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254 Cards in this Set

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what are the three most common complications under inhalant anesthesia?
1. hypotension
2. hypoventilation
3. hypothermia
what is the most common complication under injectable anesthesia?
hypoxia
when do you treat arrhythmias under anesthesia?
- if it is causing hemodynamic instability
- if it is going to cause further complications
- if the cause or the arrhythmia are treatable
what two physiological parameters contribute to tissue oxygen delivery?
1. arterial blood pressure
2. arterial blood O2 content
what two physiological parameters contribute to arterial blood pressure?
1. systemic vascular resistance
2. cardiac output
what two physiological parameters contribute to cardiac output?
1. heart rate
2. stroke volume
what three physiological parameters contribute to stroke volume?
1. preload
2. afterload
3. myocardial contractility
what are three agents/conditions that can stimulate sinus bradycardia?
1. opioids
2. hypothermia
3. vagal stimulation (push on eye, distend stomach with air)
why can sinus bradycardia be bad under anesthesia?
because it can cause hypotension → low perfusion
what are two ways to treat sinus bradycardia under anesthesia?
1. anticholinergics
2. warming
why can sinus tachycardia be bad under anesthesia?
- reduces ventricular filling time → ↓CO → hypoxia
- could indicate pain because anesthetic plane is too low
how is sinus tachycardia under anesthesia treated?
- find the cause (low plane?)
- analgesia
- increased depth
what is a type 1 and type 2 2nd degree AV block?
- Type 1: Wenckebach (beat-beat-pause-beat-beat-pause…)
- Type 2: a "regular" 2nd degree AV block
when is a 2nd degree AV block normal under anesthesia?
it is common in very fit horses
what are two classes of anesthetics that can induce a 2nd degree AV block?
1. α2 agonists
2. opioids
how and when is 2nd degree AV block treated under anesthesia?
- only if appropriate (e.g. hemodynamic effects)
- anticholinergics
how is a 3rd degree AV block treated?
pacemaker (will come up on a pre-op exam)
what drug is bigeminy associated with?
thiopental
if you have to treat VPCs or V-tach, what is the drug of choice?
lidocaine
what drug is contraindicated with the presence of ventricular escape beats? What is the indicated drug class?
- lidocaine contraindicated
- use anticholinergics to reestablish sinus rhythm
what is an acceptable MAP for small animals? Large animals in recumbency?
- small animals: 60 mmHg
- large animals: 70 mmHg
what pAO2 is the in the danger zone
60 mmHg
what are three things in surgery that may cause hypotension?
1. inhalent anesthetic agents
2. excessive depth
3. hemorrhage
what are three clinical signs (without instruments) of hypotension?
1. Tachycardia
2. Weak pulses(maybe)
3. Pale MM
what are three things that you can administer to a patient to correct hypotension during anesthesia?
1. fluids (crystalloids/colloids)
2. ± inotropes
3. ± vasopressors
what SpO2 is mild hypoxia? What is severe?
- mild: < 95%
- severe: < 90%
when are the two most common times that we would see hypoxia?
beginning and end of anesthesia
what are three circumstances that you would see hypoxia in the maintenance phase of anesthesia?
- tank runs out
- disconnected from breathing circuit
- obstruction
what must happen to see cyanosis?
5 g/dL of deoxyhemoglobin
what are two circumstances when a cyanotic patient is well-ventilated?
1. polycythemic patient (they have more blood and can easily overcome the 5 g/dL threshold)
2. anemic patients (especially small patients) may always be cyanotic
what are four signs of hypoxia (and the cause) other than cyanosis and instrument measurements?
1. Tachycardia (they need faster circulation to get oxygenated)
2. Arrhythmias (heart muscle deprived of oxygen)
3. Bradycardia (heart is deprived)
4. “Gasping” (agonal)
what are five causes of hypoxemia?
- Low FiO2 (fraction of inspired oxygen)
- V-Q mismatch (ventilation-perfusion mismatch; atelectasis)
- Shunt
- Hypoventilation (needs to be profound)
- Diffusion impairment
what are five things to do when hypoxemia is suspected/confirmed?
- Check your patient!
- Supply oxygen
- Intubation (do it / check it)
- Attempt to ventilate
- Check your machine
why do oxygen levels not correlate with CO2 levels?
oxygen levels do not correlate with CO2 levels, especially when the animal is being given supplemental oxygen. The animal has to be BREATHING to get rid of the CO2. The animal does not have to be breathing to have a good SpO2 if they are being supplied oxygen
what are five ways to assess ventilation?
- Respiratory rate
- Respiratory depth
- Respiratory pattern
- Blood gas (PaCO2)
- Capnography (EtCO2)
what are two basic reasons why CO2 levels may be elevated in the blood?
1. poorly eliminated
2. produced excessively
- what is a normal pCO2?
- what is an "acceptable" high range of pCO2?
