Laser resistant stainless steel endotracheal tube: Experimental and clinical evaluation

Lasers in Surgery and Medicine 11:301306 (1991)

Laser Resistant Stainless Steel Endotracheal Tube: Experimental and Clinical Evaluation Marvin P. Fried, MD, FAcS, S. Rao Mallampati, MD, Fang-Cheng Liu, MD, Stuart Kaplan, BS, David S. Caminear, BS, and Bernadette R. Samonte, BS Joint Center for Otolaryngology and the Deparfment of Otology and Laryngology (M.P.F.), the Surgical Research Laboratory (F.-C.L., S.K., D.S.C., B.R.S.), Harvard Medical School, and the Department of Anesthesiology (S.R.M.), Brigham & Women’s Hospital, Boston, MA.

A fire due to endotracheal tube (ET) ignition is a catastrophic event that may occur during laser surgery of the upper airway, regardless of the wavelength utilized. Although methods exist that permit laser surgery without an ET, this is frequently not feasible. The current investigation was undertaken to evaluate the efficacy of a double-cuffed stainless steel ET, first in the laboratory and subsequently in a clinical setting. Bench testing was performed using CO, (both standard and milliwatt) and KTP/532 lasers. Only the distal polyvinyl chloride cuffed end of the tube was potentially ignitable, however, the appropriate use of saline to fill the cuffs allowed only for cuff perforation without ignition. Canine testing was performed in 10 animals: 4 dogs were intubated from 3 to 4.5 hours with the laser resistant stainless steel endotracheal tube (LRSS-ET) (Laser-Flex Tracheal Tube; Mallinckrodt Anesthesia Products, St. Louis, MO) and 2 with an aluminum tape wrapped red rubber ET. Visual and histological examination were performed in both groups at 3 and 7 days. Four dogs underwent CO, laser laryngeal surgery with visual and histological examination performed at 7 days postoperatively. No untoward effects could be demonstrated due to the LRSS-ET. A clinical study was then performed in 24 patients who underwent laser surgery of the upper aerodigestive tract with either a CO, or KTP/532 laser. In all cases ventilation was adequate, the shaft of the LRSS-ET proved impervious to the laser, and the distal end of the tube protected the tracheobronchial tree safely. It is concluded that the LRSS-ET is effective and safe in both CO, and KTP-532laser surgery of the upper airway when ET intubation is deemed necessary. Key words: CO,, KTP, ignition, safety

INTRODUCTION

The use of the laser has become an established method to assist in the diagnosis and treatment of numerous disorders of the head and neck, many of which require general anesthesia. Techniques such as Venturi ventilation exist that allow surgery to be accomplished without an (ET); however, this is frequently not an appropriate or feasible alternative. Surgical procedures of the nasal passage, oral cavity and pharynx require 0 1991 Wiley-Liss, Inc.

endotracheal intubation and not Venturi ventilation. The potential for bleeding or the presence of an airway obstructing lesion necessitates the use

Accepted for publication January 25, 1991. Address reprint requests to Dr. Marvin P. Fried, 333 Longwood Avenue, Boston, MA 02115. This paper was presented at the American Laryngological Association Meeting in Palm Beach, FL, April 29, 1990.

