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Yuan I, Xu T, Kurth CD. Using Electroencephalography (EEG) to Guide Propofol and Sevoflurane Dosing in Pediatric Anesthesia. Anesthesiol Clin 2021; 38:709-725. [PMID: 32792193 DOI: 10.1016/j.anclin.2020.06.007] [Citation(s) in RCA: 7] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Abstract
Sevoflurane and propofol-based anesthetics are dosed according to vital signs, movement, and expired sevoflurane concentrations, which do not assess the anesthetic state of the brain and, therefore, risk underdose and overdose. Electroencephalography (EEG) measures cortical brain activity and can assess hypnotic depth, a key component of the anesthetic state. Application of sevoflurane and propofol pharmacology along with EEG parameters can more precisely guide dosing to achieve the desired anesthetic state for an individual pediatric patient. This article reviews the principles underlying EEG use for sevoflurane and propofol dosing in pediatric anesthesia and offers case examples to illustrate their use in individual patients.
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Affiliation(s)
- Ian Yuan
- Department of Anesthesiology and Critical Care Medicine, The Children's Hospital of Philadelphia, University of Pennsylvania, Perelman School of Medicine, 3401 Civic Center Boulevard, Philadelphia, PA 19104, USA.
| | - Ting Xu
- Department of Anesthesiology, Laboratory of anesthesia and Critical Care Medicine, Translational Neuroscience Center, West China Hospital, Sichuan University and The Research Units of West China, Chinese Academy of Medical Sciences, Chengdu 610041, Sichuan, China; Department of Anesthesiology, Sichuan Academy of Medical Sciences & Sichuan Provincial People's Hospital, 32#, 2nd Section (West), 1st Ring Road, Chengdu 610072, China
| | - Charles Dean Kurth
- Department of Anesthesiology and Critical Care Medicine, The Children's Hospital of Philadelphia, University of Pennsylvania, Perelman School of Medicine, 3401 Civic Center Boulevard, Philadelphia, PA 19104, USA; Department of Pediatrics, The Children's Hospital of Philadelphia, University of Pennsylvania, Perelman School of Medicine, Philadelphia, PA, USA
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Xu T, Kurth CD, Yuan I, Vutskits L, Zhu T. An approach to using pharmacokinetics and electroencephalography for propofol anesthesia for surgery in infants. Paediatr Anaesth 2020; 30:1299-1307. [PMID: 32965066 DOI: 10.1111/pan.14021] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 05/11/2020] [Revised: 08/16/2020] [Accepted: 08/18/2020] [Indexed: 02/05/2023]
Abstract
Safe and effective techniques for propofol total intravenous anesthesia (TIVA) in infants are not well imbedded into clinical practice, resulting in practitioner unfamiliarity and potential for over- and under-dosing. In this education article, we describe our approach to TIVA dosing in infants and toddlers (birth to 36 months) which combines the use of pharmacokinetic models with EEG multi-parameter analysis. Pharmacokinetic models describe propofol and remifentanil effect site concentrations (Ce) over time in different age groups for a given dosing regimen. These models display substantial biological variability between individuals within age groups, impeding their application to clinical practice. Nevertheless, they reveal that younger infants require a higher propofol loading dose, a lower propofol maintenance dose, and a higher remifentanil dose compared with older infants. Proprietary EEG indices (eg, Bispectral Index) can serve as a biomarker of propofol Ce in adults and children to guide dosing to the individual patient; however, they are not recommended for infants as their validity remains uncertain this population. In our experience, EEG waveforms and processed parameters can reflect propofol Ce in infants, reflected by spectral edge frequency (SEF), density spectral array (DSA), and waveform patterns. In our practice, we use a "lookup table" of age-based dosing regimens or target-controlled infusion (TCI) based on the pharmacokinetic models to deliver a target propofol Ce and co-administer remifentanil and/or regional technique for analgesia. We analyze Electroencephalogram (EEG) waveforms, SEF, and DSA to adjust the propofol dose or TCI target concentration to the individual infant. EEG analysis mitigates against biological variability inherent in the pharmacokinetic models and has improved our experience with TIVA for infants.
