Anesthesia Flashcards
What are opiod receptors?
G coupled proteins
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What are the endogenous opiod ligands?
Endorphins, enkephalins and dynorphins
How does activation of opiod receptors decrease neuronal activity?
Influk K+, decrease Ca+⇒
decreases release neurotransmittors (subsatance P, glutamate) in presynaptic cell ⇒
hyperpolarization of postsynaptic cell
How much does an opiod reduce the inhalent requirement?
40-60%
Potentcy of hydromorphone, oxymorphone, meperidine, methadone, fentanyl and buprenorphine in relation to morphine?
Hydro 8x greater
Oxymorphone 10x greater
Meperidine 10x less
Methadone 2x greater
Fentanyl 100x morphine
Buprenorphine 40x greater at the Mu agonist but binds to receptor without fully activating resulting reduced analgesia
Side effects of serotonin syndrome?
hyperthermia, anxiety, shock, rhabdomyolysis and ARF
MOA methadone?
Mu receptor agonist
NMDA receptor antagonist (N-methyl-D-aspartate)
What is unique about remifentanyl?
Metabolized by plasma esterases
No hepatic or renal metabolism
Very short half life - good for rapid awakening
MOA of naloxone
Binds competatively to Mu, Kappa, and Delta receptors
MOA benzodiazepines?
Enhance GABA (gamma-aminobutyric acid), an inhibitory NT
The GABA receptor allows Cl to enter the neuro, hyperpolarizing the cell and preventing action potentials.
What effects do benzodiazepines have?
muscle relaxation
narcosis
amnesia
no analgesia, cardio or respiratory depression
excitement = central disinhibitory effect
What are the active metabolites of diazepam and midazolam? How is this clinically relavent?
Diazepam = nordiazapem, oxazepam (both sedative with same duration as diazepam but slow clearence)
Midazolam = 1 hydroxymethyl midazolam (no activity)
Midazolam better for patients with hepatic dysfunction (ie decreased clearence)
What is acepromazine (drug class)?
phenothiazine
MOA acepromazine?
Depresses dopamine activity in the reticular activating system
alpha 1 receptor antagonist = vasodilation and hypotension and protective for some cardiac arrhythmias
Clinical effects of ACE?
moderate sedation
some muscle relaxation
no analgesia
antihistaminic
antiemetic
Dexmedetomidine MOA
Alpha 2 angonist = decrease Norepi release in CNS = sedation, analgesia and muscle relaxation
Peripheral alpha 1 agonist = vasocontriction, hypertension, arrhythmogenicity and paradoxical excitation
Hypertension = reflex bradycardia which can be compounded by decreased central sympathetic output = hypotension
Other SE: hyperglycemia, diuresis, respiratory depression
How does medetomidine effect cats different than dogs?
Dogs = hypertension and increased myocardial work
Cats = minimal hypertension; HR,CO,SV decrease alot
MOA propofol
GABA receptor agonist increasing inhibition throughout CNS
What is in propofol emulsion?
soybean oil, glycerol, egg lecithin
What is propofol infusion syndrome?
Occurs in people (not reported in animals)
Effects mitochondria - severe metabolic acidosis, refractory bradycardia, and rhabdomyolysis
MOA ketamine
NMDA receptor ANTAgonist - decrease dorsal horn windup
Dissociative anesthestic - separation between higher and unconcious function (eg muscle riditiy), maintains respiratory center sensitivity to CO2
Mild sympathomimetic (increased sympathetic) = may increase myocardial work, decrease CO
Bronchodilation
Clinical effects of ketamine?
Increase myocardial work
Decrease CO
Increase ICP
Increase intraocular pressure
Muscle rigidity
Laryngeal function maintained
Bronchodilation
How is ketamine eliminated?
Metabolized to active metabolic (norketamine) which is renally excreated (aka not good to use with severe renal disease as may be long to recover)
Only 50% converted in cats, rest excreated unchanged
What is telazol?
Tiletamine (like ketamine)
Zolazepam (benzo)
Drug class xylazine?
alpha 2 agonist
MOA barbituates?
