Nasal cannula and face mask gas flow rates when connecting to the Y-piece of the anesthesia circuit.

STUDY OBJECTIVE: To determine the relationship between the delivered gas flows via nasal cannulas and face masks and the set gas flow and the breathing circuit pressure when connecting to the Y-adapter of the anesthesia breathing circuit and using the oxygen blender on the anesthesia machine, relevant to surgery when there is concern for causing a fire. The flow rates that are delivered at various flow rates and circuit pressures have not been previously studied. DESIGN: Laboratory investigation. SETTING: Academic medical center. PATIENTS: None. INTERVENTIONS: The gas flows from each of 3 anesthesia machines from the same manufacturer were systematically increased from 1 to 15 L/min with changes to the adjustable pressure limiting valve to maintain 0-40 cm water pressure in the breathing circuit for nasal cannula testing and at 20-30 cm water circuit pressure for face masks. MEASUREMENTS: The delivered gas flows to the cannula were determined using a float-ball flowmeter for combinations of set gas flows and circuit pressures after connecting the cannula tubing to the Y-piece of the anesthesia circuit via a tracheal tube adapter. Decreasing the supply tubing length on the delivered flow rates was evaluated. MAIN RESULTS: There was a highly linear relationship between the anesthesia circuit pressure and the delivered nasal cannula flow rates, with 0 flow observed when the APL valve was fully open (i.e., 0 cm water). However, even under maximum conditions (40 cm water and 15 L/min), the delivered nasal cannula flow rate was 3.5 L/min. Shortening the 6.5-ft cannula tubing increased the flow at 20 and 30 cm water by approximately 0.12 L/min/ft. The estimated FiO2 assuming a minute ventilation of 5 L/min and 30% FiO2 ranged from 21.7% to 27.0% at nasal cannula flow rates of 0.5 to 4.0 L/min. When using a face mask and the APL fully closed, delivered flow rates were 0.25 L/min less than the set flow rate between 1 and 3 L/min and equal to the set flow rate between 4 and 8 L/min. CONCLUSIONS: When using a nasal cannula adapted to the Y-piece of the anesthesia circuit, the delivery system is linearly dependent on the pressure in the circuit and uninfluenced by the flow rate set on the anesthesia machine. However, only modest flow rates (≤ 3.5 L/min) and a limited increase in the inspired FiO2 are possible when using this delivery method. When using a face mask and the anesthesia circuit, flow rates close to the set flow rate are possible with the APL valve fully closed. Patients scheduled for sedation for head and neck procedures with increased fire risk who require more than a marginal increase in the FiO2 to maintain an acceptable pulse oximetry saturation may need general anesthesia with tracheal intubation.

Infusiones controladas por objetivo y sistemas de circuito cerrado. Límites en expansión / Target-controlled infusions and closed-loop systems: expansion limits

Introducción: La administración manual en bolo ha evolucionado desde la infusión volumétrica basada en regímenes farmacológicos estandarizados, hasta los sistemas de infusión controlada por objetivo y los más sofisticados sistemas de circuito cerrado. Objetivo: Describir los principios tecnológicos y aplicaciones clínicas extendidas de la infusión controlada por objetivo y los sistemas de circuito cerrado. Métodos: Se realizó una revisión no sistemática de la literatura, en bases de datos científicas como Cochrane Database of Systematic Reviews, Pubmed/Medline, EMBASE, Scopus, Web of Science, EBSCOhost, Science Direct, OVID y el buscador académico Google Scholar, en el mes de septiembre del año 2020. Desarrollo: La disponibilidad y portabilidad de dispositivos electrónicos con capacidad de procesamiento avanzado a precios relativamente accesibles, el perfeccionamiento del aprendizaje automático e inteligencia artificial aplicado a las decisiones médicas, y las iteraciones tecnológicas complejas incorporadas en los sistemas de circuito abierto y cerrado, desarrollados originalmente en el campo de la Anestesiología, han posibilitado su expansión a otras especialidades y entornos clínicos tan disímiles como el tratamiento de la diabetes mellitus, administración de fármacos antineoplásicos, ventilación mecánica, control de las variables hemodinámicas y la terapia antimicrobiana en pacientes críticos. Conclusiones: La infusión controlada por objetivo y los sistemas de circuito cerrado se han convertido en tecnologías maduras, seguras y viables, aplicadas clínicamente en múltiples naciones y escenarios, con un desempeño superior a los sistemas manuales tradicionales(AU)

