bluuebunny/crossref_metadata_2025_split huggingface dataset:
Temporal Summation Governs Part of the Minimum Alveolar Concentration of Isoflurane Anesthesia
Authors: Dutton Robert C. , Zhang Yi , Stabernack Caroline R. , Laster Michael J. , Sonner James M. , Eger Edmond I 
Published: November 2003

Background
General anesthesia may delay the onset of movement in response to noxious stimulation. The authors hypothesized that the production of immobility could involve depression of time-related processes involved in the generation of movement.

Methods
The delays (latencies) between onset of tail clamp (n = 16) or 50-Hz continuous electrical stimulation (n = 8) and movement were measured in rats equilibrated at 0.1-0.2% increasing steps of isoflurane. In other rats (n = 8), the isoflurane concentrations just permitting and preventing movement (crossover concentrations) in response to trains of 0.5-ms 50-V square-wave pulses of interstimulus intervals of 10, 3, 1, 0.3, or 0.1 s during the step increases were measured. These measures were again made during administration of intravenous MK801, an N-methyl-D-aspartate receptor antagonist that can block temporal summation (n = 6). Temporal summation refers to the cumulative effect of repeated stimuli. Crossover concentrations to 10- and 0.1-s interstimulus interval pulses ranging in voltage from 0.25-50 V were also measured (n = 4).

Results
The increase in concentrations from 0.6 to nearly 1.0 minimum alveolar concentration progressively increased latency from less than 1 s to 58 s. Shortening the interstimulus interval (50 V) pulses from 10 to 0.1 s progressively increased crossover concentrations from 0.6 to 1.0 minimum alveolar concentration. In contrast, during MK801 administration shortening interstimulus intervals did not change crossover concentrations, producing a flat response to change in the interstimulus interval. Increasing the voltage of interstimulus interval pulses increased the crossover concentrations but did not change the response to change in interstimulus intervals for pulses greater than 1 V.

Conclusions
Increasing the duration or frequency (interstimulus interval) of stimulation increases the concentration of isoflurane required to suppress movement by a 0.4 minimum alveolar concentration MK801 blocks this effect, a finding consistent with temporal summation (which requires intact N-methyl-D-aspartate receptor activity) at concentrations of up to 1 minimum alveolar concentration isoflurane.
Cyclooxygenase-2–dependent Superoxide Generation Contributes to Age-dependent Impairment of G Protein–mediated Cerebrovasodilation
Authors: Armstead William M. 
Published: November 2003

Background
Previous studies have observed that activation of cyclooxygenase-2 contributes to generation of superoxide anion after fluid percussion brain injury (FPI). This study was designed to characterize the effects of FPI on the vascular activity of two activators of a pertussis toxin-sensitive G protein, mastoparan and mastoparan-7, and the role of cyclooxygenase-2-dependent superoxide anion generation in such effects as a function of age.

Methods
Lateral FPI was induced in anesthetized newborn (1-5-day-old) and juvenile (3-4-week-old) pigs equipped with a closed cranial window.

Results
Mastoparan (10(-8), 10(-6) M) elicited pial artery dilation that was blunted more in newborn versus juvenile pigs (9 +/- 1 and 16 +/- 1 vs. 3 +/- 1 and 5 +/- 1%, newborn; 9 +/- 1 and 15 +/- 1 vs. 6 +/- 1 and 9 +/- 1%, juveniles). Similar results were observed for mastoparan-7 but the inactive analog mastoparan-17 had no effect on pial artery diameter. Indomethacin (a cyclooxygenase-1 and cyclooxygenase-2 inhibitor), NS398 (a cyclooxygenase-2 inhibitor), and polyethylene glycol superoxide dismutase and catalase (free radical scavengers) partially restored impaired mastoparan dilation after FPI in the newborn in a roughly equivalent manner but not in the juvenile (3 +/- 1 and 5 +/- 1 vs. 8 +/- 1 and 13 +/- 1% newborn, 6 +/- 1 and 9 +/- 1 vs. 7 +/- 1 and 10 +/- 1% juvenile for NS398 pretreatment).

Conclusions
These data show that G protein activation elicits cerebrovasodilation that is blunted following FPI in an age-dependent manner, and suggest that cyclooxygenase-2-dependent superoxide anion generation contributes to G protein activation-induced dilator impairment after the insult in an age-dependent manner.
Postcesarean Section Pain Prediction by Preoperative Experimental Pain Assessment
Authors: Granot Michal , Lowenstein Lior , Yarnitsky David , Tamir Ada , Zimmer Etan Z. 
Published: November 2003

Background
Postcesarean section pain is a common cause of acute pain in obstetrics, yet pain relief and patient satisfaction are still inadequate in many cases. The present study was conducted to determine whether preoperative assessment of experimental pain perception by quantitative sensory tests could predict the level of postcesarean section pain.

