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veterinary anesthesia


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What is the "fifth vital sign"
class I patient
has no organic or physiologic disease. the process for which surgery is required is very localized, with no systemic disturbance
Example:elective procedures, simple fracture, pin removal, small tumor
class II patient
the patient has mild systmeic disturbances which may or may not be related to the surgery and may only mildly interfere with the patient's normal activity and response to anesthesia. clinical pathologic changes may not be present
examples:obesity, neonate or geriatric, compensated mitral insufficiency
class III patient
the patient has moderate systmeic disturbance wich interfere with normal activity and response to anesthesia. clinical pathologic changes are present
examples: anemia, uremia, pneumonia, electrolyte imbalances, liver disease, renal disease, diaphragmatic hernia
class IV patient
the patient presents with life-threatening conditions. surgical intervention may be necessary to preserve life. systemic involvement and severe pathological changes are present.
examples: equine colic, hemorrhage, pneumothorax, gastric dilatation volvlus, spetic peritonitis
class V patient
the patient presents in a moribund condition, and has little chance of survival, with or without surgical intervention
examples:cerebral trauma with intracarnial hemorrhage, gastric rupture
purpose of Inhalation anesthetic delivery systems
1.Deliver metabolic oxygen 2Vaporize volatile anesthetic liquids to their vapor state
3.Control the amount of anesthetic gas delivered to the patient
4.Remove exhaled CO2
5.Provide a means to assist ventilation
anesthetic machine High pressure components
Pressures: 2000 to 50 psig
Source of compressed gas
Cylinder yoke
Cylinder valve
Pressure gauge
what will a nitrous oxide tank with any amount of liquid remaining in it read
full 750psi
anesthetic machine Medium pressure components
~ 50 psig
1.Pressure regulator
3.Flowmeter controls
4.Flush valve
5.Fresh gas inlet
anesthetic machine Low pressure components
0 to 30 cmH2O
1.Carbon dioxide absorber
2.Expiratory & inspiratory valves
3.Pop-off valve (pressure relief valve)
4.To scavenging interface
5.Pressure manometer
6.Reservoir (rebreathing) bag
7.Rebreathing (corrugated) hoses
the pressures within the breathing circuits are typically
in circuit vaporizer
located within the patient. these are generally inexpensive vaporizers which are neither temperature nor flow compensated
out of circuit vaporizer
must be located outside of the patient circuit. these are generally the precision type vaporizers
only use a circle system is pateints greater than
closed circle flow rate
4-6ml/kg/min of O2(small animals)
2-3ml/kg/min of O2(large animals)
semiclosed circle flow rate
30ml/kg/min of O2 (small animals)
10-20 ml/kg/min of O2(large animals)
nonrebreathing system flow rate
200ml/kg/min (minimum)
tidal volume=
minute ventilation=
respiratory rate times tidal volume=150-300ml/kg/min
metabolic O2 requirement
BW(kg)^3/4 times 10mls O2/min= 4-6ml/kg/min for small animals, or 2-3ml/kg/min for large animals
scavenging system consists of
1.a gas collection pop off valve-should have 19mm OD outlet
2.transfer tubing-should be 19mm corrugated tubing
3.interface if vacuum is used for waste gas removal, to prevent pressure increases or decreases from the scavenger system being transmitted to the breathing circuit
4.gas disposal tubing- keep length below 15feet. the tubing must not become occluded
5.gas disposal assembly
what are the benefits of premedication?
1.reduce patient anxiety and facilitate handling
2.reduce dose rerquirement for induction and maintenance drugs
3.provide analgesia
4.increase heart rate
5.reduce oral and bronchial secretions
what are some disadvantages of premedication?
