Laser Surgery of the Airway

What the Anesthesiologist Should Know before the Operative Procedure

The history of the use of lasers for laryngotracheal disorders, as well as a review of the various types of lasers, is presented first. Readers can refer to “Anesthesia for Laser Surgery” later in the chapter for complete information on anesthetic techniques during surgery.

The primary treatment for laryngotracheal disorders has been surgery with its associated injury. Using laser technology, procedures may be done targeting tissues, causing preferentially injury without transferring a significant amount of energy and resultant injury to surrounding normal anatomy. Different lasers with their varying wavelengths and properties can be selected to optimize these effects across different procedures.

Lasers

Mechanisms of action

The word “laser” is an acronym for Light Amplification by the Stimulated Emission of Radiation, which also describes its mechanism of action. Laser light differs from conventional light in several ways. Laser light is one specific wavelength; the photons are parallel and photons are all in phase, resulting in a focused beam of energy (Figure 1).

Figure 1.

A laser produces energy that does not dissipate over distances as does normal light, creating risk of tissue damage such as blindness and combustive events.

Unique characteristics of lasers for surgery

• Selective tissue destruction

• Focused light more discrete and less tissue trauma

• Combined with endoscopes for surgery in narrow passages

• Coagulation resulting in less bleeding

Lasers in ENT surgery

The characteristics of lasers, which are named for distinguishing properties of the medium, follow.

Visible laser – KTP (potassium-titanyl-phosphate)

KTP is strongly absorbed by hemoglobin. KTP laser is fiberoptic compatible and can be used for vascular lesions, stapes and middle ear surgery, nose and sinus surgery, and pediatric airway surgery. Penetration depth is 0.9 mm. Wavelength is 532 nm.

Visible laser – Argon

Absorbed by hemoglobin, melanin, and myoglobin and applied to the treatment of hemangiomas. Penetration depth is 0.8 mm. Wavelength is 514 nm.

Visible laser – Flashlamp pulsed dye

The flashlamp pulsed dye laser is absorbed by oxyhemoglobin. It is ideal for cutaneous vascular lesions (e.g., port wine stain, hemangiomas) and minimizes damage to surrounding tissue. Penetration depth is 0.9 mm. Wavelength is 577 nm.

Near infrared laser – Nd:YAG (neodymium:yttrium-aluminium-garnet)

Holmium:YAG is absorbed by water. The holmium laser has fiberoptic compatibility making it ideal for distal airway lesions, and it provides good hemostasis and bone ablation.

Infrared laser – CO2

CO2 is commonly used because of its usefulness. CO2 is strongly absorbed by water and can be used for glottic, subglottic, tracheal lesions, oral and glottic cancer, the pediatric airway, and laser facial resurfacing. The disadvantage of CO2 is that it cannot be used in conjunction with a fiberoptic scope so distal airway lesions may not be treated. Penetration depth is 30.0 µm. Wavelength is 10,600 nm.

Laser applications in ENT

KTP

Obliterate or palliate bronchial obstructing lesions

Palliate esophageal lesions

Coagulation of vascular lesions

Coagulation of lymphatic malformations

Argon

Hemangiomas

Flashlamp Pulsed Dye

Port wine stains

Hemangiomas

Nd:YAG

Stapes and turbinate surgery

Cutaneous applications (i.e., rhinophyma and resurfacing wrinkles)

CO2

Respiratory papillomas, nodules, and polyps

Leukoplakia

Other benign laryngeal conditions

Type of interaction with tissue (Figure 1)

Anesthesia for laser surgery

What the Anesthesiologist Should Know before the Operative Procedure

Anesthetic techniques must ensure an immobile patient, so laser energy may be directed to the target. Anesthesia during laser surgery may be conducted with or without an endotracheal tube. All conventional tubes (polyvinyl chloride) are flammable and can ignite and vaporize in the airway. Red rubber catheters may be wrapped in foil or a metal nonreflective tube may be used. The cuff is still vulnerable below the cords, so the cuff is filled with saline and sometimes methylene blue in the case of laser puncture.

