Anesthesia for Cesarean Delivery: Regional or General?




Introduction


The cesarean delivery rate has been steadily increasing and in 2009 climbed to 33%. The most common indications for cesarean delivery include prior cesarean delivery, dystocia, breech position, multiple gestation, and fetal distress. The cesarean delivery rate is likely to increase further as women are requesting an elective cesarean delivery even for their first delivery, also known as “cesarean on demand.” Although controversial, the American College of Obstetricians and Gynecologists (ACOG) has opined that it is ethical for an obstetrician to perform an elective cesarean delivery if the physician believes that the cesarean delivery promotes the health of the mother and fetus more than a vaginal delivery. Additionally, the number of women attempting a trial of labor after cesarean (TOLAC) has also decreased. The selection of regional or general anesthesia for cesarean delivery depends on the experience of the anesthesiologist, past medical history of the patient, and the indication for and urgency of the cesarean delivery. The anesthetic considerations will be discussed separately for the elective case, where there is little controversy that regional anesthesia is the preferred technique, and the emergent case, where controversy exists.




Options/Therapies


When choosing regional or general anesthesia for cesarean delivery, one must consider both maternal and neonatal outcomes. Maternal outcome studies have primarily focused on maternal mortality, and neonatal outcome studies have focused on umbilical cord pH, Apgar score, the need for ventilatory assistance at birth, and neurobehavioral scores.




Evidence


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.




Areas of Uncertainty


Most clinicians agree that for elective cesarean delivery, regional anesthesia is safer than general anesthesia for both the mother and the baby and is therefore the preferred technique. The area of uncertainty relates to emergent cesarean delivery. The overriding concern with spinal anesthesia is that the placement may take “too long.” However, choosing a general anesthetic should not be taken lightly because the leading cause of maternal morbidity and mortality remains airway catastrophes and aspiration pneumonia.


Obstetricians tend to use the terminology emergent cesarean delivery to describe many different scenarios in which there is concern about the fetus. A more useful classification may be to further classify the emergency as either urgent or stat. An urgent cesarean delivery is one in which there is some concern about the fetus and the baby should be delivered before there is further deterioration, such as the case where there are variable fetal heart rate decelerations with prompt recovery. A stat cesarean delivery is one in which time is of the essence, such as in the case of a cord prolapse with a slow fetal heart rate or maternal hemorrhage. The anesthetic choice may differ based on whether the indication for the emergent cesarean delivery is urgent or stat.




Guidelines


There are three guidelines published by ACOG, and one is published in conjunction with the American Society of Anesthesiologists (ASA) in regard to emergency cesarean delivery. The joint guideline states that hospitals should have the availability of anesthesia and surgical personnel to initiate a cesarean delivery within 30 minutes of the decision to perform the procedure. The second guideline asserts in part that (1) failed intubation and pulmonary aspiration is the leading cause of morbidity and mortality for the mother, (2) the obstetrician should be able to identify those factors that place the patient at greater risk of general anesthesia and should request an antepartum anesthesia consultation, (3) strategies to reduce the need for emergency induction of general anesthesia should be developed, including the early placement of an epidural anesthetic, (4) the term fetal distress is “imprecise, nonspecific and has little positive predictive value” and, (5) a cesarean delivery for a nonreassuring fetal heart rate pattern does not preclude the use of regional anesthesia. In a further committee opinion, ACOG reiterated their concern with the use of the term fetal distress and that it should be replaced with the term nonreassuring fetal heart rate tracing followed by a description of the fetal tracing. The ASA has developed Practice Guidelines for Management of the Difficult Airway. These guidelines are an excellent guide to the management of the unanticipated difficult endotracheal intubation, and a plan based on these guidelines is summarized in Figure 64-1 .


Mar 2, 2019 | Posted by in ANESTHESIA | Comments Off on Anesthesia for Cesarean Delivery: Regional or General?
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