Introduction: Manual bolus administration has evolved from volumetric infusion based on standardized pharmacological regimens to target-controlled infusion systems and the most sophisticated closed-loop systems. Objective: To describe the technological principles and extended clinical applications of target-controlled infusion and closed-loop systems. Methods: A nonsystematic review of the literature was carried out, during September 2020, in scientific databases such as Cochrane Database of Systematic Reviews, Pubmed/Medline, EMBASE, Scopus, Web of Science, EBSCOhost, Science Direct, OVID and the academic search engine Google Scholar. Development: The availability and portability of electronic devices with advanced processing capacity at relatively affordable prices, the refinement of machine learning and artificial intelligence applied to medical decisions, as well as the complex technological iterations incorporated into open and closed-loop systems, originally developed in the field of anesthesiology, have enabled their expansion to other specialties and clinical settings so diverse as treatment of diabetes mellitus, administration of antineoplastic drugs, mechanical ventilation, control of hemodynamic variables and antimicrobial therapy in critical patients. Conclusions: Target-controlled infusion and closed-loop systems have become mature, safe and viable technologies, applied clinically in multiple nations and settings, with superior performance compared to traditional manual systems(AU)

Behavior of a dual closed-loop controller of propofol and remifentanil guided by the bispectral index for postoperative sedation of adult cardiac surgery patients: a preliminary open study.

A dual-loop controller permits the automated titration of propofol and remifentanil during anesthesia; it has never been used in intensive care after cardiac surgery. The goal of this preliminary study was to determine the efficacy of this controller to provide postoperative sedation in 19 adult cardiac surgery patients with a Bispectral Index target of 50. Results are presented as numbers (percentages) or medians [25th-75th percentiles]. The sedation period lasted 139 min [89-205] during which the Richmond Agitation Sedation Scale was at - 5 and the Behavioral Pain Scale score at three points for all patients and observation times but one (82 out of 83 assessments). Sedation time in the range 40-60 for the Bispectral Index was 87% [57-95]; one patient had a period of electrical silence defined as Suppression Ratio at least > 10% for more than 60 s. The time between the end of infusions and tracheal extubation was 84 min [63-129]. The Richmond Agitation Sedation Scale was 0 [0-0], 0 [- 1 to 0], and 0 [0-0] respectively during the 3 h following extubation while the verbal numerical pain scores were 6 [4.5-7], 5 [4-6], and 2 [0-5]. Mean arterial pressure decreased during sedation requiring therapeutic interventions, mainly vascular filling in 15 (79%) patients. Automated sedation device was discontinued in two patients for hemodynamic instability. No patient had awareness of the postoperative sedation period. Dual closed-loop can provide postoperative sedation after cardiac surgery but the choice of the depth of sedation should take into account the risk of hypotension.

Feasibility of Fully Automated Hypnosis, Analgesia, and Fluid Management Using 2 Independent Closed-Loop Systems During Major Vascular Surgery: A Pilot Study.

Automated titration of intravenous anesthesia and analgesia using processed electroencephalography monitoring is no longer a novel concept. Closed-loop control of fluid administration to provide goal-directed fluid therapy has also been increasingly described. However, simultaneously combining 2 independent closed-loop systems together in patients undergoing major vascular surgery has not been previously detailed. The aim of this pilot study was to evaluate the clinical performance of fully automated hypnosis, analgesia, and fluid management using 2 independent closed-loop controllers in patients undergoing major vascular surgery before implementation within a larger study evaluating true patient outcomes.

