Dissociative and Inhalant Anesthetics Flashcards
What is dissociative anesthesia? What are 2 characteristics?
CNS state produced by the dissociation of different levels of the CNS from each other - depression of some portions and enhancement of the limbic system, cutting off the brain’s perception of pain
- analgesia
- superficial sleep
What are 2 common dissociative anesthetics?
- Ketamine
- Tiletamine
Superficial sleep and analgesia are characteristic of dissociative anesthesia. What actions in the brain still remain? What type of analgesia is provided?
many reflexes are maintained (laryngeal)
somatic (visceral analgesia is poor)
What action on the body do dissociative anesthetics lack?
muscle relaxation is poor —> cataleptic, rigid, extended limbs
What are the typical pharmacological effects of dissociative anesthetics on the CNS, cardiovascular system, and respiratory system?
CNS: increased cerebral blood flow and intracranial pressure
CV: depression, healthy animals = paradoxical stimulation
RESP: cats may develop apneustic breathing patterns
What 5 effects of Cyclohexylamines (dissociative anesthetics) are described in humans?
- altered visual and auditory perception without genuine hallucination
- produce feelings of detachment from environment and depersonalization
- highly addictive
- long-term effects include memory loss and depression
- hyperthermia, convulsions, death
What are 5 general indicators of subjects under the influence of Cyclohexylamines (dissociative anesthetics)?
- black stare
- confusion
- chemical odor
- cyclic behavior
- depersonalization
What is Ketamine? How is it typically used?
non-barbiturate cyclohexylamine (dissociative anesthetic) used for induction and maintenance of general anesthesia
mostly IM, IV, or infusion in combination with sedative and muscle relaxants
- cats, dogs, small ruminants, swine
- only IV in adult horses and cattle
What 3 characteristics make Ketamine unique?
- hypnotic
- analgesic
- amnestic
What is the systemic mechanism of action of Ketamine?
- interrupts the connection between the cortex and limbic system
- stimulates opioid receptors to provide sedation and analgesia
- stimulates catecholamine release to increase cardiac output and bronchodilation
What is the molecular mechanism of action of Ketamine?
classical non-competitive inhibitor of N-methyl-D-aspartate receptors (NMDARs), the ion channel involved in excitatory glutamatergic neurotransmission
What effect does Ketamine have when binding to receptors in the brain? What are some other targets?
binds to NMDA receptors on GABA interneurons, resulting in high GABA and low glutamate levels
- dopaminergic, serotonergic, opioidergic, cholinergic
- serotonin, norepinephrine, dopamine reuptake transporters
- ion channels
What is Ketamine’s plasma binding characteristic? What does this result in?
low binding to plasma proteins
lipid solubility is 5x higher than thiopental, allowing for rapid onset and extensive distribution
When can Ketamine be used alone? What drugs is it typically used with to induce general anesthesia? When is a sub-anesthetic dose preferred?
in cats for minor procedures or to facilitate restraint
tranquilizers and opioids
constant-rate infusion (CRI) for analgesia
What tranquilizers are typically combined with ketamine in horses, dogs/cats, and pigs/cattle/goats? What does this result in?
HORSES: Xylazine - muscle relaxation
DOGS/CATS: Xylazine, Diazepam, Midazolam, Dexmedetomidine - prevent seizures, muscle relaxation
PIGS/CATTLE/GOATS: Diazepam, Xylazine - muscle relaxation
What is a common adverse effect of the administration of ketamine alone in horses and dogs? What are 2 common results in cats?
seizures
- profuse salivation resulting in airway obstruction (anticholinergic drugs can prevent this)
- trance-like state
Why is a possible adverse effect on the eyes following ketamine use? How can this be avoided?
corneal ulceration
ophthalmic ointment
In what 2 situations is it typically contraindicated to use ketamine?
- animals with corneal injuries and ulcers
- animals with head trauma or intracranial tumors
What combination makes up Telazol? When is it commonly used?
Tiletamine + Zolazepam
- IM, SC, IV to produce sedation and anesthesia
- short-term anesthesia in uncooperative dogs and feral cats
What is typically combines with Telazol in horses, pigs, and small ruminants/camelids?
HORSES: Xylazine, Butorphanol
PIGS: Xylazine, Ketamine
RUM/CAM: Xylazine (can be used alone)
What are 2 possible adverse effects of Telazol in dogs? 1 general effect? In what 2 situations is it contraindicated to use Telazol?
DOGS: recovery accompanied by muscle tremors, paddling, and whining; tachycardia
GENERAL: hyperthermia
- animals with corneal ulcers
- animals with head trauma
What are inhalant anesthetics? What are their primary sites of action? How are they administered?
drugs possessing anesthetic properties and analgesia delivered via inhalation
brain and spinal cord
by an anesthetist through an anesthesia mask connected to some type of anesthetic vaporizer and an anesthetic delivery system
What 4 characteristics make inhalation anesthesia safer than injectables?
- depth of anesthesia can be more readily altered - can lighten and deepen anesthesia fast, while injectables can only make anesthesia deeper
- often safer for animals with liver or kidney problems - excreted through respiratory system
- animals are breathing 100% oxygen, while animals anesthetized with injectibles breath room air (~21% oxygen)
- most patients are intubates, which keeps the airway open
What are 3 disadvantages to inhalation anesthetics?
