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Competitive Interactions between Halothane and Isoflurane at the Carotid Body and TASK Channels. Anesthesiology 2020; 133:1046-1059. [DOI: 10.1097/aln.0000000000003520] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
Abstract
Background
The degree to which different volatile anesthetics depress carotid body hypoxic response relates to their ability to activate TASK potassium channels. Most commonly, volatile anesthetic pairs act additively at their molecular targets. We examined whether this applied to carotid body TASK channels.
Methods
We studied halothane and isoflurane effects on hypoxia-evoked rise in intracellular calcium (Ca2+i, using the indicator Indo-1) in isolated neonatal rat glomus cells, and TASK single-channel activity (patch clamping) in native glomus cells and HEK293 cell line cells transiently expressing TASK-1.
Results
Halothane (5%) depressed glomus cell Ca2+i hypoxic response (mean ± SD, 94 ± 4% depression; P < 0.001 vs. control). Isoflurane (5%) had a less pronounced effect (53 ± 10% depression; P < 0.001 vs. halothane). A mix of 3% isoflurane/1.5% halothane depressed cell Ca2+i response (51 ± 17% depression) to a lesser degree than 1.5% halothane alone (79 ± 15%; P = 0.001), but similar to 3% isoflurane alone (44 ± 22%; P = 0.224), indicating subadditivity. Halothane and isoflurane increased glomus cell TASK-1/TASK-3 activity, but mixes had a lesser effect than that seen with halothane alone: 4% halothane/4% isoflurane yielded channel open probabilities 127 ± 55% above control, versus 226 ± 12% for 4% halothane alone (P = 0.009). Finally, in HEK293 cell line cells, progressively adding isoflurane (1.5 to 5%) to halothane (2.5%) reduced TASK-1 channel activity from 120 ± 38% above control, to 88 ± 48% (P = 0.034).
Conclusions
In all three experimental models, the effects of isoflurane and halothane combinations were quantitatively consistent with the modeling of weak and strong agonists competing at a common receptor on the TASK channel.
Editor’s Perspective
What We Already Know about This Topic
What This Article Tells Us That Is New
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Choi DH, Shin TJ, Kim S, Bae J, Cho D, Ham J, Park JY, Kim HI, Jeong S, Lee B, Kim JG. Monitoring cerebral oxygenation and local field potential with a variation of isoflurane concentration in a rat model. BIOMEDICAL OPTICS EXPRESS 2016; 7:4114-4124. [PMID: 27867719 PMCID: PMC5102553 DOI: 10.1364/boe.7.004114] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/23/2016] [Revised: 08/25/2016] [Accepted: 09/09/2016] [Indexed: 06/06/2023]
Abstract
We aimed to investigate experimentally how anesthetic levels affect cerebral metabolism measured by near-infrared spectroscopy (NIRS) and to identify a robust marker among NIRS parameters to discriminate various stages of anesthetic depth in rats under isoflurane anesthesia. In order to record the hemodynamic changes and local field potential (LFP) in the brain, fiber-optic cannulae and custom-made microelectrodes were implanted in the frontal cortex of the skull. The NIRS and LFP signals were continuously monitored before, during and after isoflurane anesthesia. As isoflurane concentration is reduced, the level of oxyhemoglobin and total hemoglobin concentrations of the frontal cortex decreased gradually, while deoxyhemoglobin increased. The reflectance ratio between 730nm and 850nm and burst suppression ratio (BSR) correspond similarly with the change of oxyhemoglobin during the variation of isoflurane concentration. These results suggest that NIRS signals in addition to EEG may provide a possibility of developing a new anesthetic depth index.
