Desensitizing the posterior interosseous nerve alters wrist proprioceptive reflexes

PURPOSE

The presence of wrist proprioceptive reflexes after stimulation of the dorsal scapholunate interosseous ligament has previously been described. Because this ligament is primarily innervated by the posterior interosseous nerve (PIN) we hypothesized altered ligamento-muscular reflex patterns following desensitization of the PIN.

METHODS

Eight volunteers (3 women, 5 men; mean age, 26 y; range 21-28 y) participated in the study. In the first study on wrist proprioceptive reflexes (study 1), the scapholunate interosseous ligament was stimulated through a fine-wire electrode with 4 1-ms bipolar pulses at 200 Hz, 30 times consecutively, while EMG activity was recorded from the extensor carpi radialis brevis, extensor carpi ulnaris, flexor carpi radialis, and flexor carpi ulnaris, with the wrist in extension, flexion, radial deviation, and ulnar deviation. After completion of study 1, the PIN was anesthetized in the radial aspect of the fourth extensor compartment using 2-mL lidocaine (10 mg/mL) infiltration anesthesia. Ten minutes after desensitization, the experiment was repeated as in study 1. The average EMG results from the 30 consecutive stimulations were rectified and analyzed using Student's t-test. Statistically significant changes in EMG amplitude were plotted along time lines so that the results of study 1 and 2 could be compared.

RESULTS

Dramatic alterations in reflex patterns were observed in wrist flexion, radial deviation, and ulnar deviation following desensitization of the PIN, with an average of 72% reduction in excitatory reactions. In ulnar deviation, the inhibitory reactions of the extensor carpi ulnaris were entirely eliminated. In wrist extension, no differences in the reflex patterns were observed.

CONCLUSIONS

Wrist proprioception through the scapholunate ligament in flexion, radial deviation, and ulnar deviation depends on an intact PIN function. The unchanged reflex patterns in wrist extension suggest an alternate proprioceptive pathway for this position. Routine excision of the PIN during wrist surgical procedures should be avoided, as it alters the proprioceptive function of the wrist.

TYPE OF STUDY/LEVEL OF EVIDENCE

Therapeutic IV.

Single stimulation of the posterior cord is superior to dual nerve stimulation in a coracoid block

BACKGROUND

Both multiple injection and single posterior cord injection techniques are associated with extensive anesthesia of the upper limb after an infraclavicular coracoid block (ICB). The main objective of this study was to directly compare the efficacy of both techniques in terms of the rates of completely anesthetizing cutaneous nerves below the elbow.

METHODS

Seventy patients undergoing surgery at or below the elbow were randomly assigned to receive an ICB after the elicitation of either a single radial nerve-type response (Radial group) or of two different main nerve-type responses of the upper limb, except for the radial nerve (Dual group). Forty milliliters of 1.5% mepivacaine was given in a single or a dual dose, according to group assignment. The sensory block was assessed in each of the cutaneous nerves at 10, 20 and 30 min. Block performance times and the rates of complete anesthesia below the elbow were also noted.

RESULTS

Higher rates of sensory block of the radial nerve were found in the Radial group at 10, 20 and 30 min (P<0.05). The rates of sensory block of the ulnar nerve at 30 min were 97% and 75% in the Radial and in the Dual groups, respectively (P<0.05). The rate of complete anesthesia below the elbow was also higher in the Radial group at 30 min (P<0.05).

CONCLUSIONS

Injection of a local anesthetic after a single stimulation of the radial nerve fibers produced more extensive anesthesia than using a dual stimulation technique under the conditions of our study.

A comparison of stimulation patterns in axillary block: part 2

BACKGROUND AND OBJECTIVES

Radial plus musculocutaneous nerve stimulation may have a predominant role in the success of an axillary block, producing more extensive anesthesia of the upper limb than median plus musculocutaneous nerve stimulation. However, no comparison has been made with ulnar plus musculocutaneous nerve stimulation. We compared the extent of both sensory and motor block after ulnar plus musculocutaneous nerve stimulation or radial plus musculocutaneous nerve stimulation.

METHODS

Sixty patients were randomly assigned to receive an axillary block using either radial plus musculocutaneous or ulnar plus musculocutaneous nerve stimulation with 40 mL plain 1.5% mepivacaine. Patients were assessed for sensory block by the pinprick method at 5 and 20 minutes.

RESULTS

No statistically significant differences were found in the rates of anesthesia at 20 minutes in the cutaneous nerve distributions of the upper limb between radial plus musculocutaneous and ulnar plus musculocutaneous nerve stimulation except for the following nerves: radial (90% and 63.3%, respectively), medial cutaneous of the forearm (83.3% and 100%, respectively), and medial cutaneous of the arm (73.3% and 93.3%, respectively). Global sensory score (minimum: 0; maximum: 12 points) at 20 minutes was significantly higher after radial plus musculocutaneous than after ulnar plus musculocutaneous nerve stimulation: 12 (11-13) and 11 (10-12), respectively. The rates of median nerve blockade were 50% and 53%, respectively.

CONCLUSIONS

Radial plus musculocutaneous nerve stimulation produced more extensive anesthesia of the upper limb than did ulnar plus musculocutaneous nerve stimulation. However, there is not an optimal combination of 2 responses in axillary brachial plexus block.

Spread of injectate associated with radial or median nerve-type motor response during infraclavicular brachial-plexus block: an ultrasound evaluation

BACKGROUND AND OBJECTIVES

We have compared ultrasound characteristics of spread during infraclavicular brachial-plexus blocks by use of electrically evoked radial-nerve- or median-nerve-type distal motor responses to guide the injection of 30 mL of 1.5% mepivacaine.

METHODS

Consecutive patients who required surgery distal to the upper arm were prospectively included in this study. With radial- or median-evoked distal motor response at a stimulating current intensity of less than 0.5 mA, patients were distributed into 2 equal groups. An independent investigator blinded to the evoked response described ultrasound characteristics of the spread of local anesthetic and assessed block quality 30 minutes after placement. A quality diffusion score proportional to the extent and intensity of spread around the axillary artery was used, and dynamic movements during injection were noted.

