The utility of technetium-99m DTPA inhalational scans in artificially ventilated patients

Technetium-99m diethylenetriaminepentaacetic acid ([99mTc]DTPA) radioaerosol scans performed on 21 consecutive artificially ventilated patients were compared to 50 similar scans performed on patients breathing without mechanical assistance. All patients were referred for evaluation of suspected pulmonary embolism. The comparison revealed increased extrathoracic tracheal and mediastinal tracheal deposition but less central bronchial deposition in the artificially ventilated patients. Peripheral penetration in both groups of patients was excellent. Within the artificially ventilated group, peripheral penetration of activity seemed equally good in patients receiving positive-end expiratory pressure ventilation (n = 14) and those ventilated with normal pressures (n = 7). The frequency of regions in which aerosol activity (A) was present in the same zone as a perfusion (P) defect was the same in the controls and artificially ventilated patients (12% against 14%) but the frequency of the reverse type of mismatch (i.e., P greater than A) was significantly higher in the artificially ventilated group (42% against 14%, p less than 0.001). The results suggest that [99mTc]DTPA aerosol scans in artificially ventilated patients are associated with good peripheral penetration of activity and frequently yield valuable clinical information.