Anesthesiology
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Comparative Study
Different brain activation patterns to pain and pain-related unpleasantness during the menstrual cycle.
The changes in the functional magnetic resonance imaging signal during anticipation, pain stimulation, and the poststimulation periods were investigated to determine whether changes in sex hormones affect brain activity. ⋯ During surgical and medical procedures, requirements of anesthetic and analgesic and anxiolytic drugs may be reduced during the follicular phase and increased during the luteal phase. These results highlight the need to consider the effects of the sex hormones in women when designing clinical or neuroimaging studies or when treating patients for pain and pain-related unpleasantness.
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Spinal cord damage during interscalene brachial plexus block has been attributed to needle entry into the spinal canal. The purpose of this study was to identify the angles and depths of needle insertion that increase the likelihood of such an event, using the traditional classic interscalene approach and two more proximal entry points. ⋯ With the classic approach to the interscalene block, there is a greater possibility of the needle passing through the intervertebral foramen if the needle is advanced too deeply. More proximal entry points and techniques that use a more steeply angled needle may reduce the risk of entry into the spinal space.
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Comparative Study
Painful peripheral nerve injury decreases calcium current in axotomized sensory neurons.
Reports of Ca(2+) current I(Ca) loss after injury to peripheral sensory neurons do not discriminate between axotomized and spared neurons. The spinal nerve ligation model separates axotomized from spared neurons innervating the same site. The authors hypothesized that I(Ca) loss is a result of neuronal injury, so they compared axotomized L5 dorsal root ganglion neurons to spared L4 neurons, as well as neurons from rats undergoing skin incision alone. ⋯ Axotomy is required for I(Ca) loss. I(Ca) loss correlated with changes in the biophysical properties of sensory neuron membranes during action potential generation, which were due to I(Ca) loss leading to decreased outward Ca(2+)-sensitive K currents. Taken together, these results suggest that neuropathic pain may be mediated, in part, by loss of I(Ca) and the cellular processes dependent on Ca(2+).
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Nerve injury that produces behavioral changes of allodynia and hyperalgesia in animals is associated with electrophysiologic changes in dorsal root ganglion (DRG) cells. The introduction of drugs into the DRG or the peripheral nerve that alter calcium, sodium, or potassium channel activity may be of therapeutic benefit after nerve injury. For this reason, the authors sought to determine whether drugs that do not ordinarily cross the blood-nerve barrier will enter the DRG after intravenous or regional injection and to determine whether nerve injury alters drug access to DRGs or peripheral nerves. ⋯ In both intact and nerve-injured animals, fluorescein accumulates freely in the DRG after intravenous, epidural, or paravertebral injection. The sciatic nerve is relatively impermeable to fluorescein, but access by either systemic or regional injection is enhanced after nerve injury.
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Comparative Study
Biologically variable ventilation improves oxygenation and respiratory mechanics during one-lung ventilation.
Hypoxemia is common during one-lung ventilation (OLV). Atelectasis contributes to the problem. Biologically variable ventilation (BVV), using microprocessors to reinstitute physiologic variability to respiratory rate and tidal volume, has been shown to be advantageous over conventional monotonous control mode ventilation (CMV) in improving oxygenation during the period of lung reinflation after OLV in an experimental model. Here, using a porcine model, the authors compared BVV with CMV during OLV to assess gas exchange and respiratory mechanics. ⋯ In this model of OLV, BVV resulted in superior gas exchange and respiratory mechanics when compared with CMV. Improved static compliance persisted with restoration of two-lung ventilation.