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Affiliation(s)
- Ting Xu
- Department of Anesthesiology and Department of Translational Neuroscience Center, West China Hospital, Sichuan University & The Research Units of West China (2018RU012) Chinese Academy of Medical Sciences, Chengdu, China.,Department of Anesthesiology, Sichuan Academy of Medical Sciences & Sichuan Provincial People's Hospital, Chengdu, China
| | - Charles Dean Kurth
- Department of Anesthesiology and Critical Care Medicine and Neurology and Pediatrics, Perelman School of Medicine, The Children's Hospital of Philadelphia, University of Pennsylvania, Philadelphia, PA, USA
| | - Ian Yuan
- Department of Anesthesiology and Critical Care Medicine, Perelman School of Medicine, The Children's Hospital of Philadelphia, University of Pennsylvania, Philadelphia, PA, USA
| | - Laszlo Vutskits
- Department of Anesthesiology, Pharmacology, Intensive Care and Emergency Medicine, University Hospitals of Geneva, Geneva, Switzerland
| | - Tao Zhu
- Department of Anesthesiology and Department of Translational Neuroscience Center, West China Hospital, Sichuan University & The Research Units of West China (2018RU012) Chinese Academy of Medical Sciences, Chengdu, China
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Practicalities of Total Intravenous Anesthesia and Target-controlled Infusion in Children. Anesthesiology 2019; 131:164-185. [DOI: 10.1097/aln.0000000000002657] [Citation(s) in RCA: 24] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022]
Abstract
Abstract
Propofol administered in conjunction with an opioid such as remifentanil is used to provide total intravenous anesthesia for children. Drugs can be given as infusion controlled manually by the physician or as automated target-controlled infusion that targets plasma or effect site. Smart pumps programmed with pharmacokinetic parameter estimates administer drugs to a preset plasma concentration. A linking rate constant parameter (keo) allows estimation of effect site concentration. There are two parameter sets, named after the first author describing them, that are commonly used in pediatric target-controlled infusion for propofol (Absalom and Kataria) and one for remifentanil (Minto). Propofol validation studies suggest that these parameter estimates are satisfactory for the majority of children. Recommended target concentrations for both propofol and remifentanil depend on the type of surgery, the degree of surgical stimulation, the use of local anesthetic blocks, and the ventilatory status of the patient. The use of processed electroencephalographic monitoring is helpful in pediatric total intravenous anesthesia and target-controlled infusion anesthesia, particularly in the presence of neuromuscular blockade.
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Feasibility of Closed-loop Titration of Propofol and Remifentanil Guided by the Bispectral Monitor in Pediatric and Adolescent Patients. Anesthesiology 2015; 122:759-67. [DOI: 10.1097/aln.0000000000000577] [Citation(s) in RCA: 27] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
Abstract
Abstract
Background:
This study was designed to assess the feasibility of dual closed-loop titration of propofol and remifentanil guided solely by the Bispectral Index (BIS) monitor in pediatric and adolescent patients during anesthesia.
Methods:
Children undergoing elective surgery in this single-blind randomized study were allocated into the closed-loop (auto) or manual (manual) group. Primary outcome was the percentage of time with the BIS in the range 40 to 60 (BIS40–60). Secondary outcomes were the percentage of deep (BIS<40) anesthesia and drug consumption. Data are presented as median (interquartile range) or number (%).
Results:
Twenty-three patients (12 [10 to 14] yr) were assigned to the auto group and 19 (14 [7 to 14] yr) to the manual group. The closed-loop controller was able to provide induction and maintenance for all patients. The percentage of time with BIS40–60 was greater in the auto group (87% [75 to 96] vs. 72% [48 to 79]; P = 0.002), with a decrease in the percentage of BIS<40 (7% [2 to 17] vs. 21% [11 to 38]; P = 0.002). Propofol (2.4 [1.9 to 3.3] vs. 1.7 [1.2 to 2.8] mg/kg) and remifentanil (2.3 [2.0 to 3.0] vs. 2.5 [1.2 to 4.3] μg/kg) consumptions were similar in auto versus manual groups during induction, respectively. During maintenance, propofol consumption (8.2 [6.0 to 10.2] vs. 7.9 [7.2 to 9.1] mg kg−1 h−1; P = 0.89) was similar between the two groups, but remifentanil consumption was greater in the auto group (0.39 [0.22 to 0.60] vs. 0.22 [0.17 to 0.32] μg kg−1 min−1; P = 0.003). Perioperative adverse events and length of stay in the postanesthesia care unit were similar.
Conclusion:
Intraoperative automated control of hypnosis and analgesia guided by the BIS is clinically feasible in pediatric and adolescent patients and outperformed skilled manual control.
