Quantitative and selective assessment of sensory block during lumbar epidural anaesthesia with 1% or 2% lidocaine

Local and Regional Anaesthetic Techniques in Canine Ovariectomy: A Review of the Literature and Technique Description

Simple Summary

This review stems from a general trend of increasing attention toward surgical nociception in the veterinary field. Indeed, veterinarian anaesthetists are becoming more careful in relieving perioperative nociception, improving the analgesic protocols and therefore optimising surgical outcomes. Canine ovariectomy is a common surgical procedure with a moderate level of pain. Therefore, intraoperative analgesia is very important because pain causes various systemic inflammatory effects that slow patient recovery. This review aims to collect all recent information about local and regional anaesthetic/analgesic techniques in a review of the literature describing the technique utilised. In addition, the present review aims to provide practical guidelines for veterinary practitioners to improve the anaesthetic techniques in canine neutering through an overview of the available literature. In fact, the methods described, considering the relative simplicity of execution, can be used in daily routine practice.

Abstract

Canine ovariectomy is an elective surgery with a moderate level of pain. Despite its relative simplicity, it requires surgical pain management. This study aimed to collect all recent information about local and regional anaesthetic/analgesic techniques in a review of the literature describing the technique utilised. The various procedures described in this review use local anaesthetics to improve analgesia in the routine systemic anaesthetic protocol. The approach described in this paper is called multimodal analgesia and is used in addition to the normal standard anaesthetic protocol. These techniques proved effective in minimising responses to the surgical stimulus and ensured adequate intraoperative and postoperative analgesia. The routine use of multimodal analgesia is considered a useful alternative for pain management in canine ovariectomy, in that it minimises patient suffering, improves the recovery of rescue analgesia, increases drug savings, and improves animal outcomes. In addition, the use of these local and regional techniques ensures satisfactory analgesic coverage that lasts for the first hours postoperatively.

Analgesic comparison between topical irrigation (splash block) versus injection of lidocaine on the ovarian pedicle in canine ovariectomy

Objectives

The aim of this study was to compare the analgesic efficacy of topical irrigation versus injection of lidocaine on the ovarian pedicle to provide analgesia in bitches ovariectomy. In the current study were monitored: increased blood pressure, heart rate and respiratory rate to identify an acute intraoperative nociceptive response. These parameters were registered at six times during the surgical procedure: grasping of the ovary (time 1), dissection of the mesosalpinx (time 2), tightening of the first loop ligature (time 3), tightening of the second loop ligature (time 4), transection of the ovarian pedicle (time 5) and release of the ovary (time 6).

Material and Methods

Forty healthy bitches were randomly assigned in two groups (n = 20) to receive topical irrigation (splash block) of 2% lidocaine (C group) on both ovarian pedicle (2 mg/kg each), or an equal volume of lidocaine was injected at the same sites (R group).

Results

The results of the present study suggest that splash block may provide intraoperative analgesic effects equivalent to injection in the ovarian pedicle in dogs that have undergone ovariectomy. The lidocaine improved surgical analgesia during canine ovariectomy in both groups, and this action is not affected by the inoculation technique.

Clinical significance

Pain management in veterinary patients is a crucial component of appropriate patient care. Therefore, the need for achieving safer anaesthesia for surgical intervention is gaining much attention. Ovariectomy is a common surgical procedure in bitches with medium level of pain. This study concluded that considering its relative simplicity, low cost, and safety, both techniques could be used in daily clinical practice.

Contribution of Low-Dose Computerized Tomography With Digital Multiplanar Reconstructions in Thoracic Epidurography and Correlation With Sensory Block in Postoperative Analgesia

Background

The level of sensory block in postoperative epidural analgesia has been correlated with conventional contrast epidurography in only one study, while low-dose CT scan epidurography with multiplanar reconstruction may be a better tool for this purpose.

Objectives

The primary objective of this study was to evaluate, by CT imaging and digital multiplanar reconstruction, the spread and distribution of contrast medium injected into the epidural space through a catheter inserted in a low thoracic position for postoperative analgesia.

