MODIFICATION OF THE BIRD VENTILATOR FOR USE DURING SPONTANEOUS RESPIRATION

By incorporating an Ayre T-piece system into the circuit forthe Bird ventilator, efficient humidification and nebulizationof drugs can be provided for patients breathing spontaneously.This modification has proved very useful during "weaning" ofpatients from prolonged intermittent positive pressure ventilation,and other advantages of using this circuit are mentioned.     

Malfunction of equipment by the addition of a bacterial filter in the expiratory branch of the respiratory circuit

The addition of a continuous Flow System to the circuit of a volume cycled respirator results in an additional IMV option and shows excellent performance for this purpose. The insertion of a bacterial filter into this modified circuit resulted in a dangerous increase of airway pressures after 54 "running hours" for that filter. Test series revealed an insufficient air transmission through the filter, caused by the water vapour-saturated inspiratory gas mixture, which is necessary in long term ventilation. Furthermore it was demonstrated that wet bacterial filters cause malfunction of SIMV systems due to interference with the demand valve responsible for proper air supply. The routine use of a bacterial filter placed in the expiratory branch results in higher risks in an already risky artificial ventilation system and use-nonuse relationships seem to be questionable.     

婴儿麻醉中紧闭循环通气与Jackson-Rees回路通气呼吸动力学的比较

目的 评价Ｏｈｍｅｄａ Ｅｘｃｅｌ２１０麻醉机＋７９００呼吸机紧闭循环通气用于婴儿麻醉的可行性。方法 选择１０ｋｇ以下婴儿唇裂或腭裂手术病例３０例。以同组病例前后比较紧闭循环通气与Ｊａｃｋｓｏｎ－Ｒｅｅｓ婴儿回路通气的各项呼吸动力学指标。以呼吸频率（ＲＲ）＝２２次／ｍｉｎ,Ｉ：Ｅ＝１：１．５及ＰＥＴＣＯ２＝４０ｍｍＨｇ为控制值,相应调节潮气量。观测紧闭循环通气与Ｊａｃｋｓｏｎ－Ｒｅｅｓ婴儿回路通气     

Dynamic hyperinflation and cardiac arrest during one-lung ventilation: a case report

Purpose

Dynamic hyperinflation describes the phenomenon of progressive gas trapping that occurs in patients with severe airflow obstruction. It is associated with significant hemodynamic instability and may precipitate cardiac arrest. This report describes a case of hemodynamic collapse secondary to dynamic hyperinflation in a patient during one-lung ventilation.

Clinical features

A 50-yr-old male with a pneumothorax secondary to a ruptured bulla was transferred to the operating room for a left bullectomy. Approximately 30 minutes after initiation of one-lung ventilation in the right lateral decubitus position, sudden ST segment elevation and hypotension occurred, which was refractory to large doses of vasopressor. This culminated in a pulseless electrical activity arrest. The patient was immediately placed supine, disconnected from the ventilator circuit, and resuscitated with chest compressions, fluids, and epinephrine. Auscultation of the right chest revealed no air entry, and needle decompression followed by chest tube insertion in the right chest did not demonstrate any evidence of a pneumothorax. Approximately three to five minutes after the onset of the arrest, the patient’s hemodynamics stabilized and there was no evidence of ST elevation. The etiology of the arrest was likely due to dynamic hyperinflation.

Conclusion

This report highlights the importance of having a high index of suspicion for dynamic hyperinflation and the key to its treatment: disconnection from the ventilator circuit and cessation of mechanical ventilation to allow the lungs to return to functional residual capacity.     

Universal coaxial anesthetic system

A true universal co-axial anaesthetic system has been designed. This system may be used either as a Mapleson A circuit during spontaneous ventilation or as a Mapleson D circuit during controlled ventilation. Conversion to either system may be conveniently carried out by interchanging the pop-off valve and fresh gas inlet, without disconnecting the system from the patient. Resistance to flow of both tubes has been measured and was found to be within acceptable limits. The efficiency of this system in a Mapleson A arrangement was compared with that of a conventional Magill circuit during spontaneous breathing in 2 conscious volunteers. It was shown that no significant difference exists between these systems eith regard to rebreathing, and that the universal co-axial system may be used as efficiently and economically as the Magill circuit during spontaneous ventilation. The co-axial system can be easily connected to a circle system, combining the advantages of the two systems.     