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Unilase) and a KTP/532 laser (Laserscope). The Xanar Laser was set at 5, 10, 15 and 20 watts, a spot size of 2.0 mm with power densities correNasal, oral cavity, pharyngeal surgical site sponding t o 160, 320, 480, and 640 watts/cm2 rePotential bleeding spectively. The exposure duration was 0.1 second Obstructing tumor Concern of tumor seeding into distal airway pulses or continuous. The milliwatt I.L. Med Unilase testing utilized the following parameters: 4.5 and 8.0 watts; 0.3 mm spot size; 6,370 and of an ET, as well as a distal cuff t o protect the 11,320 watts/cm2 power densities, 0.3 second tracheobronchial tree (Table 1). pulsed mode or continuous exposure. The differWhen an ET is used during laser surgery, ences in power densities of the 2 COz laser units regardless of the laser wavelength, the potential are results of the marked difference in laser spot for ignition of the ET, fire and its consequences size. The KTP/532 laser settings were 10 watts, must be considered [l]. Various types of ETs are 0.2 mm spot size, 31,832 watts/cm2 and continucurrently being utilized, none of which consis- ous exposure. The duration of all exposures was tently protect from laser impact, do not take up one minute, unless an effect was noted at which much of the airway, are designed specifically for time the exposure was terminated. The laser laser use, have a distal cuff, and can be used for beam was always emitted through a microscope more than a single laser wavelength. A recently attachment. Oxygen was flowing through the designed (LRSS-ET) fulfills many of these needs tubes at rates of 4.0 to 5.0 L/min. Three test sites (Fig. 1). were evaluated on each tube during each bench The LRSS-ET tube body consists of a flexible test: stainless steel shaft, polyvinyl chloride stainless steel hose with a soft plastic tubing seg- (PVC) cuffs, and PVC tip. Observations were rement at the distal end. It is available in 2 sizes corded and video documentation was performed. [6.0 mm I.D. (inner diameter) with 8.5 mm O.D. (outer diameter); 4.5 mm I.D. with 7.0 mm O.D.] Canine Testing and has 2 cuffs, each with an associated selfTen mongrel dogs weighing an average 50 sealing valve and pilot balloon. The tube design lbs. were divided into 3 groups. Animals used in includes a Magill curve and a Murphy tip with this study were maintained in accordance with eye. The body of the tube is such that contact with the guidelines of the Committee on Animals of a laser beam should not cause perforation, but the Harvard Medical School and those prepared will result in the reflection of a defocused beam. by the Committee on Care and Use of Laboratory The proximal cuff, when filled with saline, should Animals of the Institute of Laboratory Animal shield the distal cuff from unintentional laser Resources, National Research Council (DHHS beam contact, thereby allowing for a tracheal seal publication No. (NIH) 85-23, Revised 1985). Anand protecting the distal tip. The tube is dispos- esthesia was administered by intravenous pentoable with a current cost of $63.00. A series of ex- barbital (Nembutal, 50 mg/ml) and maintained periments were designed to evaluate the safety using a 0-1% halothane (Fluothane) and 2.5 L/ and efficacy of the LRSS-ET in both the labora- min. oxygen. tory and clinical setting using the CO, as well as The 4 dogs of Group I were intubated with the KTP/532 laser. the LRSS-ET for 3 to 4.5 hours. Post-intubation biopsies were taken at 3 and 7 days. The left true vocal cord, arytenoid, and subglottic region were MATERIALS AND METHODS biopsied on the third post-intubation day, while In vitro, canine and human testing of a the equivalent right laryngeal structures were biLRSS-ET were performed. The in vitro and canine opsied on the seventh post-intubation day. The experiments used an 6.0 mm inner diameted8.5 status of each larynx was video recorded and a mm outer diameter ET tube, and both of the cuffs clinical impression was noted at the time of biwere filled with saline according t o manufactur- opsy. Samples were prepared histologically by er's specifications. routine method and stained with hematoxylin and eosin (H&E). Two dogs comprising Group I1 In Vitro Testing were intubated with an aluminum tape wrapped The in vitro bench tests were conducted us- red rubber ET (Realistic Tape & Rusch ET) for 3.5 ing two models of CO, lasers (Xanar and I.L. Med to 4 hours. The remaining protocol was then conTABLE 1. When Is an Endotracheal Tube Mandatory?