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Propofol effect on cerebral oxygenation in children with congenital heart disease. Pediatr Cardiol 2015; 36:543-9. [PMID: 25311762 DOI: 10.1007/s00246-014-1047-7] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 06/26/2014] [Accepted: 09/30/2014] [Indexed: 10/24/2022]
Abstract
Propofol is a short-acting, intravenously administered hypnotic agent which is used in procedural sedation in children. Propofol is known to decrease systemic vascular resistance, arterial blood pressure and can lead to desaturations and decreased systemic perfusion in children with cardiac shunting. This may result in a reduction in cerebral blood flow and oxygenation. Near-infrared spectroscopy (NIRS) can monitor cerebral tissue oxygenation in the frontal neocortex. The objective of our study was to measure the changes in cerebral oxygen and blood supply after Propofol infusion in children with congenital heart disease. Propofol infusion may reduce cerebral oxygenation in children with congenital heart disease. The study group consisted of 32 children (f:m = 18:14), with median age of 49 (5-112) months and median weight of 15 (5-34) kg. We performed NIRS derived continuous measurement of cerebral oxygenation and cardiac output using Electrical velocimetry for 5 min before and after sedation with Propofol (1-2 mg/kg i.v.) for cardiac catheterization. Simultaneously, non-invasive arterial blood pressure and transcutaneous oxygen saturation were measured. Propofol sedation led to a significant decrease in mean arterial pressure (79 ± 16 vs. 67 ± 12 mmHg) (p = 0.01) and cardiac index (3.2 ± 0.8 vs. 2.9 ± 0.6 ml/min/m(2)) (p = 0.03). In contrast, cerebral tissue oxygenation index, increased significantly from 57 ± 11 to 59 ± 10 % (p < 0.05). Sedation with Propofol increased cerebral tissue oxygenation despite a decrease in cardiac index and arterial blood pressure. This may be caused by a decreased oxygen consumption of the sedated brain with intact cerebral auto-regulation.
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Pharmacokinetics and pharmacodynamics of propofol in children undergoing different types of surgeries. Pharmacol Rep 2014; 66:821-9. [DOI: 10.1016/j.pharep.2014.04.012] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/12/2014] [Revised: 04/24/2014] [Accepted: 04/28/2014] [Indexed: 11/19/2022]
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Joram N, Gaillard Le Roux B, Barrière F, Liet JM. Place des protocoles de sédation en réanimation pédiatrique. MEDECINE INTENSIVE REANIMATION 2014. [DOI: 10.1007/s13546-013-0818-4] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/26/2022]
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Changes in the Bispectral Index in Response to Experimental Noxious Stimuli in Adults under General Anesthesia. ISRN PAIN 2013; 2013:583920. [PMID: 27335878 PMCID: PMC4893395 DOI: 10.1155/2013/583920] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 05/16/2013] [Accepted: 06/25/2013] [Indexed: 11/18/2022]
Abstract
Objective. Pain assessment is a major challenge in nonverbal patients in the intensive care unit (ICU). Recent studies suggest a relationship between the Bispectral Index (BIS) and nociceptive stimuli. This study was designed to examine changes in BIS in response to experimental noxious stimuli. Methods. Thirty participants under general anesthesia were in this quasiexperimental, within subject, pre- and poststudy. In the operating room (OR), BIS was monitored during moderate and severe noxious stimuli, induced by a thermal probe on the participants' forearm, after induction of general anesthesia, prior to surgery. Results. Significant increases in BIS occurred during moderate (increase from 35.00 to 40.00, P = 0.003) and severe noxious stimuli (increase from 37.67 to 40.00, P = 0.007). ROC showed a sensitivity (Se) of 40.0% and a specificity (Sp) of 73.3% at a BIS value > 45, in distinguishing a moderate from a severe noxious stimuli. Conclusion. BIS increased in response to moderate and severe noxious stimuli. The Se and Sp of the BIS did not support the use of the BIS for distinction of different pain intensities in the context of deep sedation in the OR. However, the results justify further studies in more lightly sedated patients such as those in the ICU.
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BIS-Guided Total Intravenous Anesthesia for Orchiopexy and Circumcision in a Child with Severe Autism: A Case Report. Case Rep Anesthesiol 2012; 2012:718594. [PMID: 23227368 PMCID: PMC3512242 DOI: 10.1155/2012/718594] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/19/2012] [Accepted: 10/30/2012] [Indexed: 12/01/2022] Open
Abstract
Autistic children are very difficult to manage in the hospital setting because they react badly to any change in routine. We describe a case of 10-year-old male patient with severe autism undergoing orchidopexy and circumcision. Following premedication, anesthesia was induced with remifentanil, propofol, atracurium, and maintained with total intravenous anesthesia (propofol and remifentanil). The Bispectral Index System was monitored for determination of the depth of anesthesia. After surgery, all infusions were discontinued. The patient was then transferred to the postanesthetic care unit. There were no adverse events observed during the anesthetic management. The patient was discharged from the hospital on the second postoperative day. Bispectral Index System-guided Total Intravenous Anesthesia can provide some advantages for patient with autism, such as hemodynamic stability, early and easy recovery, to facilitate faster discharge, to optimize the delivery of anesthetic agents, to minimize its adverse effects, and to maximize its safety.
