Medical Lecture Notes Online: General Anesthesia for Cesarean Section

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

► *Antibiotics of choice

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