define a “routine surgery”

define a “routine surgery”

• who has had a pet through surgery?

• who has monitored a surgery?

• what are the technician’s roles during surgery?

• don’t prove - improve

Anesthetic Depth• Measured by Stages I-IV

• closely monitor the immediate vitals and the developing trend you have recorded, use your teaching and experience to expect what is likely to happen and PREVENT a situation

• monitor surgical stimulus

• monitor reflexes THROUGHOUT

• ensure strong steady, expected HR

• ensure rhythmic respiration, PPV prn

• ensure average BP

• monitor body temp

• every animal is different

• use your eyes and hands over any machine ever created

Stages of Anesthesia• Stage I

• immediately following administration of a drug

• voluntary movement

• will be disoriented, may U/BM

• panting

• slight increase HR

• decreasing sensitivity to pain

• eyes centrally located, normal pupil size and LR

• normal muscle tone, normal reflexes

• by end of this stage pt is recumbent

• Stage II - excitement/involuntary stage

• involuntary struggle, vocalize, paddle, chew, yawn

• beginning loss of consciousness

• irregular respiration (apnea to pant)

• likely increased HR

• further decreased pain sensitivity

• possible nystagmus, possible dilation, present PLR

• good muscle tone

• exaggerated reflexes

• Stage III - Planes I-IV

• Pl I - light anesthesia - intubate

• RR 12-20, pattern regulating

• HR >90, strong pulse

• eyes central or rotated ventromedially, possible nystagmus, pupils constricted, yes PLR

• good muscle tone

• poor/absent swallow reflex

• lick, palpebral reflex present

• no surgery, yes intubate

• Stage III Pl II - Surgical Anesthesia

• moderate depth

• RR 8-16, more shallow

• decreased HR and BP

• possible surgical response (increased HR RR)

• eyes rotate ventromedially, pupils dilate, sluggish PLR

• muscle relaxation

• no pedal or palpebral reflex

• Stage III Pl III

• deep anesthesia

• significant cardiopulmonary depression

• RR less than 8, may need PPV (Bag) - low tidal volume

• HR 60-90

• low BP, weak pulse

• CRT 1.5-2

• no surgical response

• eyes central, moderate pupil dilation, sluggish/no PLR

• flaccid muscle and jaw tone

• Stage III Pl IV - anesthetic overdose

• very deep

• jerky/rocky respiration, abdominal breathing

• HR <60

• prolonged CRT

• pupils widely dilated, no PLR

• dry eyes

• DANGER

• Stage IV - Dying

• no respiration

• HR <40 (unexpectedly)

• no CRT, no Pulse

• cyanotic

• resuscitate if possible

WHEN IN DOUBT STOP

ANESTHESIAturn off gas or stop/reverse injectables

Anesthetic Induction• induce anesthesia - bring the animal to

the desired plane of unconsciousness.

• may also simply need to maintain anesthesia - keep the patent at the desired plane of unconsciousness

• no anesthetic agent accomplishes every (and only) effect needed - multimodal pain management and balanced anesthesia

Inhalant v Injectable• Inhalant

• adjust depth

• eliminated via lungs (primarily)

• on oxygen, easy PPV

• requires vaporizer setup

• slow induction

• waste gases

• Injectables

• no control over depth (once given)

• eliminated via liver/kidneys

• on room air, must intubate to PPV

• only need syringe and drug

• slow recovery

• possible to inject in wrong area

Injectable Induction

• Most common Injectable Induction agent

• - Ketamine/Valium Combo

• - Propofol

• ALWAYS label syringes when drawn up unless giving immediately.

• ANESTHESIA IS GIVEN TO EFFECT (titrate)

• Ideal injectable

• rapid onset induction and recovery

• nontoxic

• minimal adverse affects to cardiopulmonary system

• rapidly and safely metabolized

• offers adequate analgesia

• offers appropriate muscle relaxation

• available, affordable

• typically induction agents are given IV

• IM doses are usually available, this dose will usually be 3x the calculated IV dose (ketamine, tiletamine, dexmedetomidine)

• how will this affect anesthesia? (speed of induction, speed of recovery, control?)

