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anesth
4/23
perkowski

anesthetizing the small animal 
patient

slide: extremely cute puppy!!
slide: great dane nose near a mini 
pinscher.

choosing a technique - there are many many drugs to choose 
from. 
tailor things to the individual patient. 
important things:

history
signalment
temperament (aggressive, or calm)
PE findings
type of 
procedure (surgical, radiographs?)
your experience

PREOP EVALUATION AND 
MANAGEMENT
this is critical. you don't want to start doing any 
anesthetizing w/o knowing status of patient. look at history, PE, lab 
tests, and other diagnostics.

history: know presenting complaint, known 
conditions, any meds they are on, and any prior anesthetic history
PE 
findings: weight, body condition - thin or obese? changes how drugs are 
distributed and half life. pay special attention to respiratory, 
cardiovascular and neuro systems. look at respiratory rate, effort. also 
look at GI, musculoskeletal and urogenital system.

auscult chest- can 
you hear breath sounds on both sides? heart ok? any nasal d/c, cough?

cardiovascular system - palpate pulses, do they feel strong, weak, 
thready, or bounding? is HR normal, fast, slow, regular, irregular


tissue perfusion: mm color, character - pink or pale or blue, moist or 
tacky, CRT, general skin condition, temperature of extremities (cold 
indicates poor perfusion), mental status (depression may indicate poor 
brain perfusiON), urine output. basically if skin is inelastic and eyes 
are sunken they are about 7% dehydrated. 

signs of head trauma - 
important. eg, cat HBC. look for abrasions, fractures, etc that might 
interfere with intubation, look for any CNS signs like seizures, other. 
check for cervical instability, paralysis, paresis.

abdominal distension 
- why? fluid? organomegaly? gas? 
slide: diaphragmatic hernia and GDV at 
same time.

musculoskeletal system - thoracic trauma? flail chest? slide: 
dog shot by arrow, which penetrated abdomen and chest. urogenital system 
- palpable bladder? ruptured bladder?

look for all these things.

lab 
tests: ideally, CBC on all patients pre anesthesia to see if there are 
any underlying infections, b/c most anesthetic agents are 
immunosuppressive. a chemscreen is nice, esp for older patients. try to 
get at least a creat on all patients. look at PCV/TS, urine SG and BUN 
(azostick ok) to check hydration.

other - coag profile if animal has 
liver dz or bleeding history, blood gases for dyspneic animals, EKG if 
you feel pulse deficits, other arrhythmia, and rads as needed.

before 
actually anesthetizing any animal, we assign a physical status - 
I - 
normal healthy patient with no systemic dz
II - mild systemic dz - old 
patient, patient that's anemic, just not perfect
III - moderate systemic 
dz - mitral regurg w/exercise intolerance
IV - severe incapacitating dz - 
mitral regurg in heart failure on meds
V - moribund - not expected to 
live 24 hrs

I-V (E) - emergency case - always a bit more critical.

put 
an IV catheter into every patient getting anesthetized. it's foolish to 
give these drugs w/o having IV access b/c if something goes wrong, it 
will be hard to bail them out. most common cause of hypotension is 
inadequate volume - give preop fluids if needed, always give intraop 
fluids.

PREANESTHETIC MEDS:
why? to cause sedation, provide chemical 
restraint. most patients get some kind of premed to relax them so you can 
put in your IV cath. also they get something with analgesic properties.

these meds decrease dose requirements and side effects of other 
anasthetic agents. this is good. 
these meds also smooth out the whole 
anesthetic period. 

ANTICHOLINERGICS:

anticholinergics used commonly 
include atropine and glycopyrrolate. we said these are competitive ACH 
antagonists. used to decrease vagal influence on heart - these are 
muscarinic antagonists. why do you want to decrease vagal influence? some 
manipulations like laryngeal manipulation, or pulling on organs, cause 
increased vagal tone, also some drugs increase vagal tone, and some 
animals have high resting vagal tone. also these drugs decrease 
salivation/airway secretions.

glycopyrrolate doesn't cross the 
blood/brain barrier, atropine does. atropine can cause some excitement. 
also glycopyrrolate lasts longer. atropine is nice b/c more rapid onset 
of action. you'd use it for cardiac arrest situations. 

side effects: 
decreased GI motility - may or may not be important, big deal in horses. 
increases myocardial oxygen consumption by producing tachycardia - don't 
use in patients with underlying cardiac disease. also may increase 
incidence of cardiac arrhythmias.