隔离阀对稳定机械通气、回路内药物浓度和气体量的意义

目的：通过对有新鲜气体隔离阀（FGE valve）的麻醉机与普通麻醉机在不同流量下的机械通气性能的比较;探讨隔离阀对稳定机械通气、回路内药物浓度和气体量的意义。方法：在两种麻醉机上分别设定相同分钟通气量（MV）及安氟醚浓度于不同新鲜气流量下测定MV、气道压力、回路内麻醉气体浓度及贮气囊气体量的变化。结果：在有隔离阀的麻醉回路中,新鲜气体流量对MV、气道压力无明显影响,回路内麻醉气体浓度相对稳定,贮气囊气体量随新鲜气体量和泄漏量变化而改变。结论：隔离阀可稳定机械通气、回路内药物浓度及贮气囊中的贮气量,可适时临测和调节回路中气体量。     

A new universal anaesthetic circuit using a preferential-flow T-piece.

A new co-axial anaesthetic circuit, employing a preferential-flow T-piece which eliminates the need for valves in the circuit, has been designed. Its efficiency has been shown to compare favourably with that of conventional circuits for use in spontaneous respiration and under conditions of controlled ventilation. The proposed system has the advantage of convenience, in that there is no need to disconnect the system from the patient nor from the anaesthetic machine when it is necessary to change from spontaneous to controlled ventilation or should a circle absorber be incorporated within the circuit. The system has been shown to offer lower resistance than the Mapleson A circuit.     

The activity of the "Hygrobac DAR 352" filter in resuscitation patients

The Authors clinically evaluated the efficacy of the "Hygrobac DAR 352" filter as an antibacterial barrier in a group of patients during mechanical ventilation. After 24 hours of IPVV, a cultural sample has been taken on both sides of the filter introduced in the breathing circuit (patient's side; ventilator's side). While bacteria has been isolated on "the patient's side" of the filter, they were not present on the surface of the "ventilator's side" of the filter. Therefore, the Authors emphasize that the Hygrobac DAR 352 filter represents a good barrier against the passage of bacteria, as it avoids the contamination of the mechanical ventilator by keeping pathogenic organisms coming from patient's airways inside the filter itself.     

Does fresh gas flow rate affect monitoring requirements?

Opinions vary on the monitoring requirements associated with low flow to closed circuit anesthesia. Fresh gas flow rate affects variables of anesthesia ventilation such as the time constant of the breathing system, the inspired concentrations of O2, N2O and anesthetic vapor and the potential for rebreathing. Furthermore, very low flow rates challenge the performance of rotameters and vaporizers. Consequently, the safe conduct of minimal flow or closed circuit anesthesia mandates oximetry, which should be redundant; the use of anesthetic agent monitors ("anesthetico-meters") is extremely helpful, and so is capnometry. However, none of these safety monitors is beyond the scope of the "essential requirements" proposed for anesthesia workstations by international standard-writing groups, such as CEN or ISO. It may hence be concluded that fresh gas flow rate does affect variables to be monitored, but it does not affect essential monitoring requirements.     

Les respirateurs d'anesthésie de nouvelle génération vont-ils modifier notre pratique chez l'enfant ?

Because of specific paediatric respiratory physiology (mainly decreased compliance and functional residual capacity, increased O2 demand and CO2 production), ventilators for paediatric anaesthesia need to be powerful and able to deliver small volumes at a high rate without compression volume loss. The compensation of compliance now available on every anaesthesia machine, compensates for the volume of gas lost by compression in the circuit tubing allowing the tidal volume to reach preset commands, even for bellow in box respirators. Preset tidal volume is then totally delivered to the lung by volume-controlled ventilation because it becomes independent of total pulmonary compliance and fresh gas flow. Increased precision of electronic flowmeters and better air-tightness of circuits allow reducing with precision fresh gas flow to values approaching children's O2 consumption and N2O diffusion. New modes of ventilation are now available on anaesthesia machine. Pressure controlled mode, by increasing and maintaining mean airway pressures, ameliorates intrapulmonary gas distribution and compensates for the gas leak from uncuffed tracheal tubes. Unsteady tidal volume resulting from variation of total compliance, is the main drawback of pressure-controlled ventilation that may be overcome by using the "autoflow" mode (better described as a pressure controlled mode ensuring tidal volume) available with one of the last generation of ventilators. Increased accuracy and security of the mode "pressure assist" might increase the use of spontaneous ventilation in paediatric anaesthesia even for low weight children. However tidal volume remains variable with compliance and depth of anaesthesia, which may require several adjustments of ventilator's settings. The clinical conditions (mainly airway control) of pressure assist use for children less than 10 kg should be elucidated before recommending its use.     

