Sensory Nerve Blockade Research Articles

Efficacy of ultrasound-guided classical versus parasacral parallel shift technique of sacral plexus block for lower limb surgeries - A randomised controlled trial.

Ultrasound-guided sacral plexus block has been used for anaesthesia and analgesia in lower limb surgeries. This study aimed to compare the block performance characteristics after ultrasound-guided (USG) sacral plexus nerve block (SNB) using the parasacral parallel shift (PSPS) approach versus the classical approach in patients undergoing orthopaedic below-knee limb surgeries. In this randomised study, 144 adult patients were randomised to receive USG SNB either by the classical approach (Group C) or the PSPS approach (Group P). A fixed dose of 20 ml of 0.5% ropivacaine was administered. Patients also received USG femoral nerve block with 10 ml of 0.5% ropivacaine. The primary outcome was the scanning time between the two groups. Secondary outcomes were the needling time, sensory and motor block onset and postoperative analgesic characteristics between the two groups. A P value of <0.05 was considered statistically significant. The needling time and the scanning time were significantly lesser in Group P than in Group C (P < 0.05). Complete sensory and motor nerve blockade of the sciatic nerve was significantly higher in Group P (P = 0.029). Block performance time, time for sensory block and time for motor block were significantly less in Group P compared to Group C (P < 0.001). The postoperative analgesic characteristics were comparable between the two groups. The sacral plexus block with ultrasound-guided parasacral parallel shift technique had a lower block performance time with lesser needling and scanning time than the classical approach.

Benzonatate as a local anesthetic.

Benzonatate is an FDA-approved antitussive agent that resembles tetracaine, procaine, and cocaine in its chemical structure. Based on structural similarities to known local anesthetics and recent findings of benzonatate exerting local anesthetic-like effects on voltage-gated sodium channels in vitro, we hypothesized that benzonatate will act as a local anesthetic to yield peripheral nerve blockade. Benzonatate was injected at the sciatic nerve of Sprague-Dawley rats. Sensory and motor blockade were assessed using a modified hot plate test and a weight-bearing test, respectively. Additionally, the effect of co-injection with tetrodotoxin and Tween 80 (a chemical permeation enhancer) was examined. Myotoxicity of benzonatate was assessed in vivo by histological analysis. Benzonatate produced a concentration-dependent sensory and motor nerve blockade with no appreciable systemic effects. Co-injection with tetrodotoxin or Tween 80 produced prolongation of sensory nerve blockade. Histologic assessment showed significant inflammation and myotoxicity from benzonatate injection, even at low concentrations. This study demonstrates that benzonatate does act as a local anesthetic at the peripheral nerve, with sensory and motor nerve blockade. Benzonatate interacts with tetrodotoxin and Tween 80 to prolong nerve blockade. However, benzonatate causes significant myotoxicity, even at subtherapeutic concentrations.

What's New in Adult Reconstructive Knee Surgery.

What's New in Adult Reconstructive Knee Surgery.

Effects of sensory nerve blockade on cutaneous microvascular responses to ischemia-reperfusion injury.

Examine the effects of sensory nerve blockade on cutaneous post-occlusive reactive hyperemia (PORH) and local thermal hyperemia (LTH) following prolonged upper limb ischemia. In nine males [28years (standard deviation:6)], volar forearm skin blood flux normalized to maximum vasodilation (%SkBFmax) was assessed at control (CTRL) and sensory nerve blockade (EMLA) treated sites during the PORH response following 20-min of complete arm ischemia and during rapid LTH (33-42°C, 1°C·20s-1, held for ~30-min+20-min at 44°C) before and after ischemia-reperfusion (IR) injury. EMLA increased mean [95% confidence-interval] PORH amplitude by 21%SkBFmax ([9,33]; p=0.003), delayed time to peak by 111s ([40,182]; p=0.007) and increased area under the curve by 19,462%SkBFmax·s ([11,346,27,579]; p<0.001) compared to CTRL. For LTH, EMLA delayed onset time by 76s ([46,106]; p<0.001) Pre-IR and by 46s ([27,65]; p<0.001) Post-IR compared to CTRL. Post-IR onset time was delayed for CTRL by 26s ([8,43]; p=0.007), but was not different for EMLA (p>0.050) compared to Pre-IR. EMLA delayed time to initial peak by 24s ([4,43]; p=0.022, Main time effect) and it attenuated the initial peak by 27%SkBFmax ([12,43]; p=0.002) Pre-IR and by 16%SkBFmax ([3,29]; p=0.020) post-IR compared to CTRL. Post-IR, the initial peak was not different for CTRL (p>0.050), but it was increased by 16%SkBFmax ([5,26]; p=0.005) for EMLA compared to Pre-IR. Neither EMLA nor IR altered the steady-state heating plateau (all p>0.050). For the current model of IR injury, sensory nerves appear to have a negligible influence on the LTH response in non-glabrous forearm skin once vasodilation has been initiated.

