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PubMed1993

Amrinone enhances myocardial contractility and improves left ventricular diastolic function in conscious and anesthetized chronically instrumented dogs.

BACKGROUND: Volatile anesthetics depress left ventricular mechanical performance in vivo by altering intracellular calcium regulation. Although amrinone has been shown to reverse the negative inotropic effects of volatile anesthetics, the actions of amrinone on anesthetic-induced diastolic dysfunction are unknown. This investigation examined and compared the direct effects of amrinone on left ventricular systolic and diastolic function in conscious and anesthetized dogs. METHODS: Experiments were conducted in the presence of pharmacologic blockade of the autonomic nervous system, because autonomic activity may influence the hemodynamic actions of volatile anesthetics and amrinone in vivo. Three groups, comprising a total of 27 experiments, were conducted using 9 dogs chronically instrumented for measurement of aortic and left ventricular pressure, left ventricular dP/dt, subendocardial segment length, diastolic coronary blood flow velocity, and cardiac output. Myocardial contractility was evaluated using the preload recruitable stroke work relationship slope (Mw). Diastolic function was characterized by a time constant of isovolumic relaxation (tau), a regional chamber stiffness constant (KT), and maximum segment lengthening velocity during rapid ventricular filling (dL/dtmax). On three separate days, an amrinone bolus of 1 mg/kg, followed by an infusion at 10, 20, 40, or 80 micrograms.kg-1.min-1, was administered. Hemodynamics and ventricular pressure-segment length loops and waveforms were recorded after a 15-min equilibration at each dose in the conscious state or during isoflurane or halothane anesthesia (1.25 MAC). RESULTS: In conscious dogs, amrinone significantly increased myocardial contractility in a dose-dependent manner (Mw of 65 +/- 8 to 108 +/- 10 mmHg at the high dose). Amrinone also shortened isovolumic relaxation (tau of 32.7 +/- 2.1 to 24.8 +/- 0.9 ms at the high dose) and enhanced rapid ventricular filling (dL/dtmax of 34.8 +/- 1.2 to 45.1 +/- 2.3 mm/s at the high dose) in a dose-related fashion. In addition, amrinone reduced regional chamber stiffness (Kp of 0.49 +/- 0.09 to 0.31 +/- 0.08 mm/s at the high dose) in conscious dogs. Amrinone also enhanced left ventricular systolic (increase in Mw) and diastolic function (decreases in tau and Kp and increases in dL/dtmax) when this drug was administered to dogs anesthetized with isoflurane or halothane. CONCLUSIONS: Amrinone produced positive inotropic and lusitropic effects in both conscious and anesthetized dogs with autonomic nervous system blockade. These results indicate that amrinone-induced improvement of left ventricular performance are related to actions in diastole, as well as systole.

Amrinone↗

PubMed1994

Effects of volatile anesthetics, thiopental, and ketamine on spontaneous and depolarization-evoked dopamine release from striatal synaptosomes in the rat.

