Spinal anesthesia has the advantages of being easy to perform, requiring less time, and being more reliable than epidural analgesia. The primary disadvantage is the potential for severe hypotension – consider prehydration with 20 cc/kg, proper positioning, and keeping phenylephrine AND epinephrine on hand. Note that the risk of hypotension is higher because the block has to reach T4 (as opposed to T10 during vaginal delivery). Consider adding 5-25 ucg fentanyl or 0.1-0.2 mg morphine to the local anesthetic solution (the morphine has the added advantage of post-operative analgesia).
Epidurals offer the advantage of multiple use (which is ideal if an epidural was already placed for labor analgesia), a smoother hemodynamic course (although this may not be clinically-significant, see Visalyaputra S et al. Anesth Analg 101: 862, 2005; FREE Full-text at Anesthesia & Analgesia). The goal is to achieve a T4 level, although unsuccessful, adjuncts must often be used. Give a test-dose of local anesthetic (ex. 45 mg lidocaine) but NOT epinephrine, which is unreliable and may reduce uteroplacental perfusion. Lidocaine has the disadvantage of requiring co-administration of epinephrine, which can be problematic in women with pregnancy induced hypertension or uteroplacental insufficiency.
Increased Risks of General Anesthesia in the Parturient
While most Cesarean sections are performed under regional anesthesia, general anesthesia should always be a consideration as it is occasionally necessary. Two concerns in particular arise – the risk of aspiration (1:500 for obstetric patients versus 1:2000 for all patients) and failed endotracheal intubation (1:300 versus 1:2000 for all patients).
Because of the possibility of having to administer general anesthesia is near-constant, all pregnant women should take proton pump inhibitors in in the peri-labor period. IV H2 blockers and/or 10 mg metoclopramide 1–2 h prior to induction should also be considered. Although anticholinergics can theoretically reduce lower esophageal tone, 0.1 mg helps reduce airway secretions and is useful should a difficult airway situation arise.
Practitioners commonly administer 30 mL of 0.3 M sodium citrate 30–45 min prior to induction (antacids given 15-30 minutes prior to surgery are nearly 100% effective at raising gastric pH to > 2.5). Nonparticulate antacids such as sodium citrate do not cause pulmonary complications if aspirated. The theoretical tradeoff for sodium citrate is that gastric volume is actually increased, however data from rats showed that 0.3 cc/kg of aspirate with pH < 1.0 carried a mortality rate of 90%, whereas 1-2 cc/kg of aspirate with a pH > 1.8 carried a mortality rate of 14% [James CF et al. Anesth Analg 63: 665, 1984]. There are no prospective, randomized, controlled trials to support gastrointestinal premedication.
Stoelting recommends giving all pregnant women a non-particulate antacid (ex. bicitra) [Stoelting RK. Basics of Anesthesia, 5th ed. Elsevier (China) p. 490, 2007].
Difficult Airway Preparation
In preparation for a difficult airway multiple, different laryngoscope blades, a short laryngoscope handle, one small, styletted ETT (6-6.5 mm), Magill forceps (for nasal intubation), LMAs, a Fastrach, a fiberoptic bronchoscope, a 14-16 ga. needle with the capability for transtracheal jet ventilation, and possibly a Combitube should be available.
Thiopental at 4-6 mg/kg is the most common induction drug, as it achieves unconsciousness within 30 seconds and comes in premade vials (useful for true emergencies). Neonatal depression does not generally occur at doses < 6 mg/kg. Propofol, which leads to faster maternal recovery, has to be drawn into a syringe and has never been shown to improve neonatal outcomes – in fact, several (but not all) small studies suggest that APGAR scores are lower in propofol as compared to thiopental. Ketamine maintains hemodynamic stability via effects on the SNS, but may increase uterine tone and thus decrease placental blood flow if given in large doses. Doses of 0.25 mg/kg provide significant analgesia, and some authors believe that ketamine is the drug of choice in pregnant women of questionable hemodynamic stability. Etomidate is rarely used because it is painful on injection and produces extrapyramidal/seizure-like activity.
Maintenance often includes 50% nitrous oxide (as recommended by both Stoelting and Miller’s texts) with a low concentration of volatile (sevoflurane or desflurane). Nitrous oxide is used to minimize volatile anesthetics, which can cause uterine relaxation [Turner RJ et al. Anaesth Intensive Care 30: 591, 2002] and inhibit oxytocin-induced contractions in ex-vivo studies [Yildiz K et al. Acta Anaesthesiol Scand 49: 1355, 2005] (and possibly lead to bleeding ). Opiates, benzodiazepines, and antiemetics are generally withheld until AFTER delivery – after delivery, 20U of oxytocin should be given in addition to opiates as needed.
Incision-delivery times seem to be more important than induction-delivery times, with fetal acidosis and decreased 1 minute APGAR scores noted after incision-delivery times exceeding 180 seconds. [Datta S et al. Obstet Gynecol 58: 331, 1981]
In extreme situations (ex. acute fetal distress combined with morbid obesity), local infiltration can be used to deliver the baby.
Anesthesia in Preeclampsia
Spinal anesthesia can be safely used in pre-eclamptic patients – a study of 136 patients, 65 of which were eclamptic, showed a reduction in the incidence of hypotension (24.6% of patients, as compared to 40.8%, p = 0.044) [Aya AG et al. Anesth Analg 101: 869, 2005; FREE Full-text at Anesthesia & Analgesia]. There is no clinically significant difference between spinal and epidural analgesia – a study of 100 preeclamptics showed statistically significant but clinically insignificant differences in terms of blood pressure and ephedrine use [Visalyaputra S et al. Anesth Analg 101: 862, 2005; FREE Full-text at Anesthesia & Analgesia]