What are common barbituates?
direct activation of GABA recpetor and modulates the effects of GABA
Thiopental (thiobarbituate) and pentobarbital (oxybarbituate)
What is etomidate and MOA?
imidazole derivative
Effects GABA receptor
Side effects etomidate?
hemolysis and shock at doses >5mg/kg
muscle rigidity and myoclonus (use benzo with)
Emesis
Adrenal supressoin for 6 hours - avoid in critically ill and give dose steroid
What is alphaxalone and MOA
Steroid anesthetic
Enhances GABA and glycine-mediated CNS depression
What is the defination of MAC?
conc of anesthetic (volume/volume %) needed to prevent movement from a noxious stimulus in 50% of animals
What is MAC-BAR?
MAC blockade of adrenergic response - conc that prevents cardiac response to pain
Usually higher than MAC, in cats 10% higher than MAC
What conc of MAC is generally required to prevent movement in all patients?
1.2-1.5 x MAC
How does temperature effect MAC?
Hypothermia decreases MAC by 5% for each degree C
Adverse effects of halogeated inhalent anesthetics?
Hypotension - decreaed SVR and CO
Respiratory depressent
increased ICP
disrupt thermoregulation
malignant hyperthermia
arrhythmias = sensitize myocardium to catecholamines
Bold are dose dependent
Absorbtion of inhalents depend on 4 things:list
- blood/gas solubility of inhalent: high, slower action
- CO: high, slower action
- Minute ventilation: high, faster
- Concentration gradient between blood and alevolus: greater gradient, faster absorption
Factors that effect length of recovery from inhalents?
- Fat
- Longer anesthesia = more redistribution
- Soluability of anesthetic
MOA local anesthetics?
Dose and activity dependent (phasic)
Blockade of fast sodium channels on afferent n inhibiting nociceptive transmission
Lidocaine and bupivicaine lipophilicity and dissociation constants (pka)?
Lidocaine: lipophilic, fast onset action (<5min), short duration 45-60 min
Bupivicaine: higher lipid soluability and protein binding, longer duration of action (6-8 hours), upto 45 minutes to take effect
Mepivacine effect between the 2
What is a Bier block?
IV regional anesthesia
What is the bandage that is applied for regional anesthesia or to enansuinate the foot?
Esmarch bandage
Toxic dose of lidocaine in dogs and cats?
Dogs: >8mg/kg
Cats:>6mg/kg
Toxic dose of bupivicaine?
Dogs: 4mg/kg
Cats: 2mg/kg
Toxic effects of lidocaine?
Initial: GI - vomiting, regurg, ileus, nausea
Then: CNS - dull, siezures
Last Cardio - decreased contractility, arrythmia, death
What is succinylcholine?
Depolarizing neuromuscular blocking agent
minics acetylcholine
malignant hyperthermia
What is atracurium?
Non-depolarizing neuromuscular blockade
short duration
Hoffman elimination - indepent of renal or hepatic degredation
MOA neostigmine and edrophonium?
Reverse neuromuscular blockade
Inhibit acytelcholinesterases
Can cause cholinergic crisis: salivation emesis, vomiting, bradycardia, death, therefore sometimes given with anticholenergic
MOA anticholnergic agents (ace, glyco)?
Parasympatholytics = minimize vagal tone
High vagal tone = bradycardia
What causes increased vagal tone?
endotracheal intubation
emesis
traction ocular orbit
manipulation hepatobiliary system
Brachycephalic breeds
Opiod drugs
Describe the COX pathway
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Describe anti-inflammatory effects of NSAIDS
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Describe MOA NSAID side effects
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What is delta down?
Depression in arterial systolic pressure (collapsing of greater vessels) with IPPV
Seen with hypovolemia
What are dobutamine and dopamine?
Positive ionotropes (increased cardiac contractility)
Beta adrenergic agonists
Chronotropic effects
DOPAMINE: increase SVR
What is phenylephrine?
alpha adrenergic vasopressor
Can reverse vasodilation caused by other drugs
What is vasopressin?
nonadrenergic pressor
Used for vasoplegic shock (low systemic vascular resistence and high cardiac output) during sepsis
Describe the ASA status chart
I: no illness
II: mild compenstated systemic illness
III:moderate to severe compenstated systemic illness
IV: Disease that is constant threat to life
V: Moribund, no expected to survive
What is the risk for anesthetic death?
1 in 500-1000
What are drugs that sensitize the myocardium to catecholamine induced arrhymias?
halothane
thiopental
What is an ideal fluid type for anesthesia for cardiac cases?
Isotonic, low sodium
0.45% NaCl with 2.5% dextrose
What is the Branham reflex?
Occurs during lagation of a PDA - increased afterload causes bradycardia
MOA phenoxybenzamine?
