bluuebunny/crossref_metadata_2025 huggingface dataset:
Spinal Cord Bioavailability of Methylprednisolone after Intravenous and Intrathecal Administration
Authors: Koszdin Kari L. , Shen Danny D. , Bernards Christopher M.
Published: November 2003

Background

High-dose intravenously administered methylprednisolone has been shown to improve outcome after spinal cord injury. The resultant glucocorticoid-induced immunosuppression, however, results in multiple complications including sepsis, pneumonia, and wound infection. These complications could be reduced by techniques that increase the spinal bioavailability of intravenously administered methylprednisolone while simultaneously decreasing plasma bioavailability. This study aimed to characterize the spinal and plasma bioavailability of methylprednisolone after intravenous and intrathecal administration and to identify barriers to the distribution of methylprednisolone from plasma into spinal cord.

Methods

The spinal and plasma pharmacokinetics of intravenous (30-mg/kg bolus dose plus 5.4 mg x kg(-1) x h(-1)) and intrathecal (1-mg/kg bolus dose plus 1 mg x kg(-1) x h(-1)) methylprednisolone infusions were compared in pigs. In addition, wild-type mice and P-glycoprotein knockout mice were used to determine the role of P-glycoprotein in limiting spinal bioavailability of methylprednisolone.

Results

Despite the greater intravenous dose, concentrations of methylprednisolone in pig spinal cord were far higher and plasma concentrations much lower after intrathecal administration. After intraperitoneal administration in the mouse, the concentrations of methylprednisolone in muscle were not different between mice expressing P-glycoprotein (2.39 +/- 1.79 microg/g) and those lacking P-glycoprotein (2.83 +/- 0.46 microg/g). In contrast, methylprednisolone was undetectable in spinal cords of wild-type mice, whereas concentrations in spinal cords of P-glycoprotein-deficient mice were similar to those in skeletal muscle (2.83 +/- 0.27 microg/g).

Conclusions

These pig studies demonstrate that the spinal cord bioavailability of methylprednisolone is poor after intravenous administration. The studies in knockout mice suggest that this poor bioavailability results from P-glycoprotein-mediated exclusion of methylprednisolone from the spinal cord.
Comparative Contractile Effects of Halothane and Sevoflurane in Rat Aorta
Authors: Vinh Vu Huu , Enoki Taijiro , Hirata Shinichi , Toda Hiroshi , Kakuyama Masahiro , Nakamura Kumi , Fukuda Kazuhiko
Published: November 2003

Background

Volatile anesthetic agents have been shown to have contractile effects in vascular tissues during specific conditions. This study compared contractile effects of halothane and sevoflurane in rat aorta treated with verapamil. This study also tried to elucidate the mechanism of the contraction.

Methods

Endothelium-denuded rat thoracic aorta was used for recording of isometric tension and measurement of influx of 45Ca2+. All experiments were performed in the presence of verapamil. In recording of tension, rings were precontracted with a submaximum dose of phenylephrine, followed by exposure to halothane or sevoflurane. For measurement of influx of 45Ca2+, rat aortic strips were exposed to phenylephrine and then to additional halothane or sevoflurane. Influx of Ca2+ was estimated by incubating the strips in 45Ca2+-labeled solution for 2 min.

Results

Halothane (0.5-4.0%) induced contraction in a dose-dependent manner, whereas sevoflurane (1-4%) had no effect on tension. Influx of 45Ca2+ was strongly enhanced by halothane at 1% and 2%, but only slightly at 4%, and was not affected by 1-4% sevoflurane. SK&F 96365, a blocker of voltage-independent Ca2+ channels, abolished contraction and influx of 45Ca2+ by 1% halothane. Depletion of Ca2+ from the sarcoplasmic reticulum with ryanodine or thapsigargin reduced the contraction induced by halothane at 4% but not that at 1% and 2%.

Conclusion

Halothane is suggested to cause contraction by enhancing influx of Ca2+ via voltage-independent Ca2+ channels at concentrations up to 2% and by inducing release of Ca2+ at 4%. Sevoflurane (1-4%) is devoid of these contractile effects.
Excitatory Synaptic Transmission Mediated by NMDA Receptors Is More Sensitive to Isoflurane than Are Non-NMDA Receptor-mediated Responses
Authors: Nishikawa Koh-ichi , MacIver M. Bruce
Published: November 2003

Background

Effects of volatile anesthetic agents on N-methyl-D-aspartate (NMDA) receptor-mediated excitatory synaptic transmission have not been well characterized. The authors compared effects produced by halothane and isoflurane on electrophysiologic properties of NMDA and non-NMDA receptor-mediated synaptic responses in slices from the rat hippocampus.

Methods

Field excitatory postsynaptic potentials (fEPSPs) in the CA1 area were recorded with extracellular electrodes after electrical stimulation of Schaffer-collateral-commissural fiber inputs. NMDA or non-NMDA receptor-mediated fEPSPs were pharmacologically isolated using selective antagonists. Clinically relevant concentrations of halothane or isoflurane were applied to slices in an artificial cerebrospinal fluid perfusate. Paired pulse facilitation was used as a measure of presynaptic effects of the anesthetic agents.

