Cardiovascular System Changes in Pregnancy
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Questions and Answers

What typically happens to blood pressure during pregnancy by around 8 weeks of gestation?

  • It generally increases.
  • It remains unchanged.
  • It fluctuates wildly.
  • It typically decreases. (correct)

    • At what point during pregnancy do diastolic blood pressure and mean arterial pressure reach their lowest levels?

  • Postpartum period
  • First trimester
  • Mid-pregnancy (correct)
  • Before delivery

    • How much should the local anesthetic dose be reduced for a pregnant patient to avoid a high neural block?

  • By 30% (correct)
  • By 20%
  • No reduction is necessary.
  • By 10%

    • Why should a wedge or roll be placed under the right hip of a pregnant patient?

    <p>To prevent a decrease in cardiac output.</p> Signup and view all the answers

    What is a consequence of vessel distention within the epidural space during neuraxial blockade?

    <p>Increased risk of vascular damage.</p> Signup and view all the answers

    What type of breathing do pregnant patients favor as the uterus increases in size?

    <p>Thoracic breathing</p> Signup and view all the answers

    What effect does pregnancy have on the required amount of local anesthetics during procedures?

    <p>It decreases the required amount.</p> Signup and view all the answers

    How does the venous system change during pregnancy?

    <p>It increases capacity for distension and dilation.</p> Signup and view all the answers

    What is the average increase in blood volume by the time of delivery during pregnancy?

    <p>1-1.5 liters</p> Signup and view all the answers

    What primarily causes the increase in blood volume during early pregnancy?

    <p>Hormonal changes and metabolic demands</p> Signup and view all the answers

    Which of the following components of blood increases during pregnancy to enhance clotting?

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

    How much blood loss is generally associated with a cesarean section?

    <p>800-1000 ml</p> Signup and view all the answers

    Cardiac output during pregnancy can increase by up to what percentage at term?

    <p>40%</p> Signup and view all the answers

    When does the peak cardiac output typically occur during pregnancy?

    <p>During labor</p> Signup and view all the answers

    What is the expected timeline for cardiac output to return to normal after delivery?

    <p>2 weeks</p> Signup and view all the answers

    What can cause a decrease in cardiac output after 28 weeks of pregnancy?

    <p>Mechanical changes</p> Signup and view all the answers

    Which statement about the effects of anesthesia on gas exchange is inaccurate?

    <p>Increased oxygen delivery</p> Signup and view all the answers

    What is the key characteristic of minimum alveolar concentration (MAC) in inhalational anesthetics?

    <p>It is the concentration that prevents movement in 50% of patients.</p> Signup and view all the answers

    Which inhalational anesthetic does not cause a dose-dependent reduction in minute ventilation?

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

    What effect does positive end-expiratory pressure (PEEP) have in anesthesia?

    <p>Maintains alveolar patency</p> Signup and view all the answers

    Which of the following is NOT a negative effect of Isoflurane on the respiratory system?

    <p>Sweet odor</p> Signup and view all the answers

    Which factor is known to increase the MAC for inhalational anesthetics?

    <p>Chronic alcohol abuse</p> Signup and view all the answers

    Which inhalational anesthetic has the highest MAC value?

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

    What is a characteristic of an ideal inhalational anesthetic?

    <p>Rapid induction and recovery</p> Signup and view all the answers

    Which factor is associated with decreasing MAC?

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

    What primarily governs the partial pressure of anesthetic in body tissues?

    <p>Alveolar partial pressure</p> Signup and view all the answers

    What happens to the concentration of anesthetic in brain tissue during recovery from anesthesia?

    <p>It decreases as the anesthetic concentration lowers</p> Signup and view all the answers

    Which of the following is a misbelief about factors affecting MAC?

    <p>Sex has a significant effect on MAC.</p> Signup and view all the answers

    Which condition is NOT known to decrease MAC?

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

    What change occurs in functional residual capacity (FRC) by term during pregnancy?

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

    How much does minute ventilation increase by the second trimester?

    <p>50%</p> Signup and view all the answers

    What effect does the decrease in FRC have on the patient during apnea?