Ultrasound-Guided Saphenous Nerve Block in Rabbits (Oryctolagus cuniculus): A Cadaveric Study Comparing Two Injectate Volumes.

Simple SummaryGeneral anesthesia in rabbits is associated with significantly higher mortality than in dogs and cats. In addition, as prey animals, rabbits tend to mask signs of pain, making early detection particularly difficult. Loco-regional anesthesia represents a fundamental component of a multimodal approach to pain management and is an effective strategy to reduce the need for systemic anesthetic and analgesic drugs, thereby limiting their associated side effects. The saphenous nerve is the largest sensory branch of the femoral nerve and provides sensory supply to areas of the hind-limb. Saphenous nerve blockade allows for analgesia of the front and inner parts of the pelvic limb without affecting femoral nerve motor function, thus allowing optimal pain relief but permitting continued mobilization, which may be of particular importance in rabbits as it allows preservation of normal physiological prey behavior (e.g., hiding, kicking). This cadaveric study describes an ultrasound-guided saphenous nerve block technique in rabbits and compares the length of the nerves stained following injection of two different dye volumes. The results show that both volumes consistently stained the saphenous but not the femoral nerve. This technique has the potential to provide hind-limb analgesia while preserving femoral motor function in rabbits.Ultrasound-guided (US-guided) loco-regional anesthesia techniques allow direct visualization and blockade of sensory nerves. The saphenous nerve (SN), a terminal branch of the femoral nerve (FN), is strictly a sensory nerve for which electrical locator devices are ineffective for localization as no effector muscle contractions can be evoked. US-guided SN block in species other than rabbits produces hind-limb analgesia without affecting FN motor function. The aims of this study were to develop a US-guided SN block technique in rabbits and to compare the spread obtained using two different dye volumes. Twelve hind-limbs from six cadavers (1.6 ± 0.1 kg) were included; after randomization, the SN block was performed on the right or left hind-limb, injecting 0.05 mL kg−1 or 0.1 mL kg−1 of tissue dye in lidocaine (1:50 v:v). Subsequent dissections allowed nerve staining measurements. All SNs were identified, and 17.8 ± 4.6% and 31.0 ± 8.9% of the SN length were stained using low-volume and high-volume of the dye, respectively. Regardless of the volume used, the SN was consistently stained while the motor branch of the FN was not. This US-guided technique may provide hind-limb analgesia without affecting FN motor function in rabbits undergoing mid-distal hind-limb surgeries.

Effect of ultrasound-guided selective sensory nerve blockade of the knee on pain management compared with periarticular injection for patients undergoing total knee arthroplasty: A prospective randomized controlled trial

BackgroundUltrasound-guided selective sensory nerve blockade (SSNB) of the knee, including an adductor canal block (ACB), anterior femoral cutaneous nerve block, and infiltration between the popliteal artery and posterior capsule of the knee may provide effective motor-sparing knee analgesia for total knee arthroplasty (TKA). We hypothesized that the SSNB would manage pain better on ambulation 24 hours postoperatively compared to periarticular infiltration (PAI), when combined with postoperative continuous ACB. MethodsSeventy-two patients undergoing elective TKA under spinal anesthesia were randomly assigned to either SSNB (SSNB group) or intraoperative PAI (PAI group). All patients received postoperative multimodal analgesia, including continuous ACB. The primary outcome was pain on ambulation 24 hours postoperatively. Secondary outcomes included rest and dynamic numerical rating scale pain score, intravenous morphine requirement, functional performance measures, adverse events, satisfaction, and length of stay. ResultsThere was no difference in pain score during movement between the groups (mean difference −0.48 [−1.38 to 0.42], p = 0.3) and other immediate overall pain scores 24 hours postoperatively. Patients in the SSNB group had significantly lower intravenous morphine requirement than the PAI group for 48 hours postoperatively (0 [0, 0] vs. 0 [0, 2]; p = 0.008). There was no intergroup difference in the performance-based measures, satisfaction, and length of stay. ConclusionsThe SSNB did not provide superior postoperative analgesia, or improvement in immediate functional performance. However, it may result in lower opioid consumption postoperatively when compared with the intraoperative PAI.

