Tocolytics and Uterotonics

Question 1

tocolytic drugs include

Answer 1

magnesium sulfate
CCB's
Beta adrenergic agonists
nitric oxide donors
cyclooxygenase inhibitors
oxytocin antagonists

Question 2

how do tocolytics inhibit labor

Answer 2

generation or alteration of intracellular messengers or inhibiting synthesis or block action of myometrial stimulant

Question 3

magnesium sulfate MOA

Answer 3

alter calcium transport and availability for muscle contraction. compete with intracellular calcium, reducing myometrial contractility, hyper polarization of plasma membrane leads to inhibition of myosin light chain kinase activity. depresses motor endplate sensitivity, and muscle membrane excitability.

Question 4

what does magnesium sulfate relax.

Answer 4

relaxation of vascular, bronchial, uterine smooth muscle. decreases SVR and BP. decreases fibrin deposition, improving circulation to visceral organs

Question 5

what does magnesium sulfate treat

Answer 5

preeclampsia, seizures

Question 6

neonatal SE from mag sulfate

Answer 6

hypotonia, respiratory depression. rare

Question 7

tocolytic magnesium sulfate therapeutic range

Answer 7

4-9mg/dL (P-Q lengthened, QRS widened)

Question 8

magnesium sulfate SE

Answer 8

decreased BP, antagonism of alpha agonist, potentiation of NMB drugs.
flushing, transient hypotension, palpitations, chest pain, nausea, blurred vision, sedation, pulmonary edema, skeletal muscle weakness, CNS depression, vascular dilation

Question 9

Magnesium sulfate OD:

Answer 9

discontinue IV, secure airway, IV admin of calcium chloride, diuresis

Question 10

magnesium sulfate anesthetic implications

Answer 10

exaggerated hypotension after administration of epidural or general anesthesia
succinylcholine dose is not reduced for intubation. defasciculating doses are not required. reduce maintenance doses of non depolarizing muscle relaxants.
symptomatic hypocalcemia and respiratory compromise have occurred in cases of myotonic dystrophy.
during spinal/epidural: block pain fibers, ANS. can’t vasoconstrict.

Question 11

Nifedipine drug class and MOA

Answer 11

CCB, blocks influx of calcium ions through cell membrane. block release of calcium from SR. inhibit calcium dependent MLCK mediated phosphorylation (leads to myocetrial relaxation). also can act on K channels. when used as tocolytic, birth is delayed for 2-7 days

Question 12

SE of nifedipine

Answer 12

hypotension, dyspnea, pulmonary edema, tachycardia, headache. enhances NMB effects affecting respiratory and cardiac function

Question 13

Nifedipine anesthetic implications

Answer 13

expect hypotension with administration of neuraxial or general anesthesia. potential uterine atony that may be refractory to oxytocin and prostaglandins. both act through CCB’s.

Question 14

what should be used if uterine atony occurs

Answer 14

methylergonovine (methergine) IV

Question 15

B2 Agonists MOA and effects

Answer 15

smooth muscle relaxation. inhibition of myometrial contractility, increase in progesterone production. progesterone causes histologic changes in myometrial cells that limit spread of contractile impulses.

Question 16

common B2 agonists used

Answer 16

terbutaline
ritodrine (no longer marketed in US)

Question 17

hazards of B2 stimulation

Answer 17

increase blood sugar and insulin levels in mom within a few hours, returns to baseline by itself in 72h
potassium is redistributed to intracellular compartment, lowering K levels to as low as 3mEq/L. returns to normal in 72h
neonatal hypoglycemia r/t increased insulin secretion in response to hyperglycemia. following delivery, glucose load from mother ceases leading to rebound hypoglycemia.
fetal tachycardia is common

Question 18

SE of terbutaline

Answer 18

maternal and fetal tachycardia
dysrhythmias
ischemia
hypotension
p edema (rarely)
headache
hyperglycemia
hypokalemia
increased plasma renin and vasopressin

Question 19

terbutaline anesthetic implications

Answer 19

delay anesthesia for 60 min to allow HR to decrease
if not possible, all drugs that increase HR should be avoided
treat hypotension with phenylephrine and ephedrine

Question 20

which drugs increase HR

Answer 20

ketamine, atropine, glycopyrrolate, thiopental, pancuronium, etomidate.