- requires and anesthesia machine - cost and skill
- induction is much slower
- must deal with waste that anesthetic gas produces - safety
Where does inhalation anesthetic uptake occur? How are they distributed? Eliminated? Metabolized?
UPTAKE: delivered to lungs via face mask or tracheal tube (greater concentration = more rapid uptake)
DISTRIBUTION: CNS and other tissues dependent on regional blood flow
ELIMINATION: almost entirely eliminated by the lungs
METABOLISM: very minimal hepatic metabolism
What is vapor pressure? What does it determine in inhalant anesthetics? What can affect vapor pressure?
tendency of an inhalant anesthetic in the liquid state to enter the gaseous (vapor) state
how readily an IA will evaporate in the vaporizer
- temperature
- anesthetic
What are the 2 major classifications of inhalant anesthetics?
- VOLATILE: high vapor pressure (more readily evaporates and room temperature), so it must be delivered from a precision vaporizer specific for the anesthetic
- Isoflurane, Sevoflurane, Desflurane, Halothane, Dietyl ether - NONVOLATILE: low vapor pressure, so it can be delivered from a non-precision vaporizer
- Methoxyflurane
What is an inhalant anesthetic’s blood:gas partition coefficient? What does it mean when it’s low? High?
measure of the solubility of an IA in blood compared to alveolar gas (air)
- LOW = agent is more soluble in alveolar gas than in blood at equilibrium, making induction and recovery faster
- HIGH = agent is more soluble in blood than alveolar gas at equilibrium (absorbed in blood and tissues), making induction and recovery slower
What is an inhalant anesthetic’s minimum alveolar concentration (MAC)? How is potency related to MAC?
measure of the potency of a drug used to determine the average setting on the vaporizer that will produce surgical anesthesia
the agent with the highest potency has the lowest MAC
What can alter an inhalant anesthetic’s minimum alveolar concentration (MAC)?
- age
- body temperature
- metabolic activity
- obesity
- pregnancy
- disease state
- presence of othe drugs
What are the 3 major classes of inhalant anesthetics used today?
- HALOGENATED COMPOUNDS - Enflurane, Isoflurane, Desflurane, Sevoflurane
- DIETHYL ETHER - colorless, sweet-smelling, highly volatile, flammable, nausea common
- NITROUS OXIDE - laughing gas, nontoxic to organs, unpleasant smell
What is thought to be the mechanism of action of halogenated organic compounds?
inhibiting signals through GABA receptors, NMDA receptors, M and N receptors, and serotonin receptors
What are the pharmacological effects of halogen organic compounds on the CNS, cardiovascular system, and respiratory system?
CNS: dose-related reversible CNS depression, hypothermia, safe in epileptic animals
CV: depression, variable HR effect
RESP: ventilation depression
What adverse effects do halogenated organic compounds have on the CNS, cardiovascular system, and respiratory system?
CNS: increase intracranial pressure in patients with head trauma or brain tumors
CV: decrease blood pressure and renal blood flow
RESP: hypoventilation leading to CO2 retention and respiratory acidosis
What are the 2 most common inhalant anesthetics used in North America? How do they compare in blood:gas coefficient and mean alveolar concentration (MAC)?
- Isoflurane
- Sevoflurane
B:G C = Sevo is lower, making induction faster than Iso
MAC = Sevo is higher, making it less potent than Iso
What are some benefits to using Sevoflurane over Isoflurane? Disadvantage?
- higher controllability of anesthesia depth
- higher anesthetic index in dogs
- more expensive than Iso
How do the pharmacological effects of Sevoflurane and Isoflurane on the CNS, cardiovascular system, and respiratory system compare?
CNS:
- both maintains cerebral blood flow
CV:
- Iso: maintains cardiac output, HR, and rhythym
- Sevo: minimal cardiovascular depression
RESP:
- Iso: almost completely eliminated by the lungs
- Sevo: almost completely eliminated by the lungs with minimal hepatic metabolism
What are 2 additional effects of Isoflurane and Sevoflurane other than anesthesia?
- induces adequate to good muscle relaxation
- provides little or no analgesia after anesthesia
Desflurane is very similar to Isoflurane. What 2 characteristics make it sligntly different?
- LOWEST blood:gas partition coefficient, making induction and recovery very rapid
- MAC = 7.2-9.8%, making it the least potent inhalant agent
Halothane is very rarely used today. On what animals is it still used in?
pigs
- becoming replaced by isoflurane and sevoflurane
When is nitrous oxide commonly used as an inhalant anesthetic?
- primarily in human medicine
- some vets use as a gas at room temperature without need for a vaporizer
What is the purpose of using CNS and respiratory stimulants on a patient after anesthesia? What is the most common one used? When is it used?
shortens recovery
Doxapram
- neonate puppies and kittens after C-section with IV administration or sub-lingual drops
What are the 4 major effects of Doxapram? Why is it so commonly used
(CNS and respiratory stimulant)
1. analeptic
2. reverses respiratory depression from inhalant agents and barbiturates
3. stimulated respiration and speeds up recovery
4. lowers seizure threshold
wide margin of safety
