When she was a medical student in the former Soviet Union, Julia had seen lives ruined by rampant alcoholism and other lifestyle-related sicknesses. But it surprised her to see so much self-destructive behavior in a prosperous country like the United States, where popular culture celebrates the slender and the fit. Julia would care for 25 patients during the days and nights that a reporter was present to observe her training. Half of them had significantly contributed to their sickness through smoking, alcohol abuse, extreme obesity, or, in one case, failing for years to get treatment for diabetes.

Doctors at morning rounds said they hoped to break the obese patient’s fever, ease his breathing, and get his heart rate down, but his weight complicated all three goals. Julia and M.J. couldn’t get an electric chilling blanket underneath him, where it would be most effective, so they spread it over him. Then, Julia prepared a medication pump to give the man Lasix, a medicine that would help him urinate away the fluids that had swollen his belly and were hindering his breathing. But the man’s heart rate rose to 129 beats per minute, setting off a flashing red light on the vital-sign monitor.

M.J., who had stepped back to let Julia make decisions, couldn’t remain silent.

“What are you most worried about?” she asked, and then answered her own question. “Getting that heart rate down. ..... The name of the game is prevention. You don’t want him to have an MI [heart attack]. That will make your life very difficult today.”

For M.J., such on-the-spot decision making has become second nature. She is a big believer in seeking the advice of doctors whenever she has doubts, but the 42-year-old nurse has vastly more bedside experience than the young residents who pass through.

Within weeks of her arrival, Julia had already seen how independent-minded and forceful her teacher could be. A petite but sturdy Armenian grandmother, admitted to the ICU after hernia surgery, suddenly became delusional, insisting that her daughters were “ringing the doorbell,” and that Japanese dinner guests would arrive soon. M.J. recognized her confusion as a symptom of oxygen deprivation and stuck a suction tube down the patient’s throat to clear her congested airway. “I don’t want it! I don’t want it,” the woman hollered, but moments later, she was talking normally about her houseplants again.

M.J. has far more autonomy than nurses at most hospitals, in part because the lines of authority between nurses and doctors in Mass. General’s ICUs are sometimes blurry and often crossed. M.J., for instance, will order X-rays or change drug doses in an emergency, then get a doctor’s approval after the fact.

“A lot of times, I feel we’re here more as consultants to the nurses,” said Dr. Bill Benedetto, an anesthesiologist, who notes that doctors can have up to 10 patients at a time while ICU nurses typically focus on no more than two. The relationship relies heavily on trust and communication, he said.

Still, M.J. and other ICU nurses know the public views them as less important than doctors, and they chafed when Abby, the only nurse among the main characters on “ER,” went off to medical school a few years ago. As ICU nurse Jen Matthiesen put it, “Doctors say, ‘Oh, you’re so smart; why aren’t you a doctor?’ I say, ‘I don’t want to sleep on a cot.’.”