Low tryptophan levels are associated with postoperative delirium in the elderly

Background Postoperative delirium is a common complication in geriatric patients. Tryptophan is an amino acid precursor to the mood-stabilizing neurotransmitters serotonin and melatonin. We hypothesized that tryptophan levels are lower in elderly subjects who develop postoperative delirium. Methods A prospective observational study was performed. Subjects older than 50 years undergoing surgery with an anticipated postoperative intensive care unit admission were recruited. Postoperative delirium assessment occurred daily using the Confusion Assessment Method–intensive care unit. Peripheral serum tryptophan levels were measured 2 days after surgery. Results Forty-nine subjects (46 men) were enrolled, with an average age of 64 ± 7 years. The incidence of delirium was 43% (21 of 49). The average duration of delirium was 2.9 ± 3.0 days. Tryptophan levels were lower in the subjects who developed delirium (29.9 ± 13.3 vs 48.5 ± 19.8 μg/mL; P = .001). Conclusions Lower levels of tryptophan postoperatively were associated with the development of delirium in the elderly.