Elective Cesarean Delivery

Maternal outcomes are better with regional anesthesia than with general anesthesia. In 1997, Hawkins and colleagues found that the case fatality rate for cesarean delivery for the years 1979-1990 was 16 times greater with general anesthesia than with regional anesthesia. The same group reviewed maternal mortality case fatality rate for the years 1991-2002 and again found that the mortality rate was greater when general anesthesia was used, although only by a factor of 1.7. The reason for this difference in anesthetic techniques is primarily related to the respiratory system of the parturient. Difficult tracheal intubation in the parturient is approximately 10 times that of the general population. Furthermore, hypoxemia develops quickly during periods of apnea, and the parturient is at increased risk of pulmonary aspiration. As the incidence of general anesthesia for cesarean delivery decreases, airway experience among trainees is also decreasing. Johnson and colleagues in a study from England found that in 1988 the average trainee was only exposed to four general anesthetics for cesarean delivery during their training. In a follow-up study from the same hospital they found this number decreased further to one general anesthetic per trainee. Hawthorne and colleagues reviewed the incidence of failed tracheal intubation on their maternity unit. They found that the incidence of failed tracheal intubation, defined as the inability to successfully intubate the trachea with one dose of succinylcholine thus necessitating initiation of the failed intubation protocol, increased from 1 in 300 in 1984 to 1 in 250 in 1994. In a recent review of the etiology of maternal mortality, Mhyre and colleagues found that “airway problems” are still a leading cause of maternal mortality but that the problems occurred during emergence or tracheal extubation and not during tracheal intubation as was found in an earlier study.

Neonatal outcomes are also better or unchanged when regional anesthesia is used, although not all studies have demonstrated this. The variables generally measured are umbilical cord pH and clinical variables such as Apgar score and the need for ventilatory assistance. Reynolds and Seed performed a meta-analysis with the primary outcomes of umbilical cord pH and base deficit. They found that spinal anesthesia was associated with a decreased umbilical cord pH and greater base excess than either general or epidural anesthesia. One flaw of their analysis is that both randomized and nonrandomized studies were included as were urgent and nonurgent cases. Also, the choice of vasopressor and degree of hypotension was not controlled. In a second meta-analysis of studies in which patients were randomly assigned to general or regional anesthesia for elective procedures, no differences in umbilical cord pH, Apgar scores, or neurobehavioral scores were found among groups. It should be noted that, even in studies that found biochemical variables to be better with general anesthesia, clinical variables, such as Apgar scores and the need for ventilatory assistance, were not consistently better.

Spinal anesthesia rather than epidural anesthesia is commonly used for elective cesarean delivery because the speed of onset is quicker and the failure rate is lower. Riley and colleagues found that spinal anesthesia was more reliable and led to a more efficient use of operating room time than epidural anesthesia because the time from entering the operating room until skin incision is faster with spinal anesthesia. In a 2001 survey of obstetric anesthesia trends in the United States, Bucklin and colleagues found that approximately 95% of all elective cesarean deliveries were performed with neuraxial anesthesia and that approximately 80% were performed with spinal anesthesia. The most common complication from spinal anesthesia is hypotension, which should be aggressively treated. Ngan Kee and Lee found in a multivariate analysis that a decrease in systolic blood pressure was an important factor in neonatal outcome.

Numerous techniques for preventing hypotension after spinal anesthesia have been attempted, with varying success. The most important preventive measure is to ensure left uterine displacement so as to avoid supine hypotensive syndrome. Prehydration is not an effective measure to prevent hypotension. Rout and colleagues randomly assigned women to receive no prehydration or 20 mL/kg of a crystalloid solution before cesarean delivery. They found a smaller incidence of hypotension in the prehydrated group (55%) as compared with the control group (71%), but the total amount of fluid, the total amount of ephedrine, and the severity of the hypotension did not differ between groups. Also, the prehydrated group still had a certain amount of hypotension. Park and colleagues randomly assigned women to receive 10, 20, or 30 mL/kg of crystalloid before cesarean delivery. They found less hypotension as the amount of prehydration increased (67% versus 56% versus 47% in the 10, 20, and 30 mL/kg groups, respectively), but it did not reach statistical significance. However, even in those who received 30 mL/kg of crystalloid prehydration, there was almost a 50% incidence of hypotension.