RESULTS

Thirty-two patients were included. With radial-nerve-type motor response, the success rate of infraclavicular plexus block was 100%, but 3 supplemental axillary blocks were requested with median-nerve-type motor response. Quality diffusion scores were significantly higher with radial-nerve-type as compared with median-nerve-type motor response (P = .03). Injection after radial-nerve-type motor response resulted in a typical and reproducible ultrasound feature of posterior local-anesthetic spread associated with medial and upper movement of the axillary artery. With median-nerve-type motor response, failed blocks were associated with a specific posterior displacement of the axillary artery that resulted from superficial spread.

CONCLUSION

We have demonstrated that as compared with median-nerve-type motor response, injection performed after a radial-nerve-type motor response promoted reproducible and remarkable ultrasound spread characteristics associated with complete sensory block of the 3 cords at 30 minutes.

A Comparison of Injection at the Ulnar and the Radial Nerve in Axillary Block Using Triple Stimulation

BACKGROUND AND OBJECTIVES

A triple-stimulation technique for axillary block consists of the localization and injection of 2 nerves, median and musculocutaneous, which lie superior to the axillary artery, and of 1 nerve, the radial, which lies inferior. However, in some patients, the ulnar nerve is located first during the search for the radial nerve. The aim of this study was to verify if an ulnar motor response could be considered a satisfactory endpoint as a radial motor response.

METHODS

This study was a prospective, randomized, double-blinded study. Ninety patients received a triple-injection axillary brachial plexus block in which the radial nerve (group RAD) or the ulnar nerve (group ULN) was located and injected inferior to the axillary artery. Patients were assessed for sensory and motor block by a blinded investigator at 5-minute intervals over 30 minutes.

RESULTS

A statistically significant higher overall block success rate was recorded in group RAD (91% vs. 73%), and this result was related to a larger success rate for anesthetizing the radial nerve (95% vs. 77%). A statistically significant shorter onset time of sensory block for the radial nerve was recorded in group RAD versus group ULN (9 +/- 5 min vs. 16 +/- 7 min), whereas the reverse was true for the ulnar nerve (13 +/- 7 min for group RAD vs. 10 +/- 3 min for group ULN). The time to perform the block was slightly but statistically significantly shorter in group ULN (6.5 +/- 1.7 min vs. 7.8 +/- 1.8 min).

CONCLUSIONS

Local anesthetic injection at the ulnar nerve significantly reduces the efficacy and prolongs the onset time of the radial-nerve block when triple-stimulation axillary block is performed.

A Comparison of Proximal and Distal Radial Nerve Motor Responses in Axillary Block Using Triple Stimulation

BACKGROUND AND OBJECTIVES

Stimulation of the radial nerve at the axilla may cause either a proximal movement (forearm extension) or distal movements (supination, wrist or finger extension). In the most recent studies on axillary block, only a distal twitch was accepted as valid. However, this approach was based only on clinical experience. The aim of this study was to verify if a proximal motor response can be considered a satisfactory endpoint.

METHODS

This was a prospective, randomized, double-blinded study. One hundred fifty patients received a triple-injection axillary brachial plexus block in which the radial nerve was located by a proximal (group PROX) or a distal motor response (group DIST). Patients were assessed for sensory and motor block of the branches of the radial nerve by a blinded investigator at 5-minute intervals over 30 minutes.

RESULTS

An 81% success rate for anesthetizing the sensory distal branches of the radial nerve was seen in group PROX; a significantly higher success rate was recorded in group DIST (95%). The onset time of sensory block for the distal branches of the radial nerve was significantly shorter in group DIST (9.9 +/- 6 v 15.4 +/- 7 minutes). The time to perform the block was slightly shorter and the localization of the nerve simpler in group PROX. The overall block success rate was not significantly different in the 2 groups.

CONCLUSIONS

Local anesthetic injection at the proximal radial twitch significantly reduces the efficacy and prolongs the onset time of the radial nerve block. Searching for distal response is significantly more difficult and time consuming than searching for proximal response. However, it does not significantly increase patient discomfort or adverse effects.

The radial nerve should be blocked before the ulnar nerve during a brachial plexus block at the humeral canal

PURPOSE

The brachial plexus block through the humeral canal as described by Dupré is indicated in hand and forearm surgery. This block requires a multi-stimulation technique that emphasizes the necessity of a rigorous and safe technique. Nerve injury associated with regional anesthesia can entail significant morbidity for patients. Thus, we investigated the brachial block sequence in terms of unintended nerve stimulation as a surrogate of potential nerve injury.

METHODS

Sixty patients were randomly allocated in two groups of 30. In Group I the radial nerve was blocked before the ulnar nerve. In Group II the ulnar nerve was blocked before the radial nerve. During the radial nerve approach we recorded, if present, an ulnar nerve response. During the ulnar nerve approach we recorded, if present, a radial nerve response.

RESULTS

In Group I while looking for the radial nerve, in 50% of the cases, an ulnar motor response was recorded. In Group II while looking for the ulnar nerve, a radial motor response was recorded in 10% of the cases.

CONCLUSION

Our results indicate that the radial nerve should be blocked before the ulnar nerve when performing a brachial plexus block at the humeral canal.

Clonidine added to bupivacaine enhances and prolongs analgesia after brachial plexus block via a local mechanism in healthy volunteers

BACKGROUND AND OBJECTIVE

The addition of clonidine to local anaesthetics enhances pain relief after peripheral nerve block, but the site of action is unproven.

METHODS

Seven healthy volunteers underwent three brachial block procedures using bupivacaine 0.25% 1 mg kg(-1) + epinephrine 1:200,000 (=local analgesic) in a randomized, double-blind cross-over fashion: (a) control treatment: local analgesic with 0.9% sodium chloride solution for the block and an intramuscular injection of saline; (b) intramuscular treatment: local analgesic with 0.9% NaCl for block and an intramuscular injection of clonidine 2 microg kg(-1) and (c) block treatment: local analgesic with clonidine 2 microg kg(-1) for block and an intramuscular injection of saline.

