Among hospitals with ICUs that don't have a dedicated critical care physician during the day, however, the presence of such a doctor at night was tied to a smaller likelihood that patients would die.

The results, published in the New England Journal of Medicine, counter an argument from some in the medical community that ICUs need round-the-clock intensivists -- doctors who specialize in critical care.

"Our knee jerk reaction is to try to put intensivists in every ICU at all hours of the day, and that reaction is likely a misstep because it oversimplifies the issue," said Dr. Jeremy Kahn, senior author of the study and a professor at the University of Pittsburgh School of Medicine.

Most research has shown that having an intensivist in an ICU during the day improves the chances that patients will survive, said Kahn.

"There's been this movement to say, 'well, we need to be there at night too,'" said Dr. Allan Garland, a professor at the University of Manitoba in Winnipeg, Canada, who was not involved in the study. "But what there hasn't been is much data."

Data are important when it comes to staffing ICUs, considering there are not enough intensivists to go around and they are a much more expensive staff member than, say, a nurse.

Kahn said just half of all ICUs in the United States have access to a critical care specialist.

And several earlier studies on the impact of nighttime intensivists have had mixed results.

To try to get a clearer picture of how much they help patients survive, Kahn's group examined a larger group of ICUs.

They collected information from 49 ICUs across the U.S., covering more than 65,000 patients.

Twelve of the ICUs had an intensivist on staff at night, while the other 37 did not.

About 13 out of every 100 patients in the ICUs died within the hospital or went from the ICU to hospice care, regardless of whether there was an intensivist available at night or not.

But when the researchers divided the ICUs into two categories -- those that had intensivists overseeing patient care during the day, and those that did not -- Kahn's group got a different answer.

Among the 22 ICUs with no intensivist during the day, having one at night was tied to a 38 percent lower patient death rate than in ICUs without a day- or nighttime intensivist.

"The results of this large study seem to support previously observed associations between overall 'higher intensity staffing' and lower mortality," said Dr. Ognjen Gajic, a professor at the Mayo Clinic in Rochester, MN, who did not participate in this research.

Not all studies have agreed on this association, Gajic added in an email to Reuters Health.

Despite the new report's finding that a nighttime intensivist makes a difference if there's none during the day, the converse was not true: Among ICUs with an intensivist during the day, the percentage of patients who died within the hospital was the same regardless of whether an intensivist was also present at night.

Kahn said the findings suggest that the good intensivists do during the day carries over into the night.

It's not so much that the benefits are coming from emergency, life-saving procedures in the wee hours, he explained.

Rather, the difference intensivists make comes from "much more routine, banal, systematic things, like high quality preventive medicine, ventilator management, and most of these things can be done effectively during the day. And once you've implemented all the evidenced-based practices during the day, then what you do at night has little impact," said Kahn.

Gajic said it's possible the ICUs that have intensivists on staff during the day might also have access to those doctors at night, because they are on call.

But without knowing the particular arrangements at each hospital, it's unclear why ICUs with daytime intensivists don't benefit from having them at night, he said.

Garland said there's a need for more research on different staffing scenarios.

"One of the things that we would like to see is a consensus. You're much more confident of a result when you've had different studies…all give you the same answer. I think it's fair to say that we don't (yet) have that with respect to how intensivists should be involved in ICUs," Garland told Reuters Health.

Kahn said there might be legitimate reasons to have a nighttime specialist in the ICU, such as for training purposes.

But to improve the chances that patients will leave the ICU alive, it doesn't appear that every ICU needs an intensivist at all hours.

"For ICUs that have very robust daytime staffing, they should seriously reexamine the reasons that they're moving towards 24-hour intensivists, because it appears that there's little if any marginal gain in survival, and those resources may be better deployed in other hospitals," Kahn told Reuters Health.

SOURCE: bit.ly/JeFemx New England Journal of Medicine, online May 21, 2012.

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