Airway management

• Laser endotracheal tube

• Tubeless technique

• Jet ventilation

• Apnea with intermittent ventilation

• Inspired O2 <30%. Titrate to O2 saturation and avoid N2O

• Volatile or IV anesthesia

• Fill endotracheal tube cuff with saline

• Protect patient with saline-soaked gauze

• Saline for immediate use

• Fire safety is associated with controlling the risk factors

* Ignition sources: laser, electrocautery

* Oxidization: oxygen, nitrous oxide

* Fire source: endotracheal tubes, surgical prep solutions, and surgical drapes

Managing airway fires

• Remove burning materials.

• Extinguish materials.

• Saline to tissues affected.

• Stop the flow of oxygen and remove the circuit from the anesthesia machine.

• Resume ventilation with face mask.

• Control bleeding and evaluate extent of injury.

• Remove patient from smoke-filled room.

• Perform endotracheal intubation and ventilate with 100% oxygen.

• Bronchoscopy

• Blood gases to evaluate oxygenation.

• Evaluate for bronchial lavage and steroid therapy.

Microlaryngeal surgery

Surgery of the airway presents unique challenges to the anesthesiologist as the surgical field involves one of the prime concerns of the anesthesiologists: establishing and maintaining a patent airway. This conflict requires very close cooperation between the surgeon and the anesthesiologist and special considerations for what type of airway conduit optimizes both patient safety and surgical conditions. Concerns include controlling ventilation and maximizing surgical exposure while minimizing the risk of airway fires during laser use.

Laryngeal surgeries such as vocal cord lesions, papillomatosis, and subglottic stenosis usually involve extended direct laryngoscopy with the surgeon working through the channel of the laryngoscope (please see Figure 2A, Figure 2B, Figure 3A, Figure 3B, Figure 4A, and Figure 4B, for pre- and post- images). The room is usually set up with the OR table rotated 90 degrees from the anesthesiologist.

The CO2 laser is often used as it offers fine, discrete dissection with minimal swelling or scarring. One disadvantage of laser use is the risk of airway fire (previously discussed) and requires a “laser-safe” way to ventilate the patient during surgery. Strategies included metal endotracheal tubes (or other laser-safe ETTs) or avoiding an ETT by using jet ventilation. Each has its advantages and disadvantages and will be discussed below.

Laser tubes

Laser-safe ETTs have been available since the late 1980s. The three most commonly used today are the Mallinckrodt Laserflex, the Sheridan LASER-TRACH, and the Rusch Lasertubus. The Mallinckrodt tube is stainless steel (except for the PVC cuffs), while the Sheridan and Rusch tube utilize an embossed copper foil covered rubber tube. The older laser-resistant ETTs such as the Xomed Laser-Shield and the Bivona Frome-Cuf are less effective at preventing fires. All tubes should be considered “laser resistant” as the cuffs are still vulnerable and fires have been reported, even when laser-safe tubes have been used.

Laser-resistant ETTs offer a familiar controlled airway and allow conventional positive pressure ventilation and easy measurement of tidal volume and end-tidal gases. This allows easy use of inhalation anesthetics with minimal leak exposure. The ETT cuffs can protect against aspiration of debris but are also vulnerable to laser ignition if made from polyvinyl chloride, as most of them are. The other disadvantage to traditional laser-safe ETTs is that they can interfere with surgical access.

The anterior and posterior commissures are particularly difficult to visualize, even with a small ETT in place. Typically, the smallest effective tube is chosen (I.D. 5.0 or 6.0 mm), which has implications for fiberoptic intubation (see TORS section) as the actual lumen is even smaller than advertised since the pilot balloon tubing lies within the lumen of the tube to protect it from laser strike.

Airway management

The best way to optimize surgical exposure and avoid providing a fuel source for laser fire is to eliminate the ETT altogether. That means solving two problems: How do we ventilate the patient and how do we anesthetize him/her? The second question is easier to answer, especially with the advent of total intravenous anesthesia (TIVA) and propofol. A great deal of outpatient anesthesia is performed using a TIVA technique today and the ambulatory anesthesia section covers the topic thoroughly.

