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
What type of block is utilized in wounds or open surgical sites?
splash block
What is a splash block and what drugs are used?
a way of caring for wounds or open surgical sites using topical sprays (contianing 10% lidocaine) by direct application of 0.25% bupicacaine, or soaked gauze sponges (soaked with a mixture of local anesthetic and saline
To avoid local anesthetic overdose, what are the doses of lidocaine and bupivicaine?
lidocaine - should not exceed 4 mg/kg for the dog and 2 mg/kg for the cat
bupivacaine - should not exceed 2 mg/kg in dogs and 0.5 mg/kg in cats
Why must Bupivacaine administration into a chest tube during thoracic surgery be delayed and when should it be administered?
should be delayed ntil patient is awake because instillation of bupivacaine into the chest cavity of an anesthetized patient may cause cardiac arrhythmias
What local anesthetics can be absorbed by what mucous membranes? How quick are the results of analgesia and what is the duration of analgesia for mucous membranes?
topical sprays,drops, or ointment
cornea & conjunctiva - 0.5% proparacaine or tetracaine
nose, mouth-
larynx - lidocaine - prevents laryngospasm in cats
lining of urethra - gel containing lidocaine, tetracaine or amethocaine
60 to 90 sec
lasts for 10 - 15 min.
When giving local anesthetics where can anesthetics be infiltrated (injected in proximity to the target nerve)? What types of surgeries does this type of local anesthesia help?
intradermally, subcutaneously, or between muscle planes
skin biopsies, removal of small skin tumors, and repair of minor lacerations
What drug is most commonly used for infiltration?
lidocaine with or without epinephrine (conc. of 0.01 mg/mL of lidocaine)
For what two reasons are epinephrine added to lidocane?
- constriction of blood vessels in the area of infiltration (injection). This decreases the rate of drug adsorption and thereby prolongs the effect of the lidocaine by approx 50%
- by causing vasoconstruction, epinephrine reduces the concentration of local anesthetic that enters the circulation at any given time thereby reducing the toxicity of the drug
- increases the risk of ventricular arrhythmias - should be used withcaution in animals with known cardiac disease
Lidocaine plus epinephrine should not be used in the following applications?
incision site, ears, digits, and tails
because it may impair tissue perfusion and healing
Local anesthetics with ______ should not be administered intravenously and should be avoided when blocks of extremities are performed, as circulation to these areas may become compromised.
epinephrine
What does Lidocaine plus epinehprine do in animals with caution with known cardiac disease?
- increases the risk of ventricular arrhythmias
What 2 techniques are commonly used for infiltration of local anesthetics?
nerve blocks and line blocks
a nerve block is achieved by?
injecting local anesthetic in proximity to a nerve to desensitize a certain anatomical site
To avoid intravenous injection…?
in animals with known cardiac disease
A line block is?
a continuous line of local anesthetic placed in subcuticular tissues immediately proximal to the target area
The most effective way to block sensory nerves are?
position the block between the target area and the spinal cord
What are some clinical situations utilizing a nerve block?
lameness examinations, cornual blocks for dehorning cattle, paravertebral blocks for abdominal surgery - c sections in cattle, dental blocks (infraorbital, mental, mandibular and maxillary
Where should line blocks be positioned?
between the target area and the spinal cord because this will block the sensory neurons most effectively.
A nerve block is achieved by?
injecting local anesthetic in proximity to a nerve to desensitize a particular anatomic site
- used commonly in large animals
Use a nerve block in small animals only if?
you know the exact location of the target nerve
Before a nerve lock is performed, what must be done?
palpate the nerve to determine its location - may not be possible is nerve small
What types of clinical situations could you use a nerve block?
How long should you wait to start technique after applying block?
Lameness exams in horses
cornual blocks in dehorning cattle
paravertebral blocks for abdominal surgery - c-sections in cattle
dental blocks in dogs and cats (infraorbital, mental, mandibular, and maxillary nerve blocks)
intercostal nerve blocks - chest surgery
amputation -infiltration of nerves
declawing cats
15 - 20 min.
