Determining minimum effective anesthetic concentration of hyperbaric bupivacaine for spinal anesthesia

Nicotinamide adenine dinucleotide (NAD+) repletion attenuates bupivacaine-induced neurotoxicity

Bupivacaine is one of the most toxic local anesthetics but the mechanisms underlying its neurotoxicity are still unclear. Intracellular nicotinamide adenine dinucleotide (NAD(+)) depletion has been demonstrated to play an essential role in neuronal injury. In the present study, we investigated whether intracellular NAD(+) depletion contributes to bupivacaine-induced neuronal injury and whether NAD(+) repletion attenuates the injury in SH-SY5Y cells. First, we evaluated the intracellular NAD(+) content after bupivacaine exposure. We also examined the cellular NAD(+) level after pretreatment with exogenous NAD(+). We next determined cell viability and the apoptosis rate after bupivacaine treatment in the presence or absence of NAD(+) incubation. Finally, cell injuries such as nuclear injury, reactive oxygen species (ROS) production, and mitochondrial depolarization were detected after bupivacaine treatment with or without NAD(+) pretreatment. Bupivacaine caused intracellular NAD(+) depletion in a time- and concentration-dependent manner. Cellular NAD(+) replenishment prevented cell death and apoptosis induced by bupivacaine. Importantly, exogenous NAD(+) attenuated bupivacaine-induced nuclear injury, ROS production, and mitochondrial depolarization. Our results suggest that NAD(+) depletion is necessary for bupivacaine-induced neuronal necrosis and apoptosis, and that NAD(+) repletion attenuates neurotoxicity resulting from bupivacaine-treatment.

What Is the Minimum Effective Volume of Local Anesthetic Required for Sciatic Nerve Blockade? A Prospective, Randomized Comparison Between a Popliteal and a Subgluteal Approach

For sciatic nerve blockade, no study has defined the optimal volume of local anesthetic required to block the nerve. The current, prospective, randomized investigation was designed to find a minimum volume of 1.5% mepivacaine required to block the sciatic nerve using the subgluteal and posterior popliteal approaches. A total of 56 patients undergoing foot surgery were randomly assigned to receive sciatic nerve block by means of a posterior subgluteal (group subgluteal, n = 28) or a posterior popliteal (group popliteal, n = 28) approaches. All blocks were performed with the use a nerve stimulator (stimulating frequency, 2 Hz, intensity 1.5-0.5 mA) and a perineural stimulating catheter. In all patients, plantar flexion of the foot was elicited at <0.5 mA, to maintain consistency among groups. The volume of local anesthetic used in each patient was based on the modified Dixon's up-and-down method. Complete anesthesia was defined as complete loss of pinprick sensation in the sciatic nerve distribution with concomitant inability to perform plantar or dorsal flexion of the foot 20 min after injection. The mean volume of local anesthetic required to block the sciatic nerve was 12 +/- 3 mL in the subgluteal group and 20 +/- 3 mL in the popliteal group (P < 0.05). The ED95 for adequate block of the sciatic nerve was 17 mL in the subgluteal group and 30 mL in the popliteal group. The authors conclude that a larger volume of local anesthetic is necessary to block the sciatic nerve at a more distal site (popliteal approach) as compared with a more proximal level (subgluteal approach).

Intrathecal anesthesia

PURPOSE OF REVIEW

Development of new drugs and special techniques, as well as changes in health care organization have markedly influenced the use of spinal block and its indications. The present review overviews recent developments in local anesthetic drugs, side effects and special techniques for intrathecal anesthesia.

RECENT FINDINGS

Severe complications after spinal anesthesia are acceptably rare. The cardiovascular effects associated with sympathetic block are more frequent but may successfully be treated with volume expansion and administration of vasoactive drugs while the multimodal approach to prevention of such side effects can also reduce the incidence. Based on recent magnetic resonance imaging studies the volume of cerebrospinal fluid at the lumbosacral level is the main determinant of the effects produced by intrathecal injection of local anesthetic solutions. Unfortunately, it is not possible to estimate the volume of cerebrospinal fluid at the lumbosacral region in clinical practice, but it is clear that the total dose of local anesthetic injected into the subarachnoid space is the primary determinant of both therapeutic and unwanted effects of spinal anesthesia. There is overwhelming evidence of the potential risk for neurological dysfunction associated with spinal lidocaine. This evidence is even more relevant in outpatients, in whom lidocaine is primarily indicated. On the other hand, several studies have demonstrated the efficacy and safety of using small doses of long-acting agents, such as bupivacaine or ropivacaine, to produce a short spinal block. The addition of small doses of opioids further helps to minimize the dose of local anesthetic solution required, without affecting the recovery profile from spinal block. The extensive use of pencil-point designs for spinal needles, and the availability of needles of very small size have allowed a significant reduction in the incidence of postdural puncture headache.

SUMMARY

The changes in health care organization observed during the past few years have forced us to change the indications for and clinical uses of intrathecal anesthesia techniques in accordance with the changing needs of surgery. The development of new drugs and special techniques for spinal anesthesia will further improve the clinical use of this old but trusted technique.