Induction and Maintenance Flashcards
What two general anaesthesia can be divided into?
- Intravenous
- Inhalational
Why is it important to monitoring?
To understand the nature of the drugs and to try avoid complications from occurring.
What 7 things to consider for an anaesthetic?
- Species & Breed
- Age & Health
- Temperament
- Facilities Available
- Skill of the anaesthetist & surgeon
- Post op considerations
- Duration of operation
- Nature of operation.
When is injectable anaesthetic agents used ?
- Induction of anaesthesia
- Supplement to inhalation anaesthesia when additional rapid control is required.
- Sole anaesthetic agent for short periods
Adv of using injectable anaesthesia?
- Simple technique
- Minimal apparatus required/needed.
- Rapid onset of anaesthesia
- Non-irritant to the airways.
- No explosion or pollution hazards
- Rapid deepening if required.
Disadv of using injectable anaesthesia?
- Superficial veins may be difficult to locate
- Struggle during administration
- Once administered, it cannot be withdrawn.
- Possible apnoea on injection.
- Unsuitable for major surgery.
- Agents may be cumulative
- Agents may be irritant if given perivascularly.
What to consider when administering IV catheter?
- Good restraint and technique
- Rapid response
- Useful in emergency situations
- May be the only route
What to consider when administering IM injection?
- Certain drugs may not be absorbed.
- 3 times that of an IV dose is required.
Why are IV agents administered directly into the vein?
To pass rapidly to the brain as it has a very rich blood supply.
What happens when concentration of drug is high?
If high enough, there is a loss of consciousness and the drug then travels to other organs.
Most injectable anaesthetic drugs are metabolised by the liver, true or false?
True
What is the process of metabolising drugs?
- Converts lipids into water soluble molecules.
- Excreted easily in Bile
- Exit the body via urine and faeces.
Name 3 Barbiturates drugs?
- Thiopentone Sodium (Thio)
- Methohexitone Sodium (Breital)
- Pentobarbitone Sodium (Pentojet, Saggital).
Why are Barbiturates rarely used?
- Cumulative so top-ups result in prolonged recovery.
- Tremors and shaking on recovery.
Readily absorbed into fat - recycling of drugs occurs. - Highly alkaline - skin sloughing if given perivascular
What clinical uses involve Barbiturates drugs?
- involve seizure control (Phenobarbitone)
- Euthanasia (Pentobarbitone)
What is Alphaxalone/Alphadolone (Saffan)?
These 2 steriods are insoluble in water & are dissolved in the solvent cremephor EL
What does Alphaxalone cause?
Causes histamine release in dogs which causes severe hypotension, this agent is therefore not safe to use with dogs.
What is Alphaxalone solvent responsible for?
- Causing the mild anaphylactic reactions seen in cats which are usually not problematic unless laryngeal/pulmonary oedema occurs.
Name 7 properties of Alfaxan.
- Admin IV or deep IM
- Common in premeds
- Can be used in Dogs
- Wide safety margin
- Good muscle relaxation
- Must be discarded at the end of the day, once used.
Name 5 properties of Propofol.
- Milky, white water soluble phenol.
- Good bacteria media
- Toxic in cats!
- Reduce pain on IV inj
- Open Ampoules/bottles must be discarded after 24hrs.
What 4-5 properties of Phenol Anaesthetic?
- Short acting & rapid duration, only 2-3 mins
- Causes dose dependant CV depression and apnoea!
What is the most important thing not to do while giving phenol anaesthetic?
DO NOT ADMINISTER AS A RAPID BOLUS!!!!!
What is Phenol Anaesthetic good for?
- Animals are conscious 30 mins after a single IV injection - so good for C- SECTION
What are the properties of Ketamine?
- This agent induces a state of almost total analgesia combined with superficial sleep.
- Can be used in reptiles & birds on its own to produce sedation.
What occurs in dog & cats when using ketamine?
It will produce muscle rigidity making surgery impossible.
What can be combined, when using Ketamine?
Combined with Domitor or Benzodiazepines to relax muscles.
How can Ketamine be administered?
- Give either IV or IM route - some transmucosal absorption.
- Slow acting.
What are the adv for injectable anaesthesia?
