Predicting and preventing perioperative problems

MI and respiratory calculators can help manage perioperative risk.


Himani Gupta, MBBS, ACP Associate Member, and his colleagues had a busy year in 2011. They published one risk calculator for predicting postoperative myocardial infarction (MI), another for postoperative respiratory failure, and worked on a third for postoperative pneumonia.

“I'm not sure when [the last calculator] will be in press, but watch for it!” said Karen F. Mauck, MD, FACP, who highlighted the virtues of the MI and respiratory calculators during her Internal Medicine 2012 session “New Recommendations in Perioperative Medicine” in April.

Karen F Mauck MD FACP Photo by Kevin Berne
Karen F. Mauck, MD, FACP. Photo by Kevin Berne.

The first calculator uses five factors to predict a patient's risk of MI or cardiac arrest within 30 days of surgery: age, creatinine, procedure type, dependent functional status and American Society of Anesthesiologists (ASA) class.

Best of all, it is available as a free smartphone app and for download to a desktop. (The former site will prompt for a password, but entering any word works, Dr. Mauck said.)

The calculator's predictive performance is better than the Revised Cardiac Risk Index, and it applies to patients undergoing a variety of surgical procedures, said Dr. Mauck, an assistant professor of medicine at Mayo Clinic in Rochester, Minn. who specializes in perioperative medicine.

Further, it was derived from a historical cohort study of 469,000 patients—an “astounding number”—who came from more than 200 hospitals, she said. It was published July 2011 in Circulation. “This is an exciting new contribution to the field of perioperative medicine, but this tool will need to be further validated in other patient populations to verify its predictive performance,” Dr. Mauck said.

Using the same cohort study, Dr. Gupta and colleagues devised their second risk calculator to predict the risk of 30-day postoperative respiratory failure. This, too, has excellent predictive performance and uses only five factors to determine risk: type of surgery, emergency case, ASA class, preoperative sepsis and dependent functional class, Dr. Mauck said. It is available on the same smartphone app mentioned above as well as online, and the study featuring it was published in the November 2011 Chest.

Timing of surgery

Drilling down to a more specific group of patients, Dr. Mauck flagged a study in the May 2011 Annals of Surgery showing that patients who have surgery within two months of a recent MI have an especially high risk of 30-day postoperative MI and death.

“Physicians should consider delaying elective surgery by at least two months, and ideally four to six months, for these patients,” Dr. Mauck said. “Even at six months, the risk of postoperative MI is four times that of those without a history of recent MI. So, even if it's [beyond] six months, you and the surgeon and the patient need to be aware there is a higher risk,” she added.

A “recent MI” in the study comprised an MI that had occurred within the year prior to the surgery. The 563,000 patients in the historical cohort study underwent a range of procedures, including hip surgery, cholecystectomy, colectomy, elective abdominal aortic aneurysm repair, and lower extremity amputation. Aside from recent MI, significant predictors of 30-day postoperative MI or death, and of one-year postoperative mortality, were older age, male gender, emergent surgery, and higher scores on the Charlson Comorbidity Index, Dr. Mauck noted.

The usefulness of biomarkers

Another study examining 30-day postoperative MI and death in noncardiac surgery patients found that most patients who experience postoperative MI do not experience ischemic symptoms. Further, the mortality rate for patients who had an MI postoperatively was the same (12%), regardless of whether they had MI symptoms or not, she said.

“Cardiac biomarker measurement postop in at-risk patients is needed to detect most MIs,” Dr. Mauck said. Nearly three-fourths of the MIs occurred within 48 hours of surgery, she added.

Biomarker measurement may serve other purposes as well since the study found that patients who didn't have a postoperative MI but had isolated cardiac biomarker elevation also had a higher risk of death than those without elevated biomarkers, she noted. The study appeared in the April 19, 2011 Annals of Internal Medicine.

Preoperative fasting

Dr. Mauck also discussed how to prevent complications before surgery. She began by asking audience members about food and drink restrictions for a patient scheduled for an 8 a.m. elective procedure. Most said the patient should have no solid foods after midnight, and clear liquids only up to 2 a.m. (i.e., six hours before surgery).

This is partly correct. Food after midnight should indeed be avoided, but a patient can actually drink clear liquids all the way up until two hours before surgery, Dr. Mauck noted.

This rule, which comes from the ASA's 2011 revised practice guidelines on fasting, applies to healthy patients who are having elective surgery involving general anesthesia, regional anesthesia or sedation/analgesia, she said. It's not meant for women in labor, or for patients with impaired upper airway protective reflexes or risk factors for aspiration.

“This is actually an update of the 1999 guideline that said the same thing, and yet none of us are doing it,” said Dr. Mauck. “We tell patients nothing after midnight, and they come in totally dehydrated. So maybe [the ASA] updated the guidelines just so people will listen.”

Clear liquids include water, fruit juices without pulp, carbonated beverages, clear tea and black coffee, broth or popsicles. “I did have a patient ask if it was OK to drink his bourbon—NO! Alcohol is not on the list,” Dr. Mauck said.

A Mayo Clinic anesthesiologist has found that devout coffee drinkers are less inclined to have headaches when they wake from anesthesia if they have their morning cup of coffee before the two-hour deadline for clear liquids, she added.

With patients who have significant gastroesophageal reflux disease (GERD), physicians may want to recommend clear liquids be avoided six hours before surgery, to be on the safe side, she said. Six hours is the limit for non-human milk, too.

There's not much evidence that pharmacologic agents (like gastric acid blockades or gastrointestinal stimulants) reduce aspiration risk, so they aren't recommended for routine use, she added.