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235 Cards in this Set

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what is the mechanism of action of opioids?
- bind at pre- and postsynaptic CNS sites and peripheral tissues
- activation of opioid receptors
- presynaptic inhibition of acetylcholine, norepinephrine, and substance P release
- this decrease of neurotransmitter release decreases neurotransmission
where does opioid-modulated pain inhibition occur?
in the dorsal horn of the spinal cord
what are the cardiovascular effects of opioids?
- minimal
- bradycardia: vagal, SA node
what are the respiratory effects of opioids?
1. depression
2. decrease RR
3. decrease tidal volume
what is minute volume, and how is it calculated?
it is the volume of respired air in the alveoli per minute and is calculated: minute volume = RR x tidal volume
what are six CNS effects of opioids?
1. analgesia
2. sedation
3. excitation/dysphoria
4. nausea/vomiting
5. reset thermoregulatory center
6. may increase intracranial pressure (if PaCO2 is not controlled)
with opioids, how does the duration of sedation correlate with the duration of analgesia?
they are not correlated
what is usually required of opioids to cause excitation/dysphoria/mania?
high doses. N.B. cats are particularly susceptible
with administration of opioids, which species exhibit miosis? Which exhibit mydriasis?
- miosis: dog, rabbit, rat
- mydriasis: cat, horse, sheep, monkey
what are three GI effects of opioids?
1. emptying followed by decreased motility
2. constipation
3. increased biliary pressure
name 7 full opioid agonists
1. morphine
2. hydromorphone
3. oxymorphone
4. fentanyl
5. methadone
6. sufentanil
7. remifentanil
what is the effect and mechanism of action of guaifenesin?
- centrally acting muscle relaxant
- inhibits reflex arcs in the spinal cord and brainstem, reducing postural muscle strength
comment on guaifenesin:
- distribution
- effect on respiration
- used in which species?
- sedation
- CV effects
- widely distributed and crosses the BBB and placenta
- does not affect ventilation
- mainly used in horses and ruminants
- causes some level of sedation
- minimal CV effects; some hypotension
what are four undesirable effects of guaifenesin?
1. hemolysis and thrombosis
2. irritant to tissues
3. can accumulate in tissues if too much is infused
4. crosses the placenta
name four classes of injectable anesthetics
1. barbiturates
2. propofol
3. etomidate
4. dissociatives
what are four properties of barbiturates modified by substitution of functional groups?
1. onset and duration
2. lipid solubility
3. seizure activity
4. anticonvulsant activity
what are the three pharmacodynamic targets of barbiturates?
1. GABA-A receptor agonist
2. Glu receptor antagonist
3. ion channels
what three pharmacokinetic properties are most important in determining the depth of anesthesia with barbiturates?
1. dose
2. ionization
3. plasma protein binding
what are the two most important determinants of the duration of barbiturate anesthesia (other than dose)?
1. redistribution
2. degree of metabolism
in which dogs will barbiturate anesthesia last longer and why?
Greyhounds (and other hounds) due to slower CYP-450 metabolism
in what three ways are barbiturates metabolized?
1. oxidation of functional groups at C5 ("para" to the carbonyl)
2. desulfuration of the carbonyl (i.e. thiopental)
3. demethylation at the nitrogen
comment on the analgesic effects of barbiturates?
no analgesia
why are barbiturates desirable in patients with cerebral edema?
1. they decrease cerebral blood flow
2. they decrease cerebral metabolic rate
3. they decrease intracranial pressure
what are six CNS effects of thiopental?
1. dose-dependent depression
2. ↓cerebral blood flow, cerebral metabolic rate, and ICP
3. ↓thermoregulatory center
4. vagolytic
5. ↓respiratory center
6. ↓vasomotor center
what are five dose-dependent depressive CV effects of thiopental?
1. ↓CO
2. ↓SV
3. ↓contractility
4. ↓BP
5. ↓peripheral vascular resistance
what are three effects of thiopental on the heart?
1. initial transient ↑HR (offsets ↓BP)
2. sensitizes myocardium to endogenous catecholamines (stressed animals → possible arrhythmia)
3. ventricular arrhythmias, especially bigeminy
what are four dose-dependent respiratory effects of thiopental?
1. ↓RR
2. ↓tidal volume
3. ↑CO2 threshold
4. post-induction apnea
comment on the proper technique of thiopental administration
since it has a very high pH, it must be given with an IV catheter, not a needle. If it is injected perivascular, it will cause sloughing.
what are six advantages of thiopental?
