[The effect of fresh-gas decoupling on respiratory volume. Draegar Sulla 808V anesthesia ventilator]

In order to perform accurate low-flow anaesthesia ventilation, it is desirable to avoid the influence of fresh gas flow (FGF) and inspiration duration (ID) on the resulting minute volume (MV). The Sulla 808V anaesthesia ventilator (Draeger, Luebeck, Germany) is originally not equipped with a fresh-gas decoupling (FGD) device. Therefore, changes of FGF and ID settings applied during controlled ventilation may lead to alterations of the resulting MV. Recently, a low-cost FGD device (Carbamed, Bern-Liebefeld, Switzerland) has been developed, which can be inserted into the circle system. We investigated the effect of this device on MV in the Sulla 808V anaesthesia apparatus.

The performance of a Sulla 808V anaesthesia ventilator was tested with and without a FGD device. During ventilation of a test lung, stepwise changes of tidal volume (400-1000 ml), FGF (0.5-10 l/min), and ID (0.25-0.5) settings were consecutively applied, and the resulting MV was recorded. Correlation and mean prediction error between ventilation parameter settings and MV were calculated.

In the presence of a FGD device, the administered MV was not affected by the magnitude of FGF and ID. A mean prediction error (bias) of -3.6 l/min of the resulting MV was observed. Without FGD the bias was only-1.8 l/min, while FGF and ID revealed a pronounced influence on MV. These effects were statistically significant when using FGF exceeding 4 l/min.

The tested FGD device can easily be integrated into the circle system of conventional anaesthesia machines such as the Draeger Sulla 808V, and is available at a reasonable cost. It allows constant ventilation parameters to be maintained that remain unaffected by wide FGF and ID variations. With this FGD the performance of the ventilator can be improved considerably, and low-flow anaesthesia can be used more extensively.