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Fig. 1. Photo of LRSS-ET tube.

sistent with that of group I. Four dogs comprising Group I11 were intubated with the LRSS-ET and underwent subsequent CO, laser surgery of the larynx. Each dog had a laser cordectomy and laser arytenoidectomy while the surgeon intentionally impacted the tube in order to potentially induce ignition. Biopsies of the surgical sites were taken at 7 days post-laser surgery. The laser surgery and subsequent laryngoscopy and biopsy were video recorded and the samples were evaluated histologically with H & E stain.

choline 1mg/kg was given intravenously t o facilitate endotracheal intubation (precurarization was not used). Lidocaine (4%)in a dose of 4 cc was sprayed onto laryngo-tracheal mucosa for topical anesthesia immediately prior t o intubation. Following recovery from succinylcholine, muscle relaxation was achieved with pancuronium, atracurium or vecuronium, monitored by nerve stimulator. One patient received no muscle relaxants because of a family history of myotonia dystrophica. One patient underwent awake intubation because of an obstructing carcinoma of the piriform sinus. This was a 77-year-old female who Human Testing had no other known health problems. Although Twenty-four patients who were t o undergo there was no airway compromise, we chose t o peroral and/or laryngeal laser surgery were ap- form an awake intubation for safety. Following proached by the principal investigator for permis- adequate topicalization of the oropharyngeal airsion t o be enrolled in this study. Participation was way with 4% lidocaine spray and preoxygenation, voluntary and in accordance with the guidelines orotracheal intubation was accomplished swiftly of the Committee for the Protection of Human by direct laryngoscopy; the patient tolerated the Subjects from Research Risks of the Brigham & intubation well, which was immediately followed Women’s Hospital. Each patient signed a written by a sleep dose of thiopental and atracurium. consent. Ten patients were premedicated with 10 Three patients were intubated with a 4.5mm 1.D.I mg diazepam and 0.4 mg atropine 1 hour before 7.0mm O.D. LRSS-ET, and 21 patients intubated surgery. Six patients received 1mg of midazolam, with a 6.0mm I.D.18.5 mm O.D. LRSS-ET. Me5 received midazolam (1-4 mg) and fentanyl100- chanical ventilation was carried out at 10 cc/kg 200 pg, 1received fentanyl 100 pg and 2 patients body weight, at a rate of 8-10 respirations per were not premedicated. A radial arterial catheter minute. Anesthesia was maintained with fentawas placed under local anesthesia approximately nyl and isoflurane in 20 patients and with fentaone-half hour prior to induction to obtain samples nyl and enflurane in 4 patients. Oxygen (30%) for serial blood gas determinations. Following and Nitrous oxide (70%) were used in all cases. preoxygenation with 100% oxygen for approxi- Pulse oximeter readings were noted 5 minutes mately 1 minute, anesthesia was induced with prior to, and after induction with further readings thiopental 5 mg/kg (or more if necessary) until taken at 1minute and every 5 minutes thereafter the loss of eyelash reflex was achieved. Succinyl- into the surgical procedure. Arterial blood gases

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were measured every 5 minutes before induction

TABLE 2. Laser Procedures Utilizing the LRSS-ET

while the patient was breathing room air and again at 1, 15, an 30 minutes post-induction. After completion of surgery, the patient was awakened, transferred to the recovery room where the arterial line was removed.

Procedure

Laryngeal surgery Tonsillectomy Excision of oral cavity lesion Uvulopalatopharyngoplasty Excision of tracheal lesion Total

