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November 18, 2003
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Cardiac arrest deadlier at night

By Alice Dembner
The Boston Globe

BOSTON The finding was startling and unequivocal: Hospital patients who go into cardiac arrest during the night shift are more likely to die.

But the explanation is less clear. Do they die because there aren''t enough staff members to revive them promptly, or because physiologic changes strike the heart more severely at night?

Either way, the study carries a message for hospitals, said the lead researcher, Dr. Mary Ann Peberdy of Virginia Commonwealth University Health System. "Hospitals need to target delivery of care during the night shift."

Peberdy and a colleague examined records of nearly 18,000 cardiac arrests at 250 hospitals across the country from 2000 to 2002, taking the first systematic look at survival rates based on time of day.

Only 13 percent of patients whose hearts stopped abruptly at night survived to be discharged, compared to 18 percent of those struck during the day, according to results they presented at the American Heart Association meeting in Orlando last week.

By contrast, only about 5 percent of people who suffer cardiac arrest outside the hospital survive, according to the American Heart Association, because rescuers have only 4 to 6 minutes to reestablish a normal heart rhythm before the victim suffers brain damage. Typically, cardiac arrest, which afflicts approximately 400,000 Americans a year outside the hospital, is treated with cardiopulmonary resuscitation and electric shocks from a defribrillator. In communities where defibrillation is provided by rescue workers within 3 to 5 minutes, as many as 49 percent survive to discharge from the hospital, according to the Heart Association. Peberdy said no one has calculated the total number of cardiac arrests annually in the nation''s 2,000 hospitals.

Although the researchers found that cardiac arrests occurred at the same rate day and night, they found that hospital staff on the 11 p.m. to 7 a.m. shift were less likely to notice the symptoms of failing hearts. And they found that the nighttime cardiac arrests more often took the form of asystole, a complete stopping of the heart, rather than the heart rhythm disturbances that sometimes precede that. Taken together, Peberdy said the results suggest that "staffing is a part of the puzzle." At most hospitals, there are fewer nurses, fewer technicians and far fewer doctors on duty at night than during the day. Typically, the specialists have all gone home, leaving residents with less experience to care for patients. And fewer staff members are moving in and out of patient rooms, so there is less chance to notice a change in a patient''s condition. It''s possible, she said, that night staff missed warning signs, such as ventricular fibrillation, the uncontrolled quivering of the heart that typically preceeds asystole.

"Also, it''s a time of day when fewer hands are available to respond promptly," she said.

Although this is apparently the first study to look at patient survival rates at night, other studies have found higher death rates in hospitals on the weekend, when staffing is also lower. A study of Canadian hospitals, published in the Journal of the American Medical Association two years ago, found that patients admitted on weekends were more likely to die from a range of health crises that required quick action. Counter-intuitively, that study found no difference in deaths among patients with heart attacks.

"There are concerns about the degree of attention one is getting" at night, said Dr. Daniel Stryer, director of the Center for Quality Improvement and Patient Safety at the national Agency for Healthcare Research and Quality. "There''s an issue about availability of services -- you may not be able to get a CT scan or interventional procedure as quickly. The third level of concern is hand-offs. It''s more likely that the team that knows you best will not be there on weekends or at night."

Stryer says patients should not be alarmed by the "provocative, but really preliminary" findings of the Virginia researchers. But they should be sure there is someone around to respond quickly if they need help.

Some hospitals are already beefing up their night staff. Last year, Beth Israel Deaconess Medical Center put experienced doctors back on the night shift. A senior doctor oversees the hospital''s five intensive-care units at night and is available to help patients in other parts of the hospital if needed. During the day, by contrast, there''s a senior doctor in each ICU.

It wasn''t cardiac arrests that motivated the change, according to Dr. J. Woodrow Weiss, director of the medical ICU, but rather concern about patients with complex problems such as septic shock. The hospital is just beginning to collect data to determine if the change has made a quantifiable difference in outcomes, but Weiss says the staff of intensivists believes they are doing a better job of managing patients'' care.

"I think most hospitals will end up doing it over the next few years," said Weiss.

At Massachusetts General Hospital, residents and a cardiology fellow are on duty at night to care for patients who suffer cardiac arrest, with a senior cardiologist on call within 30 minutes, said Dr. Thomas Di Salvo, one of the cardiologists. Although that is far fewer doctors than available during the day, he said he didn''t believe that it hurt patient care. "Often residents are more capable of running . . . resuscitation than some of our senior physicians," he said because they do it more frequently.

Beyond staffing, Peberdy suggested, and the local doctors agreed, that another factor in the higher death rate might be physiological differences that make cardiac arrest more fatal at night for sick patients already in the hospital. Levels of hormones, prostaglandins and potassium, all of which can affect the heart, fluctuate over the course of a day. And heart rate and rhythm and blood pressure fall at night.

Other studies found that non-fatal heart attacks -- blockage in one of the coronary arteries -- occur more frequently in the morning. And one study found that out-of-hospital cardiac arrests were more common in the morning and in the late afternoon. But little research has yet been done to identify the specific physiological changes involved.

"I wouldn''t be surprised if the mechanism of cardiac arrest differed at different times of the day," said Di Salvo. He said there might also be differences in the patients'' underlying illnesses. "It might be that regardless of how skillfully they were resuscitated, they were at higher risk. These are interesting questions that require more exploration."

Alice Dembner can be reached at Dembner@globe.com.

Copyright 2003 Globe Newspaper Company.

Article courtesy of Zoll Medical Corp.

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