Anesthesia for MRI and Radiological Procedures - A Detailed Review

Introduction:

Interventional radiological procedures like MRI (magnetic resonance imaging) and CT (computed tomography) scans demand patients to be still during the procedure to avoid artifacts caused by moments. Patients with certain conditions that prevent them from staying still in the regular interventional radiological procedures like MRI machines, such as claustrophobia, anxiety, or a condition that causes physical pain, may require anesthesia. It is also common for children to have anesthesia for such procedures since it is often difficult for them to remain still.

What Are the Radiological Procedures Which Require Anesthesia?

1. Magnetic Resonance Imaging (MRI):

• Magnetic resonance imaging (MRI) is based on the interactions between a static magnetic field generated by the scanner and the tiny fields that arise from individual atomic nuclei.

• MRI produces particularly good images of soft tissue and provides greater contrast between different types of tissue than other imaging modalities.

• Magnetic resonance imaging (MRI) is a frequently used technique that produces particularly good images of soft tissue, providing greater contrast between different types of tissue than computerized tomography scans.

• It is used extensively for imaging the central nervous, musculoskeletal, and cardiovascular systems, as well as the pelvis and liver.

Indications:

• When the patient cannot or would not hold still.

• Pediatrics.

• Extreme pain lying on one’s back.

• Ventilator dependency.

• Claustrophobia (fear of enclosed spaces, such as the MRI tube).

• Other potential complicating factors.

Need for Anesthesia:

• An MRI study usually consists of multiple image sequences, each taking up to ten minutes to acquire, and any movement during this time will produce profound distortion of the final images.

• The number and duration of scans are variable, with some complex studies lasting up to two hours. The MRI is a noisy and claustrophobic environment with restricted access to the patient.

• The aims of anesthesia are, therefore, to provide immobility to obtain the best possible images while maintaining patient safety and comfort throughout. This is achieved by either sedation or general anesthesia, both of which require meticulous organization, education, and training of all staff involved.

2. MIBG (Iodine-131-Meta-Iodobenzylguanidine):

• An MIBG (iodine-131-meta-iodobenzylguanidine) scan is a nuclear imaging test that helps healthcare providers diagnose and assess neuroendocrine tumors.

• The caregiver injects a radioactive tracer, called iodine meta-iodobenzylguanidine (MIBG), into the bloodstream. A special camera detects the tracer and takes images inside the body. The test occurs in stages over several days.

• Neuroendocrine cells throughout the body absorb MIBG. A special camera can then detect the tracer and produce images. A medical specialist can analyze whether the images appear normal or abnormal.

Indications:

• Carcinoid tumors (neuroendocrine tumors).

• An uncommon tumor that develops in children below the age of five years in nerve cells is called neuroblastoma.

• Medullary thyroid carcinoma is a type of thyroid tumor.

• Pheochromocytoma is a tumor in the adrenal glands or other body parts.

• The doctor may also use MIBG scans to assess whether the cancer has spread or if the treatment is working.

3. Magnetoencephalography (MEG):

• Magnetoencephalography (MEG) is a noninvasive technique that records the associated magnetic fields induced during neuronal electrical activity within the brain. With a spatial resolution of about 2 millimeters, the MEG may become the localization technique of choice for subcortical epileptic foci.

• Ideally, the MEG scan requires an awake but quiescent patient to lie immobile for a few hours. The majority of patients undergoing this investigation are cooperative adults and do not require anesthesia intervention.

• However, children with complex seizure disorders and behavioral problems cannot remain quiescent for the scan duration.

• MEG is conducted in a magnetically shielded room, requiring the anesthesia machine and monitoring equipment to be located outside. Access to the patient's airway, poor lighting, remote location, adequate monitoring, and emergency suction all present challenges within the MEG environment.

• Anesthesia service for MEG in children has now become the preferred option in most cases.

4. Computed Tomography (CT):

• A CT (computed tomography) scan uses X-rays to obtain a series of cross-sectional images that are produced, and a computer is used to reconstruct the images, aiding in diagnosis and treatment planning.

• The CT scanner is a large doughnut-shaped machine, and a bed can move inside through the space provided for the same. The scan can last from five minutes to 20 minutes, which depends on the area and complexity of the scan.

• Anesthesia is required in children and adults who cannot stay still (epileptic patients) during the procedure.

• The patient will swallow the sedating agent, which is in liquid form or can be given as a nasal spray or given intravenously about 20 to 45 minutes before the scan is scheduled.

What Are the Anesthetic Agents Used in Various Diagnostic Radiological Procedures?

1. Chloral Hydrate: Acts by inducing sedation and sleep. It is given orally. Possible side effects include slow breathing rate, vomiting, irritability, and prolonged sleepiness.

2. Dexmedetomidine: Induces semi-arousable sedation without the risk of respiratory depression. This is given by the intravenous or intranasal route. Possible side effects include irritability, prolonged sleepiness, and low blood pressure. Side effects like low blood pressure can be reduced by encouraging the child to drink plenty of fluids.

3. Benzodiazepines:

• Midazolam: Midazolam is a more potent agent with a more rapid onset. It is suitable for children aged over one year undergoing brief procedures, where anxiolysis or sleep is the main requirement.

• Temazepam: Is preferred more and can cause some anxiolysis and sleep. If combined with Droperidol, it induces sleep in 70 percent of children (weighing 10 to 20 kg) undergoing MRI.

4. Barbiturates: Phenobarbital IV (intravenous route) has a long history of effective use in radiology imaging with a low incidence of respiratory depression and remains a very common sedative agent.

• It is used predominantly for CT studies.

• Methohexital is an effective sedative in IV form.

5. Intravenous Anesthetics:

• Propofol and Fentanyl are the most effective drugs for deep sedation or general anesthesia for non-painful procedures such as MRI scans or nuclear scans.

• The risk of requiring advanced airway management is high as it can induce profound respiratory depression and loss of protective airway reflexes, making it suitable for use only by persons trained in the administration of general anesthesia.

6. Inhalational Anesthetics:

• Nitrous oxide is a potent analgesic used for radiological procedures.

• Nitrous oxide should not be used in specific situations such as pneumothorax, pneumocephalus, pneumopericardium, otitis media, or bowel obstruction.

• Sevoflurane, or fluorinated Methyl isopropyl ether, has been used frequently for inhalation induction of anesthesia. Owing to its non-pungency, rapid induction, and quick elimination, Sevoflurane may be useful for sedation by professionals skilled in general anesthesia.

How Is Anesthetic Intervention Monitored during Interventional Radiological Procedures?

The most precarious periods in sedation or general anesthesia are the five to ten minutes after IV (intravenous) administration of medication and during the period immediately after the end of the procedure when procedural stimuli cease. Therefore, the following parameters should be continuously monitored.

• The level of consciousness every 15 minutes (when possible) using the Glasgow coma scale, the pediatric coma scale, and the Ramsey scale should be checked.

• Ventilation is monitored by respiratory rate, chest auscultation, and capnography every five minutes. In deeply sedated patients and when direct observation is not possible, capnography is currently the most valuable method for ventilation monitoring.

• Oxygenation is checked with pulse oximetry with appropriate alarms.

• Vital signs like blood pressure, pulse, and ECG (echocardiogram) are monitored well.

Conclusion:

The incidence of sedation or general anesthesia in radiological imaging procedures has grown considerably over the past decade, favoring anesthetist-led procedures. Although it is a relatively safe procedure, to practice safe care, one needs to observe appropriate guidelines and improve resuscitation skills for safe anesthetic intervention in diagnostic procedures.