1. CNS depression
2. fast onset (30 sec)
3. ultra-short acting (5-10 min)
4. decreases ICP
5. long shelf life
6. inexpensive
what are six disadvantages of thiopental?
1. CV depression
2. respiratory depression
3. cumulative effects
4. no analgesia
5. irritant if perivascular
6. rough recovery if given alone
propofol:
- type of molecule
- duration of action
- pharmaceutical prep
- alkylphenol
- ultra-short acting
- insoluble in water, so it comes as a 1% emulsion
comment on the shelf life of propofol
- stable at room temp
- light resistant
- supports bacterial growth because there is no preservative
what is the mechanism of action of propofol?
- GABA-A interaction
- increases the duration of opening of Cl channel
- hyperpolarization
what are five favorable CNS effects of propofol?
1. rapid onset of anesthesia
2. rapid, reversible depression of cerebral activity after redistribution
3. ↓ICP, ↓CBF
4. anticonvulsant
5. ↓intraocular pressure
what is a noteworthy side-effect of propofol that may be noticed during surgery?
isolated muscle twitching (myoclonus)
propofol:
- effect on BP
- effect on HR
- comment on arrhythmias
- hypotension (may be greater than thiopental); decreases vascular resistance
- HR same or INCREASED
- usually does not cause arrhythmias, but may enhance epinephrine-induced arrhythmias
what are four undesirable respiratory effects of propofol?
1. profound respiratory depressant
2. RATE and DOSE dependent apnea
3. may see cyanosis
4. mild hypercapnia
why must propofol be administered very slowly
because if given too fast (bolus too large), a rate-dependent respiratory depression and apnea may occur
what is a noteworthy side-effect of propofol when given to cats?
may cause Heinz body anemia
what drug is known to cause Heinz body anemia in cats?
propofol
comment on the metabolism and elimination of propofol
- cleared by the lungs and liver
- clearance from plasma exceeds hepatic blood flow
- excreted mostly as the glucuronide by the kidney
which injectable anesthetics are best for C-sections?
propofol and etomidate
what are seven advantages of propofol?
1. rapid onset
2. short acting
3. non-cumulative (versus barbiturates)
4. no tissue irritation (versus barbiturates)
5. ↓ICP and IOP
6. safe for C-section
7. no hang-over
what are six disadvantages of propofol?
1. supports bacterial growth in the container
2. short shelf life
3. CV depressant
4. respiratory depressant
5. no analgesia
6. myoclonus can occur
what is Propofol 28?
it is propofol with benzyl alcohol added to it to increase shelf life. It is good for 28 days after opening. Use with caution in cats, and the drug is meant to be a single dose only, not a CRI
what are some advantages of using propofol and ketamine together?
- less dosage of each drug needed so ↓side effects
- opposing CV effects, so theoretically balance each other out
- less CV and respiratory depression
why should etomidate be injected slowly?
because it is in 35% propylene glycol solution and can cause pain on injection and hemolysis
what is the mechanism of action of etomidate?
- not completely known
- indirectly enhances the effect of GABA
- directly ↑Chloride ion transport at high doses
what are four CNS effects of etomidate?
1. ↓CBF, ICP, CMR
2. maintains cerebral cerebral perfusion pressure (CPP = MAP - ICP)
3. anticonvulsant
4. involuntary myoclonic movements
what two drugs are known to cause involuntary myoclonic movements?
propofol and etomidate
what are the CV effects of etomidate?
minimal; drug of choice for CV compromised patients
what are the respiratory effects of etomidate?
slight depression
what is the injectable anesthetic drug of choice for patients with CV disease or those that are hemodynamically unstable?
etomidate
which drug should you use with caution in patients with Addison's disease? Why?
etomidate. It decreases the synthesis of cortisol, which occurs 3-4 hours after a single dose
what are six advantages of etomidate?
- fast onset
- ultra-short duration
- minimal cardiopulmonary effects
- ↓ICP, IOP
- good choice for unstable C-section
- wider therapeutic index
what are six disadvantages of etomidate?
1. adrenal suppression
2. no analgesia
3. retching, nausea, vomiting
4. myoclonus
5. hemolysis, pain on injection
6. expensive
what are two dissociative anesthetics used in vet med?
1. ketamine
2. tiletamine (comes combines with zolazepam, a benzodiazepine)
what is the mechanism of action of ketamine?
- non-competitive antagonist at the NMDA receptor (blocks Glu)
- may have action at opioid receptors, muscarinic, voltage-sensitive channels (Na, K, Ca), weak action at GABA-A
comment on the analgesic effects of ketamine.
