Airway for Laser Surgery

Anatomy and Physiology

Upper airway manipulations are very stimulating and often cannot be effectively performed on an awake patient. Once anesthetized, the patient cannot adequately protect their airway from aspiration and obstruction since the oropharyngeal muscle tone, expiration reflex, coughing reflex, and apnea reflex are progressively obtunded by the majority of general anesthetics.[4][5][6] Changes in the respiratory pattern invariably and progressively lead to hypoventilation and then to apnea. This introduces a need for endotracheal intubation to facilitate ventilation of the lungs and to prevent the possibility of airway obstruction and asphyxiation. An endotracheal tube with an inflated cuff effectively occludes the portion of the trachea outside of the hollow plastic tube itself, performing the above-described functions. Yet, in the case of upper airway surgery, it can also obstruct the surgical field and be vulnerable to mechanical damage from surgical manipulations, including using a laser.

Smaller-sized devices, like jet ventilation catheters, can be placed below vocal cords to insufflate oxygen, provide some ventilatory oscillations, and simultaneously allow for better visualization of the surgical field.[7] Nonetheless, they cannot completely replace the respiratory function nor protect the distal airway from aspiration or generated air contaminants and chemical hazards inherent to laser surgery. The airway may be left unprotected with intermittent mask ventilation between the periods of surgical manipulation, which provides for an unobstructed operative field. This approach is suitable for short procedures with little risk of bleeding in patients able to tolerate periods of apnea but carries the risk of laryngospasm, aspiration, and loss of control over the airway is significant and may preclude the use of this technique for many laser airway surgeries. Alternatively, the patient can be breathing spontaneously through the procedure, but this introduces a mobile surgical field and risks of plumes and anesthetic gasses inhalation by the patient and operating room personnel.[3]

Indications

If laser airway surgery is planned, intubation should be performed with designated "laser-safe" endotracheal tubes. This "laser-safe" name is a misnomer, as airway fire is still possible with these devices, but they have been designed with additional safety features such as dye-filled supplementary cuffs and are constructed of less-flammable materials such as metal.[8] Apneic techniques, spontaneous ventilation, and alternative airway devices such as laryngeal mask airways (LMAs) or jet ventilation are possible though used very infrequently in laser airway surgery for access and control reasons. A secured airway, with a specially designed tube and a team familiar with specific challenges and risks of laser airway surgery, is always the safest option.[9][10]

Contraindications

There are no absolute contraindications to using specialized endotracheal tubes to secure the airway apart from allergies to the tube material if airway surgery is required. If the patient is not healthy enough to tolerate a necessary airway surgery, alternatives such as tracheostomy should be considered.

Equipment

Commonly Used Lasers

Carbon dioxide (CO2) lasers are historically the most commonly used lasers in otolaryngologic surgery. The infrared light produced is not visible to humans at 10,600 nm and produces intense thermal injury as its chromophore is water.[11] It is necessary to use a visible-light aiming beam and to ensure this aiming beam is accurate to the invisible laser before beginning the operation. Eyes (of both the patient and the OR personnel) are especially vulnerable to the CO2 laser, though simple, clear glass or plastic is sufficient for protection.[12]

Specifications of these and other commonly used lasers (KTP, Ho:YAG, Nd:YAG, Argon, pulsed dye) are discussed elsewhere in StatPearls and are beyond the scope of this review.

Numerous endotracheal tubes were designed to withstand laser damage, maintain the integrity of their components, and minimize the risk of airway fire. Please refer to the individual product data sheets before using any new endotracheal airway tube. Below are a few examples of the most common designs of laser-resistant tubes.

• Soft and flexible white rubber tubes covered with copper foil (eg, Rusch Lasertubus) are resistant to CO₂, Nd/YAG, and Argon lasers. These are most often double-cuffed for additional protection.
• Silicone-made tubes wrapped in aluminum foil (eg, Laser shield by Xomed ) resist CO₂ and potassium titanyl phosphate (KTP) lasers.
• Stainless steel corrugated spiral ETTs (eg, Mallinckrodt Laser Flex) are suitable for CO₂ and KTP lasers. The metal core is non-flammable and kink-resistant. The risk of reflecting a laser beam is very low, yet the metal may conduct heat to surrounding tissues and materials.
• Red rubber tubes, especially if wrapped with aluminum or copper foil (eg, Sheridan Laser-Trach), have a long-standing record of safe use with CO₂ and KTP lasers but have been largely supplanted by the products above.

Many of these tubes have 2 cuffs, and current American Society of Anesthesiologists guidelines recommend these to be filled with saline, as this conveys additional protection against fire in case the laser beams pop the cuff. Adding methylene blue (or other biocompatible dye) to the saline in the cuff balloon can aid in detecting cuff perforation.[2] The surgical team should use flame-resistant surgical drapes if possible, though covering exposed skin with saline-soaked sterile towels is far more common and is effective.