- 35-45 mmHg (normal)
- 50-55 mmHg (acceptable)
what are five clinical signs of hypercapnia/Hypercarbia?
- Increased respiratory rate
- Tachycardia
- INCREASED BP
- Dark pink MMs
- Eventually, narcosis (sleepiness)
what are five reasons why hypothermia is important?
- DECERASES MAC OF INHALANT
- SHIVERING IS PAINFUL AND PHYSIOLOGICALLY EXHAUSTING
- Arrhythmias
- Delayed wound healing
- Prolonged recovery
what are the four mechanisms of heat loss?
1. conduction
2. convection
3. radiation
4. evaporation
what are three characteristics of emergence excitement?
1. disorientation
2. dysphoria
3. pain
what are the three most important things to do to treat emergence excitement?
1. TREAT PAIN
2. handle with care!
3. reassess
what are the three organic functional groups of a typical local anesthetic?
1. lipophilic portion (e.g. aromatic ring with a p-amino and carboxyl group)
2. hydrocarbon chain (e.g. ester or amide)
3. hydrophilic segment (e.g. tertiary amine)
what are five ester local anesthetics?
1. Procaine
2. Benzocaine
3. Chloroprocaine
4. Tetracaine
5. Cocaine
what are three commonly used amide local anesthetics and four others?
1. lidocaine
2. mepivacaine
3. bupivacaine
- etidocaine
- prilocaine
- levobupivacaine
- ropivacaine
which local anesthetic has a fast onset (15 min) and moderate duration (1-2 hours)
lidocaine
which local anesthetic has a fast onset (15 min) and longer duration (1-2 hours), and is commonly used in lameness evaluation of the horse and not in small animals?
mepivacaine
which local anesthetic has a slow onset and long duration (1-2 hours), and is the primary local anesthetic used in the VTH for small animals and horses?
bupivacaine
what is the mechanism of local anesthetics?
- blocks the ACVITVELY FIRING nerves of nerves ("frequency-dependent blockade")
- blocks the CLOSED and INACTIVATED Na channels
- prevents neuronal depolarization
what aspect of a nerve determines its sensitivity to a local anesthetic?
the amount of myelination. Less myelinated nerves are more sensitive than heavily myelinated nerves
in what acid/base form are solutions of local anesthetics?
in the protonated (i.e. hydrochloride salt) form
why is the rate of absorption important with local anesthetics?
Local anesthetics act locally, so absorption usually signals the end of their action
if you do a ring block, what drug do you not want to mix with the local anesthetic and why?
epinephrine, because it will vasoconstrict and cause the limb distal to the block to become ischemic
why do ester local anesthetics generally last for a much shorter period of time than amide local anesthetics?
- because pseudocholinesterases (ubiquitous) rapidly metabolize them
- amides are metabolized by hepatic CYP450 enzymes, which is a slower process
why can amide based local anesthetics cause allergic reactions?
because they are metabolized to PABA
why shouldn't you give bupivacaine IV?
because it is severely cardiotoxic
which local anesthetic is neurotoxic?
lidocaine
what is the result of cardiotoxicity with a local anesthetic? How is it treated?
- malignant arrhythmias
- treated with IV lipid administration
which local anesthetic has been especially associated with methemoglobinemia?
procaine (Cetacaine™)
what are two good places where local anesthetics are absorbed when applied topically?
- mucous membranes such as cornea and larynx
local anesthetics absorb poorly through skin. What are two exceptions?
1. EMLA cream
2. Lidoderm patch
what should you always do before injecting local anesthetic into a patient?
ASIPRATE
how do you perform a "Bier block?"
- Place IV Catheter
- Place Tourniquet
- Inject lidocaine
- Block is gone shortly after removal of tourniquet
- Time limited by tourniquet
- don't use bupivacaine!
where are three sites to perform a regional block with local anesthetics?
1. Epidural
2. Intrathecal
3. Brachial Plexus
which local anesthetic is indicated for CRI? What animals is this contraindicated and why?
- lidocaine
- not in cats because it lowers cardiac function
why is intra-articular local anesthesia controversial?
because it may be toxic to chondrocytes
What is the definition of allodynia?
Pain caused by a stimulus that does not normally provoke pain
What is the definition of analgesia?
Absence of pain in the presence of stimuli that would normally be painful
What is the definition of hyperalgesia?
An increased response to a stimulation that is normally not painful
What is the definition of hypoalgesia?
A diminished sensitivity to noxious stimulation
What is the definition of inflammatory pain?
Spontaneous pain and hypersensitivity to pain in response to tissue damage and inflammation
What is the definition of multimodal analgesia?
The use of multiple drugs with different actions, which may act at different levels of the nociceptive pathways, to produce optimal analgesia
What is the definition of neuropathic pain?
Pain originated from an injury or that involves peripheral or central nervous system and is described as burning or shooting, possibly
associated with motor, sensory, or autonomic deficits
What is the definition of nociception?
