In the instance of fever and confusion, particularly in the elderly person, the problem of “septic encephalopathy” is offered as an explanation, but it may simply be a rephrasing of the well-known problem of infection such as pneumonia leading to a global confusion or delirium that was extensively discussed in the older literature by Osler. Young has called attention to the high frequency of this disorder in critically ill patients, 70 percent of their bacteremic patients, and its accompaniment by a polyneuropathy in a high proportion of cases. Paratonic rigidity of the limbs (an oppositional action on the patient’s part that is proportioned to the effort of the examiner in moving the limbs) is an almost universal accompaniment; according to these authors, focal cerebral or cranial nerve signs are not encountered. All other potential causes of a confusional state must, of course, be excluded before attributing the state to an underlying infection.
The EEG is slowed in proportion to the level of consciousness, but it shows mild changes even in the bacteremic patient who is fully alert. The spinal fluid is normal or has a slightly elevated protein concentration. While there is no doubt that young and healthy patients may become confused when affected with high fever and overwhelming infections such as pneumonia, most cases of septic encephalopathy are of the “beclouded dementia” type in the older patient. The point made by Young is that subtle degrees of confusion are ubiquitous with serious infections of many varieties. Among the most perplexing cases of this type have been healthy older persons we have observed who acquired an agitated delirium following spinal column infection after surgery. The delirium ceased within hours of drainage of an abscess. The older literature contains similar examples with closed space infection in other locations. The chapter by Young can be consulted for an exposition of the various theories of pathogenesis of this state. High fever itself (above 40.6°C [105°F]) is probably an adequate explanation for confusion in some cases. A similar global confusional state occurs in patients with severe burns (burn encephalopathy).
All that has been stated above is true of the patient with a nondescript postoperative confusional state, in which a number of factors, such as fever, infection, dehydration, and drug and anesthetic effects, are implicated. In a study of 1,218 postoperative patients by Moller and colleagues, older age was by far the most important factor associated with persistent confusion after an operation; but a number of other factors—including the duration of anesthesia, need for a second operation soon after the first, postoperative infection, and respiratory complications—were also predictive of mental difficulty in the days after the procedure. As discussed further on, confusion appearing after a surgical procedure may suggest an underlying dementia or be predictive of the future development of dementia. What is as important is the confusional episode may not entirely resolve for weeks or months as commented below. Careful questioning of the family often reveals subtle decline is daily functioning over the prior months or years. Unacknowledged alcoholism and withdrawal effects undoubtedly cause the same problem quite often on surgical services (see also “Stroke with Cardiac Surgery” in Chap. 33).
When such patients recover from the medical or surgical illness, they usually return to their premorbid state, though their shortcomings, now drawn to the attention of the family and physician, are far more obvious than before. For this reason, families will date the onset of a dementia to the time of the medical illness or surgical procedure, and continue to minimize the previous gradual decline in cognition. In other cases, however, the acute medical illness seemingly marks the beginning of a persistent decline in mental clarity that over time can be identified as a dementing illness. A related problem that has come under study is persistent cognitive loss after critical illness. The rates of this irreversible change are apparently high, up to one-quarter of severely ill patients in some series, but accurate estimates are difficult to obtain because of the lack of pre-illness psychometric testing.