The Chief Medical Officer, sometimes called the Chief Surgeon, is the ship's senior medical officer. As such, Starfleet Command will usually assign a CMO who possesses medical expertise in the predominant lifeform of the ship in question, although this is not always possible.
The CMO oversees the operation of the entire medical department, and his staff may range from one or two assistants on smaller starships to as many as a dozen or more doctors and nurses on larger classes. In addition, specialized medical personnel may be temporarily or permanently assigned when the ship's size or mission dictates. The medical staff is usually commensurate with the ship's overall crew complement (usually from 2%-3% of the ship's complement, with a minimum of 4-5 personnel).
On larger ships, the CMO is generally a qualified surgeon and possesses basic training in emergency first aid for all crew members assigned, regardless of species. Most medical departments can, as a minimum, render emergency aid to a member of any known race in distress and keep that individual alive until a more intensive medical care can be provided, such as a Starbase or other facility. The Chief Medical Officer always has an office within the medical section, although on smaller classes the office might be shared with other individuals or serve added functions.
The primary responsibilities of the medical officer are prevention, diagnosis, and treatment of medical problems experienced by starship or station personnel. Prevention of medical problems is accomplished through the use of routine physicals. All personnel are required to submit to physical examinations as required by Starfleet Regulations or the medical officer. Diagnosis of medical problems is the accomplshed through the use of advanced medical systems. These systems include medical tricorders, biobeds, sensor clusters, and extensive medical references. Treatment of medical problems is accomplished through the use of medical resources, which include medical equipment (e.g. hyposprays, neural stimulators, etc.) as well as holistic agents (e.g. medicines, physical therapy, etc.).