Combined spinal-epidural (CSE) techniques have become popular in recent years. The technique is used by 65% of obstetric anaesthetists1 and accounted for 1014 out of 12,469 (8.1%) obstetric neuraxial blocks in the 2-week study period for the 3rd National Anaesthesia Project.2
The benefits of CSE are clearly apparent when the planned surgery is expected to outlast a single shot spinal anaesthesia. A smaller intrathecal dose of bupivacaine may also be used with CSE, with decreased cardiovascular instability, as a top-up may be given if initial block proves to be insufficient. By contrast, those advocating single shot spinal3 argue that the simplicity and speed of the technique together with avoidance of the risk of inadvertent dural puncture with a Tuohy needle outweigh the requirement to prevent hypotension with vasopressors.
The choice to perform a CSE compared with single shot spinal (SSS) de novo for caesarean delivery may depend where the individual anaesthetists was trained to perform obstetric anaesthesia. Centres containing keen proponents of CSE may exert an influence on neighbouring trusts in the same region, as graduates from each school of anaesthesia take up posts within local hospitals.
We therefore wished to test the hypothesis that there was a regional variation in the use of CSE techniques.
Data was extracted from the 2013 National Obstetric Anaesthesia Dataset to determine the rate of de novo CSE compared with single shot spinal anaesthesia for caesarean deliveryin each Trust, by calculating CSE/(CSE+SSS). The raw data for each Trust was analysed using Chi-squared and a frequency distribution histogram generated.
Data from individual Trusts were then combined into individual counties, using Trust postcode data. The rate of CSE use in each county was plotted onto a heatmap, using a bespoke Excel Macro.
A statistical analysis for clustering at a county level was performed using k-mean clustering algorithm MatLab. Data was clustered into k groups where each data point is as close as possible to the centroid of the cluster as optimally possible, thus minimising total intra-cluster variance. This is an iterative technique where the distance between each point and the centroid is calculated using Euclidean distance. To determine the correct number of clusters for the dataset, a silhouette coefficient was established for the range of k values.
140 Trusts contributed data to the National Obstetric Anaesthesia database in 2013, a response rate of 68%. Of the 136,331 caesarean deliveries, 9,702 received de novo CSE and 82,545 single shot spinal anaesthesia, giving a mean CSE rate of 10.5%. The frequency histogram shows that this data is positively skewed, with a median value of 2%, interquartile range of 0-9.25% and a maximum value of 100%. Chi-squared testing showed a significant difference in CSE rate between Trusts, p<0.0001.
There was significant evidence of geographical clustering, with an optimal clustering value of 2, giving a mean silhouette value of 0.93. This has been graphically illustrated using a heatmap, where the value for proportion of cases using CSE is plotted according to the postcode of the Trust.
The k-means clustering plot incorporating longtitude and latitude shows that where the latitude is lower, the centroid is higher on the y axis, indicating that CSE rates are higher in the South of the UK.
NOAD data is collected by obstetric anaesthetists, for anaesthetists. The reporters often feedback that their hospital information systems make it difficult to obtain accurate information, often requiring a fair amount of detective work to combine multiple sources of data so that that the data generated is reliable and of use to the anaesthetic community.
Official data published by the Health & Social Care Information Centre www.hscic.gov.uk for types of anaesthetic used for caesarean delivery in 2013/2014 showed that 8.6% had GA, 17.1% epidural, 60.4% spinal and 32.6% were unknown. Although the HSCIC data is provided for each Trust, both SSS and CSE are grouped under “spinal”, preventing further analysis.
This study confirms that neuraxial anaesthetic techniques do vary significantly by Trust and that these tend to cluster geographically, which could support the theory that anaesthetists are strongly influenced by their alma mater. Further work is required to investigate the differences in CSE rates between Trusts at each end of the frequency histogram
It will also be worth exploring ways to improve the quality of obstetric anaesthetic data collection throughout the UK so that the information with the National Obstetric Anaesthetic Database can be used as benchmark of obstetric anaesthetic practice and outcomes.