Background: Bipolar disorder is a psychiatric condition usually treated with lithium. This drug may display EEG abnormalities which are generally proportional to plasma concentrations: diffuse slow activity, spikes and triphasic waves. This case report describes changes in bispectral index (BIS) values in a lithium-medicated patient with bipolar disorder during general anaesthesia for oncological surgery. Case report: A 60-year old female patient (47kg,1.53m) with bipolar disorder, treated with carbolithium (300mg 3 times a day), was submitted to hysterectomy and retroperitoneal and iliac lymphadenectomy due to recurrent colon cancer. In the operating room, the patient was monitored for cardioscopy, SpO2, NIBP and BIS. Epidural block was achieved with morphine (2mg) and ropivacaine (45mg), followed by sufentanil (20mg), propofol (80mg) and cisatracurium (2.5mg), i.v. She was intubated and maintenance was done with desflurane and remifentanil (effector site). The patient remained with a heart rate of 96- 74 bpm, mean arterial pressure of 109-76mmHg and no significant intraoperative bleeding. BIS values remained low (25-45) and the burst suppression rate (BSR) was ≠ 0 (1-13) despite low targets of remifentanil infusion (0.5-1.2ng/dL) and low end-tidal desflurane concentrations (0.7-1.5%). Recovery was satisfactory, with discharge on the 7th postoperative day.
Discussion: In general, EEG changes induced by anesthetics initially produce excitation and frontal alpha rhythm. As the depth of anesthesia increases, waves become slower and the voltage increases (with the exception of ketamine). The stability of the hemodynamic variables suggest cerebral perfusion was not compromised in our patient, but the lithium neuronal suppressive metabolic effects, associated to toxicity intrinsic of the anesthetics produced low BIS values and BSR ≠ 0.
References: 1. Bauer G, Bauer R. EEG, Drug Efects, and Central Nervous System Poisoning. in: Schomer DL, Silva FHL. Niedermeyer's Electroencephalography: Basic Principles, Clinical Applications and Related Fields, 6th ed., Lippincott Williams & Wilkins, 2011;901-22.
Learning points: Regular use of CNS-altering medication by some patients can lead to EEG abnormalities during anesthesia.

Bispectral index monitoring of a lithium-medicated patient with bipolar disorder