- Provides rapid onset and good conditions for intubation.
How can anaesthesia be maintained?
- Can be achieved by top up doses or IV fluids.
What considerations be in place before administering agent?
Depends on patient consideration, the procedure performed, equipment available & cost.
What 2 rapid metabolised agents used?
- Alfaxan
- Propofol
What 2 Slow metabolised agents used?
- Pentojet
- Ketamine
What are inhalational Agents?
These agents can be used to induce anaesthesia, but are generally used to maintain anaesthesia.
Name a gaseous agent.
NO2 - Nitrous Oxide
Name 3 Volatile Agents?
- Halothane
- Isoflurane
- Sevoflurane
What are Chamber anaesthesia?
A closed space that can be filled rapidly with volatile agent, to ensure a smooth induction.
What species if Chamber anaesthesia used in?
“Small Furries”
How should a Chamber anaesthesia be filled?
Should be filled from the bottom.
How long is induction using a chamber anaesthesia?
Induction is generally complete in 2-3 minutes.
What consideration is in place when using Chamber induction?
- Recovery is rapid, therefore for longer procedures anaesthesia may need to be maintained via a face mask.
Why is it risky using a chamber to induce?
Health and safety risks are greatly increased with the use of either mask or chamber induction.
What is the main adv to use inhalational agents?
That the animal is intubated enabling a protecting airway.
What are the Pharmacokinetics of inhalational agents?
- Gases pass into the lungs
- Then diffuses into the pulmonary circulation.
- Then travels around the body & is distributed to the tissues.
- Then diffuses back into the blood stream and be eliminated from the lungs.
What gases carry the volatile agents into the lungs?
- Oxygen
- Nitrous Oxide
- Carbon dioxide
What 3 properties of Oxygen are there?
- Supplied in black cylinders with a white neck..
- Heavier than air and strongly supports combustion
- Colourless and Odourless.
What 3 properties of Carbon Dioxide are there?
- Supplied in Grey cylinders.
- Not commonly used
- But useful to stimulate respiration.
What 4 properties of Nitrous Oxide are there?
- Supplied in Blue cylinders
- Weak anaesthetic, but potent analgesic
- Delivered at 50:50 or 2:1 with Oxygen.
- 2nd Gas effect - enhances effect of both gas and volatile agent.
What are volatile agents ?
Describes the liquid anaesthetics that are vaporised into gases, the inhalation of which produces anaesthesia.
What is required when using volatile agents? (equipment)
A vaporiser is a device that adds volatile agent to a carrier gas at a specific temperature.
Name two properties of Halothane?
- Catecholamine sensitive
- Malignant Hyperthermia
Name 2 properties of Isoflurane?
- Smells, so breath holding common.
- Resp depression, hypotensive, arrhythmia.
Name 2 properties of Sevoflurane.
- Only licensed in Dogs, non-irritant.
- Resp depressant and hypotensive.
Name a properties of Desflurane.
Human use only
What does MAC stand for?
Minimum Alveolar Concentration
What is MAC?
This is the lowest concentration that produces no response in 50% of the patients exposed to painful stimuli.
What is the “Calculations” of MAC?
1 X MAC = Light Anaesthesia
1.5 X MAC = Surgical Anaesthesia
2 x MAC = Deep Anaesthesia
What is BGS (Blood)?
Blood Gas Solubility?
Why is BGS measured?
Is a measure of the distribution of the inhalational agent between the blood and gas phases within the body.
What does it mean having a low solubility ?
An agent with low solubility tends to remain in the gas phase in the alveoli/blood - it is carried more readily to the brain resulting in a rapid induction.
What does low solubility mean?
Low solubility = rapid induction/recovery.
What are the MAC/BGS of volatile agents?
Halothane = MAC 0.87 BGS 2.5 Isoflurane = MAC 1.2 BGS 1.5 Sevoflurane = MAC 2.3 BGS 0.63
Name 4 properties of Inhalational Anaesthetics (summary)?
- Inhalational anaesthesia requires more equipment than injectable.
- Recoveries tent to be faster after prolonged procedures.
- A provision of oxygen is present - IPPV if needed.
- Isoflurane is the most widely used agent.