cos

KTP

3

8 7 2 2 1 20

-

1 4

Total 11 7 3 2 1 24

RESULTS In vivo Testing Using the milliwatt laser (I.L. Med Unilase) (Spot size 0*3mm),the LRSS-ET was tested twice cal cord biopsy specimens at 3 and 7 days. There at 4.5 Watts (W) (6,370 W/cm2)and twice at 8.0 W were no abnormalities Seen in the subglottic mu(11,320 W/cm2)-Using the CO, laser with a 2.0 cosa. ~ 1 specimens 1 were normal after aluminum mm spot size (Xanar), the tubes were tested once taped red rubber ET intubation. at 5.0 W (160 W/cm2)and 10 W (320 W/cm2) and Although attempts were made to intentiontwice each at l5 (480 W/cm2) and 2o (640 ally impact the LRSS-ET tube while performing a W/cm2). The tube was also tested once with the cordectomy and arytenoidectomy in 4 animals, KTP/532 laser (spot size 0.2 mm) at 10 (3l7832 the tube could not be ignited. Cuff perforation ocW/cm2).Neither laser wavelength yielded a ViSi- curred in these procedures, with release of the ble alteration of the tube's shaft throughout the saline, but without ignition of the distal tip. Ob11 procedures in either pulsed or continuous servation of these 4 larynges 1 week postoperamode. tively disclosed diffuse, mild edema, with slight The tube cuffs Were impacted On looccasions granulation near the residually exposed aryteby the coz laser with power densities ranging noid cartilage. Histology showed the expected from 160 W/cm2 to 11/320 W/cm2 and Once with acute mild t o moderate inflammatory response the KTP/532 at 317832 W/cm2* the but with muscular disruption and coagulation, 7 days one, were perforated within 2 seconds under both after laser surgery. pulsed and continuous exposure by both laser wavelengths releasing the saline, but causing no Human Testing other alteration. Twenty-three patients underwent oral traThe distal polyvinyl chloride tip of the tube was impacted by the CO, laser once each at power cheal intubation with 1patient having the LRSSdensities of 480 and 640 W/cm2 (Xanar); and, ET placed via tracheotomy. The procedures pertwice at a power density of 6,370 W/cm2.Exposure formed (Table 2) involved surgery on the larynx, in the pulsed mode yielded an instantaneous sur- trachea, oropharynx and oral cavity. The KTP laface effect evidenced by pin-point burning. Con- ser was used both in the microscope-mounted and tinuous lasering produced a surface effect at the hand-held fiber modes. In almost every instance lowest power density and eventual tip ignition at the ET was in close proximity t o the site of laser the highest two power densities. The KTP/532 at surgery. In no case was there any untoward event a power density of 31,832 W/cm2was fired once in involving the laser and ET at either the shaft or the continuous mode and ignited the tube causing cuff. Intubation, as well as, extubation were easily performed in all of these patients. an intraluminal fire. Table 3 shows the oxygen saturation values Canine Testing as read by the pulse oximeter and arterial blood Observation of the larynges of the 4 dogs in- gas values determined preoperatively and intratubated with the LRSS-ET and the 2 dogs intu- operatively. All patients were oxygenated and bated with an aluminum taped wrapped red rub- ventilated well throughout the laser procedures ber ET disclosed no abnormalities at 3 or 7 days indicating the adequacy of ET size. It was noted, post-intubation. Histology of the biopsy speci- however, that wherever possible the large ET was mens after LRSS-ET intubation revealed only preferable with diminished airway resistance. mild inflammation of the arytenoid mucosa in 2 The 3 patients intubated with 4.5 inner diameter specimens at 3 days and in 3 specimens at 7 days. LRSS-ET were females, weighing 105 to 113 Minimal inflammatory response was seen in 3 vo- pounds, with small body mass.

w

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TABLE 3. Pulse Oximeter Readings and Arterial Blood Gas Analysis Results

Relationship to induction 5 minutes before induction 1 minute after induction 15 minutes after induction 30 minutes after induction

Pulse oximeter (0, Sat%) avghange 97.18 (93-100) 99 (97-100) 98.4 (96-100) 97.8 (95-100)

PO, (TORR) avghange 84.77 (63-99) 259.08 (121-565) 205.43 (96-540) 215.0 (120-526)