BACKGROUND: Recent experimental data indicate that anesthesia is often associated with significant changes in brain concentrations of dopamine (DA), an inhibitory neurotransmitter located in restricted, but functionally important, areas such as the striatum. Whether the presynaptic DA nerve endings represent potential targets for anesthetics remains unknown. Therefore, the current study was designed to investigate the effects of volatile anesthetics, thiopental, and ketamine on both spontaneous and depolarization-evoked DA release from striatal synaptosomes in the rat. METHODS: Purified striatal synaptosomes preloaded with 3H-DA were superfused with artificial cerebrospinal fluid (1 ml/min). Radioactivity obtained from 1-ml fractions was measured over 15 min; first, in the absence of any treatment (spontaneous release), then in either the absence (time-dependent control) or presence (evoked-release) of anesthetic and pharmacologic agents, and finally, again, without any pharmacologic stimulation. The compounds tested were: potassium chloride (15 and 50 mM), glutamate, N-methyl-D-aspartate (NMDA) and kainate (10(-4) M and 10(-3) M), MK-801 (10(-4) M, an antagonist of NMDA receptors) and 6-cyano-7-nitro-quinoxaline-2,3-dione (10(-4) M, an antagonist of D,L-alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionate [AMPA] receptors), halothane, enflurane, isoflurane (1, 1.5, and 2 minimum alveolar concentrations), ketamine (10(-5) and 10(-4) M), and thiopental (10(-5) and 10(-4) M). RESULTS: Volatile anesthetics induced a significant, concentration-related increase in spontaneous 3H-DA release, but thiopental and ketamine were ineffective. The effect of 2 minimum alveolar concentration enflurane (but not halothane or isoflurane) was significantly enhanced when a Mg(2+)-free cerebrospinal fluid was used, and was reduced by MK-801 application. Nomifensine (10(-5) M, a blocker of monoamine transporter) did not affect the 3H-DA release evoked by volatile anesthetics. Glutamate, kainate, NMDA, and potassium chloride induced a significant, dose-related, Ca(2+)-dependent 3H-DA release. Halothane and isoflurane produced a significant and concentration-related decrease in the 3H-DA peaks evoked by glutamate, kainate, and NMDA; however, enflurane significantly attenuated the glutamate- and kainate-mediated release, but enhanced that evoked by NMDA. Thiopental and ketamine (10(-4), but not 10(-5) M) significantly reduced the glutamate- and NMDA-stimulated release, but only thiopental decreased the kainate-induced effect. Furthermore, the effect of potassium chloride (15 mM) was significantly reduced by all anesthetics examined, whereas that of potassium chloride (50 mM) was unaffected. CONCLUSION: The authors conclude that: (1) volatile anesthetics, thiopental, and ketamine exert significant changes in both spontaneous and depolarization-evoked 3H-DA release in the rat striatum; (2) enflurane uniquely enhances NMDA-receptor mediated dopamine release; and (3) the results obtained from these receptor-mediated effects (AMPA and NMDA) may apply to postsynaptic, as well as presynaptic, glutamate receptors.

Anesthesia, Inhalation↗

PubMed1995

Stable inhibition of brain synaptic plasma membrane calcium ATPase in rats anesthetized with halothane.

BACKGROUND: The authors recently showed that plasma membrane Ca(2+)-ATPase (PMCA) activity in cerebral synaptic plasma membrane (SPM) is diminished in a dose-related fashion during exposure in vitro to halothane, isoflurane, xenon, and nitrous oxide at clinically relevant partial pressures. They have now extended their work to in vivo studies, examining PMCA pumping in SPM obtained from control rats decapitated without anesthetic exposure, from rats decapitated during halothane anesthesia, and from rats decapitated after recovery from halothane anesthesia. METHODS: Three treatment groups were studied: 1) C, control rats that were decapitated without anesthetic exposure, 2) A, anesthetized rats exposed to 1 minimum effective dose (MED) for 20 min and then decapitated, and 3) R, rats exposed to 1 MED for 20 min and then decapitated after recovery from anesthesia, defined as beginning to groom. Plasma membrane Ca(2+)-ATPase pumping and Ca(2+)-dependent ATPase hydrolytic activity, as well as sodium-calcium exchanger activity and Na+-K+-ATPase hydrolytic activity, were assessed in cerebral SPM. In addition, halothane effect on smooth endoplasmic reticulum Ca(2+)-ATPase (SERCA) was examined. RESULTS: Plasma membrane Ca(2+)-ATPase transport of Ca2+ into SPM vesicles from anesthetized rats was reduced to 71% of control (P < 0.01) compared with 113% of control for the recovered group (NS). No depression by halothane of SERCA activity, sodium-calcium exchanger, or Na+-K+-ATPase activity was noted among the CAR treatment groups. CONCLUSIONS: Plasma membrane Ca(2+)-ATPase is selectively and stably inhibited in cerebral SPM from rats killed while anesthetized with halothane, compared with rats killed without anesthesia or after recovery from anesthesia. The studies described in this report, in conjunction with previously reported inhibition of PMCA activity in vitro by a wide range of anesthetic agents, indicate a relationship between inhibition of PMCA and action of inhalational anesthetics.