Materials and Methods

Ten patients undergoing major abdominal cancer surgery with effective epidural analgesia were prospectively included at postoperative day three. Two consecutive boluses of 5 mL of a mixture of ropivacaine and contrast medium were injected at 15 minutes intervals into the epidural space. Multislice low-dose CT scan epidurography and an assessment of the sensory block were performed before and after injection of the second bolus. The primary objective was to assess the contribution of CT scan epidurography to predict a correlation between the level of sensory block and the spread of the contrast medium in the epidural space; the secondary objective was to determine the agreement between the two methods.

Results

The spread of contrast material and the clinical sensory block significantly increased after the second injection (32%; P < 0.05). However, no highly significant correlation was observed between the two methods. A gap of two spinal segments of CT opacification was observed in two patients and was confirmed by clinical assessment.

Conclusions

CT epidurography is not closely correlated with a clinical assessment of epidural block; thus, a clinical assessment of the sensory block is mandatory. The use of opioid analgesia in combination with local anesthetics may compensate for the lack of efficacy of local anesthetics alone.

Reproducibility of current perception threshold with the Neurometer(®) vs the Stimpod NMS450 peripheral nerve stimulator in healthy volunteers: an observational study

PURPOSE

Current methods of assessing nerve blocks, such as loss of perception to cold sensation, are subjective at best. Transcutaneous nerve stimulation is an alternative method that has previously been used to measure the current perception threshold (CPT) in individuals with neuropathic conditions, and various devices to measure CPT are commercially available. Nevertheless, the device must provide reproducible results to be used as an objective tool for assessing nerve blocks.

METHODS

We recruited ten healthy volunteers to examine CPT reproducibility using the Neurometer(®) and the Stimpod NMS450 peripheral nerve stimulator. Each subject's CPT was determined for the median (second digit) and ulnar (fifth digit) nerve sensory distributions on both hands - with the Neurometer at 5 Hz, 250 Hz, and 2000 Hz and with the Stimpod at pulse widths of 0.1 msec, 0.3 msec, 0.5 msec, and 1.0 msec, both at 5 Hz and 2 Hz. Intraclass correlation coefficients (ICC) were also calculated to assess reproducibility; acceptable ICCs were defined as ≥ 0.4.

RESULTS

The ICC values for the Stimpod ranged from 0.425-0.79, depending on pulse width, digit, and stimulation; ICCs for the Neurometer were 0.615 and 0.735 at 250 and 2,000 Hz, respectively. These values were considered acceptable; however, the Neurometer performed less efficiently at 5 Hz (ICCs for the second and fifth digits were 0.292 and 0.318, respectively).

CONCLUSION

Overall, the Stimpod device displayed good to excellent reproducibility in measuring CPT in healthy volunteers. The Neurometer displayed poor reproducibility at low frequency (5 Hz). These results suggest that peripheral nerve stimulators may be potential devices for measuring CPT to assess nerve blocks.

Effect of epidural neuraxial blockade-dependent sedation on the Ramsay Sedation Scale and the composite auditory evoked potentials index in surgical intensive care patients

BACKGROUND/PURPOSE

Peripheral deafferentation induced by neuraxial anesthesia reduces the degree of cortical arousal. This study investigated whether epidural analgesia blockade decreased sedation, as measured by the rapidly extracted auditory evoked potentials index, A-line autoregressive index (AAI) and Ramsay Sedation Scale (RSS) in sedated surgical intensive care patients, and looked at whether this was a concentration-dependent effect of lidocaine.

METHODS

Forty patients underwent major lower abdominal surgery and received epidural analgesia in the surgical intensive care unit. Patients were continuously sedated with propofol to achieve an RSS value of 3, randomly divided into two groups, and received epidural analgesia with 10 mL of 0.5% or 1% lidocaine. Sedation was evaluated using the RSS and AAI, and analgesia was evaluated using a visual analog scale (VAS). RSS, AAI, electromyography (EMG) activity of AAI and VAS values were recorded at 5 minutes before and 30, 60 and 90 minutes after epidural lidocaine administration.

