[A simple method for determination of the functional residual capacity during artificial ventilation (author's...

A simple method for determination of the functional residual capacity (FRC) during artificial ventilation by inert gas dilution using a rebreathing technique is described. The measurements can be made during various techniques of mechanical ventilation (eg. PEEP, IMV etc.). Myorelaxation is not required. This technique was used to assess the volume of a lung model (actual volume: 3670 ml) with the result of repeated measures being 3686 +/- 29 ml. Duplicate measurements in artificially ventilated pigs showed a coefficient of variation of +/- 3.2%. In artificially ventilated patients FRC was determined both with this technique and with a reference method, giving a difference of 111 +/- 55 ml (p less than 0.001). The errors in measurements of FRC by this method are small, and as the measurement requires a minimum of time and the apparatus is simple, the method is accurate and yet simple enough to be used on a routine basis in the intensive care unit. Even high risk patients are not disturbed by this technique. The method has the advantage that it can easily be learned by nurses and paramedical personal.