Technique for measurement of oropharyngeal clearance in the elderly

In elderly patients, gram negative bacterial colonization often preceeds nosocomial pneumonia. As we propose that a critical factor influencing this change from normal to gram negative predominance is an alteration in oral clearance, we designed this study to validate a technique for measurement of oropharyngeal clearance in a large number of nursing home residents. We modified a protocol of La Force et al who utilized an atomizer to radiolabel oropharyngeal secretions. We determined the output per spray of a DeVILBISS model 152 atomizer and found that 3 sprays of 5 mCi of 99mTc-HSA in 4 ml saline delivered 263 microCi in 0.21 ml. To measure clearance, we designed a portable, collimated ratemeter. It has a lead lined tapered aluminium frame 15 cm high, originating from a 7.5 cm rectangular base which is fitted to the scintillator. On the bench we demonstrated that this collimator, used to confine detection to the face, did not alter sensitivity and linearity of the ratemeter in our specific experimental conditions. When the ratemeter was 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 little effect on the gamma camera. Finally, in thirteen patients we assessed the ratemeter's accuracy in measurement of oropharyngeal clearance by comparing curves obtained simultaneously from the ratemeter and gamma camera. While each curve had its own characteristics, both devices provided remarkably similar data and there were no significant differences (r = 0.967, p < 0.0001). We conclude that oropharyngeal clearance can be conveniently and accurately studied in elderly patients at the bedside with a collimated ratemeter. The high sensitivity provides a measure of clearance with low levels of radioactivity exposure, allowing repeated studies over time.