Anatomical Landmarks for Intraoperative Adductor Canal Block in Total Knee Arthroplasty: A Cadaveric Feasibility Assessment.

BackgroundPostoperative analgesia after knee arthroplasty forms a basis for an optimal range of motion after surgery. Femoral nerve blocks are established as a sensory nerve blockade but at the expense of quadriceps weakness delaying postoperative mobilization. The adductor canal block (ACB) similarly provides sensory blockade but preserves quadriceps function. If ACB is performed intraoperatively, it would reduce the time and cost needed for ACBs. This study aimed at investigating possible landmarks making it feasible to perform ACB intraoperatively.Material and methodsTwenty-seven knees were used. The superior pole of the patella, medial epicondyle, and adductor tubercle was proposed as landmarks to perform the ACB through a medial parapatellar approach. A needle was directed toward the adductor tubercle until a tactile feedback was felt. Ten to 15 mL India ink were injected using this technique. The adductor canal was dissected to visualize the ink spread and determine whether the saphenous nerve and the nerve to vastus medialis were exposed to the ink.ResultsThe anatomic landmarks were easily identified in all knees. The ACB resulted in the saphenous nerve and nerve to vastus medialis being bathed in ink consistently. A volumetric relationship was noted with the injectate. No injury to the neurovascular structures was observed.ConclusionsAn accurate and safe technique with reliable anatomic landmarks was presented to perform an ACB. In addition, an increase in injected ink volume correlated to an increase in the spread of ink; thus, we postulate that 10 mL of local anesthetic may be sufficient for an adequate regional block.

Gastrointestinal Distension by Pectin-Containing Carbonated Solution Suppresses Food Intake and Enhances Glucose Tolerance via GLP-1 Secretion and Vagal Afferent Activation.

Diet-induced gastrointestinal distension is known to evoke satiation and suppress postprandial hyperglycemia; however, the underlying mechanisms remain poorly understood. This study explored how gastrointestinal distension regulates energy homeostasis by using inflating stomach formulation (ISF), the carbonated solution containing pectin that forms stable gel bubbles under acidic condition in the stomach. Here we show that, in mice, oral administration of ISF induced distension of stomach and proximal intestine temporarily, stimulated intestinal glucagon-like peptide-1 (GLP-1) secretion, and activated vagal afferents and brainstem. ISF suppressed food intake and improved glucose tolerance via enhancing insulin sensitivity. The anorexigenic effect was partially inhibited, and the beneficial glycemic effect was blunted by pharmacological GLP-1 receptor blockade and chemical denervation of capsaicin-sensitive sensory nerves. In HFD-fed obese mice showing arrhythmic feeding and obesity, subchronic ISF treatment at the light period (LP) onset for 10 days attenuated LP hyperphagia and visceral fat accumulation. These results demonstrate that gastrointestinal distension by ISF stimulates GLP-1 secretion and the vagal afferent signaling to the brain, thereby regulating feeding behavior and glucose tolerance. Furthermore, subchronic ISF treatment ameliorates HFD-induced visceral obesity. We propose the diet that induces gastrointestinal distension as a novel treatment of hyperphagic obesity and diabetes.

Effects of perineural administration of ropivacaine combined with perineural or intravenous administration of dexmedetomidine for sciatic and saphenous nerve blocks in dogs.