1.necessitates patient handling
2.may add cost
3.side effects associated with the drugs selected
atropine vs glycopyrrolate
atropine: quicker onset (30sec vs 1-2 min) and shorter duration (20min vs 60min). it also crosses the blood brain barrier and placenta. dose for small animal patients is .02-.04 mg/kg for atropine and .005-.02mg/kg for glycoprrrolate.
why is use of anticholinergics controversial in ruminants
they may reduce secretions and improve visualization of the airway, but viscosity of the secretions and so risk for obstruction of the endotracheal tube may be increased
benefical effects of phenothiazines
anti emetic
weak anti-histaminic
why is acepromazine not recommended in breeding stallions
causes paraphimiosis
how is acepromazine metabolized
by the liver
acepromazine onset and duration
intermediate onset (2-5min IV/ 30-40min SC) long duration (4-6hrs)
acepromazine most notable side effects
1.hypotension caused by vasodilation resulting form peripheral alpha1 adrenergic blockade
2.decreased PCV and inhibiton of platelet function
3.contraindicated for use in animals undergoing skin testing for allergies
what common premedication is protective against catecholamine induced dysrhythmias
what about alpha 2 agonists precludes the necessity of metabolism by the liver or renal clearance
reversal agents
benefits of alpha 2 agonists
1.hypnotic sedative in broad range of species
2.excellent analgesics by interactions at the descending inhibitory pain pathways
3.reversal agents are available
alpha 2 agonist onset of actions
minutes IV/ 20 minutes IM
commonly used alpha 2 agonists
medetomidine (small animal)
xylazine (both)
detomidine (large)
important clinical side effects of alpha 2 agonists
1.cardiovascular depression
a.decrease in HR by 40-50%
b.second degree heart block
c.xylazine sensitizes the myocardium to epinephrine induced arrhythmias
d.transient hypertenison due to alpha 2 mediated vasoconstriction, followed by hypotension
2.repiratory depression, strider and occasional cyanosis (greater when given with other drugs)
3.vomiting in cats
4.hyperglycemia (species dependent)
5.diuresis (species dependent)
6.occasional myoclonus (species dependent)
routine use of alpha 2 agonists is limited to
young heathly patients
common alpha 2 agonist reversal agents
recommend to give IM or slow IV titration because of occasional serious consequences following IV administration
what benzodiazepine recommend if SC or IM administration is indicated and why?
midazolam, because it is water soluble that becomes highly lipid soluble due to body pH. these properties allow for non-painful SC or IM administration and rapid reliable onset of clinical signs
common benzodiazepines
benefits of benzodiazepines
1.actions of GABA receptors
2.apparent sedation
3.reduce dose of the primary anesthetic
4.reduce dose of maintenance agent
5.control seizures
6.appetite stimulant in cats
7.midazolam can be safely used in patients with cardiovascular compromise
sole administration of benzodiazepines is not recommend in what genral signlement of animals
young healthy patients, shown to cause intermittently agitationg and arousal causing difficult restrainment
common clinical side effects of benzodiazepines
1.hypotension and arrhythmias are reported with rapid IV administration of diazepam. These are attributed to the propylene glycol base and not the drug itself. simalar effects are not reported with midazolam.
2.respiration may be transiently depressed following IV administration
can benzodiozepines be used for analgesia
no, no anit-nocicepitve properties
what is a benzodiozepine reversal agent
flumazenil: use for overdose
measure of the effect of a drug/maximal effect that can be produced by its administration
measure of how much drug is required to produce a stated effect
opiod uses
1.parental and regional analgesia for acute and chronic conditions
2.induction and/or maintenance of anesthesia
opiod drug potency
MU actions
supraspinal analgesia, respiratory deprssion, euphoria, bradycardia, dependence, tolerance
KAPPA actions
spinal analgesia, sedation
dysphoria and hallucinations
opiods with antagonist actions
naloxone and naltrexone are complete antagonists
nalbuphine is a partial opiod antagonist with antagonist at MU and weak agonist at KAPPA
desirable properties of opioids
1.analgesia+/- sedation or sleep like state
3.induce emesis
4.drug effects may be antagonized
5.minimal cardiovascular depression; bradycardia may be easily countered with an anti-cholinergic agent
undesirable properties of opioids
1.usage must be documented
2.potential for human abuse
3.variable responses within and bt species
4.alters CO2 response curve; dose and route dependent respiratory depression
