MRI and Anesthesia

A working protocol for MRI under general anesthesia.

M.P. Boidin MD, PhD, G.R. Wolff MD, C. Doelman MD
Afdeling Anesthesiologie
Amphia Ziekenhuis Breda
Breda, The Netherlands

Email: mpboidin@wanadoo.nl

The article also available in PDF: 74KB

Introduction

This is a report of our "Protocol 2002" which describes our dual stage anesthesia set-up with an introduction area outside the shielded MRI room, and an antimagnetic ventilator with monitor inside the room near the magnet. In the induction area, there is anesthesia cart with a Servo ventilator (Siemens), suction device and monitor Sirecust 1280 (Siemens). To serve the nurse anaesthetist there is a material cart for anesthesia equipment and a children's cart for small children’s equipment. In the RF shielded MRI room there is a ventilator Aestiva-MRI (Datex Ohmeda) a suction device and a MRI compatible monitor. The ventilator and monitor are designed for MRI compatibility but may nevertheless become attracted by the magnet. The force of attraction may be so strong that people and materials may be damaged if the equipment is not secured properly.

In the Amphia Ziekenhuis, four severely mentally retarded children or adult patients with different indications can be scheduled for MRI investigations under general anesthesia every month. In the past ten years, 250 children and fifteen adults have been served that way.

Indications for MRI under general anesthesia

Compared to X-ray techniques, the advantage of MRI diagnostics is that it can differentiate other tissues in the human body than X-ray. MRI is the method of choice where differences in the water content makes it possible to differentiate different tissues. Herniated inter-vertebral discs in the spine, soft tissue tumours in muscles, menisci in the knee joint and intracerebral pathology are the most frequent reasons for MRI. MRI is practically a non-invasive method. Hence, there are only a few indications to perform MRI in general anesthesia. The reasons include uncontrollable restlessness, severe mental retardation, psychological (fear) and psychotic syndromes that would else result into poor quality images.

Sedation or general anesthesia

In a study from London, there was a series of 1155 MRI sedations and a failure rate of 1% for chloral hydrate sedated small (5-10kg) children. Of these children 8 % needed additional intravenous sedatives. In the group of children over 10 kg, 30 % needed additional intravenous sedatives. Over 7 year-old-children can often comply with instructions to remain still. However, children with learning difficulties or claustrophobia often needed deeper level of sedation [1]. Therefore, general anesthesia is often indicated to increase safety, to improve quality of imaging, to increase the comfort of patients and for the improvement of logistics of the MRI suite [2–4]. Sedation is an option only in healthy patients who can tolerate diagnostic procedures. In very small children, general anesthesia is preferred in many cases, particularly in children with severe mental retardation. Children with severe neurological disorders frequently have accompanying diseases, hence, they must be adequately monitored, also when "only" sedation is used - in our opinion, monitoring is valuable even when no sedation is given.

Preparation

Standard laryngoscopes, monitors and ventilators are not allowed in the RF shielded MRI room. Therefore, we have designed a dual stage anesthesia system. An induction room and the place where the actual MRI take place have a different set of equipment. A classical anesthesia set-up is realised in the induction room of the MRI, whereas only special MRI compatible instruments are allowed inside the shielded MRI room. Our MRI device is a Signa Horizon LX 1,5 Tesla of GE Medical Systems. In the MRI suite, there are wall sockets for oxygen, nitrous oxide, air, suction, and a scavenging system. There are wall sockets for medical gases and electric outlets both inside the shielded room and in the induction room outside.

Nota bene

Before anesthesia personnel are allowed to enter the MRI room, they must empty their pockets. No iron items are allowed. Hence, metal keys, bank cards, ID's, watches, metal rolls for tape, pagers and mobile phones are all kept in lockers outside.

Planning the care

The departments for paediatrics and for internal medicine first meets children or adults, and are responsible for proper pre-treatment. Patient history and therapy plan needs to be evaluated before MRI. Patients may have a small breakfast if they are scheduled for the afternoon. When all prerequisites are fulfilled the patients will arrive in one of hospital’s day-surgery departments. MRI patients do not get any pre-medication, but take their own drugs as indicated. If no complications occur, the patients return home having been awake for two hours. Although some other departments might use benzodiatsepines for sedation, there might still be some residual effect after two hours, and that may prevent their use. Opioids are not indicated in MRI, because there is no pain involved in this procedure. Before anesthesia for MRI in our department, no solid food is allowed for four hours, but clear fluids the patients are allowed to drink still two hours before. After the scan, as they wish, they might get clear fluids, bread, butter and cheese or marmalade.

Induction of anesthesia before the MRI begins

Patients are asked to come to the MRI induction area. Children are induced in their own beds and the adults are placed on the special MRI patient cart. The parents of children are invited to join their children in the induction area. Patients are connected to the ECG, pulse oximetry, temperature and NIBP monitor. Adults get an intravenous drip on the back of their hands, ensuring that the IV access remains accessible during MRI. Small children are "put asleep" with bag and mask using Sevoflurane (Sevorane, Abbott) using the quick induction technique. In adults induction usually starts with intravenous propofol, methyl atropine and rocuronium bromide. Patients are intubated, connected to the ventilator and stabilised. For maintenance of anesthesia, Sevoflurane in air and oxygen is used. When patients are stable, having normal saturation, blood pressure and ECG, they are prepared for transfer to the MRI room. Before transfer, however, all such procedures that require anesthesia can be performed, e.g. arterial or lumbar puncture. No extra intravenous fluids are administered to patients.