Animals↗

PubMed1995

The effects of halothane on cardiovascular responses in the neuraxis of cats. Influence of background anesthetic state.

BACKGROUND: This study examined the effects of halothane on arterial pressure after central nervous system (CNS) pressor site stimulation in anesthetized cats, cats rendered unconscious by midcollicular transection, and conscious cats. METHODS: Two anesthetized groups and two nonanesthetized groups were used. Cats were anesthetized with either alpha-chloralose and urethane or pentobarbital. Nonanesthetized groups were cats with midcollicular transections or conscious cats with chronically implanted electrodes. Stimulating electrodes were placed into vasomotor areas of the hypothalamus (HYP), reticular formation (RF), and medulla, and arterial pressure responses to increasing stimulus currents were examined during different halothane concentrations. Two groups of cats were also anesthetized with either pentobarbital or urethane and underwent bilateral carotid artery occlusion. RESULTS: Stimulation at each CNS site produced increases in arterial pressure and heart rate. Halothane attenuated pressor responses evoked by stimulation of all loci in all groups of cats. The inhibition by halothane on these cardiovascular responses was greatest at HYP and RF sites, while the medulla was more resistant to the effects of halothane in the anesthetized animals. Midcollicular transection decreased this medullary resistance. The inhibition of pressor responses by halothane was also greater in pentobarbital-than chloralose urethane-anesthetized animals. In contrast, pressor responses elicited by bilateral carotid occlusion were attenuated by halothane similarly in both anesthetic groups. Reticular formation stimulation in conscious animals resulted in "altering responses" in addition to pressor effects, both of which were attenuated by halothane. CONCLUSIONS: Modulation of CNS cardiovascular control centers contribute to halothane-induced hemodynamic alterations. Baseline anesthesia, CNS stimulation site, and the suprabulbar system influence the effects of halothane.

Anesthesia↗

PubMed2001

Relative importance of rostral ventrolateral medulla in sympathoinhibitory action of rilmenidine in conscious and anesthetized rabbits.

The pressor region of the rostral ventrolateral medulla (RVLM) is a critical site in the sympathoinhibitory action of imidazoline receptor agonists as shown by studies in anesthetized animals. The aim of this study was to compare the importance of the RVLM in mediating the inhibitory action of rilmenidine on renal sympathetic nerve activity (RSNA) and arterial pressure in urethane-anesthetized rabbits (n = 11) and in conscious, chronically instrumented rabbits (n = 6). Bilateral microinjection of rilmenidine (4 nmol in 100 nl) into the RVLM caused a greater decrease in resting arterial pressure in anesthetized animals (-19 mm Hg) than in conscious animals (-8 mm Hg). By contrast, the decrease in resting RSNA evoked by rilmenidine was similar in conscious (-27%) and anesthetized (-36%) rabbits. Furthermore, rilmenidine microinjection into the RVLM was equally effective in inhibiting the RSNA baroreflex in both groups of animals. The upper plateau of the RSNA baroreflex decreased by 37% and 42%, and gain decreased by 41% and 44% after rilmenidine treatments in conscious and anesthetized rabbits, respectively. We conclude that the RVLM plays an equally important role in the inhibitory action of rilmenidine on RSNA in conscious and anesthetized rabbits either at rest or during baroreflex responses. A relatively moderate effect of rilmenidine on arterial pressure in conscious, chronically instrumented rabbits may relate to a lower level of sympathetic drive compared with anesthetized animals.

Animals↗

PubMed1997

Anesthetic implications of epilepsy, status epilepticus, and epilepsy surgery.

