Mohammed T. Abou-Saleh

ANAESTHETICS AND MENTAL STATE 745as in delirium in other settings, include acute illness, drugs anddrug withdrawal 1,2,13,15 but the incidence tends to rise with age.Estimates of the incidence of postoperative delirium in the over-65s range between 7% and 50%, depending on the definitionsused and the clinical circumstances 2,13,15 . The incidence tends torise with age, the urgency of surgery, the use of sedative andanticholinergic drugs and the degree of preoperative mentalimpairment. Factors (such as sepsis) that favour the developmentof delirium in a non-surgical situation 12 may also be ofrelevance postoperatively.Recent advances in the study of postoperative delirium haveincluded attempts to standardize definitions 13 and a large studyin the USA by Marcantonio et al. 15 , which attempted todevelop a clinical prediction rule in 1341 patients aged 50+having major non-cardiac surgery. The latter authors foundthat seven preoperative factors (age over 70, alcohol abuse,poor cognitive status, poor functional status, serum electrolyte/glucose disturbances, thoracic surgery and aneurysm surgery)had an independent relationship with postoperative delirium.However, the effect of intraoperative events, including anaesthesia,was not studied, as the aim was to produce apreoperative rule.O’Keeffe and Chonchubhair 13 have concluded that, in at least90% of cases of delirium following general surgery, it ispostoperative medical or surgical complications that are toblame, which implies that the appearance of delirium shouldlead to a diligent search for underlying physical medical problems.The increased incidence of postoperative delirium with age islikely to be due to causes such as these, rather than effects arisingfrom age-related differences in handling anaesthesia 16 .Postoperative Changes in Psychometric Tests in OlderPeopleDelirium is an important postoperative syndrome, but moreworrying is the possibility that dementia could occur for the firsttime as the direct result of routine surgery and/or anaesthesia (asopposed to the mental changes that might arise from anintraoperative catastrophe, such as cardiac arrest). In 1955,Bedford 17 published a much-quoted retrospective study in whichhe sought to trace those patients in the Oxfordshire area who had‘‘never been the same again’’ after an elective or emergencyanaesthetic. Over a 5 year period he was able to identify 18 caseswhere there was reasonable evidence that dementia had appearedfor the first time after surgery and anaesthesia. In interpreting thisdata, it is important to realize that a detailed assessment ofpreoperative mental function was not available, and that even incases where dementia was reported immediately followingsurgery, it did not necessarily imply that anaesthetic drugs werethe cause.In a subsequent study, Simpson et al. 18 attempted the verydifficult task of replicating Bedford’s findings in a prospectivestudy. As formal preoperative psychological assessment waspart of Simpson’s study design, only elective patients couldbe included. After considerable efforts, 678 elderly patientshaving surgery were evaluated, two-thirds of whom underwentgeneral anaesthesia. This major undertaking yielded only onepatient in whom there was good evidence that a permanentdeterioration in mental function occurred immediately afteranaesthesia.These two reports 17,18 stimulated many psychometric studies ofshort- and long-term postoperative cognitive outcome. Tables137.1 and 137.2 summarize the results of 17 such studies 19–35 ,which have looked at psychometric test performance in ageingpatients before and after surgery. Follow-up periods have rangedfrom a few days to over 3 months, and many different types ofpsychometric tests have been used. Table 137.1 contains 13 studiesin which older patients have been randomized to receive generalor regional anaesthesia, while Table 137.2 summarizes fouralternative study designs that have given an insight into the effectof age on postoperative cognitive problems. These include theISPOCD1 study, which is discussed in detail below.There are major methodological problems in carrying outclinically meaningful psychometric testing in elderly electivesurgical patients 35 . These problems become almost insuperablein patients who are admitted as emergencies, and only two of thestudies listed in Tables 137.1 and 137.2 considered non-electivepatients. Unfortunately, there is ample evidence that it is nonelectivepatients who have the highest incidence of postoperativemental events, although in many emergency cases non-anaestheticfactors, such as acute illness, are probably more culpable thananaesthetic drugs.The 13 studies in Table 137.1 compared the psychometric effectsof general anaesthesia with those associated with ‘‘regional’’techniques (local, spinal or epidural anaesthesia). Four of theearlier studies reported that the general anaesthetic groupperformed more poorly, but even here the effect was seen onlyduring the immediate postoperative period.The studies that make up Tables 137.1 and 137.2 contain awealth of detail, but some broad overall conclusions can bedrawn. As might be expected, the major effects on mental functionare seen in the first postoperative day, but some of the studiesreport minor effects on some tests for up to 7 days. The studiesthat specifically compared young and old patients found that theolder group performed slightly worse than the younger during theearly postoperative period.While short-term mental impairment following surgery is ofimportance, especially in these days of increasing day surgeryprovision 36 ,itislong-term mental impairment that is feared mostby patients, their relatives and their doctors. In the first edition ofthis textbook 37 , comfort was drawn from the fact that the bestdesignedof the long-term studies up to that date had reported noobjective evidence of mental impairment 1 month or more aftersurgery. It was noted, however, that 16% of the patients of Joneset al. 21 had complained of subjective changes in memory andconcentration at 3 months after surgery, and that these authorshad commented that these patients might have had minorintellectual changes which had been missed by the chosenpsychological tests. Since that time, the study of Williams-Russoet al. 19 has similarly reported long-term postoperative cognitivechanges in 5% of patients. Further concern has been raised by thefinding of long-term cognitive deficit in the ISPOCD1 study 32 ,which, unlike the Williams-Russo et al. study, included a group ofnon-operated control patients to meet the criticism that someof the effects reported in early studies reflected the progression ofcoincidental dementia, unrelated to surgery or anaesthesia. TheISPOCD1 study and its successor, ISPOCD2, will now bedescribed in some detail.The ISPOCD StudiesThe first International Study of Post-operative Cognitive Dysfunction(ISPOCD1) collected data between 1994 and 1996 on1218 patients aged 60+ who were undergoing major non-cardiacsurgery in 13 hospitals in eight European countries and theUSA 32 . This was a major undertaking, which was intended toanswer many of the questions about early and late postoperativecognitive dysfunction in older people that had been raised in theliterature over the previous 30 years. In the event, the results ofthe ISPOCD1 study, published in 1998 32 , still left severalunanswered questions which are being addressed in a furtherstudy (ISPOCD2), which is due to report in May 2001.