ch 6 Flashcards
The term local anesthesia (AKA analgesia - because local anesthesia blocks pain transmission) can be defined as?
the use of a chemical agent on sensory neurons to produce a disruption of nerve impulse transmission, leading to a temporary loss of sensation
Local anesthesia can be an effective, practical, inexpensive means of producing anesthesia when?
the patient is tractable, when general anesthesia is undesirable or of high risk, or when the means to deliver it safely are unavailable
Local anesthesia is?
effective, practical, and inexpensive
Advantages of local anesthesia are?
low cardiovascular toxicity, lost cost, excellent pain control in the immediate postoperative period, minimal patient recovery time
Local anesthesia is commonly utilized in? for?
ruminants for obstetric procedures, abdominal procedures and for sedation and to compliment standing sedation in horses
The choice between local anesthesia and general anesthesia is made by veterinarian on the basis of what factors?
temperament, age, species, and physical status of the patient,cost the nature of the operation to be performed and the anesthetist’s skill in performing the local anesthesia procedure
Local anesthetics are used in conjunction with general anesthesia to?
enhance pain control during and after surgery
The dose of the general anesthetic may be significantly reduced because of the?
excellent analgesia provided by the local anesthetic
Local anesthetic agents vary in?
strength, duration of effect, and method of use
What are the local anesthetic agents most commonly used for skin infiltration and application to mucous membranes?
lidocaine, bupivacaine, mepivacaine, and procaine
What local anesthetic agents are most commonly used for ophthalmic uses?
tetracaine and proparacaine
The most commonly used local anesthetic agents Lidocaine and bupivacaine are administered at a concentration of?
Lidocaine 0.5% to 2%
Bupivacaine as a 0.25% or 0.5% solution
Both Lidocaine and bupivacaine can be diluted with (if a lower concentration is desired)?
sterile saline (not water)
What is Lidocaine’s and Bupivacaine’s onset and duration of action?
Lidocaine - immediate onset of action, 1 to 2 hr. duration
Bupivacaine - 20 min onset of action, 6 hours duration
How do anesthetics differ from general anesthetics?
Local anesthetics exert their effect on neurons but the target is peripheral nervous system and spinal cord (do not affect the brain, have no sedative effects and patients are fully conscious)
General anesthetics - primarily affect neurons in the brain
General anesthetic is reserved for those drugs such as?
inhalation anesthetics, propofol, ketamine, or barbiturates that primarily affect the neurons in the brain
Preanesthetics and general anesthetics can have ____ cardiovascular and ____ effects. Local anesthetics have relatively ___ effects on the ___ and respiratory systems. Would local or general anesthetics be preferable in high risk patients?
significant respiratory few cardiovascular - local anesthetics
General anesthetics are distributed throughout the ___.
Local anesthetics exert their effects in the area ___ to the site of ____. Effective use of local anesthetic requires ___ ___ of the drug immediately ___ to the target nerve.
body closet injection precise placement adjacent
Define nerve block?
loss of sensation in a particular anatomic site, produced by injection of local anesthetic in proximity to a nerve.
Local anesthetics are relatively ineffective in areas where drug diffusion is impeded by?
fat, bone, cartilage, fascia, tendon, and other connective tissues, as well as the presence of inflammation and infection
General anesthetics are ____ across the placenta.
Local anesthetics are ____ normally transferred across the placenta to the fetus.
transferred
not
Because of local anesthetics not normally transferred across the placenta, what procedures are done because of this?
cesarean sections, obstetric manipulations and where general anesthesia is considered a high risk
What are the primary targets of local anesthetic drugs?
sensory neurons that convey sensations (pain, heat, cold and pressure) from the skin, muscles, and other peripheral tissues to the brain
Local anesthetics result in ____ or blockade of ___ channels. When the sodium channels of a ___ are blocked, the ___ cannot generate electrical impulses. A local anesthetic drug acts as a membrane _____, stopping the process of nerve ____. The result is a ___ of nerve ___. Reversal of this effect occurs as the drug is absorbed into the local ____. Local anesthetics are then ___ to the liver, where they are ____.
antagonism, sodium neuron, neuron stabilizer, depolarization loss, conduction circulation redistributed, metabolized
What neuron conveys impulses from the brain to muscle fibers and is responsible for controlling voluntary movements?
motor
Motor neurons are also sensitive to the effect of ___ anesthetics, and ___ of local anesthetic may cause temporary ___ (weakness) or ___ (loss of voluntary movement) in the area served by the affected motor neurons.
local, administration, paresis, paralysis
What is an epidural block?
use of a local anesthetic near the terminal end of the spinal cord, will result in a loss of sensation and voluntary movement to all areas innervated by the affected sensory and motor neurons
When applying an epidural block, what are the sensations that are lost (list in order of loss)?
pain, cold, warmth, touch, joint sensation, and deep pressure in the caudal abdomen and pelvic limbs
Local anesthetics also affect the neurons of the ____ nervous system. These neurons convey impulses between the ___ and the ___ vessels and internal ___ (including the heart) causing a temporary loss of ____. This loss of function is called ____ ____.
autonomic, brain, blood, organs, function
sympathetic blockade
The sympathetic blockage’s main effects are?
vasodilation (resulting in flushing and increased skin temperature of the affected area). If severe vasodilation can cause blood pressure to fall leading to hypotension
If sympathetic blockade occurs within the spinal cord (may occur if local anesthetic is allowed to diffuse into the thoracic spinal cord) what can happen?
sympathetic innervation to the heart may be blocked, resulting in bradycardia and impaired ventricular contractions, which are undesirable
Local anesthetics can be administered by what routes?
topical application, infiltration (injection), introduction into a joint, nerve plexus, vein, or the epidural space
Why can local anesthetics (such as lidocaine) be ineffective when applied directly to intact skin?
because the drug molecules are unable to penetrate the epidermis and reach the dermis where the peripheral nerves are located
What local anesthetics be used effectively in clinical situations?
Ethyl chloride, EMLA cream, topical anesthetic sprays, drops, or ointment, Bupivacaine,
How is Ethyl chloride applied and what is the duration of the topical anesthesia and what does it do and for what procedures?
sprayed on intact skin - provides partial, short-term (less than 3 minutes) analgesia by significantly cooling the skin
used for skin biopsies and other superficial procedures
How is EMLA cream applied , what is the duration of the topical anesthesia, and what does it do and for what procedure?
a cream formation containing a eutectic mixture of 2.5% lidocaine and 2.5% prilocaine applied to intact shaved skin in area to be anesthetized and covered with anocclusive dressing for 10 min. (duration of effect is 1 to 2 hours) can be used to desensitize intact skin for minor procedures such as a catheterization
