A Simple Novel Technique to Make any Supraglottic Airway Device Magnetic Resonance Imaging Compatible: A Fusion of the Past with the Present.

Sir,

A magnetic resonance imaging (MRI) study consists of multiple image sequences, each taking up to 10 min to acquire. Any movement during the procedure produces profound distortion of the final images obtained. This is especially problematic in the pediatric population and some adult patients with mental retardation or those suffering from claustrophobia. It often becomes necessary to provide either sedation or general anesthesia (GA) to these patients.

When administering GA to such patients, airway management remains a challenge because of extremely restricted access to patient's airway and limitation of availability of suitable devices to secure the airway.[12]

Supraglottic airway devices (SGDs) are a favorite choice when administering anesthesia to these patients. As compared to endotracheal tubes (ETT), the use of SGDs during MRI studies under GA has shown to significantly improve image quality.[3] However, only specially designed MRI-compatible SGDs can be used in the MRI suite. Non-MRI compatible SGDs have ferromagnetic material in their spring-loaded valve, which leads to reduced image quality, spurious interpretations of the film, and unnecessary wrong diagnoses.[4] The extent to which the image quality gets compromised depends on the quantity of ferromagnetic material within the field, the pulse sequence used, and the distance between the area of interest and the SGD.[5]

MRI compatible SGDs are more expensive and may not always be available at places where resources are limited, especially in remote locations such as the MRI suite. We thus attempted to convert a size 2.5 Ambu® Aura40™ laryngeal mask airway (LMA) into an MRI compatible device using the following technique:

The existing inflation assembly of the LMA (containing the ferromagnetic substance) was detached [Figure 1a]

Figure 1

(a) A size 2.5 Ambu® Aura40™ laryngeal mask airway with a detached inflation line, (b) inflation assembly of a red rubber endotracheal tube, (c) approximately 3 cm length of the sheath of an 18-gauge intravenous cannula, (d) various components placed together, (e) final magnetic resonance imaging compatible device

The inflation assembly of a red rubber ETT was obtained. As is known, this assembly does not have any spring loaded valve mechanism, thus rendering it free of any ferromagnetic substance [Figure 1b]

Approximately 3 cm length from the sheath of an 18-gauge intravenous (IV) cannula was cut out [Figure 1c]

The inflation assembly of the red rubber tube was connected to the broken end of the inflation line of the LMA using the IV cannula sheath as a bridge [Figure 1d and e]

Using this assembly, the cuff of the LMA was inflated with 21 ml of air as recommended for a size 2.5 LMA and observed for 5 min. The cuff remained inflated. After 5 min, the cuff was deflated completely with syringe yielding 21 ml of air, thus confirming the absence of leak

Convinced of proper functioning of the device, it was autoclaved and was subsequently used for administration of GA to children (body weight 20–30 kg) in the MRI suite uneventfully.

Thus, with this minor and simple modification, we were able to convert the Ambu® Aura40™ LMA into an MRI compatible device. This method can be used to convert almost any SGD of any size into an MRI compatible device. This is relevant, especially in a country with limited resources like ours. Indeed, revisiting the past can often solve a lot of modern day problems.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.