Uterine Anatomy and Pharmacology in Pregnancy
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Questions and Answers

What percentage of maternal CO is uterine blood flow in the 3rd trimester?

  • 15%
  • 10%
  • 25%
  • 20% (correct)

    • What is the primary source of blood flow to the gravid uterus?

  • Internal iliac arteries
  • Uterine arteries (correct)
  • Ovarian arteries
  • Renal arteries

    • What is the most common cause of postpartum hemorrhage?

  • Uterine atony (correct)
  • Placenta previa
  • Coagulopathy
  • Uterine rupture

    • What is the effect of oxytocin on uterine receptors?

    <p>Stimulation of calcium channels and prostaglandin production</p> Signup and view all the answers

    What is the mechanism of action of Mg in uterine relaxation?

    <p>Blockade of calcium receptors</p> Signup and view all the answers

    What is the effect of β2 agonist activation on uterine smooth muscle?

    <p>Relaxation</p> Signup and view all the answers

    Which of the following is a high-risk factor for postpartum hemorrhage?

    <p>Abnormal VS</p> Signup and view all the answers

    What is the action of methylergonovine (methergine)?

    <p>α1 agonist</p> Signup and view all the answers

    What is the primary mechanism of action of tocolytics?

    <p>Blocking calcium or prostaglandin synthesis</p> Signup and view all the answers

    What is the main goal of therapy when using tocolytics for preterm labor?

    <p>To transfer the mother to a tertiary care facility</p> Signup and view all the answers

    What is the effect of magnesium on seizure threshold in pre-eclampsia?

    <p>It increases seizure threshold</p> Signup and view all the answers

    What is the primary mechanism of action of nifedipine?

    <p>Antagonism of calcium channels at the sarcoplasmic reticulum</p> Signup and view all the answers

    What is the risk of using magnesium in patients with preterm labor?

    <p>Pulmonary edema</p> Signup and view all the answers

    What is the effect of ritodrine and terbutaline on smooth muscle?

    <p>It causes relaxation</p> Signup and view all the answers

    What is the formula for uterine perfusion?

    <p>(Uterine arterial pressure - uterine venous pressure)/uterine vascular resistance</p> Signup and view all the answers

    What is the effect of magnesium on the fetus when used in preterm labor?

    <p>It decreases fetal heart rate variability</p> Signup and view all the answers

    What is the effect of stimulation on glucose metabolism?

    <p>It increases blood glucose levels</p> Signup and view all the answers

    What is a pulmonary implication of terbutaline use on the maternal side?

    <p>Pulmonary edema</p> Signup and view all the answers

    What is the mechanism of action of indomethacin in the context of tocolysis?

    <p>Inhibition of prostaglandin synthetase</p> Signup and view all the answers

    What is a potential side effect of indomethacin use in the fetus?

    <p>Premature closure of the ductus arteriosus</p> Signup and view all the answers

    What is the mechanism of action of nitroglycerin in the context of uterine relaxation?

    <p>Increase in cGMP levels</p> Signup and view all the answers

    What is oxytocin primarily used for?

    <p>Postpartum hemorrhage</p> Signup and view all the answers

    What is the 'Rule of 3s' in the context of oxytocin administration?

    <p>3 units of Pit in 3 ml over 3 minutes</p> Signup and view all the answers

    What is the mechanism of action of uterotonics?

    <p>Increase in calcium levels</p> Signup and view all the answers

    What is the primary indication for the use of Hemabate in obstetrics?

    <p>Treatment of postpartum hemorrhage</p> Signup and view all the answers

    What is the primary concern when administering misoprostol to a patient with reactive airway disease?

    <p>Precipitating severe bronchospasm</p> Signup and view all the answers

    What is the mechanism of action of ephedrine?

    <p>Indirect α and β agonist</p> Signup and view all the answers

    What is the primary use of vasopressors in obstetrics?

    <p>Emergent situations</p> Signup and view all the answers

    What is the effect of PGE2 on hemodynamics?

    <p>Increases systolic volume and pulmonary vascular resistance</p> Signup and view all the answers

    What is the primary indication for the use of phenylephrine in obstetrics?

    <p>Maternal cocaine use</p> Signup and view all the answers

    What is the primary effect of hydralazine on the cardiovascular system?

    <p>Decreases peripheral vascular resistance</p> Signup and view all the answers

    What is the primary indication for the use of epinephrine in obstetrics?

    <p>Epidural test dose</p> Signup and view all the answers

    What is the primary effect of oxytocin on blood vessels?

    <p>Vasodilation</p> Signup and view all the answers

    What is the recommended dose of oxytocin for laboring patients requiring a cesarean section?

    <p>3IU bolus followed by 5-10 U infusion</p> Signup and view all the answers

    What is the effect of continuous exposure of myometrium cells to oxytocin?

    <p>Significant loss in capacity to respond to oxytocin</p> Signup and view all the answers

    What is the mechanism of action of methergine (methylergonovine)?