RESULTS

Epidural 0.5% lidocaine produced a reduction of AAI, EMG and VAS at 30, 60 and 90 minutes after administration. For 1% epidural lidocaine administration, AAI, EMG and VAS were also reduced at 30, 60 and 90 minutes after epidural lidocaine administration. However, there was no difference in the AAI between the two concentrations; moreover, no significant change was observed in the RSS.

CONCLUSION

Epidural lidocaine analgesia could potentiate sedation in patients evaluated by the AAI, but had no effect on the RSS. The present study suggests that the AAI could provide an objective and more precise index than the RSS in evaluation of sedation level in patients who are undergoing epidural pain management in the intensive care unit.

Developing biologically-based assessment tools for physical therapy management of neck pain

SYNOPSIS

Neck pain is a common and episodic condition that is treated using a spectrum of interventions known to be moderately effective but is associated with a significant incidence of chronic pain. Recently, there has been increased focus on defining biological aspects of neck pain. Studies have indicated that neurophysiological, biomechanical, and motor control abnormalities are present and may be useful either in prognosis or classification. We review some of these findings in the context of our own work defining biological markers that may form the basis for clinical tests that can be used for prognosis, classification, or outcome evaluation in patients with neck pain. We have identified abnormalities in neurophysiology using quantitative sensory testing (vibration, touch, and current perception) and response to cold provocation that are related to neck disability. We have identified altered muscle biochemistry by measuring circulating muscle proteins in a lumbar surgery model and are now applying those methods to whiplash injury. We have incorporated capnography into treatment to address central physiological changes present in some patients by monitoring and training CO2 levels. We have developed an innovative new test, the Neck Walk Index, that captures abnormal control of head movement during slow gait as a means of differentiating patients with neck pain from either unaffected controls or individuals with other pathologies. We have used time-varying 3-dimensional joint orientation kinematics to assess deficits in motor control during an upper extremity reach task, the results showing that poor coordination and control of the shoulder girdle leads to shoulder guarding and inconsistencies in elbow joint movement. Despite some promising early results, future research is needed to determine how these measures help clinicians to diagnose, evaluate, and forecast future outcome for patients who present with neck pain.

LEVEL OF EVIDENCE

Diagnosis, level 5.

The sensitization of a broad spectrum of sensory nerve fibers in a rat model of acute postoperative pain and its response to intrathecal pharmacotherapy

Further understanding of pathophysiology of postoperative acute pain is necessary for its better management. The methodology of current threshold (CT) determination by using sine-wave stimuli at 3 frequencies has been used to selectively and quantitatively analyze the function of the subsets of fibers (i.e., frequency of 5, 250, and 2000Hz recruits C-, Adelta-, and Abeta-fibers, respectively). This study investigated how surgical incision would affect the CTs, and then assessed the efficacy of intrathecal pharmacotherapy. The CT required to evoke a paw withdrawal response was assessed over time at stimulus frequencies of 5Hz (CT5), 250Hz (CT250), and 2000Hz (CT2000) in rats that had undergone surgical incision of the plantar skin and muscle. The CTs at all frequencies significantly decreased immediately after the incision. The decreased thresholds gradually recovered during the first week post-surgery. CT5 and CT250 (but not CT2000) remained significantly low even on day 7 post-surgery. Morphine at 5microg/10microL i.t. significantly reversed CT5 and CT250. NBQX (alpha-amino-3-hydroxy-5-methylisoxazole-4-propionic acid [AMPA]/kainate receptor antagonist) at 1.9 or 3.8microg/10microL i.t. significantly increased the thresholds over the pre-surgery threshold levels at all frequencies. MK-801 (N-methyl d-aspartate [NMDA] receptor antagonist) up to 13.5microg/10microL i.t. did not significantly affect CTs at any frequencies. In conclusion, a broad spectrum of sensory fibers (Abeta, Adelta, and C) is sensitized at the spinal and/or peripheral level in the postoperative acute pain state. Spinal AMPA/kainate receptors but not NMDA receptors play a significant role in this sensitization.