To evaluate the effects of using ropivacaine combined with dexmedetomidine for sciatic and saphenous nerve blocks in dogs. 7 healthy adult Beagles. In phase 1, dogs received each of the following 3 treatments in random order: perineural sciatic and saphenous nerve injections of 0.5% ropivacaine (0.4 mL/kg) mixed with saline (0.9% NaCl) solution (0.04 mL/kg; DEX0PN), 0.5% ropivacaine mixed with dexmedetomidine (1 μg/kg; DEX1PN), and 0.5% ropivacaine mixed with dexmedetomidine (2 μg/kg; DEX2PN). In phase 2, dogs received perineural sciatic and saphenous nerve injections of 0.5% ropivacaine and an IV injection of diluted dexmedetomidine (1 μg/kg; DEX1IV). For perineural injections, the dose was divided equally between the 2 sites. Duration of sensory blockade was evaluated, and plasma dexmedetomidine concentrations were measured. Duration of sensory blockade was significantly longer with DEX1PN and DEX2PN, compared with DEX0PN; DEX1IV did not prolong duration of sensory blockade, compared with DEX0PN. Peak plasma dexmedetomidine concentrations were reached after 15 minutes with DEX1PN (mean ± SD, 348 ± 200 pg/mL) and after 30 minutes DEX2PN (816 ± 607 pg/mL), and bioavailability was 54 ± 40% and 73 ± 43%, respectively. The highest plasma dexmedetomidine concentration was measured with DEX1IV (1,032 ± 415 pg/mL) 5 minutes after injection. Results suggested that perineural injection of 0.5% ropivacaine in combination with dexmedetomidine (1 μg/kg) for locoregional anesthesia in dogs seemed to balance the benefit of prolonging sensory nerve blockade while minimizing adverse effects.

Single injection Erector Spinae Plane block for vascular ring repair: Is a catheter required?

Abstract Erector Spinae Plane (ESP) blocks have been used successfully in adults to manage post-operative pain associated with thoracotomy. In pediatric patients, thoracotomy pain is often managed with multimodal analgesia and neuraxial or regional techniques. The use of a single injection ESP block in pediatric thoracotomy patients can provide sensory nerve blockade, reduce sympathetic discharge, and decrease perioperative opioid requirements. This case report describes two pediatric patients undergoing vascular ring repair via left thoracotomy where post-operative pain was managed with a single injection ESP block and multimodal analgesia.

Local anesthesia enhanced with increasing high-frequency ultrasound intensity.

The effect of local anesthetics, particularly those which are hydrophilic, such as tetrodotoxin, is impeded by tissue barriers that restrict access to individual nerve cells. Methods of enhancing penetration of tetrodotoxin into nerve include co-administration with chemical permeation enhancers, nanoencapsulation, and insonation with very low acoustic intensity ultrasound and microbubbles. In this study, we examined the effect of acoustic intensity on nerve block by tetrodotoxin and compared it to the effect on nerve block by bupivacaine, a more hydrophobic local anesthetic. Anesthetics were applied in peripheral nerve blockade in adult Sprague-Dawley rats. Insonation with 1-MHz ultrasound at acoustic intensity greater than 0.5W/cm2 improved nerve block effectiveness, increased nerve block reliability, and prolonged both sensory and motor nerve blockade mediated by the hydrophilic ultra-potent local anesthetic, tetrodotoxin. These effects were not enhanced by microbubbles. There was minimal or no tissue injury from ultrasound treatment. Insonation did not enhance nerve block from bupivacaine. Using an in vivo model system of local anesthetic delivery, we studied the effect of acoustic intensity on insonation-mediated drug delivery of local anesthetics to the peripheral nerve. We found that insonation alone (at intensities greater than 0.5W/cm2) enhanced nerve blockade mediated by the hydrophilic ultra-potent local anesthetic, tetrodotoxin. Graphical abstract.

