Lasers Med Sci 1999, 14:158–162 © 1999 Springer-Verlag London Limited
The Safety of Common Voice Prostheses with ENT Lasers A. Murray and B.J.G. Bingham Department of Otolaryngology – Head and Neck Surgery, Victoria Infirmary, Glasgow, UK
Abstract. Silicone voice prostheses, or valves, are inserted into the common tracheo-oesophageal wall of patients after laryngectomy, to allow speech rehabilitation. Granulation tissue around these voice prostheses is often removed by laser and the safety of these valves with lasers had not been confirmed. The common valves were exposed to increasing energies from the carbon dioxide, potassium-titanyl-phosphate and holmium YAG lasers, in air. The energies used were those in common clinical use. The Provox valves proved especially vulnerable to all laser energies. Other methods of removing granulation tissue should be tried prior to lasering, or the valves should be removed, as damage to them, or the patient’s airway, can result. Keywords: Equipment failure; Evaluation studies; Granulation tissue; Prosthesis design; Larynx, artificial (adverse e#ects); Laser surgery
INTRODUCTION At present, the majority of patients undergoing a total laryngectomy have a voice prosthesis inserted, as a primary or secondary procedure. The commonest complication produced by the indwelling valves is the formation of granulation tissue, around the valve [1,2]. It is suggested that airway granulation tissue may be due to local infection and can therefore respond to intensive antimicrobial therapy [3,4]. If this is unsuccessful, the excess tissue can be surgically removed, usually by laser [5]. Since the granulation tissue is related to the presence of the valve, the valve is often removed before lasering. However, it has been stated, by clinicians experienced in voice prosthesis use, that, in an attempt to maintain the function of the valve, lasering can be performed with the valve left in situ. Although e#orts have been made to assess the safety of the materials used in endotracheal tubes in the presence of otolaryngological lasers [6–10], the flammability, and therefore safety, of the common voice prostheses has not been previously investigated. This study examines the e#ect of varied laser exposure on these prostheses. Correspondence to: Mr B.J.G. Bingham, Department of Otolaryngology – Head & Neck Surgery, Victoria Infirmary, Langside Road, Glasgow G42 9TY, UK.
Fig. 1. The voice prostheses tested in these laser experiments.
MATERIALS AND METHODS The valves included in the study were the Provox 1—the Provox 2 is basically the same in terms of materials (Atos Medical, Ho¨rby, Sweden), Blom–Singer duckbill, and indwelling Blom–Singer (International Health Care Technologies, Carpinteria, California, USA), which are all commercially available (Fig. 1). The lasers used were the potassium–titranyl– phosphate (KTP), the carbon dioxide (CO2) and the holmium–yttrium–aluminium–garnett (HoYAG), at varying energy levels. The constituents of all the valves tested were similar in that they were essentially made from silicone, which is also frequently used in endotracheal tube manufacture. The radiological
The Safety of Common Voice Prostheses with ENT Lasers
markings within the Provox and indwelling Blom–Singer valves, often a vulnerable part of endotracheal tubes in laser experiments, were also tested. In addition, when testing the KTP laser, a quantity of blood was introduced onto the valves, to assess if the absorption of the green KTP laser energy was increased, as would be expected from previous experiments on middle ear prostheses [11]. The other factor assessed was whether or not Candida on the valves made any di#erence to the laser energy being absorbed. Experiments were conducted in air. The valves were tested with the ranges of power and exposure lengths used in clinical practice. Due to the di#erent modes of laser energy delivery between a collimated beam and a fibreoptic delivery system, it is technically very di$cult to achieve equal power densities at the point of laser strike. The experiments, therefore, should be seen as each laser assessing di#erent valves, rather than each valve being assessed by three di#erent equivalent laser energies. With each laser and valve combination, power was gradually increased and the valve reactions noted. The CO2 laser initially delivered 4 W at 0.2 s exposure, for five exposures, via a handpiece spot size of 600 m. The exposure and power were increased for the second and third set of strikes to 10 W, 0.2 s, for five exposures, and 16 W continuous, respectively. The KTP laser delivery was via a 600 m fibre, and started at 4 W for 0.2 s exposure, for five exposures. This was then increased to 10 W, 0.5 s, for five exposures, and then to 10 W continuous. The HoYAG laser was also delivered by a fibre, of 365 m and an initial exposure of 0.5 J for 2.5 s. The rate was eight pulses per second (pps) and total exposure was for 1 s. This was then increased to 1 J for 2.5 s, at 8 pps, and then 1 J for 2.5 s at 20 pps. The e#ects of the lasering were recorded photographically and by video.