• CRI induction agents

• oral ketamine

• uptake - speed with which the agent is absorbed into the body and begins taking effect

• IV drugs do this quickest

• IM SQ agents - must be redistributed before affecting CNS

• redistribution - the path a drug takes in the body

• IV drug is given, travels to the vessel rich brain (takes effect) then travels to muscle and fat, liver for metabolism, excreted by kidney (under perfect circumstance)

• as drug is redistributed from brain, pt begins recovering

• cumulative drug effect - drug has not left the the redistribution areas before more drug needs to be carried away from the brain - sighthounds

Injectable Induction Agents

• Barbiturates

• Cyclohexamines - dissociatives

• Neuroleptanalgesics

• Propofol

Pharmacodynamics• Ionization - polar (ionized) or non-polar (nonionized) forms - only non polarized compounds can pass through cell membranes at the brain. when pH is normal (7.4) this happens easily and as expected.

• if acidotic - compounds can diffuse in brain and exaggerate response (may require less dry to anesthetize)

• Protein Binding - compounds are either freely circulating in plasma or bound to proteins. only unbound compounds can enter brain, proteins inhibit

• if hypoproteinemic (TP > 3g/dL) - much more drug is available to enter brain, can easily be fatal

• brain is highly lipid

• Lipid Solubility - tendency of a compound to dissolve in fats/oils. aka partition coefficient

• highly lipid soluble compounds cross into brain easily and are quickly redistributed

• Redistribution

• vessel rich group - brain (CNS) heart liver kidney endocrine system

• VRG - 10% body mass, 75% blood flow

• muscle - 50% mass, 20% bldflw

• fat - 20% mass, 5% bldflw

• compounds go to the brain first, high/low concentration carries compounds away from brain to rest of VRG, onto liver for metabolism and kidney for excretion

• as compound is redistributed away from the brain the pt recovers

• low lipid soluble compounds diffuse way from the VRG and store in muscle and fat longer - this affects the high/low concentration and drugs are not carried away from the brain as quickly (especially if having to redose) - cumulative affect

• ultrashort acting barbiturates - thiopental, methohexital

Barbiturates• used for anesthesia but more for

anticonvulsants and euthanasia

• losing popularity to newer generation anesthetics

• all controlled

• stimulates GABA - inhibitory transmitter to depress CNS/cause loss of consciousness

Barbiturate Classification

• classified on chemical structure, duration of action

• Ultra-Short Acting

• Short Acting

• Intermediate Acting

• Long Acting

• alternate names

• thiobarbiturates - ultra-shorts like thiopental sodium, methohexital

• oxybarbiturates - phenobarbital, pentobarbital, thiomyalal

• pentobarbital - B-Euthanasia D (the pink stuff)

• Ultra-short acting barbiturates

• used for general anesthesia

• rapidly absorbed and redistributed (ultra-short acting)

• onset 30-60 sec

• duration 5-20 min

• recovery depends on pt (sighthounds)

• possible decreased in CO, BP, RR (possible severe), bradycardia, arrhythmia (including PC and bigeminy) coughing, laryngospasm, salivation, tidal, VT

• why is decreased tidal volume dangerous?

• no significant analgesia

• poor muscle relaxation

• must be IV - perivascular sloughing (esp thiopental)

• thiopental can stimulate PNS - can cause sensitivity to epinephrine - if given can cause arrhythmia (VPC, bigeminy, tachy/bradycardia, AV block - caution using in stressed or cadiac pt

• Short Acting Barbiturates (imedazole derivatives)

• etomidate

• guaifenesin

• etomidate - sedative/hypnotic for small animal anesthesia

• not controlled

• minimal change to cardiopulmonary function

• decreases intracranial/intraoccular pressure

• excellent for pt with shock or heart dz

• wider therapeutic range than thiopental and even propofol

• good muscle relaxation

• not common due to price and adverse effects

• no analgesia

• V, muscle movement, excitement during induction/recovery, sneezing, suppresses adrenocortical function (use premeds)

• possible phlebitis on injection though must be given IV

• rapid injection or repeat doses can cause hemolysis

• inj via IV line can help

• Guaifenesin GG (glycerol guaiacolate)

• as an injectable - sedative and muscle relaxer

• used mostly in large animal (combined with other agents for induction/recovery)

• also used (far more in companion animal medicine) as an expectorant (Cough Tabs)

