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Klinik und Poliklinik für Anästhesiologie und operative Intensivmedizin, Westfälische Wilhelms-Universität, Münster, Germany
Address correspondence and reprint requests to H. Van Aken, MD, PhD, FRCA, FANZCA, Klinik und Poliklinik für Anästhesiologie und operative Intensivmedizin, Westfälische Wilhelms-Universität, Albert-Schweitzer-Str. 33, D-48149 Münster, Germany. Address e-mail to hva{at}anit.uni-muenster.de
The evolution of obstetric anesthesia and analgesia has closely followed anesthesia for other subspecialties. In 1847, shortly after the first public demonstration of ether anesthesia for general surgery, James Young Simpson used diethyl ether for labor analgesia (1). Other methods followed, such as repeated injections of large doses of morphine and scopolamine. This technique, called "Dämmerschlaf" or "twilight sleep," often led to severe maternal and neonatal respiratory depression (2). During the initial enthusiasm for alleviating maternal discomfort, proponents of obstetric analgesia gave little thought to the neonatal effects of maternal drug administration. This was, in part, because successful labor and delivery were essentially defined in terms of maternal and fetal survival, rather than physiological variables of the newborn. In 1847, Walter Channing stated that placental transfer of ether was negligible, as he could not detect an odor of ether after having cut the umbilical cord (3). Although the significance of placental drug transfer was recognized in 1877 when Paul Zweifel proved the presence of chloroform in umbilical vessels of newborns, this knowledge did not alter clinical practice over the next decades.
One hundred years ago, in July 1900, the obstetrician Oscar Kreis, from Switzerland was the first to recognize the advantages of regional analgesia in obstetrics, when applying spinal cocaine to ameliorate labor pain in six parturients with a fully dilated cervix (4). Although the neonatal status was not mentioned, Kreis described the parturients as remarkably alert compared with women who received other available forms of labor analgesia. Major side effects in those early cases included a high incidence of postdural puncture headaches (PDPH) and vomiting, which occurred in half of the patients. In 1902, Hopkins subsequently performed the first cesarean delivery under spinal anesthesia in the United States. As early as 1923, the first reports on combined spinal-epidural anesthetics (CSE) in surgical patients appeared, initially as a combined single-shot technique (5). The basis of regional blocks for labor analgesia was founded on neuroanatomical principles, when Cleland (6) described the sensory innervation of the uterus in 1933. The following frequent use of spinal anesthesia by inexperienced personnel and the perception that monitoring was not necessary led to a frequent incidence of complications and brought discredit to the technique. At the time, mortality after spinal anesthesia was 1 in 1000 in surgical patients, a rate much more frequent than those observed for either local or general anesthesia (7). Mortality rates for cesarean deliveries performed under spinal anesthesia were reported to be 1 in 139 (8). Greenhill (9), engaged in obstetric anesthesia, therefore concluded that spinal anesthesia was the most dangerous of all forms of anesthesia for pregnant women. He repeatedly discouraged its use in obstetrics. The negative experiences with regional anesthesia resulted in an abandonment of pain relief in obstetrics until the 1950s, a period often described as the "dark ages of obstetric anesthesia" (1). It was during this time that "natural childbirth" and "psychoprophylaxis" were widely advocated to avoid serious anesthesia-related side effects (10).
Major improvements in maternal safety were made between 1940 and 1950, when 24-hour obstetric anesthesia services were established throughout the United States. The first experiences with caudal anesthesia in obstetrics suggested that this technique might enhance safety for the parturient and the fetus, and it provided good labor pain relief (11). Parturients were more willing to accept caudal anesthesia than subarachnoid injections, as the high risk of PDPH was publicly known. In the following years, lumbar epidural analgesia gained more popularity because the success rate was more frequent, local anesthetic requirements were reduced, the onset of analgesia was faster, and the catheter was positioned in a place considered less prone for infection (12). Although the first cases of continuous lumbar epidural anesthesia were performed with the insertion of ureteric catheters, different forms of self-assembled polyvinyl tubing followed. In 1962, Lee (14) introduced the first catheter with a closed tip and a lateral hole to reduce trauma on insertion (13). This catheter was further refined by adding additional holes and was later shown to provide a more reliable spread of epidural blocks in parturients.
Maternal and fetal safety were further improved with an increased understanding of both the physiologic changes during pregnancy and the side effects of central neuroaxial blocks. The measurement of umbilical drug concentrations led to a broad understanding of placental transfer of most currently used drugs. In 1953 the anesthesiologist V. A. Apgar (15) introduced a score to evaluate the newborn based on physiologic variables, thus creating a simple, although not always reliable, tool to detect the effects of anesthetics on the newborn.
