bluuebunny/crossref_metadata_2025_split huggingface dataset:
Effect of Sympathetic Nerve Block on Acute Inflammatory Pain and Hyperalgesia
Authors: Pedersen Juri L. , Rung George W. , Kehlet Henrik 
Published: November 2003

Background
Sympathetic nerve blocks relieve pain in certain chronic pain states, but the role of the sympathetic pathways in acute pain is unclear. Thus the authors wanted to determine whether a sympathetic block could reduce acute pain and hyperalgesia after a heat injury in healthy volunteers.

Methods
The study was made as a randomized, single blinded investigation, in which the volunteers served as their own controls. A lumbar sympathetic nerve block and a contralateral placebo block were performed in 24 persons by injecting 10 ml bupivacaine (0.5%) and 10 ml saline, respectively. The duration and quality of blocks were evaluated by the sympatogalvanic skin response and skin temperature. Bilateral heat injuries were produced on the medial surfaces of the calves with a 50 x 25 mm thermode (47 degrees C, 7 min) 45 min after the blocks. Pain intensity induced by heat, pain thresholds to thermal and mechanical stimulation, and secondary hyperalgesia were assessed before block, after block, and 1, 2, 4, and 6 h after the heat injuries.

Results
Of the 24 volunteers, eight were excluded because of somatic block or incomplete sympathetic block. The study revealed no significant differences between sympathetic block and placebo for pain or mechanical allodynia during injury, or pain thresholds, pain responses to heat, or areas of secondary hyperalgesia after the injury. The comparisons were done for the period when the block was effective.

Conclusion
Sympathetic nerve block did not change acute inflammatory pain or hyperalgesia after a heat injury in human skin.
Spinal Cord Motoneuron Excitability during Isoflurane and Nitrous Oxide Anesthesia
Authors: Zhou Henry H. , Mehta Mahesh , Leis Arturo A. 
Published: November 2003

Background
Recent evidence suggests that the spinal cord is an important site of anesthesia that is necessary for surgical immobility, but the specific effect of anesthetics within the spinal cord is unclear. This study assessed the effect of isoflurane and nitrous oxide on spinal motoneuron excitability by monitoring the H-reflex and the F wave.

Methods
Eight adult patients, categorized as American Society of Anesthesiologists physical status 1 or 2, who were undergoing elective orthopaedic surgery were anesthetized with 0.6, 0.8, 1.0, and 1.2 times the estimated minimum alveolar concentration (MAC) of isoflurane. Nitrous oxide was added in graded concentrations of 30%, 50%, and 70%, whereas the isoflurane concentration was decreased to maintain a total MAC of 1. The H-reflex of the soleus muscle and the F wave of the abductor hallucis muscle were measured before anesthesia and 15 min after each change of anesthetic concentration. Four or more trials of the H-reflex and 18 trials of the F wave were recorded at each concentration of anesthesia. The effect of the anesthetics on the H-reflex and F wave was analyzed using. Dunnett's test.

Results
H-reflex amplitude was decreased to 48.4 +/- 18.6% of preanesthesia level at 0.6 MAC isoflurane and to 33.8 +/- 19.1% when isoflurane concentration increased from 0.6 MAC to 1.2 MAC. F wave amplitude and persistence decreased to 52.2 +/- 33.6% and 44.4 +/- 26% of baseline at 0.6 MAC isoflurane, and to 33.8 +/- 26% and 21.7 +/- 22.8% at 1.2 MAC isoflurane. Isoflurane plus nitrous oxide (total 1 MAC) decreased H-reflex amplitude to 30.4-33.3% and decreased F wave persistence to 42.8-56.3% of baseline.

Conclusions
Both isoflurane alone and isoflurane plus nitrous oxide decrease H-reflex and F-wave amplitude and F-wave persistence. These effects suggest that isoflurane and nitrous oxide decrease motoneuronal excitability in the human spinal cord. This may play an important role in producing surgical immobility.
Esmolol Reduces Anesthetic Requirement for Skin Incision during Propofol/Nitrous Oxide/Morphine Anesthesia
Authors: Johansen Jay W. , Flaishon Ronald , Sebel Peter S. 
Published: November 2003

Background
Although beta blockers have been used primarily to decrease unwanted perioperative hemodynamic responses, the sedative properties of these compounds might decrease anesthetic requirements. This study was designed to determine whether esmolol, a short-acting beta 1-receptor antagonist, could reduce the propofol concentration required to prevent movement at skin incision.

