Anesthesia For Nonobstetric Surgery During Pregnancy

1. Anesthesia For Nonobstetric Surgery During Pregnancy May 6, 2005 R1林群博

2. General Considerations • Surgery during pregnancy: 1.5%-2% of all pregnancies in USA • The operations include: Directly related to pregnancy Indirectly related to pregnancy Unrelated to gestation

3. Concern For Anesthesia • Two major categories: Teratogenicity of the anesthetic agents Maternal and fetal physiologic changes

4. Teratogenicity(1)

5. Teratogenicity(2) • Virtually every drug and every inhalation anesthetic is teratogenic to some species under certain conditions • None has been identified as a definite human teratogen

6. Teratogenicity(3)

7. Nitrous Oxide • Ability to oxide cobalamin (Vitamin B12), inhibit methionine synthase activity • DNA production, myelin deposition, and other folate and methylation process-dependent reactions might be affected

8. Anesthetic Consideration(1) • Prudent to postpone elective surgical procedures until after delivery • The first trimester should be avoided for smiselective cases • Regional anesthesia should be entertained • Spinal anesthesia offers the least drug transfer for the degree of aesthesia achieved • Hypotension, aortocaval compression, maternal hypoxia, and acidosis: avoided and treated promptly • Other forms of regional anesthesia yield higher local anesthetic blood levels and more placental transfer

9. Anesthetic Consideration(2) • Greater risks for aspiration: Decrease in lower esophageal sphincter tone Mechanical effects of the gravid uterus Impaired gastric emptying

10. Intraoperative Monitoring • Overall goal: maintain the mother and fetus in the best possible physiological condition • Protect the patient from the usual stresses encountered in the operating room such as anxiety, pain, positioning , temperature changes, fluid and blood losses

11. Essential monitoring: BP, PR, EKG, respirations, temperature, pulse oximetry • Left uterine displacement: avoid aortocaval compression • Avoid hyperventilation: Respiratory alkalosis causes: oxyhemoglobin dissociation curve shifted to the left impair transfer of oxygen across the placenta decreases umbilical blood flow

12. Fetal Heart Rate Monitoring • Identify intraoperative conditions leading to impaired uteroplacental blood flow and fetal oxygenation • Variability decreased by hypoxia and by sedative drugs • Slowing of FHR: hypoxemia, fall in temperature or administration of drugs or anesthetic agents • Fetal tachycardia: maternal fever, maternal/fetal sepsis, drug

14. Prevention of Preterm Labor • Increased incidence of abortion and preterm delivery • Timing of the surgery • Women undergoing third-trimester procedures are at greatest risk • Prophylactic use of tocolytics • Pain should be controlled : association between postoperative pain and anxiety and uterine irritability

15. The most common abdominal procedures: Appendectomy Cholecystectomy Adnexal surgery • Laparoscopic surgery • Neurosurgery • Cardiac surgery requiring bypass

16. Appendectomy • Appendicitis: the most common nonobstetric surgical emergency during pregnancy • Appears to occur more frequently in the second and third trimesters • The mortality of appendicitis complicating pregnancy is the mortality of delay

17. Cardiac Surgery During Pregnancy • Blood volume and cardiac output: 30%-50% increase • Patients with preexisting cardiac disease: exposed to a major stress when entering the second and third trimesters of gestation

18. Cardiopulmonary Bypass • Increases the risks for fetus and adversely affects fetal oxygenation: Nonpulsatile perfusion Inadequate perfusion pressure Inadequate pump flow Embolic phenomena to the uteroplacental bed Release of renin and catecholamines

19. Moderate hypothermia during bypass: Persistent fetal bradycardia Warm cardiopulmonary bypass will improve • Increasing pump flow if FHR<80 bpm • Ensure adequate uteroplacental perfusion Pump flow 30-50% greater than usual Perfusion pressure at or above 60 mmHg • Arterial blood gases for acid-base status, oxygenation, and ventilation

21. Neurosurgery During Pregnancy • Subarachnoid hemorrhage from intracranial saccular aneurysm or arteriovenous malformation: not uncommon during pregnancy • The factors predispose to rupture: Increased cardiac output and blood volume The softening of vascular connective tissue by the hormone changes of pregnancy

22. The Usual Neurosurgical Approach • Controlled hypotension • Hypothermia • Hyperventilation • Diuresis

23. Controlled Hypotension • Volatile anesthetic, nitroglycerin, nitroprusside • Reduction in SBP of 25-30% or MBP< 70mmHg: reduction in uteroplacental blood flow • Cross placenta: fetal hypotension • Nitroprusside: converted to cyanide, which causes significant toxicity and fetal death • Discontinued when: Infusion rate> 0.5 mg/kg/hour Maternal metabolic acidosis Resistance to the agent

24. Hypothermia: fetal bradycardia • Hyperventilation: Decreased placental oxygen transfer Umbilical vessel vasoconstriction • Diuesis: significant negative fluid shift for the fetus

25. Laparoscopic Surgery During Pregnancy • Adding pneumoperitoneum to an enlarged uterus: Limit diaphragm expansion Increase in peak airway pressure Decrease in FRC Decrease thoracic cavity compliance Increased ventilation-perfusion mismatching

26. CO2 pneumoperitoneum: hypercapnia and hypoxemia • Hyperventilation: reduce uteroplacental blood flow • Reduce venous return and cardiac index: significant hypotension

27. Conclusions • Understanding the physiological changes of pregnancy and their influence on the patient • Maintaining an adequate uteroplacental perfusion • Selecting anesthetic drugs and techniques • Using regional anesthesia whenever possible • Inform the patient no anesthetic agent or adjuvant drug has as yet been proven to be teratogenic in humans • Providing fetal surveillance with external fetal heart rate monitoring and uterine activity • Making appropriate adjustments in techniques as guided by the results

28. Thanks For Your Attention!!