In the last decade, neuroaxial anesthesia-related deaths caused by local anesthetic toxicity decreased significantly for cesarean deliveries after the routine use of test doses and incremental injections (16). In the same period, anesthesia-related deaths during general anesthesia did not decline, making fatal outcomes 16.7 times more likely after general anesthesia. This more frequent mortality rate has made regional anesthesia the method of choice today.
Although epinephrine-containing test doses detect intravascular catheter placements in most patients, their usefulness in laboring patients was questioned because of unreliable heart rate increases and the risk of decreasing uterine blood flow on IV injection (17). Norris et al. (18), using a multi-orifice catheter, demonstrated that frequent catheter aspirations, incremental injections of local anesthetics, and use of the air test reliably detected IV misplaced catheters in laboring parturients. This approach is preferred by an increasing number of anesthesiologists for labor analgesia, but should not automatically be transferred to anesthesia for cesarean deliveries, where the accidental injection of larger concentrations of local anesthetics will produce systemic toxicity.
The discovery of spinal opioid receptors in the late 1970s led to a widespread use of epidurally and intrathecally administered opioids, and the combination of opioids and dilute local anesthetics in providing labor pain relief became standard practice. Using these dilute solutions, Chestnut et al. (19) and subsequently Vertommen et al. (20) demonstrated that epidural analgesia did not necessarily increase the incidence of instrumental deliveries. The modernization of regional anesthetic techniques not only reduced the incidence of side effects but also led to a wider acceptance of neuroaxial analgesia in obstetrics. Hawkins et al. (21) reported an increase in regional labor analgesia from 22% in 1981 to 55% in 1992 in the United States. Controversies on the influence of regional anesthesia on labor outcome nevertheless remained and led to a search in further reducing local anesthetic requirements. A step in this direction was taken with the introduction of patient-controlled epidural analgesic techniques, which were shown to reduce local anesthetic requirements by 30% in comparison with continuous epidural infusions (22).
A different approach in reducing local anesthetic requirements was the use of CSEs. Spinal injections were long avoided in obstetric patients because of the increased risk of PDPH and its incapacitating consequences. With the introduction of atraumatic pencil-point needles by Whitacre in 1951 (23) and the use of smaller needle sizes (27-gauge), this risk has significantly decreased (24) and has led to a renewed interest in intrathecal drug administration for labor analgesia. This made CSEs increasingly popular in some centers. It was subsequently demonstrated that intrathecal injections of opioids and local anesthetics can be safely performed, if parturients are closely monitored for signs of respiratory depression during the first hour (25), but the advantages remain debatable (26). Studies not flawed by different epidural regimen showed a faster onset of analgesia of 6–8 min, the same quality of analgesia and patient satisfaction, and no difference in motor blockade, instrumental deliveries, or cesarean deliveries (27–29). Nickells et al. (30) could only detect a difference of 2 min. The reduction in local anesthetic requirements has not been shown to influence maternal or neonatal outcome and can probably be neglected, if continuous infusions of local anesthetics are started immediately after intrathecal injection.
A potential advantage of CSEs is the possibility to ambulate and has been demonstrated in several trials (31,32). Although a large, randomized trial did not show any differences in instrumental deliveries or cesarean deliveries in ambulating versus nonambulating parturients (33), patients appreciate not being confined to their beds during the first stage of labor. Although most anesthesiologists only allow ambulation in patients receiving a CSE, a direct comparison between the two techniques revealed no differences in dorsal horn function or the ability to ambulate (28). Recent studies show that more than 90% of patients with epidural labor analgesia can safely walk, if dilute concentrations of local anesthetics and opioids are used and an additional test dose is avoided (34,35). It should be emphasized that, independent of the type of neuroaxial block, strict criteria for safe ambulation are necessary, and patients should be accompanied to avoid harm. Based on these studies, the two techniques seem to be equivalent in providing excellent labor pain relief without a major difference in side effects. There currently seems to be no reason to abandon epidural analgesia.
Regional anesthetic techniques have come a long way since their first introduction into labor analgesia. With the reassuring results that atraumatic needles have reduced the incidence of PDPH significantly, it may therefore be worthwhile to reintroduce the method of Oscar Kreis and provide a single-shot spinal analgesia for parturients requesting pain therapy for the second stage of labor. This is faster to perform and eliminates the risk of inadvertent dural puncture with large-bore epidural needles during frequent uterine contractions.
References
This article has been cited by other articles:
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  D. K. Turnbull and D. B. Shepherd Post-dural puncture headache: pathogenesis, prevention and treatment Br. J. Anaesth., November 1, 2003; 91(5): 718 - 729. [Abstract] [Full Text] [PDF]
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