Methods
Sixty consenting patients were premedicated with morphine, and then propofol was delivered by computer-assisted continuous infusion along with 60% nitrous oxide. Patients were randomly divided into three groups, propofol alone, propofol plus low-dose esmolol (bolus of 0.5 mg/kg, then 50 micrograms.kg-1.min-1), and propofol plus high-dose esmolol (bolus of 1 mg/kg, then 250 micrograms.kg-1.min-1). Two venous blood samples were drawn at equilibrium. The serum propofol concentration that prevented movement to incision in 50% of patients (Cp50) was calculated by logistic regression.

Results
The propofol Cp50 with nitrous oxide was 3.85 micrograms/ ml. High-dose esmolol infusion was associated with a significant reduction in the Cp50 to 2.80 micrograms/ml (P < 0.04). Propofol computer-assisted continuous infusion produced stable serum concentrations with a slight positive blas. Esmolol did not alter the serum propofol concentration. No intergroup differences in heart rate or blood pressure response to intubation or incision were found.

Conclusions
Esmolol significantly decreased the anesthetic requirement for skin incision. The components and mechanism of this interaction remain unclear. A simple pharmacokinetic interaction between esmolol and propofol does not explain the Cp50 reduction. These results demonstrate an anesthetic-sparing effect of a beta-adrenergic antagonist in humans under clinically relevant conditions.
Microvascular Oxygen Delivery and Interstitial Oxygenation during Sodium Pentobarbital Anesthesia
Authors: Kerger Heinz , Saltzman Darin J. , Gonzales Armando , Tsai Amy G. , Ackern Klaus van , Winslow Robert M. , Intaglietta Marcos 
Published: November 2003

Background
Anesthesia may represent a considerable bias in experimental medicine, particularly in conditions of stress (such as hemorrhage). Sodium pentobarbital (PB), widely used for cardiovascular investigations, may impair oxygen delivery by hemodynamic and respiratory depression. The critical issue, however, is whether the microcirculation can still maintain tissue oxygenation during anesthesia. To answer this question, the authors studied the effect of PB anesthesia on subcutaneous microvascular oxygen delivery and interstitial oxygenation in Syrian golden hamsters.

Methods
Sodium pentobarbital anesthesia was induced by intravenous injection (30 mg/kg body weight) and maintained by a 15-min infusion (2 mg.kg-1.min-1), with animals breathing spontaneously (PB-S) or ventilated with air (PB-V). Systemic parameters evaluated were mean arterial pressure (MAP), heart rate, cardiac index (CI), arterial oxygen tension (PaO2), arterial carbon dioxide tension (PaCO2), base excess, and pH. Microvascular and interstitial oxygen tension (PO2), vessel diameter, red blood cell velocity (vRBC), and blood flow (Qb) were measured in a dorsal skinfold preparation. Microcirculatory PO2 values were determined by phosphorescence decay.

Results
Sodium pentobarbital anesthesia significantly decreased CI, MAP, vRBC, and Qb. During PB infusion, PaO2 values were 56 +/- 12.8 mmHg (PB-S) and 115.9 +/- 14.6 mmHg (PB-V) compared with 69.4 +/- 18.2 mmHg and 61.4 +/- 12.6 mmHg at baseline. However, microvascular PO2 was reduced by 25-55% in both groups, resulting in an interstitial PO2 decrease from 23.9 +/- 5.6 mmHg (control) to 13.1 +/- 9.1 mmHg (PB-S) and 15.2 +/- 7 mmHg (PB-V). Microcirculatory PO2 values were restored 30 min after PB infusion, even though hemodynamic depression and a light anesthetic plane were maintained.

Conclusions
Sodium pentobarbital anesthesia caused impairment of microvascular oxygen delivery and interstitial oxygenation, effects that were not prevented by mechanical ventilation. Although these effects were restricted to deep anesthetic planes, prolonged hemodynamic depression suggests that caution is warranted when using PB as an anesthetic in cardiovascular investigations.
Stereospecific Effect of Bupivacaine Isomers on Atrioventricular Conduction in the Isolated Perfused Guinea Pig Heart
Authors: Graf Bernhard M. , Martin Eike , Bosnajak Zeliko J. , Stowed David F. 
Published: November 2003

Background
The local anesthetic bupivacaine is an equal mixture of two optically active isomers known to exert different cardiotoxic profiles in vivo. Enantiomer-specific forms of bupivacaine may have differential effects on cardiovascular function, specifically on cardiac electrophysiology. The authors' aim was to determine if there were any direct functional differences in the cardiac effects of bupivacaine isomers. The isolated heart was used to avoid possible indirect cardiac effects of bupivacaine, such as autonomic nervous and hormonal influences, as well as preload and afterload factors.

