“Closed” Supraglottic Airway-Guided Intubation During the COVID-19 Pandemic: A Glo Germ Follow-up

To the Editor

As a follow-up to our previous correspondence,¹ we conducted an experiment using Glo Germ (Glo Germ Company, Moab, UT) powder to evaluate the effectiveness of aerosol containment with our closed supraglottic airway-guided flexible bronchoscopic intubation (SAGFBI) technique. In the current climate of the coronavirusdisease2019 (COVID-19) pandemic, minimizing aerosolization during airway maneuvers reduces the risk of viral transmission and health care worker contamination. Glo Germ is a fluorescent liquid/gel or powder surrogate marker for the presence of pathogens.² Under ultraviolet light, it produces a fluorescent glow that enables a visual read-out and immediate identification of environmental contamination.² It is therefore used in simulation and education of infection control measures and aerosolization secondary to airway interventions.^2–4

Traditionally, airborne or droplet transmission refers to particle size <5 or >5 μm, respectively.⁵ This has implications on dispersal range: droplet transmission occurring at most over 1m as it is limited by forces of gravity; and airborne transmission occurring beyond 2m as they remain in the air over a protracted period of time.⁵ Aerosol generation happens when air currents speed up over a fluid surface, resulting in transmission of infectious particles whose sizes range from 0.05 to 500 µm.⁶ The Glo Germ particle size varies between 1 and 5 µm,² and so act as surrogate markers for virus-containing aerosol.

Closed SAFGBI creates an enclosed system using a sterile ultrasound probe cover (CIVO, South Kalon, IA) to minimize aerosol contamination. The “closed setup” was constructed as seen in theFigure. First, a size 6.0 microlaryngeal tube was preloaded onto the bronchoscope. Next, the distal closed end of the probe cover was cut and the entire length of the cord of the Ambu aScope 4 Broncho Slim (Ambu A/S, Baltorpbakken, Ballerup) was inserted within it. A small incision was made 10 cm proximal to the distal end of the probe cover, into which the patient end of a breathing circuit filter was inserted. Strong adhesive tape was used to form airtight seals connecting the probe cover: proximally with the bronchoscope handle and distally with the filter (Figure). After inserting a size 3 Ambu Auragain (Ambu A/S, Baltorpbakken, Ballerup) supraglottic airway into the manikin, 1/16th teaspoon of Glo Germ powder was deposited into its ventilation port. The closed set up was placed over, and strong adhesive tape was used to seal the distal probe cover onto, the Auragain. The filter, connected to the anesthetic circuit, can now be attached to the Auragain for controlled ventilation. However, for this demonstration, this latter maneuver was not performed. Instead, the filter remained unconnected, and we turned the fresh gas flow of 100% oxygen to 15 L/min initially. This caused aerosolization of the Glo Germ, as evidenced by its spread into the distal part of the probe cover (Figure). The gas flow was decreased to 6 L/min, with the adjustable pressure-limiting valve fully opened. SAGFBI was then performed as per our previous correspondence (Figure).¹ Oncompletion of SAGFBI, the filter was connected to the microlaryngoscopy tube. The probe cover was then carefully removed from the filter and Auragain and disposed of together as a single unit.

Figure.

Closed supraglottic-airway guided flexible bronchoscopic intubation (SAGFBI). A, The bronchoscope is first preloaded with a microlaryngoscopy tube. Airtight seals are created by taping the proximal end of the probe cover to the bronchoscope and taping the inserted filter distally. The distal end is cut to permit subsequent connection to the supraglottic airway. B and C, Performance of intubation through the supraglottic airway with glottic view visualized. The closed setup is filled up with 100% oxygen. D, Close-up view after intubation completed, showing Glo Germ deposition within the probe cover. E, No Glo Germ deposition on manikin or surrounding areas.

Aerosol contamination (represented by the presence of fluorescent Glo Germ particles) was seen within the distal end of the probe cover. No particles were not detected outside the closed setup, including on the manikin face, operator, or the surrounding environment (Figure). This provides evidence that closed SAGFBI can reduce, or prevent, aerosol contamination of health care workers and the surroundings. SAGFBI may not be aerosol generating per se if the patient is paralyzed.⁶ However, events preceding it may be aerosol generating, for example, facemask ventilation and attempts at intubation.⁵

There are limitations to this demonstration. A manikin cannot replicate the actual temperature and moisture of a human airway and this may have implications on particle dispersion.⁴ In addition, the size of Glo Germ particles may be larger than that of viral particles (which have a range of sizes) and may therefore not accurately reflect, and may even underestimate, virus dispersal distance.⁴ Further bench tests are needed to evaluate closed SAGFBI, and operators should be familiar with the technique before using it.

ACKNOWLEDGMENTS

We acknowledge and thank Ambu A/S for the loan of the manikin, monitor, and bronchoscope.

Henry Chua, MMed, Anesthesiology
Singhealth Anesthesiology Residency Program
Department of Anesthesiology
Singapore General Hospital
Singapore
henry.chua2@mohh.com.sg

Wan Yen Lim, MMed, Anesthesiology
Division of Anaesthesiology and Perioperative Sciences
Singapore General Hospital
Sengkang General Hospital
Singapore
Duke-National University of Singapore (NUS) Medical School
Singapore

May Mok, FRCA
Patrick Wong, FRCA
Division of Anaesthesiology and Perioperative Sciences
Singapore General Hospital
Sengkang General Hospital
Singapore
Duke-NUS Medical School
Singapore
Yong Loo Lin School of Medicine
National University of Singapore
Singapore