Trapping Efficiency of Venti-Scan Filters

Lucien Wielopolski, Ph.D..

Introduction The purpose of this evaluation was to test and compare the trapping efficiencies of the filters used in the Venti-Scan II and Venti-Scan III Radioaerosol Disposables. The Venti-Scan III uses a pleated HEPA filter and the Venti-Scan II uses a traditional Flat Filter media. The primary filter is the filter that is normally supplied with the Venti-Scan disposable. The secondary test filter was always a HEPA filter placed onto the exhaust port of the Primary Filter. All secondary filters were from the same manufacturing lot to eliminate variation of the filter media. Method Venti-Scan II disposable assemblies were used for testing the filter. The primary filter was mounted in the standard position for each test. The tests were performed using either the Venti-Scan II or III filter as the primary filter. A blower was connected to the hose where the mouthpiece normally is located to simulate a patient. A constant rate was set on the blower for all tests. The Oxygen flow rate of 5 liters/min. was maintained through the nebulizer. The same nebulizer, filled with approximately 6cc of 6mCi of Tc-99m labeled DTPA, was used for all measurements thus eliminating any potential variability in the nebulizer. The filters, both primary and secondary, were exposed for 5 min. to the nebulized Tc-99m DTPA. For counting purposes the whole filter was inserted into a dose calibrator. The Background was 0.03µCi. Results are listed in µCi read in the dose calibrator. Test Set A used the Venti-Scan II filter/trap as the primary filter and Test Set B used the Venti-Scan III filter/trap as the Primary filter.

Results Set A (Venti-Scan II) Primary Filter Activity in µCi Secondary Filter Activity in µCi Ratio % of Activity Trapped in the Primary Filter % of Activity Trapped in the Secondary Filter 237 .02 1185` 99.916% .084% 257 0.13 1977 99.947% .051% 261 0.20 1305 99.923% .077% 321 0.15 2140 99.953% .047% 251 0.12 2092 99.952% .048% Mean: 1740 S.D.: 458 Ratio= Primary filter activity / Secondary filter activity % of Activity Trapped in Primary Filter = Primary filter activity - Secondary filter activity _____________________________________ Primary activity Set B (Venti-Scan III) Primary Filter Activity in µCi Secondary Filter Activity in µCi Ratio % of Activity in Primary Filter % of Activity Trapped in Secondary Filter 260 0.06 4333 99.977% .023% 248 0.05 4958 99.98% .0209% - - - - - 245 0.06 4083 99.976% .024% 238 0.08 2975 99.966% 0.34% Mean: 4087 S.D.: 827 Conclusion These are relative evaluations of the filters. It appears that the Venti-Scan III filter/trap is slightly better than the Venti-Scan II filter/trap. Both filters had greater than 99.9% trappings. It should be noted that the secondary filter readings are close to the background readings which fluctuates and the primary filter retensions are all similar. Thus it can be concluded that both filters have similar trapping efficiencies with the Venti-Scan III filter possibly slightly better. Note the small sample size.