Results

Clinically relevant concentrations of halothane (1.2 vol% approximately 0.35 mM) depressed fEPSP amplitudes mediated by NMDA receptors and non-NMDA receptors to a similar degree (mean +/- SD: 63.3 +/- 14.0% of control, n = 5; 60.2 +/- 7.3% of control, n = 7, respectively). In contrast, isoflurane (1.4 vol% approximately 0.50 mM) preferentially depressed fEPSP amplitudes mediated by NMDA receptors (44.0 +/- 7.4% of control, n = 6, P < 0.001) compared with those for non-NMDA receptors (68.7 +/- 5.4% of control n = 6), indicating a selective, additional postsynaptic effect. Paired pulse facilitation of fEPSPs was increased significantly by both anesthetic agents from 1.37 +/- 0.13 to 1.91 +/- 0.25 (n = 5, P < 0.05 for halothane) and from 1.44 +/- 0.04 to 1.64 +/- 0.08 (n = 5, P < 0.01 for isoflurane), suggesting that presynaptic mechanisms are also involved in fEPSP depression produced by the anesthetic agents. Neither rise times nor decay times of fEPSPs were changed in the presence of the anesthetic agents.

Conclusions

These results indicate that fEPSPs mediated by postsynaptic NMDA receptors are more sensitive to clinically relevant concentrations of isoflurane than are non-NMDA receptor-mediated responses, but this selective effect was not observed for halothane. Both agents also appeared to depress release of glutamate from nerve terminals via presynaptic actions.
John Snow’s Practice of Obstetric Anesthesia
Authors: Caton Donald
Published: November 2003

The influence of Queen Victoria on the acceptance of obstetric anesthesia has been overstated, and the role of John Snow has been somewhat overlooked. It was his meticulous, careful approach and his clinical skills that influenced many of his colleagues, Tyler-Smith and Ramsbotham and the Queen's own physicians. The fact that the Queen received anesthesia was a manifestation that the conversion of Snow's colleagues had already taken place. This is not to say that this precipitated a revolution in practice. Medical theory may have changed, but practice did not, and the actual number of women anesthetized for childbirth remained quite low. This, however, was a reflection of economic and logistical problems, too few women were delivered of newborn infants during the care of physicians or in hospitals. Conversely, it is important to recognize that John Snow succeeded in lifting theoretical restrictions on the use of anesthesia.
Pharmacokinetics of Rapacuronium in Infants and Children with Intravenous and Intramuscular Administration
Authors: Reynolds Lynne M. , Infosino Andrew , Brown Ronald , Hsu Jim , Fisher Dennis M.
Published: November 2003

Background

A nondepolarizing muscle relaxant with an onset and offset profile similar to succinylcholine is desirable for pediatric anesthesia. The onset and offset of rapacuronium are rapid in children. In the current study, the authors determined its pharmacokinetic characteristics in children. In addition to administering rapacuronium by the usual intravenous route, the authors also gave rapacuronium intramuscularly to determine uptake characteristics and bioavailability.

Methods

Forty unpremedicated patients aged 2 months to 3 yr were anesthetized with halothane, 0.82-1.0% end-tidal concentration. When anesthetic conditions were stable, rapacuronium was injected either into a peripheral vein (2 mg/kg for infants, 3 mg/kg for children) or a deltoid muscle (2.8 mg/kg for infants, 4.8 mg/kg for children). Four venous plasma samples were obtained from each subject 2-240 min after rapacuronium administration. A mixed-effects population pharmacokinetic analysis was applied to these values to determine bioavailability, absorption rate constant, and time to peak plasma concentration with intramuscular administration.

Results

Plasma clearance was 4.77 ml x kg(-1) x min(-1) + 8.48 ml/min. Intramuscular bioavailability averaged 56%. Absorption from the intramuscular depot had two rate constants: 0.0491 min(-1) (72.4% of absorbed drug) and 0.0110 min(-1) (27.6% of the absorbed drug). Simulation indicated that plasma concentration peaks 4.0 and 5.0 min after intramuscular rapacuronium in infants and children, respectively, and that, at 30 min, less than 25% of the administered dose remains to be absorbed from the intramuscular depot.

Conclusions

In infants and children, rapacuronium's clearance and steady state distribution volume are less than in adults. After intramuscular administration, bioavailability is 56%, and plasma rapacuronium concentrations peak within 4 or 5 min.
Risk of Surgery and Anesthesia for Ischemic Stroke
Authors: Wong Gilbert Y. , Warner David O. , Schroeder Darrell R. , Offord Kenneth P. , Warner Mark A. , Maxson Pamela M. , Whisnant Jack P.
Published: November 2003

Background

The goal of this study was to determine if the combination of surgery and anesthesia is an independent risk factor for the development of incident (first-time) ischemic stroke.

Methods

All residents of Rochester, MN, with incident ischemic stroke from 1960 through 1984 (1,455 cases and 1,455 age- and gender-matched controls) were used to identify risk factors associated with ischemic stroke. Cases and controls undergoing surgery involving general anesthesia or central neuroaxis blockade before their stroke/index date of diagnosis were identified. A conditional logistic regression model was used to estimate the odds ratio of surgery and anesthesia for ischemic stroke while adjusting for other known risk factors.

Results

There were 59 cases and 17 controls having surgery within 30 days before their stroke/index date. After adjusting for previously identified risk factors, surgery within 30 days before the stroke/index date (perioperative period) was found to be an independent risk factor for stroke (P<0.001; odds ratio, 3.9; 95% confidence interval, 2.1-7.4). In an analysis that excluded matched pairs where the case and/or control underwent surgery considered "high risk" for stroke (cardiac, neurologic, or vascular procedures), "non-high-risk surgery" was also found to be an independent risk factor for perioperative stroke (P = 0.002; odds ratio, 2.9; 95% confidence interval, 1.5-5.7).

