Sampled gas need not be returned during low-flow anesthesia (original) (raw)
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Canadian Journal of Anaesthesia-journal Canadien D Anesthesie, 2002
Purpose One hundred percent O2 is used routinely for preoxy-genation and induction of anesthesia. The higher the O2 concentration the faster is the development of atelectasis, an important cause of impaired pulmonary gas exchange during general anesthesia (GA). We evaluated the effect of ventilation with 0.4FiO2 in air, 0.4FiO2 in N2O and 100% O2 following intubation on the development of impaired gas exchange. Methods Twenty-seven patients aged 18–40 yr, undergoing elective laparoscopic cholecystectomy were administered 100% O2 for preoxygenation (three minutes) and ventilation by mask (two minutes). Following intubation these patients were randomly divided into three groups of nine each and ventilated either with 0.4FiO2 in air, 0.4FiO2 in N2O or 100% O2. Arterial blood gases were obtained before preoxygenation and 30 min following intubation for PaO2 analysis. Subsequently PaO2/FiO2 ratios were calculated. Results were analyzed with Student’s t test and one-way ANOVA. P value of ≤ 0.05 was considered significant. Results Ventilation of the lungs with O2 in air (FiO2 0.4) significantly improved the PaO2/FiO2 ratio from baseline, while 0.4FiO2 in N2O or 100% O2 worsened the ratio (558 ± 47vs 472 ± 28, 365 ± 34vs 472 ± 22 and 351 ± 23 vs 477 ± 28 respectively; P < 0.05). Conclusion Ventilation of lungs with O2 in air (FiO2 0.4) improves gas exchange in young healthy patients during GA. Objectif Cent pour cent d’O2 sont utilisés habituellement pour la préoxygénation et l’induction de l’anesthésie. Plus la concentration d’O2 est élevée, plus vite peut se développer l’atélectasie, une cause importante d’anomalie des échanges gazeux pulmonaires pendant l’anesthésie générale (AG). Nous avons évalué l’effet de la ventilation avec uneFiO2 de 0,4 dans de l’air,FiO2 de 0,4 dans du N2O et 100 % d’O2 après l’intubation quand apparaissent les anomalie des échanges gazeux. Méthode Vingt-sept patients de 18–40 ans, devant subir une cholé-cystectomie laparoscopique non urgente ont reçu 100 % d’O2 pour la préoxygénation, pendant trois minutes, et la ventilation au masque, pendant deux minutes. Après l’intubation, ces patients ont été répartis de façon aléatoire en trois groupes de neuf et ventilés avec 0,4FiO2 dans de l’air ou 0,4FiO2 dans du N2O ou 100% d’O2. La gazométrie du sang artériel a été obtenue pendant la préoxygénation et 30 min après l’intubation pour l’analyse de la PaO2. Par la suite, les ratios PaO2/FiO2 ont été calculés. Les résultats ont été analysés selon le test t de Student et une analyse de variance à une voie. Une valeur de P ≤ 0,05 a été considérée comme significative. Résultats La ventilation pulmonaire avec de l’O2 dans de l’air (FiO2 de 0,4) a sensiblement amélioré le ratio PaO2/FiO2, comparativement aux données de base, tandis que 0,4FiO2 dans du N2O ou 100 % d’O2 l’ont altéré (558 ± 47vs 472 ± 28, 365 ± 34 vs 472 ± 22 et 351 ± 23 vs 477 ± 28 respectivement; P < 0,05). Conclusion La ventilation pulmonaire avec de l’O2 dans de l’air (FiO2 0,4) améliore les échanges gazeux chez les jeunes patients pendant l’AG.
