Pulmonology Coding Alert

Answer: The code for the nitrogen washout is 94727 (Gas dilution or washout for determination of lung volumes and, when performed, distribution of ventilation and closing volumes). The procedure is used for determination of lung volumes and also to find out functional residual capacity (FRC).

 

Note: Do not report 94727 in conjunction with 94726 (Plethysmography for determination of lung volumes and, when performed, airway resistance).

 

How: In nitrogen washout method, the patient inhales a known volume and concentration of nitrogen followed by 100% oxygen inhalation for 7 minutes, having been turned into the system at functional residual capacity (FRC). This causes the nitrogen present in the lungs to wash out. The medical staff collects all the expired gas from the patient and analyzes it for nitrogen (N2). The inspired and expired N2 and the expired patient volume are measured along with the FRC. The difference between the nitrogen concentrations in the initial exhaled air and final exhaled air gives the lung volume. 

 

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. 

 

Medical necessity: Pulmonologists usually recommend this method to determine lung volumes that cannot be determined from simple spirometry. A physician uses the test when she would like to know the value of the lung volumes and lung capacities in a patient. Commonly used diagnoses for justifying the N2 washout 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 (162.0-162.9), etc.