Anesthesia for magnetic resonance imaging (MRI) requires special equipment that can be used in the presence of a magnetic field. Endotracheal tube and various laryngeal mask airway devices have a variable quantity of ferromagnetic material in the pilot balloon that could reduce image quality and result in artifacts. The i-gel is a reliable, easily inserted airway device, and causes minimal interference in image quality. We used i-gel in 10 anaesthetized adult patients undergoing MRI. The quality of image, evidence of airway, tongue, and dental trauma were assessed throughout the procedure. All scans were diagnostically adequate. Therefore, we concluded that i-gel causes the least ferromagnetic interference compared with other devices and improves the quality of imaging and produces minimal artifact while scanning.
anesthesia; ferromagnetic interference; i-gel; magnetic resonance imaging;
General anesthesia is often necessary for magnetic resonance imaging (MRI), especially when patients cannot remain still. Insertion of an airway device is essential during the administration of general anesthesia, because it is difficult to access the airway when the head of patient enters into an MRI suite. Anesthesia for MRI requires special equipment that can be used in the presence of a magnetic field.1 Endotracheal tube and various laryngeal mask airway (LMA) devices have a variable quantity of ferromagnetic material in the pilot balloon that could reduce the quality of image produced and result in artifacts. The i-gel is a reliable, easily inserted airway device that provides an adequate seal, and has a low morbidity rate. It has no inflatable cuff and therefore no pilot balloon. Thus, it has only minimal interference in image quality.1, 2, 3 We herein report a series of cases (10 adult patients) in which we used i-gel for MRI and observed the response of i-gel on image quality.
2. Case report
We evaluated the safety of using i-gel (Intersurgical Ltd, UK) in 10 adult patients who reported for MRI under general anesthesia. Of the 10 patients, three had a history of head injury and were disoriented and uncooperative and five were mentally challenged. All these eight patients were scheduled for MRI of the brain under general anesthesia. The remaining two patients were subjected to MRI of the chest and spine because of severe kyphoscoliosis. The diagnosis and site of MRI are presented in Table 1. General anesthesia was administered to all these patients due to a history of severe pain upon lying down in a supine position. All the patients were subjected to detailed clinical history and relevant investigation. Anesthesia was induced on the MRI-compatible trolley immediately outside the MRI room with fentanyl (1 μg/kg) and propofol (2 mg/kg). The dose was maintained with continuous infusions of propofol (5 mg/kg/hour). The patients were monitored continuously with MRI-compatible equipment that included continuous electrocardiography, pulse oximetry, noninvasive arterial pressure, and capnography. Appropriately sized i-gel according to the manufacturer's guideline was inserted in all the patients after they received a sufficient dose of anesthesia. Image quality was assessed by a radiologist throughout the procedure. The mean duration of anesthesia was 41.9 minutes. All scans were objectively assessed by the radiologist and it was observed that they were diagnostically adequate with good image quality and with no evidence of artifacts. Therefore, none of the monitoring techniques and gadget used for airway maintenance interfered with MR function or produced image artifacts. Hemodynamic parameters were stable in all of the patients throughout the procedure. No evidence of trauma to airway and hoarseness was noticed in any patient. Therefore, we concluded that i-gel is another promising device and a good alternative that can be safely used in the MRI suite for airway maintenance.
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Movements during an MRI examination cause artifacts, and thus patients must remain motionless during the entire period. Some patients, children, and adults are claustrophobic, and are unable to lie still during the MRI scan. Pain and mental disorder may be other factors that require sedation or general anesthesia for MRI. The presence of a strong magnetic field and restricted access to the patient mean that the provision of anesthesia within MR units presents unique problems. Therefore, general anesthesia is indicated to increase safety and comfort of patients and to improve the quality of MRI image.4
Anesthetic equipment that is used in the scanning room should be MR compatible.4 The i-gel is a unique, single-use, supraglottic airway management device. It is made from a medical-grade thermoplastic elastomer and has been designed to create a noninflatable, anatomical seal of the pharyngeal, laryngeal, and perilaryngeal structures. This offers the potential for easier insertion, reduced tissue compression, and increased stability after insertion.5, 6 The i-gel supraglottic airway does not contain any metal parts, and thus did not cause any artifacts, and therefore, these may be the most appropriate for use during an MRI.2
We evaluated the presence of artifacts or any disturbance in MRI images after the use of i-gel. All 10 patients who underwent MRI did not show artifacts in any of the image. Zaballos et al3 performed an in vitro simulation study of six supraglottic devices in the MRI environment and showed that the magnetic susceptibility artifact is more prominent with the LMA ProSeal. They observed that the artifacts of classic LMA (cLMA), LMA unique, and LMA Supreme (LMA-S) were similar. Artifacts in all these devices were due to the presence of ferromagnetic material in the pilot balloon. They observed least disturbance using i-gel as well as Ambu LMA because of the absence of the metallic part, and interpreted them as the most suitable device for use in MRI.3
Taxak et al2 documented the successful use of i-gel in MRI suite for two children undergoing MRI for brain under general anesthesia. Hence, they labeled it as one of the safest devices in children who require deep sedation, proper positioning, and cooperation during an MRI. Many airway devices such as LMA and endotracheal tubes have been tried in the MRI suite, but the presence of a ferromagnetic material could reduce and degrade the image quality. Grady and Perkins7 documented in their report that separating the pilot balloon from the skin surface by at least 3 cm could prevent image distortion. del Castillo and Zaballos8 reported the successful use of LMA-S in the MRI suite. Although the LMA-S has not been previously tested for MRI compatibility, the authors used it because of its characteristics [medical-grade poly(vinyl chloride)] and the small amount of metal within the valve in the pilot balloon similar to the cLMA. Our data using i-gel yielded no artifacts, which is consistent with previous reports.
Russo et al6 studied the position of i-gel and LMA-S and documented that i-gel significantly compressed the tongue and other upper airway structures, but none of our patients reported hoarseness and sore throat after device removal.
In conclusion, administration of anesthesia during an MRI examination continues to be a challenge for anesthesiologists with regard to the selection of the proper anesthesia method as well as the selection of proper airway gadget that causes least interference and improves the quality of imaging and minimal artifact while scanning. We propose that i-gel is one such gadget that produces good imaging results without any artifact.