Methods
The hearts of 12 ketamine-anesthetized guinea pigs were perfused with Krebs-Ringer's solution (97% oxygen, 3% carbon dioxide) at constant perfusion pressure using the Langendorff technique. Atrial and ventricular bipolar electrodes were placed to measure heart rate (HR) and atrioventricular (AV) conduction time. Left ventricular pressure (LVP), coronary flow, and inflow and outflow oxygen tensions were also measured. Oxygen delivery, oxygen consumption (MVO2), and percentage of oxygen extraction were calculated. Each heart was perfused with increasing randomized concentrations (0.5, 1, 5, 10 microM) of both isomers and the racemate of bupivacaine.

Results
Racemic and isomeric bupivacaine equally and dose dependently decreased cardiac function. At 10 microM bupivacaine these changes were HR, -17 +/- 2%; LVP, -50 +/- 3%; coronary flow, -20 +/- 4%; and MVO2, -46 +/- 4%. The (+) isomer significantly prolonged AV conduction compared with the racemate and the (-) isomer at all concentrations. At 10 microM, AV time was 54 +/- 6% longer with the (+) isomer and 30 +/- 4% longer with the (+/-) racemate than with the (-) isomer. The greater delay in AV time with the (+) than the racemate or (-) isomer led to a second-degree AV dissociation in 10 of 12 of hearts treated with (+) bupivacaine.

Conclusions
This study shows that bupivacaine has an enatiomer-specific effect to delay AV conduction and to produce second-degree AV dissociation in the isolated perfused heart. This suggests that bupivacaine isomers probably have differential effects on one or more ion-specific channels regulating AV conduction. Other measured direct cardiac effects of bupivacaine appear to be independent of the isomeric form.
Halothane Prevents Postischemic Production of Hydroxyl Radicals in the Canine Heart
Authors: Glantz Lucio , Ginosar Yehuda , Chevion Mordechai , Gozal Yaacov , Elami Amir , Navot Nahum , Kitrossky Nahum , Drenger Benjamin 
Published: November 2003

Background
Recent studies indicate that during regional myocardial ischemia and subsequent reperfusion, volatile anesthetics may provide protection against free radical-related injury. The effect of halothane on free radical production during ischemia and reperfusion, in the canine heart, was investigated. The level of hydroxyl radical (.OH)-mediated conversion of salicylate to its dehydroxybenzoate derivatives (2,3-DHBA and 2,5-DHBA) was monitored.

Methods
Under general anesthesia, the heart was exposed through median sternotomy. Salicylate (100 mg/kg given intravenously) was administered 30 min before left anterior descending artery occlusion. Six dogs were studied using inhaled halothane (1.6%) 10 min before and during the 10-min ischemic period, followed by 50 min of reperfusion, and then they were compared with seven other dogs used as controls. Blood concentrations of salicylate, 2,3-DHBA and 2,5-DHBA, K+, lactate, oxygen content, and pH were monitored.

Results
An acute increase in the normalized concentrations of 2,3-DHBA and 2,5-DHBA was observed in the control animals during reperfusion. In contrast, halothane inhalation completely inhibited the production of both metabolites (P < 0.02), but 2,5-DHBA concentrations in the halothane-treated group were even less than the basal level (P < 0.05). The increase in lactate concentrations in the experimental animals was significantly less than that of controls (P < 0.05) and followed the same time-dependent pattern as the changes in K+ and pH. Halothane significantly decreased (P < 0.0001) the difference in oxygen content between coronary sinus and aortic root blood, suggesting decreased oxygen utilization during reperfusion.

Conclusions
Halothane completely inhibited the production of .OH, and its administration may protect the heart from the deleterious effect of oxygen-derived reactive species, with attenuation of the metabolic response to ischemia.
In Vivo Imaging of Nitrous Oxide-induced Changes in Cerebral Activation during Noxious Heat Stimuli
Authors: Gyulai Ferenc E. , Firestone Leonard L. , Mintun Mark A. , Winter Peter M. 
Published: November 2003

Background
Although previous studies have provided some insight into the pharmacologic aspects of nitrous oxide analgesia, the neural circuits mediating its antinociceptive effect remain relatively unexplored. Position emission tomography was used in nine volunteers to identify the loci of nitrous oxide-modulated cerebral responses to a peripheral noxious stimulus.