Brief review: Theory and practice of minimal fresh gas flow anesthesia
Canadian Journal of Anesthesia/Journal canadien d'anesthésie, 2012
The aim of this brief review is to provide an update on the theory regarding minimal fresh gas flow techniques for inhaled general anesthesia. The article also includes an update and discussion of the practical aspects associated with minimal-flow anesthesia, including the advantages, potential limitations, and safety considerations of this important anesthetic technique. Principal findings Reducing the fresh gas flow to \ 1 LÁmin-1 during maintenance of anesthesia is associated with several benefits. Enhanced preservation of temperature and humidity, cost savings through more efficient utilization of inhaled anesthetics, and environmental considerations are three key reasons to implement minimal-flow and closed-circuit anesthesia, although potential risks are hypoxic gas mixtures and inadequate depth of anesthesia. The basic elements of the related pharmacology need to be considered, especially pharmacokinetics of the inhaled anesthetics. The third-generation inhaled anesthetics, sevoflurane and desflurane, have low blood and low tissue solubility, which facilitates rapid equilibration between the alveolar and effect site (brain) concentrations and makes them ideally suited for low-flow techniques. The use of modern anesthetic machines designed for minimal-flow techniques, leak-free circle systems, highly efficient CO 2 absorbers, and the common practice of utilizing on-line real-time multi-gas monitor, including essential alarm systems, allow for safe and costeffective minimal-flow techniques during maintenance of anesthesia. The introduction of new anesthetic machines with built-in closed-loop algorithms for the automatic control of inspired oxygen and end-tidal anesthetic concentration will further enhance the feasibility of minimal-flow techniques. Conclusions With our modern anesthesia machines, reducing the fresh gas flow of oxygen to 0.3-0.5 LÁmin-1 and using third-generation inhaled anesthetics provide a reassuringly safe anesthetic technique. This environmentally friendly practice can easily be implemented for elective anesthesia; furthermore, it will facilitate cost savings and improve temperature homeostasis. Résumé Objectif Le but de cet article de synthe`se court est de fournir une mise a`jour sur la the´orie des techniques a`bas Author contributions Jan Jakobsson is the main author of this review and has made substantial contributions to the conception and design of the manuscript and the acquisition and interpretation of data. Margareta Warre´n-Stomberg, Metha Brattwall, and Fredrik Hesselvik critically revised the manuscript for important intellectual content.
Inhaled Nitric Oxide Delivery by Anesthesia Machines
Anesthesia & Analgesia, 2000
Inhaled nitric oxide (NO) is a selective pulmonary vasodilator used to treat intraoperative pulmonary hypertension and hypoxemia. In contrast to NO delivered by critical care ventilators, NO delivered by anesthesia machines can be complicated by rebreathing. We evaluated two methods of administering NO intraoperatively: via the nitrous oxide (N 2 O) flowmeter and via the INOvent (Datex-Ohmeda, Madison, WI). We hypothesized that both systems would deliver NO accurately when the fresh gas flow (FGF) rate was higher than the minute ventilation (V e). Each system was set to deliver NO to a lung model. Rebreathing of NO was obtained by decreasing FGF and by simulating partial NO uptake by the lung. At FGF Ն V e (6 L/min), both systems delivered an inspired NO concentration [NO]) within approximately 10% of the [NO] set. At FGF Ͻ V e and complete NO uptake, the N 2 O flowmeter delivered a lower [NO] (70 and 40% of the [NO] set at 4 and 2 L/min, respectively) and the INOvent delivered a higher [NO] (10 and 23% higher than the [NO] set at 4 and 2 L/min, respectively). Decreasing the NO uptake increased the inspired [NO] similarly with both systems. At 4 L/min FGF, [NO] increased by 10%-20% with 60% uptake and by 18%-23% with 30% uptake. At 2 L/min, [NO] increased by 30%-33% with 60% uptake and by 60%-69% with 30% uptake. We conclude that intraoperative NO inhalation is accurate when administered either by the N 2 O flowmeter of an anesthesia machine or by the INOvent when FGF Ն V e. Implications: Inhaled nitric oxide (NO) is a selective pulmonary vasodilator. In a lung model, we demonstrated that NO can be delivered accurately by a N 2 O flowmeter or by a commercial device. We provide guidelines for intraoperative NO delivery. (Anesth Analg 2000;90:482-8) I nhaled nitric oxide (NO) is used as an investigational treatment for intraoperative pulmonary hypertension and hypoxemia (1-3). With adult critical care ventilators (4), NO delivery is simplified because fresh gas flow (FGF) is delivered during inspiration only; the circuit is open and gas rebreathing does not occur. In neonatal ventilators (4), FGF is continuous throughout the respiratory cycle; again, the circuit is open and rebreathing does not occur. With anesthesia machines, NO delivery is more complicated because FGF is continuous and the breathing circuit semi-open; thus, rebreathing can occur. During inspiration, the patient receives a variable combination of fresh and exhaled gas. During exhalation, the circuit may be filled by FGF without NO, FGF with a set NO concentration ([NO]), or exhaled gas with a variable [NO]. The breathing circuit is further complicated by the presence of a gas reservoir (bag or ventilator bellows) and a carbon dioxide (CO 2 ) absorber. Ultimately, inspired [NO] is the result of several variables, including the [NO] added to the system, FGF rate, ratio of inspiratory-to-expiratory (I:E) time, breathing circuit size, patient minute ventilation (V e), dead space (Vd), and NO uptake.
