Anesthesia for magnetic resonance tomography in neonates, infants and young children

Abstract

Since patient cooperation in neonates and infants up to 5 years is always reduced, deep sedation is usually recommended to obtain constant high-quality images during MRI. According to the widely accepted AAP Guidelines, deep sedation is not always distinguishable from general anesthesia, substantiating the demand for state-of-the-art anaesthesia. This is particularly true in this age group, where pharmacokinetics and pharmacodynamics show wide interindividual variation. In this review we outline the techniques required to provide safe and effective patient care in the unique MRI environment. From the viewpoint of induction time, half-life of action and success rate, we have found that inhalation anesthetics and propofol present clear advantages. Both offer rapid induction and emergence, allowing outpatient examinations in a tight schedule with a reliable sedation state. Tracheal intubation or a laryngeal mask airway is required to supply volatile anesthetics and to secure the airway, since propofol in appropriate doses causes respiratory depression and loss of the protective reflexes. Positive-pressure ventilation is recommended since the reduction of tidal volumes by sedative drugs (including high-dose chloral hydrate, barbiturates) may cause atelectasis and decreased oxygen saturation. Several respirators work well outside a critical magnetic field strength of 10 mT (e.g. Draeger: Titus, Siemens: Servo 900). The use of long low-compliance tubing (4-5 m) allows the respirator to be placed at the distal end of the patient table. Sidestream capnometry and spirometry at the proximal tube connector facilitate compensation for losses in tidal volume due to gas compression. Syringe pumps work properly when kept outside the 10 mT line. Some defibrillators (e.g., Lifepac, Physiocontrol) are approved for use in strong magnetic fields. State-of-the-art monitoring is also attainable for high-risk patients, including invasive pressure measurement. Since wiring without special filters may not cross the HF shield of the examination room, hydraulic and pneumatic systems are used (blood pressure by oscillometry, airway monitoring by side-stream spirometry). Optical fibers are used for pulse oximetry. A telemetric EKG is usually provided by the MRT manufacturer. Because oscilloscopes are distorted by the magnetic field, the monitors are placed outside the examination room. In addition, this eliminates the possibility of erasing the EPROMs contained in most monitors. With the setup described, the presence of a second anesthetist within the examination room is superfluous. A second anesthesia team can shorten the time lag between examinations by overlapping induction if a separate anesthesia induction and emergence room is provided. The level of sedation required for MRI in newborn and infants can only be achieved safely and efficiently by general anesthesia performed by trained staff. Complete state-of-the-art anesthesia care can be delivered if appropriate instrumentation is used.