The impact of local anesthetic distribution on block onset in ultrasound-guided interscalene block.

BACKGROUND: Recent investigations of local anesthetic distribution in the lower extremity have revealed that completely surrounding the sciatic nerve with local anesthetic provides the advantage of more rapid and complete anesthesia in the territory served by the nerve. We hypothesized that a pattern of distribution that entirely envelops the targeted nerve roots during interscalene block would provide similar benefits of more rapid anesthesia onset. METHODS: During interscalene block guided by ultrasound with nerve stimulator confirmation, the pattern of local anesthetic distribution was recorded and later classified as complete or incomplete envelopment of the visible nerve elements in 50 patients undergoing ambulatory shoulder arthroscopic surgery. The pattern was then compared with the extent of block setup at pre-determined intervals, as well as to post-operative pain levels and block duration. RESULTS: Twenty-two patients (44%) had complete envelopment of the nerves in the plane of injection during ultrasound imaging of the interscalene block. There was no difference in the fraction of blocks that were fully set-up at 10 min with regards to complete or incomplete envelopment of the nerves by local anesthetic. All of the patients had complete setup of the block by 20 min. In addition, the post-operative pain levels and duration of block did not vary among the two groups with complete vs. incomplete local anesthetic distribution around the nerves. CONCLUSION: The presence or absence of complete envelopment of the nerve elements in the interscalene groove by local anesthetic did not determine the likelihood of complete block effect at pre-determined time intervals after the procedure.

Impact of a regional anesthesia rotation on ultrasonographic identification of anatomic structures by anesthesiology residents.

OBJECTIVE: The specific aim of this study was to determine the ability of anesthesiology residents to independently identify a series of anatomic structures in a live model using ultrasound, both before and after a 4-week regional anesthesia rotation that incorporates a standardized ultrasound training curriculum for peripheral nerve blockade. METHODS: Ten CA2 and CA3 anesthesiology residents volunteered to participate in this study. Each resident was subjected to a pre-rotation practical exam, in which he attempted to identify 15 structures at four sites of peripheral nerve blockade, in a test subject. Each resident then received specific training for ultrasound-guided nerve blocks during a 4-week regional anesthesia rotation, and then completed a post-rotation exam. The mean number of structures correctly identified on the exams was compared for significant differences utilizing a paired t-test. RESULTS: Residents were able to identify significantly more anatomic structures on the post-rotation exam as compared with the pre-rotation exam (mean 14.1 vs. 9.9, P<.001), as well as more peripheral nerve targets. The most frequently misidentified structures on the pre-rotation exam were the subclavian vein, the sciatic nerve in the popliteal fossa, and the femur. CONCLUSIONS: Ultrasound-naive anesthesiology residents, who received instruction and experience with ultrasound-guided peripheral nerve blocks on a 4-week regional anesthesia rotation, significantly improved their ability to independently identify relevant anatomic structures with ultrasonography.

A comparison of two techniques for ultrasound guided infraclavicular block.

BACKGROUND: There is some debate about the proper site and arm position and the direction of the needle for the performance of ultrasound guided infraclavicular block. METHODS: Using ultrasound, we compared the ease and success rate of a medial or a lateral approach to the brachial plexus for performing infraclavicular block in two groups of patients (n=202). The proximity of the needle to the lung in each group was also measured with and without the arm abducted from the side. RESULTS: The medial approach was quicker to perform compared with the lateral approach (9 min vs 13 min). The medial approach also had a faster onset. On average, the three cords were more readily imaged with the medial technique (92%) compared with the lateral technique (82%) and the medial technique prevented tourniquet pain more reliably (97%) vs the lateral technique (83%). In the medial technique, the plexus was also closer to the skin (3.7 cm) compared with the lateral technique (4.5 cm). The lateral approach more frequently avoided the chest wall (49%) compared with the medial technique (35%) but resulted in more frequent vascular puncture. Both approaches provided good anesthesia at the surgical site. Abducting the arm 110 degrees and externally rotating the shoulder moves the plexus away from the thorax and closer to the surface of the skin. CONCLUSION: For infraclavicular block using ultrasound guidance the medial approach is faster and easier to perform, has lower incidence of tourniquet pain and vascular puncture, and brings the plexus closer to the skin. We recommend abducting the arm 110 degrees to minimize the risk of pneumothorax. Externally rotating the shoulder also brings the plexus closer to the skin.

Anatomical variations of the phrenic nerve and its clinical implication for supraclavicular block.

This paper reports a case of simultaneous diaphragmatic and brachial plexus stimulation followed by a successful nerve block using the supraclavicular approach. An explanation for the qualitative differences in phrenic nerve block between interscalene and supraclavicular block is postulated, based on known anatomical variations.

Identification of the precipitate in alkalinized solutions of mepivacaine and bupivacaine at 37 degrees C.

Commercial and control solutions of bupivacaine (0(.)75%) and mepivacaine (1(.)5%) were alkalinized with bicarbonate until cloudy at room temperature. The solutions were heated to 37 degrees C for 2(.)5 h. The precipitates were filtered, lyophylized and analysed by fast atom bombardment mass spectrometry. Analysis showed the precipitates to be predominantly the free base of the local anaesthetic. The precipitate of the commercial bupivacaine solution also contained a small amount of the hydrochloride salt. The mepivacaine control crystals contained an unknown at molecular weight 528, which may represent a dimer of the free base and hydrochloride salt.

Models of venous admixture.

Medical students, residents, and allied health professionals often have difficulty quantitating ventilation-perfusion mismatch in ill patients. This manuscript quantitates ventilation-perfusion mismatch using the underlying physiological concepts and equations that describe mismatch. In addition, clinical problems with diagrams and worked-out solutions are supplied to help students master these equations as well as their practical limitations.

Thrombelastography as an aid to regional anesthesia: preliminary communication.

Thrombelastography (TEG), a less commonly available technique used to assess hemostatic function, has recently gained popularity. Analysis of TEG yields qualitative information about platelet function, thromboplastin generation and their interaction with the intrinsic cascade to form a stable clot. Additional information is obtained about fibrinogen and Factor XIII levels as well as the fibrinolytic system. TEG has been shown to be more sensitive and accurate than traditional coagulation tests at both predicting and treating coagulopathies. We report here three cases in which TEG was used to assess hemostatic function in patients at risk for bleeding prior to the induction of regional anesthesia. In all three cases, traditional tests were inadequate to predict the safe practice of regional anesthesia. TEG provided this information and regional anesthesia was successfully employed.