Radioaerosol Studies in Ventilator Assisted Patients

QA Programs for Uptake Probes and Well Counters

Radioaerosol inhalation lung scanning in ventilator assisted patients is not only feasible but a valuable tool that can lead to important changes in patient management. However, in these patients, radioaerosols have been less readily accepted. It generally has been felt that the central bronchial deposition and poor peripheral penetration tendencies of radioaerosols are likely to be accentuated in this patient group. With technical improvements in current delivery systems, this appears to be less of a problem and has resulted in substantially increased clinical utilization in this patient population.

Lung scans on critically-ill ICU ventilator patients are rarely performed at the bedside and the patient must be transported to the nuclear medicine department where the procedure can be carried out interfacing the patient’s ventilator to a radioaerosol delivery system. This is where the respiratory therapist comes actively into the picture. Nuclear medicine technologists are justifiably reluctant to disrupt the ventilator circuit to interface the radioaerosol delivery system and many respiratory therapists often find themselves in the nuclear medicine department with a critically-ill vent patient and little or no training about nuclear medicine or lung scanning.

Respiratory therapists who find themselves taking vent patients to nuclear medicine would be well served to make an appointment with one of the nuclear medicine technologists at a non-busy time and take the opportunity to see and examine that department’s choice of radioaerosol delivery system. This is an excellent preemptive opportunity for some meaningful interdisciplinary departmental in-service. Perhaps a practice run with a ventilator, a test lung and some saline in the nebulizer could be conducted as a learning experience so the procedure would not be foreign the next time it was conducted on a real patient. This would be a good time to discover any particular adapter or connectors that might be needed to facilitate the setup. Obtain the package literature for the specific radioaerosol delivery device in use, and read it carefully.

All of these devices have their own specialized lead shields that they are placed into during the procedure to minimize radiation exposure to the adjacent personnel. The shield must be placed close to the patient so it may be a good idea to obtain one and practice methods of arranging the shield, the patient and the ventilator to render an effective scan with a minimum of commotion. As a general rule of thumb, when interfacing these devices to the ventilator, the following scheme may apply: interface the ventilator, radioaerosol delivery system, shield and patient together and check for proper ventilation before introducing the radionuclide into the nebulizer. The patient port of the radioaerosol delivery system should be connected to the patient’s ETT or trach tube, using as short a length of tubing as possible to minimize rebreathed volume. The ‘Y’ piece of the ventilator tubing may be connected to the outlet of the HEPA or bacterial filter supplied with the radioaerosol delivery system. In this manner, any radioactive aerosol generated in the delivery system will be insufflated into the patient during the ventilator’s inspiratory phase. During exhalation, exhaled patient gas will pass through the device and its HEPA or bacterial filter, through the ventilator ‘Y’ and into the expiratory tubing on the ventilator. Any radioaerosol in the exhaled gas stream will be trapped in the HEPA or bacterial filter on the radioaerosol delivery device. The ventilator will, therefore, not be contaminated by radioactive exhaled aerosol and there should be no need to replace the circuit after the procedure. If needed, the respiratory therapist can make any ventilator adjustments based on the mechanical dead space volume.

Nuclear medicine technologists and respiratory therapists should develop a partnership to insure the safety of the patient is maintained while they are in the nuclear medicine department and high quality technical studies are performed.

1. McPeak, Michael; Nuclear medicine and the Respiratory therapist; Focus Journal Sept/Oct 2007, pp. 58- 59.