Methods
Fifty-eight women who were scheduled for elective cesarean section were enrolled in the study. Heat pain threshold and magnitude estimation of suprathreshold pain stimuli at 44 degrees-48 degrees C were assessed for both algosity (the sensory dimension of pain intensity) and unpleasantness 1 or 2 days before surgery. The day after the operation, the women reported the level of pain at the surgical wound on a visual analog scale at rest and during activity. Regression analysis was performed to evaluate the usefulness of preoperative scores in predicting postcesarean section pain.

Results
Postoperative visual analog scale scores at rest and during activity significantly correlated with preoperative suprathreshold pain scores at 44 degrees-48 degrees C (r = 0.31-0.58 for algosity and r = 0.33-0.74 for unpleasantness). The stimulus of 48 degrees C was found to be the best predictor of postoperative pain for both conditions (r = 0.434-0.527; P < 0.01). In contrast to suprathreshold pain stimuli, pain threshold was not correlated with postoperative pain.

Conclusions
The results show that a simple and quick preoperative test is useful in identifying those women who will experience greater pain after a cesarean section. This test may be suggested for caregivers to tailor the postoperative treatment to specific patient needs and to improve postoperative outcome and patient satisfaction.
A Multicenter, Randomized, Controlled Trial Comparing Bupivacaine with Ropivacaine for Labor Analgesia
Authors: Halpern Stephen H. , Breen Terrance W. , Campbell David C. , Muir Holly A. , Kronberg Jean , Nunn Robert , Fick Gordon H. 
Published: November 2003

Background
A meta-analysis of studies comparing high doses of bupivacaine with ropivacaine for labor pain found a higher incidence of forceps deliveries, motor block, and poorer neonatal outcome with bupivacaine. The purpose of this study was to determine if there is a difference in these outcomes when a low concentration of patient-controlled epidural bupivacaine combined with fentanyl is compared with ropivacaine combined with fentanyl.

Methods
This was a multicenter, randomized, controlled trial, including term, nulliparous women undergoing induction of labor. For the initiation of analgesia, patients were randomized to receive either 15 ml bupivacaine, 0.1%, or 15 ml ropivacaine, 0.1%, each with 5 microg/ml fentanyl. Analgesia was maintained with patient-controlled analgesia with either local anesthetic, 0.08%, with 2 microg/ml fentanyl. The primary outcome was the incidence of operative delivery. We also examined other obstetric, neonatal, and analgesic outcomes.

Results
There was no difference in the incidence of operative delivery between the two groups (148 of 276 bupivacaine recipients vs. 135 of 279 ropivacaine recipients; P = 0.25) or any obstetric or neonatal outcome. The incidence of motor block was significantly increased in the bupivacaine group compared with the ropivacaine group at 6 h (47 of 93 vs. 29 of 93, respectively; P = 0.006) and 10 h (29 of 47 vs. 16 of 41, respectively; P = 0.03) after injection. Satisfaction with mobility was higher with ropivacaine than with bupivacaine (mean +/- SD: 76 +/- 23 vs. 72 +/- 23, respectively; P = 0.013). Satisfaction for analgesia at delivery was higher for bupivacaine than for ropivacaine (mean +/- SD: 71 +/- 25 vs. 66 +/- 26, respectively; P = 0.037).

Conclusions
There was no difference in the incidence of operative delivery or neonatal outcome among nulliparous patients who received low concentrations of bupivacaine or ropivacaine for labor analgesia.
Postoperative Morphine Use and Hyperalgesia Are Reduced by Preoperative but Not Intraoperative Epidural Analgesia
Authors: Katz Joel , Cohen Lorenzo , Schmid Roger , Chan Vincent W.S. , Wowk Adarose 
Published: November 2003

Background
The aim of this study was to evaluate the postoperative morphine-sparing effects and reduction in pain and secondary mechanical hyperalgesia after preincisional or postincisional epidural administration of a local anesthetic and an opioid compared with a sham epidural control.

Methods
Patients undergoing major gynecologic surgery by laparotomy were randomly assigned to three groups and studied in a double-blinded manner. Group 1 received epidural lidocaine and fentanyl before incision and epidural saline 40 min after incision. Group 2 received epidural saline before incision and epidural lidocaine and fentanyl 40 min after incision. Group 3 received a sham epidural control (with saline injected into a catheter taped to the back) before and 40 min after incision. All patients underwent surgery with general anesthesia.

