Peter Marhofer

Ultrasonographic Guidance Improves Sensory Block and Onset Time of Three-in-One Blocks

The use of ultrasound reduces the onset time, improves the quality of sensory block, and minimizes the risks associated with the supraclavicular approach for brachial plexus and stellate ganglion blockade.The present study was designed to evaluate whether ultrasound also facilitates the approach for 3-in-1 blocks. Forty patients (ASA physical status II or III) undergoing hip surgery after trauma were randomly assigned to two groups. In the ultrasound (US) group, 20 mL bupivacaine 0.5% was administered under US guidance, whereas in the control group, the same amount and concentration of local anesthetic was administered with the assistance of a nerve stimulator (NS). After US- or NS-based identification of the femoral nerve, the local anesthetic solution was administered, and the distribution of the local anesthetic solution was visualized and recorded on videotape in the US group. The quality and the onset of the sensory block was assessed by using the pinprick test in the central sensory region of each of the three nerves and compared with the same stimulation on the contralateral leg every 10 min for 60 min. The rating was performed using a scale from 100% (uncompromised sensibility) to 0% (no sensory sensation). Heart rate, noninvasive blood pressure, and oxygen saturation were measured at short intervals for 60 min. The onset of sensory blockade was significantly shorter in Group US compared with Group NS (US 16 +/- 14 min, NS 27 +/- 16 min, P < 0.05). The quality of the sensory block after injection of the local anesthetic was also significantly better in Group US compared with Group NS (US 15% +/- 10% of initial value, NS 27% +/- 14% of initial value, P < 0.05). A good analgesic effect was achieved in 95% of the patients in the US group and in 85% of the patients in the NS group. In the US group, visualization of the cannula tip, the femoral nerve, the major vessels, and the local anesthetic spread was possible in 85% of patients. Incidental arterial puncture (n = 3) was observed only in the NS group. We conclude that an US-guided approach for 3-in-1 block reduces the onset time, improves the quality of the sensory block and minimizes the risks associated with this regional anesthetic technique. Implications: The onset time and the quality of a regional anesthetic technique for the lower extremity is improved by ultrasonographic nerve identification compared with older techniques. (Anesth Analg 1997;85:854-7)

Ultrasonographic Guidance Improves the Success Rate of Interscalene Brachial Plexus Blockade

Background and Objectives: The use of ultrasonography in regional anesthetic blocks has rapidly evolved over the past few years. It has been speculated that ultrasound guidance might increase success rates and reduce complications. The aim of our study is to compare the success rate and quality of interscalene brachial plexus blocks performed either with direct ultrasound visualization or with the aid of nerve stimulation to guide needle placement. Methods: A total of 160 patients (American Society of Anesthesiologists physical status classification I‐III) scheduled for trauma‐related upper arm surgery were included in this randomized study and grouped according to the guidance method used to deliver 20 mL of ropivacaine 0.75% for interscalene brachial plexus blockade. In the ultrasound group (n = 80), the brachial plexus was visualized with a linear 5 to 10 MHz probe and the spread of the local anesthetic was assessed. In the nerve stimulation group (n = 80), the roots of the brachial plexus were located using a nerve stimulator (0.5 mA, 2 Hz, and 0.1 millisecond bandwidth). The postblock neurologic assessment was performed by a blinded investigator. Results: Sensory and motor blockade parameters were recorded at different points of time. Surgical anesthesia was achieved in 99% of patients in the ultrasound vs 91% of patients in the nerve stimulation group (P < .01). Sensory, motor, and extent of blockade was significantly better in the ultrasound group when compared with the nerve stimulation group. Conclusions: The use of ultrasound to guide needle placement and monitor the spread of local anesthetic improves the success rate of interscalene brachial plexus block.