RESULTS

The onset and duration of complete blockade (sensory/motor/temperature) was evaluated in the four nerve regions of the hand and forearm. Additionally, sedation score, blood pressure, heart rate and plasma clonidine concentrations were determined. The median duration of complete sensory blockade was 270 min (range 0-600) for block treatment compared to 0 min (range 0-480) for intramuscular treatment (P < 0.05) and 0 min (range 0-180) for control treatment (P < 0.05). Motor and temperature blockade exhibited similar results. Administration of clonidine was associated with sedation and a decrease in heart rate and blood pressure independent of the route of administration. Plasma clonidine concentrations were lower for block compared to the intramuscular treatment.

CONCLUSIONS

The admixture of clonidine to bupivacaine plus epinephrine prolongs and enhances brachial plexus blockade. Lower clonidine plasma concentrations for block treatment strongly suggest a local effect.

Sensorimotor polyneuropathy with 5-aminosalicylic acid: a case report

A 69-year-old man with ulcerative colitis (UC) developed sensorimotor polyneuropathy. First, he received salazosulphapyridine (SASP) as treatment for the UC. The symptoms of UC disappeared immediately, but he developed skin eruptions and dysesthesia in his lower limbs. When SASP was changed to 5-aminosalicylic acid (5-ASA), his skin eruptions were resolved, however, he developed weakness and atrophy in his right arm as well as progressive worsening of the dysesthesia in his legs and gait disturbance. Deep tendon reflexes (DTR) were absent in all extremities. After 5-ASA was discontinued, the polyneuropathy symptoms recovered gradually. This clinical course suggests that the sensorimotor polyneuropathy may have been caused by 5-ASA.

Radial tunnel syndrome in an elite power athlete: a case of direct compressive neuropathy

Radial tunnel syndrome (RTS) is thought to result from intermittent and dynamic compression of the posterior interosseous nerve (PIN) in the proximal part of the forearm associated with repeated supination and pronation. The diagnostic criteria encompassing RTS are purely clinical and the term "radial tunnel syndrome" has become controversial because of the lack of focal motor weakness in the majority of patients diagnosed with RTS. Retrospective cadaveric and surgical studies have revealed several areas within the forearm in which the PIN may become entrapped. Recent studies have suggested that the PIN is "fixed" in the supinator muscle and that wrist pronation is the actual movement that places the most stress on the PIN. The patients most often afflicted with RTS appear to be those who perform repetitive manual tasks involving rotation of the forearm and athletes involved in racket sports. Surgical exploration with decompression of the PIN is often required in patients with RTS. We present the first case of RTS occurring in an elite power athlete and believe this case represents a direct compressive sensory neuropathy. The optimum nonsurgical treatment plan for the elite athlete in training for competition and the cause of this compressive neuropathy in power athletes will be discussed.

Modality-related scalp responses after electrical stimulation of cutaneous and muscular upper limb afferents in humans

To elucidate whether the selective electrical stimulation of muscle as well as cutaneous afferents evokes modality-specific responses in somatosensory evoked potentials (SEPs) recorded on the scalp of humans, we compared scalp SEPs to electrical stimuli applied to the median nerve and to the abductor pollicis brevis (APB) motor point. In three subjects, we also recorded SEPs after stimulation of the distal phalanx of the thumb, which selectively involved cutaneous afferents. Motor point and median nerve SEPs showed the same scalp distribution; moreover, very similar dipole models, showing the same dipolar time courses, explained well the SEPs after both types of stimulation. Since the non-natural stimulation of muscle afferents evokes responses also in areas specifically devoted to cutaneous input processing, it is conceivable that, in physiological conditions, muscle afferents are differentially gated in somatosensory cortex. The frontocentral N30 response was absent after purely cutaneous stimulation; by contrast, it was relatively more represented in motor point rather than in mixed nerve SEPs. These data suggest that the N30 response is specifically evoked by proprioceptive inputs.

Accidental subcutaneous injection of elemental mercury. A case report

Subcutaneous injection of elemental mercury is a very rare situation. The authors report the case of a 31-year-old man who accidentally injected an unknown quantity of metallic mercury into his left forearm. Several surgical procedures were required to reduce the blood and urinary levels of mercury. However, the patient never developed clinical signs of chronic poisoning. This observation confirms the lower risk of acute or chronic poisoning in subcutaneous injection of mercury and the need for early excision of contaminated tissue.

The effects of propofol on heart rate, arterial pressure and adelta and C somatosympathetic reflexes in anaesthetized dogs

The effects of propofol on mean arterial pressure, heart rate and Adelta and C somatosympathetic reflexes, recorded in renal nerves, evoked by repeated individual supramaximal electrical stimuli applied to radial nerves, were observed in anaesthetized, paralysed and artificially ventilated dogs. Propofol was infused at rates from 0.4 to 2.0 mg kg-1 min-1. Mean C and Adelta reflexes were abolished at plasma concentrations (mean, SEM) of 24.3 (3.3) and 29.2 (2.6) microg mL-1 (P < 0.05), respectively, when mean arterial pressure and mean heart rate were reduced by approximately 55% (P < 0.01) and 26% (P > 0.05), respectively. Recovery of Adelta and C reflexes occurred at plasma concentrations of 13.1 (2.3) and 9.9 (1.3) microg mL-1 (P > 0.05), respectively. There was a log- arithmically linearly related fall in mean arterial pressure by 70% up to a plasma concentration approximately 97 microg mL-1 (r 2=0.7) with a 28% reduction in heart rate which was uncorrelated with the plasma concentrations (r 2=0.12). In conclusion, propofol abolished Adelta and C responses at comparable plasma concentrations and caused a major reduction in both mean arterial pressure and heart rate which is consistent with resetting of the baroreflexes. The reduction in mean arterial pressure was logarithmically, linearly correlated with a progressive increase in plasma concentrations without evidence of a ceiling effect.