- prolongs the effect of local anesthetics
- analgesic at subclinical doses (reduces hyperalgesia and helps prevent chronic pain)
- lowers the amount of inhalant anesthesia needed
what is the disadvantage of giving ketamine orally?
high 1st pass effect
what is the injectable anesthetic drug type of choice for fractious / wild animals? Why?
ketamine. Because it can be injected IM (dart) or given orally (e.g. hissing cat)
what are four dose-dependent CNS effects of ketamine?
1. unconsciousness and analgesia
2. may cause seizures in animals with a HX of epilepsy
3. INCREASES ICP, CMR, CFP pressure, and CBP due to vasodilation
4. hallucinations
how are the hallucinatory effects of ketamine avoided?
by premedicating with sedatives, tranquilizers, or opioids
what are the CV effects of ketamine?
1. ↑HR, CO, and BP
2. CNS-based sympathetic stimulation
3. systemic vascular resistance unchanged or increased
4. negative inotrope (only seen in critical patients)
5. ↑myocardial O2 demand
6. hypotension in critically ill patients due to depletion of catecholamine stores and exhaustion of sympathetic compensatory mechanism
what is apneustic breathing? What drug commonly causes this effect?
holding breath on inspiration. Ketamine causes this.
what are seven respiratory effects of ketamine?
1. no significant depression
2. may increase RR and tidal volume
3. PaCO2 maintained
4. apneustic breathing
5. pharyngeal/laryngeal reflex intact (will try to swallow, makes intubation a little more difficult)
6. increases tracheal-bronchial secretions
7. increases salivation (need to use anticholinergics and suction)
comment on ketamine's affect on the eyes and the eye reflexes
- ↑ intraocular pressure
- eyes remain open
- palpebral and cornel reflex maintained
ketamine:
- onset
- duration
- onset: IV 40-90 seconds; IM 3-5 minutes
- duration: IV 3-10 minutes; IM 10-30 minutes
comment on the difference between using tiletamine (Telazol) on dogs versus cats
- in the dog tiletamine lasts 1.2 hours, whereas zolazepam lasts 1 hour. Emergence delirium
- in the cat, tiletamine lasts 2.5 hours, whereas zolazepam lasts 4.5 hours. Prolonged recovery, but less delirium than in dogs
what are six advantages of dissociative anesthetics?
1. unconsciousness
2. analgesia
3. CV stimulation
4. less respiratory depression
5. small volume
6. inexpensive
what are eight disadvantages of dissociative anesthetics?
1. ↑ muscle tone
2. negative inotrope (CV diseased animals)
3. ↑ICP, ↑IOP
4. eyes remain open → corneal ulcers (lube the eyes!)
5. seizures
6. ↑salivation
7. apneustic breathing
8. excitement during recovery
rank thiopental, propofol, etomidate, and ketamine from best to worst for induction
1. thiopental and propofol
2. ketamine
3. etomidate
rank thiopental, propofol, etomidate, and ketamine from best to worst for recovery
1. propofol
2. thiopental and etomidate
3. ketamine
rank thiopental, propofol, etomidate, and ketamine from best to worst for therapeutic margin
1. etomidate
2. ketamine
3. thiopental and propofol
rank thiopental, propofol, etomidate, and ketamine from best to worst for CNS effects
1. thiopental
2. propofol
3. etomidate
4. ketamine
rank thiopental, propofol, etomidate, and ketamine from best to worst for CV effects
1. etomidate
2. ketamine
3. thiopental
4. propofol
rank thiopental, propofol, etomidate, and ketamine from best to worst for respiratory effects
1. etomidate
2. ketamine
3. thiopental
4. propofol
what injectable anesthetic has the roughest induction?
etomidate
what injectable anesthetic has the worst recovery?
ketamine
what injectable anesthetic has the best therapeutic index?
etomidate
what injectable anesthetic has the worst CNS effects?
ketamine
what injectable anesthetic has the worst CV effects?
propofol
what injectable anesthetic has the worst respiratory effects?
propofol
what is the preferred method of administration of anesthetic in:
- nice animals
- aggressive/fractious animals
- nice animals: titrate to effect; takes longer, but more reliable
- aggressive/fractious: bolus; quicker effect, but may overshoot or undershoot the therapeutic window
which domestic animals are anesthetized with inhalent induction?
- small animals (guinea pigs, rodents, reptiles, etc.)
- foals via intranasal intubation
what are four things you should do after your patient is unconscious from anesthesia?
