Of the deliveries studied, 30% were by cesarean section, which accounted for 51% of all anesthesia-related complications. The incidence of anesthesia-related complications in cesarean deliveries was 2.1-3.2 times higher than the rate in vaginal deliveries across the entire maternal age spectrum, with the greatest difference seen in the 40-55 yr age group (Fig. 2).
Multivariate logistic regression modeling confirmed the excessive risk of anesthesia-related complications in cesarean deliveries (adjusted odds ratio [OR] 2.51) (Table 5, Model 1). In addition to cesarean delivery, Charlson-Deyo Comorbidity Index ≥1, rural area, being Caucasian, and scheduled admission were each associated with a significantly increased risk of anesthesia-related complications (Table 5, Model 1). When the analysis was limited to cesarean deliveries, the estimated OR of anesthesia-related complications associated with Charlson-Deyo Comorbidity Index decreased from 1.47 to 1.28 but remained statistically significant. On the other hand, the estimated OR associated with rural area increased from 1.33 to 1.65 (Table 5, Model 2).
The average LOS for women with anesthesia-related complications (3.89 ± 3.69 days [mean ± sd]) was about one-day longer than for women without anesthesia-related complications (2.92 ± 2.38 days, P < 0.0001). Overall, 96 women died in the deliveries studied, with a mortality rate of 10.3 deaths per 100,000 deliveries. Of the 96 maternal fatalities, 9.4% had at least one recorded anesthesia-related complication. Anesthesia-related complications during labor and delivery were associated with a 22-fold increased risk of maternal mortality (OR 22.26, 95% confidence interval 11.20-44.24).
Our study indicates that the incidence of anesthesia-related complications in labor and delivery was 0.46%, which varied markedly with the type of delivery, maternal preexisting medical conditions as measured by Charlson-Deyo Comorbidity Index, rural/urban area, and race. If corroborated by other researchers, these findings may provide valuable data for understanding and reducing the risk of obstetric anesthesia care. Cesarean delivery emerged as the most important risk factor for anesthesia-related complications, increasing the risk by 151% compared with vaginal delivery. Although cesarean delivery has long been recognized as a risk factor for maternal morbidity and mortality,19,20 our study provides quantitative data on the strength of the association between cesarean delivery and anesthesia-related complication with adjustment for maternal age, comorbidity, and other confounding factors. In our study, the proportion of cesarean deliveries increased from 27.5% in 2002 to 31.5% in 2005. These results are consistent with national statistics.21,22 A survey of approximately 1300 US hospitals that provide obstetric services found that only 6%-10% of mothers had no anesthesia during labor and delivery in 2001, as opposed to 11%-33% in 1992.23 With the cesarean delivery rate continuing to increase in the United States and many other countries,21,24,25 complications in cesarean delivery are an issue of increasing importance to obstetric anesthesia care.
Rural area is another risk factor for anesthesia-related complications in labor and delivery. Approximately 25% of the American population lives in rural areas but only 12.5% of surgeons practice there. Rural residents may have transportation barriers, less health workers per capita, and may take longer to seek treatment for their illnesses. It is estimated that <5% of practicing anesthesiologists work in rural areas.§ The heightened risk of anesthesia-related complications during labor and delivery for women living in rural areas may be due in part to these structural barriers to quality obstetric care. It was reported that women in rural areas receive significantly fewer epidurals than urban women during labor,26 which implies that the estimated risk associated with rural area reported in our study might be an underestimate.
There have been various case reports and studies describing the more complicated obstetric anesthetic management of women with specific preexisting complications, such as diabetes.27 Although it is expected that women with preexisting medical conditions may be more susceptible to the adverse effects of anesthesia, there are little empiric data substantiating the role of comorbidity in anesthesia-related complications during labor and delivery. Our study reaffirms that women in labor and delivery are generally a healthy group, with 97% of them having a 0 score on the Charlson-Deyo Comorbidity Index. Those who scored 1 or more on the Charlson-Deyo Comorbidity Index had a 47% higher risk of anesthesia-related complications in labor and delivery. The most common preexisting medical condition contributing to an elevated score on the Charlson-Deyo Comorbidity Index was chronic pulmonary disease, followed by diabetes.