Are high fresh gas flow rates necessary during the wash‐in period in low‐flow anesthesia?
The Kaohsiung Journal of Medical Sciences, 2020
In low-flow anesthesia (LFA), there is a wash-in period in which usually high fresh gas flow (FGF) rates are used to achieve the required initial concentration of anesthetic agent in the alveoli. The aim of this study was to compare the efficiency, safety and the consumption of desflurane in LFA using constant FGF (1 L/min) and conventional LFA using high FGF (4 L/min) during the wash-in period. Eighty patients, who were scheduled for elective surgery under general anesthesia with endotracheal intubation, were enrolled in the study. Wash-in was accomplished with 1 L/min FGF (50% O2, 50% air) and 18% desflurane in group 1; and by 4 L/min FGF (50% O2, 50% air) and 6% desflurane in group 2. Throughout the surgery, the vaporizer was adjusted to maintain 0.6 to 0.8 minimum alveolar concentration (MAC). The time required to reach 0.7 MAC was shorter in group 1 (160 seconds [135-181] vs 288 seconds [240-500], P < .001). In 6 patients in group 1 and 13 in group 2, vaporizer settings were adjusted to maintain 0.6 to 0.8 MAC (P = .
A formula to calculate oxygen uptake during low flow anesthesia based on FIO2 measurement
Journal of clinical monitoring and computing, 1998
Monitoring of oxygen uptake during general anesthesia would have several benefits, but unfortunately, this is usually not available in the clinical routine situation. The herein proposed formula to calculate oxygen uptake (.VO2) necessitates only the accurate measurement of FIO2 as well as fresh gas flow and composition. Additionally, this method is not affected by the presence of anesthetic gases. The calculation uses the difference in oxygen content between the delivered fresh gas and the resulting FIO2 in the anesthesia circle system. This gap originates from oxygen uptake (that is mainly caused by metabolic oxygen consumption) and is more pronounced if low fresh gas flows are administered. In order to obtain representative results, calculation of .VO2 should be performed only after achievement of respiratory steady state conditions. Due to its simplicity and wide availability, it has the potential to become a valuable extension in anesthesia monitoring during the performance of ...
Medical devices (Auckland, N.Z.), 2016
The Lack's circuit is a co-axial Mapleson A breathing system commonly used in spontaneously breathing anesthetized adults but still requires high fresh gas flow (FGF). The Lack-Plus circuit was invented with the advantage of lower FGF requirement. The authors compared the Lack-Plus and Lack's circuit for the minimal FGF requirement with no rebreathing in spontaneously breathing anesthetized adults. This was a randomized crossover study. We enrolled 24 adult patients undergoing supine elective surgery, with a body mass index ≤30 kg/m(2) and an American Society of Anesthesiologists physical status I-II. They were randomly allocated to group 1 (LP-L) starting with Lack-Plus then switching to Lack's circuit or group 2 (L-LP) (with the reverse pattern). After induction and intubation, anesthesia was maintained with 50% N2O/O2 and desflurane (4%-6%) plus fentanyl titration to maintain an optimal respiratory rate between 10 and 16/min. Starting with the first circuit, all the p...