A special consideration for these airway surgery patients is prevention of awareness. The prolonged direct laryngoscopy profoundly stimulates the sympathetic nervous system and can make following vital signs for evidence of awareness difficult. These patients also require profound muscle relaxation to prevent movement of the vocal cords, which occurs at much greater depths of relaxation than generalized patient movement.

Ventilating airway surgery patients without an ETT offers the bigger challenges. A number of strategies have been tried over the years and still have their place depending on duration of surgery and condition of the patient.

Mask/rigid bronchoscope ventilation

One of the oldest techniques involves keeping the patient spontaneously ventilating. This is often done with an inhalation technique (lots of contamination in the OR environment) but can be done with a propofol infusion if narcotics are minimized. Disadvantages include quickly changing planes of anesthesia, difficulty maintaining spontaneous ventilation, pollution, and risks of aspiration into the open airway.

Another technique is to intermittently ventilate an otherwise apneic patient. This can be done by mask but is usually done by intermittently placing an ETT through the operating laryngoscope so the surgeon does not have to resuspend the patient each time. Advantages include fairly good control of the airway and the ability to positive pressure ventilate, even if only intermittently. An inhalation technique can be used with minimal gas contamination of the environment.

Disadvantages include interruption of the surgery, whenever the saturation decreases (usually below 90% but sometimes higher in critically ill patients), and repeated insertion/withdrawal of an ETT, which can traumatize the vocal cord structures, although this is minimized with careful attention to detail.

Jet ventiliation

Jet ventilation is often used for airway surgery in order to provide continuous ventilation with no obstruction of the surgical field. It utilizes a high-pressure jet of gas, delivered either supraglottically or subglottically, and at either low or high frequency. The gas can be blended to include any mixture of oxygen, air, helium, or even nitrous oxide, with oxygen and air being most common.

The technique dates back to 1967 and the Sanders injector, a hand-triggered jet of gas delivered at 1-50 PSI with a jet nozzle. The jetted air accounts for a small percentage of delivered tidal volume, relying on entrained ambient air to provide the rest. This entrainment has been attributed to the Venturi effect in the past and the technique is sometimes called Venturi jet ventilation. The high flow of gas leaving a narrow jet orifice decreases the pressure at the tip and drags or entrains the surrounding air with the jet stream (Figure 5).

Figure 5.

While today this effect is more accurately attributed to an example of Bernoulli’s principle, one often sees “Venturi jet ventilation” in the older literature. To add to the confusion, this entrainment mechanism only dominates during low-frequency jet ventilation (LFJV) and is sometimes called high-pressure ventilation as well. High-frequency jet ventilation (HFJV) delivers very short jet bursts at rates >100. Here, alveolar ventilation and gas exchange involve a combination of diffusion, airway pressure, and perhaps oscillations, making the concepts of tidal volume and air entrainment less helpful.

In all cases, exhalation is passive and requires a patent upper airway for gas egress. Saunders’ original report described ventilation via a side report of a rigid bronchoscope. Jet ventilation for direct laryngoscopy was first described by Oulton and Donald in 1971.

LFJV usually requires higher driving pressure and is more often employed supraglottically or via an open channel bronchoscope. The supraglottic position allows for greater air entrainment (important at lower frequency) and less chance of barotrauma (jet tip farther from distal airways). The jet is often hand activated, using pressure from 10 to 40 PSI. It is important to start at lower pressures and titrate up as needed for adequate ventilation in order to minimize barotrauma.

Because the jet stream is relatively high (supraglottic), it must be optimally aligned by the surgeon along the laryngoscope. Proper alignment ensures the best chance for adequate ventilation and minimizes the risk of barotraumas. The alignment can change during the procedure due to the surgeon’s manipulation, surgical instrumentation, or patient movement, so vigilance in assessment of adequate ventilation is important. One of the first clues to misalignment may be auditory; a muffled sound as the jet is directed into tissue instead of the hollow lumen of the laryngoscope and airway.