Epilepsy is a clinical paroxysmal disorder of recurring seizures, excluding alcohol or drug withdrawal seizures or such recurring exogenous events as repeated insulin-induced hypoglycemia. Epilepsy has a profound impact on each individual diagnosed with this disease. Seizures have been and are thought to arise as a result of abnormalities in (a) neural circuits, (b) excitation/inhibition balance, (c) potassium, and (d) genetic abnormalities. Therapy for epilepsy is either medical, entailing the use of a variety of antiepileptic drugs, or surgical. An urgent approach to seizure control is indicated when status epilepticus occurs. When all standard therapy fails, general anesthesia can be used to control status epilepticus. Surgery is an option in the treatment of epilepsy and requires extensive preoperative evaluation. The primary concerns for the neuroanesthesiologist anesthetizing the patient with epilepsy are the capacity of anesthetics to modulate or potentiate seizure activity and the interaction of anesthetic drugs with antiepileptic drugs. Proconvulsant and anticonvulsant properties have been reported for nearly every anesthetic. If seizure spikes are to be evoked during seizure surgery, then light anesthesia with a proconvulsant anesthetic is used. Conscious analgesia can be used for awake seizure surgery. However, if electrocorticography is not planned, then a general anticonvulsant anesthetic maintenance regimen is used. The latter technique also may be useful in patients whose anesthetic management is complicated by an incidental history of epilepsy.

Anesthesia↗

PubMed1993

Favorable effects of epidural analgesia on hemodynamics, oxygenation and metabolic variables in the immediate post-anesthetic period.

Fourteen adult patients undergoing elective major abdominal surgery were divided into two groups. One group received epidural and general anesthesia (epidural group), and 20 ml of 0.125% bupivacaine and 2 mg of morphine were administered epidurally about 30 min before the end of the operation for post-anesthetic analgesia. The other group (control group) received general anesthesia alone with nitrous oxide, oxygen and enflurane. Flow-directed pulmonary arterial and radial arterial catheters were inserted preoperatively, and hemodynamic, respiratory, neuroendocrine and metabolic variables were measured serially. The data were compared during anesthesia and the immediate post-anesthetic recovery period. In the control group, the plasma epinephrine level in the post-anesthetic recovery period increased about four times over the anesthetic period. Oxygen consumption was increased and mixed venous oxygen saturation was decreased significantly. There was a close linear correlation between oxygen consumption (Y) and plasma epinephrine (X) level: Y = 285.7X + 90.5 (P < 0.01, r = 0.72). On the other hand, plasma epinephrine, oxygen consumption and mixed venous oxygen saturation did not change significantly in the epidural group in the post-anesthetic recovery period. There was also a close linear correlation between oxygen consumption (Y) and oxygen delivery (X): Y = 0.22X-32.0 (P < 0.01, r = 0.89). We conclude that the surgical stress and anesthetic reversal may seriously influence neuroendocrine responses and subsequently increase plasma epinephrine. Tissue oxygenation and metabolic imbalance may occur due to the rapid increase of epinephrine in the post-anesthetic recovery period. Epidural analgesia at this period may play a more important role and have a more favorable effect on the tissue metabolism.

Abdomen↗

PubMed1983

The effects of apomorphine upon local cerebral glucose utilization in conscious rats and in rats anesthetized with chloral hydrate.

