Ketamine與Thiamylal麻醉誘導對雙頻腦波畢氏指數(BIS)之影響

EEG-Bispectral Index Changes with Ketamine versus Thiamylal Induction of Anesthesia

背景：畢氏指數(BIS)是一種經過運算而得的腦波指數，已被認為可用以評估麻醉藥物所造成之睡眠狀態的深淺度。本研究在比較使用ketamine與thiamylal作為麻醉誘導藥物時，兩者造成畢氏指數變化的差異。方法：四十位麻醉體位分級一或二，排定接受常規手術的成年女性，隨機分成兩組。術前不給予任何麻醉藥物。畢氏指數監測使用Aspect A-1050畢氏監測器。第一組使用ketamine 1.5 mg/kg靜脈注射作為誘導藥物，而第二組使用靜脈注射thiamylal 5 mg/kg。使用靜脈注射succinylcholine 1 mg/kg協助插管，插管後，以sevoflurane-nitrous oxide維持麻醉過程。結果：麻醉誘導前，兩組畢氏指數的均數皆為96，給予誘導藥物後一分鐘，第一組為91，第二組為53 （P值< 0.05）。在麻醉誘導後5分鐘，兩組畢氏指數分別為45和37（P值< 0.05)。畢氏指數於麻醉維持過程中，兩組皆在60以下，而於麻醉結束時，回復至95以上。沒有任何病人於手術結束後有回憶，譫妄，或是幻想之情況發生。結論：Ketamine作為麻醉誘導藥物時，畢氏指數會維持在高數值而不會下降，此點與thiamylal誘導所造成之畢氏指數下降有明顯差異。在使用ketamine誘導麻醉時，病人之睡眠狀態與畢氏指數並不相符，在此情況下，畢氏指數並不適合用來做為睡眠狀態深淺之監測指數。

Background: The EEG-Bispectral Index (BIS) is a processed EEG information that has been validated as a means to measure the hypnotic effect of anesthetic drugs. In this study we evaluated the BIS changes in induction of anesthesia with ketamine in comparison with that of thiamylal. Methods: Forty ASA class I and II adult female patients undergoing elective gynecologic surgeries were enrolled into this randomized, prospective study. No premedication was given to the patient. In each patient EEG was recorded continuously from the frontal electrodes using Aspect A-1050 monitor after his arrival at the operating room. Blood pressure and heart rate were also recorded throughout the surgery. After steady baseline recordings of all necessary parameters having been accomplished Group K patients (n = 20) were given an induction dose of ketamine 1.5 mg/kg i.y., whereas Group T patients (n = 20) received thiamylal 5 mg/kg i.y. When loss of consciousness was ascertained, intubation was performed after administration of succinylcholine 1 mg/kg i.v. and anesthesia was maintained with isoflurane-nitrous oxide- oxygen. Demographics, BIS values, HR, BP were analyzed and compared. Results: The demographics were comparable between the two groups. Both groups showed a mean value of BIS of 96 with comparable BP and HR before induction. After study drug the post-induction BIS for ketamine was 94 as against 51 for thiamylal (P < 0.05), 91 against 43 post-succinylcholine (P < 0.05), 92 against 53 post-intubation (P < 0.05) and 45 against 37 five min after isoflurane. BIS remained below 60 throughout the entire course of anesthesia and returned to above 95 on emergence in both groups. None of the patients reported awareness, recall, delirium or hallucination during anesthesia. Conclusions: Ketamine - induced dissociative anesthesia produces persistently elevated BIS index which is different from thiamylal and those reported with other conventional anesthetic agents. The established range of BIS index appears not to be applicable in patients under ketamine anesthesia. Monitoring the depth of ketamine anesthesia remains to be a challenging problem.