**4.2 Anesthetic consideration in a pediatric patient with MMD**

Pediatric patients with MMD have a higher baseline cerebral metabolic rate of oxygen consumption and thus poorly tolerate any reduction in cerebral blood flow. Therefore, these children should be maintained with a normal or higher than normal mean arterial pressure; normocapnia to prevent hypocapnia mediated cerebral vasoconstriction and also prevent hypercapnia leading to cerebral blood flow steal phenomenon; adequate hydration; analgesia; and normothermia [15].

Pre-operatively children have undergone workup for neurological symptoms such as cerebral vascular imaging (MRI or MRA) and are typically on anti-platelet or anti-seizure medications. Additionally, these children are on medication (such as midodrine) that keeps the blood pressure up as these stenotic cerebral arteries depend on high blood pressure, and any medication that decreases the blood pressure can be detrimental. Children are usually anxious from possible parental separation; may benefit from the use of pre-anesthesia anxiolysis as well as the comforting presence of the parent in the operating room or virtual reality (music etc). Crying can lead to hyperventilation and hypocapnia. Additionally, these patients must be kept well hydrated to allow for adequate blood volume in the context of anesthesia-induced vasodilation. Since these patients are nil-per-oral, they should be given intravenous fluids of around one and half times their maintenance requirements pre-operatively. Also, a thorough history and physical examination necessary to determine any other associated conditions such as sickle cell disease, neurofibromatosis type 1, and trisomy 21.

Intra-operatively, these children may be induced intravenously if they have an intravenous line in place or by inhalation. Outcomes for induction are similar for both these approaches provided the blood pressure and ventilation is maintained. Intravenous maintenance with combined propofol and remifentanil may be better compared to inhalational maintenance as studies have shown reduced cerebral oxygenation with inhalational agents perhaps due to the cerebral steal phenomenon [42, 43, 73]. Phenylephrine infusion is utilized to maintain the mean arterial pressure. Hyperventilation and hypoventilation must be avoided as they are associated with negative outcomes. Sympathetic response to laryngoscopy and intubation must be blunted with intravenous lidocaine, opioid, or short-acting beta-blockers. To maintain blood pressure and ventilation, it is essential to monitor these patients with an invasive arterial line, pulse oximetry, capnography, ECG, and temperature. Additionally, intra-operative EEG is recommended. A urine catheter to monitor urine output with careful monitoring of fluid balance is needed to maintain normovolemia. Central venous access is rarely required but can be utilized in patients with difficult intravenous access. Intravenous fluids must not contain glucose.

Post-operatively, smooth extubation with adequate analgesia, hydration, and normothermia is necessary as not to potentially jeopardize cerebral blood flow. Patients who have undergone indirect revascularization are still at risk of post-operative stroke. Analgesia must be maintained usually with an opioid-based patient-controlled technique supplemented with other analgesics such as acetaminophen. Anti-emetics must be given to prevent nausea or vomiting. Recovery must be ideally carried out by trained pediatric intensive care nurses experienced in managing Moyamoya disease. Transfer of care to a high dependency unit is recommended after recovery.
