4 th year BVSc, Topics

2. ◦ Isoflurane and sevoflurane are the most commonly used
agents in this class
 Others include Desflurane, Halothane,
Methoxyflurane, and Enflurane, but these are not
commonly used
 Liquid at room temperature
 Stored in a vaporizer on an anesthetic machine
◦ Vaporized in oxygen that flows through the vaporizer

3.  Liquid anesthetic is vaporized and mixed with oxygen
 Mixture is delivered to the patient via a mask or
endotracheal tube (ET tube)
 Mixture travels to lungs (alveoli) and diffuses into the
bloodstream
 Diffusion rate is dependent on concentration gradient
(alveoli/capillary) and lipid solubility of the anesthetic
gas.

4.  Distribution to tissues is dependent on blood supply
◦ Tissues with greater blood flow (brain, heart, kidney) are
more quickly saturated with anesthetic gas.
◦ Lipid solubility of the gas determines entry into tissues
through cell walls.
 Maintenance of anesthesia is dependent on sufficient
quantities of anesthetic delivered to the lungs

5.  Reducing amount of anesthetic administered reduces amount
in the alveoli.
 Anesthetic will move from the brain into the blood and then
into the alveoli where it is finally breathed out.
 Patient wakes up.

6. Anaesthetic properties;
 It is a laughing gas.
 It is only inorganic anesthetic gas in clinical use.
 Colorless and odorless
 Non Explosive and Non Inflammable
 Gas at room temperature and can be kept as a liquid under
pressure.
 Mixed with oxygen at 40-67%, then delivered to patient.
 Used with Halothane and Methoxyflurane
to reduce the adverse effects of these gases.
Clinical use:
analgesic adjuvant used in dentistry upto 70%N2O

7.  Alveolar ventilation and the alveolar anesthetic
concentration influenced by administering a potent
inhalation anesthetic like halothane in conjunction with
N2O .
 Very early in the administration of N2O , the rate of rise of
the alveolar concentration of the concurrently administered
inhalation anesthetic is increased. This is commonly
referred to as the second gas effect, and this phenomenon
can be applied clinically to speed anesthetic induction.
 Administration of 60% N2O with halothane reduces the
amount of halothane needed to produce the M A C by about
20% to 30% in dogs.

8.  Special consideration associated with recovery after use of
N2O.
 Diffusion hypoxia is a possibility at the end of N2O
administration when the patient breathes air immediately
rather than O₂ for at least a brief transition period (i.e., 5 to 10
min). In this case a large volume of N2O enters the lung from
the blood. This early rapid inflow of N2O to the lung displaces
other gases within the lung.

9. Nitrous oxide is not commonly used in veterinary anesthesia for the
following reasons:
Weak analgesic property when used alone in domestic animal species.
Its use together with a primary inhalation anesthetic (such as halothane,
isoflurane) only reduces the amount of primary inhalation anesthetic by 25%
to 30% of the control value.
The use of nitrous oxide requires a higher fresh gas flow rate than would be
used with oxygen alone. Accordingly the total amount of the primary
anesthetic that is vaporized is increased - more anesthetic is wasted.
Risk of diffusion (dilutional) hypoxia.

10. CARDIOVASCULAR SYSTEM
Stimulate sympathetic nervous system.
Directly depresses myocardial contractility.
Arterial blood pressure ,heart rate and cardiac output are slightly increased.
RESPIRATORY SYSTEM:
Increases respiratory rate with decreases tidal volume.
Minimal change in minute ventilation.
CEREBRAL:
Increases CSF thus increasing intracranial pressure.
RENAL SYSTEM:
It decreases renal blood flow thus leads to drop in glomerular filtration rate and urinary output
.
HEPATIC SYSTEM:
Decreases the Hepatic blood flow but to a lesser extent than other inhalation agents.
GASTROINTESTINAL:
It causes post operative Nausea and Vomiting.

11. Physical properties
 Highly potent clear, sweet odor, colorless liquid, non-
inflammable
 50-75% metabolized by the liver, excreted by the kidneys.
EFFECTS ON SYSTEMS
NERVOUS SYSTEM;
 Dose dependent depresssion
 Good muscle relaxation and analgesia.
 Fluoride ions and other potentially toxic metabolites
produced by the liver= renal damage

12. RESPIRATORY SYSTEM;
 DEPRESSION
 NON IRRITATING
CVS:
 NEGETIVE IONO TROPIC EFFECT
 SENSITISES HEART TO CATECHOLAMINE
OTHER EFFECTS:
NEPHRO TOXIC,HEPATO TOXIC

13.  Colourless; pleasant smelling.
 unstable in light so packed in dark bottles.
 Contain 0.1% thymol as stablising agent.
 It is halogenated alkene.
 Non Inflammable and Non explosive.
 Least expensive
 MAC- 0.87-1.19

14.  One of most useful anaesthetics - it is non
inflammable, potent, non irritating and relatively non
toxic.
 induction and recovery are rapid (1-3 minutes)
 DOSAGE:
2 to 4% at induction
0.5 to 1.5% at maintenance in small animals
1 to 2% in large animals

15. CARDIOVASCULAR:
- Dose dependent reduction of arterial blood pressure by direct
myocardial depression. decreases cardiac output (CO)
-It causes slowing of SA node conduction resulting in
bradycardia.
RESPIRATORY SYSTEM:
-Causes rapid ,shallow breathing.
-Decrease in alveolar ventilation and P[CO₂] elevated.
-Potent bronchodilator.

