6MWD predicts cognitive dysfunction after heart surgery

By John Murphy, MDLinx
Published May 24, 2018

Key Takeaways

The 6-minute walk distance (6MWD) is used to predict postoperative complications after a variety of surgical procedures. Now, researchers have found that the 6MWD can identify patients who have a greater risk for postoperative cognitive dysfunction (POCD) after a cardiac operation, according to the results of a study published in The Annals of Thoracic Surgery.

The lower the 6MWD score, the more significant was the patient’s reduction in cognitive function after surgery, researchers found.

“This study indicates that the easy and inexpensive 6-minute walk distance is a valuable assessment for identifying patients at a high risk for POCD,” said Kazuhiro Hayashi, PT, MSc, Department of Rehabilitation, Nagoya University Hospital, Nagoya, Japan. “If we are able to identify patients who are at risk for POCD, we can provide early treatment and encourage them to better understand the dysfunction.”

Postoperative cognitive dysfunction can affect a patient’s quality of life for weeks to months after surgery, Hayashi and colleagues noted. This study, like other ones, defined POCD as a reduction of at least 2 points in the Mini-Mental State Examination (MMSE) between the period before and 2 weeks after the operation.

The researchers included 181 patients (mean age 71.4 years) who were undergoing an elective cardiac operation at Nagoya University Hospital between March 2014 and August 2015. All patients performed MMSE and 6MWD during the inpatient period.

Hayashi and colleagues found that POCD developed in 51 (28%) of the 181 patients, with 28 patients showing a reduction of 4 or more points in the MMSE. The shorter the 6-minute walk distance, the more significant was the reduction in POCD.

“According to the results of this study, a low 6MWD is one of the independent risk factors for POCD after a cardiac operation,” Hayashi and colleagues concluded. “The lower preoperative 6MWD identified patients with a longer postoperative hospital stay, consistent with previous reports.”

Specifically, patients with POCD showed significantly longer ventilation time, a higher rate of ventilation longer than 24 hours, a higher rate of ventilation exceeding 72 hours, a longer stay in the intensive care unit, a longer postoperative hospital stay, and a greater likelihood of being transferred to another hospital.

“Postoperative cognitive dysfunction is thought to be caused primarily by global or focal ischemia induced by transient restriction of cerebral blood flow,” the researchers explained. “The reduction of cardiorespiratory reserve” likely induces tissue hypoxia, which leads to multiple organ failure and postoperative complications.

To avoid those outcomes, the researchers stressed the importance of assessing each patient’s functional exercise capacity “to predict the risk of postoperative neurologic dysfunction.”

“Precise preoperative risk assessment for postoperative complications is critical,” they wrote. “Operative indication, methods of perioperative management, and postoperative health-care services should be carefully assessed, especially for patients with low 6MWD results.”

In these patients, Hayashi and colleagues recommended preoperative exercise—or prehabilitation—to improve functional exercise capacity before a cardiac operation.

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