Effects of different fresh gas flows with or without a heat and moisture exchanger on inhaled gas humidity in adults undergoing general anaesthesia: A systematic review and meta-analysis of randomised controlled trials.

BACKGROUND: The minimum inhaled gas absolute humidity level is 20 mgH2O l for short-duration use in general anaesthesia and 30 mgH2O l for long-duration use in intensive care to avoid respiratory tract dehydration. OBJECTIVE: The aim is to compare the effects of different fresh gas flows (FGFs) through a circle rebreathing system with or without a heat and moisture exchanger (HME) on inhaled gas absolute humidity in adults undergoing general anaesthesia. DESIGN: Systematic review and meta-analyses of randomised controlled trials. We defined FGF (l min) as minimal (0.25 to 0.5), low (0.6 to 1.0) or high (≥2). We extracted the inhaled gas absolute humidity data at 60 and 120 min after connection of the patient to the breathing circuit. The effect size is expressed as the mean differences and corresponding 95% confidence intervals (CI). DATA SOURCES: PubMed, EMBASE, SciELO, LILACS and CENTRAL until January 2017. RESULTS: We included 10 studies. The inhaled gas absolute humidity was higher with minimal flow compared with low flow at 120 min [mean differences 2.51 (95%CI: 0.32 to 4.70); P = 0.02] but not at 60 min [mean differences 2.95 (95%CI: -0.95 to 6.84); P = 0.14], and higher with low flow compared with high flow at 120 min [mean differences 7.19 (95%CI: 4.53 to 9.86); P < 0.001]. An inhaled gas absolute humidity minimum of 20 mgH2O l was attained with minimal flow at all times but not with low or high flows. An HME increased the inhaled gas absolute humidity: with minimal flow at 120 min [mean differences 8.49 (95%CI: 1.15 to 15.84); P = 0.02]; with low flow at 60 min [mean differences 9.87 (95%CI: 3.18 to 16.57); P = 0.04] and 120 min [mean differences 7.19 (95%CI: 3.29 to 11.10); P = 0.003]; and with high flow of 2 l min at 60 min [mean differences 6.46 (95%CI: 4.05 to 8.86); P < 0.001] and of 3 l min at 120 min [mean differences 12.18 (95%CI: 6.89 to 17.47); P < 0.001]. The inhaled gas absolute humidity data attained or were near 30 mgH2O l when an HME was used at all FGFs and times. CONCLUSION: All intubated patients should receive a HME with low or high flows. With minimal flow, a HME adds cost and is not needed to achieve an appropriate inhaled gas absolute humidity.

The Feasibility of a Completely Automated Total IV Anesthesia Drug Delivery System for Cardiac Surgery.

BACKGROUND: In this pilot study, we tested a novel automatic anesthesia system for closed-loop administration of IV anesthesia drugs for cardiac surgical procedures with cardiopulmonary bypass. This anesthesia drug delivery robot integrates all 3 components of general anesthesia: hypnosis, analgesia, and muscle relaxation. METHODS: Twenty patients scheduled for elective cardiac surgery with cardiopulmonary bypass were enrolled. Propofol, remifentanil, and rocuronium were administered using closed-loop feedback control. The main objective was the feasibility of closed-loop anesthesia defined as successful automated cardiac anesthesia without manual override by the attending anesthesiologist. Secondary qualitative observations were clinical and controller performances. The clinical performance of hypnosis control was the efficacy to maintain a bispectral index (BIS) of 45. To evaluate the hypnosis performance, BIS values were stratified into 4 categories: "excellent," "good," "poor," and "inadequate" hypnosis control defined as BIS values within 10%, ranging from 11% to 20%, ranging from 21% to 30%, or >30% of the target value, respectively. The clinical performance of analgesia was the efficacy to maintain NociMap values close to 0. The analgesia performance was assessed classifying the NociMap values in 3 pain control groups: -33 to +33 representing excellent pain control, -34 to -66 and +34 to +66 representing good pain control, and -67 to -100 and +67 to +100 representing insufficient pain control. The controller performance was calculated using the Varvel parameters. RESULTS: Robotic anesthesia was successful in 16 patients, which is equivalent to 80% (97.5% confidence interval [CI], 53%-95%) of the patients undergoing cardiac surgery. Four patients were excluded from the final analysis because of technical problems with the automated anesthesia delivery system. The secondary qualitative observations revealed that the clinical performance of hypnosis allowed an excellent and good control during 70% (97.5% CI, 63%-76%) of maintenance time and an insufficient clinical performance of analgesia for only 3% (97.5% CI, 1%-6%) of maintenance time. CONCLUSIONS: The completely automated closed-loop system tested in this investigation could be used successfully and safely for cardiac surgery necessitating cardiopulmonary bypass. The results of the present trial showed satisfactory clinical performance of anesthesia control.

