The observed 30 day SSI rate after CD in Taiwan, 0.3%, defined by five ICD codes suggested by Olsen and colleagues,7
is lower than those reported in the literature3,4
and the pooled mean rate of 3.15% (2.71–7.53%) reported by the Centre for Disease Control and Prevention's National Nosocomial Infections Surveillance System in the USA.14
By including disease codes that constitute SSI indicators suggested by another group,13
we found a 30 day SSI rate after CD of 0.9%. Taiwanese women's high utilization of free prenatal care covered by the Taiwan's National Health Insurance programme could partially explain for the low SSI rate after CD. However, the 30 day SSI rate for CD reported in the current study was probably underestimated because only inpatient claim data were used for data analysis. There could be superficial incisional infections that were treated in the outpatient settings and hence were not accounted for. On the other hand, the use of 81 SSI indicators to extract SSI cases could also result in an overestimation of the SSI rate as in a previous study only 68% of CD women with one of these codes were found to have an SSI based on medical record review.13
This study provided the first evidence that GA is associated with a higher risk of 30 day post-CD SSI compared with NA. The relative short hospital stay associated with NA compared with GA12
could partially explain the lower SSI rate, as prolonged hospital stay has been identified as a risk factor for SSI and nosocomial infections. Alternatively, prolonged hospital stay may be a result of SSI. When duration of hospital stay was added into the regression model, the risk of SSI associated with GA was only slightly reduced, suggesting that other mechanisms were involved.
Mechanisms underlying the differential impact of the modes of anaesthesia on post-CD SSIs are largely unknown. Previously, it has been argued that GA is associated with greater immunosuppression and host defence impairment compared with SA or EA.15,16
However, a recent study found that differences in the mode of anaesthesia did not affect the concentrations of serum cytokines (interleukin-6 or tumour necrosis factor-alpha) in parturients undergoing elective CD.17
Another plausible mechanism by which NA could reduce SSIs is by providing sympathetic block18,19
and thereby vasodilatation and greater surgical site tissue oxygenation.
CD has become one of the most common surgical procedures. Given the risk associated with surgery and anaesthesia, clinical decisions on deliveries should be guided by best-practice guidelines. However, the choice of anaesthesia modes has not always been based on medical indications and clinical practice guidelines. There are instances where anaesthesiologists' and/or obstetricians' individual preferences outweigh clinical indications. The strength of the study was that a population-based epidemiologic approach was used to elucidate the association of modes of anaesthesia with the 30 day SSI rate after CD. Clinicians and future parturients should be informed by findings of this study, so that informed decisions can be made.
Recent publications demonstrated that GA increased the odds of stroke in preeclamptic women after CD20
and that of SSI in individuals receiving total hip or knee replacements,10
when compared with NA. Our data also support that GA may be associated with long-term consequences and warrant further investigations.
There are certain limitations in this study that need to be addressed. First, this study analysed data from insurance claims, and thus data on prenatal and maternal characteristics that may very likely be associated with SSI were generally lacking. For example, factors that could have an effect on SSI including maternal obesity,7
type of skin closure,7
duration of surgery,8
and prenatal visits8
were not available for analysis and thus were not accounted for when examining the relationship between the mode of anaesthesia and SSI. Secondly, GA is much more likely to be used for emergency CD which is thought to be a risk factor of post-CD SSI. As we were unable to differentiate emergency from elective procedures, ‘maternal requested CD’ was extracted and controlled for in the multivariable regression models instead. Nevertheless, there was evidence indicating no significant difference in the SSI rate between elective and emergency CD.21
Thirdly, as aforementioned, only inpatient claim data were analysed, and therefore, the 30 day SSI rate might be underestimated. Finally, in this study, list-wise deletion was performed to handle missing data instead of imputing missing data. Of the 1163 cases with missing data, 870 had missing data on the date of discharge from the hospital (necessary for the calculation of LOS), 290 had missing data on the mode of anaesthesia, and three had missing data on both variables. Because imputation might not be suitable for these two variables, we decided to perform list-wise deletion instead. The 30 day SSI rates of the 1163 cases were 0.3% based on five ICD-9-CM codes and 1.5% based on 81 ICD-9-CM codes, which were similar to those of the study sample (data not shown).
In conclusion, the incidence of SSI was about 0.3–0.9% in Taiwanese women undergoing CD, with an observation period of 30 days after operation. About four in 100 women who underwent CD received GA for the delivery. GA for CD was associated with a higher risk of SSI when compared with NA.