A Physiological Validation of Spectral Analysis for Skin Flowmotion

In a series of studies, our laboratory has utilized microneurography coupled with laser Doppler flowmetry to examine sympathetic neural control of the cutaneous microvasculature during thermoregulatory stimuli. However, these techniques have limited clinical utility. Spectral analysis of the low frequency periodic oscillations in laser Doppler flowmetry‐derived red blood cell flux (i.e., skin flowmotion) is a noninvasive technique that has been used to quantify cutaneous microvascular control mechanisms (e.g., endothelial, neurogenic, myogenic). To date, conclusions regarding the mechanistic regulation of cutaneous microvascular function derived from spectral analysis have been primarily limited to basal conditions. Thus, the aim here was to examine the validity of spectral analysis to quantify sympathetic neural control of skin blood flow during a dynamic physiological stimulus (local skin heating to 42°C). We hypothesized that pharmacological blockade of sensory nerves would reduce the spectral power of the neurogenic frequency band during local heating. Eleven young healthy adults (7 women; 22±3 yrs, 25±2 kg/m2) participated. Laser Doppler flux was measured continuously during baseline (33°C) and a standardized local heating protocol (42°C) at a non‐treated control site (con) and a site treated with topical lidocaine (lido; 2.5% prilocaine+2.5% lidocaine) to pharmacologically block sensory nerves. Topical lido was applied for a minimum of 45 minutes prior to testing. Cutaneous vascular conductance was calculated and expressed as a percentage of maximum (local heat of 43°C). A raw Fourier transform was used to calculate spectral power around the 0.0095–0.02 Hz, 0.02–0.05 Hz, and 0.05–0.15 Hz frequency intervals, considered to correspond to endothelial, neurogenic, and myogenic activity, respectively. The initial peak of the local heating response was reduced by lido, (con: 62±2% vs. lido: 25±5%, p&lt;0.01), validating adequate sensory nerve blockade. However, there was no difference between sites during baseline (con: 12±1% vs. lido: 9±2%, p=0.07) or the local heating‐induced plateau (con: 95±3% vs. lido: 87±7%, p=0.20). There was no effect of lido on spectral power of any of the frequency intervals at baseline or during local heating. Total spectral power (i.e., the sum of the spectral power for all frequency bands) was significantly related to conductance in both sites at baseline (con: R2=0.69, p&lt;0.01; lido: R2=0.72, p&lt;0.01) and during local heating (con: R2=0.22, p&lt;0.02; lido: R2=0.71, p&lt;0.01). In conclusion, the physiological increase in cutaneous vascular conductance during local heating was mirrored by an increase in total spectral power. Although blockade of sensory nerves reduced the increase in conductance during the initial peak of the local heating response, it did not affect the neurogenic frequency interval derived from spectral analysis. These preliminary data suggest that skin flowmotion may not be a valid approach to evaluate neural control of cutaneous microvascular function during dynamic conditions.Support or Funding InformationAmerican Heart Association Grant #18UFEL33900164; College of Health and Human Development Summer 2019 Undergraduate Research Award; Noll Endowment for Undergraduate Research

The Duration of Nerve Block from Local Anesthetic Formulations in Male and Female Rats.

It is unknown whether there are sex differences in response to free or encapsulated local anesthetics. We examined nerve block duration and toxicity following peripheral nerve blockade in male and female rats. We studied the local anesthetic bupivacaine (free or encapsulated) as well as tetrodotoxin, which acts on a different site of the same voltage-gated channel. Sensory nerve blockade was 158.5 [139-190] minutes (median [interquartile range]) (males) compared to 173 [134-171] minutes (females) (p= 0.702) following bupivacaine injection, N= 8 male, 8 female. Motor nerve blockade was 157 [141-171] minutes (males) compared to 172 [146-320] minutes (females) (p= 0.2786). Micellar bupivacaine (N = 8 male, 8 female) resulted in sensory nerve blockade of 266 [227-320] minutes (males) compared to 285 [239-344] minutes (females) (p= 0.6427). Motor nerve blockade was 264 [251-264] minutes (males) compared to 287 [262-287] minutes (females) (p= 0.3823). Liposomal bupivacaine (N= 8 male, 8 female) resulted in sensory nerve blockade of 240 [207-277] minutes (males) compared to 289 [204-348] minutes (females) (p= 0.1654). Motor nerve blockade was 266 [237-372] minutes (males) compared to 317 [251-356] minutes (females) (p= 0.6671). Following tetrodotoxin injection (N= 12 male,12 female) sensory nerve blockade was 54.8 [5-117] minutes (males) compared to 54 [14-71] minutes (females) (p= 0.6422). Motor nerve blockade was 72 [40-112] minutes (males) compared to 64 [32-143] minutes (females) (p= 0.971). We found no statistically significant sex differences associated with the formulations tested. In both sexes, durations of nerve block were similar between micellar and liposomal bupivacaine formulations, despite the micellar formulation containing less drug.

