Small Animal GA

Question 1

what stage of GA do you want to maintain

Answer 1

stage 3; surgical anesthesia

Question 2

phase 1 of GA; period, what can the patient still do, end goal, purpose of ET tube, ideal scenario

Answer 2

• This is the period between the initial administration of the anesthetic and the loss of consciousness.
• The patient can still hear and respond to stimuli but pain threshold increases (Analgesia without amnesia)
• End goal at the end of this phase is endotracheal intubation once appropriate signs achieved
• ET tube for airway protection, ventilation and maintenance delivery
• Ideal scenario: Quick and smooth loss of consciousness, good muscle relaxation

Question 2

phase 2; type of phase, what happens, ideal scenario

Answer 2

• Excitement Phase (Potential Phase)
• Loss of consciousness but marked excitement occurs
• Rough induction, resistance, unable to intubate
• Additional induction agents needed
• Vomiting, dilated pupil, tachycardia, irregular respiration, spastic movements may be seen
• Ideal scenario: This phase is not seen

Question 2

what is phase 2 more common with? (4)

Answer 2

• Barbiturates
• Mask and chamber induction
• Inadequate dose of administration of induction agents
• Poorly sedated patients (Premedication decreases incidence and duration)

Question 3

phase 3; stage of anesthesia, patient, appearance, levels

Answer 3

• Maintenance or Surgical Anesthesia
• Patient is unconscious with good muscle relaxation present
• Eyes in ventromedial position and no nystagmus (in SA)
• Levels of depth based on level of the maintenance anesthetic agent being delivered for the surgical or diagnostic need; Light, Medium, Deep

Question 4

phase 4; what does it mean if pt is in this phase, signs, when its increased, ideal scenario

Answer 4

• Overdose = too Deep
• Severe hypoventilation or apnea
• Significant cardiovascular depression
• Progresses to arrest if not corrected
• Greater potential in critical ASA 4-5 patients

Ideal scenario: avoid this stage with proper monitoring and patient stabilization

Question 5

purpose vs reality of fasting in small animals

Answer 5

• Objective: Reduce the volume of stomach contents, which would, in turn, reduce the risk of reflux, regurgitation, and aspiration.
• Reality:
• Duration of fasting does not consistently affect the volume of stomach contents
• Gastric emptying is affected by the specific composition of food ingested
• Dry food takes longer digest than canned food, which takes longer than liquids
• Breed and conformation, medications, and many other factors also influence gastric emptying

Question 6

what type of process is regurg/reflux

Answer 6

▪ Passive process: gastric content moves up the esophagus and passes the upper esophageal sphincter (LES) to exit through mouth or nose (Do not confuse with GER)

Question 7

what can regurg/reflux lead to

Answer 7

• Aspiration pneumonia
• Ulcerative esophagitis and stricture formation (1 in 1000)
• Nasal and pharyngeal irritation

Question 8

how long to fast animals and exceptions

Answer 8

• In healthy patients 4-6 hours
• Exceptions
  1. Neonates and diabetic patients
  (shorter fasting)
  2. Brachycephalic or past history
  (longer fasting)

Question 9

why does preanesthetic condition impact the effects of induction and inhalant anesthetics

Answer 9

o There is NO safe anesthetic
o All have a level of negative Cardiovascular or Respiratory effects
o Pharmacology trials done in research animals (Healthy)

Question 10

preanesthetic conditions requiring stabilization (13)

Answer 10

-Significant dehydration (>5%)
-Blood loss > 10% blood volume
-Anemia (PCV<20%)
-Hypoproteinemia (Albumin< 20g/L)
-Severe Acidemia (pH < 7.1)
-Hypokalemia (< 2.5 mmol/L)
-Hyperkalemia (>6 mmol/L)
-Significant intrathoracic disease (Pneumothorax, pleural effusion, chylothorax…)
-Oliguria, anuria investigate cause
-Congestive heart failure
-Severe cardiac arrhythmias
-Control: Seizures, High ICP, Diabetes, Hyper/Hypothyroidism,
hyper/hypoadrenocorticism

Question 11

_____ of the patient is required to reduce chance of arrest or significant morbidity

Answer 11

stabilization

Question 12

Use of premedication will ______ the dose of induction and
maintenance agents

Answer 12

decrease

Question 13

induction agents (7)