Low-flow anaesthesia with a fixed fresh gas flow rate
Journal of clinical monitoring and computing, 2018
During the wash-in period in low flow anaesthesia (LFA), high fresh gas flow is used to achieve the desired agent concentration. In this study, we aimed to evaluate the safety of fixed 1 L/min fresh gas flow desflurane anaesthesia in both the wash-in and maintenance periods in patients including the obese ones. 104 patients undergoing surgery under general anaesthesia were included. After endotracheal intubation, fresh gas flow was reduced to 1 L/min and the desflurane vaporizer was set at 18%. The time from opening the vaporizer to end-tidal desflurane concentration reaching 0.7 MAC was recorded (MAC 0.7 time). Throughout the surgery, hemodynamic variables, FIO2, MAC and BIS values were observed. MAC 0.7 time, BIS and MAC values at the start of surgery, number of adjustments in vaporizer settings, desflurane consumption were recorded. The average MAC 0.7 time was 2.9 ± 0.5 min. MAC and BIS values at the start of the surgery were 0.7 (0.6-0.8) and 39 ± 8.5 respectively. No individua...
Journal of Clinical Monitoring and Computing, 2004
We present the principles of a new method to calculate O 2 consumption (VO 2 ) during low-flow anesthesia with a circle circuit when the source gas flows, end-tidal O 2 concentrations and patient inspired minute ventilation are known. This method was tested in a model with simulated O 2 uptake and CO 2 production. The difference between calculatedVO 2 and simu-latedVO 2 was 0.01 ± 0.02 L/min. A similar approach can be used to calculate uptake of inhaled anesthetics. At present, with this method, the limiting factor in precision of measurement oḟ VO 2 and uptake of anesthetic is the precision of measurement of gas flow and gas concentration (especially O 2 concentration in end-tidal gas, FETO 2 ) available in clinical anesthetic units.
British Journal of Anaesthesia, 2004
Background. Nitric oxide is important in vasomotor regulation. Contamination of anaesthetic gases with nitric oxide could affect gas exchange. Methods. We measured oxygenation and nitric oxide concentrations in the inspiratory and expiratory limb of the ventilator circuit in patients about to have cardiac surgery. Measurements were made before surgery when the circulation and respiratory conditions were stable. FI O 2 was set at 0.35. The breathing circuit was supplied with a fresh gas flow greater than the minute volume so that exhaled gas was not re-used. Three gas mixtures were given in sequence to each patient: oxygen and compressed air (AIRc), oxygen and nitrous oxide, and oxygen and synthetic air (AIRs) that was free from nitric oxide. All patients were given AIRs as the second gas and the other two gas mixtures (AIRc and nitrous oxide) were given randomly as the first and third gases. Results. During ventilation with oxygen-AIRc, the median nitric oxide concentration was 5.6 ppb, during ventilation with oxygen-nitrous oxide it was 5.0 ppb and using oxygen-AIRs it was 1.5 ppb. When AIRc and nitrous oxide were used, Pa O 2 was greater and venous admixture was less than when AIRs was used. The different gas mixtures did not affect pulmonary vascular pressures or cardiac ouput. Conclusions. Compressed air and nitrous oxide contain very low concentrations of nitric oxide (<10 ppb). This can affect pulmonary oxygen transfer during anaesthesia.
Low-flow anaesthesia at a fixed flow rate
Acta Anaesthesiologica Scandinavica, 2009
This study attempts to assess the safety of low-flow anaesthesia (LFA) at fixed flow rates with particular reference to the incidence of a decline in FiO(2) below safe levels of 0.3 and to determine whether LFA can be used safely in the absence of an FiO(2) monitor. A total of 100 patients undergoing procedures under general anaesthesia at fresh gas flows of 300 ml/min of O(2) and 300 ml/min of N(2)O were monitored while maintaining the dial setting of isoflurane at 1.5% for 2 h. The changes in gas composition were analysed and even a single recording of FiO(2) of <0.3 was considered sufficient to render the technique unsafe in the absence of gas monitors. The lowest recorded value of FiO(2) was 31% (v/v%). There was no incidence of adverse events necessitating the conversion from low flows to conventional flows. We conclude that low flows of 300 ml/min of N(2)O and 300 ml/min of oxygen can be used safely for a period of 2 h without the use of monitors for gas analysis of oxygen and agent in adult patients weighing between 40 and 75 kgs.