• minimal changes to cardio/resp/gi systems

• irritating to tissues perivascularly

• hemolysis in LA

• Intermediate Acting Barbiturate - pentobarbital

• Pentobarbital sodium

• used in lab animal medicine IP for euth, concentrated for SA euth

• Long Acting Barbiturate

• Phenobarbital - used mostly as anticonvulsant, can be used in sedation

• chloramphenicol can increase effect of phenobarbital

• barbiturates cross the placenta (decreased respiration for fetus on delivery)

• barbiturates enhance neuromuscular block effect of muscle relaxer

• chronic use of barbiturates (phenbarb) increase hepatic activity (can increase resistance and shortening of opioid and other meds metabolized by liver

Cyclohexamines(Dissociatives)

• most common - ketamine

• dissociatives disrupt nerve transmission (inhibit some, stimulate others). n-methyl d-aspartate (NMDA) inhibited to prevent wind-up

• wind-up - exaggerated response to low intensity pain stimulus (worsened post-op pain)

• onset - IV 90 sec, IM 2-4 min, PO 5-10 min

• dogs IV PO, cats IM PO


• recovery 2-6 hr

• great for immobilizing for brief procedures (local blocks, BCM)

• catalepsy - not surgical, awake but no response to surroundings - premed premed premed

• often combined with opioids and tranquilizers (ie telazol)

• VTI - KAG w/ buprenorphine (can cause hyperthermia post-op)

• telazol - tiletamine/zolazepem(diazepam) - lasts 14 days in fridge - can cause hypothermia

• see also ket/val

• oral ketamine - 100 mg/kg (ie fractious cat)

• open eyes, central dilated pupils,possible nystagmus, intact reflexes

• increased HR and BP w/o decrease CO

• arrhythmia

• hypersalivation, V, vocalization, jerking movements/tremors, prolonged recovery

• increase intraoccular and CSF pressures

• superficial analgesia (no visceral analgesia)

• respiratory depression/apneustic breathing (long pause, inhale, short pause, exhale)

• metabolized by liver, excreted by kidneys

• IM burns - no necrosis expected (like thiopental)

• can cause amnesia

• DO NOT USE with seizures

• possible behavior changes for hrs/days afterward

• responsible for tachycardia, vasoconstriction, increased BP

• apneustic breathing pattern

• increased salivation

• increased CSF and intraoccular pressure

• muscle rigidity

• can cause urinary obstruction

Ket/Val• ketamine/diazepam

• one of the most popular agents

• combined at equal volumes - 1.2mL Ket/1.2ml Val (for example)

• onset 30-90 sec


• recovery 30-60

• minimal cardiac depression


• smooth recovery

• some analgesia

• controlled

Tiletamine• reconstituted - 4 days room temp, 14 days refrigerated

• used in variety of species IM SQ IV

• IM only in dogs/cats

• poor visceral analgesia

• pt maintains palpebral, corneal, laryngeal, pedal reflexes

• increased salivation

• long/hard recovery, tremors, seizure, hyperthermia

• hypersensitive post-op

Propofol• ultra-short acting non-barbiturate

• phenolic compound unlike all other anesthetics

• used once to induce, repeatedly prn for maintenance, or CRI

• onset 30-60 sec


• recover in ~10, standing in 15-30 mins

• appetite stimulant in low doses

• lists 30 min recovery in cat - many practices do not use this drug in feline medicine - toxicity

• NOT controlled

• rapid redistribution, not cumulative (still prolonged recovery in sighthounds)

• the slower you give it the less you need to use (can be given too slow)

• wide safety agent- mild sedation to general anesthesia

• decreases intracranial and intraoccular pressure

• provides muscle relaxation

• antiemetic and anticonvulsant

• can be used with valium

• no significant analgesia

• highly protein bound

• severe respiratory distress/ acute apnea especially if given quickly

• bradycardia and decreased contractile strength

• if too slow - excitation, tremors, paddling, nystagmus

• ONLY milky white agent to EVER be given IV (too date)

• must be given IV

• decreases blood pressure (worse if given rapidly) - do not use in hypotensive pt

