Pharmacology for Dentistry

64 Section 2/ Drugs Acting on CNS

Enflurane can be used for prolonged
operations such as cholecystectomy and
other abdominal surgery which requires
profound muscular relaxation. It stimulates
salivary and respiratory secretions. Uterine
relaxation is similar to halothane.

No unusual effect on the gastrointes-
tinal tract has been reported with
enflurane anaesthesia, however, certain
evidence of hepatic impairment has
been obtained during and after surgi-
cal anaesthesia. Hepatic necrosis prob-
ably occurs with enflurane in rare
instances.

Heart rate decreases little and reduction
of cardiac output is less marked. Fall in
blood pressure is similar to that caused by
halothane, arrhythmias are rare.

ISOFLURANE

It is a isomer of enflurane and its chemi-
cal and physical properties are similar to
enflurane, but it is approximately 1½ times
more potent, more volatile. It has a lower
blood: gas solubility coefficient than
enflurane. It produces rapid induction and
recovery.

Systemic arterial blood pressure de-
creases progressively with increasing depth
of anaesthesia with isoflurane. It also in-
creases heart rate but arrhythmias are not
precipitated. Isoflurane depresses respira-
tion as concentration is increased. Uterine
and skeletal muscle relaxation is similar to
enflurane.

During anaesthesia, depression of renal
blood flow, decrease in rate of glomerular
filtration and urinary flow are reported but

these changes are rapidly reversed during

recovery.

METHOXYFLURANE

It is a clear, colourless liquid with a

sweet and fruity odour. It is noninflammable

and non-explosive in air or oxygen in an-

aesthetic concentrations. It is the most po-

tent inhalational anaesthetic which has a

good analgesic and muscle relaxant prop-

erties. Renal blood flow, glomerular filtra-

tion rate and urine flow are reduced as with

the halothane.

It also produces the respiratory and car-

diovascular depression as with halothane

but bradycardia is more prominent.

Methoxyflurane damages renal tubules

leading to inability to concentrate urine and

uraemia. Because of its renal toxicity, it

should not be used to achieve profound

anaesthesia nor for prolonged periods of

time.

This agent is used due to certain advan-

tages i.e. it provides profound analgesia and

good relaxation of skeletal muscles, uterine

contractions are not inhibited and postop-

erative nausea and vomiting are not

troublesome. But, due to its renal toxicity,

its use as a general anaesthetic is limited.

DESFLURANE

It is a noninflammable, non-irritant

agent and chemically related to ether. Induc-

tion with this agent is smooth and rapid. The

respiratory, hemodynamic and other

changes caused by desflurane are similar to

those of isoflurane. This agent is undergo-

ing clinical trial.