Immediate and Long-term Nervous System Effects of Anesthesia in Elderly Patients

Abstract

The structural and functional changes which aging imposes upon the nervous system are extensive, reasonably well documented, and must be considered as significant factors which reduce the pharmacodynamic aspects of anesthetic requirement in elderly patients. However, changes in pharmacokinetics play the most important role in producing residual nervous system depression and prolonged unconsciousness in elderly patients in the immediate postoperative period. The high prevalence of cerebrovascular disease in the elderly surgical population makes it inevitable that catastrophic events such as cerebrovascular accident and embolization will contribute in a small but important manner to postoperative nervous system morbidity and mortality. The frequency with which elderly patients have multiple organ system disorders also makes them at high risk of metabolic and homeostatic disruption, frequently manifest as nervous system symptomatology.

Sensitive tests of the more complex aspects of nervous system function of elderly patients such as affect, abstraction, memory and logic reveal a disturbing phenomenon: one-quarter to one-third of these individuals develop new and persistent dysfunction in the immediate or long-term periods of recovery from anesthesia. It is currently impossible to determine the relative magnitude of the contributions made by illness, the hospital environment, surgical stress or the residual effects of anesthetic drugs. Although increasingly favorable figures for gross mortality suggest that, in modern practice, age per se is no longer considered to be an absolute contraindication to general anesthesia as far as survival is concerned, there must be greater awareness that many subtle and intricate aspects of cognitive and affective mental function in these patients may be compromised even under the best of circumstances. Although permanent nervous system damage from routine general anesthesia is extremely rare, many elderly surgical patients require weeks or months to achieve full spontaneous recovery of their preoperative mental status, for reasons that are still unknown. At this stage in our understanding, one can expect a properly conducted general anesthetic to produce uneventful emergence from anesthesia and eventual full recovery of preoperative mental function if the surgical procedure contributes materially to the physical and psychological wellbeing or to the social integration of the elderly surgical patient.