Comparative evaluation of the visibility and block characteristics of a stimulating needle and catheter vs an echogenic needle and catheter for sciatic nerve block with a low-frequency ultrasound probe.

BACKGROUND: Clear visibility of the needle and catheter tip is desirable to perform safe and successful ultrasound-guided peripheral nerve blocks. This can be challenging with deeper blocks in obese patients. This study compared the visibility of echogenic and non-echogenic block needles and catheters in proximal sciatic blocks when performed with a low-frequency curved probe. METHODS: Seventy-eight patients undergoing total knee joint arthroplasty were randomized to receive an ultrasound-guided continuous sciatic nerve block using either a non-echogenic needle and stimulating catheter or an echogenic needle and echogenic non-stimulating catheter. Block needles in both groups were placed using both neurostimulation and ultrasound guidance, after which the catheter was positioned using either neurostimulation alone (Stimulating group) or imaging alone (Echogenic group). Three anaesthetists blinded to group allocation graded video clips recorded during the blocks for nerve, needle and catheter visibility. Performance characteristics and block parameters were also compared. RESULTS: No significant differences between the two groups were observed with regard to needle or catheter visibility (P=0.516). The Stimulating group required more needle redirections (P=0.009), had a longer procedure time [Echogenic median 274 s vs Stimulating 344 s (P=0.016)], and resulted in greater patient discomfort (P=0.012). There were no significant differences between the two groups in terms of block onset or completion time. CONCLUSIONS: Use of echogenic needles and catheters reduced procedure time and patient discomfort compared with a stimulating catheter system. There were no differences in the visibility scores of the two systems. CLINICAL TRIAL REGISTRATION: CTR Protocol ID: R-11-495, Clinical Trials.Gov ID: NCT 01492660.

Interrater reliability of qualitative ultrasound assessment of gastric content in the third trimester of pregnancy.

BACKGROUND: Pulmonary aspiration of gastric contents in pregnant women undergoing general anaesthesia is one of the most feared complications in obstetric anaesthesia. Bedside gastric ultrasonography is a feasible imaging tool to assess the gastric content. The purpose of this study was to investigate the reliability of qualitative bedside assessment of the gastric content performed by anaesthesiologists on third trimester pregnant women. METHODS: Pregnant women (≥32 weeks gestational age) were randomized to undergo ultrasound (US) assessments of their stomach in a fasting state (>8 h), or after ingestion of clear fluids only, or solid food. Three anaesthesiologists trained in gastric ultrasonography performed the assessments using a low-frequency curved-array US transducer (5-2 MHz). Primary outcome of the study was the consistency of raters in diagnosing the correct status of the gastric content, which was used to determine the interrater reliability among the three anaesthesiologists. Secondary outcomes were overall proportion of correct and incorrect diagnoses and the specific proportions of correct diagnosis across the three gastric content groups. RESULTS: We analysed 32 pregnant women. The interrater reliability displayed a kappa statistic of 0.74 (bias corrected 95% CI: 0.68-0.84). The overall proportion of correct diagnosis was 87.5% (84 of 96). The odds of correct diagnosis for 'solid contents' were 16.7 times the odds for 'empty', and 14.3 times for 'clear fluid'. CONCLUSIONS: Our results show the consistency of the qualitative US assessment of gastric contents of pregnant women in the third trimester by anaesthesiologists. A kappa of 0.74 suggests substantial agreement in terms of interrater reliability for this diagnostic measurement. CLINICAL TRIAL REGISTRATION: ClinicalTrials.gov identifier: NCT01564030.

Does circumferential spread of local anaesthetic improve the success of peripheral nerve block?

