Analgesia, Anesthetic Agents, And Special Techniques Flashcards
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)
List the advantages and disadvantages associated with the use of local anesthetic agents.
Low cardiovascular/respiratory toxicity, inexpensive, analgesia, doesn’t cross placenta, minimal recovery
Common in LA (standing sedation) but used in conjuncton with GA for SA, no reversal, cause arrhythmia, myocardial depression (overdose)
Lidocaine 2%
Bupivacaine 0.5%
MoA: Blocks sodium channels so sensory & motor neurons cannot depolarize
Onset: 1-5min (L), 10-20min (B)
DoA: 1-2hr (L), 4-6h (B)
Add epinephrine to Lidocaine to prolong DoA
Explain the risks involved and the adverse effects that may be seen with the use of local anesthetic agents.
- Affect motor neurons (CNS to periphery) = paresis (weakness) & paralysis (loss of voluntarily movement)
- Paresthesia: ‘tingling’ sensation
- Allergic reaction – hives, anaphylaxis
- Tissue irritant, loss of function (direct nerve inj)
- Systemic toxicity (IV w/out torniquet, large SQ)
- Sympathethic blockade (loss of sensation to SNS) – vasodilation/hypotension, hypertension
Use of local anesthesia:
Topical
EMLA cream (Lidocaine + Prilocaine) – for IV catheter placement, occlusive dressing; not to be applied eyes, broken skin/accessible to patient
Splash block: place in open wound – spray, gauzed with anesthetic & saline
Use of local anesthesia:
Infiltration
Inject under aseptic skin & in proximity of a nerve for analgesia & anesthesia to area (for skin biopsy, mass removal, minor lacerations) – onset 3-5min
Ineffective – deep tissue (muscle), scar/fibrous or inflamed tissue
Use of local anesthesia:
Outline the methods for performing a nerve block and a line block, and list clinical situations in veterinary practice un which these blocks are used.
Inject in close proximity of nerve – dental, intercostal (chest)
Line block – continuous line in SQ/ID proximal to target area (horse, cattle)
Ring block – block an encircled area (digit)
Use of local anesthesia:
Intraarticular
Inject (diluted Bupivacaine) into stifle joint
Use of local anesthesia:
Regional
Inject into major nerve plexus/in proximity to spinal cord - blocks nerve impulse to & from large area
Paravertebral – T13 to L2 (C-section)
Epidural
IV (Bier Block) <1hr local anesthesia to extremity (amputation)
Use of local anesthesia:
Epidural
Epidural block sensation in abdomen, pelvis, tail – temporary immobility, analgesia (tail amputation), debilitated animals (cannot tolerate GA)
Insert needle perpendicular within spinal canal
Explain the difference between assisted and controlled ventilation
Assisted Ventilation: ↑ amount of gas delivery (fresh gas), patient initiate inhalation
Controlled Ventilation: deliver all air patient require, patient does not make spontaneous respiratory efforts
Positive pressure ventilation (PPV): assisted and control ventilation - delivering of oxygen & anesthetic gas to patient’s lung; evaluated w/ SPO2 & ETCO2
Ventilation in awake vs. anesthetized animal
- Ventilation – movement of air in & out lung
- Active phase (inhalantion) - triggered by respiratory center in the brain & ↑ PACO2 >40mmHg, intercostal muscle push ribcage outward, diaphragm flatten
- Passive phase (exhalation) - relaxation of diaphragm & intercostal muscle ↑ PACO2 triggering another inspiration, 2x longer
- Anesthetics ↓ responsiveness of respiratory center to CO2 (less inhalation), relax intercostal & diaphragm (↓ VT, RR, RMV)
Describe the techniques of manual (periodic, intermittent) ventilation and their application to anesthesia.
Manual ventilation lungs filled O2 from ↑ pressure entering lungs as reservoir bag is squeezed, passive exhalation
Periodic bagging (1-2 breaths q 2-10min): close popoff valve, compress RV ≤20 cm H2O
Intermittent ventilation (bagging throughout procedure): close pop off valve, open every 2-3 breaths
Describe the techniques of mechanical ventilation and their application to anesthesia.
Ventilator provides intermittent ventilation – for thoracotomy/lengthy operations/LA
Patient intubated, monitor vitals & anesthestic depth
Risk of controlled ventilation – excess airway = ruptured aleveoli, ↓ cardiac output, hyperventilation, excess anesthetic depth
List the indications for the use of neuromuscular blocking agents and the hazards associated with their use.
Skleletal muscle paralyzing agents – mechanical ventilation (prevents spontaneous inspiration), orthopedic, opthalmic, C section
Always administer patient unconcious, give slow IV/CRI, ↑ inhalant potency
Can make assessing depth difficult (depress blink reflex), hypothermia (↓ muscle tone)
Describe the differences between the 2 classes of neuromuscular blocking agents, including mode of action and reversibility.
MoA: interrupt normal transmission of impulses from motor neurons
Depolorazing agents – muscle twitch & paralysis
Onset: 20 sec, short DoA
AE: Hyperkalemia, cardiac arrhythmia
Nondepolarizing – blocks receptors
AE: histamine release, hypo/hypertension, tachycardia
Pure µ agonist opioid:
Morphine, Hydromorphone, Methadone, Fentanyl (Class II)
Indication: Analgesia (moderate to severe), Sedation/CNS depression
MoA: Bind μ receptors
Route: IV, IM, SQ, Epidural/Regional
Onset: varies
DoA: most <30min
AE: bradycardia/respiratory depression, panting, hypersensitivity, vomiting (less likely Methadone), CNS hypersensitivity (Methadone)
Pure µ agonist opioid:
Buprenorphine (Class III)
Indication: Analgesia (mild/moderate), prolonged sedation
MoA: Bind μ receptors - less potent
Route: IV, IM, SQ, Epidural/Regional, Oral (cats)
Onset: 15min IV
DoA: 6-12hr IM
AE: respiratory depression – reversed with Doxapram
µ Agonist-antagonist Opioid:
Butorphanol (Class III)
Indication: Analgesia (mild/moderate visceral pain), reverse respiratory depression/sedation of μ agonist
MoA: Blocks μ, stimulate κ receptors
Route: IV, IM, SQ
DoA: 1hr IM
AE: high dose – respiratory depression (ceiling effect), hypotension, bradycardia, panting, vomiting, histamine release
Describe the uses for and procedure for application of fentanyl transdermal patch.
For use in post op patient (orthopedic, abdominal), trauma, cancer
Sized patch has Fentanyl reservoir enclosed in plastic applied to aseptic & clip skin
Mechanism of action, use, and adverse effects of NSAIDs
Indication: Analgesia (all somatic, some visceral), anti-inflammatory, antipyretic
MoA: Inhibit synthesis of prostaglandin (involved in pain & inflammation) by inactivating COX enzyme
Route: Oral, injectable
Onset: 30-60min DoA: varies by species
AE: liver damage, GI ulceration, renal toxicity, impaired platelet aggregation
List other analgesic agents
- Tramadol: at home analgesia (activity µ)
- Tranquilizers potentiate effect of opioids
- Gabapentin – neuropathic & allodynia
- Amantadine – analgesic adjunct for neuropathic pain
- Corticosteroids – anti-inflammatory
- Antidepressants/anti-anxiety - combined for neurogenic (cancer pain)
- Alpha2 agonist (short term)
- Dissociative (prevents windup)
Describe nursing care that relieves discomfort in hospitalized patients.
- Padded, clean, kennel
- Quiet area
- Avoid putting cats in bottom row cages
- Respositioning, eye drops
- Gentle handling & owner visitins
- Nutritional intervention