PHENOTHIAZINES:  most common is 
acepromazine which has antidopaminergic effects on CNS, providing mental 
calming, relaxation. these have slow onset of action. most private 
practice folks use this and expect it to work right away. but if you give 
it im it takes about 20 min or so to get peak effect. lasts 3-6 hrs. long 
duration, slow onset. the phenothiazines do not provide analgesia. note 
also that dose on label is about 10 times the needed dose.

side effects: 
alpha antagonist effects - avoid if volume status or bleeding is a 
concern b/c causes vasodilation - eg, do not give for gunshot wound. if 
you give enough that they stop bleeding, that means you have really made 
it too hypotensive, so do not listen to that argument. good thing is, 
there are minimal respiratory effects. we use it a lot in patients with 
respiratory problems. may potentiate seizures - if patient has idiopathic 
epilepsy, may produce a seizure. but sometimes ace may reduce seizure - 
that is, if you give it with ketamine, seizure is less likely. so it may 
make seizures more or less likely, depending.

BENZODIAZEPINES: most 
often used are diazepam and midazolam. fairly similar. diazepam (valium) 
is lipid soluble so is in propylene glycol solution; midazolam (versed) 
is water soluble - well absorbed IM< unlike valium. but valium is much 
cheaper. so most vets use the valium. we don't usually use it as a premed 
due to absorption problem. also in some patients there is increased 
agiitation instead of calming effect. these drugs work by binding to a 
receptor near the GABA receptor, increasing chloride conduction, 
hyperpolarizing membrane. barbiturates and etomidate and propofol all 
work via this receptor. the benzos also do not provide analgesia


DISSOCIATIVES: ketamine and tiletamine - ketamine used a lot. esp in 
cats. produces catatonic state, cat sits there and lets you do stuff. 
very cardiovascular sparing in patients that can mount a sympathetic 
response - indirect effect due to catecholamine release. causes minimal 
respiratory depression - an apneustic breathing pattern. it provides some 
selective analgesia, not visceral analgesia - it's an NMDA receptor 
antagonist . 

tiletamine is never used alone, is sold in solution with 
zolezepam as Telazol. we don't use it here b/c induction is ok, but 
recovery is rough. sometimes prolonged.

slide: cat that had ketamine - 
seems to be hallucinating. then gets very stiff, muscle rigidity occurs, 
cat has open eyes, just lyig there.

potential side effetcs: direct 
myocardial depression in patients that do not mount catecholamine 
response, increased muscle tone occurs, increased intraocular pressure 
occurs, seizures can occur, and increased intracranial pressure occurs. 
DO NOT use ketamine with head trauma or seizure cases.

OPIOIDS: we have 
a lot of opioids to use...
morphine, oxymorphone, hydromorphone, 
meperidine: all are pure agonists, bind to mu, kappa, and delta 
receptors. 
butorphanol is a mixed agonist antagonist - kappa agonist, mu 
antagonist at higher doses. 
buprenorphine: partial mu agonist

pure 
agonists do all kinds of stuff - best analgesia and sedation, but more 
respiratory depression, bradycaria, vomiting, dysphoria, decreased GI 
motility, incrased sphincter tone - consider this when doing GI 
procedures.

why do we like opioids? we use a lot of them for premeds. 
they cause sedation to help us restrain them and they are analgesic - if 
you make an incision and stimulate primary afferent nociceptor, it then 
stimulates a cord neuron which signals brain. if nociceptor keeps firing, 
spinal neuron increases messages to brain - wind up phenomenon. we want 
to prevent this. so often before surgery we give an analgesic to prevent 
this. 

also they provide some cardiovascular stability - most cause 
vagally mediated bradycardia which we can deal with. 2nd degree AV block 
common, so give with anticholinergic. 

exception - meperidine/demerol 
and morphine - these cause histamine release esp in dogs, resulting in 
vasodilation and hypotension. may get away with using these IM but not 
IV. especially avoid with mast cell tumor patients! 