Magnesium sulfate reduces intra- and postoperative analgesic requirements

In a randomized, double-blind study with two parallel groups, we assessed the analgesic effect of perioperative magnesium sulfate administration in 46 ASA physical status I or II patients undergoing arthroscopic knee surgery with total IV anesthesia. The patients received either magnesium sulfate 50 mg/kg preoperatively and 8 mg [center dot] kg-1 [center dot] h-1 intraoperatively or the same volume of isotonic sodium chloride solution IV. Anesthesia was performed with propofol (2 mg/kg for induction, 6-8 mg [center dot] kg- 1 [center dot] h- 1 for maintenance), fentanyl (3 [micro sign]g/kg for induction), and vecuronium (0.1 mg/kg for intubation). Intraoperative pain was defined as an increase of mean arterial blood pressure and heart rate of more than 20% from baseline values after the induction of anesthesia and was treated with bolus fentanyl (1-2 [micro sign]g/kg). Postoperative analgesia was achieved with fentanyl (0.5 [micro sign]g/kg) and evaluated using the pain visual analog scale for 4 h. During the intraoperative and postoperative periods, patients in the magnesium group required significantly less fentanyl than those in the control group (control group 0.089 +/- 0.02 [micro sign]g [center dot] kg-1 [center dot] min-1 versus magnesium group 0.058 +/- 0.01 [micro sign]g [center dot] kg-1 [center dot] min- 1; P < 0.05 and control group 0.021 +/- 0.013 [micro sign]g [center dot] kg-1 [center dot] min-1 and magnesium group 0.0031 +/- 0.0018 [micro sign]g [center dot] kg-1 [center dot] min-1; P < 0.01 for intraoperative and postoperative periods, respectively). We conclude that, in a clinical setting with almost identical levels of surgical stimulation, IV magnesium sulfate administration reduces intraoperative and postoperative analgesic requirements compared with isotonic sodium chloride solution administration. Implications: The perioperative administration of IV magnesium sulfate reduces intra- and postoperative analgesic requirements in patients with almost identical levels of surgical stimulus. Our results demonstrate that magnesium can be an adjuvant to perioperative analgesic management. (Anesth Analg 1998;87:206-10)

Ultrasonographic-Guided Ilioinguinal/Iliohypogastric Nerve Block in Pediatric Anesthesia: What is the Optimal Volume?

Recently, our study group demonstrated the usefulness of ultrasonographic guidance in ilioinguinal/iliohypogastric nerve blocks in children. As a consequence, we designed a follow-up study to evaluate the optimal volume of local anesthetic for this regional anesthetic technique. Using a modified step-up-step-down approach, with 10 children in each study group, a starting dose of 0.2 mL/kg of 0.25% levobupivacaine was administered to perform an ilioinguinal/iliohypogastric nerve block under ultrasonographic guidance. After each group of 10 patients, the results were analyzed, and if all blocks were successful, the volume of local anesthetic was decreased by 50%, and a further 10 patients were enrolled into the study. Failure to achieve a 100% success rate within a group subjected patients to an automatic increase of half the previous volume reduction to be used in the subsequent group. Using 0.2 and 0.1 mL/kg of 0.25% levobupivacaine, the success rate was 100%. With a volume of 0.05 mL/kg of 0.25% levobupivacaine, 4 of 10 children received additional analgesia because of an inadequate block. Therefore, according to the protocol, the amount was increased to 0.075 mL/kg of 0.25% levobupivacaine, where the success rate was again 100%. We conclude that ultrasonographic guidance for ilioinguinal/iliohypogastric nerve blocks in children allowed a reduction of the volume of local anesthetic to 0.075 mL/kg.

Ilioinguinal/iliohypogastric blocks in children: where do we administer the local anesthetic without direct visualization?

