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OB Chap 12 exam 2
Terms in this set (58)
Why is cocaine used for nasal procedures?
It's an intense vasoconstrictor used to ↓ bleeding.
What cocaine analog was produced in 1905?
What problems were associated with the ester anesthetics?
A lot of 2˚ S.E. Also contained preservatives that caused allergic reactions.
What are amides and why are they better than the esters?
Includes meds such as lidocaine (xylocaine). More stable & less allergenic.
What is the MOA of local anesthetics?
Reversibly inhibit Na-ion conductance & the action potential across the nerve cell membrane.
Explain what happens to the LA as it crosses thru a membrane?
They are lipid soluble & diffuse thru the membrane as uncharged molecules. They connivery to a charged state within the cell.
What binds with the Na channel?
The charged form.
What patients require smaller doses of LAs with spinal/epidural anesthesia and why?
Pregnant. Felt that pregnancy enhances neuronal sensitivity to LAs d/t progesterone.
Injections into what two spaces could cause the patient to immediately seize?
Intravascularly into the carotid, intravascularly into the vertebral artery while attempting scalene block.
Where do local anesthetics bind?
To any Na channel in the body including the brain, if in high enough concentration can bypass the BBB & cause respiratory depression.
What effect can high doses of bupivicaine have on a patient?
Can cause the heart to stop.
What are some signs of local anesthetic toxicity?
Metallic taste, tinnitus, perioral numbness.
Which local anesthetic has a high lipid solubility & easily crosses the BBB?
What is the treatment of allergic reactions?
Inhibit mediator synthesis & release. Reverse mediator effects, prevent inflammatory processes. Catecholamines (epi), steroids (1g of hydrocortisone).
Which local anesthetic is utilized the most in OB anesthesia?
What is the onset, peak, and duration of bupivicaine?
O=8-10 min, P=20 min, DOA=1-1/2 to 2˚
How does bupivicaine used for an epidural affect FHR and why, and how can it be prevented?
FHR decels. Causes vasodilation. Volume overload the patient prior to placing epidural.
What percentage of bupivicaine is used for motor sensory block for a c-section?
What percentage of bupivicaine is used for sensory, pain block for labor?
0.25% or less, 0.1% is good.
What percentage of bupivicaine is used for pain fibers block and what remains intact with this type of block?
.125% Light touch.
What percentage of lidocaine provides satisfactory analgesia?
What percentage of lidocaine is motor block for c-sections?
At what percentage does lidocaine produce a sensory, and partial motor block?
What are some disadvantages of lidocaine?
Doesn't have density to it, doesn't knock out c-fibers, still feel light touch with 2%. Sets up faster than 0.5% marcaine, but when MD pulls on ureters, pt will feel, but by that time the baby is out and can give fentanyl.
What type to LA is chloroprocaine?
Ester (↑ risk of allergic reactions).
When is chloroprocaine used and why?
Rapid extension of epidural block for urgent vaginal/cesarean delivery. Has a rapid onset & short DOA.
What LA is associated with sensory & motor deficit with subarachnoid injection and back pain and why does this occur?
Chloroprocaine d/t meta-bisulfite preservative.
How is LA usually delivered to a patient in labor and why?
Epidural pumps (continuous infusions), single doses not adequate for duration of labor.
What are the advantages to a continuous infusion of LA?
Stable analgesic levels, stable maternal VS, less maternal local systemic toxicity.
What can occur with repeated injection methods with LAs?
When is a single shot of LA usually used?
For late 2nd stage labor (saddle block) & pelvic relaxation for breech or forceps delivery.
What is a complication of spinal/epidural anesthesia and why does it to occur?
Hypotension. Sympathetic block leads to peripheral ventilation, ↓ venous return, ↓ maternal CO & BP.
What can occur if hypotension from spinal/epidural anesthesia if left uncorrected?
↓ uteroplacental perfusion, fetal hypoxia & acidosis.
How is hypotension caused by spinal/epidural anesthesia prevented?
With hydration, avoid aortocaval compression (rotate 10˚).
How is hypotension caused by spinal/epidural anesthesia treated?
Fluids, lateral position, trendelenberg (not long), O2, & vasopressor (ephedrine).
What is ketamine contraindicated in pregnancy?
Full stomach--does not protect airway--aspiration.
What is the most likely cause of inadequate analgesia?
Catheter position relating to other structures or malposition.
Are local anesthetics acids or bases?
List the LA that have greatest to the least CNS toxicity.
Bupivicaine → Tetracaine → Etidocaine → Lidocaine → Mepivicaine → 2-Chloroprocaine
How can a LA be mixed when a dose of 8 mcg/min is needed quickly be calculated?
Add 8 mg of drug to 250 mL and run at 15 mL/hr=8 mcg/min.
What property of bupivicaine makes it good for OB?
Highly protein bound (limits placental transfer).
Describe epidural spread.
70% upward (d/t neg thoracic pressure). 30% downward.
What is a risk with the use of indwelling subarachnoid catheters?
Cauda equina syndrome.
What is typical epidural bupivicaine dosing?
0.1% at 12-13 mL/hr
How would you treat ventricular arrhythmia associated with intravascular LA?
Lipid rescue, amiodarone.
Pt with an epidural and now has hypotension, dyspnea, inability to speak, loss of consciousness, what could be going on, and how can it be verified?
Epidural catheter in the subarachnoid or subdural space. Test dose to verify
What causes extensive motor block?
Repeated doses or many hours of local anesthetic.
Most commonly used in combo with dilute local anesthetics. Used for labor. Rapid onset, prolonged block, fewer S.E.
What is the most common S.E. from intraspinal opioids?
Pruritis which appears to be unrelated to histamine release but to the disturbed sensory input to the trigeminal nucleus.
What are the other S.E. caused by intraspinal opioids?
N&v, urinary retention (in men w/ BPH), respiratory depression, slowed progress of labor, possible PDPH.
How is the pruritis caused by intraspinal opioids treated?
1 amp narc in 1 L NS, run at 15-30cc/˚ (doesn't effect pain control).
Done by obstetrician, effective for 1st stage pain, ineffective for 2nd stage.
What is the most common complication of paracervical block?
Fetal bradycardia, the needle can also accidentally get in babies head.
What are pudendal blocks used for?
2nd stage labor. Commonly used to fix tears.
What is the goal of pudendal blocks?
Goal to block pudendal nerve distal to its formation by S2 & S4.
What does a lumbar sympathetic block block?
The visceral afferents from the uterus & cervix where they join the sympathetic chain at L2-L3.
What a lumbar sympathetic blocks good for?
Only for 1st stage labor.
Often performed w/ pundendal nerve block, done by obstetrician, only provides anesthesia for episiotomy & repair.
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