A Randomized Comparison Of Two Ultrasound Scanning Methods To Perform The Lumbar Plexus Block:PMTS-ITS Versus Shamrock

Objective:The aim of this study was to determine if Shamrock method of ultrasound guided lumber plexus block was superior to PMTS-ITS method in terms of onset time of sensory and motor blocks. In addition, clinical utility of these two methods were further evaluated by comparing other related variables, such as procedure time, frequency of needle puncture and minimum stimulation current required for contraction of the target muscle. Method:46 ASA class I or II patients scheduled to have unilateral arthroscopic knee surgery were enrolled in this study. Four patients(incomplete sciatic nerve block) and two patients(total ultrasound visibility score <10) were excluded. The remaining 40 patients were randomly divided into group P(n=20) or group S(n=20). Patients in group P were subjected to PMTS-ITS method to locate the lumbar plexus, while Shamrock method was used to locate the lumbar plexus in patients of group S. The quality of sensory blockade(including temperature and pain sensation) and motor blockade were evaluated every 5 min till 40 min post block. The procedure time for nerve block, frequency of needle puncture, depth of needle insertion, minimum stimulation current required to cause target muscle contraction and any change in mode of anesthesia were also recorded. Result:The onset time of sensory blockade was 15 min and motor blockade was 30 min in both the groups; there was no significant differences between the 2 groups(P>0.05). The procedure time for lumbar plexus block was significantly shorter in group P(437±125 secs) when compared with group S(544±180 secs)(P < 0.05). The frequency of needle puncture was significantly higher in group S(p<0.05), especially the patients who required 5 or more attempts to obtain target muscle contraction. The depth of needle insertion in group P was significantly greater than that in group S(P<0.05). There was no significant difference in isometric strength testing of quadriceps and adductor muscle and block failure rate between the two groups(P > 0.05). Conclusion:Either the PMTS-ITS method or the Shamrock method can be successfully used to perform ultrasound-guided lumbar plexus block in patients, with BMI<35, undergoing unilateral knee arthroscopic surgery. There was no significant difference in the onset time of motor and sensory blockade between the two groups. The Shamrock method required longer procedure time and greater number of needle puncture to attain the lumbar plexus block. As there are only a few clinical studies about these two methods, further clinical trials with larger number of patients are needed to determine the safety and efficacy of these two methods.