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Background: Peripheral nerve catheters (PNC) play an important role in postoperative pain treatment following major extremity surgery. There are several trials reported in the literature which investigated the efficacy and safety of ultrasound (US) and nerve stimulator (NS) guided PNC placement; however, most of these trials were only small and focused mainly on anesthesiologist-related indicators of block success (e.g. block onset time and procedure time) but not primarily on patient-related outcome data including postoperative pain during movement., Aim: This retrospective analysis compared the analgesic efficacy and safety of US versus NS guided peripheral nerve catheters (PNC) for postoperative pain therapy in a large cohort of patients., Material and Methods: Data of patients (June 2006-December 2010) treated with US (nus = 368 June 2008-December 2010) and NS (nns = 574, June 2006-May 2008) guided PNC were systematically analyzed. Apart from demographic data, postoperative pain scores [numeric rating scale (NRS): 0-10] on each treatment day, the number of patients with need for additional opioids, cumulative local anesthetic consumption and catheter-related complications were compared., Results: On the day of surgery patients treated with US-guided PNC reported lower NRS at rest (p = 0.034) and during movement (p < 0.001). Additionally, the number of patients requiring additional opioids on the day of surgery was lower in the US group (absolute difference 12.4 %, p = 0.001). Furthermore, the number of multiple puncture attempts (absolute difference 5.6 %, p < 0.001) and failed catheter placements (absolute difference 3.4 %, p = 0.06) were lower in the US group. There were no patients in both groups with long-lasting neurological impairment., Conclusion: This database analysis demonstrated that patients treated with US-guided PNC reported significantly lower postoperative pain scores and the number of patients requiring additional opioids was significantly lower on the day of surgery. The numbers of multiple punctures and failed catheter placements were reduced in the US group, which might be seen as an advantage of US-guided regional anaesthesia.

Peripheral electrical nerve stimulation is one of the standard applications in peripheral regional anesthesia in addition to the ultrasound technique. Among other findings, the visualization of needle and nerve during ultrasound-guided blockade caused a change in clinical practice of peripheral nerve stimulation in the last decade. In the present article old and new aspects of principles and clinical practice of the nerve stimulation technique are presented and summarized in a total clinical concept in order to achieve safe and successful peripheral regional anesthesia using electrical peripheral nerve stimulation.

In the present study the difference of the distances of the tip of the needle to the nerve at similar current intensities but different pulse widths (100 microseconds vs. 1000 microseconds) were determined by means of 20 blockades of the sciatic nerve using the transgluteal approach of Labat. Comparable current intensities at different pulse widths (100 microseconds vs. 1000 microseconds) were compared in the same way, using the same position of the needle. At a pulse width of 100 microseconds and a current intensity of 0.30 mA, the tip of the needle is on an average of 5.0 mm closer to the nerve than with a pulse width of 1000 microseconds and a comparable current intensity of 0.28 mA (difference statistically highly significant; p < 0.005). The comparison of the current intensities at different pulse widths at the same needle-position shows that the difference of the current intensities becomes lower when approaching the nerve. At the most distant point measured in this study, a current intensity of 0.94 mA at 100 microseconds corresponds to an aquivalent current of 0.30 mA at 1000 microseconds (difference 0.64 mA); after an approach of 5.0 mm to the sciatic nerve, this difference is significantly lower (0.30 mA at 100 microseconds, 0.11 mA at 1000 microseconds, difference 0.18 mA; p < 0.01). This means that the control of peripheral nerve stimulation is superior at a pulse width of 100 microseconds because a similar distance corresponds to a greater difference of the current. The success rate of the blockade was 95% at a current of 0.30 mA at 100 microseconds. Nerve lesions or other complications have not been seen. In conclusion, safe and successful nerve blocks in patients without polyneuropathia using the peripheral nerve stimulation seems to be obtained at a current intensity of about 0.30 mA at a pulse width of 100 microseconds.

The purpose of this study was to determine whether inferential or low-frequency stimulation can produce a stronger and less painful contraction of the quadriceps femoris muscle in 20 healthy subjects. Both currents used a pulse rate of 50 Hz. The perceived discomfort experienced with each type of electrical stimulation was quantified by the use of a visual analogue scale. An isokinetic dynamometer (Cybex) was used to assess peak torque. Paired t-test demonstrated that inferential stimulation was perceived to be significantly less uncomfortable than low-frequency stimulation and that inferential stimulation produced a significantly greater peak torque of muscle contraction than low-frequency stimulation. This study indicates that inferential stimulation can produce an electrically induced muscle contraction which is stronger and less unpleasant than low-frequency stimulation.

Pulmonary embolisms of different clinical degree of severity can be produced by means of the pulmonary embolism model according to Sedlarik by application of electrically activated blood as a thrombogenic substance. An unambiguous influence of the size and the consistency of the thrombus exists concerning the severity of the hemodynamic changes. However, the hemodynamics seems to adapt to the changed conditions of the circulation, because a tendency to normalization was observed in short-term experiments. The morphologic changes after embolisation are more typical for the severity of the clinical picture in this acute phase than the hemodynamics. A testing of the animal model in long-term experiments seem to be ingenious for that reason.