Accuracy of inhaled agent usage displays of automated target control anesthesia machines.

Automated low flow anesthesia machines report how much inhaled anesthetic agent has been used for each anesthetic. We compared these reported values with the amount of agent that had disappeared by weighing the vaporizer/injectors before and after each anesthetic. The vaporizers/injectors of the Aisys, Zeus and FLOW-i were weighed with a high precision weighing scale before and after anesthesia with either desflurane in O2/air or sevoflurane in O2/N2O. These values were compared with the values reported by the cumulative agent use display tools of the respective anesthesia machines using a linear curve fit. Twenty-five measurements were performed in each group, except for the sevoflurane data with the Aisys that were available from another study (87 pairs). We also determined the amount lost by inserting and removing the vaporizers/injectors or by performing a machine checkout, corrected the measured amounts for these artifacts and repeated the linear fits. The average amount of sevoflurane and desflurane wasted by inserting and removing the cassette for the Aisys, Zeus, and FLOW-i were 0.21, 0.12, and 0.04 mL and 0.12, 0.61, and 1.13 mL liquid agent, respectively. The average amount of sevoflurane and desflurane wasted by the machine checkout with the Aisys, Zeus, and FLOW-i were 1.78, 0.21, and 1.67 mL and 2.39, 0.67, and 4.19 mL, respectively. Performance error of the displayed amount of agent use remained within 10 % of the weighed amount, expect for amounts less than 3 mL sevofurane with the FLOW-i and less than 20 mL desflurane with the Aisys and FLOW-i. Cumulative agent usage displayed by the Aisys, Zeus, and FLOW-i is within 10 % of the measured consumption, except for low consumption cases (<3 mL sevoflurane, <20 mL desflurane). The differences may be due to either measurement error or cumulative agent display error. The current results can help the researchers decide whether the displayed amounts are accurate enough for their study purposes. The extent to which these discrepancies differ between different units of the same machine remains unstudied.

Agent consumption with the Zeus® in the automated closed circuit anesthesia mode with O2/air mixtures.

BACKGROUND: Earlier software versions of the Zeus® (Lübeck, Dräger, Germany) failed to provide true closed circuit anesthesia (CCA) conditions. We examined whether the latest software (SW 4.03 MK 04672-00) achieves this goal. METHODS: In 8 ASA I-III patients, the CCA mode of the Zeus® was used to maintain the inspired O2 (FIO2) and end-expired sevoflurane % (FAsevo) at 50 and 1.8%, respectively. The fresh gas flow (FGF) of O2 and air and the sevoflurane injection rate (=Vinjsevo, mL liquid sevo/h) were videotaped from the control screen and entered offline into a spreadsheet. Cumulative sevoflurane usage during early wash-in (=0-1 min, CDsevo0-1), late wash-in (=1-5 min, CDsevo1-5), and maintenance (=5-60 min, CDsevo5-60) was calculated, and Vinjsevo between 1 and 60 min was compared with published uptake data. RESULTS: FAsevo reached 1.8% within 101 (23) sec. CDsevo0-1 was between 1.24 (0.03) and 3.01(0.25) mL (a range is provided because no absolute Vinjsevo values were displayed once Vinjsevo was > 100 mL/h, which occurred between 15 ± 2 and 46 ± 6 sec). CDsevo1-5 was 0.81 (0.37) mL, and CDsevo5-60 was 4.63 (0.94) mL. The Vinjsevo pattern between 1 and 60 min matched previously published uptake data. Brief high FGF periods were used to maintain the target FIO2, and to refill the reservoir bag after external pressure had been applied to the abdomen; subsequent "spikes" wasted 0.08-0.19 mL and 0.14-0.49 mL sevoflurane (1-3% and 3-9% of total agent usage between 1 and 60 min, respectively). CONCLUSION: Under the conditions specified, the Zeus® approaches CCA conditions so closely that further reductions in agent usage would have minimal economic significance.

