CPT® Code 94727

Gas dilution or washout for determination of lung volumes and, when performed, distribution of ventilation and closing volumes

The CPT® Code 94727 refers to a specialized pulmonary function test known as gas dilution or washout, which is utilized to determine lung volumes and, when applicable, assess the distribution of ventilation and closing volumes within the lungs. This procedure employs a spirometry device and involves the use of helium as a test gas. In the gas dilution method, a mixture of air enriched with 25-30 percent oxygen and approximately 10 percent helium is inhaled by the patient. The purpose of this test is to measure how well helium mixes with the gases in the lungs, which allows for the calculation of lung volume based on the known volume of inhaled gases and the fraction of helium present. To ensure accurate results, clips are placed on the patient's nose to prevent the entry of ambient air during the test. The patient breathes through a mouthpiece, initially receiving room air before transitioning to the test gas. Regular tidal breaths are taken, and the concentration of helium is monitored at 15-second intervals. The test concludes when the change in helium concentration is less than 0.02 percent for a duration of 30 seconds, at which point the patient is switched back to room air. The results, including helium concentration and tidal volume, are graphically displayed for analysis. In addition to gas dilution, the washout technique measures the amount of expired nitrogen (N2) over a specified time frame, which is critical for calculating the maximum lung capacity. The test begins with the establishment of an initial N2 alveolar concentration, followed by the patient breathing room air through the mouthpiece. The nitrogen washout is conducted by having the patient inhale 100 percent oxygen (O2), while the expired N2 concentration is continuously monitored. The washout is deemed complete when the N2 concentration falls below 1.5 percent for three consecutive breaths. Similar to the gas dilution method, the results of the nitrogen washout are graphically represented, and the physician is responsible for reviewing the findings and generating a written report. Throughout the procedure, the physician may also evaluate the distribution of gases within the lungs and assess closing volumes, providing a comprehensive understanding of the patient's pulmonary function.