The effects of the dopaminergic agonist apomorphine (1 mg . kg-1 i.v.) upon local cerebral glucose utilization in 43 anatomically discrete regions of the CNS were examined in conscious, lightly restrained rats and in rats anesthetized with chloral hydrate by means of the quantitative autoradiographic [14C]2-deoxyglucose technique. In animals anesthetized with chloral hydrate, glucose utilization was reduced throughout all regions of the CNS from the levels observed in conscious animals, although the magnitude of the reductions in glucose use displayed considerable regional heterogeneity. With chloral hydrate anesthesia, the proportionately most marked reductions in glucose use (by 40-60% from conscious levels) were noted in primary auditory nuclei, thalmaic relay nuclei, and neocortex, and the least pronounced reductions in glucose use (by 15-25% from conscious levels) were observed in limbic areas, some motor relay nuclei, and white matter. In conscious, lightly restrained rats, the administration of apomorphine (1 mg . kg-1) effected significant increased in glucose utilization in 15 regions of the CNS (e.g., subthalamic nucleus, ventral thalamic nucleus, rostral neocortex, substantia nigra, pars reticulata), and significant reductions in glucose utilization in two regions of the CNS (lateral habenular nucleus and anterior cingulate cortex). In rats anesthetized with chloral hydrate, the effects of apomorphine upon local glucose utilization were less widespread and less marked than in conscious animals. In only two of the regions (the globus pallidus and septal nucleus), which displayed increased glucose use following apomorphine in conscious rats, were significant increases in local glucose utilization observed with this agent in chloral hydrate-anesthetized rats. In the pars compacta of the substantia nigra, in which apomorphine increased glucose utilization in conscious animals, significant reductions in glucose utilization were observed following apomorphine in rats anesthetized with chloral hydrate. The profound effects of chloral hydrate anesthesia upon local cerebral glucose use, and the modification by this anesthetic regime of the local metabolic responses to apomorphine, emphasize the difficulties which exists in the extrapolation of data from anesthetized animals to the conditions which prevail in the conscious animal.

Animals↗

PubMed1984

Nitrogen narcosis and pressure reversal of anesthetic effects in node of Ranvier.

To compare sodium channel block by hyperbaric nitrogen with that induced by other anesthetics and to examine the basis for pressure antagonism to anesthetic condition block, voltage clamped nodes of Ranvier were exposed to nitrogen at pressures at 1-14 atm alone and in combination with helium to a total pressure of up to 100 atm. At 7 and 14 atm nitrogen, sodium currents were reversibly depressed without accompanying changes in the current-voltage relation. The curve relating steady-state inactivation (h infinity) to voltage was shifted in the hyperpolarizing direction, as is the case with other general anesthetic agents. The time constant of inactivation (tau h) was slightly decreased at depolarized potentials. The preceding companion paper demonstrated an opposite effect of hyperbaric helium on the properties of sodium inactivation. Addition of helium pressure in the presence of nitrogen at 14 atm did not increase peak sodium current with inactivation maximally removed, but it did shift the h infinity curve back toward control levels, thus increasing sodium current at points on the slope of the curve. It is proposed that these opposing shifts in steady-state inactivation levels are the basis for pressure antagonism to anesthetic conduction block. In the case of inert gases and volatile anesthetic agents, the antagonism may be direct but has not been shown to be so. In the case of the local anesthetic benzocaine, differences in the voltage dependence of anesthetic and pressure-induced changes in tau h indicate the antagonism is indirect.

Anesthesia, General↗

PubMed1990

Cardiovascular actions of common anesthetic adjuvants during desflurane (I-653) and isoflurane anesthesia in swine.

To determine the cardiovascular actions of drugs commonly combined with inhalation anesthetics, we administered one drug from each of several classes of adjuvants to seven swine already anesthetized with equipotent concentrations (1.2 MAC) of desflurane, formerly I-653, a new inhaled anesthetic, or isoflurane. Succinylcholine (1 and 2 mg/kg), atracurium (0.6 mg/kg), and atropine (5 micrograms/kg) plus edrophonium (5 mg/kg) had no cardiovascular effects. Fentanyl was given in amounts that decreased MAC for the inhaled anesthetics by 25%-35%. A dose of 50 micrograms/kg IV had no cardiovascular effects during either anesthetic, whereas 100 micrograms/kg IV modestly increased systemic vascular resistance without changing other variables. Naloxone (100 micrograms/kg IV) during infusion of fentanyl decreased systemic vascular resistance and increased cardiac output during both desflurane and isoflurane anesthesia, increased heart rate during only isoflurane anesthesia, and did not affect mean arterial blood pressure during either anesthetic. Thiopental (2.5 and 5.0 mg/kg IV) decreased mean aortic blood pressure, cardiac output, stroke volume, and systemic vascular resistance during both anesthetics without altering heart rate or left- or right-sided cardiac filling pressures. The addition of 60% nitrous oxide caused no cardiovascular changes during desflurane anesthesia, but increased systemic vascular resistance and decreased cardiac output and stroke volume during isoflurane without altering heart rate or cardiac preload. We conclude that the usual clinical doses of adjuvants commonly administered during anesthesia have no untoward cardiovascular actions during 1.2 MAC desflurane or isoflurane anesthesia in swine.