The reception, conduction and central nervous system processing of nerve signals generated by the stimulation of nociceptors. This process leads to the perception of pain
What is the definition of physiologic pain?
Protective mechanism to make individuals move away from the cause of potential tissue damage or to avoid movement or contact with external stimuli during a reparative phase
What is the definition of preemptive analgesia?
Administration of analgesics drugs before stimulation to prevent sensitization of neurons and windup, thus reducing postoperative pain
What is the definition of somatic pain?
Pain originated from injury of bones, joints, muscle, or skin and is usually localized, constant, sharp, aching and throbbing
What is the definition of visceral pain?
Pain originated from stretching, distention or inflammation of the viscera, and is usually deep, cramping, aching or gnawing, and poorly localized
What is the definition of windup?
Sensitization of nociceptors and peripheral and central pain pathways in response to an overwhelming quantity of afferent nociceptive impulses resulting in expanded receptive fields and an increased rate of discharge
Pain caused by a stimulus that does not normally provoke pain is called what?
allodynia
Absence of pain in the presence of stimuli that would normally be painful is called what?
analgesia
An increased response to a stimulation that is normally painful is called what?
hyperalgesia
A diminished sensitivity to noxious stimulation is called what?
hypoalgesia
Spontaneous pain and hypersensitivity to pain in response to tissue damage and inflammation is called what?
inflammatory pain
The use of multiple drugs with different actions, which may act at different levels of the nociceptive pathways, to produce optimal analgesia is called what?
multimodal analgesia
Pain originated from an injury or that involves peripheral or central nervous system and is described as burning or shooting, possibly associated with motor, sensory, or autonomic deficits is called what?
neuropathic pain
The reception, conduction and central nervous system processing of nerve signals generated by the stimulation of nociceptors. This process leads to the perception of pain" is called what?
nociception
Protective mechanism to make individuals move away from the cause of potential tissue damage or to avoid movement or contact with external stimuli during a reparative phase is called what?
physiologic pain
Administration of analgesics drugs before stimulation to prevent sensitization of neurons and windup, thus reducing postoperative pain is called what?
preemptive analgesia
Pain originated from injury of bones, joints, muscle, or skin and is usually localized, constant, sharp, aching and throbbing is called what?
somatic pain
Pain originated from stretching, distention or inflammation of the viscera, and is usually deep, cramping, aching or gnawing, and poorly localized is called what?
visceral pain
Sensitization of nociceptors and peripheral and central pain pathways in response to an overwhelming quantity of afferent nociceptive impulses resulting in expanded receptive fields and an increased rate of discharge is called what?
windup
what is the three-fold chain of neurons in the nociceptive pathway and where do these neurons project?
1. First order neuron: starting at the periphery and projecting to the spinal cord
2. Second order neuron: cross the spinal cord and ascend to the brain
3. Third order neuron: projects into the cerebral cortex and other supraspinal structures
which types of neurons are involved in nociception?
Free A-delta and C nerve endings
A-delta nociceptors:
- what types of stimuli are they sensitive to?
- what are the two types?
- how fast do they discharge compared to C-fiber nociceptors?
- what type of information do they provide to the CNS?
- what is an example of they painful feelings they transduce?
- Composed of mechanoreceptors and mechanothermal receptors
- Low-threshold (<75%); High-threshold (<25%): respond only to tissue-damaging stimulation
- Discharge at a higher rate than C-fiber nociceptors
- Provide more discriminative information to the Central Nervous System
- Responsible for pricking and sharp qualities of “First Pain”
C-fiber nociceptors:
- comment on the threshold and type of stimuli they are responsive to
- what type of pain do they produce?
- what is an example of the painful feelings they transduce?
- what higher-level behaviors in the CNS do they activate?
- Almost all are High-threshold and respond to different types of stimulation (polymodal)
- Activation is responsible for slow-onset (“second”) pain that occurs after the initial insult.
- Burning and aching qualities
- Signals tissue damage and inflammation that initiates self-preservation behaviors such as avoidance and guarding and disuse.
What are the four steps of the pain pathway?
1. transduction
2. transmission
3. modulation
4. perception
A-delta fibers:
- diameter
- myelination
- conduction speed
- type of pain
- timing of the pain with respect to other pathways
- Small diameter 1-4 μM
- Myelinated
- Fast conduction
- Transmit well localized pricking, sharp pain
- “First pain”.
C-fibers:
- diameter
- myelination
- conduction speed
- type of pain
- timing of the pain with respect to other pathways
- Smaller diameter 0.4 – 1.2 μM
- Unmyelinated
- Slow conduction
- Transmit poorly localized dull or aching pain
- “Second pain”
amplification or suppression of the peripheral sensory nerve impulses at the level of the spinal cord is called what?
modulation
what is pain modulation?
amplification or suppression of the peripheral sensory nerve impulses at the level of the spinal cord
What is end result of neuronal activity of pain transmission, where pain becomes a conscious multidimensional experience?
perception
what is pain perception?
end result of neuronal activity of pain transmission. Pain becomes a conscious multidimensional experience
what are the three cortical areas involved in pain perception?