Conclusion

Our results suggest that there is an increased risk of ischemic stroke in the 30 days after surgery and anesthesia. This risk remains elevated even after excluding surgeries (cardiac, neurologic, and vascular surgeries) considered to be high risk for ischemic stroke.
Norepinephrine Facilitates Inhibitory Transmission in Substantia Gelatinosa of Adult Rat Spinal Cord (Part 1)
Authors: Baba Hiroshi , Shimoji Koki , Yoshimura Megumu
Published: November 2003

Background

The activation of descending norepinephrine-containing fibers from the brain stem inhibits nociceptive transmission at the spinal level. How these descending noradrenergic pathways exert the analgesic effect is not understood fully. Membrane hyperpolarization of substantia gelatinosa (Rexed lamina II) neurons by the activation of alpha2 receptors may account for depression of pain transmission. In addition, it is possible that norepinephrine affects transmitter release in the substantia gelatinosa.

Methods

Adult male Sprague-Dawley rats (9-10 weeks of age, 250-300 g) were used in this study. Transverse spinal cord slices were cut from the isolated lumbar cord. The blind whole-cell patch-clamp technique was used to record from neurons. The effects of norepinephrine on the frequency and amplitude of miniature excitatory and inhibitory postsynaptic currents were evaluated.

Results

In the majority of substantia gelatinosa neurons tested, norepinephrine (10-100 microM) dose-dependently increased the frequency of gamma-aminobutyric acid (GABA)ergic and glycinergic miniature inhibitory postsynaptic currents; miniature excitatory postsynaptic currents were unaffected. This augmentation was mimicked by an alpha1-receptor agonist, phenylephrine (10-60 microM), and inhibited by alpha1-receptor antagonists prazosin (0.5 microM) and 2-(2,6-dimethoxyphenoxyethyl) amino-methyl-1,4-benzodioxane (0.5 microM). Neither postsynaptic responsiveness to exogenously applied GABA and glycine nor the kinetics of GABAergic and glycinergic inhibitory postsynaptic currents were affected by norepinephrine.

Conclusion

These results suggest that norepinephrine enhances inhibitory synaptic transmission in the substantia gelatinosa through activation of presynaptic alpha1 receptors, thus providing a mechanism underlying the clinical use of alpha1 agonists with local anesthetics in spinal anesthesia.
Norepinephrine Facilitates Inhibitory Transmission in Substantia Gelatinosa of Adult Rat Spinal Cord (Part 2)
Authors: Baba Hiroshi , Goldstein Peter A. , Okamoto Manabu , Kohno Tatsuro , Ataka Toyofumi , Yoshimura Megumu , Shimoji Koki
Published: November 2003

Background

It has been reported previously that norepinephrine, when applied to the spinal cord dorsal horn, excites a subpopulation of dorsal horn neurons, presumably inhibitory interneurons. In the current study, the authors tested whether norepinephrine could activate inhibitory interneurons, specifically those that are "GABAergic."

Methods

A transverse slice was obtained from a segment of the lumbar spinal cord isolated from adult male Sprague-Dawley rats. Whole-cell patch-clamp recordings were made from substantia gelatinosa neurons using the blind patch-clamp technique. The effects of norepinephrine on spontaneous GABAergic inhibitory postsynaptic currents were studied.

Results

In the majority of substantia gelatinosa neurons tested, norepinephrine (10-60 microM) significantly increased both the frequency and the amplitude of GABAergic inhibitory postsynaptic currents. These increases were blocked by tetrodotoxin (1 microM). The effects of norepinephrine were mimicked by the alpha1-receptor agonist phenylephrine (10-80 microM) and inhibited by the alpha1-receptor-antagonist WB-4101 (0.5 microM). Primary-afferent-evoked polysynaptic excitatory postsynaptic potentials or excitatory postsynaptic currents in wide-dynamic-range neurons of the deep dorsal horn were also attenuated by phenylephrine (40 microM).

Conclusion

The observations suggest that GABAergic interneurons possess somatodendritic alpha1 receptors, and activation of these receptors excites inhibitory interneurons. The alpha1 actions reported herein may contribute to the analgesic action of intrathecally administered phenylephrine.
Synergistic Effect between Intrathecal Non-NMDA Antagonist and Gabapentin on Allodynia Induced by Spinal Nerve Ligation in Rats
Authors: Chen Shao-Rui , Eisenach James C. , McCaslin Patrick P. , Pan Hui-Lin
Published: November 2003

Background

Glutamate and non-N-methyl-D-aspartate (NMDA) receptors have been implicated in the development of neuroplasticity in the spinal cord in neuropathic pain. The spinal cord has been identified as one of the sites of the analgesic action of gabapentin. In the current study, the authors determined the antiallodynic effect of intrathecal 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX) in a rat model of neuropathic pain. Also tested was a hypothesis that intrathecal injection of CNQX and gabapentin produces a synergistic effect on allodynia in neuropathic rats.

Methods

Allodynia was produced in rats by ligation of the left L5 and L6 spinal nerves. Allodynia was determined by application of von Frey filaments to the left hind paw. Through an implanted intrathecal catheter, 10-100 microg gabapentin or 0.5-8 microg CNQX disodium (a water-soluble formulation of CNQX) was injected in conscious rats. Isobolographic analysis was performed comparing the interaction of intrathecal gabapentin and CNQX using the ED50 dose ratio of 15:1.

Results

Intrathecal treatment with gabapentin or CNQX produced a dose-dependent increase in the withdrawal threshold to mechanical stimulation. The ED50 for gabapentin and CNQX was 45.9+/-4.65 and 3.4+/-0.22 microg, respectively. Intrathecal injection of a combination of CNQX and gabapentin produced a strong synergistic antiallodynic effect in neuropathic rats.