Adjuvants, Anesthesia↗

PubMed1991

Masseter muscle spasm in children: implications of continuing the triggering anesthetic.

This retrospective study was undertaken to examine the management and outcome of children who developed isolated masseter muscle spasm (MMS) after the administration of intravenous succinylcholine during anesthetic induction. The inhalation anesthetics used for induction were continued in all of these cases. The medical records of 68 patients (male/female ratio, 1.7:1), identified from approximately 42,000 anesthetics given during the period 1980-1989, were reviewed. Fifty-seven children (2.3-12 yr old) were diagnosed as having isolated MMS, i.e., MMS without spasm of other muscles; 11 experienced generalized rigidity in combination with MMS. Anesthetic and postoperative management of these two groups differed. The overall incidence of MMS was 0.3% of inhalation anesthetics during which succinylcholine was given. Intraoperative arrhythmias occurred in 33% of the patients who developed isolated MMS and more frequently in older children. Most children experienced some degree of hypercarbia and/or metabolic acidosis, but the significance of these abnormalities in the spontaneously ventilating, fasting child is unknown. Serum creatine kinase levels when measured 18-24 h postoperatively were elevated in all but one child (n = 45). There was no long-term morbidity and no mortality. We conclude that failure of the masseter muscles to relax after succinylcholine is not uncommon in children. Based on our experience, and accepting that MMS may be part of the clinical spectrum of malignant hyperthermia, we believe that anesthesia can be continued safely in cases of isolated MMS when careful monitoring accompanies diagnostic evaluation. This differs from the current practice of discontinuing the anesthetic or switching to a nontriggering anesthetic technique.

Anesthesia, Inhalation↗

PubMed1993

Physiologic and anesthetic alterations on spinal-sciatic evoked responses in swine.

Spinal-sciatic evoked responses (ScER) have been used successfully to monitor the integrity of the anterior spinal cord during spinal surgery. To evaluate the effects of hypercarbia, hypocarbia, induced hypotension, and hypothermia on the ScER, ten swine anesthetized with ketamine were subjected to varying levels of PaCO2, hypothermia, and induced hypotension. During variation of one physiologic variable, the other variables were closely regulated. There were no significant changes associated with variations in PaCO2. Decreasing temperature provided a consistent increase in latency (r = -0.78, P < 0.001) with no significant alteration in amplitude. Graded hypotension caused little increase in latency (3.2% at 30 mm Hg). The amplitude decrease averaged 23% at 60 mm Hg with a maximal decrease of 50% at 30 mm Hg. To study inhaled anesthetics, 21 swine anesthetized with ketamine were subjected to nitrous oxide (50% and 70%). After termination of the nitrous oxide, one of the potent inhaled anesthetics (n = 7 each) was administered in 0.25 minimum alveolar concentration (MAC) increments. Nitrous oxide caused a significant decrease in amplitude (average 43% and 61% at 50% and 70%) with minimal changes in latency. There was a dose-dependent decrease in amplitude and increase in latency with all inhaled anesthetics. The ScER disappeared at 1.0 MAC with all anesthetics. There were no differences between effects of equipotent concentrations of inhaled anesthetics. These findings may be helpful in the interpretation of the ScER response during anesthesia and surgery.