Results
One hundred forty-one patients completed the study (group 1, n = 45; group 2, n = 49; group 3, n = 47). Cumulative patient-controlled analgesia morphine consumption at 48 h was significantly lower (P = 0.04) in group 1 (89.8 +/- 43.3 mg) than group 3 (112.5 +/- 71.5 mg) but not group 2 (95.4 +/- 60.2 mg), although the hourly rate of morphine consumption between 24 and 48 h after surgery was significantly lower (P < 0.0009) in group 1 (1.25 +/- 0.02 mg/h) than group 2 (1.41 +/- 0.02 mg/h). Twenty-four hours after surgery, the visual analog scale pain score on movement was significantly less intense (P = 0.005) in group 1 (4.9 +/- 2.2 cm) than group 3 (6.0 +/- 2.6 cm) but not group 2 (5.3 +/- 2.5 cm), and the von Frey pain threshold near the wound was significantly higher (P = 0.03) in group 1 (6.4 +/- 0.6 log mg) than in group 3 (6.1 +/- 0.8 log mg) but not group 2 (6.2 +/- 0.7 log mg).

Conclusions
Preincisional administration of epidural lidocaine and fentanyl was associated with a significantly lower rate of morphine use, lower cumulative morphine consumption, and reduced hyperalgesia compared with a sham epidural condition. These results highlight the importance of including a standard treatment control group to avoid the problems of interpretation that arise when two-group studies of preemptive analgesia (preincisional vs. postsurgery) fail to find the anticipated effects.
Intrathecal Morphine Reduces the Visceromotor Response to Acute Uterine Cervical Distension in an Estrogen-independent Manner
Authors: Shin Sang-Wook , Eisenach James C. 
Published: November 2003

Background
Acute uterine cervical distension (UCD) forms the basis for obstetric and some gynecologic pain. Systemic morphine inhibits the visceromotor response to UCD in rats by an action in the central nervous system, but the effect of morphine is blocked by exposure to estrogen. The purpose of the present study was to determine whether this estrogen blockade of the action of morphine reflects a spinal mechanism.

Methods
Virgin Sprague-Dawley rats received estrogen or placebo treatment for 1 week after ovariectomy. Rats were then anesthetized, and the electromyographic response in the rectus abdominis muscle to UCD was recorded in the absence and presence of cumulative dosing with intrathecal morphine.

Results
Estrogen treatment did not alter the stimulus- response relationship between UCD and reflex muscle contraction. Intrathecal morphine reduced the visceromotor reflex response to UCD in a dose-dependent manner that was unaffected by estrogen treatment.

Conclusions
These data suggest that intrathecal morphine is effective in reducing the visceromotor response to UCD and that the reduction in efficacy of systemic morphine in this model is unlikely to reflect a reduction of the efficacy of morphine at the spinal level. These data agree with clinical studies that indicate that systemic morphine, in doses that reduce acute postoperative pain, have minimal to no effect in women in labor, yet intrathecal injection of opioids provides rapid, complete analgesia.
Magnesium Chloride and Ruthenium Red Attenuate the Antiallodynic Effect of Intrathecal Gabapentin in a Rat Model of Postoperative Pain
Authors: Cheng Jen-Kun , Lai Yu-Jun , Chen Chien-Chuan , Cheng Ching-Rong , Chiou Lih-Chu 
Published: November 2003

Background
Gabapentin, a gamma-aminobutyric acid analog anticonvulsant, has been shown to possess antinociceptive effects in animal models and clinical trials. An endogenous binding site of [3H]gabapentin has been revealed to be the alpha(2)delta subunit of voltage-dependent Ca2+ channels. Magnesium chloride, ruthenium red, and spermine have been shown to modulate [3H]gabapentin binding to this binding site in vitro. In this study, the authors examined whether intrathecal magnesium chloride, ruthenium red, or spermine could affect the antiallodynic effect of intrathecal gabapentin in a rat model of postoperative pain.

Methods
Under isoflurane anesthesia, male Sprague-Dawley rats received an incision over the plantar surface of the right hind paw to produce punctate mechanical allodynia. Withdrawal thresholds to von Frey filament stimulation near the incision site were measured before incision, 2 h after incision, and every 30 min after intrathecal coadministration of gabapentin with normal saline or different doses of magnesium chloride, ruthenium red, or spermine for 2 h.