RESULTS The results (Table 1.) show that the Provox valves have a greater susceptibility to all forms of laser energy tested, compared with both types of Blom–Singer valve. In particular, the Provox radiological blue ring was extremely flammable, in direct contrast to the resistance shown by the radiological marker of
159
the Blom–Singer indwelling valve (Figs 2 and 3). Admittedly, from the position of these markers, it would be di$cult to strike them with a laser clinically, but not entirely improbable. The silicone clear portion of each indwelling valve also showed marked variation in flammability, despite both being apparently very similar in the manufacturer’s description. The Blom–Singer indwelling proved much more resistant again than the Provox, which charred and melted at lower energies. The duckbill Blom–Singer showed similar resistance to its indwelling variant. Attempting to increase the absorption of the KTP laser onto the valves by adding blood pigment, made no obvious di#erence. If anything, the liquid acted as a heat sump, protecting the valve, rather than causing more damage. This is in contrast to previous experiments with the KTP laser on middle ear prostheses [11]. The e#ect of Candida plaques during lasering, was similarly limited, with no obvious di#erence.
DISCUSSION In the presence of an oxygen-rich atmosphere, as commonly exists during airway surgery under general anaesthesia, the ignition of combustible materials by a laser can be disastrous. All materials that may be present during such conditions should either be removed or rendered as non-flammable as possible. The common endotracheal tubes have been rigorously assessed for laser safety [6–10]. Unwrapped silicone-based endotracheal tubes, to which voice prostheses are most similar in material, have been shown to be vulnerable to laser energy [7–10], although, of all the materials used for tube manufacturing, there is evidence that it is relatively resistant to the CO2 laser [6,7]. However, when energy levels are high enough, ignition occurs. We found no striking di#erence between the type of laser and its e#ect on each valve. Certainly, at clinical settings, no laser appeared to be much more potent or dangerous than any other, despite the considerable variation in their modes of action, and their di#ering power densities. The CO2 laser is the commonest currently in use in otolaryngology. The CO2 laser energy is absorbed by water and tissue vaporisation is
4 10 16 4 10 10 4 10 10 0.5/8 1/8 1/20
0.2 s 0.2 s Cont 0.2 s 0.5 s Cont 0.2 s 0.5 s Cont 2.5 s 2.5s 2.5 s
Exposure time
— + + + + ++ + + ++ + + ++
Blom–Singer duckbill
Prosthesis type
Cont, continuous. —, No obvious e#ect; +, melting; + +, charring; + + +, vaporisation.
HoYAG (J/pulses/s)
KTP+blood (W)
KTP (W)
Carbon dioxide (W)
Laser type
Power/energy setting
Table 1. Results of laser treatment of voice prostheses
— + + — — + — — + + + ++
Blom–Singer indwelling — + + — + + — — + + + ++
Blom–Singer X-ray line
+ + ++ ++ ++ ++ + ++ ++ ++ ++ +++
Provox
+ + ++ ++ ++ ++ + ++ ++ ++ ++ +++
Provox +Candida
+ + ++ ++ +++ +++ ++ ++ +++ ++ +++ +++
Provox X-ray line
160 A. Murray and B.J.G. Bingham
The Safety of Common Voice Prostheses with ENT Lasers
Fig. 2. The radiological marker of the Provox value after lasering with KTP 10 W.
Fig. 3. The radiological marker of the Blom–Singer indwelling valve after lasering with KTP 10 W.
