Although more practical than the stomach for measurement
of tissue PCO2, some potential disadvantages need
to be discussed. First, since tactile stimuli can increase
sublingual blood flow and production of saliva, the
presence of the device itself under the tongue can increase
sublingual blood flow. Most acutely ill patients are not fed orally so that the direct interference of food on sublingual
measurement is not a major problem, as it is for
gastric tonometry.