D. Marhofer

Dexmedetomidine as an adjuvant to ropivacaine prolongs peripheral nerve block: a volunteer study

BACKGROUND Dexmedetomidine is an α-2-receptor agonist which might be used as an additive to local anaesthetics for various regional anaesthetic techniques. We therefore designed this prospective, double-blinded, controlled volunteer study to investigate the effects of dexmedetomidine as an adjuvant to ropivacaine on peripheral nerve block. METHODS Ultrasound-guided ulnar nerve block (UNB) was performed in 36 volunteers with either 3 ml ropivacaine 0.75% (R), 3 ml ropivacaine 0.75% plus 20 µg dexmedetomidine (RpD), or 3 ml ropivacaine 0.75% plus systemic 20 µg dexmedetomidine (RsD). UNB-related sensory and motor scores were evaluated. RESULTS Sensory onset time of UNB was not different between the study groups, whereas motor onset time was significantly faster in Group RpD when compared with the other study groups [mean (sd)] [21 (15) vs 43 (25) min in Group RsD and 47 (36) min in Group R, P<0.05 Group RpD vs other groups]. The duration of sensory block was 350 (54) min in Group R, 555 (118) min in Group RpD, and 395 (40) min in Group RsD (P<0.01 Group RpD vs other groups, P<0.05 Group RsD vs Group R). Motor block duration was similar to the duration of sensory block. CONCLUSIONS A profound prolongation of UNB of ∼60% was detected with perineural dexmedetomidine when added to 0.75% ropivacaine. The systemic administration of 20 µg dexmedetomidine resulted in a prolongation of ∼10% during UNB with 0.75% ropivacaine. Eudra-CT No.: 2012-000030-19.

Dislocation rates of perineural catheters: a volunteer study

BACKGROUND Dislocation rates of continuous peripheral nerve block are poorly described even though this technique is frequently used in clinical practice. The present study was designed to evaluate dislocation rates over time of interscalene and femoral nerve catheters under defined experimental circumstances. Ultrasound (US) monitoring was used to detect the position of the perineural catheters. METHODS Twenty volunteers received US-guided interscalene and femoral nerve catheters. The volunteers performed standardized physical exercises in regular intervals and the position of both catheters was examined by US confirmation of the spread of fluid. The maximal time of investigation in each volunteer was 6 h. The main outcome parameters were the overall dislocation rates and the cumulative dislocation rates at a given time point. RESULTS We observed an overall dislocation rate of 15% (5% for interscalene catheters, 25% for femoral nerve catheters) and a significant correlation between time and rate of dislocations (r=0.99, P=0.001). US visualization of the spread of fluid was possible in all cases. CONCLUSIONS This is the first dedicated evaluation of dislocation rates of peripheral nerve catheters (PNCs) via US investigation. Both movement and time are considerable factors for perineural catheter displacement. US is useful for the performance of PNCs and for the continuous detection of the spread of fluid relative to the nerve and adjacent anatomical structures. Translational research is required to confirm the study results in the clinical practice.

Magnetic Resonance Imaging Analysis of the Spread of Local Anesthetic Solution after Ultrasound-guided Lateral Thoracic Paravertebral Blockade: A Volunteer Study

Background:This study was designed to examine the spread of local anesthetic (LA) via magnetic resonance imaging after a standardized ultrasound-guided thoracic paravertebral blockade. Methods:Ten volunteers were enrolled in the study. We performed ultrasound-guided single-shot paravertebral blocks with 20 ml mepivacaine 1% at the thoracic six level at both sides on two consecutive days. After each paravertebral blockade, a magnetic resonance imaging investigation was performed to investigate the three-dimensional spread of the LA. In addition, sensory spread of blockade was evaluated via pinprick testing. Results:The median (interquartile range) cranial and caudal distribution of the LA relative to the thoracic six puncture level was 1.0 (2.5) and 3.0 (0.75) [=4.0 vertebral levels] for the left and 0.5 (1.0) and 3.0 (0.75) [=3.5 vertebral levels] for the right side. Accordingly, the LA distributed more caudally than cranially. The median (interquartile range) number of sensory dermatomes which were affected by the thoracic paravertebral blockade was 9.8 (6.5) for the left and 10.7 (8.8) for the right side. The sensory distribution of thoracic paravertebral blockade was significantly larger compared with the spread of LA. Conclusions:Although the spread of LA was reproducible, the anesthetic effect was unpredictable, even with a standardized ultrasound-guided technique in volunteers. While it can be assumed that approximately 4 vertebral levels are covered by 20 ml LA, the somatic distribution of the thoracic paravertebral blockade remains unpredictable. In a significant percentage, the LA distributes into the epidural space, prevertebral, or to the contralateral side.

A pharmacodynamic evaluation of dexmedetomidine as an additive drug to ropivacaine for peripheral nerve blockade: A randomised, triple-blind, controlled study in volunteers.