DISCUSSION

Of the complications that can occur during laser surgery of the upper airway, ignition and explosion of the ET are the most catastrophic and may be the most common [ll. An ideal ET should possess certain characteristics (Table 4). No such ET currently exists. The LRSS-ET is shown to be impervious t o CO, and KTP wavelengths in our in vitro, canine and human testing. The potentially ignitable site at the level of the double-cuff can be protected when saline is instilled as the inflating agent. We found the only way to cause any ignition was t o impact the distal Murphy eye which in all clinical situations would be a virtual impossibility. There is currently no material used to manufacture an inflatable cuff that is laser impervious. The corrugated nature of the metallic shaft has the benefit of dispersing the energy upon impact, but with the disadvantage of potential abrasion of the mucosa, a phenomenon we did not observe clinically, but was noted in the histologic canine specimens. Thermal conductivity could cause a potential problem, but with the flow of ventilation gases, any heat is quickly dispersed. Our animal experiments were specifically designed for prolonged intubation, and surgical procedures that would intentionally cause the laser t o impact the ET. Our laboratory findings of laser resistance are similar to those reported by others [2,3,41. We found the LRSS-ET t o be an exceptionally safe device for surgery of the upper airway and not affected by blood or dark debris in the shaft. The absence of concern with adequacy of wrapping with a laser impervious tape, or any shaft ignition potential was very reassuring. Because of the metallic nature of the tube, however,

Arterial Blood Gases PCO, (TORR) PH avghange avghange 42.54 7.37 (35-49) (7.12-7.45) 40.00 7.40 (31-50) (7.31-7.48) 34.95 7.42 (28-50) (7.12-7.55) 38.12 7.40 (31-49) (7.30-7.48)

Base excess (MEqlL) avg./range 1.09 ( + 4 to -2) 0.75 ( + 4 to -2) 0.30 ( + 6 to -3) 0.4 ( + 5 to -4)

TABLE 4. Ideal Properties of a Laser Safe ET Tube Non-flammable cuff and shaft Malleable Thin-walled Soft, pliable, low-pressure cuff Impervious to multiple wavelengths Non-conductive electrically Disposable InexDensive

direct contact of the ET with electrocautery devices should be avoided since the potential exists for electrical transmission along the tube. The flexibility of the ET allowed for ease of intubation. Adequate oxygenation and delivery of the anesthetic agents was also obtained. The thickness of the LRSS-ET wall is somewhat greater than the conventional ET, thereby narrowing the inner diameter. Hypercarbia was not observed even 30 minutes after induction. The larger tube should be used, if at all possible, to assure for minimum airway resistance. It has been suggested [31 that the distal cuff be inflated first with saline and the proximal cuff inflated with methylene blue-tinged fluid to serve as a marker for any cuff disruption due t o laser impact. In 1 patient, not included in this series because of preoxygenation prior to obtaining the first blood gas testing, extubation was somewhat difficult. In this circumstance, the deflated cuff lodged on the under surface of adducted vocal cords. Adequate relaxation, re-inflation and deflation of the cuff allowed for extubation without untoward sequelae. The absence of an ET in the airway during laser surgery is the ideal situation in order t o prevent any potential ignition risk. This can be

Fried et al. achieved by Venturi ventilation either proximal ACKNOWLEDGMENTS

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or distal to the site of lasering. As noted above, there are circumstances when an ET is mandatory. In these situations the LRSS-ET was found to be an excellent device for CO, and KTP laser surgery. CONCLUSIONS

A LRSS-ET is evaluated and has shown t o be safe in the laboratory and human testing. The benefits include the impervious nature of the shaft and double-cuff design. The physician should be aware, however, of the narrower lumen than comparably sized outer diameter tubes, the potential of electrical conductivity, and the need for careful extubation. This device was found to be an exceptionally safe ET for both CO, and KTP laser surgery.

This study was supported by grants from the Mallinckrodt Anesthesia Products, St. Louis, MO and the Brigham Surgical Group, Brookline, MA.

REFERENCES 1. Fried MP. A survery of the complications of laser laryngoscopy. Arch Otolaryngol Head Neck Surg 1984; 110:3134. 2. Sosis MB, Heller S. A comparison of special endotracheal tubes for arc with the CO, laser. Anesthesiology 1988; 69(3A):251. 3. Garry B, Bivens HE. Laser safety in the operating room. 1. Administering anesthesia. CA Bull 1989; 41:219-223. 4. Fried MP, Mallampati SR, Caminear DS. Comparative analysis of the safety of endotracheal tubes with the KTP laser. Laryngoscope 1989; 99:748-751.