Intraoperative auditory evoked potential recordings are more reliable at signal detection from different sensor sites on the forehead compared to bispectral index.

Bispectral index (BIS) and auditory evoked potential (AEP) monitoring require the attachment of forehead sensors, posing difficulties when the surgical field involves the forehead. This study analyzed the relationship between BIS values and AEP indices from different sites on the head to establish alternative sensor locations for AEP recording. Thirty patients scheduled for elective surgery under sevoflurane anesthesia were randomly assigned to the forehead, nose or mandible groups (n = 10 patients per group). AEP sensors were placed at the assigned position for each group and BIS sensors were placed on the forehead. BIS value and AEP index were simultaneously recorded from induction until emergence from general anesthesia. Relationships between BIS values and AEP indices were analyzed using a regression method and compared between groups using Pearson's correlation coefficients. Square regression models better expressed the relationships than linear models in all groups. The z-transformed coefficient in the forehead group was the same as the nose group (p = 0.24) and significantly different in the mandible group (p = 0.0046). These findings suggest that AEPs can be accurately recorded from sensors placed on the nose. Nasal AEP might be useful for monitoring electrical activity in the brain during surgeries involving the forehead.

Efficacy and Safety of a Lidocaine and Ropivacaine Mixture for Scalp Nerve Block and Local Infiltration Anesthesia in Patients Undergoing Awake Craniotomy.

BACKGROUND: Mixtures of various local anesthetics, such as lidocaine and ropivacaine, have been widely used. However, their efficacy and safety for scalp nerve blocks and local infiltration during awake craniotomy have not been fully elucidated. METHODS: We prospectively investigated 53 patients who underwent awake craniotomy. Scalp block was performed for the blockade of the supraorbital, supratrochlear, zygomaticotemporal, auriculotemporal, greater occipital, and lesser occipital nerves with a mixture containing equal volumes of 2% lidocaine and 0.75% ropivacaine, including 5 µg/mL of epinephrine. Infiltration anesthesia was applied at the site of skin incision using the same mixture. The study outcomes included changes in heart rate and blood pressure after head pinning and skin incision, and incidence of severe pain on emergence from anesthesia. Total doses and plasma concentrations of lidocaine and ropivacaine were measured at different time points after performing the block. RESULTS: The heart rate and blood pressure after head pinning were marginally, but significantly, increased when compared with baseline values. There were no significant differences in heart rate and blood pressure before and after the skin incision. Nineteen percent of the patients (10/53) complained of incisional pain at emergence from anesthesia. The highest observed blood concentrations of lidocaine and ropivacaine were 1.9±0.9 and 1.1±0.4 µg/mL, respectively. No acute anesthetic toxicity symptom was observed. CONCLUSIONS: Scalp block with a mixture of lidocaine and ropivacaine seems to provide effective and safe anesthetic management in patients undergoing awake craniotomy.

[Ultrasound Analysis of the Anatomical Relationships between Vertebral Arteries and Internal Jugular Veins in Adults].

BACKGROUND: Accidental puncture of a vertebral artery can occur through the internal jugular vein during central venous catheterization. METHODS: We evaluated the anatomical relationships between vertebral arteries and internal jugular veins in one hundred adult patients under general anesthesia using echo image. RESULTS: The vertebral artery could be observed in all patients under the level of cricoid cartilage. Vertebral arteries ran in an outward direction toward the caudal side (3.9 mm lateral and 14.6 mm deep from the internal jugular vein : median). Mean width of vertebral artery was 4.2 mm. Because the width of central venous catheter guide wire is approx. 1 mm, accidental puncture of a vertebral artery can occur through the internal jugular vein during central venous catheterization. By the use of ultrasound analysis, the vertebral artery could be observed completely. CONCLUSIONS: It is important to identify the location of vertebral arteries under the level of cricoid cartilage and avoid the tap toward the lateral side. We can avoid accidental puncture of vertebral artery by taking care of these points.