Pharmacology for Dentistry

General Anaesthetics 67

PREANAESTHETIC MEDICATION

Preanaesthetic medication refers to the use
of drugs before the administration of an an-
aesthetic agent, which makes it more pleas-
ant and safe to the patient

The aims of preanaesthetic medication
are:

1. Reduce the anxiety and apprehension
   without producing much drowsiness.


2. To facilitate a smooth and rapid
   induction.


3. To relieve preoperative and postopera-
   tive pain or to supplement the analge-
   sic action of anaesthetics.


4. To provide amnesia for preoperative
   and postoperative period.


5. To suppress respiratory and other
   secretions and vagal stimulation
   caused by anaesthetics.


6. To minimize certain undesirable effects
   produced by anaesthetic agents like
   bradycardia and vomiting.
   To achieve all the objectives, a combina-
   tion of 2 or 3 drugs is used depending on
   the need. The commonly employed drugs
   are opioids, sedative-hypnotics, antianxiety
   agents, anti-cholinergics, neuroleptics and
   antiemetics.

OPIOIDS

These are the most commonly used
drugs. Morphine (10-15 mg IM), pethidine
(50-100 mg IM) are frequently used drugs
for their sedative and analgesic property.
They reduce the anxiety and apprehension,
produce pre- and postoperative analgesia,
help in smooth induction. They also reduce

the amount of anaesthetic required. How-

ever, they have certain disadvantages:

• They depress respiration.


• May cause fall in blood pressure during
  anaesthesia.


• Can precipitate asthma, as these drugs
  are histamine liberators.


• Pethidine may produce tachycardia by
  its vagolytic action.


• Morphine can interfere with pupillary
  signs of anaesthesia.
  SEDATIVE-HYPNOTICS
  The barbiturates like pentobarbitone,
  secobarbitone or butobarbitone (100 mg oral)
  have been used to provide sedation and to
  relieve apprehension before operation.
  Non-barbiturate sedatives like chloral
  hydrate, paraldehyde and glutethimide may
  be used.
  Promethazine (50 mg IM), an
  antihistaminic with sedative, antiemetic and
  anticholinergic properties is generally used
  in children as it causes little respiratory de-
  pression.

ANTIANXIETY DRUGS

The tranquillizers like benzodia-

zepines (diazepam 5-10 mg oral, or

lorazepam 2 to 4 mg IM, IV are now

preferred for preanaesthetic medication

because they produce tranquillity, have

better muscle relaxant property and

smoothen induction. Other tranquillizer

compounds include phenothiazines which

possess sedative, antiemetic and

antihistaminic properties. They can be

given orally as well as parenterally.