16. CEREBRAL:
 It increases cerebral blood flow.
NEUROMUSCULAR:
 Relaxes skeletal muscle and potentiates Non depolarizing neuro-
muscular blocking agents.
RENAL:
 Reduces renal blood flow, glomerular filtration rate and urinary
output.
HEPATIC:
 hepatitis by repeated administration.
• Malignant hyperthermia in swine reported,
• Exposure during pregnancy cautioned.
• Stable in contact with soda lime and thus may be used in closed
circuits.

17.  Non flammable volatile with a pungent
smell.
 Rapid and smooth induction , recovery &depth of
anesthesia can be altered easily and rapidly.
 Approved for use in dogs and horses
 MAC = 1.3% to 1.63%: helps determine
initial vaporizer setting.
 Stable at room temperature; no
preservatives needed.

18. Isoflurane:-
 Lungs: mostly exhaled as such
 Heart: lesser effects, does not sensitizes,
 Liver and Kidney: not injurious.
 Undesirable effects
 severe respiratory depression (good bronchodilator) than
does halothane
 less depression of the cardiovascular system.
 Its pungent odor has been reported to cause breath-
holding

19. CEREBRAL:
If con> 1 MAC causes increase in CSF and
Intracranial pressure.
NEUROMUSCULAR:
Relaxes skeletal muscles.
RENAL:
Decreases renal blood flow , glomerular
filtration rate and urinary output.
HEAPTIC:
Reduces hepatic blood flow.

20. CLINICAL USE:
-Fast smooth induction and recovery in
all species
DOSAGE
- Induction: 2.5 to 4.5% facilitated by
use of intravenous anaesthesia.
-Maintainance: 1 to 3%

21.  No such contraindication.
 Patient with severe hypovolemia
may not tolerate its vasodilating
effects.

22. • Sweet-smelling, Nonflammable,
nonirritating,
• used for induction and maintenance of
general anesthesia.
• Rapid and smooth induction &
recovery
 MAC of aprox. 2.4%
 It is Non pungency
 High controllability of depth of
anesthesia

23. • Unstable when exposed to soda lime and toxic metabolites are
formed (renal toxicity)
Increases plasma and urinary fluoride ions (renal and hepatic
injury)
• Metabolized (3%) more than desflurane, (<1%).
• Being tried in Avian and exotic species
• The lower blood solubility of sevoflurane compared with
isoflurane results in more rapid inductions and recoveries.

24. CARDIOVASCULAR SYSTEM:
-Mildly depresses myocardial contractility.
RESPIRATORY SYSTEM:
-Depresses respiratory rate.

25. CEREBRAL:
 Increases CSF and intra-cranial pressure.
RENAL SYSTEM:
 Slightly decreases renal blood flow. Higher Conc
Causes Nephro-toxicity
HEPATIC:
 Decreases portal vein blood flow but increases
hepatic artery blood flow thus maintaining total
hepatic blood flow.
NEUROMUSCULAR:
 Adequate muscle relaxation.

26.  Severe hypo-volemia.
 Intracranial hypertension.
 Malignant hyperthermia

27.  Closely related to isoflurane
Clear, nonflammable liquid, Pungent odor
 Expensive
 Used with a special heated electronic precision
vaporizer
 MAC = 7.2% and 9.8%
◦ Least soluble potent inhalant agent
 Eliminated by the lungs - 0.02% metabolized in liver

28.  Strong vapors cause coughing and holding the breath=
difficult to mask
 Other effects are similar to isoflurane
 Produces carbon monoxide with spent soda lime.
 Increases intracranial pressure (↑ICP)
 Recovery is twice rapid as isoflurane

29.  low potency
 its pungency and its high cost.
 It may cause tachycardia
 airway irritability when administered at concentrations greater
than 1 MAC
 Should not be used in patients with aortic valve stenosis
 May cause coughing and excitation during induction.
 Desflurane is rapidly eliminated
 awakening is therefore faster than with other inhaled agents.

30. Clinical considerations of selecting an inhalation
agent
• Metabolism % of anesthetic recovered as metabolites
Methoxyflurane up to 50%-70% is metabolized by
the liver and kidneys
Halothane up to 20-25% is metabolized
by the liver and kidneys
Sevoflurane 3.0 % is metabolized by the
liver and the kidneys
Isoflurane 0.17% is metabolized by the
liver and the kidneys
Nitrous oxide 0.004

31. Cardiopulmonary consideration
• Myocardial depression:
Halothane > or = methoxyflurane > isoflurane = sevoflurane =
desflurane > N2O
• Reduction in cardiac output:
Halothane > or = methoxyflurane > isoflurane = sevoflurane =
desflurane > N2O
• Respiratory depression:
Isoflurane = sevoflurane = desflurane > methoxyflurane >
halothane > N2O

32. - For a patient with hepatic dysfunction, the choice of inhalation
anesthetic is isoflurane, sevoflurane or desflurane - less liver
metabolism.
Isoflurane is generally considered the most widely used inhalation
anesthetic in veterinary medicine - replaced halothane.

33.  Veterinary anaesthesia and analgesia 4th edition by
Lumb and Jones.
 Hall & Clark.
Withdrawal of anesthetic agents and
administration of 100% oxygen lightens anesthesia
with recovery.
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