Determination of current threshold for paw withdrawal with sine-wave electrical stimulation in rats: Effect of drugs and alteration in acute inflammation

Electrical stimulation is widely used to assess the function of sensory nerves in humans. In the present study, the threshold current (CT) required to evoke a paw withdrawal response in rats was assessed with stepwise increases in current delivered as sinusoidal stimulation at frequencies of 2000 Hz (CT2000), 250 Hz (CT250) and 5 Hz (CT5). Baseline CT was 840+/-3 microA for CT2000, 267+/-2 microA for CT250 and 165+/-1 microA for CT5 (n=59). Intrathecal administration (1-10 microg/rat) of morphine selectively increased CT5 and CT250 (efficacy order was CT5>CT250>>CT2000=0), although systemic morphine (1-5mg/kg, S.C.) affected all three CTs (CT5>CT250>CT2000>0). Intrathecal pretreatment at day -3 of capsaicin (75 microg/rat) increased the thermal nociceptive threshold and selectively increased CT5 (CT5>>CT250, CT2000=0). Intraplantar carrageenan injection progressively decreased CT250 and CT5, but increased CT2000 for a 3h period. Intraperitoneal pretreatment with indomethacin (20mg/kg) attenuated carrageenan evoked CT alterations as well as progression of paw swelling and thermal hyperalgesia. In conclusion, low, but not high, frequency stimulation activated a withdrawal response which appears mediated by morphine and capsaicin sensitive primary afferents and this threshold was reduced in the presence of inflammation. These data suggest the validity of such stimulation in defining drug action in a nontissue injurious fashion.

Epidural ropivacaine infusion for the treatment of pain following axillary muscle-sparing thoracotomy: a dose-evaluation study

PURPOSE

We aimed to investigate the optimal dose of continuous epidural ropivacaine for effective analgesia with minimal side effects after axillary muscle-sparing thoracotomy.

METHODS

Sixty patients undergoing thoracic surgery via the axillary approach were studied. Patients were given continuous epidural ropivacaine at 6 (group R-6), 9 (group R-9), 12 (group R-12) or 18 mg x h(-1) (group R-18) in a randomized double-blinded fashion after surgery. All of the patients received nonsteroidal anti-inflammatory drugs (NSAIDs) every 6 h for 24 h postoperatively. Pain intensity was assessed under three conditions (at rest, on moving, and while coughing), at 4, 8, 16, 24, and 48 h after surgery, and the extent of sensory block was evaluated at the same time points. The ability of a patient to walk unaided was assessed at 24 and 48 h after surgery.

RESULTS

Pain intensity at rest and coughing was significantly higher in group R-6 than in the other groups at 16 h after surgery. Pain intensity during moving was significantly greater in group R-6 than in groups R-12 and R-18 at 16 h after surgery. Group R-18 exhibited a significantly greater extent of sensory block than the other groups. The number of patients who were not able to walk unaided 24 h after surgery was significantly greater in group R-18. There were no significant differences in the incidences of side effects among the groups.

CONCLUSION

Our results showed that epidural analgesia using ropivacaine, at 12 mg x h(-1), provided the best analgesia with few side effects.

Painless electrodiagnostic current perception threshold and pain tolerance threshold values in CRPS subjects and healthy controls: a multicenter study

