The Use of Oxygen/Air Blender during Transoral Laser Microsurgery with Supraglottic Manual Jet Ventilation: A Safe Approach

Background Surgical fires are known, preventable, and devastating complications of transoral microlaryngeal laser surgery. Several guidelines have recommended maintaining the fraction of inspired oxygen concentration (FiO2) at or below 30% for open delivery cases. We hereby present our experience utilizing an air/oxygen gas mixing device (blender) attached to a supraglottic manual jet ventilator during transoral laser microlaryngeal surgery in three cases to control oxygen levels. Methods Retrospective chart review of three cases and literature review. Results Three patients underwent microlaryngeal laser surgery and balloon dilation for the management of subglottic stenosis. All three patients were successfully ventilated throughout the procedures, and no major complications occurred intraoperatively. Two of three patients demonstrated symptomatic and clinical improvement at the first follow-up. Conclusions This report demonstrates the successful use of an oxygen/air blender to reduce FiO2 to fire-safe levels of less than 30% during laser surgery of the airway using jet ventilation.

A key measure to prevent airway fres is to maintain the fraction of inspired oxygen concentration (FiO 2 ) delivered to the patient at the minimum necessary to avoid hypoxia.
Given the increased fre risk related to oxygen, the Joint Commission (Oakbrook Terrace, Illinois) and the Emergency Care Research Institute recommend the use of air or FiO 2 less than or equal to 30% for open delivery cases [8].Jet ventilation (JV) has become a popular ventilation approach for microlaryngeal surgery, allowing for endoscopic intervention without the interference of an ETT [14].JV relies on the application of gas portions under high pressure through an unblocked catheter into the airway, which is open to the ambient air.Exhalation in JV is passive, and adequate gas exchange is heavily reliant on modifcation of respiratory rate, driving pressure, oxygen concentration, and inspiration time.It can be delivered in an infraglottic, supraglottic, transtracheal, or transluminal manner, with the use of an automated or manual (hand-held) device [15].In both automated and manual JV, 100% oxygen delivery is possible, but many automated jet ventilators have blenders to mix oxygen and air to reduce the FiO 2 , yet these are not

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Case Reports in Anesthesiology readily available in every center.In this report, we describe our experience with an external oxygen/air blender in reducing FiO 2 delivered by manual JV in three cases of transoral microlaryngeal laser surgery.

Case Description
A retrospective chart review was conducted of the medical records of adult patients undergoing supraglottic JV for microdirect laryngoscopy (MDL) procedures using an oxygen/air blender between June 2020 and June 2021.Ethical approval for this study was not required.Tree patients were identifed in which the approach was used.Patient characteristics and intraoperative fndings are summarized in Table 1. with respiratory failure requiring intubation and tracheostomy presented to the clinic with dysphonia and increasing dyspnea one month after tracheostomy decannulation.Te patient was found to have grade III SGS on in-ofce TNT with at least 75% subglottic narrowing and glottic narrowing due to limited abduction of true vocal folds (VFs) and signifcant swelling consistent with polypoid corditis.He subsequently underwent MDL, with KTP laser incisions of stenosis and ablation of true VFs polypoid tissue.Supraglottic jet ventilation was used with the addition of an air/oxygen blender during periods of laser activation as described previously.
Te patient was briefy intubated with a 5-0 MLT intraoperatively due to a period of oxygen desaturation <90% but was successfully extubated after termination of general anesthesia and was monitored overnight.Te patient had a complicated postoperative course, requiring tracheostomy due to continued stridor and glottic narrowing 2 days postinitial MDL.Te patient remained cannulated at the follow-up visit one month postoperatively, with in-ofce TNT at that time demonstrating multilevel airway narrowing and minimal glottic opening with patent tracheal cannula.(iii) Patient 3. A 24-year-old female presented with progressively worsening shortness of breath over 1 year and was found to have grade II SGS with 50-60% airway narrowing.Te patient underwent MDL with radial laser cuts of stenosis using CO 2 laser, balloon dilation, steroid injection, and biopsy under supraglottic jet ventilation attached to an oxygen/air blender as described previously.Tere were no complications, and after overnight monitoring, the patient was discharged one day postoperatively with improved respiratory status.Two-week follow-up revealed symptomatic improvement in breathing with minimal dysphonia and dysphagia.In-ofce TNT showed a widely patent subglottis and less than 25% airway narrowing 3 months postsurgery.
All three patients underwent MDL with radial laser cuts, balloon dilation, and steroid injections for the management of SGS.KTP laser was chosen when CO 2 laser was not available.Jet ventilation was accomplished  Case Reports in Anesthesiology under suspension laryngoscopy in all patients without difculty.An oxygen blender (MaxBlend, Maxtec, USA), connected to the jet ventilator via high-pressure noncollapsible oxygen tubing, was utilized to successfully reduce the source oxygen to less than 30% FiO 2 during laser activation in the airway.No airway fre events occurred throughout the entire duration of all procedures.Two patients (#1 and #2) required brief intubation with 5-0 MLT intraoperatively but were extubated successfully by the end of the procedure.Two patients (#1 and #3) experienced clinical and symptomatic improvement at 2-week follow-up.Patient #2 had a complicated postoperative course necessitating tracheostomy and continued to have multilevel airway stenosis with minimal improvement in glottic opening at follow-up.

Discussion
Surgical fres in otolaryngology continue to be widely reported in the literature.A survey of otolaryngologists conducted by Smith and Roy revealed that 27% of fres occurred during endoscopic airway surgery, 24% during oropharyngeal surgery, 23% during cutaneous surgery of the head and neck, and 18% during tracheostomy [16].Day et al. reviewed existing literature in 2017 and found that 97% of reported otolaryngologic fre cases involved FiO 2 levels of greater than 30% [4].Based on our extensive review of the literature, we discovered limited data regarding the actual fre risk associated with open oxygen delivery systems and specifcally jet ventilation in endoscopic laryngeal laser surgery.Generally, JV is considered safe compared to closed oxygen delivery systems (with ETT); however, it remains unclear what the expected FiO 2 is with JV as this is multifactorial [15,17].Te FiO 2 can change depending on the technique (low-versus high-fow JV), mode of delivery (supraglottic, subglottic, and transtracheal), oxygen concentration, laser power, use of nasal cannula, or use of drapes that can cause an enriched O 2 environment.
Tus, it continues to be necessary to reduce FiO 2 delivered to the JV to fre-safe levels (e.g., 30%) if JV is to be used in the presence of fre hazards as lasers such as potassium-titanyl-phosphate (KTP) or CO 2 .Some modern automated jet ventilators allow for FiO 2 selection (e.g., the Monsoon III, Acutronic ® Medical Systems, Switzerland).In our experience, these automated ventilators are not readily available.Oxygen/air blenders are widely available and can be easily adapted for use with most existing jet ventilators.We adopted this approach to simultaneously meet patient safety standards and minimize costs by incorporating widely available technology.
Tis series adds to the existing literature by reporting on the efective use of an oxygen/air blender attached to a manual jet ventilator to allow for the safe activation of lasers in the airway even in the presence of high-fow oxygen.To our knowledge, this is the only published record of the use of an oxygen/air blender in this manner.

Conclusion
Tis report of three cases demonstrates the successful and safe use of an oxygen/air blender to reduce FiO 2 to fre-safe levels during laser surgery of the airway using manual jet ventilation.Further studies and models are needed to investigate the fre risks in jet ventilation and open oxygen delivery systems in transoral laser surgery.

Table 1 :
Preoperative data and operative data.