PREANAESTHETIC CONSIDERATIONS AND PREANAESTHETICS

PREANAESTHETIC CONSIDERATIONS AND PREANAESTHETICS

Premedication/Preanaesthestic  medication includes drugs given before 10-15 minutes of local/general anaesthesia

1.To prepare the patient for smooth induction by minimising struggling, maintenance and smooth recovery from anaesthesia.

2.Facilitate restraint

3.Reduce apprehension and fear and calm the animal during induction of anaesthesia.

4.Reduce the dose of general anaesthetic and decreases irritability of CNS.

5.Reduce the toxic effects of anaesthetic drugs like salivary and tracheobronchial secretions.

6.Minimise  certain drug induced  reflex responses like vagal reflexes, bradycardia.

7.Increase analgesia after surgery.

8.Facilitate muscle relaxation.

9.Facilitate smooth recovery from anaesthesia.

10.Decrease gastric fluid volume and acidity.

11.Prevent vomition and regurgitation.

Classification of preanaesthetic medication agents

Selection of preanaesthetic agent will depend on age, physical status, species, disposition, surgical procedure(In patient/Out patient) or (Elective/Emergency) and duration required.

 

Tranquilizers	Sedatives	Narcotics	Anticholinergic agents	Muscle relaxants

 

Tranquilizer:

Eg: 1. Phenothiazine groups (Chlorpromazine, Triflupromazine, Acetylpromazine), side effect is severe hypotension.

Chlorpromazine is not used in cattle as it will have regurgitation risk, with cardiac relaxation. Dose is 0.3-0.6mg/kg B.Wt, Triflupromazine dose is 0.11mg/kg.

2.Benzodiazepine group (Diazepam)- Alpha adrenergic blocking drug, side effect is vasodialation and hypotension.

Diazepam used as muscle relaxant at the dose rate of 1mg/kg.

Sedative:

Eg: 1.Xylazine- Produces satisfactory sedation, muscle relaxation and analgesia, with side effects of bradycardia, hypotension, hypoventilation, excessive salivation.

Side effects minimized by Atropine, which inhibits rumino reticular motility, leading to ruminal atony and bloat.

Dose of thiopentone reduced by half and halothane by 40%.

Reversal for Xylazine is Yohimbine (0.25mg/kg), Tolazoline (2mg/kg), 4-Amino pyridine (0.3mg/kg), they reverse bradycardia and tachypnoea.

Dose of Xylazine is 1mg/kg in dogs, 0.1mg/kg in cattle, No I/V administration in camels, not used in pregnancy.

Detomidineat 20microg/kg is almost xylazine in action, but produces vagal stimulation, countered by acetyle promazine (0.1mg/kg).

Chloral hydrate: Low dose sedative in cattle, used as 65% solutioin, very irritant , so perivascular effusion is avoided in I/V adm. Drug slow in action, continues to deepen after infusion is stopped, tchcardia and hypotension is side effect.

Magsulf (1 : 1) with Chloral hydrate is used to minimize cardio vascular and respiratory effects and better muscle relaxation.

Narcotics are Morphine, pethidine, methadone, etorphine, pentazocine lactate.

Anticholenergic drugs:

Atropine sulphate(0.04mg/kg) and Glycopyrrolate(0.11mg/kg) , decreases salivary and brochial secretions and bradycardia, inhibits GI motility. At 0.1mg/kg atropine in ruminants causes sinus tachycardia.

Glycopyrrolate is 5 times more powerful antisialogogue.

Muscle relaxants:

Neuromuscular blocking drugs paralyse respiratory muscles at higher doses. Glyceryl guaiacolate as muscle relaxant doesnot depress myocardium and resoirations.

In cattle, GG  at 10mg/100kg BW is adequate muscle relaxant.

Pre anaesthetic drugs:

1.Atropine Sulphate: At dose rate of 0.04mg/kg, given by S/C, I/M, I/P, I/V to horses, pigs, dogs, and cats 30-45 min before anaesthesia to decrease mucous and salivary secretions. Not used for ruminants as it makes secretions much thicker.

2.Morphine: Used only for dogs, contraindicated in cats, used along with atropine , through S/C to dogs 30-40 minutes before anaesthesia for sedative effect. It induces vomition, followed by depression of vomiting centre. Depresses respiratory centre, and death of foetus by crossing placental barrier.

3.Pethidine: Similar to morphine but for all species with atrophine, safe in cats. Dose , In dogs 100mg/kg, in cats 10mg/kg.

4.Largactyl: (Chlorpromazine Hcl): Tranquilizing agent, Antiemtic, antiadrenaline and vagolytic.

Cats, Pigs and Dogs at 1mg/kg, Horse at 0.4mg/kg.

5.Siquil: (Triflupromazine) presented in 5ml vial with 20mg/ml. decreases dose of Barbiturates by half, given 5-15 min before anaesthesia.

Cats,Dogs at 1-2mg/kg I/V, Cattle 0.1mg/kg.