0.5% levobupivacaine versus 0.5% ropivacaine: Are they different in ultrasound-guided sciatic block?

CONTEXT AND AIMS: Little is known about onset and duration of sciatic block after 0.5% levobupivacaine (Levo) versus 0.5% ropivacaine (Ropi) for ultrasound-guided technique. We assessed these parameters in the ultrasound-guided block, to know for the practice. SETTING AND DESIGN: A comparative randomized double-blind study was conducted in the University Hospital. MATERIALS AND METHODS: Were included 35 adults of ASA I-II, scheduled for foot surgery, presenting clear imaging of their sciatic nerve at mid-thigh. A volume of 20 mL of either 0.5% Levo or 0.5% Ropi were injected around the sciatic nerve at mid-thigh using ultrasound guidance (out of the plane) followed by placement of a catheter to use, if necessary, for perioperative analgesia. A femoral single shot block was systematically performed to block the saphenous nerve. The onset times until complete foot block (primary outcome) and the sensory and motor block duration (secondary outcome) were assessed using Wilcoxon test. Values were expressed as medians (1(st)-3(rd) quartile). RESULTS: Except for two delayed sciatic blocks in each group, the onset time otherwise was 35 min (20-60) in Ropi versus 40 min (30-60) in Levo, P = 0.5. Sensory block lasted longer in Levo, 17 h (14-27) compared with 15 h (10-17) in Ropi, P = 0.04. No significant between-group difference was found with motor block durations, 15 h (12-18) in Levo and 15 h (12-16) in Ropi, P = 0.3. CONCLUSION: No difference of onset times was found in ultrasound-guided sciatic block whether using Levo or Ropi. Levo induced a longer-lasting sensory block.

Effect on neurostimulation of injectates used for perineural space expansion before placement of a stimulating catheter: normal saline versus dextrose 5% in water.

BACKGROUND AND OBJECTIVES: We clinically assessed the electrophysiologic effect of dextrose 5% in water (D5W) and of normal saline (NS) used for expansion of the perineural space before placing a stimulating catheter. We questioned if higher current was required with NS but not with D5W, as has been observed experimentally. METHODS: This was a prospective randomized double-blind study of ASA I to II patients scheduled for total knee replacement. Patients from 2 hospitals were randomly assigned to receive unidentified injectate D5W (n = 25) or NS (n = 25). The primary outcome was the minimal intensity of stimulation (MIS) recorded before and after 2 and 5 mL of study injectates were flushed through the needle before placing a stimulating catheter for continuous femoral and sciatic nerve blocks. Secondary outcomes included, among other parameters, MIS recorded during placement of stimulating catheters. RESULTS: No difference between groups was found with MIS before injection. However, MIS recorded during neurostimulation via the needle in all blocks was significantly higher after 2 and 5 mL of NS than after D5W. In femoral blocks, MIS recorded during placement of catheters was higher during insertion after NS than after D5W but was not different after reaching the final site, regardless of injectate used. In sciatic blocks, MIS was not different during insertion regardless of injectate but was higher after NS than after D5W after reaching the final site. CONCLUSIONS: The current needed to electrostimulate the femoral or sciatic nerve was higher after injection of NS than after D5W.

Various possible positions of conventional catheters around the femoral nerve revealed by neurostimulation.