The humidity in a Dräger Primus anesthesia workstation using low or high fresh gas flow and with or without a heat and moisture exchanger in pediatric patients.

BACKGROUND: An inhaled gas absolute humidity of 20 mg H2O·L is the value most considered as the threshold necessary for preventing the deleterious effects of dry gas on the epithelium of the airways during anesthesia. Because children have small minute ventilation, we hypothesized that the humidification of a circle breathing system is lower in children compared with adults. The Primus anesthesia workstation (Dräger Medical, Lübeck, Germany) has a built-in hotplate to heat the patient's exhaled gases. A heat and moisture exchanger (HME) is a device that can be used to further humidify and heat the inhaled gases during anesthesia. To evaluate the humidifying properties of this circle breathing system during pediatric anesthesia, we compared the temperature and humidity of inhaled gases under low or high fresh gas flow (FGF) conditions and with or without an HME. METHODS: Forty children were randomly allocated into 4 groups according to the ventilation of their lungs by a circle breathing system in a Dräger Primus anesthesia workstation with low (1 L·min) or high (3 L·min) FGF without an HME (1L and 3L groups) or with an HME (Pall BB25FS, Pall Biomedical, East Hills, NY; HME1L and HME3L groups). The temperature and absolute humidity of inhaled gases were measured at 10, 20, 40, 60, and 80 minutes after connecting the patient to the breathing circuit. RESULTS: The mean inhaled gas temperature was higher in HME groups (HME1L: 30.3°C ± 1.1°C; HME3L: 29.3°C ± 1.2°C) compared with no-HME groups (1L: 27.0°C ± 1.2°C; 3L: 27.1°C ± 1.5°C; P < 0.0001). The mean inhaled gas absolute humidity was higher in HME than no-HME groups and higher in low-flow than high-flow groups ([HME1L: 25 ± 1 mg H2O·L] > [HME3L: 23 ± 2 mg H2O·L] > [1L: 17 ± 1 mg H2O·L] > [3L: 14 ± 1 mg H2O·L]; P < 0.0001). CONCLUSIONS: In a pediatric circle breathing system, the use of neither high nor low FGF provides the minimum humidity level of the inhaled gases thought to reduce the risk of dehydration of airways. Insertion of an HME increases the humidity and temperature of the inhaled gases, bringing them closer to physiological values. The use of a low FGF enhances the HME efficiency and consequently increases the inhaled gas humidity values. Therefore, the association of an HME with low FGF in the breathing circuit is the most efficient way to conserve the heat and the moisture of the inhaled gas during pediatric anesthesia.

Oxygen concentrators performance with nitrous oxide at 50:50 volume.