We found that Caucasian women had a significantly higher incidence of anesthesia-related complications in labor and delivery than women in other racial groups. The higher incidence of anesthesia-related complications in Caucasian women may have resulted from their greater exposure to anesthetics and analgesics. Studies have shown that after controlling for factors such as insurance coverage and provider practice, Caucasian women in labor are more likely than African-American and Hispanic women to receive epidural analgesia.26,28 Moreover, the excess risk of anesthesia-related complications during labor and delivery in Caucasian women might be due in part to the fact that deliveries by Caucasian women are more likely to be nulliparous because they on average have fewer children than women in other racial groups.21 Nulliparous women are at an increased risk of complications compared with multiparous women.29
The risk of anesthesia-related complications increased slightly in scheduled admissions. The elevated risk associated with scheduled admissions is likely due to unmeasured confounders. Our data indicate that women who gave birth through scheduled admissions were more likely to have preexisting medical conditions and cesarean deliveries than women in the unscheduled admission group. Scheduled admissions may also be more likely to receive inductions and epidurals than unscheduled admissions. Although we controlled for method of delivery and comorbidity in the multivariate analysis, it is possible that the adjustment was inadequate because of the limited covariates and imperfect measurement of predelivery health status.
A few factors make it difficult to compare the results of this study with those in previous studies of anesthesia-related complications in labor and delivery. First, the majority of previous studies did not report anesthesia-related complications according to ICD-9-CM codes. Rather, they categorized complications by specific clinical manifestations, such as respiratory spasms, epidural hematoma, spinal headache, and neurological injury. Second, most previous studies of anesthesia-related complications in labor and delivery were limited to specific anesthesia techniques (e.g., epidural) or surgical procedures (e.g., cesarean section).3–13 In this study, we examined anesthesia-related complications in all deliveries in a defined population and time period regardless of anesthesia type. The spinal complications documented in our study are made up of spinal headache and root injury. Lastly, most previous studies were based on small or modest sample sizes. A meta-analysis showed that the reported incidence of epidural anesthesia-related complications was dependent on the sample size of the study, with smaller studies (<10,000 women) overestimating risk by 15-fold compared with larger ones.11 Our study sample is larger than all but one previous study, which was a retrospective review of epidural anesthesia complications involving 2,580,000 deliveries in the United Kingdom.6
Our study has several notable limitations. First, the reported incidence is subject to reporting bias. Although the hospital discharge data are collected and recorded using standardized protocols, anesthesia-related complications might be susceptible to underreporting and misclassification. Therefore, the incidence of anesthesia-related complications reported in this study is likely a conservative estimate. Studies investigating the validity of discharge data against medical records for reporting of maternal medical conditions and obstetric procedure and diagnoses have found accurate reporting of some codes (for example, cesarean deliveries, perineal lacerations, and diabetes) but poor coding of other conditions, such as asthma and postpartum complications.30–32 Because administrative data are being used increasingly for health services research, more studies assessing the data quality of hospital discharge records are needed.30
Second, information about anesthesia exposure is incomplete. The variable indicating anesthesia type was of limited use because data on this variable were missing for 30% of the deliveries. It is estimated that overall about 90% of women during labor and delivery receive some form of anesthesia.23 In the absence of complete data on anesthesia exposure, we calculated the incidence based on all deliveries, which should lead to an underestimation. The estimated ORs for the identified risk factors, however, appear to be reasonably robust given the consistent findings from the analysis restricted to cesarean deliveries.
Third, our study unit was delivery, not individual women. Many women may have given birth multiple times during the 4-yr study period. Each delivery was treated as an independent event in our analysis. Because the HCUP SID data do not allow us to link individual records over time, our analysis did not consider the possible intrasubject correlation in demographic and clinical variables. To assess this possible source of bias, we stratified the data according to single calendar year of admission. Results from the stratified analysis were similar to those based on the aggregated data.
Finally, the proprietary HCUP SID data do not contain any information on hospital characteristics. As such, we did not examine anesthesia-related complications in relation to hospital characteristics. The lack of hospital-level data may introduce bias to our results due to unmeasured confounding. Moreover, it curbs our ability to interpret some of the findings. For instance, we found that the incidence of anesthesia-related complications for women from rural areas was higher than that for those living in urban areas, but we do not know to what extent the excess risk was attributable to hospital characteristics in rural communities.
Nevertheless, this study is among the largest epidemiologic investigations of anesthesia-related complications during labor and delivery. The Agency for Healthcare Research and Quality has established patient safety indicators based on pertinent ICD-9 codes.∥ Many of these patient safety indicators have been assessed using hospital discharge data.33–35 Research on anesthesia safety indicators, however, has been scant. This study demonstrates that it is feasible to examine the epidemiology of anesthesia-related complications in a defined patient population using specific ICD-9 codes and readily accessible hospital discharge data. The findings regarding the incidence and risk factors of anesthesia-related complications during labor and delivery may provide valuable empiric data for developing interventions to improve obstetric care and serve as important benchmarks for program evaluation.
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†Available at: www.hcup-us.ahrq.gov/toolssoftware/ccs/ccs.jsp. Accessed July 1, 2008.
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§Available at: http://www.asahq.org/Newsletters/2006/12-06/schweitzer12_06.html. Accessed July 18, 2008.
∥Available at: http://www.qualityindicators.ahrq.gov/psi_overview.htm. Accessed July 28, 2008.