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
Preoperative Preparation for General Anesthesia
► History & Examination, LABs
► Airway evaluation
► Aspiration prophylaxis
► Basic machine and monitor preparation
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
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
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
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
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
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
Prevention of Aspiration
► Cricoid pressure
► Adequate oxygenation of patient
► Treat hypotension promptly
► Efficient and timely intubation
► Orogastric or nasogastric tube
► Awake extubation
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
Intraoperative Management of Parturient
► Positioning
► Oxygenation
► Monitors
► Induction of general anesthesia
► Maintenance of general anesthesia
► Emergence from general anesthesia
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
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)
Intraoperative Management-Monitors
► Pulse oximeter probe
► Right size BP cuff
► Electrocardiographic electrodes
► capnograph
► Temperature monitor readily available
► Urinary output
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
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
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
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)
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)
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
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
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
► Succinylcholine bolus when needed
► Nondepolarizing agents accordingly ie. Nimbex, Vecuronium, Rocutonium.
► *Oxytocin 10-40 U IV infusion
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
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)
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
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)
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
Factors Cause Uterine Artery Spasm
► Uterine incision
► Contraction of myometrial muscles
► Vasoconstrictors: prostaglandin released from fetus and placenta
► Maternal catecholamine release
Post Anesthesia Care
► Transport to PACU with O2
► Hypoxemia: airway obstruction and hypoventilation
► Hypotension
► Pain control
► Nausea and Vomiting
► Shivering and hypothermia
Husong Li, M.D., Ph.D.
Assistant Professor
Department of Anesthesiology
University of Texas Medical Branch at Galveston, Texas
