LOS ANGELES, July 30 (UPI) -- Requiring 5 hours of rest for surgical residents after a 16-hour day is unlikely to improve outcomes for two common operations, U.S. researchers say.

Researchers at the Los Angeles Biomedical Research Institute reviewed 2,908 laparoscopic cholecystectomies, in which the gall bladder is surgically removed through a small incision in the abdomen, and 1,726 appendectomies to remove patients' appendixes, performed at Harbor-University of California, Los Angeles, Medical Center from July 2003 to March 2009.

The procedures are the most common operations performed by residents and are often performed at night after residents have worked a long shift, the researchers say.

The study, published in the Journal of Surgical Research, says the appendectomy and cholecystectomy operations performed at night by less rested, and possibly sleep-deprived, residents had similar good outcomes compared with those performed by residents done in the daytime by those who had worked less than 16 hours.

"In terms of the two most commonly performed operations by surgical trainees, the study suggests that limiting resident shifts to 16 hours of work is unlikely to improve surgical outcomes," corresponding author Dr. Christian de Virgilio says in a statement. "Training surgeons takes more time than many other medical disciplines because the residents must learn the craft of surgery along with patient care."

Residents currently work 80 hours per week averaged over four weeks, the researchers say.