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Reed RA, Epstein KL, Bramski JH, Diehl KA, Ryan CA. The effect of xylazine on intracranial pressure in anesthetized and standing horses. J Vet Emerg Crit Care (San Antonio) 2021; 31:476-482. [PMID: 34143942 DOI: 10.1111/vec.13083] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/08/2019] [Revised: 02/18/2020] [Accepted: 03/09/2020] [Indexed: 11/28/2022]
Abstract
OBJECTIVE To determine the effect of xylazine on intracranial pressure (ICP) in standing compared to isoflurane-anesthetized horses. DESIGN Prospective, crossover study design. SETTING University Teaching Hospital. ANIMALS Six adult horses donated to the University. Horses were determined to be healthy via physical examination, complete blood count, and neurological evaluation. INTERVENTIONS Horses were anesthetized, maintained on isoflurane in oxygen in left lateral recumbency, and ventilated to normocapnia. Horses were instrumented for intraparenchymal measurement of ICP, invasive blood pressure, pulse oximetry, and end tidal gas analyzer. Xylazine 1 mg/kg was administered IV and ICP, systolic arterial pressure, mean arterial pressure (MAP), diastolic arterial pressure, and heart rate were recorded and cerebral perfusion pressure (CPP) was calculated for the following 15 minutes. Twenty-four to 36 hours following anesthetic recovery, xylazine 1 mg/kg was administered IV and ICP, heart rate, and Doppler blood pressure (BPdop) on the tail were monitored for 15 minutes. MEASUREMENTS AND MAIN RESULTS There was a decrease in ICP following administration of xylazine in anesthetized horses (P < 0.003) but not standing horses (P = 0.227). There was an increase in systolic arterial pressure, MAP, diastolic arterial pressure (P < 0.001), and BPdop (P = 0.001) following administration of xylazine. As a result, CPP increased in anesthetized horses (P < 0.03). There was a negative association between ICP and MAP in anesthetized horses (P = 0.007) but not ICP and BPdop conscious horses (P = 0.379). CONCLUSIONS Administration of xylazine to anesthetized horses resulted in an increased CPP due to decreased ICP with concurrent increased MAP. Administration of xylazine to standing horses did not result in a change in ICP. However, with the increase in BPdop found in awake horses, it is likely that CPP would also increase in awake horses following xylazine administration.
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Affiliation(s)
- Rachel A Reed
- Department of Large Animal Medicine, University of Georgia College of Veterinary Medicine, Athens, Georgia, USA
| | - Kira L Epstein
- Department of Large Animal Medicine, University of Georgia College of Veterinary Medicine, Athens, Georgia, USA
| | - Jessica H Bramski
- Department of Large Animal Medicine, University of Georgia College of Veterinary Medicine, Athens, Georgia, USA
| | - Kathryn A Diehl
- Department of Small Animal Medicine and Surgery, University of Georgia College of Veterinary Medicine, Athens, Georgia, USA
| | - Clare A Ryan
- Department of Large Animal Medicine, University of Georgia College of Veterinary Medicine, Athens, Georgia, USA
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Sturges BK, Dickinson PJ, Tripp LD, Udaltsova I, LeCouteur RA. Intracranial pressure monitoring in normal dogs using subdural and intraparenchymal miniature strain-gauge transducers. J Vet Intern Med 2018; 33:708-716. [PMID: 30575120 PMCID: PMC6430958 DOI: 10.1111/jvim.15333] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/29/2018] [Revised: 08/24/2018] [Accepted: 09/05/2018] [Indexed: 12/25/2022] Open
Abstract
Background Monitoring of intracranial pressure (ICP) is a critical component in the management of intracranial hypertension. Safety, efficacy, and optimal location of microsensor devices have not been defined in dogs. Hypothesis/Objective Assessment of ICP using a microsensor transducer is feasible in anesthetized and conscious animals and is independent of transducer location. Intraparenchymal transducer placement is associated with more adverse effects. Animals Seven adult, bred‐for‐research dogs. Methods In a prospective investigational study, microsensor ICP transducers were inserted into subdural and intraparenchymal locations at defined rostral or caudal locations within the rostrotentorial compartment under general anesthesia. Mean arterial pressure and ICP were measured continuously during physiological maneuvers, and for 20 hours after anesthesia. Results Baseline mean ± SD values for ICP and cerebral perfusion pressure were 7.2 ± 2.3 and 78.9 ± 7.6 mm Hg, respectively. Catheter position did not have a significant effect on ICP measurements. There was significant variation from baseline ICP accompanying physiological maneuvers (P < .001) and with normal activities, especially with changes in head position (P < .001). Pathological sequelae were more evident after intraparenchymal versus subdural placement. Conclusions and Clinical Importance Use of a microsensor ICP transducer was technically straightforward and provided ICP measurements within previously reported reference ranges. Results support the use of an accessible dorsal location and subdural positioning. Transient fluctuations in ICP are normal events in conscious dogs and large variations associated with head position should be accounted for when evaluating animals with intracranial hypertension.
