Evaluation of the safety of carbon dioxide laser and transnasal humidified rapid insufflation ventilatory exchange in laryngeal surgery

Introduction

Transnasal humidified rapid insufflation ventilatory exchange (THRIVE) is a method to oxygenate apnoeic patients without intubation with an airway device (1). Initially described as a method to aid the securing of difficult airways in emergency situations, its application in laryngeal surgery has gathered interest due to the improved surgical access afforded by the absence of an airway device (2). However, concern over the potential for airway fires with THRIVE has been raised by anaesthetic groups (3).

The development of an airway fire requires a “fire triad” including an ignition source, oxidizer and fuel (4). During laryngeal surgery, this triad is frequently present. Commonly a carbon dioxide (CO₂) laser is utilized (5) which creates heat that incises, vaporises or coagulates tissue and has the potential to act as an ignition source (6). Provision of oxygen is necessary to maintain saturation of the patient, which although not flammable by itself, acts as an oxidizer to allow a combustible material to burn more vigorously. Multiple fuels can be found in the operating field including endotracheal tubes, nasal prongs, sponges, drapes, gauze, hair and alcohol containing solutions (4,7).

Experimental models to simulate CO₂ laser laryngeal surgery have found that biological tissue type, oxygen concentration, laser power and the use of a smoke exhaust system effects time to ignition of an airway fire. Fat has been shown to ignite more quickly than cartilage or muscle. Higher oxygen concentration and higher laser power decreases the time to ignition, while the use of a smoke exhaust system, increases time to ignition (8). Further, an experimental model to simulate potassium titanyl phosphate (KTP) laser laryngeal surgery and THRIVE on porcine muscle and adipose tissue found that oxygen concentration, charring of tissue and adiposity were associated with a decreased time to spark and flame (9). Clinically despite the prevalence of this triad, airway fire rates are low in laser laryngeal surgery with a reported incidence around 0.4–1.5% (10,11).

While THRIVE typically uses a higher oxygen saturation compared to traditional oxygenation methods, the lack of airway device removes a potential fuel source from the airway. To date, one case of a fire with the use of THRIVE has been reported, with the polytetrafluoroethylene ridge grip of a monopolar diathermy shaft igniting after a spark was generated between the monopolar tip and dental titanium implants (12). There is currently limited published data relating to the clinical use of THRIVE and laser in laryngeal surgery with one study reporting no complications with 10 cases with use of a CO₂ laser (13) and another reporting no complication with 11 cases using a KTP laser (14). This study aims to review the use of CO₂ laser and THRIVE in laryngeal surgery for cases performed in Geelong, Victoria, Australia. We present this article in accordance with the STROBE reporting checklist (available at https://www.theajo.com/article/view/10.21037/ajo-20-41/rc).

Methods

The study was conducted in accordance with the Declaration of Helsinki (as revised in 2013). The study was approved by institutional ethics committees of Barwon Health (21.28), St John of God Health Care, Geelong (1476), and Epworth Hospital, Geelong (EH2021-687). As a retrospective study, waivers for consent were gained from each institution to identify and review records of all patients of the participating surgeons who underwent laser laryngeal surgery with THRIVE between January 2016 and December 2021 at the above institutions.

Inclusion criteria included patients older than 18 who had undergone laryngeal surgery with the use of a CO₂ laser while being oxygenated with THRIVE. Patients were identified by reviewing hospital surgical databases and personal surgical records of the lead surgeons. Identified patients were cross referenced with hospital medical records to ensure that patients fulfilled the inclusion criteria. Patient records not fulfilling the above criteria were not considered.

Operation reports, anaesthetic charts, histopathology results and medical records were used to collect patient demographics, body mass index, surgical details, THRIVE parameters, oxygen saturations and complications. Details of surgery collected included procedure type, indication, time of procedure, and documented CO₂ laser settings. Oxygenation and THRIVE parameters included flow rate, fraction of inspired oxygen concentration (FiO₂), lowest oxygen saturation, highest end tidal carbon dioxide (ETCO₂) or partial pressure of arterial carbon dioxide level (PaCO₂) and the need for intubation. Complications of interest included the occurrence of airway fires or other complications as defined by the Clavien-Dindo classification. Statistical calculations and variation analysis of groups were calculated in Microsoft Excel (Microsoft Corporation) and missing data was omitted.

All surgeons were Otolaryngologist with a recognised fellowship from the Royal Australasia College of Surgeons. All procedures occurred under intravenous general anaesthetic with paralysis. Surgeon and anesthetist preference would determine if a laryngeal mask airway (LMA) was used at the start of the case during the setup of equipment or the end. For all cases THRIVE was provided using either the MR810AEA or 950 System with Optiflow^TM Nasal Cannula system (Fisher and Paykel Healthcare, New Zealand).

