Transcript redistributed - Dr. Roberta Dev Anand

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
•
•
Stage I
Stages of Anesthesia
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
ANESTHESIA
turn 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
•
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
Inhalant v Injectable
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 windup
•
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
•
duration 30-60 min
•
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
•
ketamine/diazepam
•
one of the most popular agents
•
combined at equal volumes - 1.2mL Ket/1.2ml Val (for
example)
•
onset 30-90 sec
•
duration 5-10 min
•
recovery 30-60
•
minimal cardiac depression
•
good muscle relaxation
•
smooth recovery
•
some analgesia
•
controlled
Ket/Val
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
•
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
•
duration 2-10 min
•
recover in ~10, standing in 15-30 mins
•
appetite stimulant in low doses
Propofol
•
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 premedicated, 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
•
nontoxic
•
minimal adverse effects
•
minimally toxic to environment
•
pleasant smell
•
nonirritating (to MM)
•
rapid/gentle induction/recovery
•
easily manipulate depth of anesthesia
•
good muscle relaxation
•
safe to handle (ie nonflammable)
•
no liver/kidney involvement
•
adequate post-op analgesia
•
affordable
•
potent enough for surgical anesthesia
•
does not require special equipment
Ideal Inhalant
•
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
•
P , BGPC, MAC
V
•
Vapor Pressure
•
measurement of liquid’s ability to turn into gas
•
low PV - use non-precision vaporizer
•
higher P are more readily vaporized, reach
higher concentration faster - require a wellmaintained precision vaporizer
•
one vaporizer is specific to one agent - cannot
mix
V
•
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 muscle relaxation
•
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
depressed
depressed
cardiac
depression
slight
slight
arrhythmia
none
none
blood pressure
depressed
depressed
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
•
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