Effects of different fresh gas flows and different anesthetics on airway temperature and humidity in surgical patients: a prospective observational study.

This study was aimed to investigate the effects of different fresh gas (oxygen + air) flow rates and different anesthetics on airway temperature and humidity when using the same anesthesia machine in patients undergoing general anesthesia. In this prospective, observational study, 240 patients with American Society of Anesthesiologists (ASA) I-II between the age of 18-65 years to be operated under general anesthesia were enrolled and divided into two groups according to the fresh gas flow rate (3-6 L/min). Each of the two main groups was further divided into three subgroups according to the administered anesthetic gases and drugs. The resulting six groups were further divided into two subgroups according to whether the heat and humidity exchanger filter (HME) was attached to the breathing circuit, and the study was carried out on a total of 12 groups. The temperature and humidity of the inspired air were recorded every 10 minutes using an electronic thermo-hygrometer. The inspired temperature and humidity were greater in patients ventilated at 3 L/min compared to the 6 L/min group and in HME (+) patients compared to HME (-), regardless of the type of anesthetics. HME application makes the air more physiological for the respiratory tract by increasing the temperature and humidity of the air regardless of the anesthetic agent. This study was approved by Ethics Committee Review of Selcuk University Faculty of Medicine (No. 2017/261) in September 2017, and was registered in the Clinical Trial Registry (identifier No. NCT04204746) on December 19, 2019.

Efficacy of preoxygenation using tidal volume breathing: a comparison of Mapleson A, Bain's and Circle system / Eficácia da pré-oxigenação usando respiração em volume corrente: uma comparação dos sistemas Mapleson A, Bain e Circular

Abstract Background: Efficacy of preoxygenation depends upon inspired oxygen concentration, its flow rate, breathing system configuration and patient characteristics. We hypothesized that in actual clinical scenario, where breathing circuit is not primed with 100% oxygen, patients may need more time to achieve EtO2 ≥ 90%, and this duration may be different among various breathing systems. We thus studied the efficacy of preoxygenation using unprimed Mapleson A, Bain's and Circle system with tidal volume breathing at oxygen flow rates of 5 L.min−1 and 10 L.min−1. Methods: Patients were randomly allocated into one of the six groups, wherein they were preoxygenated using either Mapleson A, Bain's or Circle system at O2 flow rate of either 5 L.min−1 or 10 L.min−1. The primary outcome measure of our study was the time taken to achieve EtO2 ≥ 90% at 5 and 10 L.min−1 flow rates. Results: At oxygen flow rate of 5 L.min−1, time to reach EtO2 ≥ 90% was significantly longer with Bain's system (3.7 ± 0.67 min) than Mapleson A and Circle system (2.9 ± 0.6, 3.3 ± 0.97 min, respectively). However at oxygen flow rate of 10 L.min−1 this time was significantly shorter and comparable among all the three breathing systems (2.33 ± 0.38 min with Mapleson, 2.59 ± 0.50 min with Bain's and 2.60 ± 0.47 min with Circle system). Conclusions: With spontaneous normal tidal volume breathing at oxygen flow rate of 5 L.min−1, Mapleson A can optimally preoxygenate patients within 3 min while Bain's and Circle system require more time. However at O2 flow rate of 10 L.min−1 all the three breathing systems are capable of optimally preoxygenating the patients in less than 3 min.

Resumo Justificativa: A eficácia da pré-oxigenação depende da concentração inspirada de oxigênio, do fluxo de gases, da configuração do circuito respiratório e das características do paciente. Nossa hipótese foi que, no cenário clínico real, no qual o circuito respiratório não é preparado com 100% de oxigênio, os pacientes podem precisar de mais tempo para atingir EtO2 ≥ 90% e essa duração pode ser diferente entre vários circuitos de respiração. Avaliamos, portanto, a eficácia da pré-oxigenação com o uso dos circuitos não preparados Mapleson A, Bain e Circular com volume corrente de respiração com um fluxo de oxigênio de 5 L.min−1 e 10 L.min−1. Métodos: Os pacientes foram alocados aleatoriamente em um dos seis grupos, nos quais foram pré-oxigenados com o uso do circuito Mapleson A, Bain ou Circular com um fluxo de O2 de 5 L.min−1 ou 10 L.min−1. O desfecho primário de nosso estudo foi o tempo necessário para atingir EtO2 ≥ 90% com um fluxo de 5 e 10 L.min−1. Resultados: Com um fluxo de oxigênio de 5 L.min−1, o tempo para atingir EtO2 ≥ 90% foi significativamente maior com o circuito Bain (3,7 ± 0,67 min) do que com os circuitos Mapleson A e Circular (2,9 ± 0,6 e 3,3 ± 0,97 min, respectivamente). No entanto, com o fluxo de oxigênio de 10 L.min−1 foi significativamente menor e comparável entre os três circuitos respiratórios (2,33 ± 0,38 min com Mapleson; 2,59 ± 0,50 min com Bain e 2,60 ± 0,47 min com o Circular). Conclusões: Durante respiração espontânea com volume corrente normal e com um fluxo de oxigênio de 5 L.min−1, o sistema Mapleson A pode pré-oxigenar o paciente de forma ideal dentro de três minutos, enquanto os sistemas Bain e Circular requerem mais tempo. Porém, com um fluxo de O2 de 10 L.min−1, todos os três circuitos respiratórios podem pré-oxigenar o paciente de forma ideal em menos de três minutos.

