Small Animal General Anesthesia Flashcards
the ideal anesthetic technique does what (3)
- provides analgesia
- produces unconsciousness
- maintains stability of organ systems
what are the stages of general anesthesia + what happens in-between and where do we want to be in this list?
Stage 1: analgesia or induction
** loss of consciousness **
Stage 2: excitement or delirium
** start of automatic breathing **
Stage 3: surgical anesthesia
Stage 4: overdose
** potential circulatory failure **
We want to be in Stage 3
Phase 1 is the period between __________ and ____________.
What are patients like during this phase?
Administration of anesthetic and loss of consciousness (patient can still hear and respond to stimuli but pain threshold increases)
What is the end goal of Phase 1 anesthesia
endotracheal intubation for airway protection, ventilation and maintenance delivery
what is an ideal Phase 1 scenario?
Quick and smooth loss of consciousness and good mm relaxation
what does Phase 2 of anesthesia look like?
patient unconscious but markedly excited: vomiting, pupil dilation, paddling/spastic movement, tachycardia, irregular breathing
we cannot intubate due to struggling and resistance
what is an ideal Phase 2 of anesthesia
ideally we don’t see it
with what situations is Phase 2 anesthesia more common?
- barbiturates for induction
- mask and chamber for induction
- inadequate dose of induction agents used
- poorly sedated (no premed or not enough premed)
what does Stage 3 of anesthesia look like
Patient is unconscious and good muscle relaxation; eyes ventromedially and no nystagmus
what influences the levels of depth in Phase 3 (maintenance/surgery phase)
the level of maintenance anesthetic agent being delivered (ex. dialed concentration of iso)
what are the PLANES of anesthesia and what are they determined by
light, medium, and deep
determined by the level of maintenance anesthetic agent being delivered
what does Phase 4 of anesthesia look like
overdose (too deep); severe hypoventilation or apnea; severe cardiovascular depression; will arrest if not corrected
in what patients are we more likely to see Phase 4
critical ASA 4-5 patients
what are some ways to tell whether your patient is in plane 1 vs 2 vs 3 of surgical/maintenance anesthesia
eyeball position: will be ventromedially for plane 1 and 2 and move centrally for plane 3
palpebral: present in plane 1 and gone in plane 2
pupil dilated in plane 3
breath goes from regular in plane 1 to regular and shallow in plane 2 and jerky in plane 3
why do we fast patients
to decrease the volume of stomach contents to reduce the risk of reflux, regurgitation and aspiration
In reality, is it straightforward that fasting will always reduce the gastric contents and the risk of reflux, regurg and aspiration? why?
no: influenced by many factors such as diet composition, breed and conformation, and other factors (ex. GI motility, medications)
what is the difference between regurgitation and reflux
reflux means that the gastric contents pass the lower esophageal sphincter but do not pass through the upper esophageal sphincter whereas regurgitation means the gastric contents also pass the upper esophageal sphincter to exit through the mouth or nose
why do we see reflux and regurgitation in our patients
many of the drugs we use cause mm relaxation
what is the incidence of GER and what is the incidence of regurgitation
GER: 12-78%
regurgitation: 12% (meaning we only see about 12% of the 78% of cases)
what are some consequences of GER and regurgitation
- aspiration pneumonia
- nasal and pharyngeal irritation
- ulcerative esophagitis and stricture formation
what types of small animals are most prone to strictures
exotics/small mammals and small breeds
T/F long periods of fasting are associated with increased incidence of GER
T
how long should we fast healthy small animal patients and what are the exception?
4-6h
exceptions: neonates and diabetics less (ideally on liquid or soft food); brachycephalics or past history of GER more
what are some pre-anesthetic conditions that require stabilization before anesthesia
- severe dehydration (>5%)
- anemia (PVC < 20%)
- blood loss (>10% blood volume)
- hypoproteinemia (albumin < 20g/L)
- acidosis (pH <7.1)
- hypokalemia. (<2.5 mmol/L)
- hyperkalemia (>6 mmol/L)
name some diseases that require stabilization/correction before anesthesia
- intrathoracic disease
- oliguria/anuria
- congestive heart failure
- severe cardiac arrhythmias
- correct seizures, diabetes, high ICP, hyper/hypo thyroidism, hyper/hypoadrenocorticism
how do we get around the fact that 100% correction of some conditions may not be possible in all patients without anesthesia/surgery
stabilize as much as possible with fluids, electrolytes, medications and continue to evaluate with bloodwork, CRT, HP, BP
important to choose the optimal anesthetic for the patient and monitor
T/F use of premedication will reduce the dose of induction and maintenance agents
T
besides premedication, how else can we decrease the amount of induction and maintenance agents
balance protocols including:
- bolus or CRIs to reduce MAC (lidocaine, benzodiazepine, opioids, ketamine)
- local blocks
what are some induction agents options for small animals
1) propofol
2) ketamine and diazepam
3) alfaxalone
4) tank/mask (BAD)
5) neuroleptic: opioid and benzodiazepine
6) barbiturates
what are some advantages of propofol
- rapid onset and short duration of action
- can give as a CRI to maintain anesthesia
- can give perivascular without irritating tissues
- can titrate to effect
- sedation achieved at low doses
- minimal CVS and respiratory effects in stable patients at clinical doses
- can use to treat seizures; decreases CMRO2
what types of patients can propofol be used safely in
- liver dz
- kidney dz
- neonates
- pregnancy/C-section
- patients with increased ICP or IOP
what are some disadvantages of propofol
- may cause phase 2 excitement: paddling, rigidity, opisthotonus
- potentially negative CV effects (decreased HR, BP, CO)
- reduced ventilation, PaO2 and apnea possible (mitigate by giving low doses and slowly)
- can’t be given IM
- large volumes needed in large animals
- can cause Heinz body formation in cats if given for over 5 days
what is the main advantage of alfaxalone over propofol
can give alfaxalone IM but not propofol
what are similarities between alfaxalone and propofol
ALL
- can give as CRI -> TIVA
- can give perivascular as non-irritant
- decreases CMRO2
- can titrate to effect
- rapid onset and short duration of action
- sedation achieved at low doses
- can give if ICP or IOP high
- can give in pregnant
- safe in neonates <12 weeks
- minimal effects of liver and kidney
- cardio-respiratory effects minimal with clinical doses in stable patients
what are the disadvantages of alfaxalone
the same as propofol!
