A Rat Model of Unilateral Hindpaw Burn Injury: Slowly Developing Rightwards Shift of the Morphine Dose-response Curve

Pain. Jul, 2005  |  Pubmed ID: 15936884

Management of pain after burn injury is an unresolved clinical issue. In a rat model of hindpaw burn injury, we examined the effects of systemic morphine on nociceptive behaviors following injury. Injury was induced by immersing the dorsal part of one hindpaw into a hot water bath (85 degrees C) for 4, 7, or 12 s under pentobarbital anesthesia. Mechanical allodynia to von Frey filament stimulation and thermal hyperalgesia to radiant heat were assessed. Burn injury induced by the 12-s (but not 4-, or 7-s) hot water immersion resulted in reliable and lasting mechanical allodynia and thermal hyperalgesia evident by day 1. In addition, there was an upregulation of protein kinase Cgamma and a progressive downregulation of mu-opioid receptors within the spinal cord dorsal horn ipsilateral to injury as revealed by immunohistochemistry and Western blot. In both injured and sham rats, the anti-nociceptive effects of subcutaneous morphine were examined on post-injury days 7 and 14. While the morphine AD50 dose was comparable on day 7 between burn (1.61 mg/kg) and control (1.7 mg/kg) rats, the morphine dose-response curve was shifted to the right in burn-injured rats (4.6 mg/kg) on post-injury day 14 as compared with both the injured rats on post-injury day 7 and sham rats on day 14 (1.72 mg/kg). These data indicate that hindpaw burn injury reliably produces persistent mechanical allodynia and thermal hyperalgesia and that the reduced efficacy of morphine anti-nociception in chronic burn injury may be in part due to a downregulation of spinal mu-opioid receptors.

Succinylcholine: New Insights into Mechanisms of Action of an Old Drug

Anesthesiology. Apr, 2006  |  Pubmed ID: 16571955

Muscle Relaxants in Burns, Trauma, and Critical Illness

International Anesthesiology Clinics. 2006  |  Pubmed ID: 16849960

Increased Sensitivity to a Nondepolarizing Muscle Relaxant in a Patient with Acquired Neuromyotonia

Muscle & Nerve. Jul, 2009  |  Pubmed ID: 19533664

Neuromyotonia is a disorder of hyperexcitability of the peripheral nerve. It has electromyographic features of spontaneous, continuous, irregularly occurring doublets, or multiplets of motor unit potential discharges. Neuromyotonia is characterized by both myokymic and neuromyotonic discharges. To our knowledge, this is the first report in the literature to assess the sensitivity of skeletal muscle to a nondepolarizing muscle relaxant drug, rocuronium, in a woman with acquired neuromyotonia. She had a past medical history notable for prolonged postoperative paralysis following anesthesia. The patient showed increased sensitivity to the neuromuscular effects of rocuronium. This increase in sensitivity may be explained by downregulation of acetylcholine receptors in response to chronic high agonist (acetylcholine) concentrations. If patients with neuromyotonia receive anesthesia, we recommend that smaller doses of a nondepolarizing muscle relaxant be administered, accompanied by monitoring of neuromuscular function, so as to provide optimal muscle relaxation while avoiding overdose and prolonged postoperative recovery.

Measurement of Muscle Strength in the Intensive Care Unit

Critical Care Medicine. Oct, 2009  |  Pubmed ID: 20046117

Traditional (indirect) techniques, such as electromyography and nerve conduction velocity measurement, do not reliably predict intensive care unit-acquired muscle weakness and its clinical consequences. Therefore, quantitative assessment of skeletal muscle force is important for diagnosis of intensive care unit-acquired motor dysfunction. There are a number of ways for assessing objectively muscle strength, which can be categorized as techniques that quantify maximum voluntary contraction force and those that assess evoked (stimulated) muscle force. Important factors that limit the repetitive evaluation of maximum voluntary contraction force in intensive care unit patients are learning effects, pain during muscular contraction, and alteration of consciousness.The selection of the appropriate muscle is crucial for making adequate predictions of a patient's outcome. The upper airway dilators are much more susceptible to a decrease in muscle strength than the diaphragm, and impairment of upper airway patency is a key mechanism of extubation failure in intensive care unit patients. Data suggest that the adductor pollicis muscle is an appropriate reference muscle to predict weakness of muscles that are typically affected by intensive care unit-acquired weakness, i.e., upper airway as well as extremity muscles. Stimulated (evoked) force of skeletal muscles, such as the adductor pollicis, can be assessed repetitively, independent of brain function, even in heavily sedated patients during high acuity of their disease.

Nociceptive Behavior Following Hindpaw Burn Injury in Young Rats: Response to Systemic Morphine

Pain Medicine (Malden, Mass.). Jan, 2011  |  Pubmed ID: 21143761

Develop a burn injury model in young age rats.

A Single Injection of Botulinum Toxin Decreases the Margin of Safety of Neurotransmission at Local and Distant Sites

Anesthesia and Analgesia. Jan, 2012  |  Pubmed ID: 22003222

We tested the hypothesis that a single injection of botulinum toxin not only has local, but also distant effects on muscle function, biochemistry, and pharmacodynamics of atracurium.