1. reticular system
2. somatosensory cortex
3. limbic system
what are three neurotransmitters involved in peripheral sensitization of pain (primary hyperalgesia)?
1. Substance P
2. Neurokinin A
3. Calcitonin gene related peptide (CGRP)
what are four physiologic responses to neurotransmitters involved in peripheral sensitization and primary hyperalgesia?
1. Excitability of sensory and sympathetic fibers
2. Vasodilation
3. Extravasation of plasma proteins
4. Recruitment of inflammatory cells
what is the "sensitizing soup"
a group of cytokines, neurotransmitters, and other autacoids involved in secondary hyperalgesia
what is secondary hyperalgesia?
a lower response threshold for A-delta and C-fiber activation (activation of silent nociceptors) in an expanded area around the site of primary pain sensitization
what is the physiologic process of "wind-up"? (4 steps)
1. NMDA receptor activation
2. Ca influx
3. Activation of protein kinase C
4. Increased sensitivity to glutamate
where does "wind-up" occur?
dorsal horn of the SC
how does pain affect the immune system?
Increased cortisol levels impair wound healing and decrease immune system function
how does pain affect the neuroendocrine system? (3)
- Activated by Pain
- Gluconeogenesis is favored
- Impaired metabolism results in catabolism and cachexia
how does pain affect the GI system?
Sympathetic stimulation can cause shunting of blood, decreased motility, and decreased mucosal integrity
how does pain affect the CV system?
Activation of RAAS:
- fluid retention
- elevated blood pressure
- decreased renal perfusion
- Increased HR, SV, CO and myocardial O2 consumption.
what are some clinical signs in animals that have loss of normal behavior due to pain?
- Decreased ambulation or activity
- lethargic attitude
- decreased appetite
- decreased grooming (cats)
- Harder to assess in the hospital
what are some examples of abnormal behaviors associated with pain?
- Inappropriate elimination
- Vocalization
- Aggression
- Decreased interaction with other pets or family members
- Altered facial expression
- Altered posture
- Restlessness
- Hiding (especially in cats)
generally, how does an animal in pain react to touch?
Increased body tension or flinching in response to gentle palpation of injured area and palpation of regions likely to be painful, e.g., neck, back, hips, elbows
what are four physiologic parameters that may be elevated as a result of pain?
1. Heart rate
2. Respiratory rate,
3. Body temperature
4. Blood pressure
when an animal is in pain, what do their pupils do?
dilate
what are six types of scales for pain assessment?
1. simple descriptive scale
2. visual analog scale
3. numerical rating scale
4. dynamic and interactive visual analog scale
5. University of Melbourne Pain Scale (UMPS)
6. Glasgow Composite Measures Pain Scale
what are the four steps in the Dynamic and Interactive Visual Analog Scale (DIVAS) of pain assessment?
1. Observation from a distance undisturbed
2. Approached, handled, encourage to walk
3. Palpation of surgical incision and surrounding area
4. Final overall assessment of sedation and pain
what is considered to be the most accurate scale of pain assessment in animals?
The Glasgow Composite Measures Pain Scale
what are the six parameters assessed in the SHORT FORM Glasgow Composite Measures Pain Scale?
1. vocalization
2. mobility
3. demeanor/response to humans
4. attention to wound
5. response to touch
6. posture and comfort
how do you differentiate pain from dysphoria?
- pain with interaction: can be temporarily distracted or calmed; doses of opioids help; there is an identifiable source of pain
- dysphoria: difficult to distract or calm; DOSES OF OPOIDS DO NOT HELP; no identifiable source of pain
what are four basic ways to modify the nervous system to provide analgesia?
1. inhibit perception
2. modulation of spinal pathways (inhibit central sensitization)
3. inhibit transmission (inhibit impulse conduction)
4. inhibit transduction (inhibit peripheral sensitization of nociceptors)
what are four drug classes that inhibit pain perception?
1. anesthetics
2. opioids
3. α2-agonists
4. benzodiazepines
what are two classes of drugs that inhibit transmission of pain through the nerves?
1. local anesthetics
2. α2-agonists
what are three classes of drugs that inhibit pain transduction (i.e. inhibits peripheral sensitization of nociceptors)
1. NSAIDs
2. opioids
3. local anesthetics
what are seven classes of drugs that inhibit modulation of spinal pathways of pain (inhibit central sensitization)?
1. local anesthetics
2. opioids
3. α2-agonists
4. tricyclic antidepressants
5. cholinesterase inhibitors
6. NMDA antagonists
7. NSAIDs
what severity of pain are treated with opioid:
- mu-agonists?
- partial mu-agonists?
- agonists-antagonists?