BACKGROUND Previous data have indicated the efficacy of dexmedetomidine as an additive to peripheral regional anaesthesia. There are no pharmacodynamic data regarding the addition of dexmedetomidine to local anaesthetics for perineural administration. OBJECTIVE The objective of this study is to assess the dose-dependency of dexmedetomidine when injected with ropivacaine for peripheral nerve blockade. DESIGN A randomised, triple-blind, controlled study in volunteers. SETTING Department of Clinical Pharmacology, Medical University of Vienna. PARTICIPANTS Twenty-four volunteers. INTERVENTIONS All volunteers received an ulnar nerve block with 22.5 mg ropivacaine alone (R), or mixed with 50 (RD50), 100 (RD100) or 150 &mgr;g (RD150) dexmedetomidine. MAIN OUTCOME MEASURES The primary outcome was the duration of complete sensory block to pinprick and time to complete recovery of pinprick. Secondary outcomes included block success and onset time, motor block, haemodynamic parameters and sedation level. RESULTS There was a significant dose-dependent (P < 0.0001) increase in the mean duration (SD) of sensory block with dexmedetomidine: R: 8.7 (1.5) h, RD50: 16.4 (4.0) h, RD100: 20.4 (2.8) h and group RD150: 21.2 (1.7) h. Sedation was also enhanced in a dose-dependent (P < 0.001) manner. Two volunteers each receiving 150 &mgr;g dexmedetomidine had postblock paraesthesia for 72 h. CONCLUSION Dexmedetomidine mixed with ropivacaine produces a dose-dependent prolongation of sensory block and clinically relevant dose-dependent sedation. Dexmedetomidine 100 &mgr;g may represent a balance between efficacy and sedation.

Effective local anaesthetic volumes for sciatic nerve blockade: a clinical evaluation of the ED99

Previous results in volunteers have indicated the effective dose in 99% of subjects (ED99) of local anaesthetic volume to be 0.10 ml.mm−2 of cross‐sectional nerve area for sciatic nerve blockade. The objective of this prospective, randomised, double‐blind study was to investigate the ED99 of local anaesthetic for ultrasound‐guided sciatic nerve blockade in patients undergoing foot surgery, according to Dixons up‐and‐down method and probit analysis. A starting volume of 0.20 ml local anaesthetic per mm2 cross‐sectional nerve area was used. If surgical anaesthesia was judged to be adequate, the volume of local anaesthetic for the next case was reduced by 0.02 ml.mm−2, until the first block failed. Thereafter, the volume of local anaesthetic was increased by 0.02 ml.mm−2. The ED99 volume of local anaesthetic for ultrasound‐guided sciatic nerve blockade was calculated to be 0.15 ml.mm−2 cross‐sectional nerve area, which is higher than the previously evaluated ED99 volume in volunteers.

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.

Dexmedetomidine as adjunct to ilioinguinal/iliohypogastric nerve blocks for pediatric inguinal hernia repair: an exploratory randomized controlled trial

Adult meta‐analysis has identified dexmedetomidine as a potentially useful adjunct to prolong the duration of peripheral nerve blocks. However, no data exist regarding the adjuvant use of dexmedetomidine in the setting of pediatric peripheral nerve blocks.

Lumbar neuraxial anatomical changes throughout pregnancy: a longitudinal study using serial ultrasound scans.

This observational study was designed to investigate the anatomical changes of the lumbar spine over the course of pregnancy using serial ultrasound scans. We performed paramedian scans on 58 women at the L2–3, L3–4 and L4–5 levels; these were done at four periods of 11+0–13+6, 19+0–23+0, 28+0–32+0 and 38+0–40+0 weeks gestation. At each intervertebral level, the length of the interlaminar space, length of the visible intervertebral posterior dura and depth of the posterior dura mater from the skin were measured. The length of the interlaminar space and length of the visible intervertebral posterior dura mater were longer, and the depth of the posterior dura mater was shallower, with ascending spinal interspace. The depth of the posterior dura mater increased during pregnancy, although it plateaued between the third and fourth measurement periods. The other spinal measurements were not affected by gestation. These findings indicate that the L2–3 level is the most appropriate puncture site for epidural anaesthesia in pregnant women. Our results ought to be embraced as a departure point towards developing neuraxial insertion techniques guided or aided by ultrasound.

Cutaneous innervation of the hand: clinical testing in volunteers shows high intra- and inter-individual variability

Background: Many clinicians require a solid understanding of the anatomical areas supplied by specific peripheral nerves. Virtually all pertinent medical textbooks claim that the entire (palmar and dorsal) surface of the hand is supplied by three (median, radial, and ulnar) nerves and that each of these covers a well‐defined area. This study was designed to evaluate the sensory‐distribution pattern of peripheral nerves in the hand. Methods: Twelve volunteers were enrolled and randomly allocated to have median, ulnar, or radial nerve blocks to each hand on three successive days. All blocks were performed using ultrasound guidance. A neurologist carried out pinprick testing to define the sensory‐distribution area of each procedure. The hand surface was then scanned, and the sensory‐distribution area of the blocked nerve was traced, measured, and quantified in relation to the entire hand surface for descriptive and comparative statistical analyses. Results: The sensory‐distribution areas of the three nerves revealed a high degree of inter‐individual and intra‐individual variabilities. Sizeable areas were not covered by any of the three nerves, again involving great variability. Conversely, 15 of the 24 hands showed areas of overlapping supply from more than one nerve. Conclusions: Our findings suggest that the anatomical areas supplied by peripheral nerves are characterised by much greater variability than is routinely claimed. Clinical trial registration: DRKS00010707.

Feasibility and pharmacokinetics of caudal blockade in children and adolescents with 30-50 kg of body weight.

Caudal blockade, although an important technique of pediatric regional anesthesia, is rarely used in children heavier than 30 kg. This reservation is due to anatomical concerns and lack of pharmacokinetic data. We therefore set out to evaluate, in pediatric patients weighing 30−50 kg, the feasibility of ultrasound‐guided caudal blockade and the pharmacokinetics of caudally administered ropivacaine.