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Affiliation(s)
- Dong-Hyuk Choi
- Department of Biomedical Science and Engineering, Gwangju Institute of Science and Technology (GIST), Gwangju 61005, South Korea; These authors contributed equally to this study
| | - Teo Jeon Shin
- Department of Pediatric Dentistry, School of Dentistry, Seoul National University, Seoul 03080, South Korea; These authors contributed equally to this study
| | - Seonghyun Kim
- Department of Biomedical Science and Engineering, Gwangju Institute of Science and Technology (GIST), Gwangju 61005, South Korea
| | - Jayyoung Bae
- Department of Biomedical Science and Engineering, Gwangju Institute of Science and Technology (GIST), Gwangju 61005, South Korea
| | - Dongrae Cho
- Department of Biomedical Science and Engineering, Gwangju Institute of Science and Technology (GIST), Gwangju 61005, South Korea
| | - Jinsil Ham
- Department of Biomedical Science and Engineering, Gwangju Institute of Science and Technology (GIST), Gwangju 61005, South Korea
| | - Ji-Young Park
- Department of Biomedical Science and Engineering, Gwangju Institute of Science and Technology (GIST), Gwangju 61005, South Korea
| | - Hyoung-Ihl Kim
- Department of Biomedical Science and Engineering, Gwangju Institute of Science and Technology (GIST), Gwangju 61005, South Korea
| | - Seongwook Jeong
- Department of Anesthesiology and Pain Medicine, Chonnam National University Medical School, Gwangju 61469, South Korea
| | - Boreom Lee
- Department of Biomedical Science and Engineering, Gwangju Institute of Science and Technology (GIST), Gwangju 61005, South Korea;
| | - Jae Gwan Kim
- Department of Biomedical Science and Engineering, Gwangju Institute of Science and Technology (GIST), Gwangju 61005, South Korea;
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Whitehead RA, Schwarz SKW, Asiri YI, Fung T, Puil E, MacLeod BA. The Efficacy and Safety of the Novel Peripheral Analgesic Isovaline as an Adjuvant to Propofol for General Anesthesia and Conscious Sedation: A Proof-of-Principle Study in Mice. Anesth Analg 2016; 121:1481-7. [PMID: 26579656 DOI: 10.1213/ane.0000000000000996] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/05/2022]
Abstract
BACKGROUND The combination of propofol and an opioid analgesic is widely used for procedural sedation, as well as total IV anesthesia. However, opioids produce respiratory depression, a primary cause of death due to these agents. We recently reported on the antinociceptive actions of isovaline, a small nonbiogenic amino acid that does not readily cross the blood-brain barrier and acts on peripheral γ-aminobutyric acid type B receptors. Here, we explored the possibility that isovaline may be an effective and safe alternative to opioids as an adjunct to propofol for producing anesthesia. METHODS With approval from our Animal Care Committee, we conducted an in vivo study in adult female CD-1 mice using Dixon's "up-and-down" method for dose assessment. Animals received intraperitoneal saline, propofol, isovaline, fentanyl, or coadministration of propofol with isovaline or fentanyl. We assessed hypnosis by a loss of righting reflex and immobility by an absence of motor response to tail clip application. General anesthesia was defined as the presence of both hypnosis and immobility. We assessed conscious sedation as a decrease in time on a rotarod. The maximal dose without respiratory rates of <4 per minute, apnea, or death was defined as the maximal tolerated dose. RESULTS Either isovaline or fentanyl coadministered with propofol at its half-maximal effective dose (ED50) for hypnosis produced general anesthesia (isovaline ED50, 96 mg/kg [95% confidence interval {CI}, 88-124 mg/kg]; fentanyl ED50, 0.12 mg/kg [95% CI, 0.08-3.5 mg/kg]). Propofol produced hypnosis (ED50, 124 mg/kg [95% CI, 84-3520 mg/kg]) but did not block responses to tail clip application. Neither isovaline nor fentanyl produced hypnosis at doses which produced immobility (isovaline ED50, 350 mg/kg [95% CI, 286-1120 mg/kg]; fentanyl ED50, 0.35 mg/kg [95% CI, 0.23-0.51 mg/kg]). Isovaline at its analgesic ED50, coadministered with a subhypnotic dose of propofol (40 mg/kg), did not exacerbate propofol-induced deficits in rotarod performance. The median maximal tolerated dose of fentanyl coadministered with the hypnotic ED50 of propofol was 11 mg/kg (95% CI, 8-18 mg/kg). Isovaline at a maximal deliverable (soluble) dose of 5000 mg/kg produced no apparent respiratory depression or other adverse effects. CONCLUSIONS The novel analgesic, isovaline, coadministered with propofol, produced general anesthesia and conscious sedation in mice. The margin of safety for propofol-isovaline was considerably higher than that for propofol-fentanyl. This study's results show that propofol-based sedation and general anesthesia can be effectively and safely produced by replacing the conventional opioid component with a brain-impermeant peripherally acting γ-aminobutyric acid type B receptor agonist. The results provide proof of the principle of combining a peripheral analgesic with a centrally acting hypnotic to produce general anesthesia. This principle suggests a novel approach to clinical general anesthesia and conscious sedation.
