In this systematic review, we analyzed the clinical papers on PND published up to March 2021. Since the publication of the first report in 1955, there has been increasing attention to this specific field, particularly in general surgery adult-elderly patients.
Results available from observational and comparative studies along with published protocols of ongoing RCTs on surgical patients reveal that PND is an issue of major concern to the clinical academic world. Nevertheless, the growing scientific interest on PND seems to diverge from the disheartening observational data on real-life practice and physicians’ attitude to routinely test patients for POD or POCD . As an example, an on-line survey endorsed by the European Society of Anesthesiology has demonstrated that, despite PND (and particularly POD) being perceived as a relevant condition, only 7% of physicians involved in perioperative care who responded to the survey routinely monitor the majority of their patients for delirium . Apparently, academic interest rather than clinical practice has encouraged the production of scientific publications on PND, as demonstrated by their stable increase over time.
This review underlines the importance for the clinicians to pay attention to this really frequent disorder that can affect surgical patients.
A stable increase in papers on PND research in the last decades has already been observed by Mi et al. in a bibliometric analysis aimed at identifying the top 100 cited publications on PND. In this paper, the authors considered both experimental and basic science papers along with clinical (observational and comparative) studies. Within this context, the steadily growing number of studies on PND reported by the authors may reflect the interest of physicians/clinical researchers, as well as of basic science scientists. In order to focus our attention on the clinical perception of PND, pared down from basic science and pre-clinical interests, we restricted our analysis to studies that may originate from bedside practice. Interestingly, our study reveals the same increasing trend in numbers of publications on PND over time. Indeed, our systematic review describes an unexpected evolution of the interest toward a concrete clinical conception of PND that involves not only academic attention but also bedside clinical practice. This aspect has probably determined the peculiar profile of the publication curve displayed in Fig. 2. In particular, the number of papers published in the literature seems to be influenced by specific clinical research milestones in the field of PND, such as the ISPOCD1 study (published in Lancet in 1998 ) or the longitudinal assessment of neurocognitive function after cardiac surgery (published in the New England Journal of Medicine in 2001 ), or the paper published in 2018 examining the nomenclature on perioperative cognitive impairment and leading to the inclusion of PND among definitive neurocognitive disorders listed in the DSM-5 manual . The same trend can be observed in the subgroup of papers considering pediatric populations (Fig. 4), mainly polarized around the GAS trial published in Lancet in 2016 . Interestingly, Mi et al. have recognized these papers as the most cited articles focusing on cognitive changes associated with anesthesia and/or surgery .
The high prevalence of papers analyzed by Mi et al. and published in journals with an anesthesiological or surgical attraction is probably related to the search strategy adopted by the authors, confined to Web of Science database. In our bibliometric study, to better characterize the interest that a whole multidisciplinary and multiprofessional team may have in managing patients with PND, we have adopted a different search strategy encompassing several different databases, including also PubMed, Embase, CINAHL, or Cochrane . This field appears to be of particular interest to nurses, biomedical engineers, and clinical pharmacologists who have published several clinical papers in the last decades on the potential effects on PND of new drugs, disposables, or technologies nowadays routinely available at the bedside. The interest of industries and regulatory agencies has followed accordingly. The number of papers with funding disclosures has thus increased over time . All these aspects may have further contributed to the transition from basic science and preclinical interest to a more pragmatic, clinical, bedside, patients-centered research on PND.
Compared to previous bibliometric studies available for postoperative cognitive impairment, the adoption of multiple databases  and a refined search strategy have contributed to guarantee an adequate and efficient coverage of the topic in this systematic review. Our search strategy was in line with that used by the most updated guidelines on POD published in 2017 by the European Society of Anesthesiology.
Several drawbacks can be recognized in this study. First, although several articles included in this systematic review designate POD or POCD as their main focuses, the authors miss to define the clinical tools adopted to diagnose these conditions. Most papers indeed fail to use any validated scales to diagnose POD or POCD, potentially leading to inaccuracies and biases in the final bibliometric analysis. Second, the high prevalence of papers describing PND in general surgery patients can be influenced by the inclusion of orthopedic surgery in the “general surgery” group. Finally, due to the considerable number of articles screened and included in this systematic review and the impossibility to automatically determine the number of citations or the journal title during data extraction, we could not report this important bibliometric information in our analysis.