Measuring the adequacy of ventilation can be problematic. Oxygenation is relatively easy by monitoring pulse oximetry but end-tidal CO2 monitoring is difficult, intermittent, and fairly inaccurate. Adequate chest rise (and fall!) is important and should be continuously observed. Arterial blood gasses can be monitored but are labor intensive and probably not necessary for shorter cases (<40 minutes) where chest excursion is easy to visualize. In patients with poor chest movement (obese, restrictive lung disease), periodic arterial CO2 measurements may be necessary. Newer continuous transcutaneous measurement of CO2 techniques are beginning to hit the market but their effectiveness for these cases is not well established.

One disadvantage to supraglottic jet ventilation is the need to have the direct laryngoscope in place in order to jet ventilate. This requires a different method before placement (usually mask) and after withdrawal of the scope (mask or supraglottic airway often – rarely ETT). The postlaryngoscopy time may be 15 to 20 minutes depending on level of relaxation at the end of the procedure. The other disadvantage involves jetting blood and debris distally into the lower airway. There is a theoretical risk of cancer or papilloma tumor spread to the distal airways with supraglottic jet ventilation, although there has yet to be a definitive case reported.

Infraglottic jet ventilation places the jet tip below the vocal cords. This can be achieved either orally or transtracheally. These techniques can be done via handheld LFJV but lend themselves to an HFJV technique. One advantage of subglottic jet ventilation is the ability to place the jet catheter prior to direct laryngoscopy.

One can place a catheter transtracheally and there are several commercially available kits that supply the 14-gauge catheter needed. Placement can even be done under local anesthesia, prior to induction. Transtracheal catheters must be positioned correctly and secured firmly to avoid changes in position during surgery. Misplaced catheters can lead to subcutaneous emphysema, mediastinal air, and pneumothorax.

It has been recommended that correct placement of the tip of the catheter be confirmed by fiberoptic visualization prior to ventilation. In a survey of anesthesiologists on jet ventilation, most of the major complications occurred in patients having subglottic ventilation techniques. A 10-year review with over 1000 cases of airway surgery via suspension microlaryngoscopy also found the highest rate of major complications associated with transtracheal jet ventilation (TTJV).

Introduced in 1994, it is a fluoroplastic, laser-safe catheter that utilizes a basket-like distal end to ensure the jet tip remains centered in the tracheal lumen. It has two lumens, one for jet ventilation and one to monitor airway pressures. Similar catheters have been subsequently introduced. One can use manual LFJV or automated HFJV with pressure monitoring feedback to halt ventilation when airway pressures increase. The catheter does lie within the surgical field but is small (~4 mm outer diameter) and laser safety tested for CO2, KTP, and Nd:YAG lasers. One can also leave the jet ventilation catheters in place until the patient is fully awake.

Another advantage to subglottic ventilation is not having to rely on precise alignment of the jet stream along the operating laryngoscope. Subglottic ventilation also prevents the jetting of blood and debris into the distal airways. In fact, the physics of jet ventilation ensure a continuous positive pressure below the vocal cords and a pressure gradient toward the proximal, not distal, airway.

Disadvantages of subglottic jet ventilation center around the risk of barotrauma. The jet must still be aligned correctly and centered in the lumen of the airway. That is especially important for TTJV. Also, expiration is passive and dependent on a patent upper airway. If there is an obstruction at the vocal cord level, air will jet in but not find a natural, nontraumatic way out. Pressure monitoring and automatic ventilator shut-offs are somewhat protective. Still, unlike during supraglottic ventilation, where an obstruction limits flow in and out, jetting below the obstruction is more likely to lead to barotraumas, especially if manually ventilating.

Jet ventilation technique

The Sanders-type manual injector is attached to the high pressure gas source in the OR. Ideally, an oxygen/air blender serves as intermediate so FiO2 can be adjusted. Studies have looked at the feasibility of using the O2 flush valve of the anesthesia machine for jet ventilation. The newer machines can be utilized short term, in an emergency situation, but are not suited for elective jet ventilation cases.

