The 2nd character defines the particular body system or general physiological system or anatomical region involved.
Measurement and monitoring section codes represent procedures for determining the level of a physiological or physical function. Measurement and monitoring procedure codes have a first character value of “4”. The second character value for body system is either physiological systems or physiological devices. There are two root operations in the measurement and monitoring section, as defined below:
The 4th character specifies the body system measured or monitored. The fifth character specifies approaches as defined in the medical and surgical section. Instead of specifying device, the sixth character specifies the physiological or physical function being measured or monitored. Examples of physiological or physical function values are conductivity, metabolism, pulse, temperature, and volume. If a device used to perform the measurement or monitoring is inserted and left in, then insertion of the device is coded as a separate medical and surgical section procedure. The seventh character qualifier contains specific values as needed to further specify the body part (e.g., central, portal, pulmonary) or a variation of the procedure performed (e.g., ambulatory, stress).
Examples of typical procedures coded in this section are EKG, EEG, and cardiac catheterization. An EKG is the measurement of cardiac electrical activity, while an EEG is the measurement of electrical activity of the central nervous system. A cardiac catheterization performed to measure the pressure in the heart is coded as the measurement of cardiac pressure by percutaneous approach.