General Anesthesia for Cesarean Section

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General Anesthesia for Cesarean Section

• Husong Li, M.D., Ph.D.
• Assistant Professor
• Department of Anesthesiology
• University of Texas Medical Branch at Galveston,
  Texas

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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.

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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

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Preoperative Preparation for General Anesthesia

• History Examination, LABs
• Airway evaluation
• Aspiration prophylaxis
• Basic machine and monitor preparation

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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

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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

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Airway evaluation
sniffing position
Moderate head elevation, extension of
atlanto-occipital, and flexion of the lower
portion of the cervical spine
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Preparation and Prevention

• 2-3 different blades, ie MAC 34 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

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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

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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

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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

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Prevention of Aspiration

• Cricoid pressure
• Adequate oxygenation of patient
• Treat hypotension promptly
• Efficient and timely intubation
• Orogastric or nasogastric tube
• Awake extubation

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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

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Intraoperative Management of Parturient

• Positioning
• Oxygenation
• Monitors
• Induction of general anesthesia
• Maintenance of general anesthesia
• Emergence from general anesthesia

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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

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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)

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Intraoperative Management-Monitors

• Pulse oximeter probe
• Right size BP cuff
• Electrocardiographic electrodes
• capnograph
• Temperature monitor readily available
• Urinary output

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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

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Induction of general anesthesia

• Rapid sequence induction
• Cricoid pressure maintained until endotracheal
  tube cuff inflated and tube placement confirmed
• AgentsThiopental/Ketamine/Propofol/Etomidate/Succ
  inylcholine

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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

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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 62649-54)

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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)

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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

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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

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Maintenance of General Anesthesia

• PREDELIVEY
• 50 O2/50N2O/0.5 Isoflurane
• 100 O2/1-1.5 Isoflurane
• POSTDELIVERY
• 50-70 N2O/30-50O2/
• 0.5 Isoflurane/Narcotics
• Minimize volatile agents to prevent postpartum
  hemorrhage 0.5 MAC does not significantly
  increase maternal blood loss

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Maintenance of General Anesthesia

• Succinylcholine bolus when needed
• Nondepolarizing agents accordingly ie. Nimbex,
  Vecuronium, Rocutonium.
• Oxytocin 10-40 U IV infusion
• Antibiotics of choice

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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

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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
  62516-20 Crawford JS Br J anesth 1971
  43179-82 Abboud TK et al Acta Anesthesiol Scand
  1985 29 663-8)

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Awareness during General Anesthesia

• Ketamine or combine ketamine and thiopental for
  induction
• Minimize of induction to delivery interval
• 50N2O/O2 with following AGENTS reduce awareness
  to less than 1
• 0.6 isoflurane
• 1 sevoflurane
• 3 desflurane

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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 58331-335. Crawford JS. Et al.
  Br J. Anesth 1973 45726-732)
• 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 68270-5)

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Ong BY. et al Anesth Analg 1998 68270-5

• 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

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Factors Cause Uterine Artery Spasm

• Uterine incision
• Contraction of myometrial muscles
• Vasoconstrictors prostaglandin released from
  fetus and placenta
• Maternal catecholamine release

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Post Anesthesia Care

• Transport to PACU with O2
• Hypoxemia airway obstruction and
  hypoventilation
• Hypotension
• Pain control
• Nausea and Vomiting
• Shivering and hypothermia