Articles: ventilators.
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Reports of two hypoxic episodes which occurred during the use of the East Radcliffe PNA 1 ventilator in the 'complete rebreathing' mode led to the study of the efficiency of the emergency air entrainment system. The inability of this system to maintain adequate oxygen concentrations during interruption of the fresh gas supply results in the development of a hypoxic gas mixture despite patency of the entrainment valve. The reasons for this, and their clinical implications during intermittent positive pressure ventilation in the 'complete rebreathing' mode, are discussed.
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Case Reports
[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. ⋯ 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.
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A new, simple, versatile co-axial breathing system combining the features of Mapleson A, D and E type systems is described. The change from an A system to a D/E system is effected by a single switch and without reversal of the gas flow. Fresh gas flows in the order of 70 ml/kg/min are required for both spontaneous ventilation in the Mapleson A mode and controlled ventilation in the Mapleson D mode. The co-axial configuration offers the advantages of a single, lightweight breathing system with easy scavenging of anaesthetic gases, while the ability to switch between the A and D or E configurations offers the economic advantages of low fresh gas flows and the need for a single anaesthetic breathing system for all situations.
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A computerized system that uses feedback of end-tidal CO2 fraction (FETCO2) to adjust minute volume of a ventilator has been developed and tested. The effectiveness and robustness of the controller were evaluated in five anesthetized dogs. The controller responded to step-changes in the set-point for FETCO2 by adjusting minute volume so that the FETCO2 settled to the new set-point in less than 60 sec with less than 20% overshoot. ⋯ A disturbance to the controlled system was produced by releasing an occlusion of a branch of the pulmonary artery. The controller always responded to this disturbance in a stable manner, returning the FETCO2 to its desired value within 30 sec. Accurate control of arterial partial pressure of CO2(PaCO2) will require modifications enabling the system to determine the relationship between FETCO2 and PaCO2.
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Acta Anaesthesiol Scand · Dec 1984
Distribution of expiratory gas and rebreathing in a T-piece modification combined with a PEEP valve.
T-piece modifications with PEEP valves are often used in weaning from mechanical ventilation or for intubated patients not requiring ventilatory support. Distribution of expiratory gas and the extent of rebreathing in a T-piece modified with an inspiratory reservoir (ICR) and with a PEEP valve were studied in a model with various fresh gas flows (FGF), tidal volumes and frequencies at three valve settings: 0 cmH2O (ZEEP) and PEEP of 5 and 10 cmH2O (0.490-0.981 kPa). Two types of distribution of expiratory gas were delineated: type one with expiratory gas in the inspiratory limb (IL) and a high ratio of the maximum CO2 content and corresponding end-expiratory CO2 concentration in the expiratory limb (EL) (FmaxCO2/FECO2) and a type 2 with no detectable alveolar gas in the IL and a low ratio of FmaxCO2/FECO2. ⋯ The ratio of FGF to minute ventilation just preventing rebreathing during spontaneous ventilation is approximately 1, in contrast to 3 in other modifications. These advantages minimize the risk of rebreathing, even when the minute ventilation rises to that of the fresh gas flow. The T-system with a compliant inspiratory reservoir and a PEEP valve can, in most clinical weaning situations, satisfy the inspiratory peak flow of different respiratory patterns with a standard FGF of 15 l X min-1.