LA sedation/ local blocks lab Flashcards
What is the main adverse effect to be considered with acepromazine?
It decreases vascular resistance; therefore it causes vasodilation; therefore it can result in hypotension.
How does acepromazine decrease vascular resistance?
It is an alpha-1 antagonist peripherally, affecting therefore contraction of smooth muscle of blood vessels.
What is the expected degree of sedation/tranquilization from acepromazine? what if we give a high dose to a horse?
In general is a tranquilizer, mild one. The dose used is on the high end of the range. The horse will be more quiet than usual, but the head tends to remain high.
What is the main adverse effect to be considered with xylazine?
It increases vascular resistance; therefore it causes vasoconstriction; therefore it can result in hypertension.
A conscious horse has full autonomic system function. If the horse is nervous/anxious, it may already have increased sympathetic activity and as a consecuence catecholamine release (epinephrine, norepinephrine), which also cause vasoconstriction and hypertension, as well as increases in heart rate. Therefore, the hypertensive effects of xylazine may not be related to the drug but to the behavior of the horse.
In an inhalant-anesthetized horse, the administration of an alpha-2 agonist will result in an increase in blood pressure from the increase in vascular resistance, since inhalants cause decreases in vascular resistance.
how does xylazine affect blood vessels?
It is an alpha-1 agonist peripherally, affecting therefore contraction of smooth muscle of blood vessels. The alpha-2 agonistic effects also can increase vascular resistance.
expected degree of sedation/tranquilization from xylazine? what will a horse look like after a full dose?
In general is a strong dose-dependen sedative. The dose used is the full dose and should result in severe sedation.
The horse will be very quiet, the head drops significantly, therefore it is recommended to cross tied them, especially if they are in a chute and a bar is at the front of the horse, since they will rest their neck on it and this can predispose to difficult breathing from compressing the trachea. A stool can also be used to rest their chin on it.
How to increase the degree of sedation/tranquilization produced by acepromazine?
A second drug from a different pharmacological group can be administered. for example an opioid or an alpha-2 agonist.
In this lab, 0.02 mg/kg of butorphanol, IV, was administered 15 minutes after the acepromazine. These combinations are known as neuroleptanalgesic combinations, if they include a drug that sedates/tranquilizes and a second drug from a different class that causes sedation.
What is the main adverse effect to be considered with opioids?
Opioids tend to be safe for all systems, with the exception of excitement/dysphoria, that manifests as different behavior in the horse. Dysphoria is a state of grumpiness, and in this state, the patient is unaware of its behavior. Horses tend to increase locomotor function- they want to walk, shake their heads, etc., which can be annoying if the horse is supposed to remain still.
A horse that is sedated beforehand is less likely to show this behavior. A horse that requires analgesia is less likely to show this behavior.
What would happen if the injection is given intraarterial? why? why do we want to go in the vein?
-we go in the jugular vein, and the drug mixes with all the blood coming from the cranial part of the horse as it goes to the right atrium
>mixing occurs in the heart
>blood continues to the lungs, where a significant amount of the drug is inactivated, so that it is not only diluted, but decreased in concentration
-from here, the drug returns to the left side of the heart, and then on to the aorta and carotid, to go to the caudal and crainial parts of the animal
>if caudal, undergoes metabolism, extraction, inactivation, but also has peripheral effects
>cranial drug will elicit peripheral effects but also the central effect that we envisioned
==> very little of the drug injected into the vein actually goes to the brain to produce the desired effect
What if we inject in the carotid?
>drug will all go directly to the brain
>The toxic concentrations of the drug are likely to result in changes in vascular resistance in brain blood vessels- they produce a profound spasm (vasoconstriction), resembling a stroke or infarct, which depending on the branches affected by it, will induce loss of consciousness or seizure activity, or uncontrolled activity.
>A horse or ruminant injected in the carotid is likely to collapse violently and cause trauma to itself, in addition to the trauma of the brain that is occurring from the areas of infarct and lack of oxygen, which causes neuron death.
What to do if I see a carotid injection?
be safe
-once the horse is on the ground, can support horse with anesthetic, benzodiazepine, sedative….. to control siutation
>reversal of the drug will not be useful as the effect is from irritation of the vasculature
Proximal paravertebral block in bovine goes where? considerations for femoral nerve?
Blocks T13, L1, L2, and L3.
This block is also known as the Farquharson, Hall, or Cambridge technique and the term proximal refers to the proximity to the spine.
Generally, nerves T13, L1 and L2 are blocked. The inclusion of nerve L3 provides better anesthesia of the caudal third of the abdominal flank. The latter nerve is sometimes considered one of the contributors to the femoral nerve and blocking it may potentially result in hindlimb weakness; however the femoral nerve is mostly derived from L4, L5 and L6 [18], which makes ataxia very unlikely.
how to best locate the dorsal and ventral branches of the spinal nerves for a paravertebral block?
-The proximal paravertebral technique involves the perineural injection of local anesthetic in proximity to the spinal nerves as they emerge from the vertebral canal.
To locate the site of injection it is best to identify the lumbar transverse processes by counting them starting at lumbar transverse process 5, which is the most proximal and cranial to the tuber coxae; then move cranial, because lumbar transverse process 1 is not always palpable, depending on the degree of obesity of the animal, and may be confused with lumbar transverse process 2
Cattle have six lumbar vertebrae, but transverse process 6 is significantly smaller and hidden by the iliac wing
to block nerves T13, L1, L2, and L3 it is necessary to locate lumbar transverse processes 1 through 4.
the spinal needle is directed towards the lumbar transverse process and once in contact with it, it is walked-off towards the cranial edge until it advances through the intertransverse ligament and then situated ventrally for blockade of the ventral branch of nerve
how much lidocaine do we use to block ventral paravertebral branches? dorsal?
-20mL for ventral
-5mL for dorsal
how much lidocaine do we use to block ventral paravertebral branches? dorsal?
-20mL for ventral
-5mL for dorsal
for 2% lidocaine
why does a paravertebral blcok last longer than an L block?
administration of anesthetic is more circumscribed to the main nerves; therefore blocks of 90-120 minutes are produced.