Methods
Nitrous oxide-pain interactions were studied by comparing regional cerebral blood flow responses to a 48 degrees C tonic heat stimulus, applied to each volunteer's left forearm, during room air inhalation with those obtained while 20% nitrous oxide was administered. Two cerebral blood flow scans were obtained with the 15O-water technique during each condition. Locations of specific regional activation related to pain, and nitrous oxide, were identified using the statistical parametric mapping method, with a significance level of P < 0.01. Pain was rated by visual analog scale and the values were compared using Wilcoxon rank sum analysis.

Results
Pain produced cerebral activation in the contralateral thalamus, anterior cingulate, and supplementary motor area. Adding nitrous oxide during pain stimulation abolished activation in these areas but was associated with activation in the contralateral infralimbic and orbitofrontal cortices. In parallel, mean visual analog scale scores decreased significantly from 67 +/- 4 (SEM) to 54 +/- 5 (P < 0.05).

Conclusions
Nitrous oxide, at 20% concentration, appears to modulate pain processing in the brain's medial pain system, and also activates the infralimbic and orbitofrontal cortices. The potential contribution of the affected brain areas to nitrous oxide analgesia is discussed.
Positron Emission Tomography Study of Regional Cerebral Metabolism in Humans during Isoflurane Anesthesia
Authors: Alkire Michael T. MD , Haier Richard J. PhD , Shah Nitin K. MD , Anderson Cynthia T. MD 
Published: November 2003

Background
Although the anesthetic effects of the intravenous anesthetic agent propofol have been studied in the living human brain using brain imaging technology, the nature of the anesthetic state evident in the human brain during inhalational anesthesia remains unknown. To examine this issue, the authors studied the effects of isoflurane anesthesia on human cerebral glucose metabolism using positron emission tomography (PET).

Methods
Five volunteers each underwent two PET scans; one scan assessed awake-baseline metabolism and the other scan assessed metabolism during isoflurane anesthesia titrated to the point of unresponsiveness (means +/- SD; expired = 0.5 +/- 0.1%). Scans were obtained with a GE2048 scanner (4.5-mm resolution-FWHM) using the 18fluorodeoxyglucose technique.

Results
Awake whole-brain glucose metabolism averaged 6.9 +/- 1.5 mg.100 g-1.min-1 (means +/- SD). Isoflurane reduced whole-brain metabolism 46 +/- 11% to 3.6 +/- 0.3 mg.100 g-1.min-1 (P < or = 0.005). Regional metabolism decreased fairly uniformly throughout the brain, and no evidence of any regional metabolic increases were found in any brain region for any participant. A region-of-interest analysis showed that the pattern of regional metabolism evident during isoflurane anesthesia was not significantly different from that seen when participants were awake.

Conclusion
These data clarify that the anesthetic state evident in the living human brain during unresponsiveness induced with isoflurane is associated with a global, fairly uniform, whole-brain glucose metabolic reduction of 46 +/- 11%.
Baricity, Needle Direction, and Intrathecal Sufentanil Labor Analgesia
Authors: Ferouz Fazeela , Norris Mark C. , Arkoosh Valerie A. , Leighton Barbara L. , Boxer Louis M. , Corba Robert J. 
Published: November 2003

Background
Intrathecal sufentanil relieves labor pain but centrally mediated side effects are common. Preventing rostral spread of intrathecal sufentanil should limit these side effects. Both direction of the lateral opening of a pencil-point needle and drug baricity modify the spread of intrathecal local anesthetics. This randomized, prospective, double-blind study examines the effects of these variables on intrathecal sufentanil labor analgesia.

Methods
Forty laboring, full-term parturients, whose cervixes were dilated less than 5 cm and who requested analgesia for labor were enrolled. Combined spinal epidural analgesia was induced in patients in the sitting position. They were allocated to receive 10 micrograms intrathecal sufentanil diluted with either normal saline or dextrose with the aperture of the pencil-point needle directed cephalad or caudad during drug injection. Thus there were four groups of ten patients: dextrose up, dextrose down, saline up, and saline down. Sufentanil was diluted with normal saline to a concentration of 10 micrograms/ml. The study drug was made by mixing 1 ml sufentanil solution with either 1 ml 10% dextrose or 1 ml normal saline. Visual analog scores for pain, pruritus, nausea, and pain relief were recorded before and 5, 10, 15, and 30 min after drug injection.