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Abstract
Conducting clinical pharmacology research studies in pediatric patients is challenging because of ethical and practical constraints but necessary to ensure that drugs are used safely and effectively in this population. Developments in laboratory analytical techniques, such as improved assay sensitivity and the use of alternative sample matrices, can reduce blood loss and offer less invasive blood sampling, causing less trauma to the patient and fewer ethical concerns. Recent advances in data analysis techniques, which aim to extract the maximum amount of useful information from small sample numbers, should be considered when planning a clinical trial and incorporated into the study design. Using 'population' methodology allows a more flexible sampling strategy that enables valuable data to be collected in the course of routine clinical practice, rather than in a rigid, and potentially artificial, setting. Integration of pharmacokinetics and pharmacodynamics and the application of physiological approaches and simulation techniques to the analysis and interpretation of drug concentration and effect data offer new opportunities that have particular relevance to pharmacological research in the field of pediatric anesthetics.
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Affiliation(s)
- Alison H Thomson
- Strathclyde Institute of Pharmacy and Biomedical Sciences, University of Strathclyde, Glasgow, UK.
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Abstract
The pharmacokinetics of propofol are relatively well described in the pediatric population. Recent work has confirmed the validity of allometric scaling for predicting propofol disposition across different species and for describing pediatric ontogenesis. In the first year of life, allometric models require adjustment to reflect ontogeny of maturation. Pharmacodynamic data for propofol in children are scarcer, because of practical difficulties in data collection and the limitations of currently available depth of anesthesia monitors for pediatric use. Hence, questions relating to the comparative sensitivity of children to propofol, and differences in time to peak effect relative to adults, remain unanswered. K(eo) half-lives have been determined for pediatric kinetic models using time to peak effect techniques but are not currently incorporated into commercially available target-controlled infusion pumps.
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Affiliation(s)
- Ann E Rigby-Jones
- Anaesthesia Research Group, Peninsula Medical School, Peninsula College of Medicine & Dentistry, University of Plymouth, Plymouth, UK.
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Gélinas C, Tousignant-Laflamme Y, Tanguay A, Bourgault P. Exploring the validity of the bispectral index, the Critical-Care Pain Observation Tool and vital signs for the detection of pain in sedated and mechanically ventilated critically ill adults: A pilot study. Intensive Crit Care Nurs 2011; 27:46-52. [DOI: 10.1016/j.iccn.2010.11.002] [Citation(s) in RCA: 55] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/19/2010] [Revised: 11/11/2010] [Accepted: 11/12/2010] [Indexed: 11/29/2022]
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Bienert A, Kusza K, Wawrzyniak K, Grześkowiak E, Kokot ZJ, Matysiak J, Grabowski T, Wolc A, Wiczling P, Regulski M. Assessing circadian rhythms in propofol PK and PD during prolonged infusion in ICU patients. J Pharmacokinet Pharmacodyn 2010; 37:289-304. [PMID: 20544262 PMCID: PMC2889282 DOI: 10.1007/s10928-010-9161-5] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/12/2010] [Accepted: 05/29/2010] [Indexed: 12/30/2022]
Abstract
This study evaluates possible circadian rhythms during prolonged propofol infusion in patients in the intensive care unit. Eleven patients were sedated with a constant propofol infusion. The blood samples for the propofol assay were collected every hour during the second day, the third day, and after the termination of the propofol infusion. Values of electroencephalographic bispectral index (BIS), arterial blood pressure, heart rate, blood oxygen saturation and body temperature were recorded every hour at the blood collection time points. A two-compartment model was used to describe propofol pharmacokinetics. Typical values of the central and peripheral volume of distribution and inter-compartmental clearance were VC = 27.7 l, VT = 801 l, and CLD = 2.73 l/min. The systolic blood pressure (SBP) was found to influence the propofol metabolic clearance according to Cl (l/min) = 2.65·(1 − 0.00714·(SBP − 135)). There was no significant circadian rhythm detected with respect to propofol pharmacokinetics. The BIS score was assessed as a direct effect model with EC50 equal 1.98 mg/l. There was no significant circadian rhythm detected within the BIS scores. We concluded that the light–dark cycle did not influence propofol pharmacokinetics and pharmacodynamics in intensive care units patients. The lack of night–day differences was also noted for systolic blood pressure, diastolic blood pressure and blood oxygenation. Circadian rhythms were detected for heart rate and body temperature, however they were severely disturbed from the pattern of healthy patients.
