What are the advantages and disadvantages of general anesthesia for cesarean section?

What are the advantages and disadvantages of general anesthesia for cesarean section?

The major advantages of general anesthesia over regional anesthesia are the shorter preoperative prepara-tory time and the freedom from sympathectomy.

The disadvantages of general anesthesia include mater-nal aspiration and neonatal depression. In addition, general anesthesia precludes immediate maternal bonding.

Aspiration pneumonia is a leading cause of morbidity and mortality in the parturient undergoing general anes-thesia, thus general anesthesia should be reserved for the emergent situation. Before induction of general anesthesia, a careful evaluation of the airway should be performed and a nonparticulate antacid administered. Antacids increase gastric pH resulting in a decreased incidence and severity of pneumonitis should aspiration occur. Defasciculating doses of nondepolarizing muscle relaxants are avoided prior to induction because they may produce profound weakness predisposing to aspiration and may delay the onset time of succinylcholine.

After preoxygenation, induction of anesthesia can pro-ceed with essentially any of the available induction agents and application of cricoid pressure. There are some data indicating that Apgar scores and neurobehavioral scores are depressed when propofol is used, but these are contro-versial. A thiobarbiturate is often chosen for patients who are hemodynamically stable, whereas ketamine is fre-quently selected when there is hemodynamic instability or severe bronchospasm. Although thiamylal crosses the pla-centa, doses less than 7 mg/kg do not adversely affect the fetus. This is because the small amount of drug reaching the fetus is diluted by fetal blood returning from the lower half of the body before it reaches the central nervous system.

Muscle relaxation for endotracheal intubation is achieved with succinylcholine because it provides the most rapid onset amongst relaxants currently available. Succinylcholine’s duration of action may be prolonged, due to abnormally low levels of pseudocholinesterase, when compared with the nonpregnant state. The extended duration of action generally does not exceed 15 minutes and is, therefore, clinically insignificant. Muscle relaxants do not cross the placenta because they are highly ionized and have a large molecular weight.

Anesthesia is maintained with 50% nitrous oxide (N₂O) in O₂ and either isoflurane 0.3–0.5% or enflurane 0.5–0.7%. N₂O does cross the placenta but due to fetal tissue uptake it does not cause significant fetal depression if the induction to delivery time is less than 20 minutes. Sub-MAC concentrations of the potent inhaled anesthetic agents administered prior to delivery protect from mater-nal recall without causing fetal depression or uterine relaxation. After delivery of the fetus, N₂O concentrations are increased and opioids administered to supplement the anesthetic.

Extubation of the trachea follows classic full stomach precautions. The residual muscle relaxation is antagonized with an anticholinesterase and vagolytic agents and the patient must be fully awake.