- mu-agonists: moderate to severe
- partial mu-agonists: mild to moderate
- agonists-antagonists: mild
name six mu agonists used as analgesics
1. morphine
2. oxymorphone
3. fentanyl
4. hydromorphone
5. methadone
6. meperidine
name a partial mu agonist used as an analgesic
buprenorphine
name an opioid agonist-antagonist used as an analgesic for mild pain
butorphanol
name six COX-2 NSAIDS
1. Meloxicam (Metacam)
2. Carprofen (Rimadyl)
3. Etodolac (Etogesic)
4. Deracoxib (Deramaxx)
5. Firocoxib (Previcox)
6. Tepoxalin (Zubrin)
what are six contraindications of NSAID administration?
1. renal or hepatic insufficiency
2. low effective circulating volume (dehydration, hypotension, shock)
3. active GI disease
4. coagulopathies
5. concurrent use of corticosteroids or other NSAIDs
6. pregnancy
what are two cons of using α2-agonists as analgesics for long-term use?
1. low doses still have a CV effect
2. short duration of drug (CRI may be needed)
lidocaine as an IV analgesic
- site of action
- mechanism of action
- what animal (disease) is this commonly used?
- complications of lidocaine under anesthesia
- inhibits spontaneous impulses from injured nerve and from dorsal root ganglion
- NMDA receptor antagonism (neuropathic pain)
- good visceral analgesia in horses (colic)
- decreases MAC about 25% for inhalant anesthetics
low dose ketamine as an analgesic
- mechanism of action
- why is this good for burn victims?
- routes of administration
- blocks glutamate at NMDA receptor
- good for burns because it treats central sensitization and hyperalgesia
- IV, SQ, IM, epidural
when is it appropriate to give analgesia to prevent hypersensitivity and the lowest amount of post-operative pain?
before, during, and after surgery
what is an advantage of CRI opioid administration over bolus?
pain relief without the sedation/euphoria/dysphoria at the peak and without the returning pain/hypersensitization/tolerance at the trough
what opioid is commonly given transmucosally?
buprenorphine
what is an advantage of giving opioids transmucosally versus orally?
no first-pass effect
which opioid is commonly given transdermally?
fentanyl
which two types of analgesics are given intraarticularly?
local anesthetics and opioids
what are four nerves in the head to block when you would want to do dental work?
1. infraorbital
2. maxillary
3. inferior alveolar
4. mental
what is a common analgesic drug cocktail that is given intraoperatively and also post-operatively?
FLK: fentanyl, lidocaine, ketamine
what are four opioids commonly given pre-operatively?
morphine, hydromorphone, oxymorphone, fentanyl
in chemical restraint, what is required for ruminants to become recumbent? Horses?
- ruminants: sedation
- horses: they need anesthesia
chemical restraint comment on fasting for field procedures in:
- equine
- bovine
- alpaca/llama/ovine/caprine
- equine: not necessary
- bovine: if prolonged recumbency, 48-72h or solid food and 24h of liquid restriction; short recumbency: 24h of fasting
- alpaca/llama/ovine/caprine: 24h of food and 13h of water restriction
what are two reasons why are large animals (except horses) fasted before chemical restraint?
1. risk of regurgitation/aspiration
2. tympanism/hypoventilation/hypoxemia
what are five signs of sedation in large animals?
- Head drop
- Droopy eyes
- Droopy lips
- Increase distance between feet
- Ataxia
what is the major mechanism of action of acepromazine with regards to using it for standing restraint in large animals?
inhibits dopamine receptors in the brain
why is acepromazine good for sedation (i.e. chemical restraint), but not for anesthesia, when used alone?
because it has a "ceiling effect", where you reach a maximum efficacy, but the side-effects keep increasing with increasing dose.
what is the onset and duration of acepromazine when used as chemical restraint?
- onset: 20-30 min
- duration, up to 5 hours
what is the reversal agent for acepromazine when used for standing restraint?
there is none
what is a problem with acepromazine in stallions?
priapism
which large animal chemical restraint drug produces less ataxia than α2-agonists and is good for transporting animals?
acepromazine
acepromazine is not effective in what species?
swine
which sedative also can be used as a vasodilator to improve hoof circulation?
acepromazine
what is the biggest problem with oversedation in large animals (e.g. using α2 drugs in chemical restraint)?
it is harder to move the animal
comment on the use of α2 agonists in standing restraint on its effects on:
- muscles
- pain
- coordination
- GI
- renal
- muscle relaxation
- analgesia
- ataxia
- decreased GI motility
- diuresis
what is the most common reversal agent in standing restraint used with xylazine?
yohimbine
what are three α2 reversal agents used in standing restraint?
yohimbine, atipemazole, tolazoline
what are three important side effects of α2 agonists when used in standing restraint?
1. hypertension
2. bradycardia
3. arrhythmia
what is the only FDA approved α2 reversible agent for use in veterinary patients?
tolazoline
for standing restraint in field procedures, by what route of administration is xylazine administered to:
- horses?
- cattle?