(non-selective/Alpha) adrenergic ANTAGonist - convalently bonds alpha receptors
Antagonist/partial agonist seritonin 5-HT2a receptor
Doxopram use, dose and side effect?
Highlight laryngeal function (for eval LarPar)
1.1mg/kg IV
Severe glottic constriction
What nasal oxygen rate is equivalent to 40% oxygen?
100ml/kg/min
Oncotic pressure of Hetastarch?
29-32mmHg
Normal oncotic pressure?
18-22mmHg
What is the reversal agents for benzos?
Flumazenil
What are drugs that are heavily protein bound (ie effected by hypoalbuminemia)?
Propofol
Benzo
Opiods
Liver disease/hypoalbuminemia will leave more free drug and the drugs will have a stronger effect
Drugs to increased urine output, assuming adequate hydration (renal anesthesia)?
Mannitol - 0.5g/kg - also free radical scavenger that may help renal epithelial cell swelling
Furosemide - 0.2-2mg/kg IV, 0.66mg/kg/hr CRI
Dopamine - 2-5mcg/kg/min - increased output but not creatinine clearence
What is the oncotic pressure of 25% human albumin and 16% canine albumin?
Human >200mmHg
Canine 98mmHg
What is the maximum allowable intra-abdominal pressure for CO2 insuflation?
14 cm H20, greater compromise renal blood flow - prolonger >25 = anuria and ARF
What are signs of an air embolism during anesthesia monitoring?
Sudden drop EtCO2
Drop BP
Drop pulse ox
Washing machine heart murmur
Only drug shown to adversely effect neonate survival?
Xylazine
Although ketamine may be associated with decreased neonatal vigor
What is the amount used for low epidural and a high epidural?
Low: 0.2ml/kg
High: 0.3ml/kg
Inta-articular dose of perservative free morphine?
0.1mg/kg
What is the maximum bupivicaine dose recommended for dental blocks in dogs and cats?
Dogs: 2.5mg/kg
Cats: 1mg/kg
List the dental n. blocks?
Mental (rostral mandibular): mandibular second to third premolar rostral to the midline.
Infraorbital (rostral maxillary): maxillary third premolar rostral to the midline.
Inferior alveolar: mandibular third molar rostral to the midline.
Maxillary: last molar rostral to the midline, including the ipsilateral soft and hard palatal mucosa and bone
What is the does of atricurium for ocular surgeries and how long does it last?
Dose 0.1mg/kg
Lasts 20-30 min
Use of a reversal often not necessary but can be directed by a n. stimulator
What are the effects of inhalents, propofol, ketamine and thiopental on inraocular pressure?
Decrease: Inhalents
Increase: propofol, ketamine
Thiopental least effect
4 causes of hypothermia during anesthesia?
Change in hypothalamic control of thermoregulation
immobility
vasodilation
cold surfaces/eviroment
Consequences of hypothermia?
Prolonged recovery
delayed healing
decreased immunity
altered drug metabolism
cognitive depression
arrythmias
Altered coagulation (VCNA 2015)
hypotensoin (VCNA 2015)
Four mechanism of heat loss?
- Evaporation - only lungs and feet
- Conduction - through cold surfaces (10%)
- Convective - contact cold air/eater (30%)
- Radiation - loss of heat via infrared energy (50%)
How do Bair huggers prevent heat loss?
Via convection
Methods to maintain temperature during sx?
Bair hugger
warm-water circulating pads
heat-mositure exchange unit on ET tube
low-flow or close anesthesia circuits with coxial rebreathing hoses
plastic wrap
fluid warmer
What are the 5 cause of arterial hypoxemia?
VQ mismatch (most common)
hypoventilaiton
right-left anatomic shunt
decreased insipired O2
Diffusion barrier impairment
Bronchodilators may help severe VQ mismatch. List bronchdilators.
Aminophylline
Albuterol
Terbutaline
What is malignant hyperthemia?
Inherited condition - cellular ryanodine receptor
Dysregulation/excssive release of intracellular Ca++ release in muscles
causes: hypercarbia, hyperthermia, muscle spasms
confirm with muscle biopsies
How do you treat malignat hyperthermia?
Stop inhalent, switch to propofol CRI and O2
Give dantrolene = stablize sarcoplasmic reticular membrane
Drugs assoicated with malignant hyperthermia?
Inhalents, esp halothane
succinylcholine