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Lectures in Veterinary Anesthesia

Muneer S. Al-Badrany

RAPIDLY ACTING NON-BARBITURATES

Propofol:
Propofol is an intravenous anesthetic agent unrelated to barbiturates or steroid anesthetic agents. It is a rapidly acting agent which produces anesthesia of short duration without excitatory side-effects. Unlike thiopentone, propofol doesn’t produce tissue damage when injected perivascularly or intra-arterially. Greater reflex depression and more pronounced electroencephalographic changes are associated with propofol than with thiopentone.
Propofol is highly lipophilic and rapidly metabolized primarily to inactive glucuronide conjugates, the metabolites excreted in the urine.
The great attraction for using propofol in dogs and cats is the rapid and complete, excitement-free awakening, irrespective of the duration of anesthesia. A price must be paid for this, however. Animal require careful observation during the recovery period to ensure that they come to no harm from vomitting.

Lectures in Veterinary Anesthesia

Muneer S. Al-Badrany

It given i.v. route only , dose 6 mg/kg duration of anesthesia 5-10 min it can given half and half thiopentone , it can repeated the injection or can given as infusion , recovery rapid and smooth
It used in horse, goat
Etomidate Metomidate :

It given i.v given with premedication , dose 50-150 ug/kg , minimum effect C.V.S including H.R, B.P

Lectures in Veterinary Anesthesia

Muneer S. Al-Badrany

Dissociatives

Dissociative anesthesia is a state wherein the patient is "dissociated" from the environment, resembling a catatonic state. The eyes remain open, the patient is not unconscious. Muscle relaxation is not a feature and varying degrees of hypertonus and purposeful movement occur independent of surgical stimulation. There is electroencephalographic evidence of dissociation between the neothalamocortical and limbic systems, and differential depression and activation of various areas of the brain. Amnesia is present and while somatic analgesia may be intense, visceral analgesia is less reliable. Emergence excitement and delirium may occur. The dissociative anesthetics are cyclohexamines. Presently, ketamine is the most commonly used dissociative. Tiletamine is available in combination with zolazepam (a benzodiazepine) as Telazol. Phencyclidine is no longer available.

Lectures in Veterinary Anesthesia

Muneer S. Al-Badrany

The mechanism of action of ketamine has not been established. It appears that the cyclohexamines exert their effects via antagonism of CNS muscarinic acetylcholine receptors and by agonism of opioid receptors. Ketamine's pharmacokinetics resemble those of thiopental, being rapid in onset and of short duration. Ketamine is 5-10 times more lipid soluble than thiopental, ensuring rapid transfer to the CNS and recovery through rapid redistribution. Ultimate clearance from the body is dependent upon hepatic metabolism. Norketamine, an intermediate metabolite, has one-fifth to one-third the potency of ketamine and may contribute to prolonged effects. There are significant differences among species in the relative amount of free ketamine excreted in the urine. In people, dogs and horses, metabolism is extensive, while in cats, most of the drug appears unchanged in the urine. Ketamine, like the barbiturates, can induce hepatic enzymes with repeated exposure. This probably accounts, at least in part, for the tolerance that occurs with repeated exposure to the drug.
Ketamine

Lectures in Veterinary Anesthesia

Muneer S. Al-Badrany

The cardiovascular effects of ketamine resemble sympathetic nervous stimulation. Systemic and pulmonary arterial blood pressure, heart rate, cardiac output, cardiac work and myocardial oxygen consumption increase. These effects are obtunded by prior administration of tranquilizers or sedatives. In intact patients with a functioning CNS, ketamine increases myocardial contractility. However, in isolated pappilary muscle preparations or in denervated hearts, myocardial depression occurs. Ketamine’s cardiovascular effects are primarily due to direct stimulation of the CNS leading to increased sympathetic outflow from the CNS. Plasma concentrations of norepinephrine and epinephrine increase transiently following ketamine administration as a result of inhibition of their uptake at postganglionic sympathetic nerve endings. In hypovolemic patients, arterial blood pressure is better maintained with ketamine because of vasoconstriction, however tissue perfusion may suffer.

