Three hundred and thirty five patients were included in the study. The mean age (± SD) of patients was 73.5 ± 6.2 years (range, 65–96 years). Preoperative patient characteristics, surgical and medical data are shown in . The majority of patients underwent orthopaedic surgery. Preoperatively, 36% of patients received an opioid analgesic for pain. The majority of patients were intermediate surgical risk candidates, with two or more medical comorbidities.
Demographics and clinical characteristics (n=335)
Of the 335 patients studied, 108 patients (32.2%) developed delirium on postoperative day one, 120 (35.8%) on postoperative day two, and 185 patients (55%) developed delirium on either day one or day two after surgery. Patients who developed postoperative delirium on either of the postoperative days tended to be older, were more likely to be female, and had more self-reported symptoms of depression as indicated on the geriatric depression score (). One patient had missing data for delirium on postoperative day one due to mechanical ventilation and 13 patients had missing data for delirium on postoperative day two. The reasons for missing data for postoperative day two included early discharge or unavailable during interviews (n=6), refusal to answer questions (n=3), and too sleepy to respond (n=4). More importantly, the characteristics (demographic and surgical data) between patients with missing data on delirium were not different from those with delirium data. Similarly, the amount of missing data for VAS in our study was low (< 3% overall for both postoperative days), and the differences in missing data between those with and without delirium were not significantly different for the different postoperative days.
The preoperative VAS scores were not significantly different between patients who subsequently developed postoperative delirium versus those without delirium (). In contrast, patients who were delirious postoperatively experienced significantly higher VAS scores than non-delirious patients (for postoperative day one: mean postoperative VAS at rest 4.2 ± 0.23 vs. 3.3 ± 0.22, P = 0.0051; and for postoperative day two: mean postoperative VAS at rest 3.3 ± 0.23 vs. 2.5 ± 0.19, P = 0.004).
Shown are the VAS pain scores plotted as mean ± SEM for patients with and without postoperative delirium in the pre- and post-operative periods
The intraclass correlations for postoperative resting pain scores on day one and day two were significantly different than zero in patients with and without postoperative delirium (). The 95% confidence intervals for the intraclass correlation coefficients suggest that patients who were delirious were equally consistent in their reports of resting pain evaluation than those who were not delirious. The difference in the magnitude of intraclass correlations could not be explained by differences in the ranges and variances of scores. On postoperative day one, 18.6% of patients with delirium and 15.7% of patients without delirium reported resting VAS pain scores of zero (P = 0.52) and on postoperative day two, 26.5% of patients with delirium and 23.1% of patients without delirium reported resting VAS pain scores of zero (P = 0.51). The variances in resting pain scores on day one and day two for patients who were and were not delirious on day one also did not differ significantly (P = 0.82 and 0.99 respectively).
Consistency in Reporting Pain between Postoperative Day one and Day two
The presence of postoperative delirium did not limit the use of PCA opioids as shown in and . After adjusting for the VAS scores, preoperative narcotic use, surgical risk, and use of medications with CNS effects on the day of the opioid dose measurement, patients with and without delirium on postoperative day one used similar amount of hydromorphone on postoperative day one and the subsequent day (). For patients with delirium on postoperative day two, they used substantially more PCA hydromorphone than those who were non-delirious on day two (adjusted mean dose 2.24 mg ± 0.71 vs. 1.25 mg ± 0.67, P = 0.02) ().
Hydromorphone Dose by Delirium Status on POD 1 Adjusted for Current Pain at Rest, Preoperative Narcotic Use, Surgical Risk, and Use of Other Medications with CNS Effects
Hydromorphone Dose by Delirium on POD 2 Adjusted for Current Pain at Rest, Preoperative Narcotic Use, Surgery Risk, and Use of Other Medications with CNS Effects
shows that our choice of indicator variables for measuring the latent variable, delirium status, was reasonable. Three indicator variables (acute onset, inattention, and altered level of conscious) loaded highly on the latent variable that we called delirium status. The overall model fit was assessed using statistics such as the adjusted goodness-of-fit index (0.98), chi-square (X2
=23.41; dF=25; P = 0.55), root mean square residual (0.14), root mean square error of approximation (P < 0.0001)), all of which indicated an adequate fit to the proposed model. The standardized path coefficients are displayed above their respective arrows in . Rest pain on postoperative day one significantly affects both postoperative opioid use (P ≤ 0.001) and delirium status (P ≤ 0.01) on day one. Postoperative opioid use on day one significantly affects delirium on day one (P ≤ 0.05) and subsequent opioid use on day two (P ≤ 0.001). However, delirium status on day one does not affect opioid use on day two.