Tocolytics & Uterotonics Flashcards
Why are tocolytics given?
The goal of tocolytics is to allow the uterine to relax so we can delay delivery long enough, give corticosteroids, and optimize the parturient
What is the onset of tocolytics?
onset is 18 hours, maximum benefit at 48 hours
Why are tocolytics given for a neonate?
to reduce neonatal risk including respiratory distress syndrome, intraventricular hemorrhage, necrotizing enterocolitis, perinatal death
List the 6 tocolytic drugs:
magnesium sulfate calcium channel blockers B-adrenergic agonists Nitric oxide donors Cyclooxygenase inhibitors Oxytocin antagonists
Tocolytics inhibit labor by
generation or alteration of intracellular message
inhibiting synthesis or block action of a myometrial stimulant
-they are considered to have a marginal effect
What is the mechanism of action of magnesium sulfate?
- alter calcium transport and availability for muscle contraction
- compete with intracellular calcium reducing myometrial contractility
- Hyperpolarization of the plasma membrane leads to inhibition of the myosin light-chain kinase activity as magnesium
What muscles does magnesium sulfate relax?
vascular, bronchial, and uterine smooth muscle
What are two additional effects magnesium sulfate has?
depress motor endplate sensitivity
muscle membrane excitability
What does magnesium sulfate treat?
treatment of preeclampsia
relaxes vascular smooth muscle decreasing SVR &
BP
anticonvulsant (raises seizure threshold)
Decreases fibrin deposition, improving circulation
to visceral organs
What are the neonatal side effects of magnesium sulfate?
hypotonia
respiratory depression
What is the loading dose of magnesium sulfate?
4 to 6 grams IV over 20-30 minutes
What is the infusion dose of magnesium sulfate?
1 to 2 gm/hour
What is the therapeutic level of magnesium sulfate?
4 to 9 mEq/L
How long is magnesium sulfate given?
continued through delivery and up to 24 hours post delivery
What is the normal level of serum magnesium during pregnancy?
1.8 to 3 mg/dL
What is the tocolytic range of magnesium sulfate?
4 to 8 mg/dL
What EKG changes will we see with magnesium sulfate & at what range?
at 4 to 8 mg/dL we will have prolonged p to q and QRS is widened
At what range of serum magnesium is it an anticonvulsant effect?
7 to 9 mg/dL
What range of serum magnesium are tendon reflexes abolished?
10 to 12 mg/dL
What range of serum magnesium does respiratory depression occr?
> 12 mg/dL
At what range of serum magnesium does SA and AV blocks and respiratory arrest occur?
15-20 mg/dL
At what range of serum magnesium does apnea occur?
18 mg/dL
At what range of serum magnesium do we see cardiac arrest?
25 mg/dL
What are the most concerning side effects of magnesium sulfate?
CNS depression, hypotension, sedation, skeletal muscle weakness
Magnesium sulfate antagonizes
alpha agonist
Magnesium sulfate potentiates
neuromuscular blocking drugs
Other side effects of magnesium sulfate include:
flushing, palpitations, chest pain, nausea, blurred vision, pulmonary edema, and vascular dilation
How do we treat a magnesium sulfate overdose?
stop the infusion
secure airway- support breathing
administer calcium chloride
diuretics
What are the important anesthetic implications of magnesium sulfate?
-exaggerated hypotension after administration of epidural or general anesthesia
- succinylcholine dose is not reduced for intubation
defasiculating doses are not required
reduce maintenance doses of nondepolarizing
muscle relaxants
-symptomatic hypocalcemia and respiratory compromise have occurred in cases of myotonic dystrophy
What is the most commonly used calcium channel blocker?
nifedipine because it can be taken PO or sublingually
What is the mechanism of action of calcium channel blockers?
- blocks the influx of calcium ions through the cell membrane
- block release of calcium ions from the SR
- inhibit calcium-dependent myosin light chain kinase-mediated phosphorylation
- acts on potassium channels
How long is birth delayed with calcium channel blockers?
2-7 days