1. control the airway
2. check for life
3. begin monitoring and recording vitals
4. switch to maintenance anesthetic
what are two ways to make sure an endotracheal tube is properly placed?
1. visualize the tube between the arytenoids
2. look at capnograph
when checking for proper endotracheal cuff inflation, what is the proper pressure to test for leakage?
20 cm H2O
what are three ways to confirm that your endotracheal tube has been placed at the appropriate depth?
1. measure
2. palpate (feel the cuff at the thoracic inlet)
3. listen (air movement in both sets of lungs)
what are the four steps of proper intubation?
1. make sure it is in the trachea
2. inflate the cuff
3. confirm appropriate depth
4. tie it in
how should an endotracheal tube be tied?
gauze tight on the tube, but gentle on the patient's head
what is on many tubes that allows for airflow if the tube end is blocked?
Murphy eye
what unit is the diameter of an endotracheal tube measured in?
mm
what are the two types of endotracheal tube cuffs and what is the advantage of each?
1. high volume/low pressure - less risk of tracheal damage
2. low volume/high pressure - cuff flattens out well for a better seal
what are three materials that are used to make endotracheal tubes?
1. rubber (red)
2. PVC
3. silicone
what type of endotracheal tube does not have a Murphy eye?
Magill
what is a Cole endotracheal tube?
a stiff tube with no cuff that inserts more proximal than Magill or Murphy tubes
what are three alternatives to endotracheal intubation?
1. nasotracheal intubation
2. laryngeal mask
3. face mask
what are the official tank colors for
- oxygen?
- nitrous oxide?
- medical grade air?
- oxygen: green (US) white (the rest of the world)
- N2O: blue
- air: yellow
what is the minimum alveolar concentration of oxygen needed during anesthesia?
25 - 33% (note, near 100% with our anesthesia machines)
what is the pressure and volume of oxygen in a full cylinder?
1900 psig; 660 L
how do you convert from oxygen pressure to volume in an oxygen tank?
V = pressure * 0.35
the anesthesia machine's low pressure system operates under what pressure?
40-55 psig
what is the thing that is used to hang cylinders onto the anesthesia machine?
hanger yoke
how should flow meters be positioned on the anesthesia machine and why?
oxygen on the right. This is because if there is a crack in the line, the machine will still deliver oxygen.
what two variables do inhalant anesthetic vaporizers compensate for?
flow and temperature
all gases exit the anesthesia machine through what?
the common gas outlet
how often should an anesthesia machine be serviced?
every 6 - 12 months, including vaporizer calibration
if you don't have a backup tank ready to go, what is the minimum time and pressure that you should have left in the oxygen tank?
30 minutes; 200 psi
what are the two types of rebreathing systems?
1. circle system
2. Universal F
what is used to vent excess pressure in the rebreathing system?
the APL (pop-off) valve
how do you select the proper reservoir bag size in a rebreathing system?
50-75 mL/kg (5 x tidal volume)
what three things are produced when CO2 reacts with soda lime?
1. water
2. salt
3. heat
what are the two types of non-rebreathing systems?
1. Bain system
2. Mapleson system
what is measured when doing a pressure check on a breathing system?
must hold 30 cmH2O for at least 10 seconds
how does the weight of the animal determine what type of breathing system you will use?
- animals < 7kg use non-rebreathing
- animals > 7kg use rebreathing
what is the induction flow rate for a rebreathing system?
40-60 mL/kg/min
what is the maintenance flow rate for a rebreathing system?
20-40 mL/kg/min
what is the range, typical flow rate, and minimal flow rate of a non-rebreathing system
- range: 100-300 mL/kg/min
- typical: 150 mL/kg/min
- minimum: 500 mL/min
what is the one anesthetic that is NOT adsorbed by the charcoal canister at the passive scavenging system?
nitrous oxide
what are two hypothetical ways in which alveolar partial pressure can be made remain constant if it is dropping?
1. increase delivery
2. decrease uptake
during induction, how do you maximize the rate to achieve MAC?
increase the inspired partial pressure (with manual ventilation) to saturate the blood as quickly as possible and then reduce for maintenance
what two factors intrinsic to the animal affect alveolar ventilation?
1. tidal volume
2. respiratory rate
what is the time constant?
the time required for flow through a container to equal the capacity of the container (e.g. if flow is 1 L/min and the container has a 5L capacity, the time constant is 5 minutes)
what aspects of the lung affect the time constant?
functional residual capacity ÷ alveolar ventilation rate
what aspects of the anesthetic circuit affect the time constant?
circuit capacity ÷ fresh gas flow
what property of an inhalant anesthetic relates most to the speed of onset?
solubility in the blood
what is the blood:gas partition coefficient?
a measurement at equilibrium of blood solubility and therefore the speed of onset. BGPC = [blood]/[alveolar gas]
which anesthetic has the lowest blood solubility?
sevoflurane
what are the two major factors that offset the rise of alveolar pressure (P_A) during induction?