Secondary hyperalgesia to punctate mechanical stimuli. Central sensitization to A-fibre nociceptor input

Tissue injury induces enhanced pain sensation to light touch and punctate stimuli in adjacent, uninjured skin (secondary hyperalgesia). Whereas hyperalgesia to light touch (allodynia) is mediated by A-fibre low-threshold mechanoreceptors, hyperalgesia to punctate stimuli may be mediated by A- or C-fibre nociceptors. To disclose the relative contributions of A- and C-fibres to the hyperalgesia to punctate stimuli, the superficial radial nerve was blocked by pressure at the wrist in nine healthy subjects. Secondary hyperalgesia was induced by intradermal injection of 40 microg capsaicin, and pain sensitivity in adjacent skin was tested with 200 micron diameter probes (35-407 mN). The progress of conduction blockade was monitored by touch, cold, warm and first pain detection and by compound sensory nerve action potential. When A-fibre conduction was blocked completely but C-fibre conduction was fully intact, pricking pain to punctate stimuli was reduced by 75%, but burning pain to capsaicin injection remained unchanged. In normal skin without A-fibre blockade, pain ratings to the punctate probes increased significantly by a factor of two after adjacent capsaicin injection. In contrast, pain ratings to the punctate probes were not increased after capsaicin injection when A-fibre conduction was selectively blocked. However, hyperalgesia to punctate stimuli was detectable immediately after block release, when A-fibre conduction returned to normal. In conclusion, the pricking pain to punctate stimuli is predominantly mediated by A-fibre nociceptors. In secondary hyperalgesia, this pathway is heterosynaptically facilitated by conditioning C-fibre input. Thus, secondary hyperalgesia to punctate stimuli is induced by nociceptive C-fibre discharge but mediated by nociceptive A-fibres.

[1% mepivacaine and axillary block: duration of the sensory and motor blockade]

OBJECTIVES

To assess the duration of both sensory and motor blockade of brachial plexus with 40 mL 1% mepivacaine after axillary or midhumeral approach.

STUDY DESIGN

Prospective, open, non-comparative, multicentric study.

PATIENTS

One hundred and eighty patients, ASA physical class 1 and 2, scheduled for hand or forearm surgery under brachial plexus block were included.

METHODS

A midhumeral or axillary brachial plexus block using a nerve stimulator was performed with 40 mL of 1% mepivacaine. Sensory blockade was tested for each cutaneous area (median, radial, ulnar, musculocutaneous and medial cutaneous nerve of the forearm) using pin-prick. Motor blockade was assessed by grip strength of the hand. Incidence and duration of analgesia, anaesthesia and motor blockade were assessed. The incidence of tourniquet pain and the time when pain occurred were determined.

RESULTS

According to the nerve area tested, analgesia and anaesthesia were obtained in 98% and 85% of cases respectively; duration of anaesthesia was between 150 +/- 40 to 167 +/- 49 minutes and duration of analgesia was from 184 +/- 50 to 205 +/- 51 minutes. Duration of paralysis was 144 +/- 40 minutes and duration of paresis was 190 +/- 51 minutes. Pain occurred in three out of 138 patients at tourniquet inflation and in six patients after completion of surgery.

CONCLUSIONS

Mid humeral or axillary block with 40 mL of 1% mepivacaine is highly successful and provides efficient surgical anaesthesia for various surgical procedures of intermediary duration.

Infraclavicular brachial plexus block effects on respiratory function and extent of the block

BACKGROUND AND OBJECTIVES

Axillary block is devoid of severe respiratory complications. However, incomplete anesthesia of the upper limb is the main disadvantage of the technique. Theoretically, the more proximal infraclavicular approach would produce a more extensive block without the risk of pneumothorax. However, neither its effects on respiratory function nor a detailed characterization of the extent of neural block has been assessed. The goal of this study was to evaluate the possible changes in respiratory function and also the extent of the block after infraclavicular block.

METHODS

We performed an infraclavicular block with a mixture of 40 mL 1.5% plain mepivacaine and 4 mL 8.4% sodium bicarbonate in 20 patients. Forced expiratory volumes were measured before and 15 minutes after the injection of local anesthetic, and sensory and motor block were evaluated at 10 and 20 minutes.

RESULTS

We did not find significant differences from baseline in the forced expiratory volumes in any of the patients. Axillary and musculocutaneous nerve distributions had the lowest rate of sensory block at 20 minutes.

CONCLUSIONS

Infraclavicular block does not produce a reduction in respiratory function.

The use of a selective axillary nerve block for outpatient hand surgery

Although no guidelines concerning discharge criteria after axillary plexus block are available, many institutions consider recovery of motor function as a critical factor. With the midhumeral approach, the four main nerves of the upper extremity can be blocked separately using a peripheral nerve stimulator. The aim of this double-blind study was to block the radial (R) and musculocutaneous (MC) nerves with lidocaine, and the median (M) and ulnar (U) nerves with bupivacaine to recover motor function of the elbow and wrist more rapidly while maintaining long-lasting postoperative analgesia at the operative site. Patients undergoing surgery for Dupuytren's contracture were randomized into two groups in a double-blind fashion: in the control group (n = 17), each of the four nerves was infiltrated with 10 mL of a mixture of 2% lidocaine and 0.5% bupivacaine, whereas in the selective group (n = 17), the R and MC nerves were blocked with 10 mL of 2% lidocaine each and the M and U nerves were blocked with 10 mL of 0.5% bupivacaine each. Recovery of motor block was significantly faster in the selective group (231 +/- 91 vs 466 +/- 154 min). However, time to first sensation of pain was not different between groups (707 +/- 274 vs 706 +/- 291 min). In conclusion, this new approach at the midhumeral level enables the anesthesiologist to selectively administer local anesthetics on different nerves.

IMPLICATIONS

In outpatients undergoing surgery for Dupuytren's contracture, a midhumeral block was used with the musculocutaneous and radial nerves blocked by lidocaine and the median and ulnar nerves blocked with bupivacaine. Recovery of motor function and time to discharge were shorter compared with patients who received the mixture on all four nerves.

Comparison of transthecal and subcutaneous single-injection digital block techniques

A randomized double-blinded study was performed on 20 normal volunteers to evaluate 2 different techniques of single-injection digital anesthesia. Single-injection transthecal digital block technique was used to anesthetize 1 index finger and single-injection subcutaneous technique to block the other index finger. Pain and light touch were evaluated and sensory nerve-conduction studies were performed on both index fingers. These data were obtained prior to the nerve blocks and then at 10-minute intervals until recovery from the anesthesia. The method of anesthesia was found to have no effect on the distribution, onset, and duration of anesthesia. Median and radial nerve sensory nerve action potential amplitude reductions following digital anesthesia were also not influenced by the technique of anesthesia. Single-injection subcutaneous block was found to be easier to administer and to produce less pain during and 24 hours after injection than did the single-injection transthecal technique.

