Analgesia, Anesthetic Agents, And Special Techniques Flashcards
(46 cards)
Agonist
Bind and stimulate receptors
Partial Agonist
Bind and partially stimulate receptors
Agonist-antagonist
Stimulate one receptor and blocks another
Antagonist
Bind partially to a stimulator blocking effects of agonist
List anesthetics and adjuncts that can be reversed
Flumazenil-> benzodiazepines (uncommon to use)
Alpha-2 Antagonist (Atipamezole, Yohimbine)-> short DoA (redoes); avoid when anticholinergics given
Naloxone, Butorphanol-> Opioid -> given as emergency/revive neonates; rare adverse effect (correct dose)
Dose dependent
Magnitude of effect (adverse, desired) of anesthesia and adjunct is based on dose given
Preanesthetic:
Anticholinergics/Parasympatholitics (Atropine, Glycopyrrolate)
Indication: minimize bradycardia, respiratory, salivary, GI, lacrimal secretion; bronchodilator
MoA: block acetylcholine receptors
Route: SQ, IM (common), IV, IT (emergency)
Onset: 1-5 min, peak 5-20 min
DoA: 60-90 min (Atropine), 2-3 hrs (Glyco)
AE: tachycardia, arrhythmia, mydriasis, inhibit intestinal peristaltis = colic, bloat
Preanesthetic:
Phenothiazine (Acepromazine)
Indication: sedation/calming, reduce seizure threshold, anti-arrhythmic, antiemetic, antihistamine
MoA: Depress reticular activating center of brain; metabolized by liveth, cross placenta
Route: IM (dogs), IV (horse)
Onset: 15 min, peak 30-60 min
DoA: 4-8 hours (SA), 1-3 (LA)
AE: tachycardia/bradycardia, hypotension, decreased PCV
Preanesthetic:
Benzodiazepine (Diazepam/Valium, Midazolam) Class IV
Indication: anti-anxiety/calming, anticonvulsant, skeletal muscle relaxant
MoA: increase activity of Gaba = depressing CNS
Route: IV, IM (Midazolam only)
Onset: 15 min
DoA: 1-4 hr
AE: Disorientation/excitement (dogs), dysphoria/aggression (cats), pain IM site, ataxia (LA)
Preanesthetic:
Alpha-2 Agonist (Dexmedetomine, Xylazine)
Indication: Sedation, Analgesia, Muscle relaxant
MoA: Stimulate receptor of SNS ↓ release of norepinephrine, metabolized by liver, excreted urine
Route: IV, IM
Onset: 5-15min (IV), 15-30(IM) DoA: 1-4hr
AE: Aggitation/aggression, hypertension/bradycardia hypotension, respiratory depression, vomiting, hyperglycemia, hypothermia, polyuria
Preanesthetic:
Opioids
Indication: analgesia, sedation/CNS depression
MoA: bind/partially bind/displaces µ, κ receptors
Route: IV, IM, SQ, rectal, oral, transdermal, local
Onset: varies
DoA: most <30 min
AE: CNS stimulation/dysphoria (cats), bradycardia/respiratory depression, panting, hypothermia (dogs), hyperthermia (cats), V/D, ileus
Preanesthetic:
Neuroleptanalgesia
Indication: Opioid & Tranquilizier (acepromazine, alpha2agonist, benzodiazepine) for profund analgesia & sedation used for debilitated dogs minor procedure
Route: IM, slow IV
AE: Can cause excitement in cats, mania in young dogs; bradycardia fast infusion (intubate & assist ventilation)
Preanesthetic:
Propofol
Indication: Sedation/short-term GA*, muscle relaxation, antiemetic, ↓ intracranial & ocular pressure
MoA: ↑ action of GABA to depress CNS
Route: IV CRI or repeat boluses (over 1-2min, q 3-5)
Onset: 30-60sec
DoA: 2-5min, recover 20-30min
AE: Tansient excitement/tremor (induction), bradycardia, ↓ cardiac output, hypotension, respiratory depression/apnea (rapid injection)
Injectable Anesthesia:
Alfaxalone
Indication: Sedation/short-term GA*, muscle relaxation, minimal cardiovascular depression
MoA: Bind to GABA receptors (similar to Propofol)
Route: IV, IM (cats)
Onset: varies
DoA: most <30min
AE: Tachycardia, hypotension (+inhalant), respiratory depression/apnea (rapid IV), excitement (recovery)
Explain the effect of protein binding, lipid solubility, and redistribution on the pharmacokinetics and pharmacodynamics of injectable anesthetics.
