Small Animal GA Flashcards
what stage of GA do you want to maintain
stage 3; surgical anesthesia
phase 1 of GA; period, what can the patient still do, end goal, purpose of ET tube, ideal scenario
- 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
phase 2; type of phase, what happens, ideal scenario
- 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
what is phase 2 more common with? (4)
- Barbiturates
- Mask and chamber induction
- Inadequate dose of administration of induction agents
- Poorly sedated patients (Premedication decreases incidence and duration)
phase 3; stage of anesthesia, patient, appearance, levels
- 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
phase 4; what does it mean if pt is in this phase, signs, when its increased, ideal scenario
- 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
purpose vs reality of fasting in small animals
- 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
what type of process is regurg/reflux
▪ 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)
what can regurg/reflux lead to
- Aspiration pneumonia
- Ulcerative esophagitis and stricture formation (1 in 1000)
- Nasal and pharyngeal irritation
how long to fast animals and exceptions
- In healthy patients 4-6 hours
- Exceptions
1. Neonates and diabetic patients
(shorter fasting)
2. Brachycephalic or past history
(longer fasting)
why does preanesthetic condition impact the effects of induction and inhalant anesthetics
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)
preanesthetic conditions requiring stabilization (13)
-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
_____ of the patient is required to reduce chance of arrest or significant morbidity
stabilization
Use of premedication will ______ the dose of induction and
maintenance agents
decrease
induction agents (7)
- Propofol
- Alfaxalone
- Ketamine + Benzodiazepine
- Mask/Tank Inhalant
- Opioid and Benzodiazepine (neuroleptic induction)
* In very critical cases, ASA 4-5, Will not work in healthy patient - Barbiturates - not as common now
- Etomidate and Telazol = not available in Canada
propofol advantages (7)
- 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
what patients can propofol be used in
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
disadvantages of propofol (7)
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
alfaxalone advantages (6)
- 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
alfax uses
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
disadvantages of alfax
- 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)
most common induction agent
benzos …. but opioid, lidocaine or ketamine can also be used
goal of co-induction agents
- Goal is to reduce dose and volume of and potentially the negative
cardiorespiratory effects - Co-induction does smooth the induction process allowing ET intubation
ketamine/benzo advantages
- 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
advantages of mask/tank (4)
- 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
disadvantages of mask/tank (10)
- 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
neuroleptic induction; combo, safety, who wont it work in, environment
- 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
advtanges of barbituates (thiopental) (2)
-cheap
-short onset
disadvtanges of barbituates (thiopental) (7)
- 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
4 steps in the induction process
- Assess Sedation level; IV access; Equipment prepared
- Assess cardiorespiratory status (HR, MM colour, RR, monitors, pre-oxygenate)
- 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) - Intubate, perform ET cuff inflation, transfer to inhalant/maintenance anesthesia and permit positioning
appropriate signs of intubation (7)
- 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
how do you know you are in the right hole when intubation? (6)
- 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
advantages of inhalants (7)
- 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
disadvantages of inhalants (6)
- 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
what does iso/sevo MAC level decrease with (5)
o Pre-medication, intravenous agents, analgesics
o Age: lower in geriatric and neonates
o Hypothermia
o Pregnancy
o Concurrent illness
criteria for extubation for dogs
- 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
criteria for extubation for cats
- 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