BACKGROUND: The relation between the pattern of local anaesthetic (LA) spread and the quality of peripheral nerve block is unclear. METHODS: Twenty-one volunteers were randomized to receive a median nerve block with intended circumferential or intended non-circumferential spread of LA. Different predetermined volumes and needle placement techniques were used to produce the different patterns of LA spread. Volumetric, multiplanar 3D ultrasound imaging was performed to evaluate the pattern and extent of LA spread. Sensory block was assessed at predetermined intervals. RESULTS: Complete circumferential spread of LA was achieved in only 67% of cases in the intended circumferential study group and in 33% of cases in the intended non-circumferential group. Block success was similar (90%) and independent of whether circumferential or non-circumferential spread of the LA was achieved. All block failures (n=4) occurred in the intended non-circumferential group with low volumes of LA. The onset of sensory block (independent of group allocation) was faster with circumferential spread of LA [median (IQR) onset time, 15 (8; 20) min] compared with non-circumferential spread of LA [median (IQR) onset time, 20 (15; 30) min]. More LA was used for circumferential blocks [median (IQR) volume of LA 2.8 (1.3; 3.6) vs 1.3 (1.1; 2.4) ml]. CONCLUSIONS: Even under optimal conditions, it was not possible to achieve circumferential spread of LA in all intended cases. The success of median nerve block seems to be independent of the pattern of LA spread. CLINICAL TRIAL REGISTRATION: DRKS 00003826.

Effect of concentration of local anaesthetic solution on the ED50 of bupivacaine for supraclavicular brachial plexus block.

BACKGROUND: The aim of this trial was to compare the effect of concentration of bupivacaine solution on the ED50 dose required for supraclavicular brachial plexus block. METHODS: Nineteen ASA I, II, or III patients of either sex undergoing elective upper limb surgery under ultrasound-guided supraclavicular brachial block were recruited in this double-blind, randomized trial which followed an up-and-down sequential allocation design. The patients were randomly allocated to three groups who then received 0.25%, 0.375%, or 0.5% bupivacaine. The study design and analysis followed Dixon's small sample model using a 'nominal' sample size of six in each group. The data from previous research were used to guide the dose levels and dose intervals for the three groups. RESULTS: The median effective volume [95% confidence interval (CI)] for 0.25%, 0.375%, and 0.5% bupivacaine for supraclavicular block was 26.8 (18.6-38.4), 18.1 (12.1-26.0), and 12.0 (8.4-17.3) ml, respectively. The ED50 dose (95% CI) for 0.25%, 0.375%, and 0.5% bupivacaine was 66.9 (46.6-96.0), 68.0 (47.4-97.6), and 60.1 (41.8-86.3) mg, respectively. The difference in the ED50 dose between the three concentrations was not statistically significant. CONCLUSIONS: Our study demonstrates that the ED50 dose of bupivacaine for supraclavicular block is not dependent on the concentration. Lowering the concentration or the strength of the local anaesthetic leads to an increase in the volume required for successful block.

Lidocaine use in ultrasound-guided femoral nerve block: what is the minimum effective anaesthetic concentration (MEAC90)?

BACKGROUND: This study aimed to estimate the minimum effective anaesthetic concentrations of lidocaine required to block the femoral nerve under ultrasound (US) guidance in 90% (MEAC90) of patients. METHODS: A minimum of 45 patients who had undergone knee arthroscopy were included in this observational study. All the patients received US-guided sciatic, obturator, and femoral nerve blocks. The femoral nerve block was performed using 15 ml of lidocaine. The lidocaine concentration given to a patient was determined by the response of the previous patient (a biased-coin design up-down sequential method). If a patient had a negative response, the lidocaine concentration was increased by 0.1% w/v in the next patient. If a patient had a positive response, the next patient was randomized to receive the same lidocaine concentration (with a probability of 0.89) or to receive a concentration 0.1% w/v less (with a probability of 0.11). A positive response was defined as complete sensory and motor block. The patients' responses were analysed to calculate the mean MEAC90. RESULTS: Fifty-two patients were required to complete the study; 45 had a positive response and seven had a negative response. The mean MEAC90 was estimated to be 0.93% w/v [95% confidence interval (CI), 0.8-1.03%]. Lidocaine 0.93% w/v was estimated to produce a successful block in 89% (95% CI, 78-100%) of patients. CONCLUSIONS: Perineural injection of 15 ml of lidocaine 0.93% w/v under US guidance could provide successful femoral nerve block in 90% of patients.