The effect of motor activity on the onset and progression of brachial plexus block with bupivacaine: a randomized prospective study in patients undergoing arthroscopic shoulder surgery.

BACKGROUND: A decreased latency of onset of neural blockade has been noted when muscular exercise of the hand was performed after supraclavicular brachial plexus block using lidocaine. In this observational study, we examined the effect of repetitive muscle contraction of the hand on the speed of onset of interscalene brachial plexus block (ISB) using bupivacaine. METHODS: Forty patients were enrolled, all of whom received an ISB as one component of their anesthetic management for elective arthroscopic shoulder surgery. Patients were asked either to rest their arms after the performance of the ISB (nonexercise group) or to perform a repetitive hand exercise for 5 min (exercise group). Bilateral hand grip strength and tolerance to transcutaneous electrical stimulation were used to quantify the degree of motor and sensory blockade. RESULTS: Patients in the exercise group had a statistically significant lower tolerance to transcutaneous electrical stimulation 20 min after completion of the block (P < 0.05). CONCLUSIONS: Our results imply that attempting to use a frequency-dependent conduction block with repetitive motor activity as a clinical adjuvant to brachial plexus block with bupivacaine is without merit.

Buprenorphine added to the local anesthetic for axillary brachial plexus block prolongs postoperative analgesia.

BACKGROUND AND OBJECTIVES: Buprenorphine added to local anesthetic solutions for supraclavicular block was found to triple postoperative analgesia duration in a previous study when compared with local anesthetic block alone. That study, however, did not control for potentially confounding factors, such as the possibility that buprenorphine was affecting analgesia through intramuscular absorption or via a spinal mechanism. To specifically delineate the role of buprenorphine in peripherally mediated opioid analgesia, the present study controlled for these 2 factors. METHODS: Sixty American Society of Anesthesiologists (ASA) P.S. I and II, consenting adults for upper extremity surgery, were prospectively assigned randomly in double-blind fashion to 1 of 3 groups. Group I received local anesthetic (1% mepivacaine, 0.2% tetracaine, epinephrine 1:200,000), 40 mL, plus buprenorphine, 0.3 mg, for axillary block, and intramuscular (IM) saline. Group II received local anesthetic-only axillary block, and IM buprenorphine 0.3 mg. Group III received local anesthetic-only axillary block and IM saline. Postoperative pain onset and intensity were compared, as was analgesic medication use. RESULTS: The mean duration of postoperative analgesia was 22.3 hours in Group I; 12.5 hours in group II, and 6.6 hours in group III. Differences between groups I and II were statistically significant (P =.0012). Differences both between groups I and III and II and III were also statistically significant (P <.001). CONCLUSIONS: Buprenorphine-local anesthetic axillary perivascular brachial plexus block provided postoperative analgesia lasting 3 times longer than local anesthetic block alone and twice as long as buprenorphine given by IM injection plus local anesthetic-only block. This supports the concept of peripherally mediated opioid analgesia by buprenorphine.

Effect of bupivacaine and levobupivacaine on exocytotic norepinephrine release from rat atria.

BACKGROUND: The cardiotoxic mechanism of local anesthetics may include interruption of cardiac sympathetic reflexes. The authors undertook this investigation to determine if clinically relevant concentrations of bupivacaine and levobupivacaine interfere with exocytotic norepinephrine release from cardiac sympathetic nerve endings. METHODS: Rat atria were prepared for measurements of twitch contractile force and [H]-norepinephrine release. After nerve endings were loaded with [H]-norepinephrine, the tissue was electrically stimulated in 5-min episodes during 10 10-min sampling periods. After each period, a sample of bath fluid was analyzed for radioactivity and [H]-norepinephrine release was expressed as a fraction of tissue counts. Atria were exposed to buffer alone during sampling periods 1 and 2 (S1 and S2). Control atria received saline (100 microl each, n = 6 atria) in S3-S10. Experimental groups (n = 6 per group) received either bupivacaine or levobupivacaine at concentrations (in microM) of 5 (S3-S4), 10 (S5-S6), 30 (S7-S8), and 100 (S9-S10). RESULTS: Bupivacaine and levobupivacaine decreased stimulation-evoked fractional [H]-norepinephrine release with inhibitory concentration 50% values of 5.1 +/- 0.5 and 6.1 +/- 1.3 microM. The inhibitory effect of both local anesthetics (approximately 70%) approached that of tetrodotoxin. Local anesthetics abolished the twitch contractions of atria with inhibitory concentration 50% values of 12.6 +/- 5.0 microM (bupivacaine) and 15.7 +/- 3.9 microM (levobupivacaine). In separate experiments, tetrodotoxin inhibited twitch contractile force by only 30%. CONCLUSIONS: The results indicate that clinically relevant cardiotoxic concentrations of bupivacaine and levobupivacaine markedly depress cardiac sympathetic neurotransmission. A possible mechanism of local anesthetics in reducing evoked norepinephrine release from sympathetic endings is blockade of tetrodotoxin-sensitive fast sodium channels.

ALLEVIATION OF PAIN IN CANCER PATIENTS BY ADRENAL MEDULLARY TRANSPLANTS IN THE SPINAL SUBARACHNOID SPACE.

The treatment of intractable pain with currently available therapeutic regimens is often unsatisfactory due to tolerance and untoward complications. Studies in our laboratory have suggested that the transplantation of adrenal medullary tissue into the spinal subarachnoid space can significantly reduce pain in animal models, most likely via release of opioid peptides and catecholamines. The current study was an initial attempt to assess the potential for adrenal medullary transplants in the spinal subarachnoid space to alleviate pain in humans. Donor adrenal medullary tissue was prepared for transplantation in our laboratory. One cc of adrenal medullary tissue was transplanted via lumbar puncture in five patients suffering from terminal cancer pain. Pain levels were determined using a Visual Analog Pain Scale prior to and following the transplantation procedure. In addition, records of narcotic intake and activity were kept. When possible, CSF samples were collected via lumbar puncture for biochemical and cytological analysis. Four of the patients demonstrated progressive decreases in pain scores following the procedure, with concomitant reductions in narcotic intake. Three patients remained pain free, two for over 10 mo. One patient, who developed spinal cord compression secondary to metastasis, was initially pain free, but the pain returned after 10 wk. The fifth patient had no pain reduction by 1 mo following the procedure, but further information was unavailable due to poor patient compliance. In most cases, spinal cerebrospinal fluid (CSF) samples revealed increased levels of met-enkephalin and/or catecholamines following the transplants. The results of this study suggest that adrenal medullary transplants in the spinal subarachnoid space have potential as an alternative approach to the management of chronic pain in humans.