other patients not 
to use opioids in - brachycephalics, other animals with respiratory 
compromise or upper airway obstruction. patients with head trauma - resp 
depression causes increased CO2 which affects blood flow to brain.
some 
breeds: dobermans, huskies - get very excited from opioids.
cats get 
excited from opioids. also horses.
also some animals will vomit - avoid 
in patients already vomiting.

if you worry about vomiting or excitement 
or resp depressino, can try using mixed agonist antagonist like 
butorphanol or buprenorophine. side effects less severe. still pay close 
attention to ensure respiratory status is maintained. you will also get 
less analgesia as payment for getting less resp depression. butorphanol 
is good for some pain, but not a heavy orthopedic case. buprenorphine 
works well for ortho cases but is hard to reverse with naloxone. used a 
lot in lab animals. 

ALPHA 2 AGONISTS: stimulate presynaptic a2 
receptors in CNS, decreasing NE release and sympathetic outflow. 
peripherally they stimulate postsynaptic a2 receps and increase systemic 
vascular resistance. so first there is an increase in MAP then a drop. 
xylazine, medetomidine are the main ones. also HR drops off quickly after 
administration so avoid with heart problems or sick animals. can also 
cause respiratory depression and vomiting.

private practice vets use 
these b/c they are reversible with yohimbine or atepamezole (note: 
medetomidine is supposed to be a more specific A2 agonist). also, these 
have analgesic and sedative qualities - can spay a cat using ketamine 
xylazine combo.

INDUCTION AGENST: again, select based on condition of 
patient, experience, drug availablity, and procedure to be done.

in 
dogs, we use a lot of thiopental - ultrashort acting barbiturate, 
redistributes quickly to lean body tissue and is cleared by liver. useful 
for rapid sequence induction - peak effect in 30 seconds, then rapid 
redistribution. doesn't provide analgesia! work via gaba receptor.

problems: myocardial depression, may precipitate arrhythmias - not always 
but can. can cause dose dependent resp depression, causes splenic 
engorgement - avoid if doing splenectomy. if it goes perivascular, 
irritates skin or may cause sloughing (5% will cause sloughing). useful 
in patients with increased intracranial pressure - will decrease 
intracranial pressure. in human patients with elevated intracranial 
pressure they give this.

dissociatives: ketamine, telazol: direct 
depression of cardiovascular system, indirect CV sparing via catechol 
release. minimal resp depression. muscle rigidity occurs, seizures - use 
with other drugs to minimize this. maintains corneal and laryngeal 
reflexes adn increase intracranial pressure.

ketamine and valium used to 
induce cats -spray lidocaine on larynx to intubate.

benzodiazepines - 
used in combo with opioid, ketamine, other - calming in combination. 
minimal resp/cardiac effects so good adjunct in sicker patients. good 
muscle relaxer, anticonvulsant.

Propofol- amazing new drug, ultrashort 
acting IV agent, highly lipid soluble, in milky white soybean lecithin 
emulsion. bolus to effect for rapid sequence induction - rapid 
redistribution and clearance by liver and other sites. patient very alert 
on recovery. can use for short outpatient procedures. no analgesia. 
indications: upper airway obstruction/brachycephalic patients, patients 
with hepatic dysfunction because of extrahepatic clearance, short 
procedures/sedations, c-sections - will get into puppy but then leaves 
puppy and goes back to mother - also if puppy is a little sedate, it will 
wake up within 10 minutes, anti-convulsant. 

side effects - significant 
CV depression and vasodilation (venodilation). BP can be worse than with 
anything else. also dose dependent resp depression - so give tiny boluses 
slowly to effect. short duration of action is good usually but can be bad 
at times. may cause myoclonic twitching which may be severe requiring 
aborted procedure. sometimes extensor rigidity/opisthotonos occurs, esp 
in goats. can use it in cats, but some cats do not do as well as dogs - 
cats have many idiosyncracies. also in cats, over a week of repeat doses, 
will see blood problems, heinz bodies, etc. also due to vehicle, may be 
bacterial contamination of an opened vial - you can't save this stuff, if 
you don't use up a vial, you have to throw it away. yeast, staph will 
grow in an IV line after 4-6 hrs (human study)
often use with valium to 
reduce dose, and twitching.