• possible seizure like activity/reaction - rare

• expires quickly - 6 hrs at room temp - contain soy oil and egg lecithin

• Propofol 28 - benzyl alcohol

• mix all drugs well before use

• can keep expired propofol for use during euthanasia

• cost is often an issue in practice

Morphine• opioid

• onset 15-60 sec

• duration 3-6 hr

• recovery 2-4 hr

• controlled

• typical V w/i 15-20 min

• popular as CRI

• epidural

• metabolized by liver, excreted by kidneys

• post analgesia can be reversed

• possible dysphoria - a feeling of uneasiness and anxiety

• decreased GI motility, vasodilation, hypotension (possible hypertension) significant resp depression, pupil constriction

Fentanyl• opioid

• very popular analgesic

• can be used with valium/midazolam for induction

• onset 1-2 min

• duration 20-30 min (inj)

• profound sedation

• bradycardia, sensitive to sound

• controlled

• reuptake from storage sites, metabolized by liver, excreted by kidneys

• also used in CRI

• available as transdermal patch (last 3-5 days) (clip fur, wipe with water (no alcohol), apply directly to skin, hold to melt adhesive, wrap lightly, label label label)

• our pt is in the hospital, we have done our preA workup, we have pre-medicated, we have induced anesthesia, now what?

Inhalant Anesthesia

- liquid agent is vaporized with O2 an administered via breathing system

• Inhalants - most common are the rapid-action halogenated gases isoflurane/sevoflurane

• used to bring patient all the way under following premeditation and/or injectable induction or used a sole anesthetic

• why would a DVM want to use only an anesthetic gas?

• mask/induction chamber/et tube

Ideal Inhalant• nontoxic

• minimal adverse effects

• minimally toxic to environment

• pleasant smell

• nonirritating (to MM)

• rapid/gentle induction/recovery

• easily manipulate depth of anesthesia


• safe to handle (ie nonflammable)

• no liver/kidney involvement

• adequate post-op analgesia

• affordable

• potent enough for surgical anesthesia

• does not require special equipment

• generic overview

• add liquid agent to vaporizer, turn on vaporizer (in %), O2 flows through vaporizer and to the patient

• gas flows to alveoli, diffuses into blood stream, affects CNS, minimally affects liver and kidneys

• once gas stops, anesthesia stops

• if you have used premeds and it is a short procedure, what is a reason your patient would remain anesthetized (to any extent) after recovering from the gas?

• oxygen

• tanks, color, outlets

• PV, BGPC, MAC

• Vapor Pressure

• measurement of liquid’s ability to turn into gas

• low PV - use non-precision vaporizer

• higher PV are more readily vaporized, reach higher concentration faster - require a well-maintained precision vaporizer

• one vaporizer is specific to one agent - cannot mix

• Blood Gas Partition Coefficient

• agent’s ability to dissolve in blood

• affects speed of induction, recovery and aesthetic depth change

• lower BGPC - faster changes

• higher BGPC - slower changes

MAC• Mean Alveolar Concentration

• percent concentration required to prevent surgical stimulus in 50% of patients - measure of potency

• higher MAC - less potent (more drug needed for sx anes)

• typically - MAC x 1.5 (to attain sx anes)

• Diethyl Ether

• maintains stable CO, HR and rhythm, RR, and BP


• good analgesia

• very irritating to tracheal/bronchial mucosa (causes increased secretions and laryngospasms)

Halogenated Inhalant anesthetics

• used in a wide variety of species

• causes CNS depression

• muscle relaxation

• safe for seizures

• also causes cardiopulmonary depression

• causes hypothermia

• little/no analgesia post-op

• while not considered nephrotoxic, decreased blood pressure can lead to poor renal perfusion (compounded against existing renal disease, chronic use of NSAIDs or gentamicin)

• possible dose related increase in intracranial pressure

• vasodilation and decreased CO (drops BP and tissue perfusion)

• Isoflurane - purple

• PV 240, BGPC 1.46

• Sevoflurane - yellow

• PV 160, BGPC 0.68

• must use well-maintained precision vaporizer, anesthetic depth change with be faster

• CANNOT MIX vaporizers

• can move from iso anesthesia to sevo anesthesia without adverse effect

• dose-dependent hypotension (seen more with sevo)

• primary excretion via lungs

• liver metabolism/kidney excretion iso 0.2%, sevo 2-5%

• Isoflurane

• irritating to MM, pt ma hold breathe or struggle during induction -lube eyes before chamber