Anesthesia, Inhalation↗

PubMed1993

Is there a cutoff in anesthetic potency for the normal alkanes?

Vapor pressures and anesthetizing partial pressures in rats were measured for 10 consecutive normal alkanes, methane through decane. All produced anesthesia as defined by the absence of movement in response to either the application of a tail-clamp or electrical stimulation of the tail. The anesthetizing partial pressure was calculated as the average between the concentrations just permitting and preventing movement. Although nonane and decane did not provide anesthesia when given alone at their saturated vapor pressures, their anesthetic properties could be demonstrated by their ability to decrease the anesthetic requirement for isoflurane (i.e., their anesthetic potencies could be defined by studies of additivity). Anesthetic potency increased (from 9.9 atm for methane to 0.0142 atm for decane) and vapor pressure decreased (from 38.2 atm for ethane to 0.0028 atm for decane) with increasing chain length. The decrease in vapor pressure far exceeded the increase in potency. For nonane and decane, the ratio of the partial pressure required for anesthesia to the saturated vapor pressure was less than 1, being 0.48 and 0.19, respectively. We conclude that no cutoff phenomenon (i.e., no absence of anesthetic effect with longer chain alkanes) exists from n-methane to n-decane, but that larger alkanes have vapor pressures too low to permit their potency to be evident when given alone.

Alkanes↗

PubMed1993

Drosophila melanogaster as a model for study of general anesthesia: the quantitative response to clinical anesthetics and alkanes.

Using an assay of the geotactic behavior of the fruit fly, we have quantified anesthetic effects in Drosophila melanogaster. We determined dose-responses for nine conventional anesthetics and a series of n-alkanes. For the conventional anesthetics, anesthetic potency and olive oil/gas partition coefficients are well correlated. However, as one ascends the series of alkanes of chain lengths 5-11, the increase in anesthetic potency is considerably less than that predicted by olive oil solubility. These examples of agreement and disagreement with the Meyer-Overton rule provide a basis for comparing the responses of fruit flies with those of higher organisms; such comparisons suggest that the anesthetic target is evolutionarily conserved. For alkanes with chain lengths greater than 11, anesthetic effects are variable and slow to develop. This behavior reflects limited volatility and provides no evidence for a cut-off in the action of alkanes at their target.

Alkanes↗

PubMed1993

Effects of nitric oxide synthase inhibition on regional cerebral blood flow and vascular resistance in conscious and isoflurane-anesthetized rats.

Nitric oxide is an important regulator of the regional cerebral vascular tone. We compared the magnitude of nitric oxide-related changes in the vascular tone by studying the regional cerebral blood flow (rCBF) and vascular resistance in conscious and isoflurane-anesthetized rats by using a nitric oxide synthase inhibitor, NG-nitro-L-arginine methyl ester (L-NAME). In the conscious group (n = 12), after cannulation of a femoral artery and two veins under isoflurane anesthesia, rats were allowed to remain awake for 90 min. In the anesthetized group (n = 18), rats were anesthetized with 2% isoflurane and mechanically ventilated. Six rats in each group were treated with L-NAME (2 mg.kg-1 x min-1 for 30 min) or saline. For the remaining rats in the isoflurane-anesthetized group (n = 6), arterial blood pressure was increased by phenylephrine infusion to the same level as that in the L-NAME-treated, isoflurane-anesthetized rats. Regional vascular resistance was determined by the ratio of mean arterial blood pressure and rCBF which was measured by [14C]iodoantipyrine. L-NAME significantly increased mean arterial blood pressure in both the conscious (123 to 158 mm Hg) and anesthetized (82 to 144 mm Hg) rats. Regional vascular resistance increased significantly in all 12 brain regions studied with the average value increasing from 1.19 +/- 0.33 mm Hg.mL-1 x min x 100 g to 2.22 +/- 0.48 (P < 0.0001) in the conscious and from 0.78 +/- 0.27 to 1.61 +/- 0.48 (P < 0.0001) in the isoflurane-anesthetized rats.(ABSTRACT TRUNCATED AT 250 WORDS)

Amino Acid Oxidoreductases↗

PubMed1999

[The current state of leak in anesthetic machines detected by low flow leak tests].