- horses: IV
- cattle: IM
what is an important side-effect of xylazine in cows?
induces abortion in late gestation
what is a good sedative to control pain in severe colics?
xylazine
which α2 agonist can be given through the oral mucosa in aggressive or needle-shy horses?
detomidine
what is a good way to cause a seizure in a horse with α2 drugs?
inject into their carotid artery by mistake instead of the jugular
what is an important side-effect of xylazine in sheep?
acute pulmonary edema
detomidine in standing restraint of horses:
- compare to xylazine with respect to sedation and analgesia effects
- onset and duration
- what is a disadvantage post-op?
- what side-effect is stronger in this drug versus xylazine?
- better sedation, and sedation lasts longer than analgesia
- onset: 5-7 min; duration ≈ 45 min
- can mask surgical colic
- more CV depression than xylazine
what are two advantages of romifidine over other α2 drugs in standing restraint of the horse?
1. less head drop than xylazine and detomidine
2. less ataxia than other α2 drugs
what is the proper route to give xylazine reversal agents and why?
IM, because IV administration can cause CV instability
which opiod in standing restraint is most commonly used and is good for visceral pain?
butorphanol
butorphanol in standing restraint:
- what is a side-effect in horses that are not painful and/or not sedated?
- which receptors does it interact with and how?
- why might it be used with morphine?
- what is an advantage of giving this drug IV versus morphine?
- compare to morphine with respect to GI tract stasis
- can cause excitement in not sedated/not painful horses
- kappa-agonist; mu-ANTAGONIST
- used with morphine to antagonize some of the μ-effects while preserving some analgesia
- does not release histamine with IV injection; morphine does
- less GI tract stasis versus morphine
why is guaifenesin only used IV with chemical restraint?
because extravascular injection causes tissue necrosis
guaifenesin for chemical restraint:
- effects on CV and respiratory
- degree of analgesia
- risk if too concentrated
- route of administration
- minimal CV and respiratory effects
- no analgesia
- can cause hemolysis if concentration is too high
- administered IV only (necrosis) as a fast bolus and/or CRI
what is the most common agent used in horses for field procedures?
ketamine
what is a common analgesic drug cocktail that is given to horses for field procedures or a triple-drip during anesthesia?
KGX: ketamine, guaifenesin, xylazine
what are two complications of large animals in recumbency?
1. myopathy
2. tympanism in ruminants that have not been adequately fasted
what is the mortality rate of horses under general anesthesia?
1%
what are three common sedative/analgesic combinations used for horses pre-op?
1. Acepromazine ± alpha-2 agonists ± opioid
2. Acepromazine + opiod
3. Alpha-2 agonists ± opioid
why should you give morphine diluted and slowly, while observing the BP of a horse?
because it can cause histamine release when given IV
why should morphine be given with an α2 drug in horses for pre-op sedation?
because morphine alone can cause excitement
what is the most important thing to be sure of before you give horse anesthesia?
ADEQUATE SEDATION
what two injectable anesthetics should you not use in horses?
propofol and etomidate
what class of drugs is most commonly given to horses to induce anesthesia?
dissociatives (e.g. ketamine)
what happens if you accidentally inject ketamine perivascularly?
nothing
how do horses differ from donkeys and mules with injectable anesthetics?
donkeys and mules require more frequent dosing
comment on the depth of anesthesia in the horse if the horse is/has:
- blinking
- fast nystagmus
- slow nystagmus
- a strong palpebral reflex
- blinking: too light
- fast nystagmus: too light
- slow nystagmus: ok; assess other parameters
- strong palpebral reflex: this is normal under adequate anesthesia
Telazol:
- onset and duration
- induction quality
- use maintenance
- recovery quality
- onset: up to 2 minutes; duration 15-45 minutes
- good induction quality: smoother drop to ground, which is especially good for orthopedic patients
- usually you would re-dose with ketamine
- recovery can be rough due to excitement; re-dosing with ketamine will give a smoother recovery
what horses can you use propofol as induction agents?
foals
what is a long list of induction drug combinations for horses?
- Telazol (tiletamine + zolazepam)
- Ketamine + diazepam (or midazolam)
- Ketamine + GG
- Ketamine (with high dose xylazine sedation)
- Thiopental
- Thiopental + GG
- Propofol (foals)
- Propofol + Ketamine (foals)
inhalants in horse anesthesia
- advantages
- degree of muscle relaxation
- degree of analgesia
- CV and respiratory effects
- why is this tough to do in the field?
- advantages: Easier to control depth of anesthesia, Very little metabolisation
- Good muscle relaxation
- NOT analgesics
- Profound CV and respiratory depression
- field: Require anesthesia machine, which is not feasible
what is a big difference between an anesthesia machine that you would use on a dog versus a horse?
the horse anesthesia machine must be capable of much higher flow rates
what is the most popular analgesic used with horse inhalant general anesthesia? Why is it so popular?
- lidocaine
- enhances the anesthesia (e.g. ↓MAC) and ↑GI motility
what are five drugs that are used as analgesics and enhancers of inhalent anesthesia in the horse?
