Anesthesiology - Midterm 2

drraythe's version from 2016-03-04 21:59

Local anesthetics

Question Answer
Are LAs acids or bases?WEAK BASES
What are the 2 kinds of LAs (structure wise) & list off some drugs which belong in each groupAmino-Amides:

(basically, nobody cares about poor ester)
What is the MOA for local anesthetics?Works as a direct Na+ channel blockade → prevents Na+ influx to provide membrane stabilization. This means the cell membrane can't depolarize, which means there is no nerve conduction
Order of block corresponds w/ particular nerve fibers. Which fibers for 1,2,3,4,5 block?1: B-fiber
2: C & A-delta
3: A-chi(Χ)
4: A-beta
5: A-alpha (B, C + AΔ, AΧ, Aβ, Aα)
(oh look, it's ABC order backwards for part of it)
Nerve fiber B has what fxn & is involved in what order of block?Order 1. (Autonomic, preganglionic, sympathetic) (Effect of block is warmth from vasodilation)
Nerve fiber C has what fxn & is involved in what order of block?Pain, Order 2
Nerve fiber A-delta has what fxn & is involved in what order of block?Pain & temp, Order 2
Nerve fiber A-chi has what fxn & is involved in what order of block?Mm tone, Order 3
Nerve fiber A-beta has what fxn & is involved in what order of block?Touch, pressure, Order 4
Nerve fiber A-alpha has what fxn & is involved in what order of block?Motor, Order 5
Order of block corresponds w/ particular nerve fiber fxns. name loss of fxns in order of blockVasoconstriction blocked w/ 1
Pain + pain temp blocked w/ block 2
Mm tone from block 3
Touch/pressure w/ block 4
Motor activity blocked w/ block 5 (gets more severe)
Are proximal or distal regions blocked 1st?Proximal
Which is blocked 1st: small sensory, large sensory, or large motor?Small sensory 1st. then large sensory, then motor
Explain how frequency of stimulation influences onset of blockade?More frequently stimulated (in pain) nerves blocked faster (so traumatized tissue more sensitive to blockade)
The potency of a LA is related to its...Lipid solubility (nerve membrane consists of primarily lipids)
What factor of the LA influences its speed of onset? (Explain)pKa! LAs are weak bases (pKa 7.6-9.1), so the closer the LA is to the body pH (7.4) the LESS ionized they are & non-ionized diffuse easier which means they work faster. (Example of 1 w/ pKa close to body pH so it works fast is lidocaine)
Do inflamed tissues ↑ or ↓ effectiveness of LAs?↓ - Bc inflammation lowers pH of tissue & LAs are weak bases & MOST effective at a pH close to their basic pKa. So inflamed tissue = less effective
The protein binding of a LA influences it's what?Protein binding determines duration of action!! More protein bound means WORKS LONGER. (EX: Bupivacaine: 95 % protein bound – long duration. Lidocaine: 65 % protein bound – short duration)
Lipid solubility determines...Potentcy (just like brain w/ gas anesthetics-> more fat loving, more effective)
pKa determines...Onset of action. If not ionized can diffuse faster to start working faster
Protein binding determines...Duration of action. If bound to protein, sticks around for longer
How do LAs affect the blood vessels...and what is the result?Cz VASODILATION (remember B fibers control vasoconstriction, which gets blocked) which means the drug gets carried away faster, which shortens duration of effect
Adding epinephrine to an LA does what?It’s a VASOCONSTRICTER → delayed absorption, prolonged action (look out, localized ischemia possible)
Adding Hyaluronidase to LA does what?(It's an ENZYME) Increasing tissue permeability, facilitates diffusion, rapid onset
Adding Bicarbonate to LA does what?Buffers H+, faster diffusion, shortens onset & duration, injxn less painful (remember, LA are weak bases & if the pH is closer to their pKa, then their onset of action is faster...pKa=IONIZATION)
Describe the metabolism of amide LAs vs ester LAsAMIDE: SLOWLY metabolized in liver, w/ renal excretion, means they can accumulate for a long time after IV infusion
ESTER: Hydrolyzed by plasma cholinesterase (in blood) so they quickly become inactive compounds
How do loco-regional use of LAs affect MAC?They MAC (less pain → lower CO. lower CO means better diffusion into blood. Which means that it's more effective, so the MAC is lower)
MAC sparing affect means?LOWERS the MAC (i.e., if something is lowering the MAC, it's causing the induction to be more effective)
Systemic use of LAs has a CENTRAL analgesic effect, which means it might be able to...Reduce hyperalgesia
How do systemic LAs affect the GI of horses?Prokinetic effect
Do systemic LAs ↑ or ↓ arrhythmias?