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Affiliation(s)
- Ryan A Whitehead
- From the *Department of Anesthesiology, Pharmacology & Therapeutics, The University of British Columbia, Vancouver, British Columbia, Canada; and †Department of Anesthesia, St. Paul's Hospital, Vancouver, British Columbia, Canada
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Functional connectivity hubs of the mouse brain. Neuroimage 2015; 115:281-91. [DOI: 10.1016/j.neuroimage.2015.04.033] [Citation(s) in RCA: 128] [Impact Index Per Article: 14.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/28/2014] [Revised: 03/14/2015] [Accepted: 04/16/2015] [Indexed: 12/12/2022] Open
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Neural control of arterial pressure variability in the neuromuscularly blocked rat. Eur J Appl Physiol 2011; 112:2013-24. [PMID: 21947406 DOI: 10.1007/s00421-011-2160-4] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/23/2011] [Accepted: 08/30/2011] [Indexed: 10/17/2022]
Abstract
The baroreflexes stabilize moment-to-moment arterial pressure. Sinoaortic denervation (SAD) of the baroreflexes results in a large increase in arterial pressure variability (APV) across various species. Due to an incomplete understanding of the nonlinear interactions between central and peripheral systems, the major source of APV remains controversial. While some studies suggested that the variability is endogenous to the central nervous system (CNS), others argued that peripheral influences may be the main source. For decades, abnormal cardiovascular variability has been associated with a number of cardiovascular diseases including hypertension, heart failure, and stroke. Delineating mechanisms of the APV is critical for the improvement of current strategies that use APV as a clinical tool for the diagnosis and prognosis of cardiovascular diseases. In this study, with a unique chronic neuromuscularly blocked (NMB) rat preparation that largely constrains peripheral influences, we determined the CNS contribution to the post-SAD APV. First, we confirmed that SAD significantly increased APV in the NMB rat, then demonstrated that post-SAD ganglionic blockade substantially reduced APV, and subsequent intravenous infusions of phenylephrine and epinephrine (in presence of ganglionic blockade) only slightly increased APV. These data suggest that the CNS is an important source, and skeletal activity, thermal challenges or other forms of peripherally generated cardiovascular stress are not required for the post-SAD APV. In addition, we showed that bilateral aortic denervation produced a larger increase in APV than bilateral carotid sinus denervation, suggesting that the aortic baroreflex plays a more dominant role in the control of APV than the carotid sinus.