Results
Baricity, but not needle orientation, influenced pain relief and pruritus. Sufentanil in dextrose produced less itching but also less analgesia. Nine of 20 women in the dextrose groups compared with 1 of 20 in the saline groups requested additional analgesia by 30 min.

Conclusions
Little or no labor analgesia developed for patients receiving sufentanil with dextrose. A supraspinal action may contribute to intrathecal sufentanil's analgesic efficacy.
Influence of Thermoregulatory Vasomotion and Ambient Temperature Variation on the Accuracy of Core-temperature Estimates by Cutaneous Liquid-crystal Thermometers
Authors: Ikeda Takehiko , Sessler Daniel I. , Marder Danielle , Xiong Junyu 
Published: November 2003

Background
Recently, liquid crystal skin-surface thermometers have become popular for intraoperative temperature monitoring. Three situations during which cutaneous liquid-crystal thermometry may poorly estimate core temperature were monitored: (1) anesthetic induction with consequent core-to-peripheral redistribution of body heat, (2) thermoregulatory vasomotion associated with sweating (precapillary dilation) and shivering (minimal capillary flow), and (3) ambient temperature variation over the clinical range from 18-26 degrees C.

Methods
The core-to-forehead and core-to-neck temperature difference was measured using liquid-crystal thermometers having an approximately 2 degrees C offset. Differences exceeding 0.5 degree C (a 1 degree C) temperature range) were a priori deemed potentially clinically important. Seven volunteers participated in each protocol. First, core-to-peripheral redistribution of body heat was produced by inducing propofol/desflurane anesthesia; anesthesia was then maintained for 1 h with desflurane. Second, vasodilation was produced by warming unanesthetized volunteers sufficiently to produce sweating; intense vasoconstriction was similarly produced by cooling the volunteers sufficiently to produce shivering. Third, a canopy was positioned to enclose the head, neck, and upper chest of unanesthetized volunteers. Air within the canopy was randomly set to 18, 20, 22, 24, and 26 degrees C.

Results
Redistribution of body heat accompanying induction of anesthesia had little effect on the core-to-forehead skin temperature difference. However, the core-to-neck skin temperature gradient decreased approximately 0.6 degree C in the hour after induction of anesthesia. Vasomotion associated with shivering and mild sweating altered the core-to-skin temperature difference only a few tenths of a degree centigrade. The absolute value of the core-to-forehead temperature difference exceeded 0.5 degree C during approximately 35% of the measurements, but the difference rarely exceeded 1 degree C. The core-to-neck temperature difference typically exceeded 0.5 degree C and frequently exceeded 1 degree C. Each 1 degree C increase in ambient temperature decreased the core-to-fore-head and core-to-neck skin temperature differences by less than 0.2 degree C.

Conclusions
Forehead skin temperatures were better than neck skin temperature at estimating core temperature. Core-to-neck temperature differences frequently exceeded 1 degree C (a 2 degrees C range), whereas two thirds of the core-to-forehead differences were within 0.5 degree C. The core-to-skin temperature differences were, however, only slightly altered by inducing anesthesia, vasomotor action, and typical intraoperative changes in ambient temperature.
Recovery of Consciousness after Thiopental or Propofol
Authors: Flaishon R. , Windsor A. , Sigl J. , Sebel P. S. 
Published: November 2003

Background
Currently, there exists no effective monitor that can predict the probability of a patient being conscious during general anesthesia. The electroencephalogram-derived bispectral index (BIS) is a promising new method to assess anesthetic adequacy. This study used the BIS to predict the probability of recovery of consciousness after a single bolus induction dose of propofol or thiopental.

Methods
Twenty unpremedicated surgical patients were anesthetized with 4 mg/kg thiopental and 20 patients with 2 mg/kg propofol. The BIS was monitored throughout the study. After induction, before administration of neuromuscular blocking agent, a tourniquet was applied to one arm and inflated above the systolic blood pressure. This allowed preservation of the ability to move the hand after neuromuscular blocking agent onset. Patients were then prompted to squeeze the investigator's hand every 30 s, until they responded to the request. At the time of response, anesthesia was reinduced and the study terminated.

Results
The BIS at loss of consciousness and recovery of a response was not statistically different between propofol and thiopental. No patient with a BIS less than 58 was conscious. In both groups, a BIS of less than 65 signified a less than 5% probability of return of consciousness within 50 s.

Conclusion
The BIS can be used to predict probability of recovery of consciousness after a single injection of either thiopental or propofol.