Personnel present in the room must wear wavelength-specific protective eyeglasses to prevent possible laser radiation exposure and irreparable corneal or retinal injury, and signage indicating laser use should be placed on the outer face of all doors to the operating room. In general, clear glass or plastic goggles are used when working with a CO₂ laser; amber or orange filters for KTP and argon lasers; green or clear filters for Nd:YAG; blue for dye lasers.[13] High-efficiency masks should be used to protect the staff from smoke plumes. These result from tissue vaporization and contain fine microparticles (mean size 0.3 micrometers) capable of depositing in the lower airways and alveoli, potentially posing risks of affecting mucociliary clearance, interstitial pneumonitis, bronchiolitis, and mutagenicity. This is of particular concern when treating papillomatous disease, as there is a hypothetical risk of seeding papilloma.[14] Plume scavenging systems should be employed because the commonly used general room ventilation (aka "dilution ventilation") is insufficient to remove air contaminants. Room suction hose nozzle inlet may be used as well and must be kept within two inches of the operative field to effectively evacuate airborne contaminants generated by laser devices.[15]

Personnel

In addition to the standard operating room setup of a surgeon, anesthetist, scrub nurse, and circulating nurse, an additional staff member is tasked with operating the laser itself. All personnel should be appropriately trained in laser safety and equipped with wavelength-specific protective equipment.

Preparation

Appropriate airway equipment chosen in accordance with the airway management plan must be present in the room (laser-resistant ETT, jet ventilator). Personnel in the room where the laser energy source is applied must wear protective eyewear and filtering masks. In the event an airway fire occurs, syringes with saline can be premade and used for extinguishing.

Technique or Treatment

Endotracheal Intubation for Laser Surgery

Endotracheal intubation with a cuffed ETT establishes a secure, monitored, and controlled airway, allowing for positive pressure ventilation with effective delivery of respiratory gas mixture and inhalational anesthetic. However, an ideal ETT that does not ignite and has a design resembling conventional endotracheal tubes does not exist. The laser-resistant ETTs are commercially available and provide significantly superior protection against ignition compared to conventional polyvinyl chloride endotracheal tubes. These are most commonly used for laser surgery of the airway. Standard endotracheal intubation techniques apply when positioning these devices.  

Typically, the smallest acceptable ETT is chosen to maximize the exposure of the surgical field. The tracheal cuff of the laser tube (or both cuffs if dual-cuffed) is filled with normal saline mixed with a biological dye (eg, methylene blue). This will decrease the risk of ignition and serve as an indicator of cuff rupture if such occurs. The time to full inflation of the cuff may be prolonged when liquid is used as a filler, but this is rarely of clinical significance. The anesthesiologist should then minimize the delivered oxygen concentration to the smallest required concentration, avoid using nitrous oxide, and allow a few minutes for highly concentrated oxidizer gases to disperse before approving the activation of the laser.[2] The surgeon may request to temporarily deflate the cuff or even remove (and then re-insert) the tube under the direct laryngoscopic view to gain access to structures obscured by the ETT. The anesthesiologist should have a spare endotracheal airway device ready (typically an endotracheal tube of the same or smaller size) in case the existing ETT is damaged by the laser or other manipulation.

Jet Ventilation

Jet ventilation utilizes a high-pressure stream of gas delivered into the upper airway. This reduces the degree of stimulation and provides for the minimally obstructed surgical view yet yields no protection to the airway. Respiratory gas is being actively insufflated either supraglottically (via the aligned rigid bronchoscope with jet ventilator adapter positioned above the open vocal cords), transglottically (via a small-caliber transglottic catheter passed below the vocal cords), or using transtracheal approach (for patients with predicted difficult intubation or as a rescue airway utilizing a cricothyroid cannula). The last two methods help push blood and debris out of the trachea with the expiratory flow of gas. During manual jet ventilation, an injector connected to the gas supply insufflates the respiratory mixture into the trachea, but the removal of gas depends on passive exhalation and requires a patent upper airway and adequate time between jet insufflations to avoid barotrauma. The reducing valve provides the inflow pressures of 1 to 4 atmospheres.

Alveolar oxygen delivery and carbon dioxide removal mostly depend on diffusion to and from the bronchial tree, as there are only small changes in lung volumes during manual jet ventilation. Thus any small-diameter upper airway stenosis that impairs the inflow/outflow of gas creates a risk of air-trapping. Another modality, high-frequency jet ventilation, relies on delivering very small tidal volumes at very high respiratory rates (100 to 150 times a minute) to augment diffusion efficacy. Specialized equipment, properly trained personnel, and an intravenous anesthetic delivery technique (as compared to the inhalational route) are needed, as well as a blood gas monitoring must be established if the procedure is planned to be for an extended time, as inadequate gas exchange (hypoxemia, hypercarbia) is a common consequence. Mucosal dehydration, stomach insufflation, laser burn to the trachea (if no cuff was present to protect areas distal to laser application), pneumothorax, and pneumomediastinum are other possible complications of this technique.[16][17]