What are the 2 stages of SYSTEMC TOXICITY of LAs?(1) Initial CNS tox: Sedation, Disorientation, Ataxia, Muscles tremor, Convulsions, Respiratory Depression
(2) Cardiovascular tox: Depress myocardial contractility, Profound hypotension, Arrhythmias, CV collapse
What is Methemoglobinemia? Which LAs cz it?Methemoglobinemia is a blood disorder in which an abnormal amount of metHb-a form of Hb is produced. W/ Methemoglobinemia, the Hb can carry oxygen but is unable to release it effectively to body tissues. This happens w/ Prilocaine, Benzocaine
How much (%) Lidocaine will cz an irreversible block w/in minutes?5% Lidocaine
What are the LOCAL TOXICITY effects of LAs?Tissue irritation
Neurotoxicity (high concentrations) (5% Lidocaine=irreversible block)
Tissue ischemia (when using epinephrine)
Allergic rxns (esters)
Which group of LAs can cz allergic rxns?Esters (allergic to ester's Cocaine)
How would you Tx seizures induced by systemic tox of LAs?Benzodiazepines, Propofol CRI
How would you Tx CNS depression induced by systemic tox of LAs?Supportive care, mechanical ventilation
How would you Tx cardiac problems induced by systemic tox of LAs?Supportive care, fluids, O2 atropine, antiarrhythmic
What is an IV lipid emulsion & why would you use it?You can use this as resuscitation from cardiac toxicity due to LAs. May remove lipophilic toxins from affected tissue. It surrounds LA molecules in plasma
What is the onset & duration like for Lidocaine?RAPID onset (5min) (pKa close to pH) & short duration (1-2hrs) (is an amide-tissue esterases)
What special thing can you do w/ Lidocaine?Used also for Tx of ventricular tachycardias/-arrhythmias
Who is esp. sensitive to Lidocaine? Side effects?Cats-might cz laryngeal edema in cats (Lidocaine spray for ET intubation)
Uses for Lidocaine?Nerve block, Epidural/spinal, Infiltration, CRI (IV)
What is Mepivacaine onset & duration?Similar to Lidocaine's (5min onset, 1-2hr duration) (think that LI-ME similar....lime)
Uses for Mepivacaine?SC, Local infiltration, Intraarticular (there was a pic of a horse on this slide... ME the HORSE)
Which is more irritating-Lidocaine or Mepivacaine?Lido-mepi is less-bc it is preferred in HORSES & theyre sensitive babies
What is Mepivacaine preferred for?Preferred for equine nerve blocks & intra-synovial analgesia (ME the HORSE)
Bupivacaine-what is the onset & duration?SLOW onset (20-30min) & LONG duration (4-6hrs) (Bupivacaine is a BUM UNDER Pressure → i.e. goes slow)
What is Bupivacaine often used for?Nerve block, epidural/spinal
Which is more cardiotoxic-Bupivacaine or Lidocaine?BUPI more cardiotoxic-(BUP=BUM UNDER PRESSURE= SLOW ONSET & DURATION= being lazy is BAD FOR YOUR HEART)
Which is better for joints-Mepivacaine or Bupivacaine?MEPIVACAINE is USED FOR JOINTS (me the sensitive horse joint) however, BUPIVACAINE czs Damage to articular cartilage → being lazy & fat is bad for your joints
What is the kinda Bupivacaine which is less toxic?L-bupivacaine (L-B-this of Elbe the dog)
Ropivacaine-what is another form which is available? How lipid soluble is it? How cardiotoxic is it?S-Ropivacaine, less lipid soluble than bupi & SIG less cardiotoxic
Which LA allows faster return to motor fxn?Ropivacaine (think of ropes moving your limbs for you till you recover)
What is "EMLA Cream"?Eutectic Mixture of Local Anesthetics... its 2.5% Lidocaine + 2.5% Prilocaine (EMLA (Emily) PRIS open the LIDOCAINE to stop her pain)
What is EMLA cream used for? Notes about its use?Useful for skin anesthesia prior to IV catheter BUT Must wait for action (20-30 minutes) (...duh)
Explain the relationship btwn opioids & LAsOpioids ↑ efficacy & extend duration of block...Morphine often used intra-articular & epidural blocks
Explain the relationship btwn LAs & α2 adrenoceptor agonistsMedetomidine & Dexmedetomidine may extend the duration & ↑ the efficacy of local blocks
LAs can be used for did nerve blockade. What does this mean?like when you have a horse & you start blocking stuff to figure out what's wrong w/ it
List of some topical anesthetic methodsLaryngeal (spray - cats, pigs, rabbits...)