- potentially negative CV effects (drop in CO, HR, BP)
- apnea, decreased PaO2 and decreased minute ventilation (more common if larger dose given quickly)
- large doses required in larger animals
- can cause phase 2 excitement (tremors, ataxia, opisthotonus, paddling)
what is the purpose of co-induction agents in SA GA
they decrease the amount of propofol/alfaxalone needed which can be important in critical patients -> decrease dose/volume of induction agents and therefore the potential negative CVS and respiratory effects
what are examples of co-induction agents used for small animals
- benzodiazepines
- opioids
- ketamine
- lidocaine
when would we give co-induction agents in small animals
immediately after the initial IV bolus of the primary induction agent
T/F co-induction will smooth the induction process and make ET placement easier
Τ
what is the ratio of ketamine:diazepam when used as a co-induction agent in small animals
1:1
what are some advantages of ketamine/diazepam as a co-induction agent in small animals
- longer action than propofol/alfaxalone
- can titrate to effect
- no apnea
- can use low doses as sedative
- sympathomimetic (increase HR, CO, BP) for up to 10 mins
what are disadvantages of ketamine/benzodiazepines
- the sympathomimetic effects are bad in a patient with tachycardia or heart disease; it can cause tachyarrhythmias
- salivation potential
- can’t use as a CRI due to long duration (will accumulate)
- scheduled drugs
- increases CMRO2 so not good in neuro patients)
T/F a sick patient without remaining sympathetic stores will have myocardial depression and decreased CO from ketamine
T
what are the advantages of mask/chamber induction in SA
- good if no IV access (ex. neonate -> but should still be premedicating IM)
- good in exotics or dangerous wildlife
- quick and smooth induction in birds
- allows for pre-oxygenation and oxygen administration
name some of the disadvantages of mask/chamber induction in SA
- costly to use the anesthetic vapour and machine
- health and safety of staff
- need scavenging system
- causes rough, long phase 2
- no airway support as going through phase 2
- no IV access
- dose rises quickly
- dose-dependent CVS and resp depression
- cannot titrate to effect
what are the considerations with a neuroleptic “induction” in SA
- will not work in a healthy dog
- most CVS safe for a critical dog (ASA 4-5 only)
- give opioid first (fentanyl, hydromorphone, methadone)
- will not allow ET intubation even in a critical cat
- can include lidocaine to suppress cough
- requires a quiet environment
what are considerations with using barbiturates (ex. thiopental) for induction in SA
- causes bigeminal rhythm
- decreased HR, CO and arrhythmias likely
- causes apnea and hypoventilation
- causes tissue sloughing if given perivascular
- excitement possible
- scheduled drug with low availability
what are the 4 steps in the induction process (following pre-medication)
1) assess sedation level; IV access; prep equipment
2) assess cardiorespiratory status (RR, HR, MM); attach monitors if needed; pre-oxygenate if needed
3) give initial bolus of induction agent; based on level of sedation; top-up if needed
4) intubate, inflate cuff, transfer to maintenance anesthetic
what are some signs it is ok to proceed with intubation
- head lowered
- changes in eye position
- loss of lateral palpebral
- relaxed jaw tone and tongue
- no response to handler opening mouth and placing the laryngoscope
how do you know you intubated correctly (you’re in the right hole)
- direct visualization
- condensation at the end of the tube
- rebreathing bag movement
- movement of the chest when you bag the animal
- CO2 wave present in capnograph
- can inflate the cuff successfully
why do we use lidocaine spray more commonly in cats, rabbits and rats
they have a much more sensitive larynx and reactive airway that is prone to spasm
T/F the tongue/tissue in cats/rabbits/rodents is more friable than dogs
T
what is key to anesthesia maintenance
constantly evaluating depth and making dose adjustments to maintain the plane of anesthesia
what are some advantages of inhalant anesthetics for maintenance of anesthesia in small animals
- low metabolism by liver or kidneys
- fast changes in depth
- can deliver with oxygen
- act rapidly and rapid recovery
- less cardiac arrhythmias with iso compared to older inhalants
what is the biggest disadvantage of inhalants
dose-dependent cardiovascular and respiratory depression
what decreases the iso and sevo MAC level
- pre-medication, certain analgesics and agents
- age (very old or very young)
- hypothermia
- pregnancy
- concurrent disease
what monitor should always stay on during recovery
SpO2 -> moving from 100% oxygen to room air
what are some key things to do during recovery
- assess warmth
- assess pain: last dose of analgesia, discuss NSAID
- check airways
- may give a sedative depending on patient
what indicates that dogs are ready for extubation
strong medial palpebral and/or swallow reflex
what is the criteria for extubating brachycephalics
keep tube in until completely awake and head up
be prepared for an obstruction! (sedative, laryngoscope, another tube)
what is the criteria for extubating cat
when medial palpebral present, ear flick, tongue curl, whisker reflex
should be extubating before swallow reflex to prevent laryngospasm