5.may result in an increase in intracranial pressure as elevated CO2 causes cerebral vasodilation
6.Histamine release, especially meperidine;morphine to a lesser degree
7.decreased GI motility but does induce initial vomiting and defecation
morphine for premedication and/or treatment of periprocedural pain MU agonist
2.efficacious for mild to severe pain
3.good sedative in dogs
4.long duration of action and less expensive
5.side effects are dose dependent and include respiratory depression, bradycardia, vomiting, defecation, dysphoria, and histamine related vasodilation and hypotension
hydromorphone and oxymorphone for premedication and/or treatment of peri-procedural pain
1.eqully effective analgesic action as morphine
2.lower incidence of GI side effects compared to morphine histamine release
Methadone for premedication and/or treatment of peri-procedural pain
1.good results in dogs and cats however availability has been limited
Meperidine and fentanyl for premedication and/or treatment of peri-procedural pain
1.short acting (30min -1hr)
2.less sedating than other opioids
3.fentanyl has a high degree of cardiovascular safety
4.meperidine can cause histamine release when given IV
Buprenorphine for premedication and/or treament of peri-procedural pain
1.partial MU agonist
2.less potential for abuse
3.efficacy is still being study with promising results for IV and buccal administration in cats
butorphanol for premedication and/or treatment of peri-procedural pain
1.KAPPA agonist and MU antagonist
2.short to intermediate duration
3.less effective for moderate to severe pain
4. less respiratory depression and dysphoria when compared to MU agonists
hypnosis and analgesia produced by the combination of a tranquilizer and an opioid
IV opioids for post operative pain
Morphine, Fentanyl, hydromorphone most common.
use lower end of dose as a starting point for cats, while dogs recive doses in the mid range. patients on constant rate infusions should be regularly observed for both efficacy of the treatment and potentilal side effects including hyperthermia (hydromorphone in cats), bradycardia, sedation, respiratory depression and dysphoria
epidural use of opioids
1.preservative free morphine
2.reduce dose by half to 2/3 if cerebrospinal fluid is observed in the needle
3.patients are more willing to ambulate in post operative period
4.retention of urine is a common side effect
intra-articular opioid use
1.clear doseing protocol has not been established
2.preservative free morphine
3.administeration limited by size of joint
opioids for induction and maintenance of anesthesia
1.good for compromised pateints due to cardiovascular safety
2.primarily for dogs, cats have potential for significant arousal with high IV doses
3.Opioids that do not cause histamine release (fentanyl, methadone, oxymorphone, hydromorphone)
4.fentanyl is the quickest to intubation
5.concurrent use with a benzodiazepine is suggested as a means of improving muscle relaxation and providing suitable intubation conditions
5.quiet room highly recommmend
6.bradycardia common if not pretreated with anticholinergic
7.mechanical ventaltion may be required
8.cardiovascular function is better maintained when fentanyl is used at a constant rate infsuion with inhaled anesthetic by reducing the required dose
9.lower infusion rate or discontiue during last 20-30min of procedure to facilitate a return of respiratory function
opioids for treatment of chronic pain
1.use for cancer pain
2.NSAIDs work well for osteoarthritis
what can be given to help patients that might become constipated while taking oral morphine
mild natural source of fiber such as canned pumkin
hypnotic induction drugs
dose dependent effects ranging from sedation to unconsciousness
dissociative induction drugs
cataleptic state where patients may look awake and maintain muscle tone and reflex activity
1.drug will precipitate if re-constituted with acidic solution (lactated ringers)
2.peri-vascular administration can result in sloughing of the skin
3.small animal formuations1-2% large animal at 10%
4.rapid smooth onset(15-30sec) and ultra short duration of action (10-15min)
5.acidemia will increase free portion of drug and may result in overdose
6.dose is reduced by 50% following premedication
7.excitement is seen with slow administration-give initial bolus of 1/3 dose in small animals and entire dose in horses
8.hepatic metabolism
9.greyhounds have reduced ability to metabolize
10.don't use repeated doses in horses because of negative recovery
11.both intracranial and intraocular pressures are decreased compromise to cerebral perfusion
13.anticonvulsant properties