The purpose of this study is to evaluate both painless and painful sensory transmission in patients with Complex Regional Pain Syndrome (CRPS) using the automated electrodiagnostic sensory Nerve Conduction Threshold (sNCT) test. This test generates reliable, painless Current Perception Threshold (CPT) and atraumatic Pain Tolerance Threshold (PTT) measures. Standardized CPT and PTT measures using constant alternating current sinusoid waveform stimulus at 3 different frequencies 5 Hz, 250 Hz, and 2 kHz (Neurometer CPT/C Neurotron, Inc. Baltimore, MD) were obtained from CRPS subjects at a distal phalange of the affected extremity and at an ipsilateral asymptomatic control site. Matched sites were tested on healthy subjects. Detection sensitivities for an abnormal PTT and CPT test were calculated based on specificity of 90% as determined from data obtained from healthy controls. A Spearman rank correlation was used to test for a significant association between presence of allodynia and an abnormal PTT or CPT at any frequency tested. Thirty-six CRPS subjects and 57 healthy controls were tested. The highest detection sensitivity of the PTT test from symptomatic test sites was 63% for the finger and 71% for the toe. PTT abnormalities were also detected, to a lesser degree, at the asymptomatic control site (41% finger control site, 16% toe control site). The highest CPT detection sensitivity at the symptomatic site was 37% for the finger site and 53% for the toe site. CPT abnormalities were also detected at the asymptomatic control site (29% finger control site, 37% toe control site). Eighty-six percent of the CRPS subjects had either a PTT or CPT abnormality at any frequency at the symptomatic site. There was a significant correlation between presence of allodynia and presence of an abnormal CPT and PTT, respectively (P < .01). The correlation coefficient was lower for CPT than for PTT, ie, 0.34 versus 0.6 for the finger and 0.48 versus 0.67 for the toe, respectively. In studied CRPS patients an abnormal PTT was detected with higher sensitivity than an abnormal CPT. Assessing PTT may become a useful electrodiagnostic quantitative sensory test for diagnosing and following the course of neuropathic pain conditions.

Bupivacaine caudal epidural anesthesia: assessing the effect of general anesthetic technique on block onset

BACKGROUND

The primary objective of this prospective, randomized trial was to compare the effect of propofol and sevoflurane on effectiveness of regional anesthesia. As a secondary objective, we aimed at evaluating the influence of age on neuraxial block profile.

METHODS

One hundred and thirteen healthy children aged <10 years, scheduled for general or urological surgical procedures were randomly allocated to receive either propofol or sevoflurane induction and maintenance. Children received caudal or lumbar epidural block depending on their weight and expected surgery. Time to onset of surgical anesthesia, intraoperative analgesic effectiveness, residual motor blockade, postoperative pain, and adverse effects were evaluated. To assess the influence of age on these measures children were further divided into three age groups: 0-24, 25-60 and >60 months.

RESULTS

The mean time to onset of surgical anesthesia was significantly shorter in the sevoflurane group than the propofol group (3.1 vs 4.7 min, P < 0.01), independent of the type of regional technique employed. Distress on arousal in recovery was increased in children receiving sevoflurane (P = 0.03). There was no significant difference in residual motor blockade between the groups but children between 0 and 24 months receiving sevoflurane had a higher incidence of residual motor blockade 3 h after local anesthetic injection (P = 0.01).

CONCLUSIONS

This study has demonstrated that general anesthesia with sevoflurane decreases the time to onset of surgical anesthesia relative to propofol anesthesia. This effect was most marked when sevoflurane anesthesia preceded caudal epidural blockade. The basis for this effect is most likely to be related to differential binding of the two anesthetic agents to receptors in the spinal cord that mediate immobility in response to surgical stimuli.

Effects of epidural anesthesia with 0.2% and 1% ropivacaine on predicted propofol concentrations and bispectral index values at three clinical end points

STUDY OBJECTIVE

To compare the effects of 0.2% epidural ropivacaine and those of 1% epidural ropivacaine on predicted propofol concentrations and bispectral index scores (BISs) at three clinical end points.

DESIGN

Randomized double-blind study.

SETTING

University hospital.

PATIENTS

Thirty-five (35) ASA physical status I and II patients scheduled for elective surgery of the lower abdomen.

INTERVENTIONS

Patients were randomly divided into 2 groups to receive epidurally 8 mL of 0.2% or 1% ropivacaine followed by the same solution at a rate of 6 mL/h.

MEASUREMENTS

Twenty minutes after starting ropivacaine, a target-controlled infusion of propofol was started to provide a predicted blood concentration of 3 microg/mL; it increased by 0.5 microg/mL every 60 seconds until all 3 clinical end points were reached, as follows: P1, when patients lost consciousness; P2, when patients failed to show pupillary dilation and skin vasomotor reflex to transcutaneous electric stimulation applied to the upper level of loss of cold sensation; and P3, when patients failed to show pupillary dilation and skin vasomotor reflex to transcutaneous electric stimulation applied to C5.