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Affiliation(s)
- Beverly K Sturges
- Departments of Surgical and Radiological Sciences, School of Veterinary Medicine, University of California-Davis, Davis, California
| | - Peter J Dickinson
- Departments of Surgical and Radiological Sciences, School of Veterinary Medicine, University of California-Davis, Davis, California
| | - Linda D Tripp
- Office of Research, University of California-Davis, Davis, California
| | - Irina Udaltsova
- Population, Health and Reproduction, School of Veterinary Medicine, University of California-Davis, Davis, California
| | - Richard A LeCouteur
- Departments of Surgical and Radiological Sciences, School of Veterinary Medicine, University of California-Davis, Davis, California
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Williams DC, Brosnan RJ, Fletcher DJ, Aleman M, Holliday TA, Tharp B, Kass PH, LeCouteur RA, Steffey EP. Qualitative and Quantitative Characteristics of the Electroencephalogram in Normal Horses during Administration of Inhaled Anesthesia. J Vet Intern Med 2015; 30:289-303. [PMID: 26714626 PMCID: PMC4913671 DOI: 10.1111/jvim.13813] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/19/2015] [Revised: 08/27/2015] [Accepted: 11/17/2015] [Indexed: 11/30/2022] Open
Abstract
BACKGROUND The effects of anesthesia on the equine electroencephalogram (EEG) after administration of various drugs for sedation, induction, and maintenance are known, but not that the effect of inhaled anesthetics alone for EEG recording. OBJECTIVE To determine the effects of isoflurane and halothane, administered as single agents at multiple levels, on the EEG and quantitative EEG (qEEG) of normal horses. ANIMALS Six healthy horses. METHODS Prospective study. Digital EEG with video and quantitative EEG (qEEG) were recorded after the administration of one of the 2 anesthetics, isoflurane or halothane, at 3 alveolar doses (1.2, 1.4 and 1.6 MAC). Segments of EEG during controlled ventilation (CV), spontaneous ventilation (SV), and with peroneal nerve stimulation (ST) at each MAC multiple for each anesthetic were selected, analyzed, and compared. Multiple non-EEG measurements were also recorded. RESULTS Specific raw EEG findings were indicative of changes in the depth of anesthesia. However, there was considerable variability in EEG between horses at identical MAC multiples/conditions and within individual horses over segments of a given epoch. Statistical significance for qEEG variables differed between anesthetics with bispectral index (BIS) CV MAC and 95% spectral edge frequency (SEF95) SV MAC differences in isoflurane only and median frequency (MED) differences in SV MAC with halothane only. CONCLUSIONS AND CLINICAL IMPORTANCE Unprocessed EEG features (background and transients) appear to be beneficial for monitoring the depth of a particular anesthetic, but offer little advantage over the use of changes in mean arterial pressure for this purpose.