swift. Surronding tissue damage is minimal and postoperative oedema is reduced [12]. Obviously though, inorganic materials, despite having no water content, will also absorb CO2 laser energy and convert it into heat, causing melting and possible ignition [13]. This is the mechanism of injury we have demonstrated. The KTP laser is a solid state laser with a visible spectrum wavelength (green 532 nm) and is absorbed by red pigment, which may theoretically improve its haemostatic properties. KTP laser energy will pass through clear material, such as silicone, but if small particles of debris are present, ignition may follow [8]. The HoYAG is a pulsed laser (2120 nm) which has a low thermal component and removes tissue by photo-ablation [14]. It has previously been used in the aerodigestive tract [15]. Experimental evidence has shown that silicone and polyvinyl chloride endotracheal tubes can be perforated with the HoYAG laser including ‘laser safe’ tubes [10], mainly due to its distinctive mechanism of action. We have shown that all these lasers are capable of damaging voice prostheses. The most obvious finding from the experiments was the flammability of the Provox valve constituents, compared to the Blom– Singer. Manufacturing details are confidential but, although described as the same materials, it is clear from holding these valves, as well as lasering them, that their constituents are different. It is also probable that the selection of the raw materials is made on factors apart
161
from flammability. This is perhaps, an aspect which needs fuller consideration by the manufacturers concerned. The di#erence in flammability was evident across all the lasers tested. In particular, the radiological blueline of the Provox was extremely flammable, and suggests that great care should be taken when lasering around these valves, as stray hits could potentially strike this material. Our experiments were carried out in air but it is probable that the oxygen concentration in the area of a valve being lasered, would be higher, due to oxygen leakage around an anaesthetic tube, as they are often manipulated to allow access to the target tissues. This could further increase the flammability of the materials we tested, since an increase in oxygen concentration increases the likelihood of ignition. CONCLUSION If, during laser removal of granulation tissue around a voice prosthesis, the valve is accidentally struck, the consequences are much less dependent on which laser is being used, than on which valve is in place. The Blom–Singer valves appear more resistant to laser energy than the Provox, which is much more flammable, especially its radiological marker. It would seem that if granulations are a problem around valves then the simpler methods of removal, such as antibiotic treatment, silver nitrate or electrocautery, may be worth considering before resorting to a potentially dangerous laser technique. It may be safer to accept that the valve has to be removed, and then reinserted when the granulations have resolved. REFERENCES 1. Manni JJ, Van den Broek P. Surgical and prosthesis related complications using the Groningen button voice prosthesis. Clin Otolaryngol 1990; 15:515–23. 2. Van den Hoogen FJA, Oudes MJ, Hombergen G et al. The Groningen, Nijdam and Provox voice prostheses: a prospective clinical comparison based on 845 replacements. Acta Otolaryngol (Stockh) 1996; 116:119– 24. 3. Matt BH, Myer CM 3rd, Harrison CJ et al. Tracheal granulation tissue. A study of bacteriology. Arch Otolaryngol Head Neck Surg 1991; 117:538–41. 4. Brown MT, Montgomergy WW. Microbiology of tracheal granulation tissue associated with silicone airway prostheses. Ann Otol Rhinol Laryngol 1996; 105:624–7.
162 5. Punzal PA, Myers R, Ries AL, Harrell JH 2nd. Laser resection of granulation tissue secondary to transtracheal oxygen catheter. Chest 1992; 101:269– 71. 6. Ohashi N, Asai M, Ueda S et al. Hazard to endotracheal tubes by CO2 laser beam. Experimental report. ORL J OtoRhinoLaryngol Relat Spec 1985; 47:22–5. 7. Duncanavage JA, Osso# RH, Rouman WC et al. Injuries to the bronchi and lungs caused by laserignited endotracheal tube fires. Otolaryngol Head Neck Surg 1984; 92:639–43. 8. Fried MP, Mallampati SR, Caminear DS. Comparative analysis of the safety of endotracheal tubes with the KTP laser. Laryngoscope 1989; 99:748–51. 9. Simpson JI, Wolf GL, Rosen A et al. The oxygen and nitrous oxide indices of flammability of endotracheal tubes determined by laser ignition. Laryngoscope 1991; 101:981–4. 10. Kautzky M, Fitzgerald R, Dechtyar I, Schenk P. E#ects of the holmium:YAG and erbium:YAG lasers on
A. Murray and B.J.G. Bingham
11.
12.
13.
14.