• sevo is not as irritating - more ideal for masking down

• Iso is inhalant of choice for cardiac pt

• Sevoflurane

• higher BGPC - able to change anesthetic depth with smaller adjustments

• sevo - desiccated CO2 absorbent and low O2 rates - fire hazard

• change granules regularly, monitor temp of canister, use higher O2 rates as possible

• Compound A - rats - sevo reacts with KOH and NaOH - renal damage

• Doxapram - analeptic agent (stimulates resp center of brain)

• injectable used for respiratory emergencies/caesarian

• can cause hyperventilation, hypertension, arrhythmia

• acupuncture

Isoflurane Sevoflurane

muscle relaxation

good good

analagesia slight slight

resp center depresseddepresse

d

cardiac depression

slight slight

arrhythmia none none

blood pressure

depresseddepresse

d

resp elim 99% 97%

hepatotoxic

no no

nephrotoxic

no rats

• Halothane

• was the most popular, no longer available in US

• similar PV to Iso

• higher BGPC

• more likely to case arrhythmia

• more potent cardiac depressant

• Methoxyflurane

• off the market

• low PV - could use non-precision vaporizer

• higher BGPC - could not mask or use chamber

• 50-75% liver metabolism - organ damage

• Desflurane

• very high PV and low BGPC

• boiling point close to room temp, requires very pricey electronic vaporizer

• “one breathe anesthesia” - faster depth change than sevo

• no arrhythmia

• dose-dependent resp depression

• Enflurane

• too dangerous, never used

• NO2 - Nitrous oxide

• laughing gas

• one of the oldest inhalants

• gas at room temperature

• BLUE tanks, blue flowmeters

• must be combined with another gas to work (ie methoxyflurane)

• does not mix well with newer inhalants

• easily cause hypothermia

• STOP ANESTHESIA when in doubt

• “reversing anesthesia” will not immediately recover the patient

Mask• ensure proper fit - use smallest possible, dead space

• can cause epinephrine release

• very dangerous for respiratory pt

• take all precautions to protect you and the patient

• plastic/rubber

• Harris technique

• airway, aspiration, PPV?

Induction Chamber• when injectable is not available (health, fractious,

exotic, etc)

• lube eyes (if possible)

• set O2 rate, Iso 3-5%, Sevo 4-6%

• when fighting stops and pt relaxes, remove quickly and mask as needed - watch waste gases

• pt safety

• what if no chamber?

• airway, aspiration, PPV, vitals?

Endotracheal Intubation

• how do you tube a pt?

• to deliver oxygen or anesthetic mixture directly to the lungs

• PPV

• sterile?

• maintains open airway - procedures this is important for?

• minimizes aspiration risk - procedures this is important for?

• allows PPV - procedures this is important for?

• when would intubation be counterproductive?

• sizes, ID

• cuff type

• materials

• connections

• larygnoscope

• clean, working, appropriately sized tube

• tie

• tongue gauze

• light

• syringe

• stylet

• lidocaine

• O2

• lube

• PROPER POSITIONING

• Proper Anesthesia

• position/anesthesia

• grasp behind 104 204

• extend neck

• pull tongue straight out

• illuminate

• isolate glottis

• pass tube - HOLD IN PLACE

• start O2/gas - HOLD IN PLACE

• inflate cuff - HOLD IN PLACE

• confirm placement - HOLD IN PLACE

• tie in place

Meow• laryngospasm - glottis forcefully closes during

intubation

• can lead to hypoxia if severe

• 0.1mL lidocaine topical

• always intubate as soon as possible, in as few attempts

• forced intubation can cause tracheal rupture, peumothorax/pneumomediastinum, post-op cough/pain

• check distance marker

• auscult bilateral

• visualize tube in glottis

• watch bag movement (reliable?)

• feel breathe from tube

• palpate neck

• vocalization?

• EC02 shows normal waveform

• leak test machine

• watch position of head and tube and bag always - tape, elbow, weights, towels, etc

• DISCONNECT WHEN MOVING ALWAYS

• small tube, large tube, too deep/shallow

• no cuff, poor cuff, over cuff

• contamination

• infection, poor depth, aspiration, ste contamination, mucus occlusion, respiratory resistance, dead space, tracheal trauma/necrosis, atelectasis, dyspnea, hypoxia, cardiac arrest

• MUST REMOVE TUBE BEFORE PT CHEWS

Documents

define a “routine surgery”