Serum neurofilament light and postoperative delirium in cardiac surgery

Impaired cognition is a major predisposing factor for postoperative delirium but it is not systematically assessed. Anesthesia and surgery may cause postoperative delirium by affecting brain integrity. Neurofilament light in serum reflects axonal injury. Studies evaluating the perioperative course of neurofilament light in cardiac surgery have shown conflicting results. We hypothesized that postoperative serum neurofilament light values would be higher in delirious patients, and that baseline concentrations would be correlated with patient’s cognitive status and would identify patients at risk of postoperative delirium.

This preplanned secondary analysis included 220 patients undergoing elective cardiac surgery with cardiopulmonary bypass. A preoperative cognitive z score was calculated after a neuropsychological evaluation. Quantification of serum neurofilament light was performed by Simoa® technique before anesthesia, 2 hours after surgery, on postoperative days 1, 2 and 5. Postoperative delirium was assessed using the Confusion Assessment Method for Intensive Care Unit, the Confusion Assessment Method, and a chart review.

65/220 (29.5%) patients developed postoperative delirium. Delirious patients were older (years; 74 [64,79] vs 67 [59,74]; P<0.001) and had lower cognitive z scores (-0.52±1.14 vs 0.21±0.84; P<0.001). Postoperative neurofilament light concentrations increased in all patients up to day 5, but did not predict delirium when preoperative concentrations were considered. Baseline neurofilament light values were significantly higher in patients who experienced delirium. They were influenced by age, cognitive z score, renal function and history of diabetes mellitus. Baselines values were significantly correlated with cognitive z scores (r, 0.49; P<0.001), and were independently associated with delirium whenever the patient’s cognitive status was not considered (hazard ratio [95%CI], 3.34 [1.07 to 10.4]).

Cardiac surgery is associated with axonal injury, as neurofilament light concentrations increased postoperatively in all patients. However, only baseline neurofilament light values predicted postoperative delirium. Baseline concentrations were correlated with poorer cognitive scores, and independently predicted postoperative delirium whenever patient’s cognitive status was undetermined.