Lectures in Veterinary Anesthesia

Muneer S. Al-Badrany

Ketamine does not induce significant respiratory depression. An apneustic pattern of breathing is commonly seen. Bronchial dilation secondary to increased sympathetic tone occurs and protective upper airway reflexes are maintained. Airway and salivary secretions are increased. Ketamine does not significantly effect hepatic or renal function.
Cat: 10mg/kg i.m, induction 3-5 min. , duration 30 min. eye remain open all refflex present, must put eye ointment mixed with Acepromazine, xylazine, Diazepam
Dog: given with xylazine , 15mg/kg B.W + xylazine 5 mg/kg i.m
Horse: 11-33 mg/kg B.W

Lectures in Veterinary Anesthesia

Muneer S. Al-Badrany

PHARMACOLOGY OF THE INHALATION ANESTHETICS

INDIVIDUAL INHALATION ANESTHETICS

Gas Inhalation:
Cyclopropane
Nitrous oxidae

Liquid inhalation

Chloform
Ether
Halothane
Methoxyflurane
Enflurane
Isoflurane

Lectures in Veterinary Anesthesia

Muneer S. Al-Badrany

Lectures in Veterinary Anesthesia

Muneer S. Al-Badrany

Lectures in Veterinary Anesthesia

Muneer S. Al-Badrany

Lectures in Veterinary Anesthesia

Muneer S. Al-Badrany

Chloroform

Choloform is a most powerful anesthetic which is not longer used. It has toxic effect on the liver and kidney, causing fatty change in the cell, some times causing ventricular fibrillation and sudden death

Lectures in Veterinary Anesthesia

Muneer S. Al-Badrany

Diethyl Ether

One of earliest inhalation anesthetics, it is inflammable, irritant, it is colourless liquid with vapour twice as air, highly inflammable in air and explosive in O2, it destroy in air, light so it stored in amber-coloured bottle keep in dark cool place, disadvantage in addition to it is inflammability, stimulation salivation, cause nausea

Lectures in Veterinary Anesthesia

Muneer S. Al-Badrany

Halothane

Vapour concentrations of 2-4% in the inspired air produce smooth and rapid induction of anesthesia in all species of domestic animal. Anesthesia can then be maintained with inspired concentrations of 0.8-2%, The mucosa of the respiratory tract is not irritated by halothane and the agent has been shown to produce bronchodilatation and an increase in expiratory reserve volume in ponies.
Halothane causes a dose-dependent depression of cardiac output and arterial blood pressure due mainly to a negative inotropic effect.
Dose-dependent respiratory depression occurs, both the depth and rate being decreased so that the minute volume of respiration is greatly reduced, leading to a progressive rise in arterial carbon dioxide tension

Lectures in Veterinary Anesthesia

Muneer S. Al-Badrany

Isoflurane
Respiratory and cardiovascular depression are dose dependent. Heart rate is increased and cardiac output and stroke volume are reduced less than they are with halothane; a greater fall in peripheral resistance must be responsible for the similarity of the blood pressure response, for at clinical concentrations halothane has little effect on total peripheral resistance.
The high volatility of isoflurane, coupled with its low blood solubility, provide for relatively rapid induction and recovery and easy control of the depth of anesthesia. Its low solubility in fatty tissues avoids accumulation in obese subjects.

