Continuous positive airway pressure and body position alter lung clearance of the radiopharmaceutical 99mtechnetium-diethylenetriaminepentaacetic acid (99mTc-DTPA)

Abstract

The purpose of this investigation was to evaluate the pulmonary clearance rate of ^99mtechnetium-diethylenetriaminepentaacetic acid (^99mTc-DTPA) through the use of continuous positive airway pressure (CPAP) in different postures. It was a quasi-experimental study involving 36 healthy individuals with normal spirometry. ^99mTc-DTPA, as aerosol, was nebulized for 3 min with the individual in a sitting position. The pulmonary clearance rate was assessed through pulmonary scintigraphy under spontaneous breathing and under 20 and 10 cmH₂O CPAP in the sitting and supine positions. The clearance rate was expressed as the half-time (T_1/2), that is, the time for the activity to decrease to 50% of the peak value. 20 cmH₂O CPAP produced significant reduction of the T_1/2 of ^99mTc-DTPA in the supine position (P = 0.009) and in the sitting position (P = 0.005). However, 10 cmH₂O CPAP did not alter the T_1/2 of DTPA in both positions. The postural variation from supine to the sitting position with 10 cmH₂O CPAP (P = 0.01) and 20 cmH₂O (P = 0.02) also reduced the T_1/2 of ^99mTc-DTPA. High levels of positive pressure in normal lungs resulted in faster ^99mTc-DTPA clearance. Moreover, the sitting position further increased the clearance rate of the 99mTc radioaerosol imaging in the two pressure levels studied.

Key words: Continuous positive airway pressure, ^99mTc-DTPA, scintigraphy, posture.