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This gas is not often used in veterinary medicine and cannot be used alone due to its very high minimum alveolar concentration.
This gas anesthetic is no longer used due to irritation to mucous membranes and its explosive nature.
These anesthetic gases are collectively known as halogenated compounds:
- "DISH EM"
- Isoflurane (Aerrane-h,)
- Methoxyflurane (Metofane)
This value is the ability of a volatile liquid in a gas form to be absorbed by the body
Another name for the Solubility Coefficient
A high partition coefficient means:
more uptake in blood and tissues resulting in delay in alveolar concentration
A lower the partition coefficient means:
The gas will reach the nerves faster
List the gas by Partition Coefficients from lowest to highest:
- Nitrous Oxide
- Diethyl ether
What percentage of total cardiac output consumption does the vessel rich tissue group uptake?
Tissues in the vessel rich group:
What percentage of total cardiac output consumption does the muscle rich tissue group uptake?
Tissues in the muscle rich group:
What percentage of the total cardiac output consumption does the vessel poor group uptake?
Tissues in the vessel poor group
the anesthetic concentration required to prevent gross muscular movement in response to painful stimuli in 50% of a tested population
Minimum Alveolar Concentration
General concentration range for surgical anesthesia
1.2 to 1.5 MAC
Which gas anesthetic has the highest MAC (and is therefore considered the weakest gas)?
Nitrous Oxide (188-200% d, 150% c)
Which gas anesthetic has the lowest MAC (and is therefore considered the strongest gas)?
Methoxyflurane (0.23-0.30% d, 0.23% c)
List the gases by MAC values from lowest to highest
- Diethyl ether
- Nitrous Oxide
3 methods of elimination of anesthetic gases from the body
- 1. Lungs
- 2. Other routes
- 3. Biotransformation by the liver
3 factors of uptake and elimination of anesthetic gases from the lungs
- 1. Pulmonary ventilation
- 2. Blood flow
- 3. Partition Coefficient
What form are anesthetic gas in when eliminated by the lungs?
Largely unchanged (not "metabolized")
What other routes are anesthetic gases eliminated in small amounts?
- Mucous membranes
Which enzyme system is responsible for metabolizing anesthetic gases in the liver?
hepatic microsomal enzyme system
What are the toxic intermediate metabolites of gas anesthetic biotransformation?
- Fluoride ions
- Bromide ions
List the liver metabolism of anesthetic gases:
List factors that affect MAC
- Age - older needs less gas
- CNS drugs - depress inhalation
- Concurrent illness
- Temperature - lower temps reduce MAC
Veterinary proprietary name for Methoxyflurane
Human proprietary name for Methoxyflurane
Why is Methoxyflurane no longer used today?
No longer available in the US
What was the only system that methoxyflurane could be used?
Vaporizer In Circuit (VIC)
Vaporizer Outside the Circuit
Another name for VIC system
Another name for VOC
Proprietary names for Halothane
- Halothane - Abbot Laboratories
Halothane approved species
Gas anesthetics that can trigger Malignant Hyperthermia
Which gas reduces tear production in horses by 60%
What is the common effect of all gas anesthetics that prevents their use in head trauma patients
They increase the cerebral blood flow and intracranial pressure
This was the first of the "Fast Induction-Fast Recovery" Halogenated compound
Human proprietary names for Isoflurane
Veterinary Proprietary Names (MFR) of Isoflurane
- IsoFlo (Abbot)
- Iso-Thesia (Vetus Animal Health)
List the common anesthetic gases in order of induction/recovery rate, quickest first:
Human proprietary name for sevoflurane
Veterinary proprietary name (MFR) for sevoflurane
SevoFlo (Abbot Laboratories)
Approved species for Sevoflurane
What has been reported when sevoflurane is used with a desiccated CO2 absorbent?
Excessive heat in the respiratory circuit
List the 4 main precautions when using Halogenated gas anesthetics
- 1. Avoid use in head trauma/brain tumor cases due to increase cerebral flow and intracranial pressure
- 2. Avoid use in patients susceptible to Malignant Edema
- 3. Must be monitored closely
- 4. Avoid exposure to pregnant staff members
Proprietary name for Desflurane
What compound is substituted by fluorine in Desflurane gas?
Why is desflurane not commonly used in veterinary medicine?
- 1. very pungent
- 2. requires electrically heated vaporizer
Proprietary name for Enflurane
Despite it being very stable, why is enflurane not used often in veterinary medicine?
What would a concentration of 50% nitrous oxide do when combined with other anesthetic gases?
It lowers the MAC of the other anesthetic gases which can be considered when finances are tight.
Advantages of Modern Inhalation Gases:
- 1. Can alter anesthetic depth quickly
- 2. Always good muscle relaxation
- 3. Rapid induction/recovery
- 4. Elimination primarily by lungs
Disadvantages of Modern Inhalation Gases:
- 1. Complex equipment needed
- 2. Always some level of cardio-respiratory depression
- 3. Gases exposure to personnel
- 4. Expensive
3 disadvantages of sevoflurane vs. isoflurane
- 1. Can produce an increase in serum inorganic fluoride ion concentration
- 2. Can increase post-surgical BUN and creatinine values = nephrotoxicity
- 3. Can produce excessive heat when used with a desiccated CO2 absorbent
4 methods of induction
- Inhalant Gas
Ketamine hydrochloride dosage
0.1mL/lb (canine) but not more than 4mL/animal
Acetylpromazine maleate dosage when used with Propofol
0.05 - 0.20 mg/lb
4 main differences between IV and IM induction:
- 1. IM cannot be given to effect
- 2. IM dose is 2-3 times IV dose
- 3. IM takes longer to reach the brain
- 4. IM increases recovery time due to increased induction time
Manufactures of Ketamine Hydrochloride
- Ketaset/Vetalar - Pfizer
- Ketalar - Abbot Laboratories
- Keta-thesia - Vetus Animal Health
- Vetamine - generic
- Ketaject - human product
Veterinary Ketamine dosage strength
Human Ketamine strength
Approved species for Ketamine
Ketamine method of action
inhibits GABA receptors
Which reflexes do not abolish when Ketamine HCL is used alone?
