This Invited Commentary accompanies the following article:
Volk T, Wolf A, Van Aken H, Bürkle H, Wiebalck A, Steinfeldt T. Incidence of spinal haematoma after epidural puncture: analysis from the German network for safety in regional anaesthesia. Eur J Anaesthesiol 2012; 29:170–176.
Serious adverse outcomes following anaesthetic interventions are fortunately very rare. Because of the low incidences and difficulties in identifying index cases, the estimation of the numerator can be difficult. Even if a system exists to identify all index cases, it is often more difficult to estimate the denominator to scale the risk estimate. Rare events of interest to the anaesthetist of course include, for example, the incidence of unexpected failed tracheal intubation.1 Likewise, the epidemiology of incidences of serious adverse events following neuraxial regional anaesthetic procedures continues to be of interest and topical.2 It may surprise the casual reader that for an event to be defined as ‘rare’, it can actually be more common than we assume. A rare event is defined as a rate of less than one in 20 events, interestingly similar to the type 1 error rate of P less than 0.05 that is often used by convention in medical research! For the purposes of this commentary, we are of course interested in much rarer event rates than this.
In the journal this month, Volk et al. from the German Network for Safety in Anaesthesia report an audit of the incidence of epidural haematoma following nonobstetric epidural anaesthetic procedures during the 2-year period, 2009–2010.3 They present data from five cases of epidural haematoma from an estimated denominator of 33 142. This equates to an incidence of one per 6628 epidural procedures. If both the numerator and denominator reported by the authors are reliable, then the exact Clopper–Pearson 95% confidence limits can be estimated at one in 2841–20 408 procedures. In addition, they report a patient who developed an intracranial subdural haematoma following the placement of a lumbar epidural catheter.
The report by Volk et al. raises a number of issues. First is that the incidence reported by the German network is higher than other published rates for epidural haematoma. It is not clear why this should be the case. Second is that all five epidural haematomas occurred following thoracic epidural procedures and that none were associated with lumbar procedures. A crude estimate of the rate for thoracic epidural haematomas in these data may be in the region of one in 3670 thoracic epidural procedures. Third is that it is clear from some of the case histories that recommendations about timing of thromboprophylaxis4 with regard to epidural anaesthetic procedures and the imaging and diagnosis of suspected cases continue to be problematic.
Safety is defined as the condition to which risks are managed to acceptable levels. So to define safety there are two components. First is the objective component, which is the measurement of risk rates. Second is the subjective, which is what we define as an acceptable level. The difference between components gives rise to the safety margin. With advances in information and communication technologies it is clear that such epidemiological surveillance will continue to provide useful data to inform the objective component that can be used to improve the safety of our patients undergoing regional anaesthesia. To this end, Volk et al. are to be commended, as well as others in the working group who collaborate and contribute data on behalf of the German Network for Safety in Anaesthesia.
This article was checked and accepted by the Editors, but was not sent for external peer-review.
1. Basaranoglu G, Lyons G, Columb M. Failure to predict difficult tracheal intubation for emergency cesarean section. Eur J Anaesthesiol
2. Cook TM, Counsell D, Wildsmith JA. Major complications of central neuraxial block: report on the Third National Audit Project of the Royal College of Anaesthetists. Br J Anaesth
3. Volk T, Wolf A, Van Aken H, Bürkle H, Wiebalck A, Steinfeldt T. Incidence of spinal haematoma after epidural puncture: analysis from the German network for safety in regional anaesthesia. Eur J Anaesthesiol
4. Gogarten W, Vandermeulen E, Van Aken H, et al. Regional anaesthesia and antithrombotic agents: recommendations of the European Society of Anaesthesiology. Eur J Anaesthesiol