Inspiratory to End-Tidal Oxygen Difference During Nitrous Oxide Anaesthesia (original) (raw)
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Inhaled anaesthetics and nitrous oxide: Complexities overlooked: things may not be what they seem
European journal of anaesthesiology, 2016
This review re-examines existing pharmacokinetic and pharmacodynamic concepts of inhaled anaesthetics. After showing where uptake is hidden in the classic FA/FI curve, it is argued that target-controlled delivery of inhaled agents warrants a different interpretation of the factors affecting this curve (cardiac output, ventilation and blood/gas partition coefficient). Blood/gas partition coefficients of modern agents may be less important clinically than generally assumed. The partial pressure cascade from delivered to inspired to end-expired is re-examined to better understand the effect of rebreathing during low-flow anaesthesia, including the possibility of developing a hypoxic inspired mixture despite existing machine standards. Inhaled agents are easy to administer because they are transferred according to partial pressure gradients. In addition, the narrow dose-response curves for the three end points of general anaesthesia (loss of response to verbal command, immobility and au...
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.
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.
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.
Replacement of physiologically autoinhaled nitric oxide in intubated patients
European Respiratory Journal, 2003
Autoinhaled nitric oxide (NO) is produced mainly in the upper airways. Orotracheal intubation disrupts the natural autoinhalation of NO from the naso-and oropharynx. The effect of disrupting and then replacing autoinhaled NO on arterial oxygenation was investigated in intubated patients. Two groups of nine patients without lung disease were examined during anaesthesia using an inspired oxygen fraction of 0.50. In both groups, the individually produced NO of the whole respiratory tract and the upper airways was determined. The amount of NO normally autoinhaled from the upper airways was replaced for 5 min after orotracheal intubation in one group. The amount of NO from the upper respiratory tract was 47¡19 parts per billion (ppb) in the test group and the replaced NO concentration was 48¡20 ppb. No significant increase in arterial oxygen tension could be detected during the replacement of the autoinhaled NO. Haemodynamic parameters remained unchanged. In the control group, the NO from the upper airways was 34¡16 ppb. In contrast to the test group, it was not replaced after intubation. These findings suggest that in healthy subjects the autoinhalation of nitric oxide does not play an important role in arterial oxygenation during anaesthesia.
Current Ventilator and Oxygen Management during General Anesthesia
Anesthesiology, 2018
Background Intraoperative oxygen management is poorly understood. It was hypothesized that potentially preventable hyperoxemia and substantial oxygen exposure would be common during general anesthesia. Methods A multicenter, cross-sectional study was conducted to describe current ventilator management, particularly oxygen management, during general anesthesia in Japan. All adult patients (16 yr old or older) who received general anesthesia over 5 consecutive days in 2015 at 43 participating hospitals were identified. Ventilator settings and vital signs were collected 1 h after the induction of general anesthesia. We determined the prevalence of potentially preventable hyperoxemia (oxygen saturation measured by pulse oximetry of more than 98%, despite fractional inspired oxygen tension of more than 0.21) and the risk factors for potentially substantial oxygen exposure (fractional inspired oxygen tension of more than 0.5, despite oxygen saturation measured by pulse oximetry of more th...