MAIN RESULTS

The effective concentration 50 values for both predicted blood and effect-site propofol concentrations were significantly larger in the 0.2% group than in the 1% group at all end points. The BIS at every end point was significantly smaller in the 0.2% group than in the 1% group.

CONCLUSIONS

During combined epidural-propofol anesthesia, unconsciousness and lack of response to noxious stimulation occurred at lower predicted concentrations with 1% epidural ropivacaine than with 0.2% epidural ropivacaine. The results also suggest that the BIS may not be a good indicator when propofol anesthesia is combined with epidural anesthesia.

Sensory assessment of epidural block for Caesarean section

BACKGROUND AND OBJECTIVE

Comparisons between the profile of regional blocks are difficult to make because different methods of testing are used among the studies. The aims of this prospective study were to describe the profile of epidural block by using a scoring system to evaluate the density of the block as assessed by the loss to pinprick, cold and touch sensation; to evaluate the extent of differential block and to determine whether there is any relationship between these three modalities of testing.

METHODS

We studied 85 parturients undergoing elective Caesarean delivery with epidural anaesthesia with pH adjusted lidocaine 2% with epinephrine 1:400,000 and sufentanil 10 microg. Assessment of sensory block was done in each dermatomal level bilaterally for loss to pinprick, cold and light touch sensation and the density of the block was evaluated on an ordinal scale every 5 min for 20 min and thereafter at 30 and 40 min.

RESULTS

We observed a two dermatomes differential block between the complete loss of cold sensation being cephalad and the complete loss of both pinprick and light touch sensation being caudal. We established a significant correlation between the scores used to assess the density of the block in the three different modalities by considering the pinprick score as reference (Spearman's rank correlation is 0.94, P<0.001 for pinprick vs. cold, 0.97, P<0.001 for pinprick vs. light touch).

CONCLUSIONS

By scoring the density of the block on an ordinal scale, knowing the level of the block to pinprick allows one to predict the level of the block to touch and vice versa.

Clinical evaluation of clonidine added to lidocaine solution for subarachnoid analgesia in sheep

Clonidine (CL) is a alpha2-adrenergic agonist that produces analgesia in animals and humans by a non-opiate alpha2-adrenergic action in the spinal cord dorsal horn. The objective of this prospective randomized study was to investigate the clinical effects of CL/lidocaine (LD) combination administered by the subarachnoid route in sheep. Each sheep received each of three treatments, at no shorter than weekly intervals. Treatments consisted of 0.003 mg/kg CL, 1.2 mg/kg LD and a combination of CL (0.003 mg/kg) and LD (1.2 mg/kg) (CLLD). Subarachnoid injections were given in all animals between the last lumbar and first sacral vertebra. Heart rate (HR), arterial pressures, respiratory rate, rectal temperature, analgesia, sedation, and motor blockade were determined before drug administration (basal) and 5, 10, 15 and 30 min after drug administration, and at 30-min intervals until loss of analgesia occurred. The duration of analgesia after subarachnoid CLLD administration was 187 +/- 24 min (mean +/- SD), i.e. more than twice of that obtained with CL (99 +/- 19 min) or LD (55 +/- 4.4 min) alone. In all sheep, CL, administered either alone or with LD, induced moderate sedation. After subarachnoid administration of three treatments, all sheep had ataxia and subsequent sternal recumbency. The CL treatment causes decreases in blood pressure (diastolic arterial pressure and mean arterial pressure) and HR. Data suggest that the CLLD combination could be used subarachnoidally in sheep requiring prolonged surgery.