[Efficacy of preoxygenation using tidal volume breathing: a comparison of Mapleson A, Bain's and Circle system]. / Eficácia da pré-oxigenação usando respiração em volume corrente: uma comparação dos sistemas Mapleson A, Bain e Circular.

BACKGROUND: Efficacy of preoxygenation depends upon inspired oxygen concentration, its flow rate, breathing system configuration and patient characteristics. We hypothesized that in actual clinical scenario, where breathing circuit is not primed with 100% oxygen, patients may need more time to achieve EtO2≥90%, and this duration may be different among various breathing systems. We thus studied the efficacy of preoxygenation using unprimed Mapleson A, Bain's and Circle system with tidal volume breathing at oxygen flow rates of 5L.min-1 and 10L.min-1. METHODS: Patients were randomly allocated into one of the six groups, wherein they were preoxygenated using either Mapleson A, Bain's or Circle system at O2 flow rate of either 5L.min-1 or 10L.min-1. The primary outcome measure of our study was the time taken to achieve EtO2≥90% at 5 and 10L.min-1 flow rates. RESULTS: At oxygen flow rate of 5L.min-1, time to reach EtO2≥90% was significantly longer with Bain's system (3.7±0.67min) than Mapleson A and Circle system (2.9±0.6, 3.3±0.97min, respectively). However at oxygen flow rate of 10L.min-1 this time was significantly shorter and comparable among all the three breathing systems (2.33±0.38min with Mapleson, 2.59±0.50min with Bain's and 2.60±0.47min with Circle system). CONCLUSIONS: With spontaneous normal tidal volume breathing at oxygen flow rate of 5L.min-1, Mapleson A can optimally preoxygenate patients within 3min while Bain's and Circle system require more time. However at O2 flow rate of 10L.min-1 all the three breathing systems are capable of optimally preoxygenating the patients in less than 3min.

Circle (CO2 reabsorbing) breathing systems: Human applications.

Artificial breathing systems to help humans survive extreme environments are used over a range of ambient pressures, using various gases of different volumetric concentrations. These activities include anaesthesia and intensive care activity, high-altitude mountaineering, firefighting, aerospace extravehicular space activity and underwater diving operations. A circle breathing system is one in which the exhaled carbon dioxide is absorbed by an alkali substance and the remaining unused gases are recirculated, usually for the sake of economy and environment. This allows the flow of the fresh gas to be considerably reduced, thereby saving on fresh-gas supply. Circle systems are often used in the circumstances cited above, although not always at low fresh-gas flows. The circle system used in anaesthesia and intensive care has the least engineering demands made on it, although it is used on patients who are highly vulnerable; it usually provides a mixture of air and oxygen, and perhaps a breathable anaesthetic gas, all at sea-level pressure. Mountaineering and firefighting applications involve an extreme earthbound environment, with the user undergoing extreme physical work. The astronaut's spacesuit and life support system contains a high-flow circle system, the breathing gases themselves pressurising the suit as well as providing respiratory life support and thermal comfort; the gas provided is pure oxygen at about a third of sea-level atmosphere. There are numerous varieties of breathing systems for diving, including a circle system, often for clandestine naval activity; the gases used are a combination of oxygen, nitrogen and helium, to minimise the possibility of decompression sickness, nitrogen narcosis and oxygen toxicity and must be provided at a varying pressure and concentration appropriate to depth.

An evaluation of fresh gas flow rates for spontaneously breathing cats and small dogs on the Humphrey ADE semi-closed breathing system.

OBJECTIVE: To evaluate the fresh gas flow (FGF) rate requirements for the Humphrey ADE semi-closed breathing system in the Mapleson A mode; to determine the FGF at which rebreathing occurs, and compare the efficiency of this system to the Bain (Mapleson D) system in spontaneously breathing cats and small dogs. STUDY DESIGN: Prospective clinical study. ANIMALS: Twenty-five healthy (ASA score I or II) client-owned cats and dogs (mean ± SD age 4.7 ± 5.0 years, and body weight 5.64 ± 3.26 kg) undergoing elective surgery or minor procedures. METHODS: Anaesthesia was maintained with isoflurane delivered via the Humphrey ADE system in the A mode using an oxygen FGF of 100 mL kg(-1) minute(-1). The FGF was then reduced incrementally by 5-10 mL kg(-1) minute(-1) at approximately five-minute intervals, until rebreathing (inspired CO(2) >5 mmHg (0.7 kPa)) was observed, after which flow rates were increased. In six animals, once the minimum FGF at which rebreathing occurred was found, the breathing system was changed to the Bain, and the effects of this FGF delivery examined, before FGF was increased. RESULTS: Rebreathing did not occur at the FGF recommended by the manufacturer for the ADE. The mean ± SD FGF that resulted in rebreathing was 60 ± 20 mL kg(-1) minute(-1). The mean minimum FGF at which rebreathing did not occur with the ADE was 87 ± 39 mL kg(-1) minute(-1). This FGF resulted in significant rebreathing (inspired CO(2) 8.8 ± 2.6 mmHg (1.2 ± 0.3 kPa)) on the Bain system. CONCLUSIONS: The FGF rates recommended for the Humphrey ADE are adequate to prevent rebreathing in spontaneously breathing cats and dogs <15 kg. CLINICAL RELEVANCE: The Humphrey ADE system used in the A mode is a more efficient alternative to the Bain system, for maintenance of gaseous anaesthesia in spontaneously breathing cats and small dogs.

