66 Section 2/ Drugs Acting on CNSAdverse effects include laryngospasm,
high incidence of hypersensitivity reactions,
tachycardia, respiratory depression and
sometimes hypotension. Local irritation and
thrombophlebitis occur due to the alkalin-
ity of the solution. It is occasionally used as
an alternative to thiopentone.
KETAMINE
It is a new non-barbiturate anaesthetic
agent and pharmacologically related to
phencyclidine, a hallucinogen. Intravenous
ketamine produces unconsciousness and
analgesia within 30 seconds. It can be given
by intramuscular route also. It acts on the
cerebral cortex and subcortical areas.
The drug increases the heart rate, car-
diac output and blood pressure which is
due to sympathetic stimulation. Respira-
tion is not depressed, muscle tone
increases and reflexes are not abolished
during anaesthesia. Ketamine has been
recommended for short operations, un-
pleasant therapeutic and diagnostic pro-
cedures in children, operation in shocked
patients and in obstetrics.
Adverse reactions include delirium,
hallucinations and unpleasant dreams. It
should not be used in hypertensives and in
patient with ischaemic heart disease.
FENTANYL-DROPERIDOL
COMBINATION
Fentanyl is a potent short acting analge-
sic related to pethidine and belongs to group
of 4-acyl-anilinopiperdines. Droperidol is a
rapidly acting potent neuroleptic
butyrophenone derivative related to halo-
peridol. In combination, these agents pro-
duce a state of ‘neuroleptanalgesia.’
The fixed dose combination of fentanyl
(0.05 mg) and droperidol (2.5 mg/ml), 4 to
6 ml is diluted in glucose solution and in-
fused IV over 10 minutes.
Patient remains drowsy but conscious.
Respiratory depression is marked and pre-
dictable. There is slight fall in blood pres-
sure. Heart rate often decreases but myocar-
dium is not sensitized to adrenaline.
It is recommended for endoscopies, an-
giographies, burn dressings etc.DIAZEPAM
It may be used to produce light seda-
tion and amnesia for unpleasant procedures
by intravenous injection. It has also been
used for induction and to supplement ni-
trous oxide anaesthesia. The benzodiaz-
epines are further discussed in chapter
‘Sedative and hypnotics’ in detail.ETOMIDATE
It is a new intravenous anaesthetic agent
with poor analgesic property. It has a briefer
duration of action than thiopentone. It pro-
duces little cardiovascular and respiratory
depression. A single intravenous dose pro-
duces loss of consciousness within 10 sec-
onds and a state of anaesthesia.ALPHADONE
It is a slower acting steroid anaesthetic
which is a combination of two preganedione
derivatives, alphaxolone and alphadolone
acetate. It produces analgesia and sleep last-
ing 20-30 minutes. It is less irritant, blood
pressure and respiration are not much af-
fected. It has been used as an inducing agent
in place of thiopentone but due to hyper-
sensitivity reactions its use is very limited.