Real-Time Injection Pressure Sensing and Minimal Intensity Stimulation Combination During Ultrasound-Guided Peripheral Nerve Blocks: An Exploratory Observational Trial.

BACKGROUND: Nerve damage can occur after peripheral nerve block (PNB). Ultrasound guidance does not eliminate the risk of intraneural injection or nerve injury. Combining nerve stimulation and injection pressure (IP) monitoring with ultrasound guidance has been suggested to optimize needle tip location in PNB. In this prospective observational study, we hypothesized that measured pairs of IP and minimum intensity of stimulation (MIS) might differentiate successive needle tip locations established by high-resolution ultrasound during PNB. METHODS: For this exploratory study, 240 observations for 40 ultrasound-guided PNBs were studied in 28 patients scheduled for orthopedic surgery. During the progression of the needle to the nerve observed by ultrasonography, the IP was measured continuously using a computerized pressure-sensing device with a low flow rate of solution. Stimulation thresholds and electrical impedance were obtained by an impedance analyzer coupled to the nerve stimulator at 6 successive needle positions. The median (quartile) or mean (95% confidence interval [CI]) was reported. A mixed model analysis was used, and the sample was also explored using a classification and regression tree (CART) algorithm. RESULTS: Specific combinations of IP and MIS were measured for subcutaneous, epimysium contact, intramuscular, nerve contact (231 mm Hg [203-259 mm Hg] and 1.70 mA [1.38-2.02 mA]), intraneural location (188 mm Hg [152-224 mm Hg] and 0.58 mA [0.46-0.70 mA]), and subparaneural location (47 mm Hg [41-53 mm Hg] and 1.35 mA [1.09-1.61 mA]). The CART algorithm shows that the optimal subparaneural needle tip position might be defined by the lowest pressure (<81.3 mm Hg) and MIS (<1.5 mA) cutoffs. CONCLUSIONS: Our exploratory study evaluated concepts to generate hypotheses. The combinations of IP and MIS might help the physician during a PNB procedure. A low IP and low MIS might confirm a subparaneural location, and a high IP and a low MIS might be an alert for the intraneural location of the needle tip.

Population Pharmacokinetics of Levobupivacaine During Transversus Abdominis Plane Block in Children.

BACKGROUND: Levobupivacaine is commonly used during transversus abdominis plane (TAP) block in pediatric patients. However, the dosing regimen is still empirical, and the pharmacokinetic properties of levobupivacaine are not considered. Here, the pharmacokinetics of levobupivacaine during an ultrasound-guided TAP block were evaluated to optimize dosing regimen, regarding the between-subject variability (BSV) and the volume of levobupivacaine injected. METHOD: The clinical trial (prospective, randomized, double-blind study protocol) was conducted in 40 children aged 1-5 years, who were scheduled for inguinal surgery. Each patient received 0.4 mg/kg of levobupivacaine with a volume of local anesthesia solution adjusted to 0.2 mL/kg of 0.2% or 0.4 mL/kg of 0.1% levobupivacaine. Blood samples were collected at 5, 15, 20, 25, 30, 45, 60, and 75 minutes after the block injection. The population pharmacokinetic analysis was performed using the NONMEM software. RESULTS: From the pharmacokinetic parameters obtained, median Cmax, tmax,, and area under the concentration versus time curve were 0.315 mg/L, 17 minutes, and 41 mg/L·min, respectively. BSV of clearance was explained by weight. At the dose regimen of 0.4 mg/kg, none of the infants showed signs of toxicity, but in 13 patients, TAP block failed. After analysis, BSV for absorption rate constant, distribution volume, and clearance were 81%, 47%, and 41%, respectively. Residual unexplained variability was estimated to be 14%. CONCLUSIONS: For improved efficiency in the pediatric population, the dose of levobupivacaine should be greater than 0.4 mg/kg. Children's weight should be considered to anticipate any risk of toxicity.

Transversus Abdominal Plane Block in Children: Efficacy and Safety: A Randomized Clinical Study and Pharmacokinetic Profile.

