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Longitudinal assessment of hypercapnic ventilatory drive after tracheotomy in a patient with the Prader-Willi syndrome. D. Gozal, J.E. Torres, A.A. Menendez. ERS Journals Ltd 1996. ABSTRACT: The clinical course and changes in hypercapnic ventilatory drive over time were serially assessed before and after tracheostomy placement in a 14 year old, morbidly obese female patient with Prader-Willi syndrome, severe obstructive sleep apnoea, and obesity-hypoventilation syndrome. A tracheostomy became necessary after supplemental oxygen and continuous posi- tive airway pressure (CPAP) had failed to improve the severity of nocturnal hypoven- tilation. Continued improvement in the slope to rebreathing hyperoxic hypercapnia occurred from 2-10 weeks after tracheotomy in conjunction with night-time bilevel pressure ventilation, and remained unchanged thereafter. In contrast, increases in mean resting minute ventilation at an end-tidal carbon dioxide tension (PET,CO2) of 8 kPa (60 mmHg) were documented even after 30 weeks. This case study illustrates the time-frame of dynamic ventilatory changes occur- ring after removal of upper airway resistance and normalization of nocturnal alveo- lar ventilation.