BACKGROUND AND OBJECTIVES: In continuous femoral nerve blocks, the various perineural positions of the tip of a conventional catheter and their clinical implication are not completely known.We used stimulating catheters to explore the relationship of catheter tip to nerve. METHODS: American Society of Anesthesiologists physical status IYII patients scheduled for total knee arthroplasty were administered effective single-shot blocks of the obturator and sciatic nerves using ropivacaine 0.5% 10 and 20 mL, respectively. Continuous femoral blocks were performed using stimulating catheters, which were advanced blindly. Neurostimulation via catheter was performed but was masked from the investigators' sight. Before general anesthesia was induced for surgery, 5 mL of ropivacaine 0.2% was administered through the femoral nerve catheter, followed by infusion (5 mL/hr). Visual analog scale (VAS) score at rest was recorded on admission to the postanesthesia care unit. Characteristics of neurostimulation via the catheters were analyzed. RESULTS: Thirty-three patients were studied. Motor responses to stimulation via the catheters were obtained at 1 mA or less in 55% of patients and at greater than 1 mA in 45%. Various motor responses involved twitches of the pectineus (12%), sartorius (18%), or quadriceps (48%) muscles, or no muscular twitch up to 5 mA (22%). Catheter-induced motor response at 1 mA or less was associated with median values of VAS scores lower than those at greater than 1 mA (0 vs 30 mm; P = 0.008). CONCLUSION: The effectiveness of a continuous femoral block depends on neurostimulation characteristics, which likely correspond to various possible catheter tip positions. Conventional catheters provide no information on this issue. These results suggest that better VAS scores are attainable by placing catheters with neurostimulation guidance.

Epidural analgesia after scoliosis surgery: electrophysiologic and clinical assessment of the effects of bupivacaine 0.125% plus morphine versus ropivacaine 0.2% plus morphine.

STUDY OBJECTIVE: To study the electrophysiologic and clinical effects of epidural morphine combined with either bupivacaine 0.125% or ropivacaine 0.2%. DESIGN: Comparative, randomized, double-blind study. SETTINGS: Intensive care unit and hospital ward of a university hospital. PATIENTS: 18 adult ASA physical status I and II patients with degenerative or idiopathic scoliosis, undergoing posterior spinal fusion with instrumentation. INTERVENTIONS: Patients received epidural administration of 10-mL bolus of either bupivacaine or ropivacaine followed by a 6-mL/h infusion for 48 hours of unlabeled local anesthetic. In all patients, epidural morphine 5 mg was added daily. MEASUREMENTS: Assessment was focused mainly on somatosensory cortical evoked potentials, soleus H-reflex, and F waves. These electrophysiologic data were recorded before and after epidural medications. Second, respiratory rate, Paco(2), visual analog score (VAS), and side effects such as postoperative nausea and vomiting (PONV), gastrointestinal (GI) transit delay, and urinary retention were noted. MAIN RESULTS: Bupivacaine 0.125% + morphine was given to 9 patients, and ropivacaine 0.2% + morphine was given to 9 other patients. H-reflex, F waves, and somatosensory cortical evoked potential recording remained unchanged across the time of assessment. Respiratory rate and Paco(2) values were normal. VASs were indifferently low at rest, but they were lower with bupivacaine than with ropivacaine on mobilization. The frequency of PONV was indifferently high. No altered GI transit or urinary retention was noted. CONCLUSION: After epidural administration during the study conditions, bupivacaine 0.125% and ropivacaine 0.2% combined with morphine allow for neurologic examination.

Is there any need for expanding the perineural space before catheter placement in continuous femoral nerve blocks?

BACKGROUND AND OBJECTIVE: There is debate regarding the benefit of perineural space expansion before catheter placement in continuous femoral nerve block. This question is addressed in this prospective, comparative, and randomized study. METHODS: Sixty patients scheduled for total knee replacement were randomly assigned to receive continuous femoral nerve block with or without perineural space expansion using 10 mL dextrose 5% in water (D5W) flush before stimulation-guided catheter placement. Femoral block was initiated with a 5-mL bolus followed by an infusion of 5 mL/h ropivacaine 0.2% during the 2-hour surgery. The number of attempts before successful placement of the stimulating catheter and the resistance during its insertion were assessed. Patients also received obturator nerve blocks by using ropivacaine 0.75% (10 mL) and sciatic nerve blocks (20 mL). The number of boluses of ropivacaine 0.2% needed to achieve zero VAS scoring was recorded in the postanesthesia care unit during the 2-hour stay. Images of the contrast spread were also studied. RESULTS: There were 30 patients in each group. The number of successful catheter placements at the first attempt was higher with expansion than without (22 vs. 8, P = .007). The resistance felt during insertion was lower with than without expansion (P = .01). More boluses of ropivacaine were required postoperatively without expansion (P = .03). No difference between groups was found regarding the images of the contrast spread. CONCLUSION: Expansion of the perineural space with D5W is useful for catheter placement in continuous femoral nerve block.