Quantitative and fiber-selective evaluation of dose-dependent nerve blockade by intrathecal lidocaine in rats

We investigated whether cutaneous stimulus threshold (CST), as determined using a Neurometer, could be used for quantitative and differential nerve evaluation of reversible and irreversible nerve block following intrathecal lidocaine administration in rats. Rats with intrathecal catheters were randomly assigned to one of five groups (saline or 2, 5, 10, or 20% lidocaine). Prior to and 4 days after drug administration, CST was determined at 5, 250, and 2000 Hz. In the 2% lidocaine group, CST from end of lidocaine infusion to recovery from anesthesia was also monitored. Skin-clamp testing and gait observation were performed for comparison with CST findings. Behavioral examinations revealed persistent sensory or motor impairment lasting 4 days in groups receiving >/=5% lidocaine but not in the saline and 2% lidocaine groups. With 2% lidocaine, return to baseline CSTs at 5 and 250 Hz was delayed compared with thresholds at 2000 Hz. Although CSTs in the 5% group at 5 and 250 Hz increased significantly, thresholds at 2000 Hz did not differ from those in rats administered saline. CSTs with >/=10% lidocaine displayed no differences between frequencies. At each frequency, CSTs for rats with >/=5% lidocaine increased in a clearly concentration-dependent manner. These results suggest that CST testing enables evaluation of the different nerve functions for Abeta, Adelta, and C fibers in rats for lidocaine concentrations </=5% and allows quantitative assessment of persistent neurological deficit induced by lidocaine in rats.

Quantitative and selective evaluation of differential sensory nerve block after transdermal lidocaine

We evaluated the effect of transdermal lidocaine on differential sensory nerve block in 15 healthy volunteers. Lidocaine 10% gel was applied topically to a forearm and covered with a plastic film. Three types of sensory nerve fibers (Abeta, Adelta, and C fibers) were evaluated with a series of 2000-, 250-, and 5-Hz stimuli using current perception threshold (CPT) testing. Sensations of touch, pinprick, cold, and warmth were also measured. These measurements were made before the topical lidocaine (baseline), 60 min after the draping (T0), and at 1-h intervals until 5 h after T0 (T1 to T5). A significant increase in CPT compared with baseline was observed until T2 at 5 Hz and T4 at 250 Hz, whereas the increase in CPT at 2000 Hz continued throughout the study period. All subjects experienced the disappearance of pinprick and cold sensations, whereas touch and warmth sensations were detectable during the study period. We conclude that when lidocaine is applied transdermally, the sensitivity of nerves to local anesthetics is proportional to the axon diameters. However, pinprick and cold sensation are affected more strongly than other sensations at receptor sites.

IMPLICATIONS

We evaluated the effect of transdermal lidocaine on differential sensory nerve block in healthy volunteers. Our results show that the sensitivity of nerves to local anesthetics is proportional to the axon diameter.

Increased movement pain in osteoarthritis of the hands is associated with A beta-mediated cutaneous mechanical sensitivity

The relationship between joint pain and hyperalgesia has been explored in animal models of articular inflammation, but is yet to be shown in the most common rheumatologic condition: osteoarthritis. In this study, cutaneous thermal and mechanical pain thresholds were measured over the thumb of patients with osteoarthritis of the hands. In symptomatic patients, pain was manipulated through resisted active movement of the thumb. Provocation of movement pain (MP) was associated with a sustained fall in mechanical pain thresholds. Thermal pain thresholds remained stable during increases in joint pain. Increased mechanical sensitivity after exacerbation of MP was alleviated by A beta fiber blockade. It appears that superficial tenderness over the osteoarthritic thumb fluctuates with pain arising from movement of the joint. It is concluded that dorsal horn mechanisms contribute to MP-related hyperalgesia in osteoarthritis of the hands.

Comparison of 1% and 2% lidocaine epidural anaesthesia combined with sevoflurane general anaesthesia utilizing a constant bispectral index

BACKGROUND

The authors compared the effects of epidural anaesthesia with lidocaine 1% and lidocaine 2% on haemodynamic variables, sevoflurane requirements, and stress hormone responses during surgery under combined epidural/general anaesthesia with bispectral index score (BIS) kept within the range 40-50.

METHODS

Thirty-three patients undergoing lower abdominal surgery were randomly divided into two groups to receive lidocaine 1% or 2% by epidural with sevoflurane general anaesthesia. Sevoflurane was adjusted to achieve a target BIS of 40-50 during maintenance of anaesthesia with nitrous oxide 60% in oxygen. Measurements included the inspired (FI(SEVO)) and the end-tidal sevoflurane concentrations (E'(SEVO)), blood pressure (BP), and heart rate (HR) before surgery and every 5 min during surgery for 2 h. Plasma samples were taken immediately before and during surgery for measurements of catecholamines, cortisol, and lidocaine.