Conclusions

This study shows that intrathecal administration of CNQX exhibits an antiallodynic effect in this rat model of neuropathic pain. Furthermore, CNQX and gabapentin, when combined intrathecally, produce a potent synergistic antiallodynic effect on neuropathic pain in spinal nerve-ligated rats.
Xenon Does Not Alter Cardiac Function or Major Cation Currents in Isolated Guinea Pig Hearts or Myocytes
Authors: Stowe David F. , Rehmert Georg C. , Kwok Wai-Meng , Weigt Henry U. , Georgieff Michael , Bosnjak Zeljko J.
Published: November 2003

Background

The noble gas xenon (Xe) has been used as an inhalational anesthetic agent in clinical trials with little or no physiologic side effects. Like nitrous oxide, Xe is believed to exert minimal unwanted cardiovascular effects, and like nitrous oxide, the vapor concentration to achieve 1 minimum alveolar concentration (MAC) for Xe in humans is high, i.e., 70-80%. In the current study, concentrations of up to 80% Xe were examined for possible myocardial effects in isolated, erythrocyte-perfused guinea pig hearts and for possible effects on altering major cation currents in isolated guinea pig cardiomyocytes.

Methods

Isolated guinea pigs hearts were perfused at 70 mm Hg via the Langendorff technique initially with a salt solution at 37 degrees C. Hearts were then perfused with fresh filtered (40-microm pore) and washed canine erythrocytes diluted in the salt solution equilibrated with 20% O2 in nitrogen (control), with 20% O2, 40% Xe, and 40% N2, (0.5 MAC), or with 20% O2 and 80% Xe (1 MAC), respectively. Hearts were perfused with 80% Xe for 15 min, and bradykinin was injected into the blood perfusate to test endothelium-dependent vasodilatory responses. Using the whole-cell patch-clamp technique, 80% Xe was tested for effects on the cardiac ion currents, the Na+, the L-type Ca2+, and the inward-rectifier K+ channel, in guinea pig myocytes suffused with a salt solution equilibrated with the same combinations of Xe, oxygen, and nitrogen as above.

Results

In isolated hearts, heart rate, atrioventricular conduction time, left ventricular pressure, coronary flow, oxygen extraction, oxygen consumption, cardiac efficiency, and flow responses to bradykinin were not significantly (repeated measures analysis of variance, P>0.05) altered by 40% or 80% Xe compared with controls. In isolated cardiomyocytes, the amplitudes of the Na+, the L-type Ca2+, and the inward-rectifier K+ channel over a range of voltages also were not altered by 80% Xe compared with controls.

Conclusions

Unlike hydrocarbon-based gaseous anesthetics, Xe does not significantly alter any measured electrical, mechanical, or metabolic factors, or the nitric oxide-dependent flow response in isolated hearts, at least partly because Xe does not alter the major cation currents as shown here for cardiac myocytes. The authors' results indicate that Xe, at approximately 1 MAC for humans, has no physiologically important effects on the guinea pig heart.
Midazolam Selectively Potentiates the A2A- but not A1-receptor– mediated Effects of Adenosine
Authors: Seubert Christoph N. , Morey Timothy E. , Martynyuk Anatoly E. , Cucchiara Roy F. , Dennis Donn M.
Published: November 2003

Background

Inhibition of adenosine metabolism offers a unique approach to harness the cardioprotective properties of adenosine in a site- and event-specific manner. Benzodiazepines inhibit adenosine metabolism by blocking nucleoside transporter. Therefore, the authors studied the binding affinities of structurally different benzodiazepines to nucleoside transporter and benzodiazepine-induced potentiation of A1-adenosine (negative dromotropy) and A2A-adenosine (coronary vasodilation) receptor-mediated effects.

Methods

In membranes from porcine striatum and guinea pig ventricle, competition binding assays to displace [3H]nitrobenzylmercaptopurine riboside ([3H]NBMPR) from nucleoside transporter were performed using alprazolam, chlorodiazepoxide, diazepam, flurazepam, and midazolam. The augmentation by the most potent benzodiazepine of A1- and A2A-adenosine receptor-mediated responses, elicited by exogenous administration of adenosine or brief periods of global hypoxia, was subsequently studied in guinea pig Langendorff-perfused hearts.

Results

All benzodiazepines completely displaced [3H]NBMPR in a concentration-dependent manner with Hill coefficients not significantly different from unity in both striatal and ventricular membranes. Midazolam was the most potent inhibitor of nucleoside transporter (ventricle:pKi = 5.22+/-0.41, Ki = 6 microM). In isolated hearts, midazolam (5, 10, 20 microM) significantly augmented coronary flow in a concentration-dependent manner in the presence of adenosine (30 nM), an effect reversed by ZM 241385, a selective A2A-receptor antagonist. In contrast, midazolam did not increase the effect of adenosine (30 nM) on atrioventricular conduction. Similarly, midazolam potentiated A2A- but not A1-receptor-mediated effects of endogenous adenosine released during hypoxia.

