A 7-year-old female presents for Gamma Knife treatment of a right thalamic arteriovenous malformation.
The preoperative evaluation of such a patient is similar to that of any patient undergoing a procedural anesthetic. The parents should be made aware of the possible long duration of such a procedure and the potential risks of transporting a sedated or anesthetized individual from site to site.
Preparation for such a case is complicated by the need to prepare multiple non-operating room anesthetic sites, typically MRI (occasionally CT) and often neuroangiography for the planning stage as well as the Gamma Knife suite for treatment. Often there may be a significant delay between the planning and the actual treatment as the necessary calculations are made and reviewed. It is not unusual for such treatment to take several hours to the better part of a day.
This process must be scheduled and coordinated in advance so that there is minimal or no waiting time at each site.
Once it is in place, the stereotactic frame may obscure the airway, making mask ventilation or intubation impossible. The tools necessary to disassemble the frame must be with the patient at all times during planning, treatment, and transport to allow for ready access to the airway. For some frames partial disassembly to obtain emergency airway access or to optimize the head position for ventilation, will result in loss of coordinates and resimulation may be necessary. Some newer frames do allow partial airway access. You must be familiar with the specific frame being utilized, and staff members who are knowledgeable about its assembly and disassembly must be at the bedside. In an emergency, a laryngeal mask airway can sometimes be passed with the frame in place, and the patient can be ventilated through an attached flexible connector.
Since the patient will require MRI scanning, meticulous attention must be paid to avoid bringing ferrous materials or other non-MRI-compatible equipment such as oxygen tanks, monitors, leads, or probes into those restricted areas.
Local anesthesia in an awake patient, sedation, and general anesthesia, administered alone or in combination with local anesthesia, have all been utilized for this procedure.
For adults and cooperative older children or teenagers, anesthesia is not usually required. Midazolam is administered for anxioly-sis (0.05-0.1 mg/kg), and an opioid such as fentanyl (0.25-1 μg/kg) is given incrementally. Local anesthesia (usually a 1:1 mixture of 2% lidocaine and 0.5% bupivacaine, not to exceed a toxic total dose) is injected at the pin sites where the stereotactic frame is applied.
In older patients a propofol infusion (approximately 25-75 micrograms/kg/min) may be utilized for sedation (monitored anesthesia care) or, alternatively a maintenance infusion of dexmedetomidine at a rate of 0.05-0.7 mcg/kg/h (boluses of dexmedetomidine are often avoided in young children because of the risk of bradycardia) ...
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