General Anesthesia for Cesarean Section

1. General Anesthesia for Cesarean Section Husong Li, M.D., Ph.D. Assistant Professor Department of Anesthesiology University of Texas Medical Branch at Galveston, Texas

2. Introduction Cesarean-section (CS) deliveries have accounted for nearly 1 million of approximately 4 million annual deliveries in US. Approximately 15% of CS was performed under general anesthesia in US (Anesthesiology Hawkins, JL 1997). Majority of CS were done under urgent or emergent situations. In 2000, CS rate is about 22% in US, and 31.8% in UTMB.

3. Indications for General Anesthesia Fetal distress Significant coagulopathy Acute maternal hypovolemia and Homodynamic instability Sepsis or local skin infection failed regional anesthesia Maternal refusal of regional anesthesia

4. Preoperative Preparation for General Anesthesia History & Examination, LABs Airway evaluation Aspiration prophylaxis Basic machine and monitor preparation

5. Factors may complicate endotracheal intubations Weight gain Oropharynx edema Enlarged breasts Obesity with short neck Full dentition Mallampati IV and mamdibular recession History of difficult airway

6. Airway evaluation Anticipation of difficult endotracheal intubation (1 in 300 in OB and 1 in 2000 all patients) Thorough examination of neck, mandible, dentition, and Oropharynx Training and experience (Hawthorne L. Br J. Anesth 1996; 76: 680-684) Sniffing position

7. Airway evaluation

8. Preparation and Prevention 2-3 different blades, ie MAC 3&4 Miller 2 6 to 7 mm ETT tubes with stylets LMAs sizes 3 and 4 Emergency airway cart ready in the OR Fiberoptic bronchoscope Possible surgical airway equipment

9. Aspiration prophylaxis Pulmonary aspiration: 1 in 400-500 in OB versus 1 in 2000 in all surgical patients No agent or combination of agents can guarantee that a parturient will not aspirate or develop pneumonitis following failed intubations

10. Factors increase the risk of aspiration Decrease in gastric and intestinal motility delayed gastric emptying by anxiety and pain Relaxation of lower esophageal sphincter tone Increase in abdominal pressure Increase gastric acid secretion Patients not fasting

11. Prevention of Aspiration-Pharmacological agents PO 30 ml 0.3 M sodium citrate 15-30 minute prior to induction H2 blocker, ranitidine 50 mg IV Metoclopramide 10 mg IV, at least 5 minute prior to induction Omeprazole 40 mg the night before and the AM of surgery for high risk patients Ondansetron 4-8 mg IV

12. Prevention of Aspiration Cricoid pressure Adequate oxygenation of patient Treat hypotension promptly Efficient and timely intubation Orogastric or nasogastric tube Awake extubation

13. Basic Machine and Monitor Preparation Monitors: esp. capnograph Suction tubing functional Airway equipments ready and functional LMAs: 2nd line of defense of difficult airway Others: ie. meds

14. Intraoperative Management of Parturient Positioning Oxygenation Monitors Induction of general anesthesia Maintenance of general anesthesia Emergence from general anesthesia

15. Intraoperative Management-Positioning OR bed should be allowing trendelenburg and reversed positions Sniffing position Patients in supine position with a wedge under the right hip Head and back up position if preparing awake fiberoptic intubation

16. Intraoperative Management-Denitrogenation Denitrogenation with O2 as soon as patient on OR bed Seal mask to achieve 100% O2 3-5 minutes or 4 VC breaths of 100% O2 O2 saturation drops faster during apnea (increase VO2 and decrease FRC)

17. Intraoperative Management-Monitors Pulse oximeter probe Right size BP cuff Electrocardiographic electrodes capnograph Temperature monitor readily available Urinary output

18. Intraoperative Management Communicate with surgeons and nursing staffs while pt is prepared and draped for surgery Final check for your READINESS FOR INDUCTION of general anesthesia

19. Induction of general anesthesia Rapid sequence induction Cricoid pressure maintained until endotracheal tube cuff inflated and tube placement confirmed Agents:Thiopental/Ketamine/Propofol/Etomidate/Succinylcholine

20. Induction Agents-Thiopental Thiopental (STP) 2-5 mg/kg IV Fast and reliable Negative inotrope and vasodilator Cross placenta; STP concentration rarely exceed the threshold for fetal depression with dose less than 4 mg/kg No evidence of adverse effect of STP on fetus even the induction-to-delivery (ID) interval is prolonged; keep incision to delivery time less than 4-7 minutes