What is epidural anesthesia?
a regional anesthesia technique that is commonly used in both large and small animal patients - allowing the anesthetist to reliably block sensation and motor control of the rear, abdomen, plevis, tail, pelvic limbs, and perineum
What is a ring block?
when the line of local anesthetic completely encircles an anatomic part, such as a digit or teat
Where shoud line blocks be positioned?
between the target area and the spinal cord because this will block the sensory neurons most effectively.
What is regional anesthesia?
a technique whereby a local anesthetic is injected into a major nerve plexus or in proximity to the spinal cord
What is Bier block?
short term local anesthesia to an extremity using Lidocane (not Bupivacaine ) when using a tourniquet because of cardiotoxicity is likely after release of the tourniquet
What are the disadvantages when using regional anesthesia?
technical skill required and hind limb weakness (scoliosis)
What is scoliosis?
lateral curvature of the spine
What is epidural anesthesia?
a regional anesthesia technique that is commonly used in both large and small animal patients
Epidural Anesthesia is most commonly used in what 3 classes of patients?
ruminants, debilitated small animals, and patients requiring profound pain control post surgically
What are the drugs of choice for anesthesia when doing an epidural?
2% lidocaine, 0.5% bupivacaine, morphine, combinations (opiods, and alpha 2 agonists)
What is cauda equina?
where the spinal cord itself terminates in a group of neurons collectively
What is tidal volume (Vҭ)?
the amount of air that passes into or out of the lungs in a single breath
What are some adverse effects of local anesthetics?
- loss of voluntary motor control of affected body part
- temporary or permanent loss of nerve function
- tissue irritation
- paresthesia
- allergic reations
- systemic toxicity
- spinal cord trauma
- infiltration of the caudal spinal cord
- diffusion of anesthetic into the cervical and thoracic spinal cord
What is assisted ventilation
anesthetist ensures than an increased volume of oxygen and anesthetic gases is delivered to the patient, although the patient initiates each inspiration
What is controlled ventilation?
anesthetist delivers all of the air that is required by the patient, and the patient does not make spontaneous respiratory efforts. Anesthetist controls the RR and the volume and pressure of gas that the animal breaths
What is positive pressure ventilation (PPV)?
any procedure by which the anesthetist assists or controls the delivery of oxygen and anesthetic gas tot he patient’s lungs
What are the two parts of ventilation?
an active phase (inhalation) and a passive phase (exhalation)
Inhalation is initiated by?
the respiratory center in the brain and is normally triggered by an increased level of carbon dioxide in the arterial blood
What is tidal volume?
the amount of air that passes into or out of the lungs in a single breath
What is respiratory minute volume
the total amount of air that moves into and out of the lungs in 1 minute
Normal Vҭ is what in the awake animal?
10 - 15 mL/kg
How do you determine the total amount of air that moves into and out of the lungs in 1 minute (respiratory minute volume)?
multiply the average Vҭ (tidal volume - 10 - 15 mL/kg) by the respiratory rate
What problems can arise because of decreased respiratory minute volume in an anesthetized patient?
Hypercarbia, hypoxemia, and atelectasis
What triggers inhalation?
by an increased level of carbon dioxide in the arterial blood
What is hypercarbia?
PaCO₂ may rise in the anesthetized patient, because carbon dioxide produced by the body is not eliminated as rapidly as in the awake animal - can lead to respiratory acidosis
What does PaCO₂ mean?
symbol for partial pressure of carbon dioxide in the arterial blood.
Blood pH in the healthy animal is?
In anesthetized animal the blood ph may be as low as?
- 38 to 7.42
7. 20
hypoxemia?
low blood oxygen level
What is atelectasis?
Collapse of a portion or all of one or both lungs
bagging?
manual ventilation
intermittent mandatory ventilation?
when patients require bagging throughout the anesthetic period
What is mechanical ventilation?
when patient’s lungs are ventilated by a ventilator