BACKGROUND AND OBJECTIVES: Few investigations have addressed the safety of oxygen from concentrators for use in anesthesia in association with nitrous oxide. This study evaluated the percent of oxygen from a concentrator in association with nitrous oxide in a semi-closed rebreathing circuit. METHODS: Adult patients undergoing low risk surgery were randomly allocated into two groups, receiving a fresh gas flow of oxygen from concentrators (O293) or of oxygen from concentrators and nitrous oxide (O293N2O). The fraction of inspired oxygen and the percentage of oxygen from fresh gas flow were measured every 10 min. The ratio of FiO2/oxygen concentration delivered was compared at various time intervals and between the groups. RESULTS: Thirty patients were studied in each group. There was no difference in oxygen from concentrators over time for both groups, but there was a significant improvement in the FiO2 (p<0.001) for O293 group while a significant decline (p<0.001) for O293N2O. The FiO2/oxygen ratio varied in both groups, reaching a plateau in the O293 group. Pulse oximetry did not fall below 98.5% in either group. CONCLUSION: The FiO2 in the mixture of O293 and nitrous oxide fell during the observation period although oxygen saturation was higher than 98.5% throughout the study. Concentrators can be considered a stable source of oxygen for use during short anesthetic procedures, either pure or in association with nitrous oxide at 50:50 volume.

Oxygen concentrators performance with nitrous oxide at 50:50 volume / Desempenho de concentradores de oxigênio com óxido nitroso em volume de 50:50 / Rendimiento de los concentradores de oxígeno con óxido nitroso a un volumen de 50:50

Background and objectives: Few investigations have addressed the safety of oxygen from concentrators for use in anesthesia in association with nitrous oxide. This study evaluated the percent of oxygen from a concentrator in association with nitrous oxide in a semi-closed rebreathing circuit. Methods: Adult patients undergoing low risk surgery were randomly allocated into two groups, receiving a fresh gas flow of oxygen from concentrators (O293) or of oxygen from concentrators and nitrous oxide (O293N2O). The fraction of inspired oxygen and the percentage of oxygen from fresh gas flow were measured every 10 min. The ratio of FiO2/oxygen concentration delivered was compared at various time intervals and between the groups. Results: Thirty patients were studied in each group. There was no difference in oxygen from concentrators over time for both groups, but there was a significant improvement in the FiO2 (p < 0.001) for O293 group while a significant decline (p < 0.001) for O293N2O. The FiO2/oxygen ratio varied in both groups, reaching a plateau in the O293 group. Pulse oximetry did not fall below 98.5% in either group. Conclusion: The FiO2 in the mixture of O293 and nitrous oxide fell during the observation period although oxygen saturation was higher than 98.5% throughout the study. Concentrators can be considered a stable source of oxygen for use during short anesthetic procedures, either pure or in association with nitrous oxide at 50:50 volume. .

Justificativa e objetivos: poucas pesquisas abordaram a segurança do oxigênio a partir de concentradores para uso em anestesia em associação com óxido nitroso. Este estudo avaliou a porcentagem de oxigênio a partir de um concentrador em associação com óxido nitroso em um circuito de reinalação semifechado. Métodos: pacientes adultos submetidos à cirurgia de baixo risco foram alocados aleatoriamente em dois grupos e receberam um fluxo de gases frescos de concentradores de oxigênio (O293) ou de concentradores de oxigênio e óxido nitroso (O293N2O). A fração inspirada de oxigênio e a porcentagem do fluxo de gases frescos de oxigênio foram medidas a cada 10 minutos. O razão da concentração liberada de FiO2/oxigênio foi comparada em diferentes intervalos de tempo e entre os grupos. Resultados: foram avaliados em cada grupo 30 pacientes. Não houve diferença em oxigênio a partir dos concentradores ao longo do tempo para ambos os grupos, mas houve uma melhora significativa da FiO2 (p < 0,001) no grupo O293, enquanto houve uma queda significativa (p < 0,001) no grupo O293N2O. A razão FiO2/oxigênio variou em ambos os grupos e atingiu um patamar no grupo O293. A oximetria de pulso não caiu abaixo de 98,5% em ambos os grupos. Conclusão: a FiO2 na mistura de O293 e óxido nitroso caiu durante o período de observação, embora a saturação de oxigênio tenha ficado acima de 98,5% durante todo o estudo. Os concentradores podem ser considerados uma fonte estável de oxigênio para uso durante procedimentos anestésicos de curta duração, tanto puro quanto em associação com óxido nitroso em volume de 50:50. .