Lectures in Veterinary Anesthesia

Muneer S. Al-Badrany

Cyclopropane

It is expensive gas inflammable as ether and mixture with air and O2 are explosive it produced marked respiratory depression , should be administrated only in closed circut

Lectures in Veterinary Anesthesia

Muneer S. Al-Badrany

Nitrous oxide
N2o is a colouless gas with a faint, rather pleasant smell it is not inflammable or explosive but it support combustion, not irritant to respiratory system, not cause toxicity it has no effect on liver, kidney

Lectures in Veterinary Anesthesia

Muneer S. Al-Badrany

APPARATUS FOR THE ADMINISTRATION OF ANESTHETICS

ADMINISTRATION OF INHALATION AGENTS
The administration of an inhalation anesthetic requires:
1. a source of oxygen (which may be air)
2. a vaporizer or a source of anesthetic gas
3. a “patient” or “breathing” circuit

Lectures in Veterinary Anesthesia

Muneer S. Al-Badrany

Oxygen cylinders

Pressure gauge
Reducing valves or regulators
Flowmeters (rotameter)
The flowmeter consists of a glass tube inside which a rotating bobbin is free to move. The bore (diameter?) of the tube gradually increases from below upwards. The bobbin floats up and down the tube, allowing gas to flow around it. The higher the bobbin in the tube, the wider the annular space between the tube and the bobbin (orifice) and the greater the flow rate through it. The gas flow rate is read from the the top of the bobbin against a scale etched on the outside of the glass tube.

Pipeline systems

Lectures in Veterinary Anesthesia

Muneer S. Al-Badrany

Vaporizers

Factors which have most influence on the vaporization of volatile anesthetics include temperature, gas flow rate through the vaporizer, and back pressure transmitted during IPPV.. A low resistance to gas flow may also be important if the vaporizer is to be used in the breathing circuit.

Uncalibrated vaporizers
Calibrated vapoizers
Low-resistance vaporizers

Lectures in Veterinary Anesthesia

Muneer S. Al-Badrany

The purpose of the breathing circuit of an anesthetic apparatus is to convey oxygen and anesthetic to the patient, and to ensure the removal of carbon dioxide produced by the patient:
Breathing circuits
1. the open method
2. the semi-open method
a. the closed method with carbon dioxide absorption
3. b. the semi-closed method with carbon dioxide absorption
4. the semi-closed method without carbon dioxide absorption

Lectures in Veterinary Anesthesia

Muneer S. Al-Badrany

Breathing circuits

Open Method:
It used to volatilize agent such as Choloform and Ether They are dropped on to the surface of gauze and held over the
Semi-opend Method :
All the inspired air is made to pass through the mask on which vaporiztion agent occurs
Open, semi-open method of administration are seldom used because with them it is difficult to maintain a stable anesthetic state, anesthetic will dilution by breathing , and it not supply adequate O2

Lectures in Veterinary Anesthesia

Muneer S. Al-Badrany

Lectures in Veterinary Anesthesia

Muneer S. Al-Badrany

Lectures in Veterinary Anesthesia

Muneer S. Al-Badrany

Breathing circuits

Closed method with Co2 absorption
Principle:
Anesthetic gases and vaporus are physiologically indifferent, in that they are exhaled from the body unchanged, but when exhaled they are mixed with Co2. The exhaled mixture can be directed into closed bag and if CO2 is removed and sufficient O2 to satisfy the metabolic requirements is added, the same gas can be rebreathed continuously from the bag
Co2 is removed by directing exhalted gas on soda lime ( mixture 90% calcium hydroxide and 5% sodium hydroxide together 5% of Silicate it used as granules forms and is packed in canister

Lectures in Veterinary Anesthesia

Muneer S. Al-Badrany

A more clinical usefull definition of circuits is based on the two methods by which carbon dioxide is removed from the circuit. Either the circuit is designed so that the expired gases are vented to the atmosphere and cannot be rebreathed (non-rebreathing systems) or the expired gases are passed through an absorber which contains soda lime to remove the carbon dioxide (rebreathing systems).

Lectures in Veterinary Anesthesia

Muneer S. Al-Badrany

Non-rebreathing circuits:

Carbon dioxide removal depends on the fresh gas flow rate, and on the minute and tidal volumes of respiration of the patient.