Opioids: useful for induction. not in normal 
patients which will get excited, but in sicker patients will give nice, 
slow, titrated induction. used often with benzos. fentanyl, oxymorphone, 
hydromorphone used most often. these are resp depressants but that is ok 
if you plan to intubate and ventilate. great analgesia

ETOMIDATE: 
ultrashort acting IV agent, minimal CV/resp effects, no analgesia. the 
problem is that some patients will twitch. as a single agent causes 
vomiting. often use oxymorphone/valium then some etomidate. also can 
cause adrenocortical suppression - after induction will suppress 
adrenocortical axis for about 6 hrs - avoid in addisonian patients! a 
problem sometimes - in people in continuous infusions in ICU, mortality 
was higher than in people not on etomidate infusions. giving steroids 
brought mortality rate back down. for bolus, not such a big deal.


Maintenance: 
isoflurane and halothane are best inhalants - duration of 
action not dependent on metabolism. rapidly adjustable depth of anesth. 
can cause CV and resp depression, so if patient isn't tolerating this can 
switch to other fentanyl infusion, propofol infusion.

monitoring: EKG, 
BP, esoph stethescope, pulsoximetry - not measuring o2 tension, measuring 
Hb saturation. remember that. if you are on 100% O2, O2 sat should be 
over 95%. 

postop care - fluids, analgesics. 
----break-------

ok, 
moving on....complications in small animal anesthesia:

we see a lot of 
complications.
what do we do for a patient that comes in as an emergency, 
or has known metabolic disease? history is really important, PE is 
critical in figuring out how to deal with it, assessment of intravascular 
volume is important as is checking for electrolyte abnormalities. 

do 
your PE as previously discussd.
ventricular arrhythmias are common in 
patients presenting as emergencies, esp patients that were hit by car


assessing intravascular volume is important b/c body uses compensatory 
mechanisms like splenic contraction, venoconstriction,a nd increased HR.

to assess - palpate pulses, measure BP, assess tissue perfusion, look at 
PCV/TS as well as urine SG/BUN. note that PCV/TS may be normal with acute 
hemorrhage. 
assessing hydration is important.

CBC, chemscreen - you'd 
like to get them if you can.
PCV/TS, BUN - really try to get at least 
these, also BG.

goals of preop fluid therapy:

PCV > 25% and < 60% and 
TS > 3.5 g/dl and < 8.5 or 9 g/dl
sighthounds will have higher PCV.
if 
solids are low can give colloids
reasonable HR
CRT < 2 sec, moist pink 
mms, palpable periph pulses, MAP > 60 mmHg

electrolyte abnormalities - 
mild ones no big deal, big ones big deal
sodium is tightly regulated and 
changes are rare.
potassium imbalance most common, hyperkalemia causes 
increased resting potential and increases myocardial excitability 
->arrhythmogenic.

preop agents - do you use them in sick patients? 
depends on patient. can't use IM agent in animal with poor perfusion due 
to absorption problems, may not need any restraint if severely depressed. 
all depends.

Cardiovascular instability: why is system unstable? primary 
cardiac disease or secondary to trauma, metabolic disease? 

treat these 
patients differently! choice of agent depends on underlying disease 
process - is there heart failure? arrhythmia? if there is heart failure, 
how bad is it? most patients presenting with CV instability will not 
require premeds, and in fact we usually do not use them in most of these 
patients. if premeds are required, opioids are generally preferred - 
minimal CV depression, good analgesia. we may or may not use an 
anticholinergic - may worry about tachycardia, so it depends on patient 
and how sick they are. these are given only if premed is really needed. 

what about phenothiazines? depends on the problem. if animal was HBC and 
volume depleted, or has big metabolic derangement, no, don't giev it. or 
if patient is in heart failure, don't give - the vasodilation is a 
problem and you can't reverse it. if you are just sedating animal for 
echocardiogram, they may give a small dose of ace plus some butorphanol 
to calm animal enough to get an echo. but if you're going to go to 
surgery and use anesthetic agents, you probably don't want to use any 
acepromazine along with those other drugs.
ketamine, although CV sparing 
in the presence of catecholamines, it also is negative inotrope. for a 
GDV case, you could use ketamine but worry about it. Alan Klide doesn't 
like using ketamine in dogs, so they don't use it here, but other vets 
like it. In dogs, seizure dose is close to therapeutic dose. you can 
induce with ket/val and that's ok, but don't premed with it in a dog. 