Moving the patient to the MRI room

In the MRI room, patients are connected to the monitor and Aestiva ventilator. All patients have their ears protected with earplugs. Because there is heavy ventilation in the MRI room to keep the temperature in the magnet at a constant level, patients are wrapped in blankets. This prevents convection, decreased temperature and shivering after the procedure. When the patient is placed into the MRI instrument, the only visual contact is the monitor display. Oxygen, air and sevoflurane are continuously administered. On the MRI compatible monitor, physiological and ventilation parameters are displayed, including pressure and volume of ventilation, pressure/volume loop, inspiratory and expiratory oxygen concentration and capnography. Physiologic parameters, NIBP, pulse oximetry and heart rate are measured. The monitor is placed near the window of the MRI unit so that it is optimally visible from behind the MRI main console. The anesthetist and the nurse anaesthetist maintain their normal anesthesia records.

End of the session

When MR imaging is complete, administration of sevoflurane is discontinued. Usually, the patient then awakens in 3 to 5 minutes. When the patient is awake and breathes spontaneously, the ET tube is removed and the patient is transferred to the induction room. There, he is placed in his own bed and transported by the anesthetist to the recovery room of the OR area.

The nurse anesthetist prepares the induction room for the next patient. Patients leave the hospital approximately two hours after they wake up from anesthesia. They drink at least one cup of water and they are offered something to eat before they leave the hospital. When indicated, they get drugs to counteract vomiting and nausea. Approximately 7 % of these patients show some amount of postoperative nausea or vomiting (PONV). The day surgery nurses have standing orders on how to handle problems after minor surgery and diagnostic procedures, such as MRI investigations. Post-spinal headache has been observed twice and both cases had spontaneous remissions. In case of doubt or when patients show extraordinary physiologic signs the anaesthetist is always the first medical specialist who is called upon, and a patients having any problems can always stay overnight in the hospital when necessary.

Lessons learned

In the past eight years approximately 250 children and 15 adult patients were treated in this way. It proved possible to enter the MRI room at any time, which facilitated observation of the patient and quick care if any threatening situations would have occurred. We found it possible to evacuate the patient from the MRI instrument within half a minute; transfer to the safety of the induction room could be completed within one minute. As soon as the MRI room door opens the measurements will stop, but they continue when the door again closes.

Special topics that require attention

Metals: The tiny metal spring within the valve of the cuff-pilot is a source for concern. This tiny spring produces a black information hole with a diameter of 5 cm in the imaging. For children under ten years an ET tube without a cuff is applied. Larger children and adults get ET tubes with a cuff. The cuff pilot drops from the angle of the mouth down in the area of measurement. The small brain parts, or the cheek and sinuses are excluded from imaging when the cuff pilot is near the skin. The solution is to tape away the cuff pilot with the tube and the ventilator tubes. The same is applicable for iron buttons in pyjama's and other (baby) clothing. When ECG electrodes need to be positioned in the imaging area, they have to be replaced with special carbon MRI electrodes. The imaging is not influenced when very small iron or iron-like objects are well out of the way.

Communication with the patient: It appears not to be reasonable to require the attendance of personnel in the MRI room, near the patient. The combination of noise and isolation would make it difficult to concentrate for long time periods. Therefore, it was decided that observation of the patient should be performed from behind the main console through a wide screen window. Even inside the MRI room, it would be hardly possible to observe the patient closely, because he is wrapped up in blankets. When people want to stay in the MRI room during measurements, ear protection is necessary. In the case of (simple) stable anesthesia and well-monitored patients it appears sufficient to observe the patient through the MRI room window. It is possible at any time to enter the room without danger to the personnel or the patient.

Objects: Metal objects in the MRI room are potentially dangerous. A strict protocol is directed towards safety for patients and personnel. Every individual has his own responsibility, but when one is not accustomed to working in a strong magnetic field, people should be forced to a strict protocol. Metal objects can be displaced from the pockets of people and swept to the interior of the magnet with increasing speed. The interior of the MRI instrument can be damaged, the patient or the personnel can be hurt and the iron objects can be damaged.

Sedation: Considering the chance of morbidity and even mortality during sedation, adequate monitoring is necessary. The monitor used in general anesthesia in MRI is also applicable for sedated children. Easy logistics and planning should enable all personnel involved in MRI to get access to this instrument. Not only should patients be connected to the monitor, there should also be a trained nurse be present to observe the vital parameters. Training in the operating room to handle the monitor is a prerequisite. When sedation fails and MRI is still necessary, general anesthesia should be considered.

Literature:

1. Shepherd JK, Hall-Craggs MA, Finn JP, Bingham RM. Sedation in children scanned with high-field magnetic resonance; the experience at the Hospital for Sick Children, Great Ormond Street. Br J Radiol 1990; 63: 794-797
2. Malviya S., Voepel-Lewis T., Eldevik O.P., Rockwell D.T., Wong J.H., Tait A.R.. Sedation and general anaesthesia in children undergoing MRI and CT: adverse events and outcomes. BJA 2000; 84(6): 743-748.
3. Hollman GA, Elderbrook MIK, Van Den Lagenberg B.. Results of a pediatric sedation program on head MIRI scan. Success rates and procedure duration times. Cli Pediatr 1995; 34: 300-305
4. Cote' C.J. Sedation for the pediatric patient. A review. Pediatric clinics of North America, 1994; 41: 31-58.
5. Lawson G.R. Sedation of children for magnetic resonance imaging. Arch Dis Child 2000; 82: 150-153.
6. Wellis V., Practice guidelines for MRI & MRT. StanfordUniversity, Ped. Anesth. and Pain Man. http://pedsanesthesia.stanford.edu/guide/guideline-mri.html

Last updated: 1 August 2002Created
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