Anesthesia for the Pregnant Patient Undergoing Nonobstetric Surgery

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Anesthesia for the Pregnant Patient Undergoing
Nonobstetric Surgery

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• surgery during pregnancy
• 2 of pregnant women/year, involving 75,000
  anesthetics.
• Trauma, ovarian cysts, appendicitis, breast
  tumors, cervical incompetence
• Several unique problems
• alterations in maternal physiology.
• possible teratogenic effects of anesthetic
  agents.
• maintenance of uterine perfusion and effects of
  anesthetic interventions on the fetus.
• prevention of premature labor, the highest cause
  of fetal loss.

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Physiologic Changes of Pregnancy
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• Increase in cardiac output and blood volume
• 30-40 higher by 28 weeks(begin 1st trimester).
• Susceptible to hypotension.
• d/t aortocaval compression in the supine
  position.
• Fetal compromise even in the asymptomatic mother.

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• Respiratory change
• decrease in functional residual capacity(FRC).
• Begin 2nd trimester, 20 decrease in FRC, 20
  increase in oxygen consumption.
• Airway closure during normal tidal ventilation in
  the supine position.
• Predispose to rapid falls in PaO2 during periods
  of apnea or airway obstruction.
• minute ventilation increases(50 at term).
• Capillary engorgement throughout the respiratory
  tract.
• trauma during placement of airways and gastric
  tubes.
• Smaller sized tube, avoid nasal intubation or
  nasogastric tubes.

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• Increased risk of aspiration
• Increase the level of gastrin, progesterone.
• Enlarged uterus
• displace pylorus, alters the function of G-E
  junction.
• Heartburn
• indicates a lower pressure gradient across the
  G-E junction.
• Preoperative aspiration prophylaxis
• nonparticulate antacid, H2 blocker,
  metoclopramide.

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• Neurologic changes
• a 25-40 decrease in MAC for inhalational
  anesthetics.
• A 30 decrease in dosage requirement for local
  anesthetics in the epidural and subarachnoid
  spaces.
• Maternal hyperventilation with alkalosis.
• a left-ward shift of the oxyhemoglobin
  dissociation curve.
• Increasing maternal affinity for oxygen and
  decreasing release to the fetus.
• Positive pressure ventilation
• 25 fall in uterine blood flow.

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Teratogenecity and Safety of Anesthetic Agents
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• Factors affecting the potential teratogenecity of
  of a drug.
• timing of administration.
• individual sensitivity to the agent.
• The threshold or amount of exposure.
• The naturally occurring incidence of congenital
  anomalies.

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• The day 15 to 90 of gestation
• organogenesis is occurring.
• Most vulnerable to teratogenic effects,
  susceptibility to teratogenic agents is highest.
• After 13 weeks, organogenesis is complete.
• growth retardation or functional effects rather
  than structural defects.

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• Medical and social factors
• Diabetic mothers
• 4-12 incidence of major congenital anomalies.
• Use of cocaine and heroin
• associated with microcephaly and other
  abnormalities of brain developments.
• paternal exposure to drugs
• cocaine
• binds to sperm, enter the ovum at the time of
  conception.
• Increased incidence of congenital anomalies.

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• Small Animal Studies
• Problems
• variability in drug-induced teratogenic effects
  among species.
• In animal studies, investigators does not monitor
  or control closely.
• does not simulate usual operating room.
• But doing comparable studies in humans require
  exposure of large numbers of pregnant woman.

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• Animal studies have indicated the safety of
  several drugs.
• Morphine, fentanyl, sufentanil, alfentanil.
• Thiopental, methohexital, etomidate, ketamine.
• Halothane, enflurane, isoflurane
• not teratogenic in 0.75 MAC doses.
• lidocaine 500 mg/kg/day.
• Benzodiazepine drugs
• 1975, increased exposure to diazepam in women
  whose infants had a cleft lip anomaly was
  reported.
• package inserts,
• an increased risk of congenital malformations
  associated with the use of benzodiazepine drugs
  has been suggested in several studies.

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• Nitrous Oxide
• Inactivates Vitamine B12, inhibit methionine
  synthetase, affecting production of DNA
  precursors.
• Reduction of methionine synthetase activity
  interferes with folate metabolism.
• give folate preoperatively to pregnant women
  undergoing general anesthesia.
• A reduction in neural-tube defects when folic
  acid supplementation is given.
• Nitrous oxide enhances adrenergic tone and causes
  vasoconstriction.
• halogenated agents(halothane and isoflurane)
• attenuate enhanced adrenergic tones, preserving
  uterine blood flow.
• Anomalies and resorptions are prevented.

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• Occupational Exposure studies
• The personnel chronically exposed to low levels
  of anesthetic gases.
• an increase in the incidence of spontaneous
  abortion and congenital anomalies.
• Methodologic weakness
• recall bias, confounding variables.
• Control these variables
• no increased rate of abortion, no decrease in
  birth weight, no increase in congenital
  anomalies, and no increase in perinatal
  mortality.

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• Studies on Outcome after Surgery during Pregnancy
• A consistent increase in fetal mortality because
  of preterm labor with delivery of a previable
  fetus.
• Canada (1971-1978)
• no increase in conganital anomalies, an increased
  risk of spontaneous abortion in women in the
  first or second trimester.
• No increased risk of abortion for those receiving
  no anesthetic, spinal anesthesia, or local
  anesthetics.
• Surgical procedure had a significant effect.