14.may increase sen to somatic pain
15.increas HR with immediate transient decrease in contractility
16.ventricular dysrhythmias more commonin unsedated and/or hypoxemic patients
17.decreased PCV
18.decreased respiratory rate
1.don't refrigerate
2.discard open vial within 6-24hr
3.decreases intra crainal pressure
5.horses get excited with adminsteration
6.onset of action 20-30sec
7.duration is less than 10min
8.additional bolus can be given to the dog and horse to prolong anesthesia
9.side effects in the cat are heptaic enzyme saturation, heinz-body anemia, general malasiae, anorexia, and diarrhea when administred daily
10.cardiovascular depression
11.arterial hypotension is the most common side effect
12.negative inotropic effects
13.increased risk of wound infection
14.give slow to avoid respirtory depression
15.can lessen side effcts with prior administration of IV fluids
1.hyperosmalor-pain and hemolysis of RBC. minimze by diluting drug
2.premedication highly recommended
3.side effects myoclonus, vomiting
4.interferes with cortsol synthesis for a period of 6-24hrs-give short acting glucocorticoid prior to use
5.minmimal cardiopulmanary effects (decreased HR and respiratory rate) make it a good choice for critically ill cats
1.onset of action is 30-45sec IV 20min IM
2.prolonged effect in patients with renal disease
3.seizure like behavior and hallucinations
4.give benzodiozepine to improve muscle relaxation
5.increases intracrainal and intraocular pressure
6.NMDA antagonist may be useful in reduction of wind up pain
7.increase HR contractiltity and blood pressure
8.don't use in restrictive or hypertropohic caridac disease
9.hypoventilation and hypoxemia unless exictement is observed
10.pharynegeal responses (swallowing) may be maintained following drug administration. this coupled with increases in tracheobronchial and salivary secretions can make intubation more challenging
1.available in a mixture with zolazepam (telazol)
2.refrigerate after reconstitution
3.stings on injection like ketamine
4.recument 5-10 IM
5.prolonged sedation and/or residual aataxia may last 2-4 hrs.
6.hypothermia, hepatic or renal insufficiency and hyoxemia may contribute to residual effects
7.cardiovascular and respiratory effcts similar to ketamine
which inhaled anesthetic has the highest risk to cause incresed sensitivity to catecholamine induced arrhythmias
halothane becuase it is an aliphatic hydrocarbon, others are ether derivatives
vapor pressure
measure of the tendency for molecules in the liquid state to enter the gasesous form.high vapor pressure should be used with a precsion vaporizer outside the patient breating circuit
which gas anesthetic makes a nephrotoxic compound when mixed with sodalime
sevoflurane- should not be used under closed circuit for long periods of time. methoxyflurane and halothane decompose in the presence of sodalime
when other factors are constant, induction and recovery are most rapid for the agent with the _________ blood/gas partition coefficient
oil gas partition coefficient
inversely related to anesthetic potency. therefore drugs such as desflurane with low oil/gas partition coefficient have a higher dose requirement to achieve the same anesthetic level when compared to halothane or methoxyflurane
minimum alveolar concentration: measure used to determine the potency for the inhaled agents
inhaled anesthetics cardiovascular effects
1.decreased MAP: direct myocardial depressent
2.greatest with halothane and methoxyflurane
3.cerbral blood flow increased
4.renal and hepatic blood flow decreaesed
5.may increase automaticity of the heart and blunt baroreceptor reflexes
inhaled anesthetics respiratory effects
1.dose dependent decrease in alveolar ventilation
2.isoflurane and desflurane generally depress more than sevoflurane, halothane or methoxyflurane- maginifed in horses
2.due to decreased rate or TV
3.pulmonary vasoconstriction, halothane has been reported to be most effective at preventing bronchospasm in patients with this concern
inhaled anesthetics CNS effects
1.reversible dose dependent depression
2.can cause seizures
3.sevoflurane reported seizure like activity in childern
4.potential to increase intracranial pressure. hyperventaltion as been used to decrease cerebral blood flow. best documented with isoflurane
inhaled anesthetics hepatic and renal effects
1.blood flow decreased (more prominat with halothane and methoxyflurane)
2.halothane not recommend in known hepatic disease
3.high output renal failure with methoxyflurane- increased risk wtih NSAID or aminoglycosides
4.limit sevofolurane use with renal failure
maligant hyperthermia and inhaled anesthetics
associated with halothane, but any one can induce it.
