Piezoresistive transducers were calibrated before measurements. ![]() Before the experiment, a complete automated check was performed on the ventilator before use, followed by a 30 min stabilization period. Room temperature, barometric pressure, and hygrometry were measured on the day of investigation. The experiment was conducted over a 1 day period for each ventilator. Signals were amplified, sent to analogue–digital hardware (Biopac MP150, BIOPAC Systems, Inc., Goleta, CA, USA), and recorded at 400 Hz (AcqKnowledge ®3.8.2, BIOPAC Systems, Inc.). V′ and Pao ports were connected to piezoresistive transducers (BD Gabarith™, Vogt Medical Vertrieb GmbH, Karlsruhe, Germany). Pneumotachograph was linear over the −10 to +10 litre s −1 V′ range. The pneumotachograph was inserted between the Y-piece of the ventilatory circuit and the Pao port. ![]() N., Germany) as a port for airway opening pressure (Pao) measurement. The set-up comprised: (i) brand new ventilators, fully checked by the manufacturer: Aisys™ (GE Datex-Ohmeda, München, Germany), Flow-i™ (Maquet, Solna, Sweden), and Primus™ and Zeus™ (Dräger, Lübeck, Germany) (Table 1) (ii) one-lung configuration test lung (TTL, Michigan Instruments, Grand Rapids, MI, USA) with adjustable compliance ( C, ml cm −1 H 2O) and parabolic resistors ( R, cm H 2O litre −1s −1) (iii) a double-limb ventilatory circuit (Smoothbore breathing system, 1.6 m limb, Intersurgical, Workingham, UK) (iv) a data acquisition system containing a pneumotachograph (Fleish 4 pneumotachograph, Fleish, Lausanne, Switzerland) for airflow ( V′) measurement, and a straight connector (VBM Medizintechnik GmbH, Sulz a. We aimed to investigate the impact of the FGF rate on V T during VCV with the primary hypothesis being that the FGF rate did not influence it. 4–7 Because the effect of FGF on V T has not been widely investigated and algorithm and software versions regularly improve anaesthesia ventilators, we launched a bench study to measure the delivered V T from four anaesthesia ventilators. Automatic compensation for gas compression improves the V T accuracy of ventilators without this type of algorithm. ![]() In order to render the delivered V T equal to the set V T, ventilators use an FGF decoupling system that diverts FGF or modulates the set V T depending on the set FGF. Varying FGF would result in variations of the total delivered V T. The product of FGF and inspiratory time gives the fresh gas volume to be added to the set V T for ventilators that are not FGF decoupled. Fresh gas flow (FGF) is used to deliver oxygen and anaesthetic gases and to remove CO 2. 2, 3 One reason for this is that algorithms differ between different ventilators.Īnaesthesia ventilators have specific features. It has been shown that the actual V T may significantly differ from the set V T in modern ICU ventilators. 2 When a ventilator is switched on, the units of gas volume are set by default on the ATPD, BTPS, or body temperature pressure dry (BTPD) scale. By simply changing the scale, the amount of volume would change by an average of 10%. The situation is further complicated depending on whether the gas volume is expressed as ambient temperature–pressure dry (ATPD) or body temperature–pressure-saturated (BTPS) in the ventilator. Therefore, gas compression and thermal expansion act in opposite ways. Humidifying and heating the inspired gas mixture increases the gas volume. 1 Dry (0% relative humidity) and cold (15☌) gas must be conditioned to enter the lung as water-saturated (47 mm Hg and 100% relative humidity) and warmed (temperature close to 37☌). ![]() In the volume-controlled ventilation (VCV) mode, gas compression and hygrometric conditions should be properly managed by the ventilators. The clinical significance of these findings is uncertain, but anaesthetists should be aware of the potential for imprecision.Īnaesthesia ventilators must adapt to various lung mechanics and maintain the same ventilatory settings as those often selected for patients in intensive care unit (ICU), such as PEEP or tidal volume ( V T). Some of the new ventilators tested were more accurate than others. Set and delivered tidal volumes differed when compliance and resistance were changed, although the effect of fresh gas flow was less. This study investigated the accuracy of delivered tidal volume in four new ventilators under different conditions.
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