Conclusions

Structurally distinct benzodiazepines inhibit nucleoside transporter to different degrees. Midazolam selectively augments A2A- but not A1-receptor-mediated effects of adenosine by inhibiting nucleoside transporter.
Perioperative Heat Balance
Authors: Sessler Daniel I. , Todd Michael M.
Published: November 2003

Hypothermia during general anesthesia develops with a characteristic three-phase pattern. The initial rapid reduction in core temperature after induction of anesthesia results from an internal redistribution of body heat. Redistribution results because anesthetics inhibit the tonic vasoconstriction that normally maintains a large core-to-peripheral temperature gradient. Core temperature then decreases linearly at a rate determined by the difference between heat loss and production. However, when surgical patients become sufficiently hypothermic, they again trigger thermoregulatory vasoconstriction, which restricts core-to-peripheral flow of heat. Constraint of metabolic heat, in turn, maintains a core temperature plateau (despite continued systemic heat loss) and eventually reestablishes the normal core-to-peripheral temperature gradient. Together, these mechanisms indicate that alterations in the distribution of body heat contribute more to changes in core temperature than to systemic heat imbalance in most patients. Just as with general anesthesia, redistribution of body heat is the major initial cause of hypothermia in patients administered spinal or epidural anesthesia. However, redistribution during neuraxial anesthesia is typically restricted to the legs. Consequently, redistribution decreases core temperature about half as much during major conduction anesthesia. As during general anesthesia, core temperature subsequently decreases linearly at a rate determined by the inequality between heat loss and production. The major difference, however, is that the linear hypothermia phase is not discontinued by reemergence of thermoregulatory vasoconstriction because constriction in the legs is blocked peripherally. As a result, in patients undergoing large operations with neuraxial anesthesia, there is the potential of development of serious hypothermia. Hypothermic cardiopulmonary bypass is associated with enormous changes in body heat content. Furthermore, rapid cooling and rewarming produces large core-to-peripheral, longitudinal, and radial tissue temperature gradients. Inadequate rewarming of peripheral tissues typically produces a considerable core-to-peripheral gradient at the end of bypass. Subsequently, redistribution of heat from the core to the cooler arms and legs produces an afterdrop. Afterdrop magnitude can be reduced by prolonging rewarming, pharmacologic vasodilation, or peripheral warming. Postoperative return to normothermia occurs when brain anesthetic concentration decreases sufficiently to again trigger normal thermoregulatory defenses. However, residual anesthesia and opioids given for treatment of postoperative pain decreases the effectiveness of these responses. Consequently, return to normothermia often needs 2-5 h, depending on the degree of hypothermia and the age of the patient.
Randomized Trial of Diaspirin Cross-linked Hemoglobin Solution as an Alternative to Blood Transfusion after Cardiac Surgery
Authors: Lamy Maurice L. , Daily Elaine K. , Brichant Jean-François , Larbuisson Robert P. , Demeyere Roland H. , Vandermeersch Eugene A. , Lehot Jean-Jacques , Parsloe Malcolm R. , Berridge John C. , Sinclair Colin J. , Baron Jean-François , Przybelski Robert J.
Published: November 2003

Background

Risks associated with transfusion of allogeneic blood have prompted development of methods to avoid or reduce blood transfusions. New oxygen-carrying compounds such as diaspirin cross-linked hemoglobin (DCLHb) could enable more patients to avoid allogeneic blood transfusion.

Methods

The efficacy, safety, hemodynamic effects, and plasma persistence of DCLHb were investigated in a randomized, active-control, single-blind, multicenter study in post-cardiac bypass surgery patients. Of 1,956 screened patients, 209 were determined to require a blood transfusion and met the inclusion criteria during the 24-h post-cardiac bypass period. These patients were randomized to receive up to three 250-ml infusions of DCLHb (n = 104) or three units of packed erythrocytes (pRBCs; n = 105). Further transfusions of pRBCs or whole blood were permitted, if indicated. Primary efficacy end points were the avoidance of blood transfusion through hospital discharge or 7 days postsurgery, whichever came first, and a reduction in the number of units of pRBCs transfused during this same time period. Various laboratory, physiologic, and hemodynamic parameters were monitored to define the safety and pharmacologic effect of DCLHb in this patient population.

Results

During the period from the end of cardiopulmonary bypass surgery through postoperative day 7 or hospital discharge, 20 of 104 (19%) DCLHb recipients did not receive a transfusion of pRBCs compared with 100% of control patients (P < 0.05). The overall number of pRBCs administered during the 7-day postoperative period was not significantly different. Mortality was similar between the DCLHb (6 of 104 patients) and the control (8 of 105 patients) groups. Hypertension, jaundice/hyperbilirubinemia, increased serum glutamic oxalo-acetic transaminase, abnormal urine, and hematuria were reported more frequently in the DCLHb group, and there was one case of renal failure in each group. The hemodynamic effects of DCLHb included a consistent and slightly greater increase in systemic and pulmonary vascular resistance with associated increases in systemic and pulmonary arterial pressures compared with pRBC. Cardiac output values decreased more in the DCLHb group patients after the first administration than the control group patients. At 24 h postinfusion, the plasma hemoglobin level was less than one half the maximal level for any amount of DCLHb infused.

Conclusions

Administration of DCLHb allowed a significant number (19%) of cardiac surgery patients to avoid exposure to erythrocytes postoperatively.
Multiple Dose Pharmacokinetics of Oral Transmucosal Fentanyl Citrate in Healthy Volunteers
Authors: Egan Talmage D. , Sharma Amarnath , Ashburn Michael A. , Kievit Jur , Pace Nathan L. , Streisand James B.
Published: November 2003

Background

Oral transmucosal fentanyl citrate (OTFC) is a solid form of fentanyl that delivers the drug through the oral mucosa. The clinical utility of multiple doses of OTFC in the treatment of "breakthrough" cancer pain is under evaluation. The aim of this study was to test the hypothesis that the pharmacokinetics of OTFC do not change with multiple dosing.