    <p>α1 activation</p> Signup and view all the answers

    Why should methergine (methylergonovine) be avoided in certain patients?

    <p>Due to its risk of retinal damage, pulmonary edema, and cerebral hemorrhage in hypertensive patients</p> Signup and view all the answers

    What is the effect of oxytocin on systemic vascular resistance?

    <p>Decreases it</p> Signup and view all the answers

    What is the role of prostaglandins in uterine tone and contractions?

    <p>Essential for uterine tone and contractions</p> Signup and view all the answers

    What is the mechanism of action of prostaglandins?

    <p>Increases Ca2+ leading to uterine contraction</p> Signup and view all the answers

    What percentage of maternal cardiac output is uterine blood flow in the third trimester?

    <p>20%</p> Signup and view all the answers

    Which of the following is a low-risk factor for postpartum hemorrhage?

    <p>Singleton pregnancy</p> Signup and view all the answers

    What is the action of β2 agonist activation on uterine smooth muscle?

    <p>Decreases calcium levels</p> Signup and view all the answers

    What is the primary source of blood flow to the gravid uterus?

    <p>Uterine arteries</p> Signup and view all the answers

    What is the effect of magnesium on uterine smooth muscle?

    <p>Relaxes smooth muscle</p> Signup and view all the answers

    What is the middle layer of the uterus?

    <p>Myometrium</p> Signup and view all the answers

    What is the most common complication of postpartum hemorrhage?

    <p>Uterine atony</p> Signup and view all the answers

    What is the effect of prostaglandins on uterine smooth muscle?

    <p>Stimulates smooth muscle contraction</p> Signup and view all the answers

    What is the primary goal of administering steroids to the mother in preterm labor?

    <p>To reduce neonatal morbidity associated with immature lungs</p> Signup and view all the answers

    What is the effect of magnesium on uterine contractions in preterm labor?

    <p>It relaxes uterine smooth muscle</p> Signup and view all the answers

    What is the mechanism of action of calcium channel blockers in tocolysis?

    <p>They block calcium at binding sites on the sarcoplasmic reticulum</p> Signup and view all the answers

    What is the risk of using β-mimetics in preterm labor?

    <p>Pulmonary edema</p> Signup and view all the answers

    What is the indication for administering antibiotics to the mother in preterm labor?

    <p>To prevent neonatal group-B strep infection</p> Signup and view all the answers

    What is the effect of nifedipine on uterine smooth muscle?

    <p>It relaxes uterine smooth muscle more than other CCBs</p> Signup and view all the answers

    What is the effect of magnesium on the fetus when used in preterm labor?

    <p>It decreases fetal heart rate variability</p> Signup and view all the answers

    What is the indication for using magnesium in preterm labor?

    <p>To prevent seizures in pre-eclampsia</p> Signup and view all the answers

    What is the primary effect of indomethacin on fetal development?

    <p>Premature closure of ductus arteriosus</p> Signup and view all the answers

    Why is terbutaline used for external cephalic version?

    <p>To relax the uterus and prevent distress</p> Signup and view all the answers

    What is the mechanism of action of nitroglycerin in uterine relaxation?

    <p>Inhibition of GC leading to increased cGMP</p> Signup and view all the answers

    What is the primary indication for the use of uterotonics?

    <p>Postpartum hemorrhage</p> Signup and view all the answers

    How does oxytocin stimulate uterine contractions?

    <p>By increasing calcium influx</p> Signup and view all the answers

    What is a potential side effect of indomethacin use in the fetus?

    <p>All of the above</p> Signup and view all the answers

    What is the recommended dose of terbutaline for tocolysis?

    <p>25 mg IV/SQ</p> Signup and view all the answers

    Why is uterine hypertonicity a concern during labor?

    <p>It can lead to fetal distress</p> Signup and view all the answers

    What happens to oxytocin receptors in active labor compared to non-laboring patients?

    <p>They decrease</p> Signup and view all the answers

    What is the effect of oxytocin on systemic vascular resistance?

    <p>It decreases it</p> Signup and view all the answers

    What is the mechanism of action of methergine (methylergonovine)?

    <p>α1 activation → uterine contraction</p> Signup and view all the answers

    What is the primary use of prostaglandins in obstetrics?

    <p>Uterine contraction</p> Signup and view all the answers

    What is the effect of continuous exposure of myometrium cells to oxytocin?

    <p>Decreased oxytocin receptor expression</p> Signup and view all the answers

    Why should methergine (methylergonovine) be avoided in certain patients?

    <p>It can cause hypertension and peripheral vasoconstriction</p> Signup and view all the answers

    What is the recommended dose of oxytocin for laboring patients requiring a cesarean section?

    <p>3 IU bolus followed by 5-10 U infusion</p> Signup and view all the answers

    What is the effect of oxytocin on cardiac output?