The most proximal and accurate site for sampling end-tidal CO2 in infants

The most proximal site to sample end-tidal CO₂ with reasonable accuracy in infants during pulmonary ventilation using a Mapleson D circuit remains controversial. The utilisation of high fresh gas flow near the site of gas sampling dilutes the expired gas and causes an underestimation of end-tidal CO₂. In this study a laboratory model was used to identify, qualitatively and quantitatively, the most proximal site in the Mapleson D circuit where the measurement of end-tidal CO₂ is not influenced by mixing with fresh gas. A fresh gas flow rate of between 2 and 15 L · min^?1 with a respiratory rate of 20–30 · min^?1 and a tidal volume of 30–100 ml · min^?1 was evaluated. This experiment was divided into two parts. Firstly, an infant lung model was used to visualize the site of mixing between fresh gas and smoke-labelled exhaled gas. Secondly, fresh gas flow and expired gas flow were controlled and the end-tidal CO₂ concentration was measured along the length of the anaesthetic circuit to identify the site of mixing of fresh gas and expired gas during steady-state conditions. Three expired gas flows were studied at six fresh gas flows. In all our studies, the rate of fresh gas flow and expired gas flow influenced the site of mixing and degree of dilution but no mixing was observed distal to the point at which the endotracheal tube connector narrows to the diameter of the endotracheal tube (P < 0.05). This laboratory study allows us to suggest that the most proximal and acceptably accurate site to sample end-tidal Co₂ in infants during ventilation with the Mapleson D circuit is at the point of narrowing of the endotracheal tube connector with the endotracheal tube.     

Arterial Carbon Dioxide Tensions during Anaesthesia with Manual Ventilation A Descriptive Study of the Effects of Various Non-Polluting Circuits

In 660 supine, intubated and anaesthetized, healthy patients scheduled for various elective surgical procedures, the distribution of arterial carbon dioxide tension (PaCO2) was investigated during manual non-monitored ventilation. The study comprised six equal groups: group 1: ventilation with a circle circuit absorber system; group 2: ventilation with the Hafnia A circuit using a total fresh gas flow (FGF) of 100 ml . kg-1 . min-1; groups 3-6: ventilation with a Hafnia D circuit with fresh gas flows of 100, 80, 70 and 60 ml . kg-1 . min-1, respectively. The mean PaCO2's of the first three groups were situated in the lower range of normocapnia (the observations in the first group having the greatest total range), whereas the rebreathing (Hafnia A and D) circuits resulted in a clustering of observed data. Employing the rebreathing circuits, protection against hypocapnia can be achieved by lowering the fresh gas flow. The most satisfying result was obtained with the Hafnia D circuit with a fresh gas flow of 70 ml . kg-1 . min-1 resulting in normocapnia with a modest and limited spread towards hypo- and hypercapnia. FGF in excess of this level must be considered as wasted. The study indicates that corrections of fresh gas flows for age are superfluous. Use of relaxants and type of surgery had no influence on the observations.     

A new concept in controlled ventilation of children with the Bain anesthetic circuit

The Bain anesthesia circuit was studied as a semi-open or partial rebreathing system during controlled ventilation in 16 children weighing from 7.5 to 48 kg. During anesthesia the lungs were ventilated with a volume ventilator set at three times the calculated alveolar ventilation to provide optimum mixing in the exhalation tube of the Bain circuit. Fresh gas inflow rates initially were set equal to the calculated alveolar ventilation, and after 30 to 45 min, PCO2, PO2 and pH values were measured. At the same time, the fractional concentration of mixed expired carbon dioxide (FECO2) was recorded from a capnograph inserted between the ventilator and the Bain circuit. After initial readings, the fresh gas inflow was varied over a range of 1,400-3,000 ml/m2/min at 20-min intervals, with the arterial blood-gas values and FECO2 recorded at each setting. The results indicate that a lower fresh gas inflow than previously recommended can be used safely in children. When the minute ventilation is three times the fresh gas inflow, values for FECO2 correlate closely with PaCO2 values; with a fresh gas inflow of 2,500 ml/m2/min,PaCO2 values can be maintained near 40 torr.     

