We read with interest the recent article by Flink et al.  1in which the authors evaluated the frequency of postoperative delirium (POD) in 106 elderly patients aged 65 yr or older after elective knee replacement. The screening for POD was thorough and well-conducted with recognized screening tools, with an incidence of 25% on days 2–3 postoperatively. The pathophysiologic mechanisms are multiple, including anemia, electrolyte disturbances, infection, pain, and benzodiazepine and opioid use.2 

Patients with obstructive sleep apnea are at an increased risk of postoperative complications in general, and this is especially true when combined with opioid-based analgesia in the postoperative period.2,3It is therefore unfortunate that this otherwise well-conducted study did not include data on pain, opioid use, and other sedatives, because this may worsen the adverse effects of obstructive sleep apnea. In addition, there was little specific information on the anesthetic technique per se .

The incidence of POD of 25% seems high in an elective, nondemented surgical population. Our group recently found no cases of POD in a similar population of patients undergoing knee and hip replacement.4However, our patients received multimodal optimized care with reduced opioid use and only moderate postoperative pain, combined with short length of stay (mean 2.6 days). We believe that future studies evaluating the complex cognitive outcome of POD with multiple pathophysiologic mechanisms should include an optimized multimodal enhanced recovery program (the fast-track methodology)3–5to provide a better understanding of POD and preventive techniques.

*Rigshospitalet, University of Copenhagen, Copenhagen, Denmark. lene.krenk@rh.regionh.dk

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
Sanders RD, Pandharipande PP, Davidson AJ, Ma D, Maze M. Anticipating and managing postoperative delirium and cognitive decline in adults. BMJ. 2011;343:d4331
Krenk L, Rasmussen LS, Kehlet H. New insights into the pathophysiology of postoperative cognitive dysfunction. Acta Anaesthesiol Scand. 2010;54:951–6
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
Kehlet H, Mythen M. Why is the surgical high-risk patient still at risk? Br J Anaesth. 2011;106:289–91