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Zhou C, Gan J, Liu J, Luo WJ, Zhang WS, Chai YF. The Interaction Between Emulsified Isoflurane and Lidocaine Is Synergism in Intravenous Regional Anesthesia in Rats. Anesth Analg 2011; 113:245-50. [DOI: 10.1213/ane.0b013e31821e9797] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/05/2022]
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Nitrous oxide and isoflurane are synergistic with respect to amplitude and latency effects on sensory evoked potentials. J Clin Monit Comput 2010; 24:113-23. [DOI: 10.1007/s10877-009-9219-3] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/21/2009] [Accepted: 12/30/2009] [Indexed: 11/26/2022]
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Eger EI, Tang M, Liao M, Laster MJ, Solt K, Flood P, Jenkins A, Raines D, Hendrickx JF, Shafer SL, Yasumasa T, Sonner JM. Inhaled anesthetics do not combine to produce synergistic effects regarding minimum alveolar anesthetic concentration in rats. Anesth Analg 2008; 107:479-85. [PMID: 18633026 DOI: 10.1213/01.ane.0000295805.70887.65] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
Abstract
BACKGROUND We hypothesized that pairs of inhaled anesthetics having divergent potencies [one acting weakly at minimum alveolar anesthetic concentration (MAC); one acting strongly at MAC] on specific receptors/channels might act synergistically, and that such deviations from additivity would support the notion that anesthetics act on multiple sites to produce anesthesia. METHODS Accordingly, we studied the additivity of MAC for 11 anesthetic pairs divergently (one weakly, one strongly) affecting a specific receptor/channel at MAC. By "divergently," we usually meant that at MAC the more strongly acting anesthetic enhanced or blocked the in vitro receptor or channel at least twice (and usually more) as much as did the weakly acting anesthetic. The receptors/channels included: TREK-1 and TASK-3 potassium channels; and gamma-aminobutyric acid type A, glycine, N-methyl-D-aspartic acid, and acetylcholine receptors. We also studied the additivity of cyclopropane-benzene because the N-methyl-D-aspartic acid blocker MK-801 had divergent effects on the MACs of these anesthetics. We also studied four pairs that included nitrous oxide because nitrous oxide had been reported to produce infraadditivity (antagonism) when combined with isoflurane. RESULTS All combinations produced a result within 10% of that which would be predicted by additivity except for the combination of isoflurane with nitrous oxide where infraadditivity was found. CONCLUSIONS Such results are consistent with the notion that inhaled anesthetics act on a single site to produce immobility in the face of noxious stimulation.
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Affiliation(s)
- Edmond I Eger
- Department of Anesthesia, S-455, University of California, San Francisco, CA 94143-0464, USA.
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Abraham MH, Acree WE, Mintz C, Payne S. Effect of anesthetic structure on inhalation anesthesia: implications for the mechanism. J Pharm Sci 2008; 97:2373-84. [PMID: 17847069 DOI: 10.1002/jps.21150] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
Abstract
Many previous attempts (e.g., the Meyer-Overton hypothesis) to provide a single set of physical or chemical characteristics that accurately predict anesthetic potency have failed. A finding of a general predictive correlation would support the notion of a unitary theory of narcosis. Using the Abraham solvation parameter model, the minimum alveolar concentration, MAC, of 148 varied anesthetic agents can be fitted to a linear equation in log (1/MAC) with R(2) = 0.985 and a standard deviation, SD = 0.192 log units. Division of the 148 compounds into a training set and a test set shows that log (1/MAC) values can be predicted with no bias and with SD = 0.20 log units. The two main factors that determine MAC values are compound size and compound hydrogen bond acidity, both of which increase anesthetic activity. Shape has little or no effect on anesthetic activity. Our observations support a unitary theory of narcosis by inhalation anesthetics. A two-stage mechanism for inhalation anesthesia accounts for the observed structural effects of anesthetics. In this mechanism, the first main step is transfer of the anesthetic to the site of action, and the second step is interaction of the anesthetic with a receptor(s).
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Affiliation(s)
- Michael H Abraham
- Department of Chemistry, University College London, 20 Gordon Street, London WC1H 0AJ, UK.