Results
Intrathecal gabapentin (30, 100, 200 microg) dose-dependently reduced incision-induced allodynia. Hexahydrated magnesium chloride (5, 10, 20 microg) and ruthenium red (0.2, 2, 20 ng) noncompetitively inhibited the antiallodynic effect of gabapentin. Spermine at doses not inducing motor weakness (30, 60 microg) did not affect the antiallodynic effect of gabapentin. The antiallodynic effect of intrathecal morphine (1.5 microg) was not affected by hexahydrated magnesium chloride (20 microg), ruthenium red (20 ng), or spermine (60 microg).

Conclusions
These results provide behavioral evidence to support that the alpha(2)delta subunit of Ca2+ channels may be involved in the antiallodynic action of intrathecal gabapentin in the postoperative pain model.
Assessment of Differential Blockade by Amitriptyline and Its N -Methyl Derivative in Different Species by Different Routes
Authors: Gerner Peter , Haderer Anna E. , Mujtaba Mustafa , Sudoh Yukari , Narang Sanjeet , Abdi Salahadin , Srinivasa Venkatesh , Pertl Christof , Kuo Wang Ging 
Published: November 2003

Background
Increasing the duration of local anesthesia and/or creating greater differential blockade (i.e., selective block of pain-transmitting nerve fibers) has been attempted by modifying currently available agents. Most drugs show a different profile depending on the model or species studied. This study was designed to investigate the differential nerve-blocking properties of amitriptyline and its quaternary ammonium derivative in rats and sheep.

Methods
The Na+ channel-blocking properties of N-methyl amitriptyline were determined with the patch clamp technique in cultured GH(3) cells. Various functions (motor, nociception, proprioception-ataxia) were compared in rats (spinal and sciatic nerve blockade) and sheep (spinal blockade) with amitriptyline, N-methyl amitriptyline, lidocaine, and bupivacaine (partially from historical data).

Results
In vitro testing revealed N-methyl amitriptyline to be a potent Na+ channel blocker similar to amitriptyline but with a much longer duration of action. All drug concentrations tested in both the sciatic nerve model and the spinal block model produced no significant differential blockade in rats. Three of six rats in the 20-mM N-methyl amitriptyline group showed residual blockade 4 days after sciatic nerve injection. However, in the sheep spinal model, amitriptyline and in particular N-methyl amitriptyline displayed significant differential blockade at most time points. Sheep data for lidocaine and bupivacaine seemed to be more comparable to the clinical experience in humans than did rat data.

Conclusions
Amitriptyline and N-methyl amitriptyline are potent Na+ channel blockers and show greater differential blockade in sheep than in rats. This differential blockade in sheep is greater than that produced by lidocaine or bupivacaine.
Mechanisms of Sevoflurane-induced Myocardial Preconditioning in Isolated Human Right Atria In Vitro
Authors: Yvon Alexandra , Hanouz Jean-Luc , Haelewyn Benoît , Terrien Xavier , Massetti Massimo , Babatasi Gérard , Khayat André , Ducouret Pierre , Bricard Henri , Gérard Jean-Louis 
Published: November 2003

Background
The authors examined the role of adenosine triphosphate-sensitive potassium channels and adenosine A(1) receptors in sevoflurane-induced preconditioning on isolated human myocardium.

Methods
The authors recorded isometric contraction of human right atrial trabeculae suspended in oxygenated Tyrode's solution (34 degrees C; stimulation frequency, 1 Hz). In all groups, a 30-min hypoxic period was followed by 60 min of reoxygenation. Seven minutes before hypoxia reoxygenation, muscles were exposed to 4 min of hypoxia and 7 min of reoxygenation or 15 min of sevoflurane at concentrations of 1, 2, and 3%. In separate groups, sevoflurane 2% was administered in the presence of 10 microm HMR 1098, a sarcolemmal adenosine triphosphate-sensitive potassium channel antagonist; 800 microm 5-hydroxy-decanoate, a mitochondrial adenosine triphosphate-sensitive potassium channel antagonist; and 100 nm 8-cyclopentyl-1,3-dipropylxanthine, an adenosine A(1) receptor antagonist. Recovery of force at the end of the 60-min reoxygenation period was compared between groups (mean +/- SD).

