LAUSR

By a secondary analysis of the data from their previously published prospective observational study, Konishi et al. compared the incidence of postoperative cognitive dysfunction (POCD) after sevoflurane and propofol general anaesthesia in combination with spinal anaesthesia for hip arthroplasty in elderly patients, and showed that the incidence of POCD was not significantly influenced by the type of anaesthesia used. Given that POCD is associated with major adverse consequences, for example, an increased mortality rate, reduced quality of life, and delayed longterm recovery, their findings have potential implications. To differentiate the real effect of one intervention on the primary endpoint, however, all other risk factors have to be standardised for avoidance of potential bias. We noted that several important issues in this study were not well addressed. First, the study subjects were elderly patients undergoing hip arthroplasty, with a mean age of about 70 years. Some baseline data of patients were provided, but none of these variables can reflect the general physical status of patients, which has an impact on postoperative recovery. In clinical practice, the general physical status of patients can be easily evaluated by the risk prediction tools, such as American Society of Anesthesiologists physical status classification, frailty index, revised Lee’s cardiac risk index, Charlson comorbidity index, and others. It has been shown that the American Society of Anesthesiologists physical status classification is a good predictor for POCD in elderly patients. Moreover, as frail elderly patients are more likely to have pre-existing cognitive impairment with reduced cognitive reserve, they are most vulnerable to POCD. Second, the mean bispectral index was significantly lower in the sevoflurane group than in the propofol group, but details of intraoperative management were not provided. Thus, it is difficult to determine the extent of influence that anaesthetists’ interventions might have on the occurrence of POCD. For example, the authors described that hypotension was treated by an anaesthetist with a combination of intravenous fluid bolus, metaraminol, ephedrine, or phenylephrine. However, incidences of hypotension and use of vasoactive drugs were not given and compared between groups. The available evidence indicates that maintenance of stable intraoperative haemodynamics can reduce the incidence of POCD in elderly patients. Similarly, a recent meta-analysis shows that perioperative use of dexmedetomidine can reduce the incidence of POCD and improve the postoperative mini-mental state examination score. In contrast, intraoperative blood transfusion of >3 units is an independent risk factor for POCD in elderly patients after total hip replacement surgery. Finally, postoperative complications were not provided, though postoperative infections and respiratory complications have been significantly associated with an increased risk of POCD after major noncardiac surgery. Thus, we believe that addressing the above issues would improve the transparency of this study and interpretation of the findings.