Servicio de Anestesiologia y Reanimacion, Hospital del Mar, Passeig Marítim 25, 08003 Barcelona, Spain
Corresponding author: LTrillo@imas.imim.es
Accepted for publication: January 13, 2003
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Abstract |
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Br J Anaesth 2003; 91: 2902
Keywords: anaesthesia, general; monitoring, auditory evoked potential
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Introduction |
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Case report |
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The patient was awake and alert on arrival in the operating room. Standard monitoring was started and an infusion of lactated Ringers solution was started using a cannula in the back of his left hand.
Three electrodes (A-Line AEP; Danmeter, Odense, Denmark) were then positioned at mid-forehead (+), left mastoid () and left forehead (reference) together with a pair of small headphones to deliver the auditory click stimulus. These were connected to an Alaris AEP MonitorTM. The mean (SD) AAI value before induction was 72.5 (7.8).
Oxygen (100%) was given via a face-mask and anaesthesia induced by administering boluses of propofol 90 mg and remifentanil 60 µg i.v. Cisatracurium 6 mg i.v. was administered to aid tracheal intubation. A slight delay before connecting the tubing for drug administration caused a brief increase in the AAI just after induction of anaesthesia, and the AAI and EMG reached 65 and 50% respectively (Fig. 1). Ventilation was started using a face-mask, and a cannula was then placed in the left foot to continue propofol and remifentanil delivery through two Perfusor® fm pumps (Braun, Melsungen, Germany). The trachea was intubated and the patient was placed in the Kocher position.
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After intubation the AAI value began to fluctuate between 10 and 60, but cardiovascular measurements were stable. Immediately after skin incision, the AAI increased sharply from 20 to 70. Three minutes later the systolic blood pressure increased from 100 to 150 mm Hg. The propofol and remifentanil infusions were increased gradually according to the research plan to 6 mg kg1 h1 and 1.5 µg kg1 min1 respectively, but the AAI, pulse rate and blood pressure did not change. After 5 min, the EMG activity increased suddenly from 0 to 60% and the blood pressure increased to 180 mm Hg. The tubing on the patients foot was checked and it was discovered that the insertion point of the cannula had accidentally come out and no drugs were being infused i.v.
The tubing was promptly fixed and the AAI began to decrease immediately. In 5 min the systolic blood pressure returned to the normal value. Both indicators remained within the normal range until the end of the procedure. Drug infusion was then stopped and the patient woke up 9 min later, when he was extubated.
When questioned after awakening, the patient recalled being aware during surgery, hearing the doctors voices in the operating room and feeling painful manipulations in his throat. He remembered being unable to speak or move before falling asleep again. He was not able to recall the intensity of the pain or the doctors words. A detailed explanation was given to the patient regarding his experience and he reported no further dissatisfaction.
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Discussion |
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An increase in the AAI, particularly when there had been no changes in drug dosage, should have prompted immediate checking of the i.v. delivery system. Because both infusions were outside the vein, the pump alarms were not activated. It was not until the blood pressure had reached 180 mm Hg that a problem with the infusion was suspected.
Measurements of pulse and blood pressure are poor predictors of the hypnotic state during propofol anaesthesia, but the AAI and the bispectral index are useful measures.2 Our observations support this. Each increase in the AAI preceded changes in blood pressure by at least 5 min. The sudden increase in the EMG signal was not accompanied by other clinical signs of lack of muscular relaxation (swallowing, limb movement or airway pressure increase).
Other monitors of depth of anaesthesia are useful when an accidental lack of anaesthetics causes awareness during i.v. and inhalation anaesthesia.7 We also show that monitoring the depth of hypnosis during general anaesthesia adds important information that could help prevent awareness. A prompt response to this information is essential, as awareness can precede haemodynamic changes by several minutes.
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References |
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