Continuing Education Activity
Maintenance of a patent airway and adequate ventilation during the surgery of the upper respiratory tract can be difficult due to the need to maintain an unobstructed view of structures in the surgical field. It is usually achieved by placing a smaller sized specialized (laser resistant) endotracheal tubes, jet ventilation devices, and utilizing intermittent or spontaneous ventilation techniques. This process is also complicated by using medical lasers that can cause a fire in an oxidizer rich (oxygen, nitrous oxide) environment. Numerous recommendations exist, and comprehensive guidelines were created to minimize the risks inherent to these types of surgeries. This activity reviews the methods of ensuring adequate ventilation in a patient undergoing laser airway surgery, mechanisms of associated adverse events, and methods to prevent them and highlights the interprofessional team's roles in caring for the patients undergoing laser airway surgery.
- Review the risk factors common for laser surgeries of the airway.
- Describe the technique of maintaining a safe airway during the laser surgery of the upper respiratory tract.
- Identify the most common adverse events associated with the laser surgery of the airway.
Medical lasers are used in multiple medical procedures nowadays, including ophthalmic, dermatologic, plastic, and dental surgeries, as well as more invasive intraabdominal, cardiothoracic, neurologic, gynecologic, and urologic procedures. Lasers provide a source of focused, coherent light capable of transmitting intense energy to a precise location. This is used to destruct (burn) or cut tissues (due to photo-acoustic shock wave effects) and to provide hemostasis (highly pigmented tissues, like blood, selectively absorb laser light). Importantly, lasers can ignite flammable materials present in the operating field, such as endotracheal tubes, sponges, and catheters. They also pose a risk of eye injury (both to the patient and operating room personnel), laser plume, electrical tripping, and release of chemical contaminants. Multiple media can be energized to create a laser, and the choice of such depends on the type of procedure performed, location, and physician preference.
Upper respiratory tract and tracheal surgeries are often challenging, as the airway is often compromised and manipulated, while shared by both the anesthesiologist and surgeon. The addition of laser introduces a source of ignition that is especially dangerous when supplemental oxygen is added to the inspiratory gas mixture. This dilemma is constantly discussed, and multiple techniques were developed to provide ventilation to an anesthetized patient while keeping the surgical field maximally accessible and minimizing laser-related hazards. The common ventilatory strategies include conventional endotracheal intubation, jet ventilation, intermittent apnea technique, and spontaneous breathing.
Multiple methods and numerous "laser-resistant" endotracheal tubes (ETT) were designed to protect the operating field from the hazards of medical lasers. The American Society of Anesthesiology now recommends these as the default endotracheal airway during laser surgery of the respiratory tract. The cuff is the most vulnerable part of the ETT. During intubation, once the tube passes through the vocal cords, the balloon at its distal end (cuff) is inflated with air (or saline) to occlude the trachea external to the tube and thus directs all the gas flows from the ETT exclusively to the trachea, and vice versa. If the cuff is marked by a laser, it becomes compromised and can no longer seal the trachea. This leads to a gas mixture rich in oxygen and potentially flammable anesthetic gasses used to ventilate a patient that can escape to the upper airway and surgical field. A fire may be ignited during this event or subsequent use of the laser. The ETT materials (gauze, drapes, dried blood, and tissues) are the most common fuels.
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 his or her 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.
Changes in the respiratory pattern invariably and progressively lead to hypoventilation and then apnea. This introduces a need for endotracheal intubation to facilitate ventilation of the lungs and to prevent the possibility of airway obstruction and asphyxiation from multiple causes. 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 the use of laser.
Smaller sized devices, like jet ventilation catheters, can be placed below vocal cords to insufflate oxygen, provide some oscillations, and simultaneously allow for better visualization of the surgical field. Nonetheless, they cannot completely replace the respiratory function nor protect the distal airway from aspiration or generated air contaminants and chemical hazards that are inherent to laser surgery. The airway may be left unprotected with intermittent mask ventilation performed in between the periods of surgical manipulation, which provides for an unobstructed operative field. This approach is suitable for short procedures in patients who can tolerate periods of apnea but carries the risks of laryngospasm, aspiration, and loss of control over the airway. 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 OR personnel.