BACKGROUND: The transversus abdominis plane (TAP) block has become a common regional anesthesia technique for pain management in a wide variety of abdominal procedures. Evidence to support any particular local anesthetic regimen as well as pharmacokinetic and systemic toxicity risks of TAP block remain insufficiently studied in children. The aim of this study was to compare the analgesic effects and investigate pharmacokinetic profile of levobupivacaine after ultrasound-guided TAP block using a low volume/high concentration (LVHC) or a high volume/low concentration (HVLC) solution in children. METHODS: This prospective randomized study included children scheduled for day-case inguinal surgery. Children were randomized to receive TAP block using 0.4 mg·kg levobupivacaine as either HVLC (0.2 mL·kg of 0.2% levobupivacaine) or LVHC (0.1 mL·kg of 0.4% levobupivacaine). The primary outcome was the number of children who required opioid rescue analgesia postoperatively. Pharmacokinetic profile study of levobupivacaine was also performed. RESULTS: Seventy patients were equally randomized, and 65 were included in the final analysis. Seventy-one percent of patients did not require any postoperative opioid analgesia. The number of patients who received rescue analgesia was 12 (35%) in the LVHC group and 7 (23%) in the HVLC group (relative risk, 0.64; 95% confidence interval [CI], 0.29-1.42; P = .26). Mean pain scores (FLACC [faces, legs, activity, cry, and consolability]) at postanesthesia care unit discharge did not differ between LVHC and HVLC groups, respectively, 0.39 ± 0.86 and 1 ± 1.71 with mean group difference -0.60 (95% CI, -1.27 to 0.06; P = .08). The pharmacokinetic profile of levobupivacaine was comparable in the 2 groups: the mean total and free levobupivacaine peak concentrations were 379 ± 248 and 3.95 ± 3.16 ng·mL, respectively, occurring 22.5 ± 11 minutes after injection. The highest total and free levobupivacaine concentrations collected, respectively, 1360 and 15.1 ng·mL, remained far below theoretical toxic thresholds. CONCLUSIONS: In children, quality of postoperative pain control provided by TAP block using levobupivacaine 0.4 mg·kg administered as either HVLC or LVHC did not differ and was associated with a very low risk of local anesthetic systemic toxicity.

Comparison of a GPS needle-tracking system, multiplanar imaging and 2D imaging for real-time ultrasound-guided epidural anaesthesia: A randomized, comparative, observer-blinded study on phantoms.

BACKGROUND: The real-time ultrasound-guided paramedian sagittal oblique approach for neuraxial blockade is technically demanding. Innovative technologies have been developed to improve nerve identification and the accuracy of needle placement. The aim of this study was to evaluate three types of ultrasound scans during ultrasound-guided epidural lumbar punctures in a spine phantom. METHODS: Eleven sets of 20 ultrasound-guided epidural punctures were performed with 2D, GPS, and multiplanar ultrasound machines (660 punctures) on a spine phantom using an in-plane approach. For all punctures, execution time, number of attempts, bone contacts, and needle redirections were noted by an independent physician. Operator comfort and visibility of the needle (tip and shaft) were measured using a numerical scale. RESULTS: The use of GPS significantly decreased the number of punctures, needle repositionings, and bone contacts. Comfort of the physician was also significantly improved with the GPS system compared with the 2D and multiplanar systems. With the multiplanar system, the procedure was not facilitated and execution time was longer compared with 2D imaging after Bonferroni correction but interaction between the type of ultrasound system and mean execution time was not significant in a linear mixed model. There were no significant differences regarding needle tip and shaft visibility between the systems. CONCLUSIONS: Multiplanar and GPS needle-tracking systems do not reduce execution time compared with 2D imaging using a real-time ultrasound-guided paramedian sagittal oblique approach in spine phantoms. The GPS needle-tracking system can improve performance in terms of operator comfort, the number of attempts, needle redirections and bone contacts.

Ultrasound-guided tranversus abdominis plane block for herniorrhaphy in children: what is the optimal dose of levobupivacaine?

BACKGROUND: Regional anaesthesic techniques are commonly used for the management of pain following lower abdominal surgery in children. The transversus abdominis plane (TAP) block has shown promise for perioperative analgesia, but data on the optimal dose regimen are limited. OBJECTIVE: To evaluate the optimal dose of levobupivacaine for successful ultrasound-guided TAP block in children. DESIGN: A dose finding prospective study using Dixon's up-and-down sequential method. SETTING: University Hospital Paediatric Anaesthesia Unit. PATIENTS: Twenty-seven consecutive children aged 1 to 5 years scheduled for day-case elective herniorrhaphy. INTERVENTION: After standardised induction of general anaesthesia, ultrasound-guided TAP block was performed with a fixed volume of 0.2  ml  kg(-1) of levobupivacaine solution. The dose of levobupivacaine was determined by Dixon's up-and-down method starting from 0.5  mg  kg(-1)with an interval of 0.1 mg   kg(-1). Block failure was defined as a 20% increase in heart rate or mean arterial pressure from baseline. Rescue analgesia consisted of intravenous remifentanil infusion during surgery and intravenous nalbuphine in the postanaesthetic care unit (PACU). Patients were assessed using the FLACC (face, legs, activity, cry and consolability) pain scale, the rescue analgesic consumption in the PACU and day-case unit and the postoperative pain measure for parents score at home. MAIN OUTCOME MEASURES: The mean effective dose of levobupivacaine resulting in an effective TAP block in 50% of cases (ED50) obtained by using Dixon's up-and-down sequential method. The ED50 and ED95 were further estimated by bootstrapping. RESULTS: The ED50 according to the up-and-down staircase method was 0.22  mg   kg(-1) [95% confidence interval (CI) 0.19 to 0.25]. Bootstrap replicates of the original dataset resulted in ED50 and ED95 estimates of 0.16  mg    kg(-1) (95% CI 0.11 to 0.24) and 0.43 mg  kg(-1)(95% CI 0.30 to 0.57), respectively. CONCLUSION: As part of a multimodal analgesia strategy, ultrasound-guided TAP block with 0.2  ml  kg(-1)of 0.2% levobupivacaine provides successful peroperative analgesia in 95% of children who underwent herniorrhaphy.