Intermittent Apnea Technique

The patient is intubated and extubated intermittently with the airway exposed using the suspension laryngoscopy. When intubated, the patient is hyperventilating, and the ETT is removed to allow for a period of apnea and laser application. The duration of apnea is individually determined, guided by pulse oximetry and end-tidal carbon dioxide values. In general, periods of apnea up to 5 min are allowed, assuming oxygen saturation and end-tidal carbon dioxide (EtCO₂) levels remain reasonable (eg, SpO₂ above 90% and EtCO₂ between 40 and 60 mm Hg.). The addition of continuous respiratory gas delivery via a high-flow nasal cannula may further increase the apneic period.[18][19] Inhalational anesthetics cannot be delivered constantly using this method; thus, total intravenous anesthesia is preferred. This technique is more common in pediatric ENT surgery: although laser-resistant ETTs with small internal diameters are available, their outer diameter is still larger due to the presence of additional insulation layers, thus interfering with the space available in the pediatric airway. Aspiration, laryngospasm, and loss of airway are the feared, yet infrequent, complications of technique.[3][20][21]

Spontaneous Ventilation Technique

The patient is anesthetized, maintaining spontaneous ventilation, and an oxygen-enriched gas is delivered through a side port of the operating laryngoscope or a catheter. Ventilation cannot be assisted. Inhalational anesthetics are best avoided since these will invariably escape into the operating room environment. This technique offers unobstructed access to the larynx, but there is a moving surgical field since muscle relaxants cannot be used. It also provides no protection from pulmonary aspiration or laryngospasm nor prevents pollution of the operating room environment with anesthetic gases and laser plumes.

Complications

The complications inherent to medical laser procedures are surgical fire, iatrogenic burns to surrounding tissues, and ocular injury.[22]

Risk of fire: Following electrosurgical devices, surgical lasers are considered the second most common source of operating room fires.[23] Surgeries of the pharynx, larynx, and trachea are the most at-risk procedures, respectively.

If an airway fire occurs:

• Remove the fuel source (immediately remove the ETT and other burning fragments).
• Remove the source of ignition (stop the laser).
• Eliminate the oxidizer flow (disconnect the circuit, and stop ventilation and the delivery of gasses).
• Extinguish the remaining fire, if any, with saline.
• Continue anesthesia (via intravenous route).
• Mask ventilated with 100% FiO_2.
• Perform direct/video laryngoscopy or bronchoscopy to assess the damage and remove debris. Bronchial lavage may be needed to wash out fragments.
• Re-establish the airway (eg, re-intubate, place a laryngeal mask).
• Assess for damage to the oropharynx and face.
• Consider intensive care unit admission and tracheostomy if needed.[2]

Risk of Iatrogenic Burns

Burns can occur in addition to airway fires, due to accidental exposure of tissues to laser or from the reflection of the laser beam from reflective surfaces in the operative field. The presence of a cuffed ETT limits the possibility of the beam reaching the distal trachea and airway without rupturing the cuff balloon first. Applying saline-soaked gauze to the mucosal areas adjacent to the surgery site is an effective way to prevent such collateral damage.

Ocular Injury

Ocular injuries result from the direct exposure of the eye to the laser or a reflection of the beam. Depending on the physical properties of the laser, several structures can be affected, yet the most commonly involved are the cornea (water-rich) and retina (pigment-rich). Personnel outside the operating room must be warned of using a laser via appropriate signage on the outer surface of all doors to the laser operating room. Any windows in the laser operating room should be covered with opaque coverings. The risk of ocular injury can be significantly decreased by using wavelength-specific filters on safety glasses worn by the patient and operating room personnel.[24] Laser eye injuries are considered an emergency as they can cause permanent blindness. Symptoms include a sensation of a bright flash of colored light and, sometimes, a popping sound matching with the activation of the laser, followed by the loss of visual acuity and the presence of floaters in the visual field.[25] Other laser hazards, like laser plumes, have been shown to have cancerogenic potential. These can be mitigated by using plume scavenging systems and personal high-efficiency filtering masks.[26]

Clinical Significance

Maintenance of the patient's airway and adequate ventilation during upper respiratory tract surgery can be difficult due to the need to maintain an unobstructed view of the operative field. This is usually achieved using a smaller specialized (laser-resistant) ETT, jet ventilation devices, and intermittent or spontaneous ventilation techniques. The use of medical lasers is also complicated by the risk of surgical fire in an oxidizer-rich (oxygen, nitrous oxide) environment. Numerous recommendations exist, and comprehensive guidelines must be followed to minimize the risks inherent to these types of surgeries.

Enhancing Healthcare Team Outcomes

Every healthcare team member must take precautions during laser surgery of the upper airway to avoid harm to themself, the patient, or other operating room personnel. Wear proper protective equipment, which includes a high-efficiency mask and wavelength-specific protective eyeglasses.

To decrease the risk of airway fire:

• Use the lowest concentration of oxygen possible
• Avoid using nitrous oxide as an anesthetic (at high temperatures, it can release oxygen and act as an oxidizer)
• Limit laser use to short pulses and the lowest power
• Activate the laser only when the tip of the laser source is visible, and the endotracheal tube is out of reach of the source.
• Cover the patient's face and chest with wet towels, and protect the eyes with wavelength-specific eye protection
• Have saline-filled large (eg, 50 mL) syringes within reach during procedures with a high risk of ignition
• Know the nearest location of a fire extinguisher and a water source