Specialized endotracheal tubes and techniques aimed at minimizing the risk of airway fire should be used with any application of a therapeutic energy source (laser, electrocautery) capable of igniting a fire in the airway.
Three components must be present for a fire to occur, and these are ubiquitous in operating rooms: an oxidizer (oxygen, nitrous oxide), an ignition source (electrocautery, laser, defibrillators), and a fuel (fabric, medical plastic, ignitable organic tissues and gasses, surgical prep solutions). The presence of these components must be thoroughly assessed, and risk factors of combustion must be minimized to the maximally possible extent.
Commonly Used Lasers
Carbon dioxide (CO2) lasers are the most commonly used in otolaryngologic surgery. The infrared light produced is absorbed by biologic media (blood, solid tissues, water) with minimal penetration depth and independent of pigmentation, thus minimizing the possibility of collateral damage. It is invisible to the human eye and produces intense thermal injury.
An Nd:Yag laser has the deepest tissue penetration of all the lasers currently used. Specifications of these and other commonly used lasers (KTP, Ho:YAG, Argon, Dye) are discussed in specialized literature and are beyond the scope of this review.
Numerous endotracheal tubes were designed with the purpose to withstand laser damage, maintain the integrity of its components, and minimize the risk of airway fires. Please refer to the individual product data sheets before the use of any new endotracheal airway tube. Below are a few examples of the most common designs of laser resistant tubes used.
- Soft and flexible white rubber tubes covered with copper foil (e.g. 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 (e.g. Laser shield by Xomed ) resist CO2 and potassium titanyl phosphate (KTP) lasers.
- Stainless steel corrugated spiral ETTs (e.g. Mallinkrodt Laser Flex) are suitable for CO2 and KTP lasers. The metal core is noninflammable and is 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 (e.g. Sheridan Laser-Trach) have a long-standing record of safe use with CO2 and KTP lasers.
Many of these tubes have two cuffs and current American Society of Anesthesiologists guidelines recommend these to be filled with saline. It conveys additional protection against fire in case the laser beams strike the cuff. Yet, it also may prolong the process of cuff inflation and deflation. Adding methylene blue (or other biocompatible dye) to the saline can aid in detecting cuff perforation.
Use flame-resistant surgical drapes if such are available.
If compatible with the technique of procedure, have saline-soaked gauze applied to the mucosal areas adjacent to the site of surgery to prevent collateral laser damage and minimize the risk of ignition.
Personnel present in the room must wear wavelength-specific protective eyeglasses to prevent possible laser radiation exposure and irreparable corneal or retinal injury. In general, clear glass or plastic goggles are used when working with CO2 laser; amber or orange filters for KTP and argon lasers; green or clear filters for Nd:YAG; blue for Dye lasers.
High-efficiency masks should be used to protect the staff from smoke plumes. These are the result of tissue vaporization and contain fine microparticles (mean size 0.3 micrometers) that are capable of depositing in the lower airways and alveoli, posing risks of affecting mucociliary clearance, interstitial pneumonitis, bronchiolitis, and mutagenicity. Plume scavenging systems should be employed because the commonly used general room ventilation (aka "dilution ventilation") is not sufficient 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.
Appropriate airway equipment chosen in accordance to the airway management plan must be present in the room (laser resistant ETT, jet ventilator, etc.). Personnel present in the room where laser energy source is applied must wear protective eyewear and filtering masks. Syringes with saline can be premade and used for extinguishing in the event an airway fire occurs.