Performance Characteristics of Five New Anesthesia Ventilators and Four Intensive Care Ventilators in Pressure-support Mode: A Comparative Bench Study

Background: During the past few years, many manufacturers have introduced new modes of ventilation in anesthesia ventilators, especially partial-pressure modalities. The current bench test study was designed to compare triggering and pressurization of five new anesthesia ventilators with four intensive care unit ventilators.

Methods: Ventilators were connected to a two-compartment lung model. One compartment was driven by an intensive care unit ventilator to mimic "patient" inspiratory effort, whereas the other was connected to the tested ventilator. The settings of ventilators were positive end-expiratory pressures of 0 and 5 cm H2O, and pressure-support ventilation levels of 10, 15, and 20 cm H2O with normal and high "patient" inspiratory effort. For the anesthesia ventilators, all the measurements were obtained for a low (1 l/min) and a high (10 l/min) fresh gas flow. Triggering delay, triggering workload, and pressurization at 300 and 500 ms were analyzed.

Results: For the five tested anesthesia ventilators, the pressure-support ventilation modality functioned correctly. For inspiratory triggering, the three most recent anesthesia machines (Fabius, Dragerwerk AG, Lubeck, Germany; Primus, Dragerwerk AG; and Avance, GE-Datex-Ohemda, Munchen, Germany) had a triggering delay of less than 100 ms, which is considered clinically satisfactory and is comparable to intensive care unit machines. The use of positive end-expiratory pressure modified the quality of delivered pressure support for two anesthesia ventilators (Kion, Siemens AG, Munich, Germany; and Felix, Taema, Antony, France). Three of the five anesthesia ventilators exhibited pressure-support ventilation performance characteristics comparable to those of the intensive care unit machines. Increasing fresh gas flow (1 to 10 l/min) in the internal circuit did not influence the pressure-support ventilation performance of the anesthesia ventilators.     

Vergleichende Untersuchung über die Abscheidungsleistung von Bakterienfiltern unter Beatmungsbedingungen

Two commercially available bacterial filters to be used as part of the mechanical ventilation unit during anaesthesia were tested for hygienic criteria. Manufacturers claim that bacterial breathing filters have a filtration capacity of about 99.995%, so that there would be no need for thermal disinfection of tubing and ventilation circuits after each use. One filter is designed for a single use only, the other can be used up to 24 times after sterilisation. Both filters consist of hydrophobic glass fibres. Methods. During simulated mechanical ventilation for 24 h, an alcoholic suspension of Bacillus subtilis was atomised in front of the filters tested. A gelatine membrane filter was integrated in the ventilation circuit and captured the filtered gas behind the test filter. Results. During simulated mechanical ventilation for 24 h, the filtration capacity of both the disposable and reusable filters (Table 2) did not confirm the manufacturers' short-term technical findings over 8 s (DIN-EN 143). Conclusions. The use of bacterial filters during mechanical ventilation reduces the probability of bacterial contamination, but does not make sterilisation of the tubes and ventilation circuit unnecessary.     

THE JOHANNESBURG A-D CIRCUIT SWITCH: A valve device for converting a co-axial Mapleson D into a co-axial Mapleson A system

A simple valve device is described for a co-axial tubing anaestheticsystem which enables selection of the circuit characteristicsof either a modified Mapleson A system for spontaneous breathingor a modified Mapleson D system for controlled ventilation.Thus, the system allows an economical fresh gas flow to be usedduring either controlled or spontaneous ventilation. The modeof ventilation may be changed during anaesthesia without adjustingthe patient tubing or the attachment of the system to the anaestheticmachine.     

REBREATHING CHARACTERISTICS OF THE BAIN CIRCUIT An Experimental and Theoretical Study

The Bain circuit was studied in a model lung on the assumptionthat, in addition to the ratio of fresh gas flow to total ventilation(FG/E), different time fractions of the respiratory cycle might influencerebreathing. We found that the time fraction for active expiration(FE_t) governed rebreathing for each FG/E value. With FE_t, as an independentvariable, a theoretical formula was derived for rebreathing.Rearranging this formula made it possible to calculate the necessaryincrease in ventilation to keep end-tidal carbon dioxide constantfor each FG/E. Thus, at a fresh gas flow of 70 ml kg^-1 min^-1,I has to be increased 2.6 times. For spontaneously breathing patients inhalation anaestheticsthat do not depress carbon dioxide sensitivity seem to be bettersuited to use in the Bain circuit. The FE_CO2 can then kept constantthrough increased ventilation in spite of the concomitant increasein rebreathing     