alpha2 agonists are definitely contraindicated, no question. REMEMBER 
THAT!

cardiac arrhythmias - you have to determine if they are 
significant- atrial or ventricular? underlying cause? CHF/electrolyte 
imbalance/trauma? frequency - increasing? decreasing? are they multifocal 
(bad) or unifocal? are they associated with decreased CO/perfusion? are 
they close together? 

Induction of patients with CV disease:
use a slow, 
titrated induction.
-opioid + benzo, sometimes with lidocaine to 
desensitize airway and act synergistically with other drugs. if say a 
puppy is having a balloon angioplasty, might add some etomidate to make 
it more rapid sequence induction.

maintaining animals with CV disease- 

inhalants preferred. 
isoflurane preferred - despite greater decrease in 
arterial pressure in normal patients, iso is a vasodilator whereas 
halothane is a myocardial depressant and an arrhythmogenic agent. 

frequently patients do not tolerate inhalants. then you flush with O2 and 
give fentanyl infusion, or boluses of oxymorphone, hydromorphone. maybe 
supplement with benzo. may use etomidate. propofol - m aybe, can cause a 
lot of CV depression.
if there are still problems, try to keep light and 
use NMBA - vecuronium or cis-atracurium are nice to the CV system - but 
you have to ensure adequate analgesia.

intraoperative monitoring of CV 
disease patient:
heart rate and rhythm: EKG, esophageal stethescope

peripheral pulse quality, CRT: BP - direct, indirect.
MM color, 
pulsoximeter (measures O2 sat, requires adequate pulse)

v-tach - tx with 
lidocaine.

if patient gets hypotensive, remember it's due to decrease in 
CO, SVR or volume. figure out what it is. then use a drug to fix it. if 
they are vasodilated, give pressor like phenylephrine, if heart failure 
give inotrope like dobutamine, if really bad maybe epi. 

postop care of 
CV diseased patients: maintain volume! intravascular volume and tissue 
perfusion are important. howver, if they are in heart failure be 
conservative, avoid fluid overload which may cause pulmonary edema. use 
lower fluid rates. if patient has CV instability due to trauma, also make 
sure you use a lot of fluids - add colloids if TS is falling, don't lower 
fluid rate. add packed red cells as needed if PCV falls. also - provide 
adequate analgesia!

trauma myocarditis - maintain perfusion and 
volume!!!!!!! really important.

again - find primary problem. if animal 
has cardiac dz, no premed or opioid. induce with opioid/benzo - avoid 
ketamine which increases HR and O2 consumption of myocardium. avoid 
thiopental, avoid a lot of propofal though a little is ok. maintain on 
inhalants if possible, if not, try opioids. if they come in b/c of 
trauma, again, rarely will you need premeds. induction with opioids, 
benzos. sometimes ketamine is ok, but worry bout direct effect, and maybe 
you can maintain with inhalants. 

what about patients with pulmonary dz? 
two problems. 
lungs full of fluid that can't oxygenate, or airway 
obstruction so can't ventilate. if primary problem is oxygenation tx is 
different from if primary problem is ventilation.

for all respiratory dz 
patients: MINIMIZE STRESS esp if not ventilating well, as with laryngeal 
paralysis which in dogs isn't left sided but is more often bilateral. on 
hot day, dog pants, breathes heavily, and arytenoids get sucked in to 
occlude the airway the harder the dog breathes, until dog gets all upset 
and ends up passing out b/c it tries harder and harder and harder until 
it can't breathe at all. break the cycle! number one tx for that: 
acepromazine is number one choice to calm an animal with upper airway 
obstruction. you can't restrain them for an IV cath, but you can give a 
little ace and let them sit in O2 for half an hour. also can use ace in 
cats. sometimes ketamine in cats having difficulty breathing. 
DO NOT use 
alpha2 agonists in critical cases. do not use opioids in animals with 
respiratory compromise! respiratory depressants are contraindicated. 
sometimes if they arne't ventilating well you may want to use a little 
butorphanol - dog with tracheal tear may get ace and butorphanol for 
calming. this is the only opioid you might use. 

