Obstetrics & Gynecology:
Anesthesia-Related Maternal Mortality in the United States: 1979–2002
Hawkins, Joy L. MD; Chang, Jeani MPH; Palmer, Susan K. MD; Gibbs, Charles P. MD; Callaghan, William M. MD
From the Department of Anesthesiology, University of Colorado School of Medicine, Aurora, Colorado; the Centers for Disease Control and Prevention, Atlanta, Georgia; the Oregon Anesthesiology Group, Portland, Oregon; and the Department of Anesthesiology, University of Florida School of Medicine, Gainesville, Florida.
The authors thank the Centers for Disease Control and Prevention in Atlanta, Georgia, for allowing us to review their maternal mortality data for this study. The findings and conclusions in this report are those of the authors and do not necessarily represent the official position of the Centers for Disease Control and Prevention.
Corresponding author: Joy L. Hawkins, MD, Department of Anesthesiology, 12631 E. 17th Avenue, Mail Stop 8203, Aurora, CO 80045; e-mail: Joy.Hawkins@ucdenver.edu.
Financial Disclosure The authors did not report any potential conflicts of interest.
OBJECTIVE: To examine 12 years of anesthesia-related maternal deaths from 1991 to 2002 and compare them with data from 1979 to 1990, to estimate trends in anesthesia-related maternal mortality over time, and to compare the risks of general and regional anesthesia during cesarean delivery.
METHODS: The authors reviewed anesthesia-related maternal deaths that occurred from 1991 to 2002. Type of anesthesia involved, mode of delivery, and cause of death were determined. Pregnancy-related mortality ratios, defined as pregnancy-related deaths due to anesthesia per million live births were calculated. Case fatality rates were estimated by applying a national estimate of the proportion of regional and general anesthetics to the national cesarean delivery rate.
RESULTS: Eighty-six pregnancy-related deaths were associated with complications of anesthesia, or 1.6% of total pregnancy-related deaths. Pregnancy-related mortality ratios for deaths related to anesthesia is 1.2 per million live births for 1991–2002, a decrease of 59% from 1979–1990. Deaths mostly occurred among younger women, but the percentage of deaths among women aged 35–39 years increased substantially. Delivery method could not be determined in 14%, but the remaining 86% were undergoing cesarean delivery. Case-fatality rates for general anesthesia were 16.8 per million in 1991–1996 and 6.5 per million in 1997–2002, and for regional anesthesia were 2.5 and 3.8 per million, respectively. The resulting risk ratio between the two techniques for 1997–2002 was 1.7 (confidence interval 0.6–4.6, P=.2).
CONCLUSION: Anesthetic-related maternal mortality decreased nearly 60% when data from 1979–1990 were compared with data from 1991–2002. Although case-fatality rates for general anesthesia are falling, rates for regional anesthesia are rising.
LEVEL OF EVIDENCE: II
The Division of Reproductive Health at the Centers for Disease Control and Prevention (CDC) maintains surveillance data on pregnancy-related mortality in the United States. They note that, although death from complications of pregnancy has decreased by 99% since 1900, there have been no further decreases in the past two decades.1,2 Those at greatest risk in their report were women of African-American race, women older than 34 years of age, and women who received no prenatal care. Among women who died after a live birth, the leading causes of death were embolism and hypertensive disorders of pregnancy.2,3 It has been estimated that 28–40% of maternal deaths could be prevented by changes in individual actions or in system changes.4–6
In contrast to overall maternal mortality, anesthetic causes of maternal mortality have progressively declined and now account for less than 2% of pregnancy-related maternal mortality in the United States.1,2 Obstetric anesthesiologists have used workforce surveys documenting how anesthetic care is provided,7 practice guidelines with evidence-based recommendations for care,8 and international,9 national,10 and state11 reviews of anesthesia-related maternal mortality to improve patient safety. The American Society of Anesthesiologists (ASA) Closed Claims Project reviews closed malpractice claims for obstetric anesthesia from their database and publishes the findings for practice improvement.12 Team training and simulation on labor and delivery units are used to improve performance in emergency situations.13 Despite these efforts, adverse events still occur. This study examines 12 years of maternal deaths related to anesthesia from 1991 to 2002, and compares the results to previous published data from 1979 to 1990 to estimate trends in anesthesia-related maternal mortality over time and to compare the risks of general and regional anesthesia during cesarean delivery.10
MATERIALS AND METHODS
In 1987, the CDC's Division of Reproductive Health, in collaboration with state health departments and the American College of Obstetricians and Gynecologists Maternal Mortality Study Group, established the Pregnancy Mortality Surveillance System. This system provides ongoing surveillance of all pregnancy-related deaths reported through individual state health departments, maternal mortality review committees, media, and individual providers. The Pregnancy Mortality Surveillance System collects data regarding all reported deaths that are causally related to pregnancy. The first step is to identify all deaths occurring during pregnancy or within 1 year of pregnancy. Methods used to establish this temporal relation between pregnancy and death include a pregnancy check box marked on the death certificate, a death certificate that otherwise indicated the woman was pregnant at the time of death, 14 or a death certificate of a reproductive-aged woman that had been matched with a birth certificate or fetal death certificate for a delivery that occurred within 1 year before the woman's death.
