Preanaesthetic Medication



Preanaesthetic Medication
·         Preanaesthetics are drugs given prior to anaesthesia usually to prepare the patient for administration of general anaesthetic agent
·         Preanaesthetic medication use in a particular patient depends on, the animals physical condition and temperament, amount of sedation or analgesia required, type of anaesthetic agent, type of surgical procedure, etc.,
Preanaesthetics are used with one or more of the following aims,
a.       To reduce the amount of general anaesthetic needed and to increase the margin of safety.
b.      To calm / restrain the patient so that anaesthesia can be administered without fight or struggling.
c.       To reduce secretions of salivary glands and mucus glands of respiratory tract, thus maintaining a free airway.
d.      To reduce the gastric and intestinal motility and to prevent vomiting while the patient is under anaesthesia.
e.      To block the vagal reflex, thus preventing cardiac slowing and asystole
f.        To relive preoperative and postoperative pain.
g.       To reduce excitement, struggling and crying during recovery period.

Anticholinerigic
·         These drugs are used to reduce salivary and bronchial secretions and to prevent or treat vagally induced cardiac arrhythmias caused by the anaesthetic drug.
·         Eg: Atropine and glycopyrronium

Sedative / Tranquillizers
·         These agents produce mental calming, decrease motor activity and increase threshold to external stimulai.
·         Important groups include phenothiazines (acepromazine, promazine), butyrophenones (droperidol, azaperone), α – 2 adrenoreceptor agonist (xylazine and medetomidine), benzodiazepine (diazepam and midazolam)

Opioid analgesics
·         These are often used alone or in combination with tranquillizers.
·         When analgesics are used in premedication, only strong opioids have proven adequate because even minor pre-operative pain is considered deleterious to smooth induction of anaesthesia.
·         Commonly used opoid agonist are morphine, oxymorphone, pethidine and fentanyl.

Neuroleptanalgesia
·         Combination of tranqillizers (neuroleptics) and opoids,  called neuroleptanalgesics produce a state of CNS depression and analgesia that may cause dramatic behavior modification and change in aggressiveness in animals .
·         The most common combination is fentanyl and droperidol.

Central muscle relaxants
·         Guaifenesin is a central acting muscle relaxant that is used intravenously with thiobarbiturates and ketamine for induction of anaesthesia.

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