1. anesthetic blood solubility
2. cardiac output
what are the four body compartments, in order of decreasing cardiac output, that are considered when using inhalant anesthetics?
1. vessel-rich group (75% CO)
2. muscle group (18% CO)
3. fat group (5.5% CO)
4. vessel poor group (1.5% CO)
why can compromised cardiac output lead to higher levels of anesthesia in the brain?
during low cardiac output, blood flow will divert to the vessel-rich group (brain, heart, lungs), which comprises only 10% of the mass of the body. So more anesthetic agent will reach the brain because a greater amount of the cardiac output will flow through the brain.
versus a normal animal, how fast will the clinical onset of anesthesia occur in animals that are
- sick or debilitated?
- CV compromised?
- stressed or excited?
- hypotensive?
- sick, debilitated, CV compromised, and hypotensive will all have a more rapid onset because they will have a higher circulation to their brain because of impaired cardiac output
- stressed or excited animals will have a slower onset of anesthesia because they have a higher cardiac output, more blood flow to muscles, etc., and more expiration of gas via the lungs
what are three factors of the body / inhalant anesthetic that will cause a faster rise in alveolar pressure and therefore a faster onset of anesthesia?
1. good alveolar ventilation
2. low cardiac output
3. low anesthetic solubility
what is MAC? How is it determined?
- minimum alveolar concentration
- percent at which 50% of animals will not move in response to a surgical stimulus
what is the appropriate MAC for surgical anesthesia in most animals?
1.2 - 1.3 x MAC
what property of an inhalant anesthetic relates most to its potency?
MAC
what are eight factors that decrease the MAC of inhalants?
1. hypothermia
2. pregnancy
3. very old or very young age
4. hypothyroidism
5. hypotension (MAP < 50 mmHg)
6. Hypoxemia (< 40 mmHg)
7. Hypercarbia (> 95 mmHg)
8. concomitant anesthetic drugs (inhalants, injectables, sedative, analgesics)
what are three physiologic factors that can increase the relative MAC of an inhalant?
1. hyperthermia
2. hyperthyroidism
3. CNS stimulant drugs (↑CNS catecholamines; e.g. ephedrine, amphetamines)
comment on the analgesic effects of inhalant anesthetics
they provide no analgesia
what are three effects, on the CNS vasculature, of inhalant anesthetics?
1. ↑CBF
2. ↓CMR
3. ↑ICP
what is the minimum and maximum MAP to maintain a CBF of 50 mmHg?
minimum: 60 mmHg; maximum: 160 mmHg
at what PaCO2 will induce hyperventilation?
PaCO2 < 35 mmHg
what two dose-dependent effects do inhalant anesthetics have on the heart?
1. ↓contractility
2. ↓CO (more pronounced at high doses)
how does MAP change with inhalant anesthesia alveolar concentration?
it decreases linearly. Different anesthetics have different slopes and different MAP values at 1 x MAC
why can stress/excitement predispose an animal to cardiac arrhythmias when they are under inhalant anesthetics?
because stress/excitement leads to ↑catecholamines; inhalant anesthetics sensitize the myocardium to catecholamine-induced arrhythmias
what is IPPV?
intermittent positive-pressure ventilation (mechanical ventilation, e.g. with the reservoir bag)
what are four factors that influence cardiovascular effects with inhalant anesthetic agents?
1. mode of ventilation (e.g. spontaneous vs. mechanical)
2. noxious stimulation
3. duration of anesthesia (after several hours; this is more important in research than a clinical setting)
4. concurrent drug administration
what are two ways that sedatives and injectable anesthetics administered concurrently with inhalant anesthetics affect the cardiovascular system?
(decrease MAC)
1. decrease effects from inhalant
2. may accentuate CV depression
under inhalant anesthesia, how do positive inotropes/vasopressors
- affect MAC?
- affect CV depression?
- they do not affect the MAC
- they counteract CV depression by ↑CO, and may consequently lighten anesthetic depth
what is the Apneic index?
a measure of how much anesthesia (e.g. in 50% of animals) will stop breathing in measures of multiples of MAC
what is hypoxic drive? How is it influenced by inhalant anesthetics?
