Anesthesia for the Pregnant Patient Undergoing Nonobstetric Surgery

1. Anesthesia for the Pregnant Patient Undergoing Nonobstetric Surgery R4 오 재 열

2. 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.

3. Physiologic Changes of Pregnancy

4. 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.

5. 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.

6. 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.

7. 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.

8. Teratogenecity and Safety of Anesthetic Agents

9. 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.

10. 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.

11. 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.

12. 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.

13. 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.”

14. 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.

15. 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.

16. 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.

17. 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

19. Anesthetic Management of the Pregnant Surgical Patient

20. 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.

21. 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.

22. 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.

23. 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.

24. 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.

25. 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.

26. 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.

28. Special Situations

29. 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 >O) of more than 4 L in the first 48 hours. • Concomitant tocolytic use.

30. 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.

31. 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.

32. 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.

33. 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.

34. 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.