 98 ready for weaning patients were included and divided into success n71 and failure n27 groups based upon their weaning outcome. Before weaning, the RSBI values were determined under the patients disconnecting from the ventilator RA-no ventilator and still connecting to the ventilator with 4 different settings fraction of inspired oxygen FiO2 21 or 40 combined with continuous positive airway pressure CPAP 0 or 5 cm H2O. The patients were extubated after completing the weaning trials. Successful weaning was defined as patients free from the ventilator for over 48 hours. 