Inhalant anaesthetics Volatile or gaseous e.g. ether methoxiflurane halothane isoflurane sevoflurane desflurane nitrous oxide

Methods of induction of inhalation anesthesia 1-Open method: - It can be used for ether or ethyl chloride spray, by dropping it on a piece of gauze or lint that should be kept of the nostril of the animal. This piece of gauze can be stretched over a wire frame to form a mask with preservation of free flow of air between the mask and the face. Disadvantages: 1-Lack of control of ventilation, as oxygen enrichment should be always given during general anesthesia 2-Excessive loss of volatile agents

Methods of induction of inhalation anesthesia 2-Semi-open method: - All inspired air is made to pass through the mask in which the vapor of anesthetic agent is present. The space between the mask and the face is closed with double thick layer of gamgee. Disadvantages: Same as open method

Methods of induction of inhalation anesthesia 3-Semi-closed method: - Vapors flow from anesthetic apparatus into reservoir bag from which the animal inhales through endotracheal tube, while part of all exhaled mixture passes out through an expiratory valve into the atmosphere.

Methods of induction of inhalation anesthesia 4-Closed method: - In this method, vapors flow from anesthetic apparatus into reservoir bag from which the animal inhales through endotracheal tube. The exhaled anesthetic agent, which is mixed with Co2, is directed to closed bag at which Co2 is removed (by soda lime of 90% calcium hydroxide, 5% sodium hydroxide, and 5% silicates and water to prevent powdering) and O2 is added, then the same vapor is re-breathed. Advantages: It is a simple method that consumes less anesthetic agent

Methods of induction of inhalation anesthesia Hinz's Box It is a glass or transparent plastic box used for inhalation anesthesia (ether) in cat and dog. Advantages: 1-Require no restraint and no assistant 2-Minimised anesthetic emergency 3-Animal passes into a state of anesthesia with minimal amount of struggling

Stages of general anesthesia 1-Stage I (Stage of voluntary excitement or Induction stage): - a-The animal is conscious b-Respiratory and pulse rates increase c-Dilatation of the pupil d-Urine and faces may be voided 2-Stage II (Stage of involuntary excitement or Delirium stage): - a-Loss of consciousness b-Exaggerated reflex to stimuli c-Very irregular respiration d-Eye ball moves from side to side e-Vomiting may occur due to pharyngeal reflex

Stages of general anesthesia 3-Stgae III (Stage of surgical anesthesia): - a-Increase regular automatic breathing b-Fixation of the eyeball c-Absence of all reflexes d-Complete muscle relaxation 4-Stage IV (Over dose stage): - a-Complete paralysis of thoracic muscles with active diaphragm, which causes bulging of the relaxed abdominal wall while the relaxed thoracic wall moves inward like resting position during expiration b-The respiration is gasping in character as a result of jerky movement of the diaphragm. c-The pulse rate increase d-The pupil dilate and the eyeball present in fish-eye appearance due to cessation of lachrymal secretion e-The animal enters stage of death with coma and cyanosis

Treatment of overdoses inhalation anesthesia: - 1-Stop of gas inhalation 2-Increase oxygen supply 3-Artificial respiration 6-Warming of the animal by straw Complications of over doses of anesthesia: - 1- Syncope, and pathologic affection of respiration and circulation 2-Respiratory arrest 3-Liver intoxication

Problems encountered in general anesthesia in bovine: - General anesthesia in bovine is so dangerous so that nerve block and infiltration analgesia are preferred.

Generally, the problems encountered in bovine general anesthesia are: 1-Bloat and regurgitation: - the excessively formed gas in the rumen can't be regurgitated normally with the animal in lateral recumbency, due to higher level of ruminal fluid. This large amount of gases causes: a-Interference with the already impaired respiration, caused by the recumbence position and pressure on diaphragm b-As the pressure increases it will press the cardiac opening that is augmented by the depth of anesthesia, with relaxation of the cardiac opening, so that the fluid flows from the rumen, then it may be collected in the pharyngeal region and may be aspirated leading to drenching pneumonia or death 2-Anoxia: - It resulted from: a-Respiratory embarrassment by compression of the lower lung due to lateral recumbency. b-Deep anesthesia causes more diaphragmatic breathing c-Pressure on diaphragm by abdominal viscera

3-Radial paralysis: - This condition may lasts from few minutes to few weeks and its occurrence depends up on: a-Length of time of recumbency b-Body weight c-Thickness of subcutaneous fat generally this condition can be avoided by placing inflated tire under the point of shoulder at the time of casting 4-Salivation: - Use of atropine sulfate reduces amount of saliva.