Health departments in the 50 states, the District of Columbia, and New York City voluntarily provide CDC with copies of death certificates that are causally related to pregnancy. For deaths that occur after a live birth or stillbirth, the matching birth or fetal death certificates are also provided by the health departments. These certificates provide information not otherwise available on the death certificate (eg, prenatal care, live birth order, and maternal health and medical information). In addition to requesting certificates of deaths that are causally related to pregnancy, beginning with deaths occurring in 1991, states were asked to send certificates of all deaths that occurred during pregnancy or within 1 year of pregnancy, regardless of the cause of death or relation between pregnancy and the death.
A woman's death is classified as pregnancy-related if it occurred during pregnancy or within 1 year of pregnancy and resulted from complications of the pregnancy, a chain of events that was initiated by the pregnancy, or the aggravation of an unrelated condition by the physiologic effects of the pregnancy or its management. Clinical epidemiologists at CDC reviewed and classified each pregnancy-related death regarding the immediate and underlying cause of death, associated obstetric conditions, and the outcome of pregnancy. Of all pregnancy-related deaths (n=5,946) submitted to CDC for 1991–2002, 86 were determined to be caused by anesthesia-related complications. The numerator file (deaths) contained no identifiers and had information only about the deceased individual, and the denominator file (births) was de-identified and available for public use. Hence, this analysis did not require review by an institutional review board.
For this study, three obstetric anesthesiologists independently reviewed the de-identified pregnancy-related death certificates and matched live birth or fetal death certificates for each of the 86 anesthesia-related cases to confirm that the death resulted from a complication of anesthesia. If all three anesthesiologists confirmed from the vital records information that the death resulted from anesthesia-related complications, they then determined the cause of death, procedure for delivery, and type of anesthesia provided. Because vital records are often incomplete on the events surrounding the death, if the codes from all three anesthesiologists did not match, they discussed what information they used to reach their conclusion. If they still could not agree, the information was coded as unknown. After an initial analysis of these cases, the 24 abortion-related deaths, the three deaths associated with an ectopic pregnancy, and three deaths with unknown pregnancy outcome were excluded so that 56 cases associated with an obstetric delivery (live births or stillbirths) were evaluated to be consistent with our previous report.11 Pregnancy mortality rates per million live births were calculated using national data on live births from the 1991–2002 natality files of the National Center for Health Statistics.
To compare the risks of general and regional anesthesia during cesarean delivery, case-fatality rates were estimated by the following procedure. First, the national number of live births was determined for each year during the period 1991–2002. Second, national cesarean delivery rates for each year, derived from the natality file of CDC's National Center for Health Statistics, were applied to the number of live births, and then the number of cesarean deliveries was calculated for the time period. This estimate was then apportioned to administration of general and regional anesthesia according to estimated annual percentages from obstetric anesthesia workforce survey data that included a stratified random sample of 1,300 hospitals selected from the American Hospital Association's “Guide to the Healthcare Field” and stratified by geographic region and number of births for that year.7 It was assumed that the percentage of regional compared with general anesthesia used would be similar in hospitals in which deaths occurred to that in the national sample. The average cesarean delivery rate during this period was 22%; according to results from the workforce survey, general anesthesia was used in approximately 14% of cases and regional anesthesia was used in approximately 86%.