After draping the patient and achieving a view of the glottis by suspension laryngoscopy with an operating laryngoscope, multiple wet towels were use draped the patient’s head. A smoke evacuator in the form of a either a clip-on smoke evacuator tube or an inbuilt port was used.

Laser surgery was performed by using a free beam or a laser fiber. A free beam was created by using either a Ultrapulse Encore or a AcuPulse Duo CO₂ fractional laser (Lumenis, Israel) attached to a stereo microscope with a micromanipulator. A AcuPulse Duo CO₂ fractional laser (Lumenis, Israel) with a fiber was used with either a stereo microscope or rigid telescope.

The hospital’s theatre laser safety protocol was followed in every case including warning signs and block out shutters on door windows, laser test firing before the patient enters the theatre, eye protection for all staff and patient, a bucket of water next to the operating table and wet towels to drape the patient. In the event of smoke or flaring laser use was discontinued and power decreased.

Results

The records of 54 individual patients undergoing 106 procedures with five different surgeons over a five-year period at the institutions (University Hospital Geelong, St John of God Geelong Hospital and Epworth Hospital) fulfilling the study’s criteria were identified. The characteristics of patients and indications for surgery are listed in Table 1.

Forty-three procedures were performed at University Hospital Geelong, 47 at St John of God Geelong Hospital and 16 at Epworth Hospital, Geelong. The most common procedure was laser division and balloon dilatation of subglottic stenosis (SGS) with laser used to divide the stenotic band prior to balloon dilatation (53 of 106), followed by laser resection of vocal cord lesions (26 of 106), laser of laryngeal papilloma (12 of 106), laser division of glottic webs (6 of 106), laser resection of supraglottic lesion (3 of 106), laser vocal cordotomy or arytenoidectomy for vocal cord palsy (3 of 106), laser resection of subglottic lesions (2 of 106) and laser tracheoplasty (1 of 106). Total procedure length, defined as documented anaesthetic start time until the patient departed theatre ranged from 30 to 210 minutes with an average of 61 minutes.

Thirty-one cases utilized a Ultrapulse Encore (Lumenis, Israel) CO₂ fractional laser with a free laser beam. The remaining 75 cases used a Accupulse Duo (Lumenis, Israel) CO₂ fractional laser, 71 with a free laser beam and four with a laser fiber. Documented laser settings were available for 98 of the 106 cases. The average laser power was 4.3 W with a range from 1 to 16 W. Pulse frequency varied from 10 Hz to continuous. There was no significant difference in laser power between procedure groups on a single factor analysis of variance (ANOVA) [F(7, 90)=1.01, P=0.42].

All cases used a Optiflow^TM system (Fisher and Paykel, New Zealand) with either an MR810AEA humidifier (43 of 106) or a 950 humidifier (63 of 106). Flow rates were documented in 100 cases (100 of 106) with rates ranging from 30 to 90 L/min. The most frequently documented flow rate was 70 L/min (74 of 106), followed by 60 L/min (16 of 106). Fraction of inspired oxygen was documented in 95 cases (95 of 106). Eighty-eight cases documented a FiO₂ of 100%. Three cases documented initially lower concentrations with commencement at 50% (2 of 3) and 70% (1 of 3) respectively before increasing to 100% at an unspecified time during the procedure. A further six cases documented a FiO₂ of 90% and a single case documented a FiO₂ of 50%.

The lowest recorded oxygen saturations ranged from 38% to 100%, with an average of 96%. Carbon dioxide levels were not frequently recorded (7 out of 106), with the most common measure being ETCO₂ during or at the end of the case (6 out of 7) and one case using intraoperative arterial blood gases. Fifty-six of the 106 cases required an airway device at some stage of the procedure. Twenty-five cases used a LMA at the start of the case. Twenty-one required temporary intubation with a microlaryngoscopy tube (MLT) or LMA for either hypoxia or hypercapnia with subsequent removal prior to recommencement of laser surgery. Twenty-four used an LMA placed at the end of the procedure. Two patients required both an intraoperative MLT and LMA at the end of the procedure. Three cases converted to intermittent low frequency supraglottic jet ventilation due to hypoxia during the case. In all cases jet ventilation was provided by handheld intermittent low frequency jet via a Benjamin injection cannula (8574 GZ) attached to the side of the laryngoscope. There was no significant difference between the average BMI of patients requiring or not requiring mid procedure intubation or jet ventilation (29.87 vs. 30.15) on a single factor ANOVA [F(1, 96)=0.032, P=0.85] A summary of cases is listed in Table 2.

No airway fires were recorded in any operative reports, anaesthetic charts, or medical records. Three complications were documented. The first involved the nasal cannula tubing charring, but not igniting, after failure to adequately protect the tubing with wet sterile towels after repositioning of the patient midway through the case. The second involved a patient developing new onset rapid atrial fibrillation requiring medical management in the recovery room and a third patient developed post-operative stridor that was self-limiting in the recovery room.