Justificación y objetivos: pocas investigaciones han abordado la seguridad del oxígeno a partir de concentradores para su uso en anestesia en asociación con el óxido nitroso. Este estudio evaluó el porcentaje de oxígeno de un concentrador en asociación con el óxido nitroso en un circuito de reinhalación semicerrado. Métodos: pacientes adultos sometidos a cirugía de bajo riesgo fueron asignados aleatoriamente en 2 grupos, para recibir un flujo de gases frescos de concentradores de oxígeno (O293) o de concentradores de oxígeno y óxido nitroso (O293NO). La fracción inspirada de oxígeno y el porcentaje del flujo de gases frescos de oxígeno fueron medidos cada 10 min. La relación concentración liberada de FiO2/oxígeno fue comparada en diferentes intervalos de tiempo y entre los grupos. Resultados: treinta pacientes fueron evaluados en cada grupo. No hubo diferencia en el oxígeno de los concentradores a lo largo del tiempo para ambos grupos, pero sí hubo una mejoría significativa en la FiO2 (p < 0,001) en el grupo O293, mientras que hubo una caída significativa (p < 0,001) en el grupo O293NO. La relación FiO2/oxígeno varió en ambos grupos, alcanzando una meseta en el grupo O293. La oximetría de pulso no descendió por debajo del 98,5% en ningún grupo. Conclusión: la FiO2 en la mezcla de O293 y óxido nitroso cayó durante el período de observación, aunque la saturación de oxígeno quedó por encima de un 98,5% durante todo el estudio. Los concentradores pueden ser considerados una fuente estable de oxígeno para uso durante procedimientos anestésicos de corta duración, tanto puro como en asociación con el óxido nitroso en volumen de 50:50. .

Automated titration of propofol and remifentanil decreases the anesthesiologist's workload during vascular or thoracic surgery: a randomized prospective study.

Closed loop target-control infusion systems using a Bispectral (BIS) signal as an input (TCI Loop) can automatically maintain intravenous anesthesia in a BIS range of 40-60 %. Our purpose was to assess to what extent such a system could decrease anesthesia workload in comparison to the use of a stand alone TCI system manually adjusted to fit the same BIS range of 40-60 % (TCI Manual). Patients scheduled for elective vascular or thoracic surgery were randomized to the TCI Loop or TCI Manual method for administering propofol and remifentanil during both induction and maintenance of general anesthesia. Assessment of workload was performed by an independent observer who quoted each time the physician looked at the BIS monitor. The number of propofol and remifentanil target modifications, the percentage of time of adequate anesthesia i.e. BIS in the range 40-60 and hemodynamic data were recorded. Eighteen patients per group were enrolled. Characteristics, duration of surgery and propofol-remifentanil consumption were similar between groups. However, the percentage of time in the BIS range 40-60 % was higher in the TCI Loop versus TCI Manual groups (94 % ± 12 vs. 74 % ± 19, p < 0.001). Mean arterial pressure was lower with TCI Manual (78 ± 6 vs. 88 ± 13 mmHg, p < 0.001). The number of times the anesthesiologist watched the controller or BIS monitor (p < 0.05) and the number of manual adjustments (p < 0.001) performed in each group was lower with TCI Loop group during induction and maintenance of anesthesia. An automated controller strikingly frees the anesthesiologist from manual intervention to adjust drug delivery.

Comparison of minimal fresh gas requirements of baby enclosed afferent reservoir and Jackson Rees anesthetic circuit for general anesthesia in spontaneously breathing children.