BACKGROUND:Ultrasonographic observation of peripheral nerve blocks enables direct visualization of the spread of local anesthetic around the targeted nerves. Similarly, ultrasonography may be used to determine the site of local anesthetic placement when landmark-based techniques are used. We performed a study to determine the actual location of local anesthetic when ilioinguinal/iliohypogastric nerve blocks are performed using landmark-based techniques in children in an attempt to explain a failed block. METHODS:After induction of general anesthesia (1 minimum alveolar anesthetic concentration halothane and laryngeal mask airway), 62 children scheduled for inguinal surgery received an ilioinguinal/iliohypogastric nerve block based on standard anatomical landmarks. Ultrasonography was then used to determine the actual location of local anesthetic placement. The anesthesiologist performing the block was blinded to the ultrasonographic investigation. Successful blocks were recorded either when the local anesthetic surrounded the nerves or were based on clinical signs after skin incision. RESULTS:In 14% of the blocks, the local anesthetic was administered correctly around the nerves resulting in successful blocks. In the remaining 86%, the local anesthetic was administered in adjacent anatomical structures (iliac muscle 18%, transverse abdominal muscle 26%, internal oblique abdominal muscle 29%, external oblique abdominal muscle 9%, subcutaneous 2%, and peritoneum 2%), and 45% of these blocks failed. CONCLUSION:Accurate placement of local anesthetic around the ilioinguinal/iliohypogastric nerves in children is seldom possible when landmark-based techniques are used. In the majority of patients, the local anesthetic was inaccurately placed in adjacent anatomical structures with unpredictable block results.

Levobupivacaine versus racemic bupivacaine for spinal anesthesia.

Levobupivacaine is the pure S(−)-enantiomer of racemic bupivacaine but is less toxic to the heart and central nervous system. Although it has recently been introduced for routine obstetric and nonobstetric epidural anesthesia, comparative clinical studies on its intrathecal administration are not available. We therefore performed this prospective randomized double-blinded study to evaluate the anesthetic potencies and hemodynamics of intrathecal levobupivacaine compared with racemic bupivacaine. Eighty patients undergoing elective hip replacement received either 3.5 mL levobupivacaine 0.5% isobaric or 3.5 mL bupivacaine 0.5% isobaric. Sensory blockade was verified with the pinprick test; motor blockade was documented by using a modified Bromage score. Hemodynamic variables (e.g., blood pressure, heart rate, pulse oximetry) were also recorded. Intergroup differences between levobupivacaine and bupivacaine were insignificant both with regard to the onset time and the duration of sensory and motor blockade (11 ± 6 versus 13 ± 8 min; 10 ± 7 versus 9 ± 7 min; 228 ± 77 versus 237 ± 88 min; 280 ± 84 versus 284 ± 80 min). Both groups showed slight reductions in heart rate and mean arterial pressure, but there was no intergroup difference in hemodynamics. We conclude that intrathecal levobupivacaine is equal in efficacy to, but less toxic than, racemic bupivacaine.

Magnetic resonance imaging of the distribution of local anesthetic during the three-in-one block.

The three-in-one technique of simultaneously blocking the femoral, the lateral femoral cutaneous (LFC), and the obturator nerves by a single injection of a local anesthetic was first described in 1973, and it was suggested that the underlying mechanism was one of cephalad spread resulting in a blockade of the lumbar plexus. Today, the technique is widely used in surgery and pain management of the lower limb. Many investigators have, however, reported suboptimal analgesia levels, particularly in the obturator nerve. The purpose of this prospective study was to trace the distribution of a local anesthetic during a three-in-one block by means of magnetic resonance imaging (MRI). Seven patients scheduled for surgery of the lower limb were analyzed with the aid of a primary MRI and then received three-in-one blocks using 30 mL of bupivacaine 0.5% under the guidance of a nerve stimulator. A secondary MRI was performed to determine the distribution pattern of the local anesthetic. It emerged that the local anesthetic blocks the femoral nerve directly, the LFC nerve through lateral spread, and the anterior branch of the obturator nerve by slightly spreading in a medial direction. No involvement of the proximal and posterior portions of the obturator nerve was observed, nor was there any cephalad spread that could have resulted in a lumbar plexus blockade. We therefore conclude that the basis of the three-in-one block is confined to lateral, medial, and caudal spread of the local anesthetic, which effectively blocks the femoral and LFC nerves, as well as the distal anterior branch of the obturator nerve. Implications We demonstrate by using magnetic resonance imaging that the mechanism of a three-in-one block is one of lateral, caudal, and slight medial spread of a local anesthetic with subsequent blockade of the femoral, the lateral femoral cutaneous, and the anterior branch of the obturator nerves. It does not involve cephalad spread of the local anesthetic with blockade of the lumbar plexus.