- hypoxic drive is when the body uses O2 receptors instead of CO2 receptors to regulate respiration. It causes pulmonary vasoconstriction to ↑ blood flow rate through the lungs
- inhalant anesthetics suppress hypoxic drive
which receptors normally control ventilation?
CO2 pressure receptors
under our normal inhalant anesthetic protocol, what two things cause decreased lung volume?
1. atelectasis (partially due to the fact that there is no nitrogen; "nitrogen is the skeleton of the alveoli")
2. relaxation of the intercostal muscles and the diaphragm
what are three local respiratory effects that occur due to inhalant anesthesia?
1. decreased lung volume
2. bronchodilation → increased dead space ventilation
3. irritation of the airway due to pungency (sevo is the least irritating)
what are three hepatic effects of inhalant anesthetics?
1. depression of hepatic function or hepatocellular damage - mild, transient, or permanent (ISO, SEVO, DES maintain adequate O2 tissue supply and are less likely to cause liver injury)
2. reduce intrinsic hepatic clearance of drugs
3. reduce hepatic blood flow
what are three dose-dependent effects of inhalant anesthetics on the kidney?
1. ↓renal blood flow
2. ↓glomerular filtration
3. ↓low urine output (but kidney still concentrates the urine)
why do inhalent anesthetics cause depressive effects on the kidney?
mainly because the renal blood pressure is lower; effects are reversed after anesthesia
what are two nephrotoxic effects of sevoflurane?
1. SEVO breakdown causes ↑serum fluoride concentration
2. soda lime produces Compound A, which has been shown to be nephrotoxic in rats (but no clear evidence in dogs, cats, or horses)
what is the major pathway by which inhalent anesthetics are eliminated from the body?
lungs
which species are affected by malignant hyperthermia?
swine and humans
what drug is used to treat malignant hyperthermia?
Dantrolene IV
how do inhalant anesthetics affect the following?
- HR
- SV
- CO
- PVR (peripheral vascular resistance)
- BP
- RR
- HR: ↑
- SV: ↓
- CO: ↓
- PVR (peripheral vascular resistance): ↓↓
- BP: ↓
- RR: ↓
what are the five major ways in which we determine anesthetic depth?
1. respiratory signs
2. CV effects
3. eye signs
4. reflexes
5. muscle tone
what are three respiratory signs used to determine anesthetic depth?
1. rate
2. depth
3. presence of abdominal effort
what are four CV signs used to determine anesthetic depth?
1. HR
2. BP (arterial)
3. MM color
4. CRT
what are three eye signs used to determine anesthetic depth?
1. eye position
2. nystagmus
3. is the animal blinking (without stimulus)
what are four reflexes used to determine anesthetic depth?
1. palpebral
2. corneal
3. pupillary light
4. pedal (toe pinch) / prick coronary band in large animals
comment on the major clinical signs of the four planes of Stage 3.
- Plane 1: nystagmus, slower RR
- Plane 2: ventromedial pupil, relaxed jaw tone
- Plane 3: central pupil, corneal reflex absent
- Plane 4: decreased BP, shallow respirations
Characterize Stage 1:
- movement
- respiration
- pulse
- BP
- voluntary movement, alert and arousable
- respiration may be rapid
- normal to rapid pulse
- normal to high BP
Characterize Stage 2:
- movement
- pulse
- BP
- respiratory reflexes
- eye signs
- muscle tone
- involuntary movement
- rapid pulse
- high BP
- patient can swallow and cough
- nystagmus, pupils constricted, pupillary light response present
- high muscle tone
Characterize Stage 4:
- eye signs
- pulse
- BP
- respiration
- central dilated pupil; no pupillary light reflex; no corneal reflex
- rapid pulse
- low BP
- apnea or agonal breathing
what are four major classes of anesthesia premeds?
1. anticholinergics
2. tranquilizers/sedatives
3. opioids
4. guaifenesin
anticholinergics:
- mechanism of action
- reversibility
-competitive agonist of Ach at muscarinic cholinergic receptors
- reversible effect
what are three uses of anticholinergics in premedication for anesthesia?
1. prevent and treat bradycardia
2. decrease respiratory secretions
3. decrease salivation
when used in anesthesia, what two specific effects does atropine have on the heart?
1. increase heart rate
2. 2° AV block at low doses
what are the effects of atropine on the
- respiratory system?
- eye?
- GI tract?