Answer 13

1. Propofol
2. Alfaxalone
3. Ketamine + Benzodiazepine
4. Mask/Tank Inhalant
5. Opioid and Benzodiazepine (neuroleptic induction)
   * In very critical cases, ASA 4-5, Will not work in healthy patient
6. Barbiturates - not as common now
7. Etomidate and Telazol = not available in Canada

Question 14

propofol advantages (7)

Answer 14

• Sedation achieved at low doses
• Rapid onset and short duration
• Titration to effect allows for smooth inductions
• Decreases CMRO2 and can be used to treat seizures
• Can be given as constant rate infusion (CRI) – TIVA ; To maintain general anesthesia (good recoveries)
• Non-irritant if injected perivascular
• Cardio-respiratory effects minimal with clinical doses in stabilized patients; Side effects can be minimized by titration and slow administration

Question 15

what patients can propofol be used in

Answer 15

o Liver disease patients (Extra-hepatic metabolism)
o Neonates
o Renal disease patients
o Pregnancy and C-section
o Patients with increased ICP or IOP

Question 16

disadvantages of propofol (7)

Answer 16

Potential negative CV effects of lowered BP, HR and cardiac output
- Dangerous in critical patients with ongoing cardiovascular instability

Apnea, reduced minute ventilation and PaO2
- More common: high doses and rapid administration
- More dangerous: when oxygen not available

Paddling, rigidity and opisthotonus can be seen with induction
- Cholinergic effect (do not confuse with excitement or seizure)
- Usually self limiting and low incidence (1.2-9%)

Heinz body formation with repeated daily use in cats
- More than 5 consecutive days

Cannot be given IM (pain at injection and poor absorption

Large volumes required in larger animals

Have to discard/waste unused volumes after 12 hours
- New formulations up to 28 days

Question 17

alfaxalone advantages (6)

Answer 17

• Sedation achieved at low doses
• Rapid onset and short duration
• Titration to effect allows for smooth inductions
• Decreases CMRO2 and can be used when ICP is high
• Can be given as constant rate infusion (CRI) – TIVA ; To maintain general anesthesia Non-irritant if injected perivascular
• Cardio-respiratory effects minimal with clinical doses in stabilized patients; Side effects can be minimized by titration and slow administration

Question 18

alfax uses

Answer 18

o Minimal effects on liver and kidney
o Safe in dogs and cats <12 weeks
o Pregnancy and C-section
o Patients with increased ICP or IOP

Question 19

disadvantages of alfax

Answer 19

• Potential negative CV effects of lowered BP, HR and cardiac output
• Dangerous in critical patients with ongoing cardiovascular instability
• Apnea, reduced minute ventilation and PaO2
• More common: high doses and rapid administration
• More dangerous: when oxygen not available
• Tremors, ataxia, opisthotonus-like posture and transient paddling can be seen at recovery in both dogs and cats
• Large volumes required in larger animals (especially for IM)

Question 20

most common induction agent

Answer 20

benzos …. but opioid, lidocaine or ketamine can also be used

Question 21

goal of co-induction agents

Answer 21

• Goal is to reduce dose and volume of and potentially the negative
  cardiorespiratory effects
• Co-induction does smooth the induction process allowing ET intubation

Question 21

ketamine/benzo advantages

Answer 21

• Titration to effect is possible
• Longer action than propofol or alfaxalone
• Low doses can be used for sedative effect
• No apnea
• Sympathomimetic effects of ketamine
  o Which maintains or increases HR, BP and CO. An advantage in healthy animals as pre-medicant agents and inhalants will lower these parameters
• Possible increase in HR may not be ideal in cases already
  tachycardic or with certain cardiac diseases
• Tachyarrhythmia potential
• Salivation potential
• Increases CMRO2 (Not ideal induction agent if brain disease)
• A sick patient without remaining sympathetic stores will have myocardial depression and reduced CO from the ketamine
• Both Ketamine and benzos are scheduled drugs
• Can not be used to maintain anesthesia for long periods

Question 22

advantages of mask/tank (4)

