Simply being older doesn't increase the risk of developing complications after surgery, said a new study. However, being frail and having cognitive problems does increase risk.

In addition to frailty, depressive symptoms and smoking were associated with developing complications following surgery, says the study which was published in the journal BMC Medicine.

The study also found that a patient's American Society of Anesthesiologists score, which evaluates the physical health of a patient before surgery and is traditionally assessed as a risk factor for postoperative complications, was not linked with postoperative complications in older patients.

Researchers at Toronto's St. Michael's Hospital examined 44 existing studies including more than 12,000 patients 60 years and older. The studies reported postoperative outcomes including complications, postoperative mortality, length of hospitalization, functional decline, and whether patients were discharged home or to another hospital or long-term care facility.

"The fact that age and ASA status were not risk factors for postoperative complications is somewhat surprising, because these are the factors a clinician would typically look at when assessing a patient's risk of developing complications after surgery," said lead author Dr. Jennifer Watt.

Overall, the researchers found that 25 per cent of older patients experienced some complications following elective surgery.

"Older adults are a diverse group of patients whose risk of postoperative complications is not solely defined by their age, comorbidities or the type of surgical procedure they receive," said Dr. Watt. "This study highlights how common postoperative complications are among older adults undergoing elective surgery, and the importance of geriatric syndromes, including frailty, in identifying older adults who may be at risk."

The authors also noted that there are proven interventions for several risk factors the study identified, including improving a patient's nutrition and physical fitness, and quitting smoking before surgery.

Other factors also influence the chances of complications. A 2017 study published in Neurosurgery found that patients who undergo surgeries in the evening or night have an increased risk of complications when compared to patients whose surgeries took place earlier in the day.

The study showed that the odds of a complication were increased by more than 50 percent for procedures with start times between 9 p.m. and 7 a.m. Chances of complications for longer surgeries in later time periods were even higher.