OBJECTIVE: The authors compared the baby enclosed afferent reservoir (Baby EAR) with the Jackson-Rees (JR) anesthesia circuit for the minimal fresh gas flow (FGF) requirement with no and clinically acceptable rebreathing in spontaneous breathing anesthesia among pediatric patients. MATERIAL AND METHOD: The present study was a randomized crossover study. Twenty patients, weighing 5 to 20 kg with ASA physical status I-II were enrolled. They were allocated to group 1 (EAR-JR) starting with Baby EAR then switching to JR or group 2 (JR-EAR), reversedpattern. After induction and intubation, anesthesia was maintainedwith a N2O/O2 combination with sevoflurane 1 to 3% and fentanyl. Starting with the first circuit, all patients were spontaneously ventilated with FGF 500 mL/kg/min for 10 minutes, and then gradually decreased by 50 mL/kg/min every five minutes. End-tidal CO2 (ETCO) and inspired minimum CO2 (imCO) were recorded until rebreathing (imCO2 >2 mmHg) occurred and continued until rebreathing was not clinically acceptable (imCO2 >6 mmHg). The anesthesia breathing circuit was switched and the procedure repeated. RESULTS: The minimal FGF at no rebreathing of Baby EAR and JR were 192.5±76.6 and 347.5±108.2 mL/kg/min; p<0.001. At acceptable rebreathing, the values were 117.5±46.7 and 227.6±90.6 mL/kg/min; p< 0. 001. CONCLUSION: Baby EAR can be used safely, effectively, and requires less FGF than JR in pediatric anesthesia in patients weighing 5 to 20 kg.

Evaluation of closed-loop anesthesia delivery for propofol anesthesia in pediatric cardiac surgery.

OBJECTIVE: The objective of this study was to compare the feasibility of closed-loop anesthesia delivery with manual control of propofol in pediatric patients during cardiac surgery. METHODS: Forty ASA II-III children, undergoing elective cardiac surgery under cardiopulmonary bypass (CPB) in a tertiary care hospital, were randomized to receive propofol either through a closed-loop anesthesia delivery system (CL group) or through traditional manual control (manual group) to achieve a target BIS of 50. Patients were induced and subsequently maintained with a propofol infusion. The propofol usage and the efficacy of closed-loop system in controlling BIS within ±10 of the target were compared with that of manual control. RESULTS: The maintenance of BIS within ±10 of target and intraoperative hemodynamic stability were similar between the two groups. However, induction dose of propofol was less in the CL group (2.06 ± 0.79 mg·kg(-1) ) than the manual group (2.95 ± 1.03 mg·kg(-1) ) (P = 0.006) with less overshoot of BIS during induction in the closed-loop group (P = 0.007). Total propofol used in the off-CPB period was less in the CL group (6.29 ± 2.48 mg·kg(-1) h(-1) vs 7.82 ± 2.1 mg·kg(-1) h(-1) ) (P = 0.037). Phenylephrine use in the pre-CPB period was more in the manual group (16.92 ± 10.92 µg·kg(-1) vs 5.79 ± 5.98 µg·kg(-1) ) (P = 0.014). Manual group required a median of 18 (range 8-29) dose adjustments per hour, while the CL group required none. CONCLUSION: This study demonstrated the feasibility of closed-loop controlled propofol anesthesia in children, even in challenging procedures such as cardiac surgery. Closed-loop system needs further and larger evaluation to establish its safety and efficacy.

Pulmonary carbon dioxide elimination for cardiac output monitoring in peri-operative and critical care patients: history and current status.

Minimally invasive measurement of cardiac output as a central component of advanced haemodynamic monitoring has been increasingly recognised as a potential means of improving perioperative outcomes in patients undergoing major surgery. Methods based upon pulmonary carbon dioxide elimination are among the oldest techniques in this field, with comparable accuracy and precision to other techniques. Modern adaptations of these techniques suitable for use in the perioperative and critical are environment are based on the differential Fick approach, and include the partial carbon dioxide rebreathing method. The accuracy and precision of this approach to cardiac output measurement has been shown to be similar to other minimally invasive techniques. This paper reviews the underlying principles and evolution of the method, and future directions including recent adaptations designed to deliver continuous breath-by-breath monitoring of cardiac output.