neuromuscular blockade and inhaled anesthetics
isoflurane has greatest synergy. careful moitoring is essential to prevent overdose
vapor pressure of inhaled ansethics lowest to highest
blood gas partition coefficient for inhaled ansethetics lowest to highest
MAC inhaled ansethetics lowest to highest
how do you monitor neuromuscluar blockcade
2hz stimulus over 2 seconds or "train of four" and 50hz stimulus over 5 sec or "tetanus"
8 pros and 5 cons of benzodiazepines
1.cardiopulmonary sparing
3.Midazolam is H2O soluble
4.mild tranquilization/anxiolytic
5.decreases MAC
6.Reversible with Flumazenil
7.good muscle relaxation
1.May cause excitement in cats/ some dogs
2.effects prolonged with liver dz
3.diazepam not H2O soluble
4.diazepam is painful on injection
5.diazepam may cause sterile abscessation if given IM
6.Midazolam is expensive analgesia
3 pros and 7 cons
1.good sedative
2.lowers threshold for arrhythmias
3.antiemetic (centrally antidopaminergic)
1.not reversible
2.hypotension (alpha blockade- vasodilation)
3.platelet aggregation inhibition
4.long acting, especially with liver dz
5.mild respiratory depressant analgesia
7.lowers seizure threshold in epileptics
Alpha 2 agonists
4 pros and 9 cons
1.excellent sedation
2.excellent muscle relaxation
3.mild analgesia (especially GI pain)
4.reversible with yohimbine or atipamezole
1.hypertension, followed by hypotension (central sympathetic blockade resulting in decreased cardiac output)
2.severe bradycardia
3.may cause emesis
4.first, second, or third degree AV block
5.increased sensitivity to catecholamine induced arrhythmias
6.may cause stridor in brachycephalic breeds
7.depresses respiratory center
8.promotes diuresis
9.inhibits insulin-hyperglycemia may result
pure agonist opioids
4 pros and 7 cons
1.excellent analgesia/euphoria
2.reversible with naloxone, naltrexone
3.mild cardiopulmonary effects (bradycardia and decreased respiratory rate- dose dependent)
4.synergistic with tranquilizers/ sedatives
3.decreased GI motility
4.controlled drugs
5.morphine and meperidine can cause histammine release whin given IV
7.excitement/aggression in some cats
partial agonists and agonist/antagonist opioids
6 pros and 3 cons
1.tend to cause less dysphoria than pure agonists
2.butorphanol can be used in small doses to antagonize dysphoric effects of pure agonists
3.buprenorphine is long lasting (6-8hrs) and can be given orally/buccally to cats
4.butorphanol is the most potent cough suppressant of all the opioids
5. less likely to cause vomiting than pure opioids
6.good analgesic effect eithout significant dysphoria in cats
1.may be less analgesic than pure agonists
2.butorphanol is very short acting (1-2hrs)
3.controlled drugs
4 pros and 8 cons
1.rapidly acting general anesthetic
2.rapidly metabolized and redistributed cumulative effect with repeat administration
4.easily titrable
1.hypotension (vasodilation)
2.respiratory depression/apnea analgesia
4.may cause muscle twitching
5.may cause pain on IV injection
6.inravenou route only
7.can cause heinz body anemia in cats
8.may predispose to wound infection
5 pros and 8 cons
1.water soluble- can go IM
2.rapid anesthesia
3.supports cardiovascular system (direct sympathetic stimulation)-may increase blood pressure and heart rate
5.good anesthetic in cats
1.may cause apneustic breathing pattern
2.will cause myocardial depression if catecholamine depleted, which may lead to hypotension
3.increases intracranial pressure
4.increases salivary secretions
6.painful on IM injection
7.metabolized by liver in dogs and excreted unchanged in urine in cats
8.not reversible
3 pros and 6 cons
1.cardiopulmonary sparing
3.sparing to brain circulation
2.may cause vomiting
3.may cause twitching
4.suppresses adrenocortical axis
5.propylene glycol base- may cause hemolysis
6.IV only
barbiturates (thiopental)
4 PROS and 6 cons
1.relatively cardiopulmonary sparing
2.maintains cerebral blood vessel response to CO2
3.short acting
1.may cause arrhythmias
2.may cause transient apnea
3.cumulative with repeat doses
4.liver metabolized- recoveris may be prolonged with liver dz
5.will cause sloughing if extravasation occurs
6.cumulative with repeat dosing

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