21. Induction Agents-Propofol Propofol 1-2.5 mg/kg IV Rapid induction and rapid awakening Negative inotrope and vasodilator May inhibit oxytocin induced uterine contraction Can be rapidly cleared from neonatal circulation Dose greater than 2.8 mg/kg may result in lower apgar scores and lower neurobehavioral scores at 1 hour after delivery comparing with STP, but similar neurobehavioral scores by 4 hours after delivery (Celleno D. Br J Anesth 1989; 62:649-54)

22. Induction Agents-Ketamine Ketamine 1-2.0 mg/kg IV Modest hemorrhage or parturient asthma Provide rapid analgesia, hypnosis, and amnesia May depress myocardium and reduce CO and BP in severe hypovolemic patients Avoid in hypertensive patients More than 2 mg/kg may associate with fetal depression Maternal psychotropic profiles: dreaming, dysphoria, hallucination during emergence (benzodiazepine reduce the side effects)

23. Induction Agents-Etomidate Etomidate 0.2-0.3 mg/kg IV Cause little CV depression-for HD unstable parturient Neonatal adrenal suppression? pain at injection site Myoclonus

24. Induction Agents-Succinylcholine Succinylcholine (SUX) 0.3 to 1.5 mg/kg IV Spontaneous ventilation may resume in 2-3 minutes with low dose SUX (0.3-0.5 mg/kg), but peak time delayed by about 10-15 seconds 3rd line of defense of difficult airway Recovery from intubation dose of SUX is unchanged in the pregnant patients

25. Maintenance of General Anesthesia PREDELIVEY 50% O2/50%N2O/0.5% Isoflurane 100% O2/1-1.5% Isoflurane POSTDELIVERY 50-70% N2O/30-50%O2/ 0.5% Isoflurane/Narcotics Minimize volatile agents to prevent postpartum hemorrhage; 0.5 MAC does not significantly increase maternal blood loss

26. Maintenance of General Anesthesia Succinylcholine bolus when needed Nondepolarizing agents accordingly ie. Nimbex, Vecuronium, Rocutonium. *Oxytocin 10-40 U IV infusion *Antibiotics of choice

27. Emergence from General Anesthesia Stomach emptied via an OG tube Upper airway suctioned Nondepolarizing agents reversed adequately Opioids for pain relief Extubation when patients regain protective reflexes; are able to maintain airway; respond appropriately to verbal commands; and are hemodynamically stable

28. Awareness during General Anesthesia High incidence between induction of anesthesia and delivery of the fetus Administration of only 50% N2O in oxygen without other agents results in maternal awareness in 12-26% of cases (Warren TM Anesth Analg 1983; 62:516-20; Crawford JS Br J anesth 1971; 43:179-82 Abboud TK et al Acta Anesthesiol Scand 1985; 29: 663-8)

29. Awareness during General Anesthesia Ketamine or combine ketamine and thiopental for induction Minimize of induction to delivery interval 50%N2O/O2 with following AGENTS reduce awareness to less than 1 % 0.6% isoflurane 1% sevoflurane 3% desflurane

30. Fetus Consideration during Emergency Cesarean Section Decision to Incision or interval: 30 minutes? Uterine Incision to Delivery (UD) interval should be less than 3 minutes (Datta et al Obstet & Gynecol 1981; 58:331-335. Crawford JS. Et al. Br J. Anesth 1973; 45:726-732) Neonates delivered after 3 minutes following uterine incision had lower apgar and acidotic blood gas Ultimate neonatal outcome? (Ong BY. Et al Anesth Analg 1998; 68:270-5)

31. Ong BY. et al Anesth Analg 1998; 68:270-5 Increase incidence of low 1 minute apgar scores in elective under GA Increase incidence of low 1 and 5 minutes apgar scores in emergency under GA No different in ultimate neonatal outcome

32. Factors Cause Uterine Artery Spasm Uterine incision Contraction of myometrial muscles Vasoconstrictors: prostaglandin released from fetus and placenta Maternal catecholamine release

33. Post Anesthesia Care Transport to PACU with O2 Hypoxemia: airway obstruction and hypoventilation Hypotension Pain control Nausea and Vomiting Shivering and hypothermia