Answer 22

- Allows for pre-oxygenation and oxygen administration - Option is IV access is not possible - Safer for personnel when dealing with wildlife - Quick and smoother induction in birds

Question 23

disadvantages of mask/tank (10)

Answer 23

* Dose rises quickly * Titration to effect NOT possible * Stressful and with long excitement phase * No IV access * No airway support or protection as go through excitement phase * Require the use of costly anesthetic machine, vaporizer, breathing system * Must have equipment knowledge to be able to use safely * Health and Safety of Staff * Scavenging required to prevent pollution * Dose dependent cardiovascular and respiratory depression

Question 24

neuroleptic induction; combo, safety, who wont it work in, environment

Answer 24

* Opioid/Benzodiazepine Combinations to enable ET intubation * Most cardiovascular safe option in compromised Dog * ASA category 4-5 population * Will not work in healthy dog * Does not allow for ET intubation even in critical cats * IV dose of hydromorphone, methadone or fentanyl followed immediately by midazolam or diazepam * Lidocaine IV can be included to supress cough * Quiet environment needed since animal is not unconscious

Question 25

advtanges of barbituates (thiopental) (2)

Answer 25

-cheap -short onset

Question 26

disadvtanges of barbituates (thiopental) (7)

Answer 26

* Negative CV effects: reduced BP, CO, arrhythmias likely * Bigeminal rhythm (normal complex, then VPC) * Apnea, hypoventilation * Excitement on induction possible * Irritating if given perivascular = tissue slough * Scheduled, currently low availability * Prolonged recovery if repeated doses in sight hounds or fat patients

Question 27

4 steps in the induction process

Answer 27

1. Assess Sedation level; IV access; Equipment prepared 2. Assess cardiorespiratory status (HR, MM colour, RR, monitors, pre-oxygenate) 3. Initial first “bolus” volume (mls) of induction agent ~Based on sedation level ~Each drug has a dose rangewith general guidelines ~Assess depth level to proceed to ET intubation ~Give appropriate additional incremental IV boluses if needed (titration) 4. Intubate, perform ET cuff inflation, transfer to inhalant/maintenance anesthesia and permit positioning

Question 28

appropriate signs of intubation (7)

Answer 28

* Relaxation & lowering of head * Eye rotation * Loss of lateral palpebral * Relaxed jaw tone * No tongue movement * No response to handler opening mouth * No response to laryngoscope placement

Question 29

how do you know you are in the right hole when intubation? (6)

Answer 29

* Direct visualization * See condensation, or feel breath at end of ET tube * See anesthetic bag movement once attached to circuit * When you ‘bag’ or breathe for animal the chest moves * Presence of CO2 wave in capnograph * Can perform ET cuff inflation... If you cannot get a seal and still hear air leakage – you are in the esophagus not trachea

Question 30

advantages of inhalants (7)

Answer 30

* Added patient safety * Administered with oxygen through endotracheal tube (ET) * May be delivered with mask (but less safe) * Act rapidly and rapid recoveries (no accumulation) * Quick changes of anesthetic depth and recovery * Minimal metabolism by liver or kidneys * Produce less cardiac arrhythmias compared to older inhalants

Question 31

disadvantages of inhalants (6)

Answer 31

* Require the use of costly anesthetic machine, vaporizer, breathing system and ET tubes * Must have equipment knowledge to be able to use safely * Health and Safety of Staff * Scavenging required to prevent pollution * Dose dependent cardiovascular and respiratory depression * Requires careful monitoring

Question 32

what does iso/sevo MAC level decrease with (5)

Answer 32

o Pre-medication, intravenous agents, analgesics o Age: lower in geriatric and neonates o Hypothermia o Pregnancy o Concurrent illness

Question 33

criteria for extubation for dogs

Answer 33

* Dogs: STRONG medial palpebral and/or swallow reflex indicate patient ready to extubate * May also see dogs stretch move legs or head * Return of swallow important if you have seen gastro-esophageal reflux * Brachycephalic dogs have different criteria for extubation!; Keep ET tube until completely awake, head up

Question 34

criteria for extubation for cats

Answer 34

* Extubate when a medial palpebral reflex present * Look also for ear flick, whisker reflex, tongue curl * Extubate earlier than return of swallow reflex, or movement to prevent laryngospasm at recovery