The orthogonal two-needle technique: a new axillary approach to the brachial plexus

Ninety-eight patients scheduled for elbow, forearm, wrist or hand surgery were allocated randomly to one of two different techniques of brachial plexus block, both using the axillary approach. The blocks were all performed at the level of the insertion of the lateral margin of the pectoralis major muscle on the humerus. The same mixture and volume of anaesthetic solution (30 mL of a mixture of equal parts of 0.5% bupivacaine with adrenaline 1:200 000 and 2% lignocaine) was injected through two needles positioned above and below the axillary artery, in the fascial compartments containing the median and ulnar nerves, respectively. Confirmation of correct needle placement was obtained by elicitation of paraesthesias. In one group of patients (n = 40) the needles were inserted parallel to the axillary artery pathway and the anaesthetic solution was injected toward the apex of the axilla. In a second group (n = 58) the needles were inserted orthogonally with respect to the neurovascular bundle pathway, aimed towards the posterior fascial compartment containing the radial nerve. Using the second technique, all the terminal branches of the brachial plexus were more frequently involved in the block, including the distribution of the musculocutaneous nerve. It seems likely that the inclination of the needles causes a preferential spread of the anaesthetic solution which follows the direction of the needle shaft.

Physiological effects produced by botulinum toxin treatment of upper limb dystonia. Changes in reciprocal inhibition between forearm muscles

Patients with upper limb dystonia have abnormal reciprocal inhibition between flexor and extensor forearm muscles. To see whether botulinum toxin treatment alters segmental motor system function, we studied reciprocal inhibition between forearm flexor and extensor muscles, before and after botulinum toxin injection in forearm muscles in 12 patients with upper limb dystonia. Reciprocal inhibition was studied by conditioning the H reflex in forearm flexors with a radial nerve stimulus delivered at a range of time intervals. Botulinum toxin injection improved upper limb dystonia. Before botulinum toxin injection, the dystonic patients had a decreased second phase of reciprocal inhibition. After botulinum toxin injections this second abnormal phase of reciprocal inhibition increased. Botulinum toxin did not change the first phase of reciprocal inhibition. Botulinum toxin treatment also reduced the M wave and the H reflex by a similar amount but left the Hmax:Mmax ratio unchanged. Ample evidence has shown that the therapeutic effects of botulinum toxin in dystonia depend mainly on its neuromuscular junction blocking action. Our data now suggest a concurrent indirect effect on spinal cord circuitry, probably through the action of botulinum toxin on the intrafusal neuromuscular junction.

Radial or brachial artery injections for intraarterial regional anesthesia for hand surgery?

BACKGROUND AND OBJECTIVES

The aim of this study was to determine the optimal injection site for the intraarterial regional anesthesia for hand surgery.

METHODS

Forty-two adult patients undergoing elective hand surgery were studied. 0.5% lidocaine plain 1.5 mg/kg was injected over 3 minutes into the radial artery (group 1), or the brachial artery (group 2) through a 22 or 20 gauge Teflon catheter.

RESULTS

Two patients (one in each group) were excluded due to technical problems. Onset of analgesia in the hand was faster after radial artery injection (P < .05). Onset of analgesia in the forearm was similar in both groups. Catheterization time, operating conditions, motor block, offset of analgesia, injection, surgical and tourniquet pain scores, and patient's acceptance were similar. Ten patients in group 1 and nine patients in group 2 needed supplemental analgesia at the start of surgery. Median nerve paresthesias were unintentionally elicited during catheterization in three patients in group 2. Six patients (two in group 1 and four in group 2) had minor systemic adverse effects after tourniquet release. Seven patients in group 1 and five in group 2 developed minor bruises after catheterization. No permanent sequelae of injections were observed.

CONCLUSIONS

Radial artery is preferred for intraarterial regional anesthesia. Compared with the brachial artery, injection in the radial artery produces faster analgesia in the hand and reduces the risk of damage to the median nerve.

Preferential channelling of anaesthetic solution injected within the perivascular axillary sheath

Preferential channelling of anaesthetic solution injected into the perivascular axillary sheath was investigated in 40 patients undergoing elective orthopaedic upper-limb surgery. Three needles, with different approaches and inclinations, were inserted near the three main terminal branches of the brachial plexus using an axillary approach. Separate boluses of anaesthetic solution (12 ml of a mixture of equal parts of 0.5% bupivacaine with 1:200,000 adrenaline and 2% lignocaine) were injected in random order through each needle, and back flow through the other two needles was noted. Back flow was observed, mainly in the needle nearest to the radial nerve during injection of the anaesthetic solution in the superior and inferior aspects of the brachial artery, and in the needle close to the ulnar nerve when the injection was performed posterior to the artery, near the radial nerve. These results could be related to the trapping of anaesthetic solution in unconnected compartments and to the slope of the needle injecting the anaesthetic solution which spreads preferentially along a gradient following the needle shaft direction.

Warm local anaesthetic--effect on latency of onset of axillary brachial plexus block

A double-blind, controlled trial was conducted to determine whether warming local anaesthetic reduces the onset time of axillary brachial plexus block. Forty patients were randomised into two groups. The control group received local anaesthetic solution at room temperature (22 +/- 1 degrees C), while the experimental group received the solution at body temperature (37 +/- 1 degrees C). A solution of 40 ml of lignocaine 1.5% with adrenaline 1:200,000 was used for all patients. Warming the local anaesthetic was not demonstrated to reduce the latency of onset of blockade.

