Online SLICE: a tool for continuous monitoring of respiratory mechanics

Introduction

The clinical use of respiratory mechanics is limited due to complicated measurement methods and restricted bedside availability of the achievable information. For observational and interventional studies in the ICUs of the university clinics of Freiburg we developed a laptop-based tool, which provides online information about the mechanical state of the patient's respiratory system on a breath by breath basis.

Methods

We developed a program in LabView (National Instruments, Austin, TX, USA) on a laptop that is able to read the internal data of a ventilator (Evita 4; Dräger Medical, Lübeck, Germany) in real time. A serial connection is established using the MEDIBUS protocol. Pressure, flow and volume provided by the ventilator are read into the laptop at 125 Hz, analyzed and visualized. The signal analysis provides dynamic compliance and resistance in dependence of alveolar pressure [1, 2]. Statistics and trends are displayed on request of the user.

Active manipulations of the settings of the ventilator are possible and were used for animal experiments. With appropriate maneuvers (by controlling the volume/time or pressure/time curve) it is possible to derive mechanical properties of the respiratory system separated according to inspiration and expiration.

Results

In an animal (n = 6) and an observational patient (n = 30) study at University Hospital Freiburg the system was evaluated. Figure 1 shows a screen plot of the online monitor during an experiment performed on healthy anesthetized sheep. Trends are visualized by overlaying older data in different colors with actual data. The physician gets immediate feedback on whether changes of ventilator settings show the expected effects.

Figure 1

abstract P12

Conclusion

Online monitoring of respiratory mechanics provides additional information about changes in the state of a patient's respiratory system. Thus the physician is enabled to evaluate the therapeutic strategy online and to base the settings of the ventilator on current trends observed in the data.