induction: preoxygenate 
the animal, b/c if you have problem intubating you want higher plane of 
oxygenation at start.

drugs: if inability to ventilate is the problem: 
propofol +/- benzo - use small boluses titrated to effect to avoid resp 
depression. 
could use ket/val - ketamine is resp depressant but mainly 
just causes apneustic pattern.
thiopental - also requires use of small 
boluses - sometimes causes excitement - if animal has laryngeal 
paralysis, ok to use, but if it might be tumor or other problem 
preventing rapid intubation, don't use - try propofol.
NOT opioids.

at 
induction - have a variety of ET tubes at hand, b/c you may have problems 
intubating. you may run into a tumor mass obstructing the airway. 
sometimes only a red rubber catheter will pass. never assume you will be 
able to intubate. have a trach set ready, have small catheters ready. 
make sure you know that whatever happens you will get it somehow 
intubated, you will get control of airway somehow. cats that can't 
breathe are really scary to anesthetize. 

maintenance: 
-support 
ventilation!! if patient's problem is inability to ventilate due to upper 
airwya obstruction they will usually be ok once intubated. if the problem 
is diaphragmatic hernia, you need to ventilate for them. if problem is 
inability to oxygenate, you need to ventilate the. TV 10-20 ml/kg, RR 
8-12 bpm, peak airway pressure about 20 cm H2O
patient positioning isn't 
always that important, but can be - if only one lung is good, keep the 
good lung on the up side. if fluid is in left lung, try to keep right 
side up, or keep sternal, as much as possible. 

how do you monitor 
ventilation? watch RR and resp depth - can measure with spirometer, can 
use capnograph which meausres exhaled %CO2. ETCO2 is close to arterial 
CO2 value - usually about 5-10 mmHg less than arterial CO2. remember, by 
definitiion, ventilation tells you about changes in CO2 - if over 40, 
you're hypoventilating, if less than 40, you're hyperventilating. 


ventilation can affect oxygenation. 
alveolar gas equation says that PaO2 
= PiO2 - PaCO2/0.8
so your partial pressure of inspired O2 on room air is 
usually about 150 mmHg, and your normal CO2 is about 40, and resp 
quotient is 0.8, so usually you end up with 150-50=100 mmHg. so partial 
pressure in arterial blood should be 85 to 95 - a bit less than in 
alveolus. 
if you hypoventilate and CO2 goes up to 65, PaO2 will go down 
to 70 mmHg. but when under anesthesia, hypoventilation won't affect 
oxygenation b/c you are on 100% oxygen, so while O2 drops down, it only 
goes from 713 mmHg to 663 mmHg. so on 100% O2, hypoventilation won't 
cause problems with oxygenation. you monitor ventilation by looking at 
CO2. 

what about ability to oxygenate? collapsed lung lobes, 
atelectasis, etc can result in shunting of blood and reduced oxygenation. 
look at mm color - not that sensitive, PartO2 has to approach that in 
venous blood before cyanosis occurs. the pulsoximeter monitors O2sat, not 
PO2 - so it is sensitive when partial pressure falls below about 60, but 
isn't sensitive when PO2 is say, 80. arterial PO2 should be about 500 
when PaO2 is 663, so pulsox can give false sense of security. you need a 
blood gas to be sure.

postop care
extubation - be careful. be sure it's 
time. be sure reflexes have returned. keep them really calm. may give 
some ace or butorphanol postop in laryngeal paralysis dogs. analgesia is 
important. 

opiods? butorphanol or buprenorphine only. could do an 
epidural
local anesthetics - intercostal nerve blocks, interpleural 
infusion

what about patients with HEAD TRAUMA?
head trauma, increased 
intracranial mass, increased ICP.

intracranial compartment contains 
cells and interstitial fluid, CSF, and blood. patients with a mass have 
too many cells. head trauma produces edema - increased interstitial 
fluid. 
normally when you anesthetize a patient they are on the low end 
of the intracranial compliance curve where large changes in volume 
produce small increases in pressure. 
patients with trauma or tumors are 
already living on the edge of the compliance curve and so small changes 
in volume can cause large changes in pressure, and you have to keep 
intracranial volume changes to a minimum. we do this by manipulating the 
cerebral blood volume which is the only thing we can change rapidly.