Lack of a ceiling effect for intrathecal buprenorphine on C fibre mediated somatosympathetic reflexes

We observed that buprenorphine 20 micrograms kg-1 i.v. in dogs caused an initial significant reduction in both A delta and C fibre mediated somatosympathetic reflexes evoked by tibial and radial nerve stimulation, to approximately 75% and 70% of control values. Larger doses (up to 100 micrograms kg-1 i.v.) had progressively less effect and the mean responses were depressed to only approximately 65% and 55% of control, indicating a ceiling effect. Buprenorphine 450 micrograms intrathecally (i.t.) completely abolished tibial C fibre reflexes, but 20% of A delta responses could not be eliminated with doses up to 1050 micrograms i.t. Fentanyl 100 micrograms kg-1 i.v. or 150 micrograms i.t. after buprenorphine i.v. or i.t., respectively, had little additional effect. This study confirms the limited ceiling effect of buprenorphine on nociceptive reflexes when administered systemically, and provides evidence that when administered i.t. in sufficient doses it abolishes the C responses (lack of ceiling effect for C responses), but the A delta responses show a plateau or ceiling effect.

Specific enhancement by fentanyl of the effects of intrathecal bupivacaine on nociceptive afferent but not on sympathetic efferent pathways in dogs

BACKGROUND

Bupivacaine alone, or in combination with opioids, has been shown to provide adequate pain relief without motor paralysis. This study examined the effects of bupivacaine administered intrathecally on sympathetic efferent and A delta- and C-fiber-mediated afferent pathways in dogs and the interactions with intrathecal fentanyl.

METHODS

Spontaneous activity in renal sympathetic nerves was observed, as were reflex somatosympathetic responses mediated by A delta and C fibers evoked by supramaximal electrical stimulation of the tibial and radial nerve. Bupivacaine was administered intrathecally in doses of 0.5, 1, 2, and 3.5 mg, each in 0.5 ml, and 7 mg in 1 ml with or without pretreatment with 5.4 mg intrathecal fentanyl (ED25 for depression of C tibial reflexes) in each of five preparations.

RESULTS

Bupivacaine caused a dose-dependent inhibition of both A delta- and C-fiber-mediated somatosympathetic responses evoked by tibial nerve stimulation. The depression of radial and tibial nerve reflexes and spontaneous renal sympathetic activity was similar. Pretreatment with fentanyl (5.4 micrograms, intrathecally) depressed tibial C-fiber reflexes by only 23.8% without any significant effect on either tibial A delta or radial A delta and C fiber responses. Fentanyl markedly enhanced the effect of subsequent doses of bupivacaine on tibial A delta and C reflexes without any additional effect on either spontaneous sympathetic activity or radial responses.

CONCLUSIONS

Intrathecal bupivacaine has no selectivity for the afferent and efferent pathways, and intrathecal fentanyl acts synergistically to enhance the effect of bupivacaine on the afferent pathway without a measurable effect on sympathetic outflow.

Radial and median nerve conduction velocities in workers exposed to lead, copper, and zinc: a follow-up study for 2 years

To evaluate the interactive effects of lead, zinc, and copper on the peripheral nervous system in man, we measured maximal motor and sensory conduction velocities (MCV and SCV) in the distal radial and median nerves in 19 gun metal foundry workers with asymptomatic increased absorption of these metals twice at a 12-month interval. The workers' initial blood lead (BPb) concentrations ranged from 16 to 64 (mean, 42) micrograms/dl. The principal findings in the present study indicated that (1) radial and median nerve conduction velocities were significantly slowed in the gun metal foundry workers; (2) indicators of lead absorption were inversely related to radial nerve conduction velocities, whereas indicators of copper and zinc absorption were positively correlated with the radial and median nerve conduction velocities; and (3) yearly changes in MCV in the radial nerve and in SCV in the median nerve were positively correlated with the changes in indicators of copper and zinc absorption. These findings suggest that zinc and copper antagonize the subclinical neurologic effects of lead. Also, the radial and median nerve conduction velocities provide important indicators of subclinical lead toxicity.

[The measurement of the sensory antidromic nerve conduction velocity in the dog]

Sensory neurography is a diagnostic aid in the evaluation of peripheral nerve function. Up to now, the measurement of the orthodromic nerve conduction velocity has been supposed to be the only valuable method in veterinary medicine. However, there is always a certain risk because the procedure requires immobilized animals. In this article, the measurement of the sensory antidromic nerve conduction velocity in the superficial radial and the superficial peroneal nerve of the dog is described as an alternative method. Usually, this procedure can be done without immobilisation or general anesthesia. Thus, the antidromic nerve conduction velocity represents a valuable screening method for evaluation of peripheral nerve function. In dogs without changes in laboratory values and without signs of neurologic disease, the nerve conduction velocity is 52.5 +/- 6.6 m/s (mu +/- s) for the superficial radial nerve and 49.4 +/- 5.7 m/s (mu +/- s) for the superficial peroneal nerve.

[The major nerve trunks are not the primary action site of intravenous regional anesthesia]

In a patient suffering from a deep penetrating wound of the left forearm and radial nerve injury, the administration of intravenous regional anesthesia (IVRA) was followed by prompt analgesia of the whole arm while intense pain could still be elicited by stimulating radial nerve stump. Complete radial nerve block was present 10 min later confirming that initial blockade of nerve terminals substantially contributes to IVRA and suggesting that a 10 min delay is indicated for optimal analgesia after IVRA whenever a major nerve injury is suspected.

Axillary plexus block using a peripheral nerve stimulator: single or multiple injections

This prospective, randomized, double-blind study was undertaken to evaluate the success rates of axillary brachial plexus block performed with the help of a peripheral nerve stimulator when either one, two or four of the major nerves of the brachial plexus were located. Seventy-five patients undergoing upper limb surgery were randomly allocated to one of the following five groups according to the nerve and number of nerves to be located; G-1: musculo-cutaneous, radial, median and ulnar nerves; G-2: musculo-cutaneous plus one of the other three nerves; G-3: radial nerve; G-4: median nerve; G-5: ulnar nerve. The sensory block was evaluated before surgery and cutaneous anaesthesia was considered to be present when the needles of a Wartenberg Pinwheel were no longer felt in all the dermatomes of the nerves implicated in the surgical site. Otherwise, the block was considered to need completion before surgery. Only one out of the 15 patients in G-1 and G-2 needed completion of their block before surgery whereas seven out of 15 for G-3 and eight out of 15 for G-4 and G-5 needed completion of their block (P less than 0.01). We conclude that when performing an axillary block with the help of a peripheral nerve stimulator, stimulation of the musculo-cutaneous nerve and one other nerve or stimulation of all four major nerves of the brachial plexus gives a higher success rate than stimulation of only one nerve, whether the stimulated nerve is the median, radial or ulnar.