Tetrodotoxin, Epinephrine, and Chemical Permeation Enhancer Combinations in Peripheral Nerve Blockade.

Chemical permeation enhancers (CPEs) have the potential to improve nerve blockade by site 1 sodium channel blockers such as tetrodotoxin (TTX). Here, we investigated the efficacy and toxicity of CPE-enhanced nerve blockade across a range of TTX concentrations using 2 CPEs (sodium octyl sulfate and octyl trimethyl ammonium bromide). We also tested the hypothesis that CPEs could be used to reduce the concentrations of TTX and/or of a second adjuvant drug (in this case, epinephrine) needed to achieve prolonged local anesthesia METHODS:: Sprague-Dawley rats were injected at the sciatic nerve with combinations of TTX and CPEs, with and without epinephrine. Sensory and motor nerve blockade were assessed using a modified hot plate test and a weight-bearing test, respectively. Systemic and local toxicities of the different combinations were assessed. Addition of increasing concentrations of TTX to fixed concentrations of CPEs produced a marked concentration-dependent improvement in the rate of successful nerve blocks and in nerve block duration. CPEs did not affect systemic toxicity. At some concentrations, the addition of sodium octyl sulfate increased the duration of block from TTX plus epinephrine, and epinephrine increased that from TTX plus CPEs. The addition of epinephrine did not cause an increase in local toxicity, and it markedly reduced systemic toxicity. CPEs can prolong the duration of nerve blockade across a range of concentrations of TTX. CPEs could also be used to reduce the concentration of epinephrine needed to achieve a given degree of nerve block. CPEs may be useful in enhancing nerve blockade from site 1 sodium channel blockers.

Ultrasound-guided femoral nerve block using a ventral suprainguinal approach in healthy dogs

ObjectiveTo determine whether an ultrasound (US)-guided femoral nerve block using a ventral suprainguinal approach could be successfully achieved in sedated dogs; to measure the time to execute the nerve block, onset time, duration, and complete block rate in sensory and motor nerves; and to examine any differences between two volumes for injection. Study designBlinded crossover experimental study. AnimalsA total of 10 clinically healthy adult Beagle dogs. MethodsThe femoral nerve of the right pelvic limb was infiltrated with 0.5% bupivacaine at 0.4 (treatment 0.4B) or 0.2 mL kg−1 (treatment 0.2B), or saline at 0.4 mL kg−1 (control) in sedated dogs. The sensory and motor nerve functions were scored on a scale of 0 (complete blockade) to 2 (normal). The onset time and duration of the sensory and motor nerve blockade were compared between treatments 0.4B and 0.2B using a Wilcoxon signed rank test. Sensory and motor nerve function scores for each of the three treatments were compared at multiple time points using a nonparametric multiple comparisons test. ResultsThe time to execute the nerve block was 2.5 ± 0.9 minutes (n = 30). For both 0.4B and 0.2B treatments, the onset times of both the sensory and motor nerve blockades were 15 minutes. The durations of the sensory nerve blockade for 0.4B and 0.2B were 9.9 ± 1.4 and 10.0 ± 1.2 hours, respectively, and those of the motor nerve blockades were 10.5 ± 1.3 and 10.2 ± 1.3 hours, respectively. No adverse effects were noted. No significant difference was observed between 0.4B and 0.2B. Conclusions and clinical relevanceA US-guided femoral nerve block using a ventral suprainguinal approach demonstrated a short onset and long duration with 0.5% bupivacaine 0.2 mL kg−1 and can be performed under sedation in dogs.