To assess the current state of leak in anesthetic machines, we selected 66 units of anesthetic machines for inspection and repair from various medical institutions. Based on a newly designed inspection flow chart a low flow leak test for internal circuits of the anesthetic machines was performed. The conventional low flow leak test was also performed for smooth detection of leak for rational evaluation. Only 39% of the anesthetic machines met the standard of the low flow leak tests, and leak was detected in the remaining 61%. The average residual leak mounted to 0.97 l.min-1, with the maximum of 5.3 l.min-1. Canisters, corrugated tubes, and vaporizers were considered the primary causes of leak. After the inspection and repair, leak in 77.5% of the anesthetic machines either disappeared or decreased and the average residual leak dropped to 0.34 l.min-1. However, 47% of the anesthetic machines still failed to meet the standard of the low flow leak tests. To further improve the situation, more detailed inspection and repair are necessary especially for precise detection of the cause of leak in the internal circuit of anesthetic machines which often remains undetected.

Anesthesiology↗

PubMed2000

[Assessment of application of computerized local anesthetic delivery system in periodontal ligament injection].

OBJECTIVE: To assess the pain intensity and anesthetic effect in peridontal ligament injection using the computerized local anesthetic delivery system made by Milestone company in USA. METHODS: 40 cases were selected,and comparing the periodontal ligament injection through using the computerized local anesthetic delivery with traditional manul local anesthesia. RESULTS: By using the computerized local anesthetic delivery system the pain in peridontal ligament injection was significantly less than traditional methods. There was no difference in anesthetic effect when teeth were extracted. CONCLUSION: The peridontal ligament injection usually as an adjunctive anesthesia method could attain good anesthetic effect and would have a wide application by using the computerized local anesthetic delivery system.

English Abstract↗

PubMed2005

Progressive suppression of motor evoked potentials during general anesthesia: the phenomenon of "anesthetic fade".

Transcranial motor evoked potentials (MEPs) are useful for assessing the integrity of spinal cord motor tracts during major spine surgery. Anesthetic agents depress the amplitude of MEPs in a dose-dependent fashion. Anecdotal reports suggest that MEP responses degrade or "fade" over the duration of a surgery, despite unchanged anesthetic levels or other physiologic variables. This phenomenon has not been systematically analyzed. We performed a retrospective study of 418 patients who underwent spine surgery at UCSF using intraoperative MEP monitoring. We excluded patients who experienced variations in physiologic parameters that might affect MEP signals and those who developed new neurologic deficits. We identified 46 neurologically intact patients and 16 myelopathic patients who had surgery performed using a constant desflurane/N2O/narcotic or desflurane/propofol/narcotic anesthetic regimen. The minimum voltage threshold needed to produce an MEP response of at least 50 microV in amplitude was recorded at the beginning ("baseline") and end of surgery. The voltage threshold was higher at the end of the case than at baseline for each patient, regardless of anesthetic regimen. In normal patients, the rate of rise of the threshold was similar for those receiving propofol (11.4 +/- 6.9 V/hr) or N2O (9.7 +/- 5.9 V/hr) (P = not significant). Myelopathic patients demonstrated a larger rate of rise in voltage threshold, 23.4 +/- 12.2 V/hr, versus normal subjects (P < 0.01). The rate of rise of voltage threshold is inversely proportional to anesthetic duration. Prolonged exposure to anesthetic agents necessitates higher stimulating thresholds to elicit MEP responses, separate from the dose-dependent depressant effect. This retrospective study is limited and cannot explain the mechanism for this observed fade in signals. Recognition of anesthetic fade is essential when interpreting changes to the MEP response to avoid false-positive findings.

Adult↗