    <p>Decreases reserve leading to hypoxia</p> Signup and view all the answers

    What is the recommended action for patients undergoing general anesthesia in relation to oxygen?

    <p>Pre-oxygenate with 100% O2</p> Signup and view all the answers

    What factor complicates intubation in the obstetric population?

    <p>Swollen respiratory tract from venous engorgement</p> Signup and view all the answers

    What is the increase in oxygen consumption during pregnancy?

    <p>20-50%</p> Signup and view all the answers

    What should be prepared for intubation because of respiratory changes during pregnancy?

    <p>Smaller endotracheal tubes</p> Signup and view all the answers

    What happens to the renal plasma flow and glomerular filtration rate at term during pregnancy?

    <p>Increases by 50-60%</p> Signup and view all the answers

    Study Notes

    Cardiovascular System Changes During Pregnancy

    • Blood volume increases progressively, reaching 1-1.5 liters more at delivery.
    • Plasma volume increases more than red blood cell production, leading to relative anemia.
    • Increased clotting factors (fibrinogen, factors VII, X, and XI) enhance clotting, minimizing bleeding during delivery.
    • Increased blood volume meets the metabolic demands of the mother and fetus, supporting blood loss during delivery.
    • Average blood loss during vaginal delivery is 400-500 ml, while cesarean section involves 800-1000 ml.
    • Cardiac output increases up to 40% at term, primarily in the first and second trimesters.
    • Cardiac output peaks during labor due to increased heart rate and stroke volume.
    • Heart chambers and myocardium enlarge to handle the increased blood volume.
    • Cardiac output returns to normal 2 weeks after delivery.
    • Despite increased cardiac output and blood volume, blood pressure does not typically rise unless pregnancy-induced hypertension exists.
    • Blood pressure drops around 8 weeks of gestation, reaching its lowest point at mid-pregnancy with a 5-10 mmHg decrease in diastolic pressure and mean arterial pressure.
    • Venous capacity increases by up to 150%, potentially delaying subcutaneous and intramuscular medication absorption.
    • Venous distention in the epidural space can increase the risk of vascular damage and bleeding during neuraxial blockade.
    • Hormonal changes during pregnancy reduce the required dose of local anesthetics for neuraxial blockade by 30%.
    • Using the same local anesthetic dose as in non-pregnant patients can lead to a profound neural block.

    Anesthetic Considerations for Cardiovascular Changes During Pregnancy

    • Never lay the patient supine, use a wedge or roll to "tip" the patient to the left. This prevents supine hypotension syndrome/aortocaval compression.
    • Pregnant patients rely on sympathetic outflow to maintain systolic blood pressure. Preload with 1-2 liters of crystalloid fluids before neuraxial blockade.
    • Vessel distention in the epidural space increases the risk of vascular damage during neuraxial blockade.
    • Vessel distention reduces intrathecal and epidural spaces, requiring a 30% dose reduction of local anesthetics.
    • Subcutaneous and/or intramuscular medication absorption can be delayed.

    Respiratory System Changes During Pregnancy

    • The growing uterus places pressure on the abdomen, causing the pregnant patient to favor thoracic breathing over abdominal breathing.
    • Functional residual capacity (FRC) decreases by 20% at term, returning to normal 48 hours after delivery.
    • This decrease in FRC reduces the patient's respiratory reserve, potentially leading to rapid hypoxia if apnea occurs.
    • Tidal volume (normal volume with each breath) increases by 40%.
    • Minute ventilation increases by 50% by the second trimester, with a respiratory rate increase of 15%.
    • These changes accelerate inhaled anesthetic uptake.
    • Alveolar ventilation increases by 70% at term.
    • Oxygen consumption increases by 20-50%.
    • The combination of decreased FRC and increased oxygen consumption can cause hypoxia.
    • Venous engorgement leads to a swollen respiratory tract, challenging visualization during laryngoscopy.
    • Obstetrics patients are more difficult to intubate than the non-pregnant population.
    • A smaller endotracheal tube may be needed.
    • Manipulation during laryngoscopy can cause bleeding, obstructing the view.

