Abnormal Level of Arousal as a Predictor of Delirium and Inattention: An Exploratory Study

Objective: Abnormal level of arousal (LoA) and inattention are key features of delirium. However, the extent to which abnormal LoA alone might predict delirium and inattention is unclear. Here we tested the hypotheses that (1) patients with abnormal LoA have delirium, and (2) abnormal LoA is associated with worse performance on tests of attention. Methods: Thirty acute hip fracture patients aged 64-97 years underwent assessments of LoA, delirium status, and attentional functioning in the 24 hours before surgery and at 2-4 and 7-10 days after surgery. The Observational Scale of Level of Arousal (OSLA) and the Richmond Agitation-Sedation Scale (RASS) were used to assess LoA. Sustained attention was measured with the Edinburgh Delirium Test Box. Delirium was assessed with the Confusion Assessment Method and the Delirium Rating Scale-Revised-98. Results: Ten patients (33%) were diagnosed with delirium. Abnormal LoA as measured by the OSLA was strongly associated with the presence of delirium. The area under the receiver operating characteristic curve was 0.89 (95% confidence interval: 0.81-0.97), with a sensitivity of 0.87 and a specificity of 0.81. Area under the curve, sensitivity, and specificity for the RASS were 0.81 (95% confidence interval: 0.68-0.94), 0.80, and 0.79, respectively. Abnormal LoA was associated with worse attentional deficits preoperatively and at postoperative days 2-4 (p < 0.01). Conclusion: These exploratory findings suggest that abnormal LoA is a strong indicator of delirium. Also, abnormal LoA is strongly associated with inattention as measured by an objective cognitive test. These findings suggest that acute-onset abnormal LoA could be used as a trigger for delirium assessment in routine clinical practice. Future work will help to clarify further the interrelationships among abnormal LoA, inattention, and delirium.