Minimal flow and half-closed system ventilation in lung surgery

BACKGROUND: This study aimed at determining the applicability of minimal flow anaesthesia in lung surgery. METHODS: The standards anaesthesiological technique was modified to perform minimal flow half-closed system ventilation. For procedures on left lung orobronchial intubation was performed by a White no. 41 and no. 39 orotracheal tube, respectively in male and in female patients, in order to achieve a perfect tight of bronchial cuff and prevent gas loss from the circuit, because of the greater calibre of the right stem bronchus. The metal double lumen connector was replaced by a plastic tube that is clamped to exclude the lung from ventilation, whenever necessary. Fibrin glue was systematically applied on the bronchial stump or resected lung tissue before restoring ventilation. RESULTS: No significant changes were recorded in heart rate, arterial systolic and diastolic pressure, end-expiratoy CO2 concentration, oxygen saturation, airways maximum and minimum pressure. CONCLUSIONS: Minimal flow half-closed system ventilation can be easily performed also in pulmonary surgery provided that gas loss from the circuit is 50 ml/min by means of specific technical adjustments.     

Fourier Analysis of Effects of Varying Pressure Waveforms in Electrical Lung Analogs

Six voltage waveforms were devised to simulate pressure curves of varying configuration for use in artificial ventilation. These waveforms were subjected to Fourier analysis and terms of the resulting series applied to a simple two-branch resistive-capacitive circuit intended to represent a lung analog using computer simulation. Current (analagous to flow) and charge (analogous to volume) in each branch could be graphically displayed. Differences among the waveforms in such attributes as efficiency, inspiratory work, volume introduced per unit of mean pressure applied, and relative volume distribution between the two branches could be demonstrated. All waveforms were capable of delivering a predetermined volume to the circuit with adjustment of their peak pressure (voltage). It was not possible to designate any of the waveforms as "superior" since advantage in one attribute, such as efficiency, was accompanied by deficiencies in other characteristics such as uneven volume distribution. Despite obvious severe limitations on physiological interpretations of such data, Fourier analysis of respiratory waveforms appears to be a useful teaching, illustrative, and exploratory method.     

Performance characteristics of five new anesthesia ventilators and four intensive care ventilators in pressure-support mode: a comparative bench study

BACKGROUND: During the past few years, many manufacturers have introduced new modes of ventilation in anesthesia ventilators, especially partial-pressure modalities. The current bench test study was designed to compare triggering and pressurization of five new anesthesia ventilators with four intensive care unit ventilators. METHODS: Ventilators were connected to a two-compartment lung model. One compartment was driven by an intensive care unit ventilator to mimic "patient" inspiratory effort, whereas the other was connected to the tested ventilator. The settings of ventilators were positive end-expiratory pressures of 0 and 5 cm H2O, and pressure-support ventilation levels of 10, 15, and 20 cm H2O with normal and high "patient" inspiratory effort. For the anesthesia ventilators, all the measurements were obtained for a low (1 l/min) and a high (10 l/min) fresh gas flow. Triggering delay, triggering workload, and pressurization at 300 and 500 ms were analyzed. RESULTS: For the five tested anesthesia ventilators, the pressure-support ventilation modality functioned correctly. For inspiratory triggering, the three most recent anesthesia machines (Fabius, Dr?gerwerk AG, Lübeck, Germany; Primus, Dr?gerwerk AG; and Avance, GE-Datex-Ohemda, Munchen, Germany) had a triggering delay of less than 100 ms, which is considered clinically satisfactory and is comparable to intensive care unit machines. The use of positive end-expiratory pressure modified the quality of delivered pressure support for two anesthesia ventilators (Kion, Siemens AG, Munich, Germany; and Felix, Taema, Antony, France). Three of the five anesthesia ventilators exhibited pressure-support ventilation performance characteristics comparable to those of the intensive care unit machines. Increasing fresh gas flow (1 to 10 l/min) in the internal circuit did not influence the pressure-support ventilation performance of the anesthesia ventilators. CONCLUSION: Regarding trigger sensitivity and the system's ability to meet inspiratory flow during pressure-supported breaths, the most recent anesthesia ventilators have comparable performances of recent-generation intensive care unit ventilators.