    Anesthetic Considerations for Respiratory Changes During Pregnancy

    • Patients undergoing regional anesthesia should receive supplemental oxygen.
    • Patients undergoing general anesthesia should be pre-oxygenated with 100% O2 before induction.
    • Patients may desaturate despite pre-oxygenation due to increased oxygen consumption and decreased FRC.
    • Be prepared for difficult intubation. Swollen mucous membranes may hinder visualization. Ensure optimal positioning for laryngoscopy.
    • Have smaller endotracheal tubes readily available.
    • Exercise caution during laryngoscopy, as bleeding can obscure the view.

    Renal System Changes During Pregnancy

    • Renal plasma flow and glomerular filtration rate increase by 50-60% at term.
    • These changes correlate with increased cardiac output and blood volume.
    • Increased renal function eliminates anesthetic drugs more rapidly.

    Anesthetic Considerations for Renal System Changes During Pregnancy

    • Anesthetic doses may need adjustment due to increased renal clearance.

    Inhalational Anesthetics Overview

    • Inhalational anesthetics are delivered via inhalation through a face mask, laryngeal mask airway, or endotracheal tube connected to a vaporizer and anesthetic delivery system.
    • Used primarily for maintenance of anesthesia, some can be used for induction.
    • MAC: The minimum alveolar concentration (MAC) is the alveolar concentration that prevents movement in 50% of patients during a standardized stimulus like a surgical incision.
    • Factors Increasing MAC (more volatile needed for anesthesia):
      • Hyperthermia
      • Hypernatraemia
      • Sympatho-adrenal stimulation
      • Chronic alcohol abuse
      • Chronic opioid abuse
      • Increases in ambient pressure
      • Hypercapnia
      • Decreasing age
      • Thyrotoxicosis
    • Factors Decreasing MAC (less volatile needed for anesthesia):
      • Nitrous oxide
      • Hypothyroid/myxedema
      • Hypocapnia
      • Hypothermia
      • Hyponatraemia
      • Increasing age
      • Hypoxaemia
      • Hypotension
      • Anemia
      • Pregnancy
      • CNS depressant drugs
      • Other drugs: lithium, lidocaine, magnesium, Acute alcohol abuse
    • Sex, Weight, and Duration of anesthesia do not affect MAC.
    • Common Inhalational Anesthetics:
      • Nitrous oxide (MAC 105%)
      • Halothane (Fluothane) (MAC 0.75%)
      • Isoflurane (MAC 1.2%)
      • Desflurane (MAC 6.0%)
      • Sevoflurane (MAC 2.0%)

    Ideal Inhalational Anesthetic Characteristics

    • Non-flammable, non-explosive at room temperature
    • Stable in light, liquid, and vaporizable at room temperature
    • Stable at room temperature with a long shelf life
    • Compatible with soda lime, plastics, and metals
    • Environmentally friendly (no ozone depletion)
    • Cheap and easy to manufacture
    • Non-toxic
    • Rapid induction and rapid recovery
    • Safe with no toxic side effects
    • An ideal inhalational anesthetic does not currently exist.

    Pharmacokinetics of Inhalational Anesthetics

    • Forward movement of inhalational agents is driven by partial pressure gradients.
    • This movement begins at the vaporizer and continues through the breathing circuit, alveolar tree, blood, and tissues.
    • The objective is to achieve equal partial pressures on both sides of each barrier.
    • Alveolar partial pressure determines the partial pressure of the anesthetic in all body tissues, eventually reaching equilibrium.
    • After equilibration, the alveolar and brain partial pressures of the gas become equal.
    • Induction rate and waking time are influenced by uptake, ventilation, and concentration.
    • Partial pressure is the ratio of the amount of substance in one phase to the amount in another.

    Recovery from Anesthesia

    • Recovery depends on lowering the concentration of anesthetic in brain tissue.

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    Description

    Explore the adaptations of the cardiovascular system during pregnancy in this quiz. Discover how blood volume increases, the implications of relative anemia, and the changes in cardiac output. Understand the physiological modifications that support both mother and fetus during labor and delivery.

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