This case report represents two issues of clinical importance. First, the EEG of this elderly patient with septic shock showed apparent abnormal patterns before anesthesia induction through surgery. Second, the neurological behaviors, such as delirium, of this patient with abnormal EEG may have been induced by perioperative invasion. Therefore, intraoperative cEEG monitoring may predict SAE even if septic shock patients do not have any symptoms.
The BIS of our patient was 30 and EEG displayed slow waves without burst and suppression before anesthesia induction, indicating that she already had SAE at that time. In patients with delirium, routine EEG commonly shows an increased slow-wave activity and a slow and disrupted alpha rhythm [3,4,5,6]. Nielsen et al. revealed that delirious episodes in patients with sepsis are associated with the disappearance of high-frequency electrographic cEEG activity and increased in power of low-frequency activity . They also reported the association of EEG and the Confusion Assessment Method for the Intensive Care Unit (CAM-ICU). Normal CAM-ICU scores were associated with continuous or nearly continuous high-frequency cEEG beta activity, preserved cEEG reactivity, and normal cEEG background activity. Conversely, patients with CAM-ICU scores of delirium exhibited a suppressed background cEEG actively. The suppressed cEEG was not observed in any patient without delirium. Although there are reports of patients with sepsis in the ICU , there are few reports of EEG during anesthesia in patients with sepsis.
Cerebral rhythmic EEG activity reflects the cortical neurons’ ability to synchronize input from thalamocortical and corticocortical neurons. Generation of high-frequency cortical activity requires fast spiking of high energy–demanding somatostatin-positive interneurons .
Ketamine is commonly used for patients with shock. Ketamine, which is an N-methyl-d-aspartate antagonist, activates the EEG, despite its sedative effects. Some features of EEG activation by ketamine, such as increases in β-activity, BIS, and SEF95, have already been described . Ketamine also increases the alpha peak frequency, with simultaneous shifting of the bicoherence peak . In this case, such features could not be observed, despite performing TIVA with ketamine as the primary anesthetic.
The abnormal neurological behaviors of this patient may have been induced by not only sepsis but also surgical invasion. Elderly patients with sepsis may be sensitive to anesthetics. An aged brain is significantly vulnerable to immune stimuli compared with a younger brain. Microglia of the aged brain take on a “primed” or “sensitized” phenotype, characterized by dystrophic morphology, progressive accumulation of metabolic stress, increased cell-surface expression of antigen recognition molecules, and an exaggerated inflammatory response to immune challenge . Primed microglia show an increased production of proinflammatory cytokines in response to immune stimulation with a peripheral inflammatory challenge . This patient’s EEG might reflect neuroinflammation. Her neurological behaviors with abnormal EEG may have been induced by surgical invasion and preexisting gastrointestinal perforation itself. Perioperative procedures requiring general anesthesia prolonged neuroinflammation, probably resulting in delirium. The initial processes involved in SAE could lead to cerebral damage ; hence, it is important to detect the presence of SAE earlier.
In conclusion, intraoperative cEEG monitoring in elderly patients with sepsis may be useful to predict SAE. The applicability of BIS monitoring for assessing the depth of anesthesia in elderly patients with sepsis should be performed carefully. Predicting SAE from perioperative EEGs may help improve neurological outcomes.