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Affiliation(s)
- D C Williams
- William R. Pritchard Veterinary Medical Teaching Hospital, School of Veterinary Medicine, University of California, Davis, CA
| | - R J Brosnan
- Departments of Surgical and Radiological Sciences, School of Veterinary Medicine, University of California, Davis, CA
| | - D J Fletcher
- Section of Emergency and Critical Care, Cornell University, Ithaca, NY
| | - M Aleman
- Medicine and Epidemiology, School of Veterinary Medicine, University of California, Davis, CA
| | - T A Holliday
- Departments of Surgical and Radiological Sciences, School of Veterinary Medicine, University of California, Davis, CA
| | - B Tharp
- Department of Neurology, University of California Davis Medical Center, Sacramento, CA
| | - P H Kass
- Population Health and Reproduction, School of Veterinary Medicine, University of California, Davis, CA
| | - R A LeCouteur
- Departments of Surgical and Radiological Sciences, School of Veterinary Medicine, University of California, Davis, CA
| | - E P Steffey
- Departments of Surgical and Radiological Sciences, School of Veterinary Medicine, University of California, Davis, CA
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Williams DC, Aleman MR, Brosnan RJ, Fletcher DJ, Holliday TA, Tharp B, Kass PH, Steffey EP, LeCouteur RA. Electroencephalogram of Healthy Horses During Inhaled Anesthesia. J Vet Intern Med 2015; 30:304-8. [PMID: 26376458 PMCID: PMC4913644 DOI: 10.1111/jvim.13613] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/19/2015] [Revised: 07/23/2015] [Accepted: 08/05/2015] [Indexed: 11/27/2022] Open
Abstract
Background Previous study of the diagnostic validity of electroencephalography (EEG) to detect abnormalities in equine cerebral cortical function relied on the administration of various drugs for sedation, induction, and maintenance of general anesthesia but used identical criteria to interpret recordings. Objectives To determine the effects of 2 inhalation anesthetics on the EEG of healthy horses. Animals Six healthy horses. Methods Prospective study. After the sole administration of one of either isoflurane or halothane at 1.2, 1.4, and 1.6 times the minimum alveolar concentration, EEG was recorded during controlled ventilation, spontaneous ventilation, and nerve stimulation. Results Burst suppression was observed with isoflurane, along with EEG events that resembled epileptiform discharges. Halothane results were variable between horses, with epileptiform‐like discharges and bursts of theta, alpha, and beta recorded intermittently. One horse died and 2 were euthanized as the result of anesthesia‐related complications. Conclusions and Clinical Importance The results of this study indicate that the effects of halothane and isoflurane on EEG activity in the normal horse can be quite variable, even when used in the absence of other drugs. It is recommended that equine EEG be performed without the use of these inhalation anesthetics and that general anesthesia be induced and maintained by other contemporary means.
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Affiliation(s)
- D C Williams
- William R. Pritchard Veterinary Medical Teaching Hospital, School of Veterinary Medicine, University of California, Davis, CA
| | - M R Aleman
- Departments of Medicine and Epidemiology, School of Veterinary Medicine, University of California, Davis, CA
| | - R J Brosnan
- Surgical and Radiological Sciences, School of Veterinary Medicine, University of California, Davis, CA
| | - D J Fletcher
- Section of Emergency and Critical Care, Cornell University, Ithaca, NY
| | | | - B Tharp
- Department of Neurology, University of California Davis Medical Center, Sacramento, CA
| | - P H Kass
- Population Health and Reproduction, School of Veterinary Medicine, University of California, Davis, CA
| | - E P Steffey
- Surgical and Radiological Sciences, School of Veterinary Medicine, University of California, Davis, CA
| | - R A LeCouteur
- Surgical and Radiological Sciences, School of Veterinary Medicine, University of California, Davis, CA
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Abstract
Inhaled agents represent an important and useful class of drugs for equine anesthesia. This article reviews the ether-type anesthetics in contemporary use, their uptake and elimination, their mechanisms of action, and their desirable and undesirable effects in horses.
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Affiliation(s)
- Robert J Brosnan
- Department of Surgical and Radiological Sciences, School of Veterinary Medicine, University of California, Davis, One Shields Avenue, Davis, CA 95616, USA.