Case fatality rates were calculated by dividing the observed number of deaths associated with general or regional anesthesia during cesarean delivery by the estimated number of administrations of that type of obstetric anesthesia during cesarean delivery in the same period. To estimate the risk associated with general anesthesia relative to that for regional anesthesia, rate ratios were calculated with the case fatality rates for regional anesthesia as the referent. We based 95% confidence intervals on the logit case-fatality rate and used the Taylor series method for variances.15 The results were compared with previous data reported from 1979 to 1990.10
To compare U.S. data with data from the United Kingdom, pregnancy mortality rates were calculated by triennium. Because the denominator for U.S. rates is based on the number of live births, whereas the rates from the United Kingdom are based on all “maternities” (the count of mothers who delivered live births, stillbirths, pregnancy terminations, ectopic pregnancies, and abortions), these rates are not perfectly analogous but should allow for comparison.9
From 1991 to 2002, a total of 86 pregnancy-related deaths were associated with complications of anesthesia, accounting for 1.6% of total pregnancy-related deaths in the United States. The overall pregnancy-related mortality ratio for deaths related to anesthesia complications is 1.2 per million live births for 1991–2002, a decrease of 59% from 2.9 per million live births for 1979–1990. The pregnancy-related mortality ratios from anesthesia are very similar in the United States and in the United Kingdom (Table 1). The pregnancy-related mortality ratio related to anesthesia in the United States has steadily decreased in each subsequent 3-year period from 4.3 in 1979–1981 to 1.0 in 2000–2002 except for a slight increase of 0.1 from the periods 1994–1996 and 1997–1999. Similar to the United States, the pregnancy-related mortality ratio related to anesthesia has decreased from 8.7 in 1979–1981 to 3.0 in 2000–2002 in the United Kingdom.
Of the 86 deaths designated as anesthesia-related, 27 early losses were excluded (24 abortion deaths and three ectopic deaths) and three deaths were excluded because of unknown pregnancy outcome. The 56 remaining cases resulted in a live birth or stillbirth to focus on birth outcomes, consistent with previous reports.10 Table 2 compares the selected maternal demographic and pregnancy characteristics during obstetric delivery for 1991 through 2002 with previous data reported from 1979 to 1990. The distribution of maternal age for anesthesia-related deaths for 1991–2002 has varied somewhat as compared with the previous data. Pregnancy-related deaths related to anesthesia mostly occurred among younger women, aged 20–24 years, 27% for 1991–2002 and 32% for 1979–1990, but the percentage of anesthesia-related deaths among women aged 35–39 years has increased substantially from 5% for 1979–1990 to 18% for 1991–2002. The distribution of maternal race and prenatal care initiation remained comparable for both study periods. Among women who died after delivery of live birth or stillbirth during 1991–2002, the delivery method was known for 86% (48 of 56) of the women. Almost all women who died from complications of anesthesia during delivery for 1991–2002 were undergoing a cesarean delivery (86%), very similar to our previous report (82%). Approximately 14% of the delivery procedures could not be determined, but no known death was associated with a vaginal delivery for 1991–2002.
The estimated case fatality rate of general anesthesia during cesarean delivery decreased from 16.8 deaths per million general anesthetics for 1991–1996 to 6.5 deaths per million general anesthetics for 1997–2002 (Table 3). In contrast, the estimated case fatality rate of regional anesthesia during cesarean delivery increased slightly from 2.5 deaths per million regional anesthetics to 3.8 deaths per million regional anesthetics. In general, the risk of death attributed to general anesthesia during cesarean delivery is consistently higher than death attributed to regional anesthesia during cesarean delivery; however, this disparity is reduced from 6.7 for 1991–1996 to 1.7 for 1997–2002. Overall, the leading causes of anesthesia-related pregnancy deaths for 1991–2002 were intubation failure or induction problems (23%), respiratory failure (20%), and high spinal or epidural block (16%). However, the causes varied by the type of obstetric anesthesia administered. About two-thirds of deaths associated with general anesthesia were caused by intubation failure or induction problems, but for women whose deaths were associated with regional anesthesia during cesarean delivery, more than one-fourth (26%) were caused by high spinal or epidural block, followed by respiratory failure (19%), and drug reaction (19%).
Complications related to anesthesia still occur, despite anesthetic-related maternal mortality decreasing nearly 60% when data from 1979–1990 were compared with data from 1991–2002. Data suggest that the anesthetic death rate has stabilized at about one death per million live births10,16 (Table 1). Historically, increased maternal risk has been associated with general anesthesia. During the 1970s and 1980s, 17 women died as a result of general anesthesia for every one who died from regional anesthesia. By the early 1990s, this had improved to six general anesthetic deaths for every regional anesthetic death. Case fatality rates for general anesthetics have decreased substantially, whereas those for regional have increased slightly, and, in the most recent time period studied, there is no significant difference in rates between the techniques (Table 3).