Propofol macroemulsion large particles scatter light (cloudy/milky) from milk fat, glycerin, oil
• Lipid soluble = 1-5% unbonded passes through brain (more potent if hypoproteinemic)
• 95-99% bounded to plasma proteins
• Diffuses heart, kidney, liver (rich in vessels) → muscle → fat once blood concentrate ↓
• Metabolized by liver, excreted by urine (1-2hrs)
Injectable Anesthetic:
Barbiturates (not commonly used)
Class III
Indication: GA for lab animals, epilepticus/intractable seizures, euthanasia solution
Use as IV injectable replaced by propofol, alfaxalone & inhalants
Injectable Anesthesia:
Dissociative
Ketamine, Benzodiazepine, Ketamine+Diazepam/Midazolam
Class III
Indication: Catelepsy (unresponsive, muscle rigidity), somatic analgesia
MoA: Inhibit NMDA receptors = prevent windup
Route: SQ, IV, IM
Onset: 1-2min IV, 10min IM DoA: 20-30min
AE: intact reflexes, stimuli sensitivity, nystagmus (cats), apneustic respiration, ↑ HR, cardiac output, MAP, intracranial & ocular pressure, tissue irritation
Nitrous Oxide (N2O)
Indication: Speeds induction & recovery, additional analgesia (with added agents), MAC reducing = reduces cardiopulmonary & respiratory AE
Seldom use as Iso & Sevo already produce rapid induction & recoveries
Define vapor pressure and how this property affects action and use of inhalants.
Amount of pressure excreted by gaseous form of substance when gas & liquid is in equilibrium
Tendency to evaporate in vaporizer – based on agent & room temperature
Available inhalants are volatite (evaporates readily) so uses agent specific precision vaporizer*
*Isoflurane stored in nonprecision Stevens vaporizer specifically made for it
Define partion coefficient (BGPC) and how this property affects action and use of inhalants.
Solubility of inhalant anesthetic in blood compared to alveolar gas
Inhalants ↓ BGPC = faster induction, response to change in vaporizer setting, recovery
↑ BGPC = highly soluble in blood & tissue
Define minimum alveolar concentration (MAC) and how this property affects action and use of inhalants.
Average setting used to produced anesthesia
(↓ MAC = more potent)
Estimated vaporizer setting: 1x MAC = light stage III
1.5 x MAC = surgical anesthesia
(Iso Maintainenance ~1.5-2.5% Sevo ~2.5-4%)
*Setting based on age, metabolic activity, body temperature, patient condition (dz, obese, pregnant)
Inhalant Anesthetic:
Isoflurane, Sevoflurane, Desflurane
- Isoflurane: most common induction/maintenance
VP: 240mmHg
BGPC: 1.46
MAC: 1.3-1.63 - Sevoflurane: less irritating, minimal odor, costly
VP: 160mmHg
BGPC: 0.68
MAC: 2.3-2.5 - Desflurane: pungent, induce breath holding, sympathethic storm (transient ↑ HR, BP – humans)
VP: 700mmHg
BGPC: 0.42
MAC: 7.2-9.8
- special vaporizer to prevent boiling
- ‘one breath anesthesia’, least potent
Describe the uptake, distribution, and elimination of the commonly used inhalation anesthetic agents.
MoA of inhalants: Unknown, may inhibit nerve cell function in brain & spinal cord
Uptake of inhalants: Fresh gas diffuse in alveolar membrane → blood based
Distribution: Induce – diffuse in vascularized organs (↑ alveoli ↓ blood), enter brain, diffuse back to alveoli when vaporizer discontinued (↑ blood ↓ alveoli)
Eliminated by lungs, minimal liver metabolism
Analeptic (CNS Stimulant):
Doxapram
Indication: Induce respiration, recovery in emergency, reverse effects of inhalants & barbiturates
Route: IV, PO/sublingual/umbilical vein - neonates
Onset: 2 minutes (IV)
AE: Wide margin of safety; hyperventilation, hypertension, arrhythmia, lowers seizure threshold, can cause CNS damage (provide O2 support)