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Brosnan RJ, Steffey EP, Escobar A, Palazoglu M, Fiehn O. Anesthetic induction with guaifenesin and propofol in adult horses. Am J Vet Res 2011; 72:1569-75. [DOI: 10.2460/ajvr.72.12.1569] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
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Brosnan RJ, Steffey EP, LeCouteur RA, Esteller-Vico A, Vaughan B, Liu IKM. Effects of isoflurane anesthesia on cerebrovascular autoregulation in horses. Am J Vet Res 2011; 72:18-24. [DOI: 10.2460/ajvr.72.1.18] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
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Brosnan RJ, Esteller-Vico A, Steffey EP, LeCouteur RA, Liu IKM, Vaughan B. Effects of head-down positioning on regional central nervous system perfusion in isoflurane-anesthetized horses. Am J Vet Res 2008; 69:737-43. [DOI: 10.2460/ajvr.69.6.737] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
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Yankeelov TE, DeBusk LM, Billheimer DD, Luci JJ, Lin PC, Price RR, Gore JC. Repeatability of a reference region model for analysis of murine DCE-MRI data at 7T. J Magn Reson Imaging 2007; 24:1140-7. [PMID: 17024660 DOI: 10.1002/jmri.20729] [Citation(s) in RCA: 51] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/10/2023] Open
Abstract
PURPOSE To test the repeatability of a reference region (RR) model for the analysis of dynamic contrast-enhanced MRI (DCE-MRI) in a mouse model of cancer at high field. MATERIALS AND METHODS Seven mice were injected with 10(6) 4T1 mammary carcinoma cells and imaged eight to 10 days later on a Varian 7.0T scanner. Two DCE-MRI studies were performed for each mouse (separated by 2.5 hours). The RR model was used to analyze the data, and returned estimates on the perfusion-permeability index (Ktrans) for the RR and the tissue of interest (TOI), as well as the extravascular extracellular volume fraction (ve) for the TOI. RESULTS When the first injection was compared with the second injection, all parameters tested were highly correlated (r2=0.90, 0.62, 0.82 for the RR Ktrans, TOI Ktrans, and TOI ve, respectively, with P<0.001 for all). To observe a statistically significant change (at the 5% level) in a treatment study with seven animals in each group, log10 changes of 0.084 and 0.077 in the tumor Ktrans and ve, respectively, are required. CONCLUSION If a reliable arterial input function (AIF) is unavailable, the RR model is a reasonable alternative to measuring MRI contrast-agent (CA) kinetics in mouse models of cancer at high field.
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Affiliation(s)
- Thomas E Yankeelov
- Institute of Imaging Science, and Department of Radiology and Radiological Sciences, Vanderbilt University, Nashville, Tennessee 37232-2310, USA.
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Brosnan RJ, LeCouteur RA, Steffey EP, Imai A, Farver TB. Intracranial elastance in isoflurane-anesthetized horses. Am J Vet Res 2004; 65:1042-6. [PMID: 15334836 DOI: 10.2460/ajvr.2004.65.1042] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
OBJECTIVE To determine whether high intracranial pressure (ICP) during spontaneous ventilation (SV) in anesthetized horses coincides with an increase in intracranial elastance (ie, change in ICP per unit change of intracranial volume). ANIMALS 6 adult horses. PROCEDURE Anesthesia was induced and maintained in each horse for 5 hours with isoflurane at a constant dose equal to 1.2 times the minimum alveolar concentration. Direct ICP measurements were obtained by use of a strain gauge transducer inserted in the subarachnoid space, and arterial blood pressure was measured from a carotid artery. Physiologic responses were recorded after 15 minutes of normocapnic controlled ventilation (CV) and then after 10 minutes of SV. Aliquots (3 mL) of CSF were removed from each horse during SV until ICP returned to CV values. Slopes of pressure-volume curves yielded intracranial elastance. RESULTS Intracranial elastance ranged from 0.2 to 3.7 mm Hg/mL after removal of the first aliquot of CSF Slopes of pressure-volume curves were largest following removal of the initial CSF aliquot, but shallow portions of curves were detected at relatively high ICPs (25 to 35 mm Hg). A second-order relationship between SV ICP and initial intracranial elastance was found. CONCLUSIONS AND CLINICAL RELEVANCE In horses anesthetized with isoflurane, small changes in intracranial volume can cause large changes in ICP Increased intracranial elastance could further exacerbate preexisting intracranial hypertension. However, removal of small volumes of CSF may cause rapid compensatory replacement from other intracranial compartments, which suggests steady-state maintenance of an increase in intracranial volume during isoflurane anesthesia in horses.
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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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