AUTOMATIC WEANING FROM MECHANICAL VENTILATION USING AN ADAPTIVE LUNG VENTILATION CONTROLLER

Study objective: To evaluate a new method of closed-loop mechanical ve ntilation using an adaptive lung ventilation (ALV) controller in patie nts with different pathologic causes of respiratory failure at a time when they first met standard weaning criteria. Study design: Prospecti ve, open, selected case study. Setting: The 10-bed, multidisciplinary respiratory intensive care unit at Groote Schuur hospital, which is a teaching unit of the University of Cape Town. Patients: Twenty-seven p atients (9 patients in each of 3 groups: normal lungs, parenchymal lun g disease, and COPD) who required prolonged mechanical ventilation and who met standard weaning criteria were included. Our institutional co mmittee for ethical research approved the study and informed consent w as obtained. Interventions: The patients were mechanically ventilated and had daily measurements of vital capacity, respiratory rate, and ar terial blood gas analysis until they met standard weaning criteria. On the day that each patient met the weaning criteria, a closed loop con trol algorithm providing ALV was implemented on a modified ventilator (Hamilton AMADEUS) with a PC-based lung function analyzer. After measu ring gross alveolar ventilation, patients were placed in ALV and venti latory and hemodynamic parameters were measured at baseline, 5 min, 30 min, and 2 h. Pertinent parameters measured included airway pressures , pressure support levels, respiratory rates, rapid shallow breathing indices, airway resistance indices, and patient respiratory drive and work indices. Measurements and results:In 22 patients, ALV reduced pre ssure support to 5 cm H2O and an intermittent mandatory ventilation ra te of 4 breaths/min within 30 min, and all but 1 of these patients wer e successfully extubated within 24 h. In four patients, pressure suppo rt was maintained by ALV at a mean level of 14.6 cm H2O +/- for 2 h an d these patients were recorded as having failed to wean. There was a m easurable difference in an index of airway resistance relative to musc ular activity between the successfully weaned and failed wean patients with COPD during the attempted wean by the ALV controller. Conclusion s: ALV will provide a safe, efficient wean and will respond immediatel y to inadequate ventilation in patients when standard weaning criteria are met.