Discussion

This is the largest published series demonstrating the use of CO₂ laser and THRIVE in laryngeal surgery in Australia. In our series no airway fires were identified. This was despite a range of laser power and beam characteristics, nasal flow rates of 70 L/min or more and a FiO₂ of 100% in the majority of cases.

Increasing oxygen concentration is a known risk factor for the development of airway fires and recommendations suggest using concentrations below 50% (8) and 40% during CO₂ laser surgery (15). THRIVE is typically delivered using 100% oxygen at flow rates of 40 to 70 L/min through nasal cannula (1,2). While the exact physiological mechanisms of THRIVE is currently the subject of investigation, two proposed mechanisms for gas exchange include supraglottic turbulence and cardiogenic oscillations. These two mechanisms have been shown to explain carbon dioxide gas expulsion and ventilation. Higher nasal canula flow rates up to 70 L/min have also been shown to create increased turbulence throughout the airway compared to lower flow rates (16). To the author’s knowledge, no studies have investigated the relationship between oxygen concentration at the glottis with THRIVE. Given the open nature of the circuit to atmospheric air, airway turbulence and transfer of both oxygen and carbon dioxide the actual concentration of oxygen at the glottis may be significantly lower than 100% and reduce the risk of fire ignition.

The removal of a potential fuel with the absence of an airway device offers another explanation why the chance of an airway fire is reduced when using THRIVE. Many case reports of airway fires involve ignition and burning of the airway device (17,18). Unfortunately cases of airway fires despite laser specific endotracheal tubes have also been reported (11,19) as have airway fires using other oxygen delivery methods such as high frequency jet ventilation catheters (20).

Biological tissue is also known to have the potential to act as a fuel source in laser surgery. Evaporated water from irritated tissue is known to create ‘laser smog’ a steam containing fine fat and protein which is released into the immediate environment and has the potential to inflame (8,21). One study using an experimental model with fresh porcine tissue and 20 L/min of respiratory gas released 10 mm from the CO₂ laser irradiation site found sparking of tissue at laser powers of 6 W, flaring at 10 W and sustained fire at 12 W when using a 250 Hz superpulse mode. With a laser power of 10 W, higher oxygen concentrations were associated with a decreased time to ignition. Concentrations of 60% or more resulted in immediate flare, while a concentration of 35% took 42 seconds to flare. The authors concluded that oxygen concentration should be limited to 40%, laser power should be ideally be less than 6 W, and individual pulses be limited to 10 seconds or less (15). In an experimental KTP laser laryngeal surgery model using THRIVE, no sparks or flames were observed when laser firing at fresh porcine tissue was limited to 5 second or less regardless of oxygen concentration, laser settings or adiposity of tissue (9). In the current study the average laser power was 4.3 W and most cases recorded laser power below 6 W (78 of 106). It appears prudent to use the lowest laser power setting possible while limiting sustained use in a single area to reduce the chance of ignition in all laser cases.

A further factor that may have reduced the chance of fire was the use of an exhaust system during the cases. The removal of laser smog with an exhaust system has been shown to increase the time to ignition in experimental models (8). Although not individually documented the authors of the current study routinely use smoke evacuators or suction to remove laser smog from the operative field.

Surgeons should always remain alert to the potential of both airway and operating theatre fires in all laser cases. Of note the current nasal cannula and tubing used for THRIVE are not laser proof and could represent a potential fuel source. In one case the nasal cannula tubing was seen to char, but not ignite, after the operating surgeon removed the wet towels to reposition the patient and nasal cannula midway through the case. These towels were subsequently not replaced adequately before recommencing laser use. Surgeons should be alert to all potential fuel sources during laser surgery including hair and drapes and take measures to reduce the risk of ignition of these sources. It was the practice of all surgeons to drape the heads of patients with multiple wet sterile towels during the case.

A further two other perioperative complications were noted. The first involved an 81-year-old patient developing new onset rapid atrial fibrillation in the recovery room. New non-sustained arrythmias in elderly patients during THRIVE cases has been documented (22). A potential mechanism for the development for arrythmia may include acute hypercapnia with subsequent eucapnia post operatively. Hypercapnia is recognised to lead to hypertension, arrhythmia and cardiovascular mortality (22). In sheep hearts, acute hypercapnia has been found to temporarily reduce atrial fibrillation vulnerability, however this significantly increased upon return to eucapnia. This effect was not seen in hypoxemia (23). Hypercapnia during THRIVE cases has been shown to progress in a linear fashion as apnoeic time increases (1,24). Although not frequently recorded in this cohort, a ETCO₂ above 90 mmHg was recorded three times (3 of 7) either during or at the end of the case. This raises the potential importance of monitoring for, and avoiding, significant hypercapnia particularly in patients vulnerable to atrial fibrillation or other cardiac arrhythmias.