Effect of low and high concentrations of alfentanil administered intrathecally on A delta and C fibre mediated somatosympathetic reflexes

We have studied the effects of alfentanil administered intrathecally on somatosympathetic reflexes evoked by stimulation of radial and tibial nerves in 10 anaesthetized and paralysed dogs. In five animals, alfentanil was administered in doses of 100, 100, 200 and 400 micrograms in 0.8 ml and 800 micrograms in 1.6 ml prepared from the formulation of 500 micrograms ml-1. Five others received alfentanil (high concentration formulation, 5 mg ml-1) in doses of 500 and 2000 micrograms in 0.5 ml and 5000 micrograms in 1 ml. C fibre tibial nerve reflexes were depressed by 100 micrograms and abolished with doses of 200-400 micrograms, but the A delta response remained unaffected. A delta responses were depressed also and abolished, respectively, by doses of alfentanil 2000 micrograms and 5000 micrograms. At the larger, but not the smaller, concentration there was evidence of baroreflex sensitization probably caused by systemic absorption of the drug.

Auditory event-related potential (P300) in relation to peripheral nerve conduction in workers exposed to lead, zinc, and copper: effects of lead on cognitive function and central nervous system

By measuring auditory event-related potential (P300 and N100) and peripheral nerve conduction velocities, the subclinical effects of lead, zinc, and copper on the central and peripheral nervous system were examined in 22 male gun metal foundry workers exposed to these metals. Their blood lead (BPb) concentrations ranged from 12 to 59 micrograms/dl (median 30). Control subjects were 14 healthy workers, employed at the same factory, who had never been occupationally exposed to these metals. In the gun metal foundry workers, the latencies of P300 and N100 were significantly prolonged; the latency of P300 was significantly correlated with BPb concentrations and other indicators of lead absorption. Similarly, the maximal motor and sensory conduction velocities in the radial and median nerves were significantly slowed, and were significantly correlated with indicators of lead absorption. The data suggest that lead exposure at low levels affects cognitive and central auditory nervous system function together with peripheral nerve conduction.

[Experiences with continuous nerve block of the wrist]

Continuous nerve blocks are effective analgesics for physiotherapy following operative procedures on gliding tissues. In the upper extremity, continuous axillary blocks are regularly used, leading to weak muscular action and even paralysis, although active muscle action is wanted. With continuous wrist blocks, extrinsic motor function of the hand remains undisturbed. Placement of a polyethylene catheter near the nerves with instillation of a local anesthetic (carbostesine 0.5, 3-4 ml per nerve) provides complete anesthesia of the hand without loss of extrinsic motor function. After 124 nerve blocks in 60 patients, no complications (infections, nerve irritations or lesions) have been observed. Continuous wrist blocks are indicated for postoperative treatment after tenolysis, joint mobilisation or arthrolysis, open reduction and internal fixation and in certain cases of chronic pain care.

Kainic acid microinjected into the cat raphe dorsal nucleus modulates the somatosensory evoked potentials and their cycles of excitability

Studies were made on the effect of the neuroexcitatory agent kainic acid, microinjected into raphe dorsal nucleus by glass micropipette and an air pressure system in doses ranging from 0.2 to 24.0 nmol (in volumes from 0.05 microliter to 0.47 microliter), on the somatosensory evoked potentials and their cycles of recovery (excitability) obtained from cortex (primary somatosensory and parietal associative), thalamus (ventral posterolateral nucleus and centre median nucleus), mesencephalic reticular formation and raphe dorsal nucleus. Kainic acid in doses higher than 3 nmol exerted an activating effect on the evoked potentials and their recovery cycles especially in thalamus and mesencephalic reticular formation. The analysis of these electrophysiological parameters revealed that the non-specific structures were involved to a larger extent in the activating effect of kainic acid than the specific ones. The morphological changes were not severe and were limited to a part of the raphe dorsal nucleus neurons. Our data indicate that kainic acid injected into raphe dorsal nucleus modulates (in direction of facilitation) the somatosensory evoked potentials and their cycles of excitability obtained in some brain structures. The results suggest that this nucleus is involved in the somatosensory information processing in a non-specific manner.

Changes in the EEG-reactions to repetitive peripheral and central electrical stimulation by intraraphedorsal kainic acid in the cat

The effect of kainic acid (KA) microinjected into the dorsal raphe nucleus (NRD) of the cat through glass micropipette by means of an air pressure system in doses ranging from 2.3 to 23.5 nmol on the electroencephalographic (EEG)-reactions elicited by repetitive (6-10 Hz) peripheral (somatic and visual) or central electrical stimulation was investigated. A significant facilitation of the driving reaction evoked by rhythmic subcutaneous electrical stimulation of the forepaw was found after KA, while the driving reaction elicited by repetitive photostimulation did not change. The cortical rhythmic reactions to repetitive electrical stimulation of the specific and nonspecific nuclei of the thalamus and of the caudate nucleus (where inhibitory mechanisms are known to be involved) diminished or disappeared when generalized paroxysmal spontaneous activity occurred after kainic acid. The EEG-reaction to stimulation of the mesencephalic reticular formation was significantly facilitated after KA. The repetitive electrical stimulation of the ventral posterolateral nucleus, the centre median and the mesencephalic reticular formation also provoked the appearance of paroxysmal EEG activity or afterdischarge which in some cases developed into epileptic seizures. The data show that kainic acid injected into the dorsal raphe nucleus increases (probably by disinhibition) the excitability level of some forebrain structures connected with the nucleus.

