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Drugs in Pregnancy

  • N2O has been shown to be a weak teratogen in rodents after high concentrations (50%) are administered for prolonged periods (>24 hours) of time.
  • Large retrospective study showed no difference in incidence of stillbirth or overall congenital anomalies. However, there was an increased incidence of LBW and an increased rate of neural tube defects with exposure in the first trimester.
  • Benzodiazepines have been associated with craniofacial defects (e.g. cleft palate).
  • The evidence dose not support this association and, on occasion, it may be appropriate to provide preop anxiolysis.
  • However, regular use, particularly in the first trimester, should be avoided.

Questions

Postoperative Period

Anesthetic Management

Drugs in Pregnancy

  • Vd increased (secondary to increase in blood volume)
  • Plasma cholinesterase levels decreased by 25%
  • However, prolonged NM blockade with succinylcholine is uncommon as the increased Vd offsets the impact of decreased drug hydrolysis
  • Both Vec & Roc show longer durations of action with normal doses in pregnant patients
  • Nimbex, which undergoes Hoffman elimination, demonstrates a significantly shorter duration of action in pregnant patients
  • Teratogenicity
  • Defined as the observation of any significant change in the function or form of a child secondary to prenatal treatment.
  • Perioperative events leading to severe maternal hypotension pose the greatest risk to the fetus.
  • Hyperthermia is shown to be teratogenic, but hypothermia is not.
  • The impact of any drug depends on the dose and the gestational age at which it was administered.
  • During the first trimester, primarily during the period of organogenesis (days 31-71), the embryo is most susceptible to structural abnormalities.
  • Polar molecules such as NMBs do not cross the placenta in significant amounts (only 10-20% of maternal concentrations).

Anesthetic Plan

  • Room is prepped for GA
  • Prophylaxis against aspiration pneumonitis with H2-blocker (Famotidine)

  • Prior to spinal, 1 L of LR given over 30 min
  • Ephedrine and Neosynephrine drawn up
  • ASA monitors applied, O2 via NC
  • Spinal Anesthesia in sitting position (L4/L5) --12 mg (1.6 mL) of 0.75% Bupivacaine with 25 mcg of Fentanyl
  • Pregnant women require less LA to achieve the same level of anesthesia as non-pregnant women (due to hormonal and mechanical factors)
  • Desire anesthesia at level of umbilicus (T10)
  • Patient tolerated procedure well--no need to convert to GA

Physiologic Changes During Pregnancy

  • GI
  • Circulating progesterone causes a reduction in lower esophageal sphincter tone and a slight increase in gastric acidity.
  • 16 weeks+, at increased risk of developing aspiration pneumonitis.

History

Defibulation

  • 24 yo female, 5'5", 67 kg
  • 21 weeks pregnant (G1P0), no reported complications
  • Home meds: Prenatal vitamins
  • NKDA, no significant PMH
  • Never smoked, denies ETOH use

  • From Somalia -- experienced female genital mutilation (Type III) at the age of 6
  • Requests reversal (defibulation) in order to give birth vaginally
  • Central & Peripheral Nervous Systems
  • 30% reduction in the MACs of volatile anesthetics.
  • Neural tissue demonstrates increased sensitivity to the effects of LAs. Both therapeutic and toxic levels are reduced by ~30%.
  • Reversal is best performed before pregnancy or at least within the second trimester of pregnancy around 20 weeks gestation.

  • Reduces the possibility of extensive lacerations that can occur when the fetal head stretches the scarred tissue.

  • Reduces the chances of fetal asphyxia or stillbirth if a woman progresses unaided to the second stage of labor.

References

  • T or F: There is an inverse relationship between maternal and fetal PaCO2.

  • During pregnancy:

A) MAC decreases

B) FRC decreases

C) LA requirements increase

D) All of the above

E) A & B only

  • Mhuireachtaigh, R.N. and O'Gorman, D.A.

Anesthesia in pregnant patients for nonobstetric surgery. Journal of Clinical Anesthesia (2006) 18, 60-66.

  • Reitman, E. and Flood, P. Anaesthetic

considerations for non-obstetric surgery during pregnancy. British Journal of Anaesthesia 107 (S1): i72-i78 (2011).

