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We thank Professor Kratz and Professor Diefenbacher for their important commentary on postoperative delirium (POD) as another form of cognitive impairment after surgery. Though our work focused on low cognitive reserve as a risk factor that develops in young adulthood (and thus usually decades before surgery), POD is indeed a central postoperative risk factor for subsequent postoperative cognitive dysfunction (POCD). Thus, POD and POCD seem to be closely related not only to one another but also to both preoperative clinical (1) and cognitive risk factors. We would like to point out that cognitive impairment prior to surgery is associated with low cognitive reserve and is a known risk factor for the development of POCD (2) and POD (1). Interestingly, it seems that cognitive reserve may play an exceptional role as a risk factor: our study showed that a low level of education increases the risk of POCD, whereas it does not appear to be associated with POD (1) (although some isolated evidence in this direction has been reported for indicators of cognitive reserve other than education [3]). Therefore, while POD increases the risk of POCD, it appears that the two conditions may have distinct underlying mechanisms. In order to determine possible causal connections, the interplay between cognitive reserve, which develops early in life, and risk of late-life disease including POD and POCD should now be assessed in detail. Until that goal is accomplished to pave the way for therapeutic breakthroughs, we agree with the authors that—in view to prevent POCD—clinical practice should aim to provide the best possible care to patients with delirium.

DOI: 10.3238/arztebl.2017.0362b

On behalf of the authors:

Insa Feinkohl, PhD

Max-Delbrück Zentrum für Molekulare Medizin (MDC), Berlin, Germany

insa.feinkohl@mdc-berlin.de

Conflict of interest statement

The author declares that no conflict of interest exists.

1.
Gosselt ANC, Slooter AJC, Boere PRQ, Zaal IJ: Risk factors for delirium after on-pump cardiac surgery: a systematic review. Critical Care 2015; 19: 346 CrossRef MEDLINE PubMed Central
2.
Millar K, Asbury AJ, Murray GD: Pre-existing cognitive impairment as a factor influencing outcome after cardiac surgery. Br J Anaesth 2001; 81: 63–7 CrossRef
3.
Sczynski JS, Inouye SK, Kosar CM, et al.: Cognitive and brain reserve and the risk of postoperative delirium in older patients: analysis of data from a prospective observational study. Lancet Psychiatry 2014; 1: 437–43 CrossRef MEDLINE
4.
Feinkohl I, Winterer G, Spies CD, Pischon T: Cognitive reserve and the risk of postoperative cognitive dysfunction—a systematic review and meta-analysis. Dtsch Arztebl Int 2017; 114: 110–7 VOLLTEXT
1.Gosselt ANC, Slooter AJC, Boere PRQ, Zaal IJ: Risk factors for delirium after on-pump cardiac surgery: a systematic review. Critical Care 2015; 19: 346 CrossRef MEDLINE PubMed Central
2.Millar K, Asbury AJ, Murray GD: Pre-existing cognitive impairment as a factor influencing outcome after cardiac surgery. Br J Anaesth 2001; 81: 63–7 CrossRef
3.Sczynski JS, Inouye SK, Kosar CM, et al.: Cognitive and brain reserve and the risk of postoperative delirium in older patients: analysis of data from a prospective observational study. Lancet Psychiatry 2014; 1: 437–43 CrossRef MEDLINE
4.Feinkohl I, Winterer G, Spies CD, Pischon T: Cognitive reserve and the risk of postoperative cognitive dysfunction—a systematic review and meta-analysis. Dtsch Arztebl Int 2017; 114: 110–7 VOLLTEXT

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