Colloid rather than crystalloid prehydration has also been studied. Ueyama and colleagues were the first to randomly assign women undergoing cesarean delivery to receive either 1500 mL of a crystalloid (lactated Ringer solution) or 500 mL or 1000 mL of a colloid solution (hydroxyethyl starch). The incidence of hypotension was 75% in those who received the crystalloid, 58% in those who received 500 mL of the colloid, and only 17% in those who received 1000 mL colloid. A more recent study confirmed these findings and also found that cardiac output was unchanged between crystalloid and colloid groups. Even in studies that demonstrated that colloid is associated with less hypotension, it has not been shown to improve neonatal outcomes.

Coloading, administering IV fluid rapidly at the time of spinal anesthesia rather than before the anesthetic, has been suggested as an alternative, but this too has not led to decreased hypotension. A meta-analysis of studies comparing preloading with coloading did not find a difference in the incidence of hypotension: 59% in the coloading group and 62% in the preloading group.

Some have recommended prophylactic pressor agents to prevent hypotension. Both ephedrine and phenylephrine have been used, and the most success has been with high-dose phenylephrine infusion along with crystalloid coloading. The problem with this modality is that many of the patients had reactive hypertension. Because most women and their neonates tolerate hypotension without long-term sequelae, the use of the technique has been questioned; it should be used judiciously, and maternal comorbidities should be taken into account. Treatment of hypotension should be aggressive, and the use of phenylephrine has been shown to be better than ephedrine for treating hypotension. This benefit included better hemodynamic control, less maternal nausea and vomiting, and improved acid–base status in the neonate.

Emergency Cesarean Delivery

Maternal outcome is also improved when regional anesthesia is used for an emergent cesarean delivery because of the difficulty with tracheal intubation. Airway concerns during an emergency cesarean delivery are even greater than in the elective scenario. Endler and colleagues reviewed maternal deaths in the state of Michigan from 1972 through 1984. They found that the emergent situation was a risk factor for difficult tracheal intubation and that the inability to successfully intubate the trachea was the principal cause of death in 11 of 15 patients.

Neonatal outcome for the emergent cesarean delivery is also better with regional anesthesia than with general anesthesia. A number of retrospective studies but only one prospective study addressed anesthetic technique and its impact on the neonate during urgent cesarean delivery. All the retrospective studies have been fairly consistent and have found that neuraxial anesthesia has an advantage over or is equivalent to general anesthesia in regard to Apgar scores and requirement for assisted ventilation. Bowring and colleagues found that not only were Apgar scores better in those who received regional anesthesia but also the admission rate to the neonatal intensive care unit was lower in the regional anesthesia group.

In the only prospective study, Marx and colleagues evaluated neonatal outcomes for women who underwent cesarean delivery because of fetal distress. The choice of anesthetic—general, spinal, or an extension of an existing epidural catheter—was made by the mother immediately before administration of the anesthetic. There were 126 women in the study of whom 71 chose general anesthesia, 33 chose spinal anesthesia, and 22 chose extension of their epidural anesthetic. The time from decision to perform a stat cesarean delivery until skin incision was less than 20 minutes in all patients. However, the time from decision to perform the cesarean delivery until skin incision was greater in the regional anesthesia groups as compared with the general anesthesia group. Despite this difference in starting time, they were unable to detect a significant difference in 5-minute Apgar scores or umbilical arterial or venous pH among the three groups; however, the 1-minute Apgar score was greater in the regional anesthesia groups than in the general anesthesia group.

A potential flaw in the Marx study and the retrospective studies is that the definition of what constituted an emergency cesarean delivery was not made clear. Nonetheless, the data support the use of spinal anesthesia for most cases of emergency cesarean delivery. The main concern with choosing spinal anesthesia is the time required for the patient to be anesthetized for the surgery. Obviously, each case should be individualized, but many skilled clinicians can quickly perform spinal anesthesia and are choosing spinal anesthesia for all but the most emergent cases, (e.g., cord prolapse); even in those scenarios, many are choosing spinal anesthesia if the mother has a potential difficult airway or has other comorbidities.