Pulmonology Coding Alert

Question: What is the CPT for lung volumes by nitrogen wash out? Tell me more about how it is used and based on what diagnosis.

New Jersey Subscriber

Answer: The code for the nitrogen washout is 94240 (Functional residual capacity or residual volume: helium method, nitrogen open circuit method, or other method).

How: The patient breathes oxygen for 7 minutes, having been turned into the system at functional residual capacity (FRC). All the expired gas is collected from the patient and analyzed for nitrogen (N2). The nurse/medical staff measures the inspired N2, expired N2, and expired patient volume. He also determines the FRC. By substracting the expired reserve volume -- patient blows out all the air from the end expiratory position to residual volume -- the residual volume (RV) is determined. It is the only lung volume of 4 which cannot be measured directly.

Another test similar to the N2 washout is helium dilution method, wherein the patient is turned into a system containing only air and helium (He). The patient breathes for 7 minutes mixing the He with the air in the lungs. Since the He is inert, it doesn't dissolve into the lung tissue. Again the nurse measures the inspired and expired He levels, as well as the volume of the He container from which the patient breathes and the FRC is measured. The RV is determined by substracting the ERV from the FRC.

When to use N2 washout: A physician uses the test when she would like to know the value of the lung volumes and lung capacites in a patient. There are now no LCDs or NCDs concerning the ICD-9-CM codes which can be used to support medical necessity, but common ones used are shortness of breath (786.05), asthma (493.0x-493.9x), chronic bronchitis and emphysema (491.0-496), interstitial lung diseases (515-518.3), sarcoidosis (135), lung cancer (162- 162.9), etc. You can read about PFTs in Chapter 14 of the ACCP Coding for Chest Medicine, and ICD-9-CM codes in Appendix B of the same book.