- respiratory system: bronchodilation
- eye: mydriasis (pupil dilation)
- GI tract: stasis
comment on the ability of atropine to cross
- the BBB
- the placenta
crosses both the BBB and placenta
atropine:
- routes of administration
- duration of action
- metabolism
- administered SQ, IM, IV
- duration: 60-90 min
- hepatic metabolism; cats, rats and rabbits have atropine esterases that metabolize atropine faster than other animals
what must you consider when administering atropine to cats?
they have hepatic atropine esterases that metabolize atropine faster than other animals. Need higher or more frequent doses.
what are two anticholinergic drugs typically administered as premedication to anesthesia?
atropine and glycopyrrolate
name three classes of tranquilizers/sedatives typically administered as premedication to anesthesia
1. phenothiazines
2. benzodiazepines
3. α2 agonists
what type of drug is atropine?
anticholinergic (parasympatholytic)
what type of drug is glycopyrrolate?
anticholinergic (parasympatholytic)
in what ways does glycopyrrolate differ from atropine in the context of premedication for anesthesia?
- does not cross the BBB
- does not cross the placenta
- longer onset and duration
if a pregnant bulldog comes in for an emergency C-section for dystocia, and is experiencing bradycardia, what drug would you administer and why?
you would administer glycopyrrolate (versus atropine), an anticholinergic because it will ↑the mother's HR, but since it does not cross the placenta, will not ↑the fetus' heart rates (note: ↑fetal heart rate during dystocia lowers their prognosis due to risk of hypoxia)
what are three contraindications of using anticholinergics for anesthetic premedication?
1. preexisting tachycardia
2. narrow angle glaucoma and synechia (adhesion of iris to cornea or lens)
3. horses - may cause colic
what class of drug is acepromazine?
a phenothiazine
what are four uses of acepromazine for anesthetic premedication?
1. sedation (strong)
2. antiemetic
3. antiarrhythmetic
4. antihistamine
what are three mechanisms of action of acepromazine that are important in anesthetic premedication?
1. CNS dopamine blockade
2. antiseritonergic
3. α1 blockade
what are four basic CV effects of acepromazine?
1. vasodilation
2. reflex tachycardia (from baroreceptors compensating for vasodilation)
3. decreases myocardial sensitization
4. decreases PCV (splenic relaxation due suppression of vasomotor reflex), TP, and platelet function
comment on acepromazine in the context of anesthetic premedication:
- respiratory effects
- CNS effects
- seizure risk
- analgesia
- minimal respiratory effects
- CNS depression and sedation
- does not decrease seizure threshold (as opposed to the obsolete chlorpromazine)
- no analgesia
how long before surgery should acepromazine be given to utilize its antiemetic effects?
30 minutes
why should acepromazine be used with caution in intact male horses?
it causes relaxation of the retractor penis muscle, and since it has a long duration, could lead to injury
what are four contraindications of acepromazine due to its vasodilator effects?
1. severe liver disease
2. hypovolemia
3. anemia
4. shock
what serious side-effect can occur when using acepromazine with excited animals?
epinephrine reversal: because α1 activity is blocked, epinephrine will cause a β2-mediated peripheral vasodilation, leading to severe hypotension
what are five advantages of using acepromazine as a premedication?
1. good sedation
2. decreases the MAC (minimum alveolar concentration) of inhalant anesthetics
3. minimal respiratory effects
4. antiarrhythmetic
5. very inexpensive
what are four disadvantages of using acepromazine as a premedication?
1. irreversible
2. high doses lead to hypotension
3. no analgesia
4. long lasting
what are four indications for benzodiazepines as a premedication?
1. mild sedation
2. anxiolysis
3. anticonvulsant
4. muscle relaxation
what is the mechanism of action of benzodiazepines?
- binds to GABA-A receptors
- increases the affinity of GABA
- increase the frequency of channel opening
- potentiates the inhibitory effects of GABA
what are the CV effects of diazepam?
- minimal
- since it is in 40% propylene glycol, it may cause a venous thrombus or pain on injection
what are the respiratory effects of diazepam?
- minimal, but may exaggerate depressant effects of opioids
what are six desirable and undesirable CNS effects of diazepam?
1. calming effect
2. reduce fear and anxiety
3. minimal sedation
4. disinhibition (paradoxical excitement), especially in young animals
5. anticonvulsant
6. muscle relaxation
diazepam:
- routes of administration
- polarity
- absorption
- metabolism
- elimination
- IM or IV (PO not used in anesthesia and erratic absorption SC)
- highly lipophilic
- well absorbed by GI (but not used PO)
- hepatic metabolism produces active metabolites
- excretion in the urine & feces
what are three benzodiazepines used in premedication?