Results
Hypoxic preconditioning (90 +/- 4% of baseline) and sevoflurane 1% (82 +/- 3% of baseline), 2% (92 +/- 5% of baseline), and 3% (85 +/- 7% of baseline) enhanced the recovery of force after 60 min of reoxygenation compared with the control groups (52 +/- 9% of baseline). This effect was abolished in the presence of 5-hydroxy-decanoate (55 +/- 14% of baseline) and 8-cyclopentyl-1,3-dipropylxanthine (58 +/- 16% of baseline) but was attenuated in the presence of HMR 1098 (73 +/- 10% of baseline).

Conclusions
In vitro, sevoflurane preconditions human myocardium against hypoxia through activation of adenosine triphosphate-sensitive potassium channels and stimulation of adenosine A(1) receptors.
Morphometric Effects of the Recruitment Maneuver on Saline-lavaged Canine Lungs
Authors: Lim Chae-Man , Soon Lee Sung , Seoung Lee Jin , Koh Younsuck , Sun Shim Tae , Do Lee Sang , Sung Kim Woo , Kim Dong-Soon , Dong Kim Won 
Published: November 2003

Background
In the face of widespread use of lung-protective, low-volume ventilation in patients with acute lung injury, interest in the recruitment maneuver (RM) is growing. Little is known about lung-morphometric effects of the RM as compared with positive end-expiratory pressure (PEEP) titration (PT) without the RM.

Methods
RM was defined as a stepwise change in PEEP from baseline to 10, 20, 30, and 20 cm H(2)O every 30 s, after which PEEP was reset at the lower inflection point + 2 cm H(2)O. For PT, PEEP was simply increased from baseline to the lower inflection point + 2 cm H(2)O. Both maneuvers were performed in 10 lung-lavaged dogs. Computed tomography of the lung was performed before and 30 s and 30 min after the maneuver.

Results
Thirty seconds after the maneuver, the decrease in the amount of nonaerated plus poorly aerated lung was greater and decreases in Hounsfield units in the caudal and dorsal lung regions were greater with the RM than with the PT. The hyper-aerated lung volume after the RM tended to be greater than that after the PT. At 30 s and 30 min after the maneuver, gas plus tissue volume, gas-only volume, and gas-tissue ratio of the lung were greater with the RM than with the PT. At both time points after the maneuver, the coefficient of variation of regional Hounsfield units, an index of regional heterogeneity of aeration, was lower with the RM than with the PT.

Conclusions
Compared with PT, the RM resulted in a greater lung volume, better aeration of the most dependent lung, and less regional heterogeneity of aeration. However, the RM tended to induce a greater increase in hyperaerated lung volume than did the PT.
Tolerance to Acute Isovolemic Hemodilution
Authors: Van der Linden Philippe , De Hert Stefan , Mathieu Nathalie , Degroote Françoise , Schmartz Denis , Zhang Haibo , Vincent Jean-Louis 
Published: November 2003

Background
Acceptance of a lower transfusion trigger in the perioperative period requires study of the effects of anesthetic depth on the tolerance to acute isovolemic anemia. Anesthetic agents with negative effects on the cardiovascular system may exert proportionately greater depressant effects on cardiac output response than on tissue oxygen demand, reducing tolerance to acute isovolemic anemia.

Methods
In the first study, animals were anesthetized with halothane (n = 14; 23.8 +/- 4.8 kg, mean +/- SD). In a second study, animals were anesthetized with ketamine (n = 14; 24.3 +/- 4.7 kg). In each study, dogs were randomly allocated to receive either low or high concentrations of anesthetic. Oxygen delivery and oxygen consumption were determined from independent measurements during a stepwise isovolemic hemodilution protocol. In each dog, critical oxygen delivery was determined from a plot of oxygen consumption versus oxygen delivery using a least-sum-of-squares technique. Critical hemoglobin (hemoglobin) was determined from a plot of hemoglobin versus oxygen consumption using the same method.

Results
With both agents, the higher anesthetic concentration was associated with decreased oxygen consumption, resulting in a lower critical oxygen delivery. However, critical hemoglobin was significantly higher in the animals receiving the higher anesthetic dosage (1.5 vs. 1.0 minimum alveolar concentration of halothane: 4.1 +/- 1.3 vs. 2.3 +/- 0.5 g/dl, P < 0.05; high- vs. low-dose ketamine: 3.7 +/- 1.4 vs. 2.5 +/- 0.6 g/dl, P < 0.05). This was related to a marked blunting of the cardiac output response to hemodilution in the animals receiving the higher anesthetic dosage.

Conclusions
Increased anesthetic depth with halothane or ketamine resulted in a decreased tolerance to acute anemia, as reflected by a significant increase in critical hemoglobin concentration.