1. morphine
2. lidocaine
3. butorphanol
4. xylazine
5. ketamine
describe the following signs of LIGHT anesthesia in the horse:
- corneal reflex
- palpebral reflex
- lateral nystagmus
- unstimulated blinking
- eyeball position
- tear production
- corneal reflex: brisk
- palpebral reflex: brisk
- lateral nystagmus: present
- unstimulated blinking: present
- eyeball position: centered
- tear production: present
describe the following signs of ADEQUATE anesthesia in the horse:
- corneal reflex
- palpebral reflex
- lateral nystagmus
- unstimulated blinking
- eyeball position
- tear production
- corneal reflex: present
- palpebral reflex: slowed
- lateral nystagmus: absent
- unstimulated blinking: absent
- eyeball position: rotated (not in every horse)
- tear production: absent
describe the following signs of DEEP anesthesia in the horse:
- corneal reflex
- palpebral reflex
- lateral nystagmus
- unstimulated blinking
- eyeball position
- tear production
- corneal reflex: absent
- palpebral reflex: absent
- lateral nystagmus: absent
- unstimulated blinking: absent
- eyeball position: centered
- tear production: absent
what are four reasons why you want to use an invasive blood pressure monitor in horses under general anesthesia?
- leading cause of death is CV collapse
- high incidence of myositis in horses
- keep above 70 mmHg
- blood pressure spikes before eye changes when they wake up
what is an advantage and a disadvantage to providing positive pressure ventilation to the horse during anesthesia?
- prevents atelectasis
- causes CV depression
what is the preferred positive inotrope type to use in horses under general anesthesia?
β-agonists (versus α1 agonists)
what is the preferred specific positive inotrope given to horses under general anesthesia
dobutamine (versus dopamine, vasopressin, or norepinephrine)
what are six things to do/give to the horse during recovery from general anesthesia?
1. Sedation
2. Oxygen
3. Airway support (Oral or nasal tube)
4. Empty bladder
5. Cover eyes
6. Nasal decongestion (vasoconstrictors)
what are eight complications of general anesthesia in the horse?
1. Hypotension/CV collapse
2. Hypoventilation
3. V/Q mismatch
4. Myopathy
5. Nerve paralysis
6. Fractures
7. Airway obstruction (nasal swelling)
8. Excitement
fasting for bovine anesthesia:
- adults
- milk-fed calves
- Adults 18-24 hours if possible
- Milk-fed calves just a few hours
what are three common sedation protocols for bovine pre-op?
1. Alpha-2 agonist – REMEMBER LOWER DOSE
2. Alpha-2 agonist + butorphanol
3. Alpha-2 agonist + ketamine
what are the two most common local anesthetics given to bovines?
1. lidocaine
2. bupivacaine
what are five bovine injectable anesthesia protocols?
1. Ketamine
2. Ketamine + Diazepam
3. Ketamine + GG
4. Thiopental
5. Thiopental + GG
normal parameters of bovine inter-operative anesthesia:
- HR
- RR
- eye position
- BP
- HR: 60-80 beats per minute
- RR: 20-30 breaths per minute
- Eye position: Ventral rotation indicates surgical anesthetic depth; Central position could indicate too light OR too deep (!)
- Blood pressure: same as other mammals; Normotension is important to prevent myopathy
what are five potential complications during bovine general anesthesia?
1. tympany
2. regurgitation (don't use atropine)
3. hypoventilation
4. movement
5. hypotension
comment on using dobutamine in the bovine during anesthesia
they are VERY sensitive to it's tachycardic effects
bovine recovery from general anesthesia:
- optimal position
- excitement
- when do you extubate?
- sternal ASAP
- little to no excitation on recovery
- extubate only when they have good airway control
what are five things that make small ruminant general anesthesia a pain in the ass?
1. very narrow dental arcade
2. relatively long face and thick tongue
3. they regurgitate often
4. they may bloat
5. eye position is less useful than pupil size and shape
comment on the problem of regurgitation of small ruminants under anesthesia:
- plane of anesthesia at induction
- type of tube
- use of atropine
- you may need to make them "deeper" at induction to reduce regurgitation
- use a cuffed ET tube
- don't use atropine; it just makes secretions thicker
what are three common complications of small ruminant general anesthesia?
1. hypoxia
2. rumen tympany
3. hypotension
what are two sedation/analgesia protocols for the small ruminant?
1. Alpha-2 agonist
2. Alpha-2 agonist + opioid
what are four injectable induction protocols in the small ruminant?
1. Ketamine + Diazepam
2. Telazol
3. Thiopental
4. Propofol (smaller animals)
what is the best way to make sure that a small ruminant is properly intubated?
capnograph
small ruminant recovery from general anesthesia:
- optimal position
- excitement
- when do you extubate?
