The Influence of Arm Positioning on Ultrasonic Visualization of the Subclavian Vein: An Anatomical Ultrasound Study in Healthy Volunteers.

We hypothesized that placing the arm in 90° abduction, through 90° flexion and 90° external rotation, could improve ultrasound visualization of the subclavian vein. In 49 healthy volunteers, a single operator performed a view of the subclavian vein in neutral position and abduction position. A second blinded operator measured the cross-sectional area of the subclavian vein. Abduction position increased the cross-sectional area of the subclavian vein from 124 ± 46 (mean ± SD) to 162 ± 58 mm (P = 0.001). An increase of the cross-sectional area of ≥50% was observed in 41% volunteers (95% confidence interval, 27%-56%, n = 20); this technique offers an alternative approach (maybe safer) for ultrasound-guided catheterization of the subclavian vein.

Comparison of the visualisation of the subclavian and axillary veins: An ultrasound study in healthy volunteers.

OBJECTIVE: To compare the area of the lumen of the axillary and subclavian veins using ultrasound (US) in 50 healthy volunteers. METHODS: Using an ultrasound device, depth, area, short axis vein length and long axis vein, vein-artery and vein-pleura distances were measured for axillary and subclavian approaches. RESULTS: The mean cross-sectional area of the axillary vein was greater than the mean cross-sectional area of the subclavian vein (327±89 mm2 versus 124±46 mm2, P<0.001). Both the mean transverse (10±2mm versus 9±2mm) and longitudinal axes (39±8mm versus 17±7mm) of the axillary vein were greater than those of subclavian vein (P<0.01, P<0.001, respectively). The depths of the axillary and subclavian veins were similar (21±6mm versus 20±6mm, P=0.43). The axillary and subclavian arteries were visualised in 3 and 45 volunteers, respectively (P<0.001). The pleura was seen in 25 and 37 volunteers with the axillary and subclavian approaches, respectively (P=0.01). The distance between the pleura and the subclavian vein was smaller (6±2mm versus 8±3mm, P<0.04). CONCLUSION: The present US study shows that visualisation of the axillary vein under US is greater than that for the subclavian vein, mainly due to a better alignment with the long axis of the axillary vein leading to a greater cross-sectional area of the axillary vein. TRIAL REGISTER NUMBER: NCT01647815.

Comparison of the parasacral approach and the posterior approach, with single- and double-injection techniques, to block the sciatic nerve.

BACKGROUND: The purpose of this study was to compare parasacral and Winnie's single- or double-injection approaches for sciatic nerve block. METHODS: One hundred fifty adults scheduled to undergo lower limb surgery were randomized to receive on the sciatic nerve 20 ml ropivacaine, 0.75%: single bolus for parasacral and Winnie's single injection. For Winnie's double injection, the peroneal and tibial nerves received separately 10 ml plus 10 ml. Blocks were performed with the use of nerve stimulator (intensity < 0.5 mA, 1 Hz). For the parasacral method, a line was drawn between the posterior superior iliac spine and the ischial tuberosity; needle entry was at 6 cm inferior to the posterior superior iliac spine. RESULTS: The groups were similar. Time to perform the block was 2 (1-5) min for the parasacral method, with no difference from Winnie's single injection (3 [1-10] min), but was shorter with double injection (5.5 [2-15] min) (P = 0.0001). Onset of sensory block was similar in the parasacral (25 [7.5-50] min) and Winnie single-injection groups (25 [5-50] min) but significantly longer in the double-injection group (15 [5-50] min). Success rates for complete block were similar in the parasacral (66%) and Winnie's double-injection groups (68%) after 30 min but higher in the Winnie's single-injection group for tibial sensory and motor block (48%) (P < 0.017). CONCLUSION: Time to perform a parasacral block was short, and the parasacral approach had a high success rate and a short onset time. Therefore, this block might be a useful alternative to Winnie's modification for sciatic nerve block.

Comparison of the effects of racemic bupivacaine, levobupivacaine, and ropivacaine on ventricular conduction, refractoriness, and wavelength: an epicardial mapping study.

BACKGROUND: The study was designed to compare the effects of equimolar concentrations of racemic bupivacaine, levobupivacaine, and ropivacaine on ventricular conduction, anisotropy, duration and homogeneity of refractoriness, and wavelengths, and to provide a potency ratio for effects on conduction velocity. METHODS: Isolated frozen rabbit hearts (which leave a thin layer of surviving epicardial muscle) were treated with 0.1, 1, and 10 mum racemic bupivacaine, levobupivacaine, or ropivacaine. Left ventricular longitudinal and transverse conduction velocities, anisotropic ratio, minimum pacing cycle length, use dependency, duration and dispersion of ventricular effective refractory period, and wavelengths were studied. A high-resolution mapping system was used for data acquisition. In addition to two-way analysis of variance for repeated measures, data for conduction velocities were fitted simultaneously using a nonlinear mixed-effect modeling program to allow intergroup comparison. RESULTS: Each agent induced a concentration- and use-dependent slowing of conduction velocities, with no change of the anisotropic ratio. The use-dependent effect of levobupivacaine is similar to that of racemic bupivacaine concerning longitudinal conduction velocity. Fitting of conduction velocities provided a racemic bupivacaine to levobupivacaine and to ropivacaine ratio of 1:1.38 for concentration effect at 1,000-ms pacing cycle length, and 1:0.74 for use-dependent effect at 600-ms pacing cycle length. Racemic bupivacaine and levobupivacaine prolonged the ventricular effective refractory period, whereas ropivacaine did not. No dispersion in ventricular effective refractory period values occurred. All three agents induced significant decreases in wavelengths. This effect was not different among groups. CONCLUSIONS: Differences among racemic bupivacaine, levobupivacaine, and ropivacaine at equimolar concentrations are mainly caused by the use-dependent effects on conduction velocities and the concentration-dependent effects on ventricular effective refractory period. Therefore, one must take into account the corresponding pacing rates when comparing the potency ratios of local anesthetics.