Many advances have occurred in the practice of obstetric anesthesiology since the first collection of anesthetic-related maternal mortality data between 1979 and 1990. Although there was increased popularity of regional anesthetic techniques during that time period, case fatality rates for regional anesthesia decreased.7,17 Factors associated with the decline included withdrawal of concentrated epidural bupivacaine, awareness of local anesthetic toxicity and inadvertent intrathecal injections associated with epidural anesthesia, increased use of test doses, and incremental dosing of epidural catheters. However, during the same time period, the case fatality rates for general anesthesia increased, leading anesthesiologists to avoid general anesthesia when possible and to research ways to make general anesthesia safer. Further improvement occurred when data were collected from 1991 to 1996. During that time period, there was a decline in the case fatality rates for general anesthesia with improvement of the overall risk ratio between general and regional anesthesia. These advances could be attributed to better anesthetic monitoring and published standards for anesthetic care. Pulse oximetry, capnography, and the Difficult Airway Algorithm18 are all examples of ASA practice improvement efforts that have reduced deaths resulting from ventilation and intubation complications. The case fatality rates for general anesthesia continued to decrease from 1997 to 2002, and the relative risk of general compared with regional anesthesia fell to 1.7 (95% confidence interval [CI] 0.6–4.6; P=.2), a nonsignificant difference. Of interest, two studies reviewed failed intubations in obstetrics during 1993–199819 and 1999–2003.20 These studies revealed failed intubation rates were 1:249 and 1:238, respectively, similar to the original 1:280 rate for failed intubation in obstetrics published in 1985,21 but there were no maternal deaths in either recent series.
During the past two decades, anesthesiologists have focused on improving their management of difficulty airway–failed intubation, gaining expertise with the laryngeal mask and other airway devices. In cases of hemorrhage with hemodynamic instability or prolapse of the umbilical cord, general anesthesia may be the most appropriate choice for cesarean delivery. The Maternal-Fetal Medicine Units Network quantified anesthesia-related complications associated with cesarean delivery in 37,142 cesarean deliveries for singleton gestations.22 They reported that 93% of mothers received a regional anesthetic with a 3% failure rate and rare maternal morbidity. General anesthesia was more likely to be used (odds ratio [OR] 6.9) for cases when the decision-to-incision interval was less than 15 minutes or when ASA status was 4 or higher, that is, the most emergent cases and the sickest patients. Improvements in case fatality rate for general anesthesia are especially notable considering it is used for the highest risk patients and most hurried emergencies. Our data suggest that general anesthesia should not be avoided when necessary because the mortality rate is extremely low, only 6.5 per million general anesthetics (Table 3). New guidelines address appropriate recovery room management after general anesthesia and additional monitoring for obese patients at risk for sleep-obstructed breathing because of concerns about complications occurring during the postoperative period.23,24
Despite these encouraging reports demonstrating the safety of general anesthesia for obstetrics, there are new reports of increasing complications during regional anesthesia. Although a recent description of obstetric anesthesia liability claims by the ASA Closed Claims Project12 indicated that claims for maternal death and brain damage were decreasing, claims for nerve injury were increasing and are now the most common cause of litigation. In some cases there were undetected intrathecal catheters and providers were not always prepared to treat these emergencies. Four cases describe patients with cardiac arrest due to high block being transferred to an operating room for resuscitation because there was no resuscitation equipment in the labor room. Similarly, the Doctors Insurance Company reported on 22 anesthesia malpractice closed claims filed after maternal cardiac arrests on labor and delivery wards between 1998 and 2006.25 Outcomes were poor: 10 of 22 women died, 11 had anoxic brain damage, and only one survived neurologically intact. Only one case involved general anesthesia and failed intubation. Thirteen cases were respiratory arrests after epidurals or spinals. Eight followed labor epidural placement with unintentional subarachnoid block and five occurred during spinal anesthetics for cesarean delivery. None of the operating room cases had audible alarms on the monitors at the time of arrest, making delay in response likely. In seven cases, resuscitation was delayed while the patient was moved to the operating room, either to facilitate delivery or because airway equipment was not available in the labor room. Errors such as these may contribute to an increase in case fatality rates from regional anesthesia.
Although the Pregnancy Mortality Surveillance System is the most comprehensive maternal mortality database available at the national level, maternal mortality data are difficult to collect, and more information is needed about individual cases where a bad outcome or “near miss” occurred.26,27 Access should be voluntarily provided or statutorily required for all information, including the anesthesia records, in an environment in which concerns about liability do not detract from an accurate analysis of the event and how it might be prevented in the future.
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