Cal. HSC § 1799.110

(a) In any action for damages involving a claim of negligence against a physician and surgeon arising out of emergency medical services provided in a general acute care hospital emergency department, the trier of fact shall consider, together with all other relevant matters, the circumstances constituting the emergency, as defined herein, and the degree of care and skill ordinarily exercised by reputable members of the physician and surgeon’s profession in the same or similar locality, in like cases, and under similar emergency circumstances.

(b) For the purposes of this section, “emergency medical services” and “emergency medical care” means those medical services required for the immediate diagnosis and treatment of medical conditions which, if not immediately diagnosed and treated, could lead to serious physical or mental disability or death.

(c) In any action for damages involving a claim of negligence against a physician and surgeon providing emergency medical coverage for a general acute care hospital emergency department, the court shall admit expert medical testimony only from physicians and surgeons who have had substantial professional experience within the last five years while assigned to provide emergency medical coverage in a general acute care hospital emergency department. For purposes of this section, “substantial professional experience” shall be determined by the custom and practice of the manner in which emergency medical coverage is provided in general acute care hospital emergency departments in the same or similar localities where the alleged negligence occured.