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Shilpa Trivedi*
Introduction
The last few years have seen a lot of
technical advances in radiological imaging. The realization of full potential of ultrasound, computed tomography (CT), and magnetic resonance imaging (MRI), have dramatically improved the ability to detect and diagnose diseases. These modalities are now increasingly used for minimally invasive surgeries and for various therapeutic procedures. For example it has now become possible for radiologists using their imaging techniques, to place biopsy needles precisely in various organs to obtain tissue for diagnosis. They are also used while performing neurological procedures like stereotactic location of lesions. All this has increased the need for the anaesthetist’s involvement in the radiology suite to provide general anaesthesia and to advice and assist the management of patients who need to be sedated during these procedures.
Need for the anaesthetist during these procedures
In both diagnostic and therapeutic radiology procedures, the patient must remain immobile and sometimes for long periods (MRI with MRA which may require the patient to be immobile for about 1 to 2 hrs). Patients co-operation is required which may not be possible in case of patients with altered sensorium, patients having severe pain, children, patients with convulsions, with tremors or involuntary movements, anxious or claustrophobic patients, etc. Insertion of needles, catheters, for biopsy, injection of contrast dyes also can affect the patients ability to co-operate and to lie still. CT for cardiac angiography requires the presence of anaesthetists to regulate and monitor the heart rate and various other parameters.
Thus the anaesthetist is required to keep the patient calm, sedated; to take care of the airway, breathing and circulation, to take care of the reactions which may occur due to the procedure or due to the dye injected (like bronchospasm, hypotension, bradycardia, severe anaphylactic reactions or cardiac or respiratory arrest); to regulate the heart rate or to take care of an already tried but failed sedation, etc.
The Anaesthetic procedure
Before the administration of any form of anaesthetic it is important to
- Take an informed written consent
- To check the status of fasting
- To take a detailed history regarding the present illness, hypertension, diabetes mellitus, cardiac problems, bronchial asthma, any allergies to drugs etc.
- It is important to remember that some of these patients are acutely ill and the diagnosis may not have been achieved and thus appropriate treatment may not have been started.
In patients with head injury the fasting status may not be clear and patients may be full stomach and this may increase the risks of aspiration of gastric contents after the sedation.
- Detailed physical examination and assessment of baseline vital signs (temperature, pulse, respiratory rate and blood pressure) and patency of airway has to be done.
- Risk factors for sedation like macroglossia, micrognathia, cyanotic heart diseases, CCF, hypotonia, seizures, bronchospasm, etc. have to be identified.
- Patients undergoing MRI must be asked for the presence of ferro magnetic substances in their body like pacemakers, aneurysm clips, metallic foreign objects in the eye, orthopaedic implants, insulin pumps, etc. as these may be affected due to the magnetic field or they may affect the scan.
- Oxygen supplementation facilities must be available.
ASA Guidelines for monitoring in CT/MRI suite
* Continued presence of a qualified anaesthetist throughout the procedure
* Monitoring of patients oxygenation, ventilation, circulation and temperature
Recommendations –
- Cardioscope- for continuous ECG display
- Pulse oximeter- for oxygen saturation
- Non invasive BP- measures effectiveness of circulation
- End tidal CO2 – early detection of ventilator disconnection.
These ideal conditions are available in very few centres in India and what we have at our disposal is our own five senses with which we - 1. Observe the respiration continuously, 2. Feel the pulse, 3. Observe the colour of the patient for cyanosis.
Anaesthesia Techniques
Different types of anaesthetic agents can be used depending on the type of patient and the procedure to be performed and the facilities available.
1. Verbal Reassurance
Some anxious or claustrophobic patients may be made to lie still just by explaining the procedure to them in details and by reassuring them. The presence of a relative or an anaesthetist with them inside the room may help.
Newer MRI machines which are more open (not enclosed), and more patient friendly are a boon.
2. Analgesics
These are useful in patients where underlying condition is painful.
Common drugs used are injectable diclofenac sodium, pentazocine, fentanyl and tramadol.
3. Sedation techniques
- Syrup Trichlorphos for infants and small children
- Midazolam- (oral, IM and IV) extremely useful. Other drugs used alone or in combination with midazolam are ketamine, propofol and Thiopentone sodium.
Various gradations of sedations are required and can be achieved by using a combination of the various drugs. Whatever the combination it is preferable (though not always possible) to maintain “conscious sedation’ a state in which a patient can respond to verbal commands, can retain protective reflexes and can independently maintain the airway. Deep sedation may be required and is a state in which the patient is not easily aroused and airway reflexes and patency is lost.
4. General anaesthesia
Endotracheal intubation or with laryngeal mask airway—safest method
Maintenance drugs – isoflurane, sevoflurane and muscle relaxants when indicated.
Difficulties encountered
* CT and MRI anaesthesia is actually anaesthesia in a remote location where the facilities of an operating room are not always available.
* Compounded with this are the problems due to the procedure and the bulky CT and MRI machines.
* Limited patient access especially in the MRI room is one of the most important danger.
* Visibility may not be clear because of the lighting in the room.
* Non availability of the trained personnel to the anaesthetist.
* Monitoring equipment interfere with and may degrade the images.
* Need to exclude ferromagnetic components.
* Anaesthesia equipment and monitoring.
This is the biggest problem area for anaesthetist
All equipments have to be MRI compatible, i.e. they all need to be made from non ferromagnetic substances. Every apparatus including the laryngoscopes (its batteries), endotracheal tubes, LMAs, the circuits, the machine itself, the vapourizers used, need to be made from non ferromagnetic substances. Ideally the anaesthetist needs to be involved right from the beginning i.e. while planning the room so as to give idea for the oxygen outlets, suction outlets, etc.
One solution is to use extra long connections and to keep the equipment outside the room.
There is a potential risk of patient burns resulting from current induction in the monitoring leads induced by the oscillating RF fields.
Thus monitoring each physiologic parameter poses its own distinct and unique problems. Even precordial and oesophageal stethoscopes may not function well due to the interference created by the noise of the scanner.
Monitoring interference is not such a big problem in CT scans.
Professional hazards
The main problem in CT is the danger of radiation to the anaesthetist.
In MRI the problem is not so much of radiation but those of noise.
Post procedure
Transferring these sedated patients to a safe place or to their respective hospitals has to be achieved safely. The patients need to be monitored till they are safe to be transferred.
Conclusions
MRI compatible anesthesia machines and equipment are available and infact less than 10% the cost of the MRI. Ideally they should be purchased together as a package. And last but not the least, most of these procedures are considered to be minor and the remuneration provided to the anaesthetist for them is so meager that it does not justify the amount of time, energy, mental tension and above all risks involved.
Anaesthesia for these procedures is a highly skillful job achieved in absolutely unfavourable circumstances for “? peanuts“. This brings in a certain reluctance to conduct these anaesthetics and then it is finally the patient who suffers as he does not often get highly skilled professional service where it is most needed.
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