大腦是麻醉的標靶器官。麻醉過淺可能會導致創傷性術中覺醒；而麻醉過深會誘發血流動力學不穩定，增加術後譫妄和認知功能障礙的風險。老年手術病人經常出現術後譫妄（POD），其定義為認知和注意力的急性障礙。術後譫妄病人常會進展成認知障礙的慢性階段，即術後認知功能障礙（POCD）。術後譫妄和術後認知功能障礙都與術後併發症率、住院時間和死亡率增加有關。
　　手術後的全身炎症反應可導致各種器官損傷/功能障礙，包括認知障礙。揮發性麻醉劑已被證明可激活線粒體凋亡途徑，抑制神經新生並降低神經傳遞的功效。此外，全身麻醉劑會引起腦血管內皮細胞的結構變化並增加血腦屏障通透性，因而破壞腦血管屏障的完整性。總體來說，手術和麻醉都會影響大腦功能。大腦衰老的變化包括大腦質量減少、有髓神經纖維萎縮引起的白質減少、突觸連接下降引起的皮質密度變薄和神經傳遞缺乏。所有這些變化都會導致認知和記憶力下降。老化的大腦較易受到手術創傷和麻醉的不利影響，導致術後譫妄和術後認知功能障礙。
　　施行一級預防術後譫妄和術後認知功能障礙優於治療。術後譫妄和術後認知功能障礙的病因包括手術、麻醉和病人的相關因素。藉由使用己處理的腦電圖 （pEEG）的麻醉深度監視器引導的精確麻醉似乎是預防術後譫妄和術後認知功能障礙的一種方法。此外，有研究發現接受非心臟手術的老年病人採行pEEG 引導麻醉也可減少術後疼痛、減少止痛藥需求和減少術後噁心/嘔吐發生率。M-Entropy™（熵引導）是一種運用己處理腦電圖pEEG的麻醉深度監測器。我們發現接受常規非心臟手術且術後使用靜脈自控式止痛的病人，術中的熵引導麻醉監測可有效地降低術後譫妄發生率，雖然熵引導的麻醉操作並沒有減少術後疼痛、術後鎮痛劑需求量和術後噁心/嘔吐發生率。總體而言，通過麻醉深度監測去施行“精準”麻醉，可使病人受益。
　　麻醉醫師應該提供病人大腦一個特殊照顧：通過精準麻醉、減少傷害。
　　The brain is the target organ of anesthesia. Inadequate anesthesia may induce traumatic intraoperative awareness; whereas, excessive anesthesia causes hemodynamic instability and increase the risk of delirium and cognitive dysfunction. Elderly surgical patients frequently experience postoperative delirium (POD) which is defined as an acute disturbance in cognition and attention. POD patients may develop a chronic phase of cognitive impairment (postoperative cognitive dysfunction, POCD). Both of POD and POCD are associated with increased morbidity, hospital length of stay and mortality.
　　Systemic inflammatory responses following surgery can cause various organ injury/dysfunction including cognitive impairment. Volatile anesthetics have been shown to activate mitochondrial apoptosis pathway, suppress neurogenesis and decrease neurotransmission. General anesthetics induce structural changes in brain vascular endothelial cells and increase blood-brain barrier permeability resulting in disrupting integrity of the blood-brain barrier. Collectively, both of surgery and anesthesia affect the brain functions. Aging changes in the brain include decreased brain mass, reduced white matter due to shrinkage of myelinated nerve fibers, thinning cortical density due to declining synaptic connections and neurotransmitters deficiency. All of the changes play a role in declining cognition and memory. The aging brain may be vulnerable to the detrimental effects of surgical trauma and anesthesia leading to POD and POCD.
　　Primary prevention of POD and POCD is superior to treat it. The etiology of POD and POCD includes surgery-, anesthesia-, and patient-related factors. Precision anesthesia guided by a monitor of anesthetic depth based on the processed electroencephalogram (pEEG) seems a way to achieve the prevention of POD or POCD. In addition, pEEG-guidance anesthesia was found to be associated with reduced postoperative pain, decreased analgesic requirements and less postoperative nausea/vomiting in elderly patients undergoing non-cardiac surgery. M-Entropy™ is an anesthetic pEEG monitoring. We discovered that entropy-guided anesthesia decreased the incidence of POD although pEEG-guided anesthesia did not reduce postoperative pain, postoperative analgesic requirements and postoperative nausea/vomiting in elective non-cardiac surgical patients receiving intravenous patient-controlled analgesia. Overall, patients will be benefit from “precision” anesthesia via the anesthetic depth monitoring.
　　Do Patients’ Brain a Favor: Do Less Harm via Precision anesthesia.