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Shafer SL, Hendrickx JFA, Flood P, Sonner J, Eger EI. Additivity Versus Synergy: A Theoretical Analysis of Implications for Anesthetic Mechanisms. Anesth Analg 2008; 107:507-24. [PMID: 18633029 DOI: 10.1213/ane.0b013e31817b7140] [Citation(s) in RCA: 45] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/05/2022]
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Hendrickx JFA, Eger EI, Sonner JM, Shafer SL. Is Synergy the Rule? A Review of Anesthetic Interactions Producing Hypnosis and Immobility. Anesth Analg 2008; 107:494-506. [PMID: 18633028 DOI: 10.1213/ane.0b013e31817b859e] [Citation(s) in RCA: 185] [Impact Index Per Article: 11.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
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Abstract
BACKGROUND Carbon dioxide decreases halothane minimum alveolar concentrations (MAC) in dogs when Paco(2) exceeds 95 mm Hg. We sought to confirm these findings for several potent inhaled anesthetics in rats. METHODS Groups of eight rats were anesthetized with halothane, isoflurane, or desflurane. MAC was determined for each anesthetic alone, and then with increasing concentrations of inspired CO(2). A fourth group was given CO(2) alone to determine the MAC of CO(2). RESULTS Increasing inspired CO(2) concentrations produced a linear dose-dependent decrease in MAC of each potent inhaled anesthetic. With elimination of CO(2), the MAC of isoflurane and desflurane returned to the original MAC. As determined by extrapolating these data to 0% of the inhaled anesthetic, the MAC of CO(2) was approximately 50% of 1 atm. Given alone, CO(2) proved lethal. CONCLUSIONS Unlike dogs, no threshold for the CO(2)-MAC response arose with halothane, isoflurane, or desflurane in rats. The ED(50) for CO(2) is also approximately 50% greater in rats than reported in dogs.
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Affiliation(s)
- Robert J Brosnan
- Department of Surgical and Radiological Sciences, School of Veterinary Medicine, University of California, Davis, CA 95616, USA.
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Brosnan RJ, Yang L, Milutinovic PS, Zhao J, Laster MJ, Eger EI, Sonner JM. Ammonia has anesthetic properties. Anesth Analg 2007; 104:1430-3, table of contents. [PMID: 17513636 DOI: 10.1213/01.ane.0000264072.97705.0f] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/13/2023]
Abstract
BACKGROUND A recent theory of anesthesia predicts that some endogenous compounds should have anesthetic properties. This theory raises the possibility that metabolites that are profoundly elevated in disease may also exert anesthetic effects. Because in pathophysiologic concentrations, ammonia reversibly impairs memory, consciousness, and responsiveness to noxious stimuli in a manner similar to anesthetics, we investigated whether ammonia had anesthetic properties. METHODS The effect of ammonia was studied on alpha1beta2 and alpha1beta2gamma2s gamma-amino butyric acid type A, alpha1 glycine, and NR1/NR2A N-methyl-D-aspartate receptors, and the two-pore domain potassium channel TRESK. Channels were expressed in Xenopus laevis oocytes and studied using two-electrode voltage clamping. The immobilizing effect of ammonia in rats was evaluated by determining the reduction in isoflurane minimum alveolar concentration produced by IV infusion of ammonium chloride. The olive oil-water partition coefficient was measured to determine whether free ammonia (NH3) followed the Meyer-Overton relation. RESULTS Ammonia positively modulated TRESK channels and glycine receptors. No effect was seen on alpha1beta2 and alpha1beta2gamma2s gamma-amino butyric acid type A receptors or NR1/NR2A N-methyl-d-aspartate receptors. Ammonia reversibly decreased the requirement for isoflurane, with a calculated immobilizing EC50 of 1.6 +/- 0.1 mM NH4Cl. The Ostwald olive oil-water partition coefficient for NH3 was 0.018. At a pH of 7.4, and at the anesthetic EC50, the NH3 concentration in bulk olive oil is 0.42 muM, approximately five orders of magnitude less than observed by anesthetics that follow the Meyer-Overton relation. CONCLUSIONS These findings support the hypothesis that ammonia has anesthetic properties. Bulk oil concentration did not predict the potency of ammonia.
