Is Delirium After Cardiac Surgery Related to Plasma Amino Acids and Physical Condition?

The authors studied interrelationships between plasma levels of amino acids, physical condition (as apparent from cortisol, albumin, and thyroid hormone concentrations), and postoperative delirium in 296 patients undergoing elective cardiac surgery. Both plasma tryptophan (Trp) and ratio of Trp to the other large neutral amino acids (oLNAA) were reduced in delirious patients compared with control patients. The lower availability of Trp for the brain in delirious patients may lead to decreased serotonergic function. Besides, the ratio of phenylalanine (Phe) to the oLNAA was increased in delirium, which may result in a higher synthesis of cerebral dopamine and norepinephrine. Delirious patients were also in poorer physical condition than nondelirious patients, having decreased albumin level and increased ratio of inactive reverse triiodothyronine (T₃) to active T₃. Decreased Trp and increased Phe availability may give rise to an imbalance in cerebral neurotransmitters and thus contribute to delirium.