1. diazepam
2. midazolam
3. zolazepam (always comes as a 1:1 mixture with tiletamine (Telazol), a dissociative anesthetic)
how does midazolam differ from diazepam?
- water soluble at acidic pH
- lipid soluble at physiologic pH
- can be given SC
- shorter duration than diazepam
- more expensive
what is the reversal agent for benzodiazepines?
flumazenil
flumazenil:
- indications
- mechanism of action
- duration of action
- benzodiazepine reversal
- competitive antagonism at the GABA receptor
- short acting: 60 minutes
what are four indications of α2 receptor agonists
1. sedation
2. analgesia
3. muscle relaxation
4. anxiolysis
what are three cardio effects of α2 receptor agonists?
1. bradycardia
2. first-degree AV block (↑PR interval)
3. second-degree AV block
what are the two Phases of CV effects when administering α2 receptor agonists, the mechanism, and clinical signs?
- 1st phase: initial hypertension/vasoconstriction from agonism of post-synaptic α1 and α2 receptors; decreases cardiac output up to 50%
- 2nd phase: hypotension/vasodilation from presynaptic α2 agonism → ↓synaptic outflow; decreased myocardial perfusion, pale mucous membranes
what are four respiratory effects of α2 receptor agonists?
1. decrease RR
2. may decrease tidal volume
3. respiratory depression potentiated with other sedatives
4. peripheral venous desaturation
what are four CNS effects of α2 receptor agonists?
1. dose-dependent sedation
2. analgesia
3. muscle relaxation
4. personality changes
what are seven "other" side-effects of α2 receptor agonists?
1. emesis (cats)
2. ↓GI motility
3. ↓thermoregulation
4. hyperglycemia
5. ↑uterine tone
6. ↑urine production
7. nasal congestion/facial edema (bad for horses, who are nose breathers)
what are the six steps of general anesthesia?
1. patient assessment
2. patient preparation
3. premedication
4. induction
5. maintenance
6. recovery
in anesthesia, what is considered
- neonatal?
- juvenile?
- geriatric?
- neonatal: <1 mo.
- juvenile: < 3mo
- geriatric > 75% life expectancy
what is the minimal database needed for anesthesia?
- PCV, TP, glucose, BUN/Azo, USG
what are four components of a basic pre-anesthesia patient assessment?
1. history
2. PE
3. blood work
4. additional exams (e.g. rad, US, EKG)
what an ASA I status?
normal, healthy patient, elective procedure
what an ASA II status?
slight to mild systemic disease, no obvious clinical signs
what an ASA III status?
mild to moderate systemic disease with clinical signs under control
what an ASA IV status?
severe systemic disease, life threatening, patient decompensated
what an ASA V status?
moribund patient, not expected to survive > 24 h
what aspect of anesthesia is not technically considered a component of general anesthesia?
pain management
what is the preferred α2 receptor antagonist to be used as a reversal agent?
atipemazole (Antisedan™)
atipemazole:
- type of drug
- indications
- onset of action
- route of administration
- dosage
- α2 antagonist
- reversal of α2 drugs
- reversal in 5-10 minutes
- given IM only to avoid effects of sudden reversal
- dose = volume of medetomidine or dexmedetomidine given
name three α2 receptor antagonists used for reversal of α2 drugs.
1. atipemazole (preferred)
2. yohimbine (less α2 selective)
2. tolazoline (least α2 selective)
name five α2 agonists used for premedication
1. xylazine
2. detomidine
3. medetomidine
4. dexmedetomidine
5. romifidine (horses only)
what are nine contraindications for α2 agonists?
1. preexisting cardiac disease (arrhythmias)
2. hypotension
3. shock
4. severe hepatic disease
5. renal insufficiency
6. urinary tract obstruction (cats, ruminants)
7. epilepsy
8. last trimester of pregnancy (cattle)
9. diabetes
comment on species differences in sensitivity to xylazine
cattle > horse = dog = cat > pig
in which animals is detomidine approved for use?
horse and cattle
how can you cause inadvertent arousal of an animal under an α2 agonist?
auditory stimuli
why would romifidine be chosen over other α2 agonists for horse premedication?
less ataxic effects than the others
what are four advantages of α2 agonists in premedication?
1. dose-dependent sedation
2. dose-dependent analgesia
3. muscle relaxation
4. reversal agent (e.g. atipemazole)
what are four disadvantages of α2 agonists for premedication?
1. significant CV depression
2. mild respiratory depression
3. emesis (cats)
4. inconsistent in excited patients