Lung scanning, or ventilation-perfusion (V/Q) scanning, is a nuclear study performed to assist in diagnosing acute and chronic pulmonary conditions. These diseases cause decreased pulmonary blood flow and hamper air flow and gas exchange, resulting in a ventilation-perfusion imbalance. A radiopharmaceutical is injected IV or inhaled; scanning is performed to obtain views of the lungs and evaluate blood flow or perfusion (perfusion scan) and patency of the pulmonary airways or ventilation (ventilation scan). One or both scans are performed to obtain clinical information that assists in differentiating among the many possible pathological conditions revealed by the procedure. The scan results are correlated with other diagnostic studies such as pulmonary function, chest x-ray, pulmonary angiography, and arterial blood gases.

Lung perfusion scanning is performed primarily to diagnose pulmonary embolism, especially when the chest x-ray is normal. Because blood flow is restricted in the area of an embolus, perfusion defects or areas of decrease or absence of activity are visualized by scanning. The radionuclide 99mTc as technetium Tc 99m macroaggregated albumin (MAA) or technetium Tc 99m human albumin microspheres (HAM) is injected IV and distributed throughout the pulmonary vasculature, depending on the gravitational effects of perfusion. Normally, gravity causes an uneven distribution of blood flow with a three to five times greater flow volume in the lower than in the upper regions of the lungs. Many diseases decrease the pulmonary blood flow, and the multiple views of areas of visible activity of the radionuclide assist in the differentiation of these diseases based on these gravitational effects.³⁴

Lung ventilation scanning is performed with perfusion scans to provide specific information about perfusion abnormalities by differentiating between pulmonary embolism and other pulmonary diseases. Ventilation also is not uniform in the lungs because of gravity, causing a one to two times greater intrapleural pressure in the apex than in the base of the lungs. Abnormalities are visualized by imaging areas of decreased activity in the lungs after inhalation of a radionuclide as xenon Xe 133 gas or krypton Kr 81m gas. The compound is distributed through the airways with the inspired air. Defects in regional ventilation are identified as areas not norm-ally well ventilated with regular breathing, based on the gravitational effect on ventilation. The areas of decreased activity indicate that the total lung volume is not ventilated. Diagnosis of COPD and pulmonary embolism is confirmed by perfusion and ventilation studies that reveal a match or mismatch between perfusion and ventilation. COPD causes a match of perfusion and ventilation (abnormal ventilation in an area of a perfusion defect), and pulmonary embolism causes a mismatch of perfusion and ventilation (normal ventilation in an area of diminished perfusion).³⁵

• Normal perfusion and ventilation of lungs and V/Q ratio; no pulmonary embolism, COPD, tumors, pneumonia, atelectasis, or pulmonary hypertension

• Inability of client to remain still during the procedure or to breathe through a mask for the ventilation study
• Improper positioning during the inhalation of the radiopharmaceutical, because gravity affects the distribution of the material in the lungs
• Other nuclear scans performed on the same day, which would affect the distribution of the radionuclide
• Conditions that can simulate a perfusion defect similar to pulmonary embolism, such as emphysema, effusion, or infection, because these conditions affect perfusion or ventilation³⁶

[Show Section Outline]

Indications

Perfusion Study

• Diagnosing pulmonary embolism when the chest x-ray is normal (Pulmonary embolism is revealed by areas of decreased activity.)
• Differentiating between pulmonary embolism and other pulmonary disease such as pneumonia, pulmonary effusion, atelectasis, asthma, bronchitis, tumors, and emphysema revealed by a perfusion defect matching an abnormal area on the chest x-ray
• Evaluating perfusion changes associated with CHF and pulmonary hypertension
• Detecting lung displacement by fluid or chest mass
• Detecting malignant tumor of the lung revealed by perfusion defects resulting from bronchial obstruction
• Evaluating pulmonary function preoperatively in clients with pulmonary disease

Ventilation Study

• Diagnosing COPD revealed by areas of abnormal ventilation, with washout images and decreased activity representing defects in regional ventilation in single-breath images
• Differentiating between COPD (abnormal ventilation in an area of perfusion defect) and pulmonary embolism (normal ventilation in an area of decreased perfusion)
• Evaluating pneumonectomy when performed with a perfusion study to determine the potential for pulmonary insufficiency
• Determining smoke inhalation injury that could lead to edema, infection, or atelectasis

Contraindications

• Pregnancy, unless the benefits of performing the procedure greatly outweigh the risks to the fetus

[Section Outline]

• Indications
  • Perfusion Study
  • Ventilation Study
• Contraindications

Nursing Care Before the Procedure

Client teaching and physical preparation are the same as for any nuclear scan study (see section under "Brain Scanning").

• Inform the client of the scanning schedule and explain that the study takes 30 minutes.
• Inform the client that a breathing mask is used to administer the radiopharmaceutical for the ventilation study, and allay anxiety associated with this procedure.
• History should include information about the pulmonary status, recent x-ray results, and the determination of whether the client can lie flat or needs to elevate the head on pillows to facilitate breathing during the procedure.

Perfusion Study. The client is placed on the examining table in a supine position. The syringe containing the radiopharmaceutical is shaken to resuspend the particles, and the material is administered IV. The client is requested to remain still during the scanning, and imaging is performed immediately to obtain anterior, posterior, both lateral, and both oblique views. Multiple views are the best confirmation of perfusion defects within the lung vasculature.

Ventilation Study. The client is placed in an upright position with the camera positioned posteriorly. The client is requested to remain still during the scanning. The mask is positioned over the nose and the gas containing the radiopharmaceutical is injected into the intake port of the mask as the client takes a deep inspiration. Single-breath images are obtained. After this imaging, the client rebreathes the gas containing the radiopharmaceutical in a closed spirometry system for 4 minutes, allowing the gas to enter the abnormal lung areas. Images are obtained during and at the end of this procedure. Valves are then readjusted to allow the client to breathe room air that washes out the gas. Washout images are obtained for 6 minutes at 30- to 60-second intervals. After these images, additional scanning can be performed in the oblique positions to allow location of abnormal anteroposterior areas.³⁷ Ventilation scanning can be performed using krypton Kr 81m gas on clients unable to perform breathing techniques needed for the study. These images can be obtained regardless of the timing of perfusion studies; otherwise, ventilation studies are performed before perfusion studies.

Nursing Care After the Procedure

Care and assessment after the procedure are the same as for any nuclear scan study (see section under "Brain Scanning").

• Ensure ease of breathing by elevating the client's head on pillows, if needed.