Minimal local anesthetic volume for peripheral nerve block: a new ultrasound-guided, nerve dimension-based method.

Background and Objectives: Nerve blocks using local anesthetics are widely used. High volumes are usually injected, which may predispose patients to associated adverse events. Introduction of ultrasound guidance facilitates the reduction of volume, but the minimal effective volume is unknown. In this study, we estimated the 50% effective dose (ED50) and 95% effective dose (ED95) volume of 1% mepivacaine relative to the cross-sectional area of the nerve for an adequate sensory block. Methods: To reduce the number of healthy volunteers, we used a volume reduction protocol using the up-and-down procedure according to the Dixon average method. The ulnar nerve was scanned at the proximal forearm, and the cross-sectional area was measured by ultrasound. In the first volunteer, a volume of 0.4 mL/mm2 of nerve cross-sectional area was injected under ultrasound guidance in close proximity to and around the nerve using a multiple injection technique. The volume in the next volunteer was reduced by 0.04 mL/mm2 in case of complete blockade and augmented by the same amount in case of incomplete sensory blockade within 20 mins. After 3 up-and-down cycles, ED50 and ED95 were estimated. Volunteers and physicians performing the block were blinded to the volume used. Results: A total 17 of volunteers were investigated. The ED50 volume was 0.08 mL/mm2 (SD, 0.01 mL/mm2), and the ED95 volume was 0.11 mL/mm2 (SD, 0.03 mL/mm2). The mean cross-sectional area of the nerves was 6.2 mm2 (1.0 mm2). Conclusions: Based on the ultrasound measured cross-sectional area and using ultrasound guidance, a mean volume of 0.7 mL represents the ED95 dose of 1% mepivacaine to block the ulnar nerve at the proximal forearm.

The dose-response of caudal ropivacaine in children.

BACKGROUND Ropivacaine, a new local anesthetic, is less cardiotoxic in adults and is less likely to cause motor blockade than is bupivacaine. The authors evaluated the clinical effectiveness and hemodynamic effects of ropivacaine compared with bupivacaine and the pharmacokinetics of ropivacaine when given for caudal blocks in 56 children 4.1 +/- 1.2 yr old (mean +/- SD). METHODS Patients scheduled for inguinal hernia repair were randomly given a caudal injection (0.75 ml/kg) of ropivacaine, 0.25% (R0.25 group); ropivacaine, 0.5% (R0.5 group); or bupivacaine, 0.25% (B0.25 group). Postoperative measurements included the duration of analgesia, which was our primary outcome variable, and hemodynamic and respiratory monitoring for 4 h in the recovery room. Thereafter, analgesic requirements for the following 24 h were assessed by an independent observer on the ward using an observational pain-discomfort scale, which gives a cumulative score from 5 to 15 to estimate the quality of analgesia by assessment of behavioral objective parameters. Plasma levels of ropivacaine were measured before the procedure was started and 5, 10, 15, 20, 25, 30, and 45 min and 1, 2, 4, 6, 8, and 24 h after caudal block. RESULTS A significantly longer (P < 0.0001) duration of analgesia (median [range]) was observed in the R0.5 group (1,440 [335-1,440] min), whereas the R0.25 group (208 [175-340] min) and the B0.25 group (220 [100-390] min) were comparable. All groups showed a significant decrease in mean arterial blood pressure and heart rate from baseline values, but differences between groups were not observed. CONCLUSION Ropivacaine is well tolerated and provides effective analgesia when given for caudal blockade in small children for inguinal hernia repair.

Pilot study of neuraxial imaging by ultrasound in infants and children.

Background : Ultrasonography is becoming an important adjunct in regional anesthesia. Epidural anesthesia may pose significant challenges in infants and children because of difficulties in identifying the epidural space. In addition, epidural catheters are sometimes difficult to advance. The present study was performed to evaluate an optimal ultrasound technique for direct visualization of neuraxial structures in children.