TECHNIQUE FOR MEASUREMENT OF OROPHARYNGEAL CLEARANCE IN THE ELDERLY

In elderly patients, gram negative bacterial colonization often precee ds nosocomial pneumonia. As we propose that a critical factor influenc ing this change from normal to gram negative predominance is an altera tion in oral clearance, we designed this study to validate a technique for measurement of oropharyngeal clearance in a large number of nursi ng home residents. We modified a protocol of La Force et al who utiliz ed an atomizer to radiolabel oropharyngeal secretions. We determined t he output per spray of a DeVILBISS model 152 atomizer and found that 3 sprays of 5 mCi of Tc-99m-HSA in 4 ml saline delivered 263 mu Ci in 0 .21 ml. To measure clearance, we designed a portable, collimated ratem eter. It has a lead lined tapered aluminium frame 15 cm high, originat ing from a 7.5 cm rectangular base which is fitted to the scintillator . On the bench we demonstrated that this collimator, used to confine d etection to the face, did not alter sensitivity and linearity of the r atemeter in our specific experimental conditions. When the ratemeter w as collimated and its window off, its sensitivity was 5 times greater than the gamma camera with no loss of linearity. However, distance had a significant effect on the ratemeter's sensitivity whereas it had li ttle effect on the gamma camera. Finally, in thirteen patients we asse ssed the ratemeter's accuracy in measurement of oropharyngeal clearanc e by comparing curves obtained simultaneously from the ratemeter and g amma camera. While each curve had its own characteristics, both device s provided remarkably similar data and there were no significant diffe rences (r = 0.967, p < 0.0001). We conclude that oropharyngeal clearan ce can be conveniently and accurately studied in elderly patients at t he bedside with a collimated ratemeter. The high sensitivity provides a measure of clearance with low levels of radioactivity exposure, allo wing repeated studies over time.