Methods

Twelve healthy adult volunteers received intravenous fentanyl (15 microg/kg) or OTFC (three consecutive doses of 800 microg) on separate study sessions. Arterial blood samples were collected for determination of fentanyl plasma concentration by radioimmunoassay. The descriptive pharmacokinetic parameters (maximum concentration, minimum concentration, and time to maximum concentration) were identified from the raw data and subjected to a nonparametric analysis of variance. Population pharmacokinetic models for all subjects and separate models for each subject were developed to estimate the pharmacokinetic parameters of fentanyl after multiple OTFC doses.

Results

The shapes of the profiles of plasma concentration versus time for each dose of OTFC were grossly similar. No change was noted for maximum concentration or time to maximum concentration over the three doses, while minimum concentration did show a significantly increasing trend. Terminal half-lives for intravenous fentanyl and OTFC were similar. A two-compartment population pharmacokinetic model adequately represented the central tendency of the data from all subjects. Individual subject data were best described by either two- or three-compartment pharmacokinetic models. These models demonstrated rapid and substantial absorption of OTFC that did not change systematically with time and multiple dosing.

Conclusions

The pharmacokinetics of OTFC were similar among subjects and did not change with multiple dosing. Multiple OTFC dosing regimens within the dosage schedule examined in this study can thus be formulated without concern about nonlinear accumulation.
Extrahepatic Metabolism of Sevoflurane in Children Undergoing Orthotopic Liver Transplantation
Authors: Van Obbergh Luc J. , Verbeeck Roger K. , Michel Ives , Lim Serene , Veyckemans Francis
Published: November 2003

Background

Sevoflurane is metabolized by cytochrome P450 and produces inorganic fluoride. The anhepatic phase of liver transplantation provides a useful tool to study the extrahepatic metabolism of drugs. The authors therefore studied the extrahepatic metabolism of sevoflurane by measuring the fluoride production in children receiving sevoflurane solely during the anhepatic phase of orthotopic liver transplantation.

Methods

Children with end-stage liver disease undergoing orthotopic liver transplantation were studied. Anesthesia was provided with isoflurane, sufentanil, and pancuronium. In one group, isoflurane was replaced by sevoflurane as soon as the liver was removed from the patient and maintained until reperfusion of the new liver. Arterial blood samples were drawn at induction, before removal of the liver, 15 min and 30 min after the beginning of the anhepatic phase, at the unclamping of the new liver, and finally 60 and 120 min after the unclamping. Plasma fluoride concentrations were determined by ion-selective electrode.

Results

No differences between the two groups (n = 10) regarding age, weight, duration of the anhepatic phase, or basal level of inorganic fluoride were found. The fluoride concentration increased significantly as soon as sevoflurane was introduced; it remained stable in the group receiving isoflurane. The peak fluoride concentration was also significantly higher in the first group (mean +/- SD: 5.5 +/- 0.8 microM (sevoflurane group) versus 1.4 +/- 0.5 microM (isoflurane group) P < 0.05).

Conclusions

These results demonstrate the existence of an extrahepatic metabolism of sevoflurane at least in children with end-stage liver disease.
Comparison of Conventional Surgical versus Seldinger Technique Emergency Cricothyrotomy Performed by Inexperienced Clinicians
Authors: Eisenburger Philip , Laczika Klaus , List Michaela , Wilfing Astrid , Losert Heidrun , Hofbauer Roland , Burgmann Heinz , Bankl Hans , Pikula Branko , Benumof Jonathan L. , Frass Michael
Published: November 2003

Background

Cricothyrotomy is the ultimate option for a patient with a life-threatening airway problem.

Methods

The authors compared the first-time performance of surgical (group 1) versus Seldinger technique (group 2) cricothyrotomy in cadavers. Intensive care unit physicians (n = 20) performed each procedure on two adult human cadavers. Methods were compared with regard to ease of use and anatomy of the neck of the cadaver. Times to location of the cricothyroid membrane, to tracheal puncture, and to the first ventilation were recorded. Each participant was allowed only one attempt per procedure. A pathologist dissected the neck of each patient and assessed correctness of position of the tube and any injury inflicted. Subjective assessment of technique and cadaver on a visual analog scale from 1 (easiest) to 5 (worst) was conducted by the performer.

Results

Age, height, and weight of the cadavers were not different. Subjective assessment of both methods (2.2 in group 1 vs. 2.4 in group 2) and anatomy of the cadavers (2.2 in group 1 vs. 2.4 in group 2) showed no statistically significant difference between both groups. Tracheal placement of the tube was achieved in 70% (n = 14) in group 1 versus 60% (n = 12) in group 2 (P value not significant). Five attempts in group 2 had to be aborted because of kinking of the guide wire. Time intervals (mean +/- SD) were from start to location of the cricothyroid membrane 7 +/- 9 s (group 1) versus 8 +/- 7s (group 2), to tracheal puncture 46 +/- 37s (group 1) versus 30 +/- 28s (group 2), and to first ventilation 102 +/- 42s (group 1) versus 100 +/- 46s (group 2) (P value not significant).

Conclusions

The two methods showed equally poor performance.
Heterogenous Patterns of Sensory Dysfunction in Postherpetic Neuralgia Suggest Multiple Pathophysiologic Mechanisms
Authors: Pappagallo Marco , Oaklander Anne Louise , Quatrano-Piacentini Amy L. , Clark Michael R. , Raja Srinivasa N.
Published: November 2003

Background

Postherpetic neuralgia (PHN) is considered by some investigators to be predominantly a deafferentation-type central pain syndrome; others suggest that activity of remaining peripheral nociceptors plays a critical role. The authors investigated the sensory dysfunction in subjects with PHN of varying duration and at different sites to gain further insight into the mechanisms responsible for the clinical features of neuropathic pain. In addition, the relationships between ongoing pain and pain evoked by mechanical and thermal stimuli were compared in patients with trigeminal and truncal PHN, to determine if the pathophysiologic mechanisms differed among subjects.