RESULTS

During surgery, both groups were similar for HR, BP and BIS, but FI(SEVO) and E'(SEVO) were significantly higher and more variable with lidocaine 1% than with 2%. Intraoperative plasma concentrations of epinephrine and cortisol were found to be higher with lidocaine 1% as compared with 2%.

CONCLUSIONS

To maintain BIS of 40-50 during combined epidural/general anaesthesia for lower abdominal surgery, sevoflurane concentrations were lower and less variable with lidocaine 2% than with 1%. In addition, the larger concentration of lidocaine suppressed the stress hormone responses better.

Sevoflurane Requirements to Suppress Responses to Transcutaneous Electrical Stimulation During Epidural Anesthesia with 0.5% and 1% Lidocaine

We sought to determine general anesthetic requirements to suppress skin vasomotor reflex (SVmR) and pupillary dilation (PD) in response to transcutaneous electrical stimulation (TES) during combined epidural-general anesthesia. Thirty-five patients undergoing lower abdominal surgery were randomly divided into 2 groups to epidurally receive 0.5% (Group 1) or 1% lidocaine (Group 2) with sevoflurane anesthesia. A bolus injection of either lidocaine was followed by the infusion of the same solution, and the central dermatomal level of loss of cold sensation (C) was determined. After the induction of general anesthesia with 5% sevoflurane and 67% nitrous oxide, nitrous oxide was discontinued, and sevoflurane concentration was decreased. TES was given at both site C and site three dermatomal segments (U) cephalad to C to determine the end-tidal sevoflurane concentration required to suppress SVmR and PD. End-tidal sevoflurane concentration that suppressed both responses was larger in Group 1 than in Group 2 at both sites and was larger at site U than at site C in both groups. We conclude that sevoflurane requirements to suppress SVmR and PD in response to TES during combined epidural-general anesthesia are different depending on the concentration of lidocaine and the site where surgical stimulation is applied.

IMPLICATIONS

We evaluated sevoflurane requirements to suppress skin vasomotor reflex and pupillary dilation in response to a transcutaneous electrical stimulation at the surgical site during combined epidural-general anesthesia. Our results indicate that when epidural anesthesia is combined, general anesthetic requirements decrease depending on the lidocaine concentration for epidural anesthesia and the site where surgical stimulation is applied.

Effects of Tourniquet Ischemia on Current Perception Thresholds in Healthy Volunteers

The neuroselective effects of tourniquet ischemia/compression in healthy volunteers were evaluated using the automated electrodiagnostic sensory Nerve Conduction Threshold (sNCT) test. The sNCT evaluation generates reliable, painless Current Perception Threshold (CPT) measures. Standardized CPT measures using constant alternating current sinusoid waveform stimulus at 3 different frequencies 5 Hz, 250 Hz, and 2 kHz (NeurometerEG CPT/C Neurotron, Inc. Baltimore, MD) were obtained from 10 individuals at baseline and after 5, 10, 15, and 20 minutes of tourniquet ischemia and 30 minutes post-tourniquet release. The data were analyzed to determine the significance of any changes in CPTs. Increases in CPTs after 15 and 20 minutes of tourniquet ischemia at 2000 Hz and 250 Hz reached statistical significance. There were no significant changes in 5 Hz CPT measures. The results of this study demonstrate the ability of the sNCT test to quantify previously described differential neuroselective effects of tourniquet ischemia on sensory nerve function. Demonstration of statistically significant increases in CPT values at 2000 Hz and 250 Hz secondary to tourniquet ischemia, with no change in 5 Hz CPT values, is consistent with the understanding that 2000 Hz sine wave stimuli activate the large myelinated sensory fibers, 250 Hz sine wave stimuli activate small myelinated sensory fibers, and 5 Hz sine wave stimuli activate small unmyelinated sensory fibers.