Comparison of ultrasound- and electrostimulation-guided nerve blocks of brachial plexus in dogs

ObjectiveTo compare the effectiveness of ultrasound- and electrostimulation-guided nerve blocks of the brachial plexus and to determine whether ultrasound guidance is feasible in conscious dogs. Study designBlinded, crossover, experimental study. AnimalsSix clinically healthy adult Beagle dogs. MethodsThe nerves of the brachial plexus of the right thoracic limb were blocked under ultrasound guidance (UNB) in conscious dogs and under electrostimulation guidance (ENB) in anesthetized dogs with bupivacaine (0.4 mL kg–1, 0.25%). Saline (0.4 mL kg–1) was injected in control animals. Sensory nerve blockade was evaluated by scoring cutaneous sensation in targeted nerves. Motor nerve blockade was evaluated based on weight bearing, conscious proprioception and withdrawal reflex scores. Times to execute the technique in UNB and ENB were compared using t tests (p < 0.05). Scores for sensory and motor nerve blockades in each treatment were compared with scores before treatment and with control treatment scores using nonparametric repeated-measures two-way analysis of variance. Time to onset and duration of sensory nerve block were assessed using scores for four sensory nerve functions. A successful sensory nerve block was defined by decreases in scores for these functions. Success rates of nerve blocks were compared among treatments using McNemar’s test. ResultsIn UNB and ENB, onset times of sensory nerve blocks were 1 hour and 1.5 hours, respectively. Onset times of motor nerve blocks were 0.5 hour in both treatments. In UNB and ENB, durations of sensory nerve block were 3 hours and 0.5 hour, respectively, and durations of motor nerve block were 7.5 hours and 6.5 hours, respectively. Success rates did not differ between the techniques. Conclusions and clinical relevanceThe UNB brachial plexus block had a shorter onset time and longer duration than ENB. UNB can be performed in conscious dogs or those under mild sedation.

Effects of epidural anesthesia with tramadol, ropivacaine or tramadol-ropivacaine combination, in bitches undergoing ovariohysterectomy under anesthesia with isoflurane

Epidural anesthesia is a locoregional anesthetic technique that provides analgesia and muscle relaxation in the-retroumbilical region. The combination of opioids and local anesthetics increased the intensity and duration of analgesia by causing immediate motor and sensory nerve blockade, and improved recovery after surgery. The objective was to comparatively evaluate the trans- and postoperative cardiorespiratory and analgesic effects of epidurally administered tramadol, ropivacaine and tramadol-ropivacaine combination in dogs undergoing elective ovariohysterectomy. The effect of isoflurane concentration was also evaluated. This study was performed on 24 female mongrel dogs, pre-medicated with chlorpromazine (0.5 mg kg-1, IV) and, anesthetized with propofol and isoflurane. The dogs were randomly divided into three groups. The first group receveid epidural tramadol (2 mg kg-1, GT group), the second group received ropivacaine (1.5 mg kg-1, GR group), and the third group received a tramadol-ropivacaine combination at the above-mentioned doses (GTR group). At pre-defined time points, classified into pre-, trans-, and postoperative periods, cardiorespiratory variables and analgesia were analyzed for a period of up to 420 min following epidural anesthesia. The check analgesia was check of approximately 105, 217 and 382 minutes, in GR, in GT and GTR respectively, and no cardiovascular and respiratory depression. The drugs used in this study are considered safe and effective for ovariohysterectomy due to the cardiorespiratory stability and trans-operative analgesia provided by them. However, the combination of ropivacaine and tramadol ensured a greater reduction in the inhaled anesthetic dose and better analgesia during in the postoperative period.

The contribution of sensory nerves to the onset threshold for cutaneous vasodilatation during gradual local skin heating of the forearm and leg

During local skin heating, the temporal onset of vasodilatation is delayed in the leg compared to the forearm, and sensory nerve blockade abolishes these differences. However, previous work using rapid skin heating did not allow for determination of sensory nerve influences on temperature thresholds for vasodilatation. Two sites were examined on both the forearm and leg, one control (CTRL), and one treated for sensory nerve blockade (EMLA). Skin blood flux was monitored using laser-Doppler probes, with heaters controlling local skin temperature (Tloc). Tloc was increased from 32–44°C (+1°C·10min−1). Stimulus–response curves were constructed by fitting a four-parameter logistic function. EMLA significantly increased Tloc onset in the forearm (CTRL=35.3±0.4°C; EMLA=36.8±0.7°C) and leg (CTRL=36.5±0.4°C; EMLA=38.4±0.5°C; both P<0.05). At both CTRL and EMLA, Tloc onset was higher in the leg compared to the forearm (both P<0.05). In the forearm, median effective temperature to elicit 50% vasodilatation (ET50) was similar between sites (CTRL=39.7±0.3°C; EMLA=40.2±0.4°C; P=0.09); however, in the leg, EMLA significantly increased ET50 (CTRL=40.2±0.3°C; EMLA=41.0±0.3°C)(P<0.05). At CTRL sites, no limb difference was observed for ET50 (P=0.06); however, with EMLA, ET50 was significantly higher in the leg (P<0.05). EMLA significantly increased the gain of the slope at the forearm, (CTRL=0.31±0.01%CVCmax·°C−1; EMLA=0.45±0.07%CVCmax·°C−1), and leg (CTRL=0.37±0.05%CVCmax·°C−1; EMLA=0.54±0.04%CVCmax·°C−1)(both P<0.05). At CTRL sites, the gain was significantly higher in the leg (P<0.05); however, for EMLA, no significant limb difference existed (P=0.10). These data indicate that the onset of vasodilatation occurs at a lower temperature in the forearm than the legs, and sensory nerves play an important role in both limbs.

