Throughout numerous references in the film, it is understood to be depicted in (then) present-day 1990, yet on Billy Mahoney's tombstone it reads that he died in 1976. After the cemetery scene, Joe and Randy get picked up by David where Randy states that "Billy died 17 years ago", changing the depicted present date to 1993.
We see Nelson take potassium chloride from the bottle and inject it right into his arm. But the way one does it, is to draw blood from the arm into the syringe top where it mixes with the blood. Then the whole mixture is injected back into the body. A medical student would know this.
When Joe walks home (after the scene when David visits his old schoolyard), along with the guys carrying the big posters, the steadicam operator and the focus puller are reflected in a store window of the house.
When everyone is preparing to put Nelson under for the first time, Nelson squeezes the syringe squirting fluid out of the needle then taps on the syringe to force any bubbles to the top of the syringe. This is the opposite of the way you actually get all of the air out of a syringe.
During the Gross Anatomy dissection, the medical students are told to remove the ascending colon to the transverse colon, then to continue to the sigmoid colon until reaching the appendix. The appendix is located on the right side of the colon, at the beginning of the ascending colon. The above description would put it on the left side, near the end of the sigmoid (the last part of the colon before the rectum).
While a defibrillator is of no use if a patient has truly flatlined, a patient in a "fine v-fib" rhythm can appear to have flatlined but still be revived with the paddles. Therefore, when in doubt, the Advanced Cardiac Life Support guidelines call for administering the shock, though it's not the treatment of choice.
When Rachel goes to inject Nelson in the neck, the syringe close-up reveals a spring contracting inside the casing. This is an often used prop that lets needles retract into the syringe and then come back out when pressure is released.
The goof item below may give away important plot points.
One of the first steps in intubation is to extend the patient's neck and insert the laryngoscope, lifting upward in order to visualize the vocal cords. When Rachel is supposedly trying to intubate Nelson, his neck is flexed and she is barely inserting the laryngoscope.