Tocolytics & Uterotonics Flashcards
Tocolytics
Relax uterus to delay delivery
Inhibit labor via generation or alteration intracellular messengers and/or inhibit synthesis or block action of myometrial stimulant
Administer concomitantly w/ corticosteroids
Onset ≈ 18hrs
Maximum effect at 48hrs
Magnesium Sulfate
Vascular, bronchial, & uterine smooth muscle relaxation
Preeclampsia treatment - relaxes VSMC, ↓SVR/BP, anticonvulsant, ↓fibrin deposition improving circulation to visceral organs
Neonatal SE - hypotonia & respiratory depression
Magnesium Sulfate MOA
Alter Ca2+ transport & availability for muscle contraction
Complete w/ intracellular Ca2+ → reducing myometrial contractility
Hyperpolarization plasma membrane leads to inhibition myosin light-chain kinase activity
Depress motor endplate sensitivity
Muscle membrane excitability
Magnesium Sulfate Dose
Loading dose 4-6g IV over 20-30min
Infusion 1-2g/hr
Therapeutic level 4-9mEq/L
Continue through delivery & 24hrs post-delivery
Serum Magnesium
1.8-3 mg/dL Tocolytic range 4-8mg/dL Anticonvulsant 7-9mg/dL Tendon reflexes abolished 10-12mg/dL Respiratory depression >12mg/dL SA/AV blocks (respiratory arrest) 15-20mg/dL Apnea 18mg/dL Cardiac arrest 25mg/dL
Magnesium Sulfate SE
Hypotension Sedation Skeletal muscle weakness CNS depression Flushing Palpitations Chest pain Nausea Blurred vision Pulmonary edema Vascular dilatation
Magnesium Sulfate Overdose
Discontinue infusion
Secure airway
IV calcium chloride admin
Diuresis
Magnesium Sulfate Anesthetic Implications
Hypotension after epidural or general anesthesia administration
Succinylcholine dose not reduced for intubation
Symptomatic hypocalcemia and respiratory compromise have occurred in myotonic dystrophy cases
Calcium Channel Blockers
Nifedipine commonly used PO or sublingually
Ca2+ Channel Blockers MOA
Block calcium ions influx through cell membrane
Block calcium release from SR
Inhibit calcium-dependent myosin light chain kinase mediated phosphorylation
Acts on potassium channels
Ca2+ Channel Blockers SE
Hypotension exaggerated w/ neuraxial or general anesthesia Dyspnea Pulmonary edema Tachycardia Headache
Ca2+ Channel Blockers Anesthetic Implications
Expect hypotension w neuraxial or general anesthesia
Potential uterine atony refractory to oxytocin and prostaglandins
- Both act through Ca2+ channels
- Adequate IV access and Methergine to treat uterine atony
β2 Agonists
β2 receptors result in smooth muscle relaxation
Myometrial contractility inhibition
Increase progesterone production - progesterone causes histologic changes in myometrial cells that limit contractile impulse spread
Ex: Terbutaline
β2 Stimulation
↑ blood sugar & insulin levels
K+ redistributed to intracellular compartment lowering levels (as low as 3mEq/L)
Returns to baseline w/in 72hrs
Neonatal hypoglycemia
↑ insulin secretion in response to hyperglycemia
Following delivery glucose load from the mother ceases leading to rebound hypoglycemia
Fetal tachycardia common
β2 Agonists SE
Maternal & fetal tachycardia Dysrhythmias Ischemia Hypotension Pulmonary edema Headache Hyperglycemia Hypokalemia ↑ plasma renin & vasopressin
β2 Agonists Anesthetic Implications
Delay anesthesia for 60min to allow heart rate to decrease
Avoid drugs that increase heart rate - Ketamine, Atropine, Glycopyrrolate, Thiopental, Pancuronium, Etomidate
Monitor IV administration d/t fluid overload & pulmonary edema risk
Treat hypotension w/ Phenylephrine or Ephedrine
Nitric Oxide Donors Inhibitors
Nitroglycerine
↑ cyclic guanosine monophosphate (cGMP)
Inactivates myosin light-chain kinase causing smooth muscle relaxation
Cyclooxygenase Inhibitors
NSAIDs
Converts arachidonic acid to prostaglandin H2
Non-selective: Indomethacin
COX-2 selective: Celecoxib
COX Inhibitors Anesthetic Implications
Platelet inhibition associated w/ non-selective COX inhibitors
Transient & reversible
Neuroaxial anesthesia not contraindicated
Other maternal side effects minimal and have little concern for anesthesia
Tocolytics Anesthetic Implications
Neuraxial preferred over general anesthesia
Know baseline BP
Maternal hemorrhage poorly tolerated d/t Magnesium vasodilation
Succinylcholine muscle relaxant choice for rapid sequence induction
Utertonics
Uterine atony leading postpartum hemorrhage cause
- Fundal massage
- Administer oxytocin
Oxytocin
Endogenous hormone produced by posterior pituitary gland - lowers threshold for uterine smooth muscle depolarization
Synthetic oxytocin (Pitocin, Syntocinon) are octapeptides
- Fewer side effects than endogenous
- r/t antidiuretic hormone
Routinely administered after delivery
20-40u/L isotonic IV solution over 15-20min
Used prophylactically to reduce blood loss after delivery
Infusions at low controlled rate are used to induce labor
Oxytocin Anesthetic Implications
Vasodilation or ↓SVR
Significant hypotension & tachycardia
Avoid IV boluses
Ergot Alkaloids
2nd line uterine atony treatment
Effective to decrease postpartum blood loss & PPH
Produce tetanic uterine contractions restricting their use during post-delivery period
MOA not clear
α adrenergic agonist effect?
Methergine - synthetic
Ergotrate - semisynthetic
Methergine
0.2mg IM Contractions occur w/in minutes Repeat dose in 15-20min Total 0.8mg Ø IV bolus administration → Profound hypertension → Severe N/V → Cerebral hemorrhage
Methergine Anesthetic Implications
Do NOT use:
- Pregnancy-induced or chronic hypertension
- Peripheral vascular disease or ischemic heart disease (MI risk)
Monitor BP carefully and have vasodilating drugs available
N/V occurs in 10-20% women
Effect on vomiting center - cerebral vasodilation admin phenylephrine
Prostaglandins
80-90% effective in post-partum hemorrhage refractory to oxytocin and ergot alkaloids
Second option when Methergine contraindicated
Prostaglandins MOA
↑ myometrial Ca2+ levels subsequently ↑ myosin light-chain kinase activity & uterine contraction
Reduced need for post-op hysterectomy r/t uterine atony
Hemabate
15-Methylprostaglandin F2a (Hemabate)
250mcg IM
Repeat 15-30min
Total dose 2mg
Misoprostol
Prostaglandin E1 Analog Reduced blood loss 800-1000mcg Sublingual or buccal Not preferable to other uterotonics for active 3rd stage labor management
Prostaglandins Anesthetic Implications
Carboprost (Hemabate) in women w/ reactive airway disease → bronchospasm & ventilation-perfusion mismatch & hypoxemia (asthma patients at risk)
Misoprostol used in patients w/ reactive airway disease or pulmonary hypertension