Corneal, cutaneous (EMLA-Eutectic Mixture of Local Anesthetics)
"Splash block" on surgical wounds.
Interpleural/intraperitoneal local anesthesia-WHICH DRUG? ADMIN? How to prevent stinging?BUPIVACAINE (want a SLOW DRUG bc I want my innards to not hurt for as long as possible) admin via chest drain or into abd. Cavity. (4-6 hrs effective analgesia). *you can dilute w/ sodium bicarb to prevent stinging
Infiltrational & incisional anesthesia → useful for what? Explain how you do itUseful for repair of small lacerations or skin mass removal. You do a line block before Sx incision & then before or after the closure. You basically do multiple small SC injxns around area to be desensitized
Intra-articular → commonly used for what? What is given POST-op?Commonly used for stifle Sx/arthroscopy (Mepivacaine is recc for articular Sx) & POST op Bupivacaine is given ((even tho it can cz articular joint damage...?) ...possibly combined w/ Lidocaine. **NOTE: if tissues inflamed, use opioids-LAs wont be very effective
Facial/dental nerve blocks-which are the nerves that are/can be blocked? (4)Mental nerve block
Mandibular nerve block (inferior alveolar)
Infraorbital nerve block
Maxillary nerve block
Mental nerve block-part of what nerve & blocks what stuff?Part of mandibular nerve of TRIGEMINUS (CN V). It blocks the bone, incisors & soft tissue rostral to 2nd mandibular premolar (its the hole at the front of the mandible)
Mandibular nerve block-aka? What is this nerve a part of? what's the area affected by this block? What are the 2 techniques?Aka inferior alveolar nerve block (by angle of jaw). This is a branch of the trigeminal n (CN V) & the areas blocked are mandibular bone, teeth, soft tissue & tongue on infiltrated side. 2 techniques are intraoral & extraoral (on either side of the angle of the jaw)
Infraorbital nerve block-part of what nerve? Blocks what tissues? If the block starts to move caudal, what other block does it become?Part of maxillary branch of trigeminal (V). Blocks bone, soft tissue & dentition rostral to maxillary 1st moral. If LA moves backwards, becomes maxillary block
Whats the only reason you'd do a MAXILLARY block instead of an infraorbital?If you needed to block the soft palate
Areas desensitized by a maxillary nerve block?Maxillary bone (Inject behind last tooth in maxilla)
Upper teeth
Soft tissues
Upper lip
What is a retrobulbar block used for? What are some of the side effects?Produces proptosis (protrusion of eyeball) due to volume injected. Distorts globe an czs ↑ in IOP-but it's used for eye enucleation, so whatever
What is a digital nerve block used for? What nerves does it block? What is an alternative block you can use?Used in onychectomy/digit amputation. You are blocking the superficial branches of the radial & median nerves & dorsal & palmar branches of the ulnar nerve. Can do a RING BLOCK as an alternative
What on earth is a BIER BLOCK? Explain how you do it(AKA IVRA-intravenous regional anesthesia) This is a technique of "IV LOCAL" anesthetic. Place venous catheter, tightly wrapped leg w/ vetwrap from distal to prox to drive out blood then tourniquet was place prox to catheter, then through catheter inject local anesthetic. Commonly used in human med. however the time you have for Sx is limited bc of ischemia-ischemia happens after 60 min. so only have 60 min for procedure. If open tourniquet too early, then systemic effects which is bad. Timed window you cant go below or above. Also good visibility bc less blood all over the place.
Epidural anesthesia/analgesia (EDA)-where do you do this & how to you use landmarks? How is the animal laying?Use LUMBOSACRAL SPACE, L7-S1. Orientation is the wings of the ilia, L7 transverse projection. Animal can be sternal or lateral
Speed at which you want to inject for an epidural (EDA)SLOW injxn over a minute
Where exactly do you inject in epidural?OUTSIDE OF THE DURA MATER