Lack of opiate effects on cat C polymodal nociceptive fibers

The direct application of preservative-free morphine sulfate (1.5%, 1 ml, 19.8 mumol) or fentanyl (0.06%, 1 ml, 1.07 mumol) on the superficial radial or saphenous nerve of cats did not alter the response of single C polymodal nociceptive fibers (PMNs) to noxious radiant heat stimulation of their peripheral receptive fields. Intravenous administration of fentanyl (100 or 200 micrograms/kg, 0.179 or 0.358 mumol/kg) also showed a similar lack of effect on the radiant heat evoked responses of single PMNs. Slight changes in the mean latencies following drug administration were recognized, which were not statistically significant. The use of morphine (1.5%, 1 ml, 19.8 mumol) with preservatives (chlorbutanol 0.5% and sodium bisulfite less than 0.1%) caused conduction block of PMNs within 6-15 min. Subsequent washout of the drug resulted in the return of the unitary discharges within 8 min. Lidocaine (0.25 and 0.5%, 10.7 mumol and 21.4 mumol) caused conduction block within 5-18 min. These data support the classically held concept that opiates, in clinically useful concentrations, do not alter peripheral nerve function.

Fentanyl and alfentanil suppress brainstem pain transmission

The effects of intravenously administered fentanyl (25 micrograms/kg, n = 9; 50 micrograms/kg, n = 5) and alfentanil (12.5 micrograms/kg, n = 5; 25 micrograms/kg, n = 7) on the noxiously evoked, single-unit activity of cells in the nucleus reticularis gigantocellularis (NRGC) were studied in decerebrate cats. Only cells of the NRGC excited exclusively by supramaximal electrical stimulation of A delta fibers (noxious stimulation) of the superficial radial nerve were studied. The noxiously evoked activity of all cells in the NRGC was suppressed by the administration of opioids (by 58 and 88% for fentanyl, 25 micrograms/kg and 50 micrograms/kg, respectively; by 35 and 78% for alfentanil 12.5 micrograms/kg and 25 micrograms/kg, respectively). Fentanyl and alfentanil effects were antagonized by the intravenous administration of naloxone. These results indicate that opioid suppression of noxiously evoked activity is seen in neurons located in the brainstem, and thus suppression of brainstem neurons may be important in the production of fentanyl and alfentanil analgesia.

The correlation between the recovery rate of neurotoxic esterase activity and sensitivity to organophosphorus-induced delayed neurotoxicity

Neurotoxic esterase (NTE) has been proposed to be the initiation site of organophosphorus compound-induced delayed neurotoxicity (OPIDN). There are two apparent problems associated with this hypothesis: NTE activity in the brain returns to nearly normal levels before the onset of the neuropathy, and NTE is present in and inhibited by organophosphorus compounds in young animals and other species which are relatively insensitive to the neurotoxic effects of these compounds. This paper presents data suggesting that differences in the recovery rates of NTE activity may account for some of these discrepancies. First, the onset of recovery of NTE activity following sc administration of 1.7 mg/kg of O,O-diisopropylphosphorofluoridate (DFP) in the hen sciatic nerve occurred several days later than in the brain. Furthermore, recovery was slower in distal than proximal parts of the nerve. This information indicates that NTE activity is depressed for a longer period at the site of the neuropathy than it would appear from the measurement of NTE activity in brain. Second, the rate of recovery of NTE activity was faster in the brains of chicks, of rats, and of hens treated with a daily po dose of 15 mg/kg cortisone acetate than it was in untreated hens. However, there was no significant increase in the NTE recovery rate in the peripheral nerves of the chicks or the cortisone-treated hens. Thus, it appears that although slower distal recovery could account for the greater sensitivity of longer axons to OPIDN, other factors are operating in chicks and cortisone-treated hens.

Selective effect of fentanyl on group III and IV somatosympathetic reflexes

The effect of fentanyl on sympathetic reflexes evoked by supramaximal electrical stimulation of the radial nerve, and the subsequent reversal of its effects by naloxone, have been observed in 10 dogs anaesthetized with alpha-chloralose, paralysed with suxamethonium and artificially ventilated. During infusions of 5 micrograms kg-1 min-1 the late, long-latency, sympathetic response evoked by unmyelinated fibres was abolished at a mean dose of 27 micrograms kg-1 (SD 12.6 micrograms kg-1) after which the early, short-latency response evoked by small myelinated fibres was eliminated at a mean dose of 90.3 micrograms kg-1 (SD 54.6 micrograms kg-1) so that there was no longer any response to stimulation of the radial nerve. During a subsequent infusion of naloxone (200 micrograms min-1) the late response returned to control values at a mean dose of 0.5 mg and subsequently the early response reappeared to return to control values at a total dose of 1.6 mg. In 2 preparations phrenic nerve activity was abolished after 6.1 and 17.4 micrograms kg-1 of fentanyl and returned immediately before the late response, during the infusion of naloxone. In 2 preparations, induced tolerance occurred so that the early response could not be eliminated.

The transcortical reflex triggered by cutaneous or muscle stimulation in the cat with a penicillin epileptic focus: relative importance of regions 3a and 4

After establishment of a cortical penicillin epileptic focus in the cat, stimulation of an anterior paw muscle can evoke a late myographic response (LMR) in the same muscle via a transcortical reflex. It is shown here that (1) an LMR can also be obtained with cutaneous stimulation in the region of the muscle; (2) an LMR cannot be elicited when the focus in on area 3a; (3) after inactivation of area 3a by TTX, the motor cortex evoked potential and spike thresholds are increased for proprioceptive but not for cutaneous stimulation, and the LMR persists. It is concluded that area 4 is the critically important structure for the triggering of an LMR. The results concerning area 3a are discussed in terms of this region's efferent connections to the motor cortex and to the spinal cord.

Cutaneous and subcutaneous complications of calcium infusions

Five infants with hypocalcemia experienced complications after treatment with calcium gluconate intravenously. Inadvertent soft tissue extravasation resulted in erythema, subcutaneous calcification, tissue necrosis, skin slough, and transient radial nerve damage with wrist drop, the latter previously unreported. The soft tissue lesions may be mistaken for cellulitis, abscess, calcified hematoma, or osteomyelitis, resulting in unnecessary antibiotic therapy or surgical intervention. Initially, no clinical abnormality may be apparent. The lesions appear from days to weeks following extravasation. Radiographs are initially negative but soft calcification appears in one to three weeks. Follow-up x-ray films show complete resorption of the calcium over several months. Skin sloughs heal in four to six weeks without skin grafting. Extreme care in the parenteral use of calcium gluconate and conservative treatment of the complications is advocated.