ABC News’ Jim Avila and Bryan Lavietes report:

A nationally known anesthesiologist testified today that singer Michael Jackson died because he stopped breathing and his doctor was not equipped to revive him.

“The single most important thing in anesthesia is moving air and oxygen into the lungs” said Dr. Stephen Shafer of Columbia University in New York.

Shafer was the last witness for the prosecution in the Conrad Murray involuntary manslaughter case in Los Angeles Superior Court.

Conrad Murray is seen in this Sept. 29, 2011 file photo. (Al Seib/AP Photo)

Shafer testified without charging his normal fee because he said the public needed to know that propofol is only deadly if misused in an improper setting.

“Everyday in the operating room, I get the question am I going to get the drug that killed Michael Jackson? This is not a fear they need to have,” said Shafer. ”When these drugs are given by people who know what they’re doing, they have nothing to fear.”

The juror was shown a video entitled ”An Overview of Safe Administration of Propofol,” which demonstrated the elaborate equipment and personnel used when the anesthetic propofol is administered for surgery.

The demonstration showed how a propofol injection pump is set up and used safely in an operating room setting.

Shafer highlighted how a proper anesthesiologist prepares for propofol use: by having many emergency medical devices on hand, an extensive informed consent process, and copious medical note-taking.

The video featured examples of what happens when things go wrong in surgery – and how those emergencies are dealt with.

If a patient stops breathing, the anesthesiologist tilts the head to open the airway.

If the cessation of breathing is prolonged, then a mask is put on the patient’s face and air is forced into the lungs.

If the patient goes into cardiac arrest, Shafer said the first thing that an anesthesiologist does is “call for help!” “You’re gonna need it,” Dr. Shafer explained, “and you’re gonna need it now.”

Conrad Murray has been described by prosecutors as criminally, grossly negligent because he administered the dangerous anesthetic without proper equipment, back-up personnel and did not immediately call 911.

Instead Murray launched into what prosecutors say was inappropriate and ineffective CPR.

Shafer testified that the amount of propofol Murray ordered to treat his one and only patient at the patient’s home was “an extraordinary amount” – 15.5 liters or 4.09 gallons.

If convicted, Murray could face four years in prison for involuntary manslaughter in the singer’s death.