P rimary brain tumors rarely present during pregnancy. 1 Awake craniotomy is often indicated for procedures requiring intraoperative monitoring of speech or motor function to facilitate tumor resection while minimizing the risk of compromising neurologic function. Anesthesia options include monitored anesthesia care or general anesthesia with intraoperative awakening. Propofol, used alone or in combination with a short-acting opioid, is commonly used for sedation during awake craniotomy, but

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... ients are at risk for respiratory depression with this technique. Dexmedetomidine is an α2-adrenergic receptor agonist that can be used for sedation during craniotomy requiring intraprocedural speech or motor functional mapping. 2 The advantages of dexmedetomidine in this setting include titratable sedation and analgesia with minimal respiratory depression. The management of increased intracranial pressure and volume can be critical to the outcome of neurosurgical procedures. Mannitol produces a reduction in intracranial volume by creating an osmotic gradient across the blood-brain barrier, causing water to leave the brain and enter the intravascular space. To our knowledge, the effect of mannitol use during pregnancy on intrauterine volume and fetal well-being has not been described. 3 Complications may arise from induction of a dehydrated maternal state resulting in hypotension and uterine hypoperfusion, potentially leading to fetal injury and fetal dehydration. 4 Because anesthesia providers may be requested to administer mannitol to patients in the perioperative period, it is critical to understand the impact of this drug on uterine fluid status and fetal well-being. Anesthetic drugs such as dexmedetomidine can potentially affect uterine fluid status, uterine contractility, and fetal well-being, possibly influencing the effect of mannitol on the uterofetal unit. We describe the use of dexmedetomidine for a craniotomy requiring intraprocedural speech and motor mapping during pregnancy. We also quantify the effect of perioperative mannitol on intrauterine volume and fetal well-being during this procedure. The patient provided consent to allow the use of her medical information for research and publication. CASE DESCRIPTION A 27-year-old gravida 2, para 1 woman at 7 weeks of gestation developed new-onset seizure as well as mild receptive and expressive aphasia. Imaging was deferred until the second trimester of pregnancy, and magnetic resonance imaging without contrast, completed at 16 weeks of gestation, demonstrated a relatively circumscribed intra-axial mass in the posterior superior left temporal lobe measuring 4.5 × 3.2 × 3.5 cm (Fig. 1) . The posterior margin of the tumor was adjacent to Wernicke area. She was referred to our institution at 19 weeks of gestation for neurosurgical consultation and was subsequently scheduled for a left frontotemporal craniotomy with intraprocedural motor and speech mapping for resection of the tumor at 20 weeks of gestation. The patient weighed 70 kg and her height was 172 cm (body mass index 23.8 kg/m 2 ). Given that the effect of mannitol on intrauterine volume or fetal well-being has not been well described, it was decided, in consultation with the patient, that fetal assessment and intrauterine volume assessment would be obtained before surgery and at repeated intervals after surgery and during hospitalization. Informed consent to assess intrauterine volume was obtained from the patient before measurements. The institutional review board deemed this report exempt from research approval because the ultrasonography assessments, including intrauterine volume assessments, were part of the patient's plan of care. The uterine volume measurements were obtained using abdominal ultrasonography immediately before surgery, in the postanesthesia recovery unit immediately after surgery, on the morning after surgery, and on the second postoperative day by the same individual (BCB). We describe the use of dexmedetomidine for an awake neurosurgical procedure in a pregnant patient and quantify the effect of mannitol on intrauterine volume. A 27-year-old woman underwent a craniotomy, with intraprocedural motor and speech mapping, at 20 weeks of gestation. Sedation was maintained with dexmedetomidine. Mannitol at 0.25 g/kg IV was administered to control brain volume during surgery. Internal uterine volume was estimated at 1092 cm 3 before surgery and decreased to 770 and 953 cm 3 at 9 and 48 hours, respectively, after baseline assessment. No adverse maternal or fetal effects were noted during the intraoperative period or up to 48 hours postoperatively.