    <p>It increases cardiac output</p> Signup and view all the answers

    What is the primary concern when administering Hemabate to a patient with reactive airway disease?

    <p>Precipitating severe bronchospasm</p> Signup and view all the answers

    What is the effect of PGE2 on hemodynamics?

    <p>Increases SVR and PVR</p> Signup and view all the answers

    What is the primary indication for the use of ephedrine in obstetrics?

    <p>Hypotension following neuraxial placement</p> Signup and view all the answers

    What is the effect of hydralazine on the cardiovascular system?

    <p>It is a direct arteriole dilator</p> Signup and view all the answers

    What is the primary mechanism of action of vasopressors in obstetrics?

    <p>Alpha-1 agonist</p> Signup and view all the answers

    What is the main goal of therapy when using misoprostol in postpartum hemorrhage?

    <p>To treat postpartum hemorrhage</p> Signup and view all the answers

    What is the primary indication for the use of phenylephrine in obstetrics?

    <p>Maternal cocaine use</p> Signup and view all the answers

    What is the effect of misoprostol on the fetus?

    <p>It increases fetal heart rate</p> Signup and view all the answers

    Study Notes

    Uterine Anatomy and Physiology

    • Uterine arteries (branches of internal iliac arteries) are the primary source of blood flow to the gravid uterus
    • Uterine blood flow is 500-900 ml/min, accounting for 20% of maternal cardiac output in the 3rd trimester
    • The uterus is composed of three layers: perimetrium (outer), myometrium (middle, muscular), and endometrium (inner)

    Uterine Atony and Postpartum Hemorrhage

    • Uterine atony is the most common cause of postpartum hemorrhage, complicating up to 10% of deliveries
    • Risk factors for uterine atony include: low risk (singleton pregnancy, <4 previous deliveries, unscarred uterus, absence of history of postpartum hemorrhage), medium risk (prior cesarean or uterine surgery, >4 previous deliveries, multiple gestation, large uterine fibroids, chorioamnionitis, Mg sulfate use, prolonged oxytocin use), and high risk (previa, accreta, increta, percreta; Hct <30%; bleeding at admission; known coagulation defect; history of postpartum hemorrhage; abnormal vital signs)

    Uterine Receptors

    • The uterus is made up of smooth muscle with multiple receptors, including oxytocin receptors, prostaglandins, α1, and β2
    • Oxytocin acts directly on oxytocin G-protein receptors to stimulate calcium channels and increase prostaglandin production, leading to smooth muscle contraction
    • α1 agonists, such as methylergonovine, stimulate smooth muscle contraction
    • β2 agonists, such as terbutaline, relax smooth muscle
    • Magnesium competes with calcium receptors, leading to uterine relaxation

    Tocolytics

    • Tocolytics are medications used to slow or stop contractions
    • Mechanisms of action include decreasing calcium influx or blocking prostaglandin synthesis
    • Indications include preterm labor, uterine tetany, retained placenta, and fetal head entrapment
    • Goals of therapy include transferring the mother to a tertiary care facility, administering antibiotics to prevent neonatal group-B strep infection, administering steroids to decrease neonatal morbidity associated with immature lungs, and treating any underlying cause of preterm labor

    Medications for Uterine Relaxation

    • Magnesium IV bolus (4-6 g) over 20-30 minutes followed by 1-2 g/hr infusion: blocks calcium at binding sites on sarcoplasmic reticulum, used for seizure prophylaxis with pre-eclampsia
    • Nifedipine: antagonizes calcium channels at sarcoplasmic reticulum, has a greater effect on the uterus compared to other calcium channel blockers
    • Ritodrine and terbutaline: selective β2 agonists, stimulate gluconeogenesis, and decrease blood glucose and insulin secretion
    • Indomethacin: inhibits cyclooxygenase-1 and -2, preventing prostaglandin synthesis, prolongs pregnancy by 2-7 days in preterm labor
    • Nitroglycerin: inhibits guanylate cyclase, increases cGMP, and inhibits calcium influx, leading to smooth muscle relaxation, used for rapid uterine relaxation in cases of head entrapment or fetal distress

    Uterotonics

    • Oxytocin: stimulates calcium influx, increases prostaglandin production, and causes smooth muscle contraction
    • Methylergonovine: α1 agonist, stimulates smooth muscle contraction, used for postpartum hemorrhage
    • Prostaglandins: naturally occurring hormones, stimulate smooth muscle contraction, used for postpartum hemorrhage and induction of labor

    Vasopressors

    • Epinephrine: α1 and β1 agonist, used in epidural "test dose" to rule out epidural catheter misplacement
    • Ephedrine: direct α and β agonist, indirect inhibitor of norepinephrine reuptake, used for hypotension following neuraxial placement
    • Phenylephrine: α1 agonist, vasopressor of choice in maternal cocaine use, maintains cardiac output even with a decrease in heart rate

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