We thank Drs. Krenk and Kehlet for their comments on our study,1and we appreciate their concerns. The type of anesthesia used for our patients is listed in tables 1 and 2 of our article. There was no effect of type of anesthesia on postoperative delirium. In the majority of our patients (89 of 106, 84%) a femoral nerve catheter was inserted before surgery, through which they received a constant infusion of local anesthetic postoperatively. An additional seven patients received postop epidural analgesia. Regional analgesia in both instances was supplemented with oral celecoxib and pregabalin, and opioid as needed.

The incidence of postoperative delirium in our patient population is similar to that reported by others in knee arthroplasty patients.2In contrast, Dr. Krenk’s impressive study of fast-track hip and knee arthroplasty (of which we were unaware before our article submission) revealed no postoperative delirium.3However, there are significant differences between the studies. In particular, delirium in our study was diagnosed not only on the basis of nursing, physical therapy, and physician notes (as in Dr. Krenk’s study), but also by using Confusion Assessment Method and Delirium Rating Scale-Revised-98 administered by a dedicated, specifically trained nurse, and reviewed by a psychiatrist. Most of our cases were mild, thus we probably detected many cases that might not have been noted by ward nurses with many other responsibilities. We agree with Drs. Krenk and Kehlet that opioids can enhance postoperative complications in obstructive sleep apnea patients. Despite implementation of fairly consistent regional analgesia to minimize such effects, we still observed an effect of obstructive sleep apnea. Indeed, it is likely that some patients with apnea went undiagnosed or were not known. These false negatives would tend to weaken the observed effect in our analysis, suggesting that an even stronger effect of obstructive sleep apnea on delirium might exist.

*Duke University Medical Center, Durham, North Carolina. kwatr001@mc.duke.edu

Flink BJ, Rivelli SK, Cox EA, White WD, Falcone G, Vail TP, Young CC, Bolognesi MP, Krystal AD, Trzepacz PT, Moon RE, Kwatra MM. Obstructive sleep apnea and incidence of postoperative delirium after elective knee replacement in the nondemented elderly. ANESTHESIOLOGY. 2012;117:788–96
Contín AM, Perez-Jara J, Alonso-Contín A, Enguix A, Ramos F. Postoperative delirium after elective orthopedic surgery. Int J Geriatr Psychiatry. 2005;20:595–7
Krenk L, Rasmussen LS, Hansen TB, Bogø S, Søballe K, Kehlet H. Delirium after fast-track hip and knee arthroplasty. Br J Anaesth. 2012;108:607–11