Endotracheal intubation for Laser Surgery
Tracheal 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 which 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, as compared to conventional PVC 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 biologic dye (e.g. methylene blue). This will decrease the risk of ignition, as well as 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. The anesthesiologist should then minimize the delivered oxygen concentration to the smallest required concentration, yet avoiding hypoxia, avoid using nitrous oxide, and allow a few minutes for highly concentrated oxidizer gases to disperse before approving the activation of the laser. 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 in case the existing one gets damaged by the laser or surgical manipulation.
Jet ventilation utilizes a high-pressure stream of gas that is delivered into the upper airway. It 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 to avoid barotrauma. The reducing valve provides the inflow pressures of 1 to 4 atmospheres. Alveolar oxygen delivery and carbon dioxide removal are mostly dependent 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 (100-150 times a minute) to augment the diffusion efficacy. Specialized equipment, properly trained personnel, and an intravenous anesthetic delivery technique (as compared to inhalational route) are needed, as well as a blood gas monitoring must be established if the procedure is planned to be long, 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.
Intermittent Apnea Technique
The patient is intubated and extubated intermittently with the airway exposed using the suspension laryngoscopy. When intubated, the patient is hyperventilated 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 and end-tidal carbon dioxide (EtCO2) levels remain reasonable (e.g. SpO2 above 90% and EtCO2 between 40 and 60 mmHg.). The addition of continuous respiratory gas delivery via high-flow nasal cannula may further increase the apneic period. Inhalational anesthetic 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.
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 OR environment. This technique offers unobstructed access to the larynx, but there is a moving surgical field since muscle relaxants cannot be used. It also offers no protection from pulmonary aspiration or laryngospasm, nor prevents pollution of the OR environment with anesthetic gases and laser plumes.
Common risks associated with airway maintenance techniques during laser surgery of the upper airway are described in the technique section.
The complications inherent to medical procedures that use laser are surgical fire, iatrogenic burns to surrounding tissues, and ocular injury.
Risk of fire: Following electrosurgical devices, surgical lasers are considered to be the second most common source of operating room fires. Surgeries of the pharynx, larynx, and trachea are the most at-risk procedures, respectively.
If an airway fire occurs:
- Remove the source of ignition (stop the laser).
- Remove the fuel source (remove the ETT and other burning fragments)
- Eliminate the oxidizer flow (disconnect the circuit, stop ventilation and delivery of gasses)
- Extinguish the remaining fire, if any, with water or saline.
- Continue anesthesia (via intravenous route)
- Mask ventilate with a 100% FiO2
- 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 (e.g. re-intubate, place a laryngeal mask).
- Assess for damage to the oropharynx and face.
- Consider ICU admission and tracheostomy if needed.
Risk of Iatrogenic Burns
Apart from being a result of airway fires, burns can occur due to accidental non-planned exposure of tissues to laser or 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. The application of saline-soaked gauze to the mucosal areas adjacent to the site of surgery is an effective way to prevent such collateral damage.
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 various structures can be affected, yet most commonly involved are the cornea (water-rich) and retina (pigment-rich). Personnel outside of the operating room must be warned of the use of a laser. The risk of ocular injury can be significantly decreased by the use of wavelength-specific filters on safety glasses worn by the patient and operating room personnel. 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 presence floaters in the visual field.
Other laser hazards, like laser plume, have been shown to have cancerogenic potential. These can be mitigated by the use of plume scavenging systems and personal high-efficiency filtering masks.
Maintenance of the patent's airway and adequate ventilation during the surgery of the upper respiratory tract can be difficult due to the need to maintain an unobstructed view of operated structures. It is usually achieved by using a smaller size 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 causing a 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 member of the healthcare team must take precautions during laser surgery of the upper airway to avoid harm to self, 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 the laser use to short pulses and lowest power
- activate the laser only when the tip of the laser source is visible and the endotracheal tube is out of the reach from the source
- cover the patient's face and chest with wet towels
- have saline-filled large (e.g. 50 ml) syringes within reach during procedures with high risk of ignition
- know the nearest location of a fire extinguisher and a water source