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Affiliation(s)
- Agnieszka Bienert
- Department of Clinical Pharmacy and Biopharmacy, Karol Marcinkowski University of Medical Sciences, ul. Marii Magdaleny 14, 61-861, Poznań, Poland.
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Abstract
The current role of TIVA in children is limited because of hardware limitations, and pharmacokinetic and monitoring issues. Nonetheless, the role of TIVA in children has been increasing in the past decade, in part because of surgical and medical indications. If TIVA is to become more widely used, it must be easy and simple to set up, without serious drawbacks and without added risks. Currently, many drugs destined for use with TIVA in children are off-label, and their pharmacology is poorly understood. Such off-label designations must be resolved if TIVA is to become more widely used. At the same time, many institutions have a limited number of infusion pumps, which creates a serious bottleneck and restriction on the use of TIVA.. If a true TIVA technique is used, i.v. access must be established before induction of anesthesia, which will require a means to establish i.v. access painlessly, e.g., using a topical local anesthetic. This is not a common practice in a number of jurisdictions but must be introduced if TIVA is to expand in its scope in children. Currently, I believe that we deliver a 'partial' TIVA technique in which TIVA occasionally follows an inhalational induction but in the future when the current obstacles have been resolved, I believe that we will be able practice a true TIVA technique ubiquitously in children.
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Affiliation(s)
- Jerrold Lerman
- Department of Anesthesiology, Women and Children's Hospital of Buffalo, Buffalo, NY 14222, USA.
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Münte S, Klockars J, van Gils M, Hiller A, Winterhalter M, Quandt C, Gross M, Taivainen T. The Narcotrend Index Indicates Age-Related Changes During Propofol Induction in Children. Anesth Analg 2009; 109:53-9. [DOI: 10.1213/ane.0b013e3181a49c98] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022]
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Lerman J, Jöhr M. Inhalational anesthesia vs total intravenous anesthesia (TIVA) for pediatric anesthesia. Paediatr Anaesth 2009; 19:521-34. [PMID: 19453585 DOI: 10.1111/j.1460-9592.2009.02962.x] [Citation(s) in RCA: 76] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/01/2022]
Affiliation(s)
- Jerrold Lerman
- Women's and Children's Hospital of Buffalo, 219 Bryant St, Buffalo 14222, NY, USA.
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Variation of bispectral index monitoring in paediatric patients undergoing propofol-remifentanil anaesthesia. Eur J Anaesthesiol 2008; 25:821-5. [DOI: 10.1017/s0265021508004559] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
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Tirel O, Wodey E, Harris R, Bansard JY, Ecoffey C, Senhadji L. Variation of bispectral index under TIVA with propofol in a paediatric population. Br J Anaesth 2008; 100:82-7. [PMID: 18070785 DOI: 10.1093/bja/aem339] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
BACKGROUND In this prospective observational study, we aim to explore the relationship between age and bispectral index (BIS) values at different plasma concentrations of propofol. METHODS Fifty children aged from 3 to 15 yr were included. Anaesthesia was induced using a target-controlled infusion of propofol with the Kataria pharmacokinetic model together with a bolus of remifentanil followed by a continuous infusion rate at 0.2 microg kg(-1) min(-1). Target plasma propofol concentration was initially stabilized to 6 microg ml(-1) and continued for 6 min. The target was then decreased and stabilized to 4 microg ml(-1) and then to 2 microg ml(-1). BIS values, plasma propofol concentration, and EEG were continuously recorded. In order to explore the relationship between variations in propofol concentration and the EEG bispectrum, we used a multiple correspondence analysis (MCA). Results are shown in median (range). RESULTS We found no statistical difference between BIS values with propofol 6 microg ml(-1) [23 (12-40)] and 4 microg ml(-1) [28 (9-67)]. At 2 microg ml(-1), BIS was significantly different [52 (24-71)], but a significant correlation between the age of children and BIS values was found (r2=0.66; P<0.01). There was little change in children's position between 6 and 4 microg ml(-1) in the structure model of the MCA. From 4 to 2 microg ml(-1), the position of children moved only on axis 2. CONCLUSIONS These results showed the difficulty to interpret BIS values because of the absence of significant change for higher plasma propofol concentration variation or because of the link with age for the lower plasma concentration.
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Affiliation(s)
- O Tirel
- INSERM, U642, F-35000 Rennes, France.
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