- maintain sternal recumbency
- usually no excitation
- extubate when they are swallowing effectively
which two types of large animals are obligate nasal breathers?
horses and camelids
what is an extremely important thing to be sure of when anesthetizing a camelid?
accurate weight
what is the preferred sedation/analgesia protocol for camelids, what are two others?
- α2 and buprenorphine (preferred)
1. xylazine
2. α2 + butorphanol
what two injectable drugs can cause perivascular necrosis?
thiopental and guaifenesin
what are three injectable induction protocols for camelids?
1. Ketamine + Diazepam
2. Propofol (smaller animals)
3. Thiopental
camelid anesthesia maintenance:
- HR
- RR
- BP
- eye position
- HR: 40-80 bpm
- RR: 20 bpm
- BP: same as other mammals
- eye position: less useful; pupil size and shape are more indicative
comment on eye position with camelids under general anesthesia:
- palpebral reflex
- spontaneous blink
- nystagmus
- palpebral reflex: maintained at adequate depth
- spontaneous blink: too light
- nystagmus: not usually visible
what do camelids tend to do during recovery that is weird?
Curl necks backward and swing head during recovery
how long should an adult pig be fasted before anesthesia?
12-24 hours
where is an IV catheter placed in a pig?
ear vein
what is different about the trachea of a pig (with regard to intubation) versus other animals?
it makes a dorsal bend at the level of the laryngeal vestibule, so the tube must be manipulated to get good intubation
what are the four steps of intubating a pig?
- position
- arytenoid visualization and treatment
- ET tube specifics
- technique to pass the tube
- Sternal recumbency, neck stretched up, mouth open with gauze
- Laryngoscope to visualize arytenoids, & spray lidocaine
- ET tube with stylet bent at tip into a curve
- Pass tube until you meet resistance, then turn 180 up, advance, and turn back down
what are two breeds of pigs predisposed to malignant hyperthermia?
Landrace and Duroc
what triggers malignant hyperthermia in pigs?
stress, depolarizing muscular blockers, inhalants (esp. halothane)
how do you treat malignant hyperthermia in the anesthetized pig?
- remove all inhalant
- actively cool the pig
- ventilate
- ± dantrolene (supposedly stabilized Ca release from the SR)
what are four complications of anesthesia in the pig?
1. malignant hyperthermia
2. regurgitation
3. hypothermia (no hair!)
4. hypotension (same likelihood as other animals)
comment on recovery of swine from anesthesia:
- temp
- smoothness
- monitor temperature closely; warming often needed
- recovery is generally smooth
which sedative is not very good for use in swine?
acepromazine
what are four premed/sedative protocols for swine general anesthesia?
1. Telazol
2. Telazol + xylazine
3. Ketamine ± midazolam ± butorphanol
4. Also Telazol, ketamine, xylazine (TKX) – but this takes them deeper, in between premed and induction
what are four injectable induction protocols used in swine?
1. Ketamine ± diazepam
2. Propofol (smaller animals)
3. Telazol
4. Thiopental – phlebitis in small vessels
what are two physiologic characteristics of the cat that complicates anesthesia in them versus dogs?
1. hepatic enzyme deficiencies
2. laryngospasm
fasting for general anesthesia in the cat:
- adults
- young kittens
- adults: 8-12 hours
- kittens: 1-2 hours
why is UA important in the feline pre-op exam?
because renal failure is common
how long does it take lidocaine to relax the arytenoids?
30 sec - 1 minute or so
if you apply lidocaine to a cat's arytenoids and after about 2 minutes, you are still getting laryngospasm, what are two things you can do other than applying more lidocaine to help intubation?
1. use a stylet
2. use more induction drug
normal parameters of feline inter-operative anesthesia:
- HR
- RR
- eye position
- BP
- HR: 120-160 bpm
- RR 10-20 bpm
- eye: ventro-medial
- BP: same as other mammals
what are three potential complications during feline general anesthesia?
1. hypothermia - small or skinny patients
2. hypotension - very sensitive to volume overload, so watch your drip rate
3. bronchoconstriction - underlying asthma, reactive airway
how can you tell if a cat may be having bronchoconstriction during general anesthesia?
squeeze the reservoir bag; if bronchoconstriction, the bag may be stiff
what are three complications of feline general anesthesia during the recovery phase?
1. HYPERthermia - "cats get hot"; young healthy animals
2. HYPOthermia: common; warming PRN (don't use a heat lamp)
3. slow recovery - delayed metabolism? Reversal?
what comprise a "kitty bomb" or "kitty magic"?
ketamine, dexmedetomidine, opiod (e.g. butorphanol or buprenorphine)
what are three sedation protocols for feline general anesthesia?
1. "kitty bomb": ketamine, dexmedetomidine, opiod
2. acepromazine + opiod (slow - 20 minutes)
3. ketamine + midazolam ± opiod (not common; 5 minutes)
what are three injectable induction protocols for feline general anesthesia?
1. propofol
2. diazepam + ketamine
3. Telazol