ACE 19B Sample Question
An 81-year-old man undergoes surgery with general anesthesia. He is maintained on 2.0% end-tidal sevoflurane with 50% oxygen in air. His blood pressure is 100/60 mm Hg and his heart rate is 74/min. He is given 50 µg of fentanyl for analgesia. A processed electroencephalogram (EEG) was applied. Based on the EEG below, which of the following would be the MOST appropriate next action?
A. Administer muscle relaxantX
B. Decrease sevoflurane ✔
C. Administer fentanyl X
Read the discussion below.
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Monitoring the intraoperative processed electroencephalogram (EEG) may be useful in avoiding anesthetic overdose, particularly in older patients. The most obvious EEG feature of excessive anesthesia is burst suppression, which is easily seen on the EEG trace in the clinical scenario. In the density spectral array spectrogram, the periods of suppression appear as sharply defined perpendicular stripes of colder colors (blue or black). The burst suppression ratio, defined as the fraction of the EEG spent in suppression per epoch, measures the fraction of time during a given interval that the EEG is suppressed (74 in the trace shown). Decreasing the sevoflurane is the most appropriate next action in this scenario to decrease burst suppression and raise blood pressure.
Although an association has been observed between the duration of EEG suppression and subsequent delirium, which may be especially relevant to older and frail patients, it is not yet clear if prolonged EEG suppression is harmful. The anesthetic requirement decreases by 6% to 8% per decade after the age of 40 years. The estimated minimum alveolar concentration for an 81-year-old patient is approximately 1.4% sevoflurane; thus, the dose of 2.0% sevoflurane described in the clinical scenario may be excessive.
The appearance of burst suppression is indicative of excessive anesthesia and is not a response to a noxious stimulus. Thus, the administration of fentanyl would not be appropriate.
The need for muscle relaxation should be guided by monitoring of neuromuscular blockade, not processed EEG.
- Gropper MA, Cohen NH, Eriksson LI, Fleisher LA, Leslie K, Wiener-Kronish JP, eds. Miller’s Anesthesia. 9th ed. Elsevier; 2020:693.
- Purdon PL, Sampson A, Pavone KJ, Brown EN. Clinical electroencephalography for anesthesiologists: part I: background and basic signatures. Anesthesiology. 2015;123(4):937-960. doi:10.1097/ALN.0000000000000841
- Hight DF, Kaiser HA, Sleigh JW, Avidan MS. Continuing professional development module: an updated introduction to electroencephalogram-based brain monitoring during intended general anesthesia. Can J Anaesth. 2020;67(12):1858-1878. doi:10.1007/s12630-020-01820-3
- Mapleson WW. Effect of age on MAC in humans: a meta-analysis. Br J Anaesth. 1996;76(2):179-185. doi:10.1093/bja/76.2.179
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