Why must an anticholinergic be used with Ketamine HCL?
Ketamine causes hypersalivation
Uses of Glycopyrrolate
- 1. antisialagoue
- 2. prevent/treat bradycardia due to vagal reflexes
- 3. treat diarrhea/bladder spasms
- 4. antidote for organophosphate poisoning
Oral route for Induction
Not generally an option for basal anesthetic but can be sprayed into the mouth of a fractious animal
Two drugs that can be used orally to produce a level of consciousness in a fractious animal to be approached for proper induction of anesthesia:
Manufacturers of fentanyl
- Duragesic - Janssen Pharmaceutica
- gen Fentanyl - Abbott Laboratories
Species approved for fentanyl
no veterinary species
Onset of effect for fentanyl (duragesic) patches
Duration of effect for fentanyl (duragesic) patches
List the 4 strengths of fentanyl (duragesic) patches
25, 50, 70, 100 mcg/hr
For mask induction to be feasible, the inhalant must have what type of partition coefficient?
Why might a mask induction be used?
Critically ill, pediatric or geriatric patients may not be able to tolerate parental methods due to renal/liver insufficiencies
Drawbacks of mask induction
- 1. personnel exposed to waste gases
- 2. fear causes catecholamine release which may predispose patient to cardiac arrythmias and hypotension
- 3. difficult to use mucous membrane, crt and ocular indicators because of mask
- 4. increased oxygen usage
Species in which chamber induction is appropriate
How do you know the chamber is the correct size for the patient?
It is large enough for the patient to lie down with neck extended
According to McKelvey, the anesthetist has two major tasks during surgery:
- 1. Ensure vital signs remain within limits
- 2. Maintain the patient at the appropriate anesthetic depth
List the parameters to be monitored:
- Pulse strength and blood pressure
- Palpebral reflex
- Respiratory rate and depth
- Oxygenation and SpO2
- Oxygen Flow Rate
- Fluid administration
- Mucous membrane and capillary refill time
- Anesthetic gas flow rate
- Heart Rate
What does monitor mean?
How often should vital signs be checked?
This term refers to those parameters that indicate the response of the patients homeostatic mechanisms to anesthesia
This term refers to an involuntary response to a stimulus
What is the purpose of monitoring vital signs and reflexes?
To determine anesthetic depth
Give 5 reasons for a drop in blood pressure:
- General anesthesia
- Pre-anesthesia like acetylpromazine that produces hypotension in blood vessels
- Depth of anesthesia
- Hypovolemia (blood/fluid loss)
- Dehydration (blood/fluid loss)
List the vital signs
- Heart rate and rhythm
- Blood pressure
- Capillary Refill time
- Mucous membrane color
- Respiratory Rate/depth
What percentage does tidal volume decrease under anesthesia?
Which opioids commonly produce panting?
- Fentanyl (Duragesic)
- Hydromorphone (Dilaudid)
Normally expiration takes how long with respect to inspiration?
Twice as long
When is temperature loss the greatest during general anesthesia?
The first 20 minutes
List factors that contribute to temperature loss:
- 1. Wet skin
- 2. No shivering
- 3. Reduce metabolic rate
- 4. Vasodilation due to anesthetics
- 5. Open cavity
List side effects of reduced temperature in an anesthetized patient:
- 1. prolonged recovery
- 2. slow liver enzyme metabolism of the anesthetics
- 3. Bradycardia
- 4. Decreased MAC
- 5. Painful shivering
- 6. Decreased anti-cholinergic effectiveness
- 7. Increased O2 requirement
2 methods to decrease heat loss
- 1. Circulation hot water heating pads
- 2. Forced air warming devices
2 Forced Air Warming devices
- 1. Bair Hugger (Gaymar)
- 2. Hot Dog Warming System (Augustine Biomedical)
List the reflexes monitored
- 1. Jaw Tone (Muscle reflex)
- 2. Pedal
- 3. Palpebral
- 4. Pinnal
- 5. Pupillary Light Reflex
- 6. Corneal Reflex
- 7. Pupil Size (except with anticholinergics)
- 8. Response to surgical stimuli
- 9. Heart and respiratory rate
Palpebral reflex can still be seen at the surgical level when these drugs are used:
- 1. Barbiturates
- 2. Methoxyflurane (Metafane)
When is the Pedal reflex normally lost?
What situation is the Pinnal reflex particularly useful?
Determines when a cat given ketamine HCL anesthetic level (diminishes at the end of Stg 3 p1)
Which reflex is generally the last reflex to abolish and when is it finally absent?
Corneal, stage 3 plane 4
At what rate should the patient be left on oxygen after surgery?
1 minute/hr of surgery
Length of recovery depends on:
- 1. Type of anesthetic used
- 2. Length of anesthesia
- 3. Condition of the patient (hypothermia/organ dysfunction
- 4. Route of administration
List the stages of recovery that should be followed:
- 1. Look for the swallowing reflex to return
- 2. Remove tube (be sure it is uncuffed first)
- 3. Place animal in sternal recumbency
- 4. Leave on maintenance fluids until told otherwise
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