The value of adding sciatic block to continuous femoral block for analgesia after total knee replacement.

BACKGROUND AND OBJECTIVES: The benefit of adding a sciatic nerve block to the femoral block to improve analgesia after total knee replacement is controversial. The aim of this study is to address this controversy in a prospective, comparative, and randomized study. METHODS: Patients were allocated randomly to receive a continuous femoral nerve block or continuous blocks of both the femoral and sciatic nerves. Stimulating catheters were used in all cases. A loading dose of 15 mL ropivacaine 0.75% was injected into each catheter, followed by administration of ropivacaine 0.2% (2-5 mL/h infusion via the femoral catheter; bolus 10 mL repeated every 12 hours in the sciatic catheter). The primary outcome was visual analog scale (VAS) scores (0 = no pain, 100 mm = worst pain) in postanesthesia care unit and in the 48-hour period after surgery. The secondary outcomes were amplitude of knee flexion, morphine consumption, and occurrence of postoperative nausea and vomiting (PONV). RESULTS: The VAS scores at rest were significantly higher when there was only continuous femoral nerve block than when there was both continuous femoral and sciatic nerve blocks. This difference progressively decreased and disappeared at 36 hours after surgery. The combined femoral and sciatic blocks decreased the morphine consumption by 81% and significantly decreased the occurrence of PONV. CONCLUSION: During the 36 hours immediately after total knee replacement, the combination of continuous femoral and sciatic nerve blocks improves analgesia while decreasing morphine consumption and PONV.

Computed tomography scanning of the sciatic nerve posterior to the femur: Practical implications for the lateral midfemoral block.

BACKGROUND AND OBJECTIVES: Using computed tomography (CT) scans of the thighs, this study addresses sciatic nerve anatomy at the injection site for the lateral midfemoral sciatic nerve block. It addresses the recommendation of neutral leg rotation to facilitate block placement. METHOD: This prospective and descriptive study involves 21 patients scheduled for CT scan imaging of the lower limbs. Transverse CT scans were analyzed at 20, 25, and 30 cm distal to the upper border of the greater trochanter (GT) of the femur with the knee externally rotated by 30 degrees. The angle alpha formed by the broad axis of the sciatic nerve and the coronal plane, skin-to-nerve distance, great vessel-to-nerve distance, division of the sciatic nerve, and widths of the perineural space were assessed. Values are expressed as mean +/- SD. RESULTS: At 20, 25, and 30 cm distal to the GT, the alpha angle was 50 degrees +/- 14 degrees, 55 degrees +/- 13 degrees, and 56 degrees +/- 26 degrees, respectively. This angle increased to nearly 90 degrees when the knee was rotated to a neutral position. The skin-to-nerve distance was 5.9 +/- 1.1 cm, 5.4 +/- 0.9 cm, and 5.7 +/- 1.1 cm. The section width of the perineural space was 1.8 +/- 0.9 cm(2), 3.9 +/- 2 cm(2), and 5.6 +/- 2.4 cm(2). The sciatic nerve was divided in 27% of subjects at 20 cm and in 90% at 30 cm distal. CONCLUSION: The characteristics of sciatic nerve anatomy described in this study support observations and clinical recommendations regarding lateral midfemoral sciatic nerve block.

Continuous peripheral nerve blocks with stimulating catheters.

