately 4 percent enflurane in
inhaled. Arterial blood pressure decreases
progressively as the depth of anaesthesia is
increased with enflurane, about the same
degree as it does with halothane inhalation.
The anaesthesia produces rapid induction
with quick recovery.