The Ma gill circuit:
With this system rebreathing is prevented by maintaining the total gas flow rate from the cylinders slightly in excess of the patient’s respiratory minute volume. The animal inhales from the bag and wide-bore tubing. The exhaled mixture passes back up the tubing displacing the gas in it back into the bag until it is full.To ensure minimal rebreathing of the expired gases the fresh gas flow rate should be equal to, or greater than, the minute volume of respiration of the patient

Lectures in Veterinary Anesthesia

Muneer S. Al-Badrany

Lectures in Veterinary Anesthesia

Muneer S. Al-Badrany

Lectures in Veterinary Anesthesia

Muneer S. Al-Badrany

T-piece systems (Ayre):

The low resistance and small dead-space make the T-piece system very suitable for use with cats and small dogs.
An open tube acts as a reservoir and there are no valves. The exhaled gases are swept out of the open end of the reservoir tube by fresh gases flowing in from the anesthetic apparatus during the expiratory phase.
There are three modifications of the T-piece system:
1.there is no expiratory limb
2.the capacity of the expiratory limb is greater than the tidal volume
3.the capacity of the expiratory limb is less than the tidal volume

Lectures in Veterinary Anesthesia

Muneer S. Al-Badrany

Lectures in Veterinary Anesthesia

Muneer S. Al-Badrany

Coaxial systems:

There are two types of coaxial circuits, the Bain system and the Lack system, in use. In the Bain type fresh gas passes up the central tube and expired gas through the outer sleeve. The Lack circuit uses the alternative arrangement in which fresh gas flows up the outer sleeve and expiration takes place down the inner tube. This arrangement was designed to aid scavenging of expired gas.

Lectures in Veterinary Anesthesia

Muneer S. Al-Badrany

Rebreathing circuits -

Anesthetic gases and vapours are said to be more or less physiologically ‘indifferent’, in that they are largely exhaled from the body unchanged, but when exhaled, they are mixed with carbon dioxide. The exhaled gas can be directed into a closed bag and if the carbon dioxide is removed and sufficient oxygen added to satisfy the metabolic requirements of the animal, the same gas or vapour can be rebreathed continuously from the bag. In anesthesia, the carbon dioxide is usually removed by directing the exhaled mixture over the surface of soda lime. This is a mixture of 90 % calcium hydroxide and 5 % sodium hydroxide together with 5 % of silicate and water to prevent powdering.

Lectures in Veterinary Anesthesia

Muneer S. Al-Badrany

To-and-fro system:

A canister full of soda lime is interposed between the animal and the rebreathing bag, fresh gases being fed into the system as close to the animal as possible to effect changes in the mixture rapidly. This system is simple and efficient but has a few drawbacks. It is difficult to maintain the heavy, akward apparatus in a gas tight condition and the inspired gases become undesirably hot due to the chemical action between the soda lime and the carbon dioxide. Furthermore,’ irritating dust may be inhaled from the soda lime and give rise to a bronchitis. Nevertheless the system is the one most used in veterinary anesthesia (inexpensive).

Lectures in Veterinary Anesthesia

Muneer S. Al-Badrany

Lectures in Veterinary Anesthesia

Muneer S. Al-Badrany

Lectures in Veterinary Anesthesia

Muneer S. Al-Badrany

Lectures in Veterinary Anesthesia

Muneer S. Al-Badrany

The circle system:

The circle system for carbon dioxide absorption incorporates an inspiratory and an expiratory tube with unidirectional valves to ensure a one-way flow of gases. The rebreathing bag and soda lime canister are placed between these tubes. Circle-type absorber units are not, as a general rule, suitable for cats and small dogs of less than about 15 kg body weight because of the resistance offered by even the best designed units and because of the inevitable degree of rebreathing which occurs at the T-piece connection to the patient.
Circle absorber units are more efficient absorbers of carbon dioxide than are to-and-fro units because their dead-space is constant since all the charge of soda lime is available to the respired gases. Exhaustion of soda lime is noticed more suddenly than in to-andfro absorbers and once it occurs the inspired carbon dioxide concentration may soon become excessive.