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Affiliation(s)
- Robert J Brosnan
- Department of Surgical and Radiological Sciences, School of Veterinary Medicine, University of California, Davis, Calif 94143-0464, USA
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Multiple synaptic and membrane sites of anesthetic action in the CA1 region of rat hippocampal slices. BMC Neurosci 2004; 5:52. [PMID: 15579203 PMCID: PMC543467 DOI: 10.1186/1471-2202-5-52] [Citation(s) in RCA: 48] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/17/2004] [Accepted: 12/03/2004] [Indexed: 11/10/2022] Open
Abstract
BACKGROUND Anesthesia is produced by a depression of central nervous system function, however, the sites and mechanisms of action underlying this depression remain poorly defined. The present study compared and contrasted effects produced by five general anesthetics on synaptic circuitry in the CA1 region of hippocampal slices. RESULTS At clinically relevant and equi-effective concentrations, presynaptic and postsynaptic anesthetic actions were evident at glutamate-mediated excitatory synapses and at GABA-mediated inhibitory synapses. In addition, depressant effects on membrane excitability were observed for CA1 neuron discharge in response to direct current depolarization. Combined actions at several of these sites contributed to CA1 circuit depression, but the relative degree of effect at each site was different for each anesthetic studied. For example, most of propofol's depressant effect (> 70 %) was reversed with a GABA antagonist, but only a minor portion of isoflurane's depression was reversed (< 20 %). Differences were also apparent on glutamate synapses-pentobarbital depressed transmission by > 50 %, but thiopental by only < 25 %. CONCLUSIONS These results, in as much as they may be relevant to anesthesia, indicate that general anesthetics act at several discrete sites, supporting a multi-site, agent specific theory for anesthetic actions. No single effect site (e.g. GABA synapses) or mechanism of action (e.g. depressed membrane excitability) could account for all of the effects produced for any anesthetic studied.
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Leon A, Mayzler O, Benifla M, Semionov M, Fuxman Y, Eilig I, Passuga V, Doitchinova MK, Gurevich B, Artru AA, Shapira Y. Determining Minimum Alveolar Anesthetic Concentration of Halothane in Rats: The Effect of Incremental Change in Halothane Concentration and Number of Crossovers. Anesth Analg 2004; 99:1822-1828. [PMID: 15562080 DOI: 10.1213/01.ane.0000139651.82022.1d] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/05/2022]
Abstract
Computer simulations for the technique of estimating minimum alveolar anesthetic concentration (MAC) in patients (quantal design) suggest that incremental concentration changes and the number of crossovers affect MAC. We hypothesized that these variables may also apply to estimating MAC in rats (bracketing design). This study tested that hypothesis and also examined whether these variables might mask differences in MAC between groups in which MAC might be expected to differ (pregnant [P] versus nonpregnant [NP]). There were 2 cohorts (n = 27 and n = 30 rats). Each cohort included NP females, females in early P, and females in late P. MAC was tested by using an incremental concentration change of 0.20% and one within-subject crossover in the first cohort and by using an increment size of 0.10% and four crossovers in the second cohort. MAC was statistically significantly increased in the three groups in the second cohort (NP, 1.16 +/- 0.12; early P, 1.14 +/- 0.10; late P, 1.07 +/- 0.10; mean +/- sd) compared with values in the three comparable groups in the first cohort (NP, 0.95 +/- 0.06; early P, 1.01 +/- 0.09; late P, 0.93 +/- 0.13). Values did not differ among groups within each cohort. Post hoc simulations indicated that up to 36% of the difference between cohorts was due to increment size, with the balance due to experimental factors. Our findings confirmed the hypothesis that increment size affects estimates of MAC when a bracketing design is used.
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Affiliation(s)
- Avner Leon
- *Division of Anesthesiology, ‡Department of Surgery, and §Department of Neurosurgery, Soroka Medical Center, Beer Sheva, Israel; †Faculty of Health Science, Ben-Gurion University of the Negev, Beer Sheva, Israel; ∥Department of Surgery, Barzilay Medical Center, Askelon, Israel; and ¶Department of Anesthesiology, University of Washington School of Medicine, Seattle, Washington
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