Measurement of carbon dioxide levels during THRIVE cases presents a challenge. Monitoring partial pressure of arterial carbon dioxide (PaCO₂) represents the reference standard during ventilation. However, arterial puncture is painful, time-consuming with risks including infection and tissue or nerve damage (25). The lack of an airway device means ETCO₂ levels cannot be monitored unless an airway device is placed either during or after the procedure. Doing so either interrupts the surgery or identifies hypercapnia at the end of the procedure when its ill effects may have already caused harm. Transcutaneous measurement of carbon dioxide (TcCO₂) has been described as a non-invasive alternative to arterial blood monitoring. A recent systematic review with meta-analysis concluded that while there can be substantial differences between transcutaneous and arterial measures, clinically acceptable measures and accuracy can be achieved (26). Further, there is limited published data to support the accurate correlation of TcCO₂ to PaCO₂ during THRIVE cases (2,27). Although not used in this study, the use of TcCO₂ measures may have alerted the surgical team to increasing hypercapnia in patients, allowing for placement of airway devices to reduce CO₂ levels and avoid its ill effects.

The second complication, spontaneously resolving stridor after laser resection of a supraglottic lesion, occurred without any intubation of the airway. This complication likely represents laryngospasm from manipulation or irritation of the supraglottis or glottis. This complication is well recognised from intubation with airway devices (28) and is not necessarily specific to the use of THRIVE.

This study also highlights the need for temporary endotracheal intubation or LMA use to ventilate patients during THRIVE cases. While the use of an LMA at the start of the case had become the practice of some surgeons to facilitate the surgical setup, 19% of cases required temporary intubation with an MLT or LMA placement at some point during the case (21 of 106) and 23% used an LMA at the end of the case (24 of 106). Three cases required low frequency intermittent supraglottic jet ventilation due to hypoxia with THRIVE. This should remind surgeons and anaesthetists of the need to have these airways devices readily available during the case. Further, surgeons should remember that these devices represent a potential fuel source, and the use of the laser should be discontinued while they remain in the operative field.

While this represents some of the first data regarding the use of CO₂ laser and THRIVE in laryngeal surgery it is not without limitation. Firstly, this is a retrospective study of a small sample size relying on medical records. As such the absence of airway fire may reflect a small sample, reporting bias or documentation errors. Secondly only initial laser settings were documented which may have changed significantly throughout the procedure. Characteristics such as beam size were not readily available. Further it is not possible to determine if oxygen concentrations were occasionally adjusted by the anaesthetist during laser use, although this was not observed by the surgeons involved.

Conclusions

The use of CO₂ laser and THRIVE in laryngeal surgery appears safe. However, surgeons should remain aware of the potential for airway or operating theatre fires in all laser cases and take precaution to minimize risks. Surgical teams should be prepared for intermittent intubation, LMA placement or the conversion to intermittent jet ventilation during cases. Finally, surgical teams should also be mindful of hypercapnia during THRIVE cases, particularly in elderly patients at risk of arrythmias.

Acknowledgments

Funding: None.

Footnote

Reporting Checklist: The authors have completed the STROBE reporting checklist. Available at https://www.theajo.com/article/view/10.21037/ajo-20-41/rc

Data Sharing Statement: Available at https://www.theajo.com/article/view/10.21037/ajo-20-41/dss

Peer Review File: Available at https://www.theajo.com/article/view/10.21037/ajo-20-41/prf

Conflicts of Interest: All authors have completed the ICMJE uniform disclosure form (available at https://www.theajo.com/article/view/10.21037/ajo-20-41/coif). The authors have no conflicts of interest to declare.

Ethical Statement: The authors are accountable for all aspects of the work in ensuring that questions related to the accuracy or integrity of any part of the work are appropriately investigated and resolved. The study was conducted in accordance with the Declaration of Helsinki (as revised in 2013). The study was approved by institutional ethics committees of Barwon Health (21.28), St John of God Health Care, Geelong (1476), and Epworth Hospital, Geelong (EH2021-687). As a retrospective study, waivers for consent were gained from each institution to identify and review records of all patients of the participating surgeons who underwent laser laryngeal surgery with THRIVE between January 2016 and December 2021 at the above institutions.

Open Access Statement: This is an Open Access article distributed in accordance with the Creative Commons Attribution-NonCommercial-NoDerivs 4.0 International License (CC BY-NC-ND 4.0), which permits the non-commercial replication and distribution of the article with the strict proviso that no changes or edits are made and the original work is properly cited (including links to both the formal publication through the relevant DOI and the license). See: https://creativecommons.org/licenses/by-nc-nd/4.0/.

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