Combination of dexamethasone and local anaesthetic solution in peripheral nerve blocks: A meta-analysis of randomised controlled trials.

Dexamethasone decreases postoperative pain and prolongs the duration of local anaesthetic peripheral nerve blocks in studies including a limited number of patients. The objective of this study is to evaluate the effect of combining dexamethasone with local anaesthetic on sensory and motor peripheral nerve blockade in adults. A systematic review with meta-analysis of randomised controlled trials. We systematically searched in Medline, Embase, Google Scholar and Cochrane Controlled Trials Register up to December 2013. Randomised trials testing dexamethasone combined with local anaesthetic. Twelve trials (1054 patients, 512 receiving perineural dexamethasone) were included. Ten studies evaluated dexamethasone for brachial plexus nerve block. Four to 10 mg dexamethasone-containing local anaesthetic solutions had a faster onset of action and resulted in a significant increase in the duration of analgesia [weighted mean difference (WMD) 351 min, 95% confidence interval (95% CI) 288 to 413, P < 0.001] and motor blockade (WMD 277 min, 95% CI 167 to 387, P < 0.001) compared with local anaesthetic solutions alone. Time to onset of sensory and motor blocks was significantly reduced with dexamethasone (WMD -78 s, 95% CI -112 to -44, and -90 s, 95% CI -131 to -48, respectively). Dexamethasone significantly decreased postoperative nausea and vomiting (PONV, 9 vs. 27%, relative risk 0.36, 95% CI 0.19 to 0.70). Subgroup analyses showed that dexamethasone approximately doubled the duration of postoperative analgesia when it was combined with intermediate-acting (lidocaine, mepivacaine) or long-acting (bupivacaine, ropivacaine) local anaesthetics. Combining dexamethasone with local anaesthetics results in a prolongation of the duration of peripheral nerve block.

Additives to local anesthetics for peripheral nerve blocks: Evidence, limitations, and recommendations

The therapeutic rationale, clinical effectiveness, and potential adverse effects of medications used in combination with local anesthetics for peripheral nerve block therapy are reviewed. A wide range of agents have been tested as adjuncts to peripheral nerve blocks, which are commonly performed for regional anesthesia during or after hand or arm surgery, neck or spine surgery, and other procedures. Studies to determine the comparative merits of nerve block adjuncts are complicated by the wide variety of coadministered local anesthetics and sites of administration and by the heterogeneity of primary endpoints. Sodium bicarbonate has been shown to speed the onset of mepivacaine nerve blocks but delay the onset of others. Epinephrine has been shown to prolong sensory nerve blockade and delay systemic uptake of local anesthetics, thus reducing the risk of anesthetic toxicity. Tramadol, buprenorphine, dexamethasone, and clonidine appear to be effective additives in some situations. Midazolam, magnesium, dexmedetomidine, and ketamine cannot be routinely recommended as nerve block additives due to a dearth of supportive data, modest efficacy, and (in the case of ketamine) significant adverse effects. Recent studies suggest that administering additives intravenously or intramuscularly can provide many of the benefits of perineural administration while reducing the potential for neurotoxicity, contamination, and other hazards. Some additives to local anesthetics can hasten the onset of nerve block, prolong block duration, or reduce toxicity. On the other hand, poorly selected or unnecessary additives may not have the desired effect and may even expose patients to unnecessary risks.