The Sanders-type high pressure ventilation setup should also have a regulator so that pressure can be adjusted, usually in the range of 10-50 PSI. It is important to start at the lowest pressure needed to achieve adequate chest expansion and increase incrementally as needed. Jetting should be done at a frequency of 20 with an I:E ratio of 1:2. FiO2 can be increased (with surgical notification) or tidal volume can be increased by either increasing driving pressure or increasing inspiratory time. Be very careful that sufficient time be allowed for adequate expiration or airway pressures can increase dangerously, leading to barotrauma.

HFJV utilizes many of the same concepts but has some important distinctions. In HFJV (VF > 100), gas exchange depends on the interplay of working pressure of the jet and ventilation frequency. As working pressure increases, there is a nonproportional increase in insufflated gas volume. Conversely, as VF increases, so too will dead space, which can reduce CO2 elimination. Of the two, working pressure is by far the dominant force in gas exchange but as VF increases to rates ≥150/min, CO2 elimination can be decreased to negligible levels, in essence creating apneic oxygenation.

I:E ratio may be even more important during high-frequency ventilation with changes seen almost immediately at the alveolar level. In general, as you increase the inspiratory time, oxygenation tends to improve as auto-PEEP increases. CO2 elimination may be reduced as expiratory time decreases. In actual practice, there are many factors in play; even with small changes in I:E ratio, and improving oxygenation is probably better served by focusing on working pressure and VF.

Airway pressures are generally low during high-frequency ventilation (~3 millibars) but can increase dangerously if exhalation is compromised by either extreme ventilator settings, or more likely obstruction of gas egress. Airway pressures can build quickly so it is imperative that airway pressures are monitored and ventilation automatically halted when pressures are too high.

Transoral robotic surgery

Transoral robotic surgery (TORS) utilizes a transoral approach for surgery of the larynx, usually via an operating laryngoscope. Because of the limited exposure of the surgical field, traditional endoscopic surgery can be technically difficult. The instruments are long and awkward to manipulate. The robotic approach utilizes “wristed” implements and increases the degrees of motion at the tip of the instrument.

In addition, both the microscope’s optics and laser operating tip can be positioned deep within the surgical field with the TORS approach. In most cases, 3 arms are used. One carries the double video endoscope, giving the surgeon an excellent three-dimensional view of the surgical field. The other two arms can be adapted for different instruments (electrocautery, pickups, etc.) (Figure 6).

Figure 6.

The surgeon operates the robotic arms from a separate console in the OR with an assistant at the head of the patient to operate suction and retraction as needed (Figure 7).

Figure 7.

Human studies first appeared in the literature in 2006 with emphasis on feasibility, safety, and teachability of the technique.

Types of surgery performed include lesions of the oropharynx, supraglottic structures, and hypopharyngeal lesions. Base of tongue and tonsillar cancers have garnered the bulk of cases to date. While overall numbers are small, early results have shown a decrease in blood loss, length of stay, and overall complications compared to conventional treatment. More work needs to be done with regard to functional outcomes and overall cost effectiveness in light of the high start-up costs and increased operating time required with the TORS approach.

Anesthetic concerns revolve around the airway, at both intubation and extubation. Most cases utilize the CO2 laser so a laser-safe ETT is required. In addition, space is limited so a small ETT (5.0 or 6.0 I.D.) is often requested.

These patients can be a challenge to intubate, especially those with large base of tongue lesions or extensive right tonsillar cancers. However, awake fiberoptic intubation can be difficult when using a laser-resistant tube as the small I.D. lumen is further compromised by the pilot balloon tubing which runs within the lumen of the ETT to protect it from laser strike (Figure 8).

Figure 8.

Fortunately, modern fiberoptic intubating bronchoscopes continue to offer increased optics at smaller sizes. Olympus and Storz make several fiberoptic bronchoscopes with distal tips measuring 2-5 mm. Keep in mind that smaller fiberoptic scopes mean smaller working suction ports and less stability when railroading an ETT into the trachea. Video laryngoscopy may play an important role in these patients as they facilitate visualization of the glottis and small tubes can then be placed atraumatically under “direct video vision.” In our practice, most patients can be intubated by direct laryngoscopy. Our next option is Glide scope intubation after induction and rarely do we utilize awake fiberoptic intubation, or even more rarely awake tracheostomy.