cerebral perfusion pressure CPP = MABP - ICP. as intracranial pressure 
goes up, if mean arterial pressure hasn't changed, CPP goes down - less 
blood, O2 to brain.
brain autoregulates blood flow from about ICP 50-150 
mmHg. with head trauma, masses present, ability to autoregulate 
decreases, and cerebral perfusion depends more on BP. avoid swings in BP. 
also, brain needs O2. if O2 is ok, reduced perfusion isn't that 
important, but if O2 is below 60 mmHg (knee of Hb/O2 dissociation curve), 
cerebral blood flow increases rapidly to increase O2 delivery - bad. 

finally, CO2 - this is really important for acid base balance. as CO2 
increases, you get a respiratory acidosis. brains hate acid. brain is 
sensitive to CO2 changes, and as CO2 goes up, for a small increase in Co2 
you get a big increase in cerebral blood flow. so we try to keep CO2 low, 
and if anything we hyperventilate to keep cerebral blood flow and volume 
down, to decrease ICP.

increased cerebral metabolic rate also increasese 
ICP b/c CO2, lactic acid are produced, increasing blood flow. fever, 
pain, seizure, ketamine all contribute to this effect. NO KETAMINE for 
patients with head trauma, brain tumors. 
thiopental decreases the 
cerebral metabolic rate and ICP.

patients with increased ICP: premeds 
are rarely required. maybe give anticholinergic -generally we give 
steroids to decrease CSF volume, lasix to decrease interstitial fluid 
volume, and mannitol to decrease fluid volume. NO ketamine. NO ace due to 
seizure problem and decreased perfusion pressure. don't give opioids for 
premeds - makes CO2 go up. rarely with gunshot wound to head or other 
very painful trauma may use butorphanol. harder to monitor mentation. NO 
alpha2 agonists.

induction agents: thiopental is the best - reduces ICP, 
CBF
opioids + benzo - don't use opioid to premed, but can induce with it 
b/c you are going to intubate and ventilate, so opioid is ok. 
lidocaine 
- often given as part of induction to help desensitize airway and prevent 
coughing. all this stuff often given together.
etomidate may be used, but 
worry about vomiting
propofol can be used also - not as good for brain as 
thiopental though.

maintenance
inhalants - ? disrupt autoregulation. the 
more you give the worse it is. isoflurane probably is best, halothane 
worst. so usually if using an inhalant use low amount like 1/4%, well 
below mac of 1.2% - but you can't give more b/c it increases cerebral 
blood flow. also you have to hyperventilate them to avoid the problem 
with vasodilation. 
thiopental boluses
opioid boluses
propfol or 
etomidate infusion, fentanyl infusion



recovery: avoid excitement. keep 
ventilation good - hard if you used a lot of narcotics. give steroids. if 
you need analgesia, maybe butorphanol or buprenorphine, or epidural 
depending.

renal dysfunction: 
what's special about them? tend to have 
electrolyte problems, esp Ca++. 
preoxygenate them. 
optimize CV function

assure adequate hydration
use opioids, benzos to be nice to CV system
can 
use ketamine, but esp in cats it gets excreted by kidney - so think about 
how the drug is metaboliezd - may have really prolonged recovery - do not 
use ketamine in renal transplant recipients!

monitor urine output 
intraop - .5 ml/kg/hr is normal when awake, maybe lower during sx due to 
low metabolic rate

tx: fluids, mannitol, furosemide, dopamine 
(diuretics). two diuretics is better than one.

hepatic dysfunction - 
liver does a lot of things - plasma proteins, albumin, etc. many patients 
will be hypoalbuminemic, have coagulopathy, need fresh frozen plasma. may 
be hypoglycemic, may seizure. give plasma, give glucose. remember liver 
blood flow is already low in O2 so preoxygenate these patients. also 
remember most drugs are metabolized in liver, so induction is best done 
by masking with inhalant. can give opioids and reverse them, or can use 
propofol. be nice to CV system. 
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