Methods

In 63 subjects with PHN, quantitative sensory testing was performed in the region of maximum allodynia or ongoing pain and the corresponding contralateral site. The intensity of ongoing pain was recorded. Sensory thresholds for warmth, coolness, heat pain, and cold pain were determined. Pain induced by various mechanical stimuli (dynamic, static, punctate) was rated using a numerical rating scale of 0-10.

Results

The mean rating of ongoing PHN pain was 7.3 +/- 2.0 (mean +/- SD). Allodynia induced by one or more mechanical stimuli was observed in 78% of subjects. A smaller subset (40%) had hyperalgesia to heat or cold stimuli. In subjects with duration of PHN of < or = 1 yr duration, but not in those with duration of > 1 yr, the intensity of ongoing pain correlated with intensity of allodynia induced by dynamic stimuli. Deficits in thresholds for heat and cold pain were observed in the affected region of subjects with PHN in the thoracic dermatomes (P < 0.005), but not in the trigeminal distribution. No relationship was observed between the thermal deficits and ongoing pain or mechanical allodynia in the groups of subjects with either trigeminal or thoracic PHN.

Conclusion

Despite a common cause, the patterns of sensory abnormalities differ between subjects. Particular differences were noted between groups with facial or truncal PHN and between groups with recent or more chronic PHN. The observations suggest that the relative contributions of peripheral and central mechanisms to the pathophysiology of pain differ among subjects and may vary over the course of PHN.
Effect of Edrophonium and Neostigmine on the Pharmacokinetics and Neuromuscular Effects of Mivacurium
Authors: Szenohradszky Janos , Fogarty Declan , Kirkegaard-Nielsen Hans , Brown Ronald , Sharma Manohar L. , Fisher Dennis M.
Published: November 2003

Background

Previous studies demonstrated that both edrophonium and neostigmine affect mivacurium's pharmacokinetics, thereby potentially affecting its recovery profile. However, those studies were not clinically relevant because mivacurium was still infused after the antagonists were given. In the present study, the authors gave antagonists (or placebo) after discontinuing a mivacurium infusion, thereby obtaining data that are more clinically relevant.

Methods

In 18 patients, mivacurium was infused at 10 microg kg(-1) x min(-1) for 40 min, the infusion was discontinued for 15 min and then restarted at the same rate for another 40 min. Patients were randomized to receive 500 microg/kg edrophonium, 50 microg/kg neostigmine, or saline at discontinuation of the second infusion; all subjects received 1 mg atropine. Plasma was sampled during the final 10 min of each infusion to determine steady state mivacurium concentrations and for 15 min after each infusion. Twitch tension was recorded. Mivacurium concentrations after each of the two infusions were compared.

Results

After discontinuation of the second infusion, mivacurium concentrations were larger than those after the first infusion at 2 min with edrophonium and at 2, 4, and 7 min with neostigmine. With both neostigmine and edrophonium, twitch tension recovered after infusion #2 more rapidly than after infusion #1; however, the magnitude of this effect was small

Conclusion

Edrophonium transiently slows the rate at which mivacurium concentrations decrease; this is consistent with our previous findings. Neostigmine has a similar, although longer, effect. Despite altering mivacurium's elimination characteristics, both drugs facilitate neuromuscular recovery, although their benefit is small.
Comparative Spinal Distribution and Clearance Kinetics of Intrathecally Administered Morphine, Fentanyl, Alfentanil, and Sufentanil
Authors: Ummenhofer Wolfgang C. , Arends Rosalin H. , Shen Danny D. , Bernards Christopher M.
Published: November 2003

Background

Despite widespread use, little is known about the comparative pharmacokinetics of intrathecally administered opioids. The present study was designed to characterize the rate and extent of opioid distribution within cerebrospinal fluid, spinal cord, epidural space, and systemic circulation after intrathecal injection.

Methods

Equal doses of morphine and alfentanil, fentanyl, or sufentanil were administered intrathecally (L3) to anesthetized pigs. Microdialysis probes were used to sample cerebrospinal fluid at L2, T11, T7, T3, and the epidural space at L2 every 5-10 min for 4 h. At the end of the experiment, spinal cord and epidural fat tissue were sampled, and each probe's recovery was determined in vitro. Using SAAM II pharmacokinetic modeling software (SAAM Institute, University of Washington, Seattle, WA), the data were fit to a 16-compartment model that was divided into four spinal levels, each of which consisted of a caternary arrangement of four compartments representing the spinal cord, cerebrospinal fluid, epidural space, and epidural fat.

Results

Model simulations revealed that the integral exposure (area under the curve divided by dose) of the spinal cord (i.e., effect compartment) to the opioids was highest for morphine because of its low spinal cord distribution volume and slow clearance into plasma The integral exposure of the spinal cord to the other opioids was relatively low, but for different reasons: alfentanil has a high clearance from spinal cord into plasma, fentanyl distributes rapidly into the epidural space and fat, and sufentanil has a high spinal cord volume of distribution.

Conclusions

The four opioids studied demonstrate markedly different pharmacokinetic behavior, which correlates well with their pharmacodynamic behavior.
Effect of Barbiturates on Hydroxyl Radicals, Lipid Peroxidation, and Hypoxic Cell Death in Human NT2-N Neurons
Authors: Almaas Runar , Saugstad Ola D. , Pleasure David , Rootwelt Terje
Published: November 2003

Background

Barbiturates have been shown to be neuroprotective in several animal models, but the underlying mechanisms are unknown. In this study, the authors investigated the effect of barbiturates on free radical scavenging and attempted to correlate this with their neuroprotective effects in a model of hypoxic cell death in human NT2-N neurons.

