1 Zürich, Switzerland 2 New York, USA
EditorWe read with interest the study of Sandhu and Capan.1 We would like to congratulate the authors for trying to find new ways to improve the safety and success rate of infraclavicular brachial plexus block. The use of an ultrasound device in this area looks interesting, but the authors should take into account the limitations of the technique. The definition provided by a 2.5 MHz probe will not let you identify small structures such as the cords of the brachial plexus. In order to locate such anatomical structures, you need at least a 7.5 MHz probe,2 knowing even this probe will lose contrast in deep tissues (e.g. in obese patients or those with anatomical variations). Therefore, an ultrasound device is most effective for easy patients! It is true that you will always be able to identify the vein and artery. Then you may assume the location of the nerves, but this technique does not take into account any anatomical variation in the site of the nerves, which can be identified by nerve stimulation.
In the discussion, the authors mentioned our study3 and stated that their overall success rate was 86%. This biases the result, as we clearly stipulated that in the case of a proximal muscle response, the drug would not be injected, as the failure rate is too high. Only distal muscular responses would be accepted.
We would be interested to know more about patient acceptance of the procedure, as penetration of the pectoral muscle with a thin needle is sometimes painful.3 What about a large 17 or 18G Tuohy needle?
Although sophisticated methods may be helpful in some circumstances, we believe no device will ever replace good training in the field of peripheral nerve block.
M. Nadig
G. Ekatodramis
A. Borgeat
Zürich, Switzerland
EditorThere are several interesting points raised by Drs Nadig, Ekatodramis and Borgeat. We agree that the 2.5 MHz probe gives a grainier image than higher frequency (3.57.5 MHz) probes. However, we disagree with Nadig and colleagues that the cords of the brachial plexuses cannot be imaged with a 2.5 MHz probe. We were able to recognize the cords of the brachial plexus as hyper echoic structures. The higher penetration of the 2.5 MHz probe also allowed us to visualize to a depth of 28 cm with our device. This provided an advantage in obese patients. Contrary to Nadig and colleagues belief, we were able to achieve successful blocks not only in easy patients, but also in patients with no identifiable landmarks. One patient in our study weighed 500 lb and was anaesthetized successfully on two different occasions, once for pinning of four metacarpal fractures and subsequently for plating of a proximal humerus fracture, using a 2.5 MHz probe. Another patient weighing 375 lb similarly had a successful block. Obesity has never been an obstacle to performing this technique.
We used a 2.5 MHz transducer because this was the only device available to us at that time. After using this probe in more than 300 patients, and demonstrating the superiority of the technique over neurostimulation in our hands, we were able to convince the hospital administration to purchase our current 3.57 MHz ultrasound device, which gives superior images, exclusively for peripheral nerve blocks. The new device has been used in more than 1000 patients. The ultrasound technique has virtually replaced the stimulator technique in our institution over the last 2 yr.
In their letter, Nadig and colleagues state that we could only identify the cords by assumption based on their proximity to well-visualized blood vessels, and we could not image them. As we clearly emphasized in our article,1 imaging the nerves was of paramount importance in this technique. They also state that neurostimulation, but not our technique, is capable of identifying anomalies of the brachial plexus. It is difficult for us to understand their logic. For example, flexion of the wrist and fingers, that indicated a distal response in their study,3 can be produced by stimulation of the median nerve, ulnar nerve, the medial cord, or the lateral cord of the brachial plexus. Thus if there is an anatomical variation in any one of these nerves, how can neurostimulation help to identify the anomaly? With the ultrasound technique, however, imaging permits differentiation of anomalies without difficulty.
Regarding success with this technique, the cases we reported were the first of the series, with most of the failures occurring in the early part of study. Presently, our success rate is close to 100%, with residents administering the blocks. Patients with end-stage renal disease, who have had both the nerve stimulator and ultrasound technique used on them, preferred the latter. All of the patients who came for repeat hand surgery preferred to have this block.
The entry point is anaesthetized with lidocaine 12 ml injected with a 27G needle after sedation with midazolam 2 mg, and fentanyl 50 µg, which allows all our patients to tolerate the procedure very well. Administered 2 min before introduction of the block needle, these agents put the majority of our patients to sleep. They wake up in 56 min, by which time the block and the catheter are already placed. Most of the patients do not even recall having the large needle go in. Nearly all of the anesthesiology faculty in Bellevue Hospital Center, New York use the ultrasound-guided technique; the nerve stimulator technique is used rarely, mostly for teaching an alternate modality. After seeing the success rate and rapid onset of this technique, the surgeons prefer to operate under regional anaesthesia. We have increased the number of blocks we perform from fewer than 200 a year before 1999, to about 1000 per year since we started using this technique.
N. S. Sandhu
L. M. Capan
New York, USA
References
1 Sandhu NS, Capan LM. Ultrasound-guided infraclavicular brachial plexus block. Br J Anaesth 2002; 89: 2549
2 Martinoli C, Bianchi St, Dahame MH, Pugliese F, Bianchi-Zamorani MP, Valle M. Ultrasound of tendons and nerves. Eur Radiol 2002; 12: 4455[CrossRef][ISI][Medline]
3 Borgeat A, Ekatodramis G, Dumont C. An evaluation of the infraclavicular block via a modified approach of the Raj technique. Anesth Analg 2001; 93: 43641