One of the advantages of the TORS is being able to avoid tracheostomy for these cases. However, airway swelling can occur postoperatively and put these patients at risk for postoperative airway obstruction. How do we protect these patients? In its infancy, TORS patients were often left intubated for 24-48 hours to avoid this problem. As we have gained experience, more patients are now extubated at the end of the procedure but how can we tell when it is safe?

In a review of the University of Pennsylvania experience, certain “high-risk” groups are left intubated at the end of the procedure. These include dissection near the vallecula or epiglottis, prolonged cases in which tongue swelling is a concern, and supraglottic partial laryngectomies. Their indications for tracheostomy are resections involving both the tongue base and a portion of the epiglottis, prior difficult intubations, and medical indications such as morbid obesity. Tongue-based lesions are particularly concerning. Data at the Mayo Clinic showed a third of our TORS patients had tracheostomies; all had base of tongue tumors. We also utilize the “reversible extubation” technique described by Mort and others, where we extubate over an airway exchange catheter. We usually leave the catheter in place for 30-120 minutes, although prolonged use has been described in ICU patients. More work needs to be done to stratify the risks in these patients and hone the approach to airway management postoperatively.

Safety considerations

Lasers can cause injuries to both the patient and procedural personnel via the beam energy (i.e., retina, fire, and noxious waste of oxidation). Laser safety can only be ensured by following rigid criteria for operation which protects patients and personnel.

Laser light energy: eye protection

The cornea and retina are at risk from exposure to laser light, and must be protected with the appropriate eye protection, and without proper precautions cataract formation and blindness are possible. Eye protection must be used in accordance with the particular laser energy in use. Glasses with glass or plastic lenses are adequate protection for CO2 laser, but contact lenses are not. A warning sign be place on the door warning visitors to the procedural area as to the laser danger. Patients need the same protection (i.e., moist multilayer gauze pads on eyes during laser therapy).

Laser light energy: skin protection

During the laser procedure, skin, teeth, and mucous membranes outside the field must be protected. This may be done by placing a double layer of moist gauze, and for larger areas, surgical towels may be needed. The moistness must be present throughout the procedure to maintain the protective barrier.

Byproducts of combustion: plume hazard

Relate to the plume radiation and content. The smoke plume is a byproduct of the laser interacting with the treated tissue. The plume radiation risks arise from the plume reacting with the laser energy. There is concern this radiated plume may be mutagenic. Also, papillomavirus and other viruses produce airborne particles when treated although clinical transmission has not been documented. Other plume hazards may include temporary blindness. Continuous smoke evacuation is required.

Fire

The fire safety during laser procedures on the airway is extremely important because of the high risk. The presence of oxygen will allow materials such as drapes to burn very quickly. The most immediate danger is the ETT being hit by the laser energy, and the burning ETT may cause a devastating airway injury to the patient. It is important for to be vigilant and to know how to react in such an emergency. See previous section for management.

Safety regulations

The safe use of lasers is regulated by three US federal regulations. The Safe Use of Lasers in Education Institutions regulates the safe use during educational use. The Safe Use of Lasers in Health Care Facilities regulates the installation, operation and maintenance of lasers in health care facilities. The laser industry is regulated by the American National Standard for Safe Use of Lasers.

m. Does the patient have a history of allergy to anesthesia?

Malignant hyperthermia (MH)

Docum cinylcholine and inhalational agents. Follow a proposed general anesthetic plan: total intravenous anesthesia with propofol ± opioid infusion ± nitrous oxide. Ensure an MH cart is available [MH protocol].

Family history or risk factors for MH

Local anesthetics/muscle relaxants:

Recall that local anesthetics belong to two chemical classes (amides and esters). If a true allergy is present, it is most likely due to an ester class local anesthetic. Indeed, even in this rare situation the allergy may be from a local anesthetic metabolite such as para-amino-benzoic acid (PABA) or a preservative. If a true allergy is suspected, either a local anesthetic from another chemical class should be used or local anesthetic use should be withheld.

What's the Evidence?

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