Methods

Hydroxyl radicals were generated by ascorbic acid and iron and were measured by conversion of salicylate to 2,3-dihydroxybenzoic acid. The effect of barbiturates on lipid peroxidation measured as malondialdehyde and 4-hydroxynon-2-enal was also investigated. Hypoxia studies were then performed on human NT2-N neurons. The cells were exposed to 10 h of hypoxia or combined oxygen and glucose deprivation for 3 or 5 h in the presence of thiopental (50-600 microM), methohexital (50-400 microM), phenobarbital (10-400 microM), or pentobarbital (10-400 microM), and cell death was evaluated after 24 h by lactate dehydrogenase release.

Results

Pentobarbital, phenobarbital, methohexital, and thiopental dose-dependently inhibited formation of 2,3-dihydroxybenzoic acid and iron-stimulated lipid peroxidation. There were significant but moderate differences in antioxidant action between the barbiturates. While phenobarbital (10-400 microM) and pentobarbital (10-50 microM) increased lactate dehydrogenase release after combined oxygen and glucose deprivation, thiopental and methohexital protected the neurons at all tested concentrations. At a higher concentration (400 microM), pentobarbital also significantly protected the neurons. At both 50 and 400 microM, thiopental and methohexital protected the NT2-N neurons significantly better than phenobarbital and pentobarbital.

Conclusions

Barbiturates differ markedly in their neuroprotective effects against combined oxygen and glucose deprivation in human NT2-N neurons. The variation in neuroprotective effects could only partly be explained by differences in antioxidant action.
An Experimental Itch Model in Monkeys
Authors: Ko M. C. Holden , Naughton Norah N.
Published: November 2003

Background

The most common side effect of spinal opioid administration is pruritus, which has been treated with a variety of agents with variable success. Currently, there are few animal models developed to study this side effect. The aim of this study was to establish a nonhuman primate model to pharmacologically characterize the effects of intrathecal administration of morphine.

Methods

Eight adult rhesus monkeys were used. Scratching responses were videotaped and counted by observers who were blinded to experimental conditions. Antinociception was measured by a warm-water (50 degrees C) tail-withdrawal assay. The dose-response of intrathecal morphine (1-320 microg) for both scratching and antinociception in all subjects was established. An opioid antagonist, nalmefene, was administered either intravenously or subcutaneously to assess its efficacy against intrathecal morphine.

Results

Intrathecal morphine (1-32 microg) increased scratching in a dose-dependent manner. Higher doses of intrathecal morphine (10-100 microg) produced thermal antinociception in a dose-dependent manner. On the other hand, nalmefene (10-32 microg/kg intravenously) attenuated maximum scratching responses among subjects. Pretreatment with nalmefene (32 microg/kg subcutaneously) produced approximately 10-fold rightward shifts of intrathecal morphine dose-response curves for both behavioral effects.

Conclusions

These data indicate that intrathecal morphine-induced scratching and antinociception are mediated by opioid receptors. The magnitude of nalmefene antagonism of intrathecal morphine is consistent with microL opioid receptor mediation. This experimental itch model is useful for evaluating different agents that may suppress scratching without interfering with antinociception. It may also facilitate the clarification of mechanisms underlying these phenomena.
Isoflurane and Pentobarbital Reduce AMPA Toxicity In Vivo in the Rat Cerebral Cortex
Authors: Kimbro J. Reed , Kelly Paul J. , Drummond John C. , Cole Daniel J. , Patel Piyush M.
Published: November 2003

Background

Isoflurane and pentobarbital can reduce alpha-amino-d-hydroxy-5-methyl-4-isoxazole-propionate (AMPA) receptor-mediated toxicity in vitro. However, their effect on AMPA toxicity in vivo is not known. The present study was undertaken to evaluate the effects of isoflurane and pentobarbital on the in vivo neurotoxicity produced by AMPA.

Methods

Wistar-Kyoto rats were allocated to one of seven groups (n = 8 per group): isoflurane 1 minimum alveolar concentration, isoflurane electroencephalogram burst suppression (EEG-BS), low-dose pentobarbital, pentobarbital EEG-BS, NBQX, conscious, and sham groups. AMPA 30 nm was injected into the cortex. An equivalent volume of cerebrospinal fluid was injected into the cortex in the sham group. In the NBQX group, 200 nm NBQX was injected into the cortex with the AMPA. In the isoflurane and pentobarbital groups, anesthesia was maintained for a period of 5 h. Animals in the conscious, NBQX, and sham groups were allowed to awaken immediately after the AMPA injection. Injury to the cortex was evaluated 48 h later.

Results

Isoflurane reduced AMPA-induced cortical injury (4.5 +/- 1.9 mm3 and 1.7 +/- 0.8 mm3 in the 1 minimum alveolar concentration and EEG-BS groups, respectively) in comparison to the conscious group (7.2 +/- 0.8 mm3). Pentobarbital reduced cortical injury when administered in EEG-BS doses (2.2 +/- 0.7 mm3) but not when administered in sedative doses (8.6 +/- 0.9 mm3). NBQX reduced AMPA-induced cortical injury (1.2 +/- 0.5 mm3).

Conclusions

Isoflurane and pentobarbital reduced cortical AMPA excitotoxicity. The magnitude of injury reduction was similar to that produced by NBQX when the anesthetics were administered in EEG-BS doses. These results are consistent with the previously demonstrated ability of isoflurane and pentobarbital to inhibit AMPA receptor responses.