The increasing use of PET for assessing cerebral blood flow, oxygen metabolism, and blood volume in critically ill patients has created a need for reliable technical solutions for delivering (15)O-tracer gases to mechanically ventilated subjects. Our objective was to create such a solution. We designed a ventilator add-on unit that enables complex functional brain studies using labeled oxygen and carbon monoxide gases as tracers. The unit manages both steady-state and bolus inhalations, and the

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... latter can be manually initiated using a remote trigger. All parts conducting breathing gases can be sterilized. The unit can be operated during both spontaneous pressure support breathing and volume-controlled ventilation. It supports the standard safety features and alarms of the ventilator and includes an overflow valve in the bolus reservoir. The count rate curves obtained using the new unit were similar to those from the standard bag-inhalation method. The unit we describe offers an economical and easily operated solution for providing uninterrupted ventilator treatment while performing PET brain studies, and the provided treatment meets intensive care criteria.