An ADARPEF survey on respiratory management in pediatric anesthesia.

BACKGROUND: There have been recent changes with regard to tools and concepts for respiratory management of children undergoing general anesthesia. OBJECTIVES: To determine the practice of pediatric anesthetists concerning: preoxygenation, breathing systems, ventilation modes, anesthetic agent and airway device, strategies for a general anaesthetic of less than 30 min using spontaneous respiration, and opinion about technical aspects of ventilation. METHODS: Online questionnaire sent by e-mail to all the anesthetists registered on the mailing list of the French-speaking Pediatric Anesthetists and Intensivists Association (ADARPEF). RESULTS: 232 questionnaires (46%) were returned. More than 25% of anesthetists surveyed declared that they do not perform preoxygenation before induction for children <15 years old, apart from neonates and clinical specific situations. When performed, <65% chose a FiO2 higher than 80%. Inhalational induction with sevoflurane is the preferred mode of induction set at 6% or 8%, respectively, 69% [62-75] vs 25% [18-31]. For induction, the circle system was the most popular circuit used in all ages. The accessory breathing system-Mapleson B type-was predominantly used for neonates (44% [37-54]). For maintenance of an anesthesia lasting <30 min in spontaneous breathing, the use of laryngeal mask increased with age, and the endotracheal tube was reserved for neonates (40% [33-48]). Pressure support ventilation was rarely used from the beginning of induction but was widely used for maintenance, whatever the age-group. Results differed according to the type of institution. CONCLUSION: Ventilation management depends on the age and institutions in terms of circuit, airway device or ventilation mode, and specific differences exist for neonates.

Mapleson's Breathing Systems.

Mapleson breathing systems are used for delivering oxygen and anaesthetic agents and to eliminate carbon dioxide during anaesthesia. They consist of different components: Fresh gas flow, reservoir bag, breathing tubes, expiratory valve, and patient connection. There are five basic types of Mapleson system: A, B, C, D and E depending upon the different arrangements of these components. Mapleson F was added later. For adults, Mapleson A is the circuit of choice for spontaneous respiration where as Mapleson D and its Bains modifications are best available circuits for controlled ventilation. For neonates and paediatric patients Mapleson E and F (Jackson Rees modification) are the best circuits. In this review article, we will discuss the structure of the circuits and functional analysis of various types of Mapleson systems and their advantages and disadvantages.

A comparison of the 'Maxima' and the modified Ayre's T-piece breathing systems in spontaneously breathing cats.

OBJECTIVE: To compare the fresh gas flow requirements of the 'Maxima' and Jackson-Rees modified Ayre's T-piece (JRMATP) in spontaneously breathing anaesthetized in cats. STUDY DESIGN: Prospective randomized clinical study. ANIMALS OR SAMPLE POPULATION: Fifteen adult cats (6 male, 9 female, 3.1 ± 0.4 kg [ x¯ ± SD]). MATERIALS & METHODS: After pre-anaesthetic medication with acepromazine and pethidine, anaesthesia was induced using thiopentone and the trachea was intubated with a cuffed endotracheal tube. This was attached to either a 'Maxima' or a JRMATP breathing system; allocation was randomized. Anaesthesia was maintained with halothane delivered in a 1 : 1 oxygen : nitrous oxide mixture. Initial total fresh gas flow (FGF) was set at 600 mL kg-1 min-1. After 20 minutes, FGF was reduced in increments of 200 mL min-1 until rebreathing (inspired CO2 concentration >0.2%) occurred. At this point, FGF was increased to 600 mL kg-1 and the process was repeated with the other breathing system. The respiratory rate and airway pressure at the endotracheal tube connector were monitored throughout anaesthesia. RESULTS: The mean fresh gas flow that prevented rebreathing with the Maxima system (164 ± 39 mL kg-1) was significantly less (p < 0.0001) than that required in the modified T-piece (455 ± 0.77 mL kg-1). Respiratory rates and airway pressures at the endotracheal tube connector were not significantly affected by breathing system employed. CONCLUSIONS: In terms of the gas flow requirements that prevent rebreathing, the 'Maxima' breathing system is more efficient than the modified Ayre's T-piece in spontaneously breathing cats anaesthetised with halothane.