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• Sweden(1973-1981)
• the incidence of low-birth weight infants(less
  than 1500g) and perinatal death was increased.
• The illness played a significant role in
  determining the outcome.
• Intra-abdominal, pelvic, and uterine pathology
  pose the highest risk to the pregnancy.
• Summary
• No anesthetic agent except cocaine has been shown
  to be teratogenic in humans.
• Hypoxia, hypercarbia, and hypotension
  contributing to decreased uterine perfusion are
  capable of inducing malformations and even
  causing fetal death at any stage of gestation

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Anesthetic Management of the Pregnant Surgical
Patient
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• Preoperative Assessment
• All patient of child-bearing age should be
  questioned about the possibility of being
  pregnant.
• If possible, elective surgery should be delayed.
• lower risk of preterm labor and delivery if
  surgery is done in the second trimester.
• Risks to the fetus and possible loss of the
  pregnancy should be discussed by the
  anesthesiologist and surgeon.
• The patient should be assured of the low risk of
  direct harm to the fetus by anesthetic drugs or
  techniques.

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• Premedication
• narcotics or barbiturates.
• Antisialagogue glycopyrrolate(no central
  effects to mother).
• Aspiration prophylaxis
• Careful evaluation of the airway
• Prophylactic tocolysis
• indomethacin suppositories.
• Beta-agonist or magnesium sulfate
• The patient should be educated on symptoms of
  premature labor.
• Remain on her side during transport.

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• Intraoperative Management
• Hypoglycemia shold be avoided.
• An external Doppler device and tocodynamometer
• to monitor fetal heart rate and uterine
  contractions.
• Should be used after 20 weeks gestation.
• Hypoxia
• the most common teratogen and cause of fetal
  distress during surgery.
• Decelerations inadequate uterine perfusion.
• Induced hypotension or CPB
• the fetus is excellent monitor to assess the
  adequacy of maternal perfusion.

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• Safe anesthetic management is more important than
  the particular agent or technique used.
• Avoid hypotension and hypoxia.
• Preoxygenation before general ansthesia.
• to prevent rapid desaturation
• A rapid sequence induction with cricoid pressure.
• decrease the risk of aspiration.

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• Induction agents
• thiopental and etomidate
• Propofol
• Ketamine
• a dose less than 2 mg/kg during early gestation.
• Inhalational agents
• decrease uterine tone and inhibit contractions.
• At levels above 2.0 MAC, decrease maternal blood
  pressure and cardiac output, leading to fetal
  acidosis.
• Nitrous oxide
• adverse effects were reversed with the addition
  of inhalational agents.
• Reversal agent
• Not cross placenta.

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• Regional anesthesia
• minimal drug exposure to the fetus.
• No change in fetal heart rate variability.
• Avoid hypotension fluid preloading, left
  uterine displacement.
• Drug requirements are decreased during pregnancy.
• Ephedrine preserves uterine blood flow,
  preferred pressor.

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• Postoperative Care
• In the recovery room, continue monitoring fetal
  heart rate and uterine activity.
• should be continued for at last 24 hours.
• Postoperative pain management
• epidural or intrathecal narcotics.
• NSAIDs avoid after 32 weeks gestation.

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Special Situations
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• Postoperative pulmonary edema or ARDS(risk
  factors)
• gestational age older than 20 weeks.
• Preoperative respiratory rate more than 24
  breaths/min.
• Preoperative temperature higher than 100.4 F.
• A fluid load (I gtO) of more than 4 L in the first
  48 hours.
• Concomitant tocolytic use.

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• Trauma
• No. 1 cause of maternal death.
• Fetal loss d/t maternal death or placental
  abruption.
• Early ultrasound
• Indications for an emergent c-sec.
• a stable mother with a viable fetus in distress.
• Traumatic uterine rupture.
• Gravid uterus interfering with intra-abdominal
  repairs in the mother.
• A mother who is unsalvageable and a viable fetus.
• If the fetus is previable or dead, focus on
  optimizing the mother.

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• Neurosurgery
• Intracranial aneurysms and AV malformations.
• Induced hypotension
• Reduces uterine perfusion.
• Require fetal monitoring.
• Hyperventilation
• reduces maternal cardiac output.
• High doses of mannitol
• causes fetal dehydration.

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• Fetal surgery
• Postoperative preterm labor
• the biggest problem
• Tocolysis
• preoperative indomethacin, intraoperative and
  postoperative magnesium sulfate.
• High doses of inhalational agents.
• for maternal and fetal anesthesia.
• For uterine relaxation during surgery.

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• Laparoscopy
• Used as a diagnostic tool to avoid unnecessary
  laparotomy.
• CO2 pneumoperitoneum
• does not cause fetal hemodynamic changes, but
  induces a fetal respiratory acidosis.
• Maintain intra-abdominal pressure as low as
  possible.
• Use N2O instead of CO2 as the insufflating gas.
• Fetal shielding during cholangiograms,
  intraoperative fetal monitoring, pneumatic
  stockings, left lateral table rotation, an open
  technique for trocar placement.

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Conclusions

• Pregnant patient undergoing surgery must be
  approached with caution and respect, but not
  fear.
• Anesthetic agents have an extremely low or
  nonexistent risk of teratogenecity.
• Most important variable for surgery during
  pregnancy is safe skilled anesthetic management.