BACKGROUND AND OBJECTIVES: This study evaluated the efficacy of stimulating catheters used for continuous peripheral nerve blocks as a means of immediate verification and confirmation of correct catheter position. METHODS: This observational study presents our experience with 130 stimulating catheters used in 40 intersternocleidomastoid, 24 axillary, 47 femoral, and 19 lateral midfemoral sciatic nerve blocks. Placement characteristics (amperage, depth of introducer needle or catheter insertion, elicited motor responses), subsequent postoperative analgesia, and catheter position evaluated with the radiopaque dye analysis were all studied. RESULTS: Except in femoral blocks, characteristics of motor responses elicited (1 Hz, 0,1 ms) by the introducer assembly and catheter differed. The amperage required to elicit motor responses typically was higher with the catheter than with the introducer needle (1.6 [0.2 to 4 mA] v 0.5 [0.4 to 1 mA] P <.0001). The ability to elicit a motor response with the stimulating catheter correlated with successful clinical anesthesia in 124 cases. Opacified radiography showed no aberrant position in these cases. Three catheters for upper limb block failed to stimulate, provided poor anesthesia, and had radiologic evidence of aberrant position. Even though they failed to stimulate, 3 catheters for sciatic block functioned well, and the opacified radiography showed correct position. CONCLUSION: The ability to electrostimulate nerves using an in situ catheter increases success rate in catheter placement for continuous peripheral nerve blocks. Further controlled investigations are necessary to compare this technique with more conventional methods in terms of cost and utility for various peripheral nerve blocks.

Combined spinal cord monitoring using neurogenic mixed evoked potentials and collision techniques.

STUDY DESIGN: Neurogenic mixed evoked potentials are used routinely to monitor the spinal cord during spine surgery. This study investigates the differential sensory-motor contribution by using collision techniques. OBJECTIVE: To demonstrate that neurogenic mixed evoked potentials do contain a motor component. SUMMARY OF BACKGROUND DATA: Spinal cord monitoring is now routinely used during spine deformity surgery. Neurogenic mixed evoked potentials (i.e., potentials recorded from lower limb nerves after spinal cord stimulation) represent a reliable and sensitive technique. However, their specificity (sensory and motor spinal pathways) remains debated. METHODS: Neurogenic mixed evoked potentials and collisions were performed in 24 consecutive patients during scoliosis surgery. Neurogenic mixed evoked potentials were elicited by a high thoracic spinal test stimulation and recorded from the tibial nerve at the ankle. A peripheral conditioning stimulation was delivered at the popliteal fossa 15 ms before spinal stimulation, inducing an ascending volley. The antidromic ascending motor component stops at the anterior horn cell level, whereas the orthodromic sensory component reaches the dorsal columns. The 15-ms interstimulus interval between peripheral conditioning and spinal test stimulation makes the collision with descending volleys occur in the spinal cord. The descending sensory volley is blocked, whereas the descending motor volley is unaffected. RESULTS: Reproducible evoked potentials were recorded from the tibial nerve in all the patients studied when the conditioning stimulation was performed. These conditioned neurogenic mixed evoked potentials consist of a small and polyphasic wave whose amplitude represents approximately 26% that of the wave of unconditioned neurogenic mixed evoked potentials. It is likely that they correspond to motor spinal pathway activation. CONCLUSION: Both standard and conditioned neurogenic mixed evoked potentials are proposed to provide combined sensory and motor spinal pathway monitoring.

Paradoxical air embolism from patent foramen ovale in scoliosis surgery.

STUDY DESIGN: A case was reported in which paradoxical air embolism arose from the patent foramen ovale in scoliosis surgery. OBJECTIVES: To present a case of suspected paradoxical air embolism after scoliosis surgery. SUMMARY OF BACKGROUND DATA: Embolic accident during scoliosis surgery may be caused by air, thrombus, or fat. There is growing attention on patent foramen ovale involved in paradoxical embolism. The devastating consequences are caused by multiple artery occlusions. METHODS: Details of a recent documented neurologic complication (paraplegia, weakness of right arm, and blurry vision) after scoliosis surgery have been analyzed in medical publications. RESULTS: The surgical procedure was not imputed. The causative role of epidural catheter for analgesia was considered, but it is likely that a paradoxical embolism occurred in this case, based on the multifocal (cerebral and spinal) neurologic dysfunction, the evidence of cerebral ischemia (on computed tomography), and the presence of a patent foramen ovale (on postoperative transesophageal echocardiography). Although no intraoperative embolism detection was available, air embolism was highly suspected because there was no absolute argument to exclude cruor or fatty embolism. CONCLUSIONS: It is critical to detect a patent foramen ovale before surgery and cerebral embolization intraoperatively. This might permit ascertainment of the etiologic diagnosis in case of a complication in surgery for scoliosis.