الفهرس 
General Anesthesia and Intraoperative AwarenessOnly 14 pages are availabe for public view
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Abstract
SUMMARY
Awareness under general anesthesia can finally be considered as the ”invisible scar of surgery”. This unexpected and undesirable patient wakefulness under general anesthesia has been considered as a source of pain and torture to many individuals after surgery.
The incidence of awareness in general surgical population has been estimated to be 0.1 to 0.2%. A higher incidence is reported for obstetric general anesthesia 0.4% and can increase up to 1.0 to 1.5% in high-risk cardiac surgical patients and trauma cases.
Risk factors for awareness include:
Patient related factors (such as unstable hemodynamics, drug addicts, alcoholics and difficult airway).
Surgical factors (certain types of surgeries such as trauma, obstetric and high risk cardiac surgery) which requires caution in general anesthetic drugs.
Anesthesia related factors related to unbalanced anesthetic technique.
Malfunctioning anesthetic equipments especially that responsible for delivering anesthetic gases or vapors lead to insufficient amount of the anesthetic to ensure patient unconsciousness. Doctor related factors such as negligence, unchecking of the anesthesia machine to detect any errors in vaporizes and ventilators or unattending the patient throughout the operation to detect early the clinical signs of awareness and adjust the concentrations of anesthetic drugs.
The incidence of awareness is considered to be higher in cardiac surgical patients for several reasons:
The use of high-dose opioid techniques with minimal hypnotic drug administration to provide greater neuro-humeral stress ablation and a more stable hemodynamic profile.
Tendency to decrease the anesthetic drugs as cardiac patients are more likely to have impaired cardiovascular function.
The dilutional effects of cardiopulmonary bypass (CPB) may also play a part, especially during rewarming.
Emerging evidence has therefore aroused that intraoperative monitoring of ”depth of anesthesia” can significantly decrease the risk of awareness especially in high risk patients.
The BIS index is the first approved and reliable monitor that enables assessment of the hypnotic component
of anesthesia. The BIS index is a processed EEG parameter calculated from several features of the cortical EEG index. This index uses a dimensionless number scaled from 100 (the awake state) to 0 (deep coma). BIS values of (40 to 60) reflect adequate hypnotic effects and has been established as the proper value for surgical anesthesia.
The aim of the present work was to compare between propofol, and midazolam as sedative-hypnotic during CPB in adult open heart surgery. This comparison will include monitoring the depth of anesthesia using BIS, hemodynamic parameters, and the occurrence of perioperative awareness.
This study was carried on 60 patients of both sexes, ASA II or III physical status between 18 and 70 years of age undergoing elective open heart surgery using CPB. Routine intraoperative monitors were applied to all patients before induction of anesthesia. In addition, BIS index VISTA™ monitor was connected to the patients via BIS Quatro™ sensor which was applied to their forehead before induction of anesthesia.
General anesthesia was standardized in all patients before CPB. During CPB, patients were randomly allocated to lie in two equal study groups. In the first group (30 patients) Propofol infusion was applied to the
cardiopulmonary bypass with a rate of 3mg/kg/hr. While in the second group (30 patients) midazolam infusion of 0.05 mg/kg/min.
BIS index and MAP values were obtained every five minutes during CPB. Also, an auditory stimulus (100dB, duration 60 sec) was presented five times during CPB.
Postoperatively: The patients were mechanically ventilated. The time at which the patients first opened their eyes and respond to verbal stimuli was recorded. The time of extubation was also recorded.
Patients were interviewed on each of the first 2 days after the operation. At the first Interview, they will be asked to describe their experience of anesthesia. At the second one, the patients will be asked specifically about recall of any special sound during the operation.
The study showed the following results:
The bispectral index monitor proved to be useful in monitoring the level of hypnosis in high risk surgeries for awareness.
Propofol or Midazolam infusion given during CPB significantly decreased BIS values to be within 40-60 which is considered an adequate level of hypnosis for
surgery. Although Bis Values in Propofol group was significantly lower than midazolam group, both drugs can be used safely and efficiently to abolish patient awareness during GA for open heart surgery.
No postoperative recall was found in the two groups of patients confirmed by the ―auditory stimulus recall test‖ indicating that this test is a reliable test for awareness.
There were no statistically significant differences between the two groups of patients as regards mean arterial blood pressure, the use of vasoactive drugs during CPB (Nitroglycerin) or post CPB (Adrenaline) although MAP in the midazolam group was slightly higher than propofol group.
There were statistically significant differences between the two groups of patients as regards recovery parameters as the patients in propofol group first opened their eyes postoperatively, and early extubated than patients in midazolam group.
Finally, management and prevention of awareness during general anesthesia for open heart surgery should be feasible and learned to avoid psychological aftereffects especially PTSD and to avoid litigation