  • World Health Organization (www.who.int)
  • Fetal monitoring
  • Continuous FHR monitoring is feasible from 18 weeks gestation
  • FHR variability is useful indicator of fetal well-being and can be monitored from 25 weeks gestation
  • Anesthetic agents reduce both baseline FHR and FHR variability
  • Persistent fetal bradycardia indicates fetal distress
  • Neostigmine has been noted to cause fetal bradycardia when given with glyco because of the reduced placental transfer of the glyco

Physical Findings

  • Hypotension poses a major risk to fetus
  • Caused by hypovolemia, anesthetic drugs, central neuraxial blockade, or aortocaval compression.
  • Uteroplacental circulation is not subject to autoregulation so perfusion is entirely dependent on adequate maternal BP.
  • IV fluid boluses can be used to treat hypotension, but pregnant patients are predisposed to pulmonary edema due to increased capillary permeability.
  • Ephedrine and neosynephrine are both effective and considered safe.
  • Tocometry during this period is useful as postop analgesia may mask awareness of mild early contractions and delay tocolysis.
  • Adequate analgesia is important in the postop period, as pain has been shown to increase the risk of premature labor.
  • A surge in catecholamines can also impair uteroplacental perfusion.
  • Opioids are considered safe, but NSAIDs should be avoided, because of the risk of premature closure of the ductus arteriosus.
  • HR: 68, BP: 121/78, RR: 15, O2 sat: 99% on RA, T: 37.1 C
  • FHR 136 with good variability

  • Mallampati Class II airway, normal mouth opening and neck flexion
  • Lungs CTA
  • S1/S2, no murmurs/gallops/bruits
  • Hct 36, K 3.9, BUN 9, Cr 0.8, Plts 212
  • Fetal well-being is best ensured by careful maintenance of stable maternal hemodynamics and oxygenation.
  • Changes in maternal position can have profound hemodynamic effects.
  • Tburg and RT should be carried out slowly.
  • For GA, RSI induction should be preceded by meticulous denitrogenation with 100% O2 for 5 minutes and application of effective cricoid pressure.
  • PPV should be used with care and ETCO2 levels should be maintained WNL.
  • Maternal hypercarbia limits gradient for CO2 diffusion from fetal to maternal blood and can lead to fetal acidosis, increasing risk of fetal loss.
  • Patients should be extubated fully awake in the LUD position after orogastric suctioning.

Physiologic Changes During Pregnancy

Female Genital Mutilation

  • Also known as "female genital cutting" or "female circumcision"
  • According to the World Health Organization (WHO), it includes "all procedures that involve partial or total removal of the external female genitalia, or other injury to the female genital organs for non-medical reasons."
  • Practiced mainly in 28 countries in western, eastern, and north-eastern Africa, particularly Egypt and Ethiopia, and in parts of Asia and the Middle East.
  • Rooted in gender equality, cultural identity, ideas about purity, modesty, and attempts to control women's sexuality by reducing their sexual desire.
  • Four different classifications, with Type III (infibulation) being the most severe. It includes fusion of the wound with a small hole left for the passage of urine and menstrual blood. The wound is partially opened on the wedding night for intercourse and again for childbirth.
  • Cardiovascular & Hematologic
  • CO peaks in 2nd trimester (up to 50% higher than baseline value), HR increased by 25% and SV by 30%
  • BP under goes minor changes
  • At 12 weeks+, aortocaval compression in supine position becomes clinically relevant
  • Supine hypotensive syndrome is associated with CO reduction of up to 20%
  • Left uterine displacement achieved at tilt of 15-30 degrees
  • Dilutional anemia present
  • Benign leukocytosis up to 15,000 during pregnancy
  • Increased clotting factors VII, VIII, X and XII
  • Hypercoagulable state = high risk of thromboembolic events

Physiologic Changes in Pregnancy

  • Respiratory
  • Increased risk of developing hypoxemia and rapid desaturation
  • Increase in minute ventilation (due to increases in both RR & TV)
  • Gravid uterus exerts a restrictive effect on respiratory mechanics --> decrease in FRC of 20% at term
  • Failed intubation is the leading cause of maternal death caused by anesthesia
  • Anatomical changes related to both weight gain and edema of the upper airway and VCs

Anesthetic Considerations for Non-Obstetric Surgery During Pregnancy

Ashley Mowery

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