Question 21

Nitroglycerine drug class and MOA

Answer 21

nitric oxide donor. nitric oxide is necessary for smooth muscle tone. acts by increasing cycling guanosine monophosphate (cGMP)
inactivates MLCK causing smooth muscle relaxation.

Question 22

SE of nitroglycerine

Answer 22

maternal hypotension, headache

Question 23

NSAIDS drug class and MOA

Answer 23

cyclooxyrgenase inhibitors. converts arachidonic acid to prostaglandin H2 which is a substrate for tissue specific enzymes critical to giving birth. prostaglandins enhance formation of myometrial gap junctions. increase available intracellular calcium via raising transmembrane influx and sarcolemmal release, reduce prostaglandin levels by inhibiting cyclooxyrgenase enzymes which results in decreased uterine contraction

Question 24

cyclooxygenase inhibitors of use

Answer 24

indomethacin (nonselective)

celecoxib (cox 2 inhibitor) (tocolytic efficacy equal to mag sulfate in preventing preterm birth within 48h.

Question 25

General Anesthetic Considerations for Tocolytics

Answer 25

tocolytic PK and PD knowledge is essential
neuraxial preferred over general anesthesia
patients on mag sulfate are candidates for neuraxial
mag causes vasodilation, maternal hemorrhage is poorly tolerated
succinylcholine is muscle relaxant of choice for RSI. mag sulfate potentiates both types of muscle relaxants. defasciculatoin and priming are not recommended

Question 26

Oxytocin class and MOA

Answer 26

endogenous hormone produced by posterior ptuitary gland.
lowers threshold for depolarization of uterine smooth muscle. depolarization is enhanced by activation of calcium channels and increased prostaglandin production

Question 27

synthetic oxytocin

Answer 27

octapeptides. cause fewer side effects than endogenous oxytocin. related to ADH.

Question 28

uses for oxytocin

Answer 28

prophylactically to reduce blood loss after delivery. infusions at low controlled rate are also used to induce labor.

Question 29

anesthetic implications of oxytocin

Answer 29

causes a degree of vasodilation or decreased SVR which can result in significant hypotension and tachycardia. associated with IV bolus of oxytocin, avoid boluses

Question 30

ergot alkaloids use

Answer 30

effective for decreasing postpartum blood loss and PPH. produce tetanic uterine contractions restricting their use during post delivery period

Question 31

2 types of ergot alkaloids

Answer 31

methergine (synthetic, dont bolus)

ergotrate (semisynthetic)

Question 32

methergine SE

Answer 32

profound HTN
severe n/v
cerebral hemorrhage

Question 33

methergine anesthetic implications

Answer 33

do not use in women with preexisting HTN, pregnancy induced or chronic.
PVD or ischemia heart disease.
monitor BP carefully and have vasodilation drugs avail
n/v occurs in 10-20% of women

Question 34

prostaglandins MOA

Answer 34

increases myometrial calcium channels and subsequently increases MLCK activity and uterine contraction.

Question 35

hemabate use

Answer 35

reduced the need for postop hysterectomy for uterine atony.

Question 36

misoprostol

Answer 36

prostaglandin E1 analog. reduced blood loss at c section and as effective as oxytocin. for d&c’s

Question 37

reactive airway disease

Answer 37

carboprost use can result in bronchospasm, ventilation perfusion mismatch and hypoxemia. monitor oxygen saturation and lung sounds. misoprostol can be used in patients with reactive airway disease or pHTN