Thoracic epidural analgesia

We read with great interest the editorial by Kamming and Davies [1] regarding the choice of thoracic epidural anaesthesia in cardiac surgery. While the authors provided an interesting analysis, we believe their conclusion regarding the 50% chance of this technique’s failure warrants further comment. Kamming and Davies reported that in two large studies [2,3] ‘epidurals have failed to achieve adequate analgesia in between 33% and 50% of patients’. On the basis of these figures and on the apparently high percentage of failure they appear to demonstrate for thoracic epidural anaesthesia, the authors questioned whether patients should in fact be submitted to this kind of anaesthesia. Both of the studies cited by them [2,3] included patients who underwent abdominal surgery. Although not specified in either study, it is likely that the thoracic epidural catheters used during surgery were placed in the middle or lower thoracic region and it is known that the approach to the epidural space is more difficult at these levels than at a higher level in the high thoracic area, for example C7–T3. As a result, we would argue that it is not possible to extrapolate the failure rate of middle thoracic epidurals to high thoracic epidurals. Additional studies recently conducted on larger and smaller scales confirm a lower percentage of failure in the use of thoracic epidurals for cardiac surgery. Focusing on high thoracic epidurals, Chakravarthy and colleagues [4] found that of 2113 patients submitted to thoracic epidural anaesthesia (C7–T3) for cardiac surgery, there was inability to locate the epidural space or to insert the catheter in 0.9% of the patients and that there was a blood tap in 0.09%; in all the other patients the level of the block was tested preoperatively. In studies involving more than 500 patients, both Pastor [5] and Sanchez [6] experienced a global failure rate around 2.5%. The first author reported ‘nine failed puncture and four failed blocks’, that is the thoracic epidural was correctly functioning in the remaining 508 cases. Sanchez abandoned the procedure in 12 patients because ‘blockade was uncertain’; he found one dural puncture and one unsuccessful catheter placement. Therefore, in the other 557 patients, the epidural block was properly functioning. We reported a successful catheter insertion in 104 out of 106 patients submitted to coronary surgery. The degree of sensory blockade was tested before surgical incision and found to be C7–T1 to T6–T7 in all patients. Moreover, for the first postoperative 24 h, visual analogue pain scores were recorded to be 0.9 at rest and 1.7 during coughing, showing a properly functioning epidural [7]. In addition, in our own centre, we monitored data concerning 677 patients consecutively submitted to high (T1–T3) thoracic block for coronary surgery and we found a failure rate of 6.9%. The reasons for failure include: the inability to find the epidural space (3.8% of patients); the catheter not positioned (1%); and the block not properly functioning (2.1%). In 2.6% of the patients scheduled for thoracic epidural anaesthesia, the technique was aborted for dural puncture (1%) or blood tap (1%) or for vasovagal reaction (0.6%) during attempts at insertion. Two possible causes could be cited to explain the rate of failure, which is higher than reported by other authors. Firstly, our protocols, which are strictly followed, allow only three attempts to find the epidural space before abandoning the technique. Secondly, and no less importantly, all of the 11 anaesthetists amongst our staff, including the youngest, are experienced. Subsequently, our study reflects the experience of a whole group and not just of a single operator. We would contend therefore that the risk of failure of a thoracic epidural block and therefore of inadequate analgesia, sympathetic blockade and attenuation of the stress response is much less, around 10% and not 1 : 2 as reported by Kamming and Davies. While we agree that the use of thoracic epidural anaesthesia for cardiac surgery remains subject to debate, we would suggest that the problem lies not in the high failure rate of this technique but in the lack of a multi-centre prospective randomized trial demonstrating a reduction of mortality and morbidity.