The dynostatic algorithm in adult and paediatric respiratory monitoring

Abstract

Introduction: Positive pressure ventilation carries a risk of aggravating systemic and lung disease. Monitoring of ventilatory pressure and volume is important to minimize this risk. Conventionally, the pressure of the respiratory system is measured outside the patient. Tra-cheal pressure measurement is one step closer the alveoli and alveolar pressure can be cal-culated by an appropriate algorithm. Volume and pressure may possibly be reduced by using low-density gas mixtures of Helium and Oxygen.Methods: A small fibre optic pressure transducer was evaluated for tracheal pressure mea-surement in paediatric patients and a polyethylene catheter for pressure measurement in adult patients. The dynostatic algorithm (DSA) is based on the equation of motion and the assumption of equal inspiratory and expiratory resistance and compliance at isovolume. The DSA utilises flow and tracheal pressure signals to calculate an alveolar P/V- and an alveolar P/t-curve continuously during ongoing ventilation. The DSA was evaluated clini-cally and in lung models by comparison of calculated and measured alveolar pressure. A Pitot type venturimeter was calibrated for use with low-density gas mixtures; the calibra-tion may be incorporated in the DSA for a preliminary clinical study using He/O2. Results: The fibre optic pressure transducer and polyethylene catheter functioned satisfac-torily in clinical pressure measurement in intubated positive pressure ventilated children and adults, respectively. The tracheal pressure recording provided an improved possibility of detecting peak inspiratory pressure and intrinsic PEEP compared to proximal measure-ment. The DSA reliably calculated alveolar pressure in lung models and provided a number of interesting clinical observations concerning inflection points and overdistension.Conclusions: The Dynostatic Algorithm offers the clinician the option of improved respiratory monitoring in adult and paediatric intensive care patients.