15.
endotracheal tubes. ORL J OtoRhinoLaryngol Relat Spec 1993; 55:105–9. Wanamaker HH, Silverstein HS. Compatibility of the argon and KTP lasers with middle ear implants. Laryngoscope 1993; 103:609–13. Roodenburg JLN, Panders AK, Vermey A et al. Histology of lasered tissue. In: Oswal VH, Kashima HK, Flood LM (eds) The CO2 Laser in Otolaryngology and Head and Neck Surgery. John Wright (imprint of Butterworth Scientific), 1988, Ch 4. Mihashi S, Jako GJ, Incze J et al. Laser surgery in otolaryngology: interaction of CO2 laser and soft tissue. Ann NY Acad Sci 1976; 267:263–94. Kautzky M, Susani M, Steurer M, Schenk P. Soft tissue e#ects of the holmium:YAG laser: an ultrastructural study on oral mucosa. Lasers Surg Med 1997; 20:265–71. Gleich LL, Rebeiz EE, Pankratov MM, Shapsay SM. The holmium:YAG laser-assisted otolaryngologic procedures. Arch Otolaryngol Head Neck Surg 1995; 121:1162–6.
Paper received 3 January 1998; accepted after revision 25 November 1998.
The Safety of Common Voice Prostheses with ENT Lasers A. Murray and B.J.G. Bingham Department of Otolaryngology – Head and Neck Surgery, Victoria Infirmary, Glasgow, UK
Abstract. Silicone voice prostheses, or valves, are inserted into the common tracheo-oesophageal wall of patients after laryngectomy, to allow speech rehabilitation. Granulation tissue around these voice prostheses is often removed by laser and the safety of these valves with lasers had not been confirmed. The common valves were exposed to increasing energies from the carbon dioxide, potassium-titanyl-phosphate and holmium YAG lasers, in air. The energies used were those in common clinical use. The Provox valves proved especially vulnerable to all laser energies. Other methods of removing granulation tissue should be tried prior to lasering, or the valves should be removed, as damage to them, or the patient’s airway, can result. Keywords: Equipment failure; Evaluation studies; Granulation tissue; Prosthesis design; Larynx, artificial (adverse e#ects); Laser surgery
INTRODUCTION At present, the majority of patients undergoing a total laryngectomy have a voice prosthesis inserted, as a primary or secondary procedure. The commonest complication produced by the indwelling valves is the formation of granulation tissue, around the valve [1,2]. It is suggested that airway granulation tissue may be due to local infection and can therefore respond to intensive antimicrobial therapy [3,4]. If this is unsuccessful, the excess tissue can be surgically removed, usually by laser [5]. Since the granulation tissue is related to the presence of the valve, the valve is often removed before lasering. However, it has been stated, by clinicians experienced in voice prosthesis use, that, in an attempt to maintain the function of the valve, lasering can be performed with the valve left in situ. Although e#orts have been made to assess the safety of the materials used in endotracheal tubes in the presence of otolaryngological lasers [6–10], the flammability, and therefore safety, of the common voice prostheses has not been previously investigated. This study examines the e#ect of varied laser exposure on these prostheses. Correspondence to: Mr B.J.G. Bingham, Department of Otolaryngology – Head & Neck Surgery, Victoria Infirmary, Langside Road, Glasgow G42 9TY, UK.
Fig. 1. The voice prostheses tested in these laser experiments.
MATERIALS AND METHODS The valves included in the study were the Provox 1—the Provox 2 is basically the same in terms of materials (Atos Medical, Ho¨rby, Sweden), Blom–Singer duckbill, and indwelling Blom–Singer (International Health Care Technologies, Carpinteria, California, USA), which are all commercially available (Fig. 1). The lasers used were the potassium–titranyl– phosphate (KTP), the carbon dioxide (CO2) and the holmium–yttrium–aluminium–garnett (HoYAG), at varying energy levels. The constituents of all the valves tested were similar in that they were essentially made from silicone, which is also frequently used in endotracheal tube manufacture. The radiological
The Safety of Common Voice Prostheses with ENT Lasers
markings within the Provox and indwelling Blom–Singer valves, often a vulnerable part of endotracheal tubes in laser experiments, were also tested. In addition, when testing the KTP laser, a quantity of blood was introduced onto the valves, to assess if the absorption of the green KTP laser energy was increased, as would be expected from previous experiments on middle ear prostheses [11]. The other factor assessed was whether or not Candida on the valves made any di#erence to the laser energy being absorbed. Experiments were conducted in air. The valves were tested with the ranges of power and exposure lengths used in clinical practice. Due to the di#erent modes of laser energy delivery between a collimated beam and a fibreoptic delivery system, it is technically very di$cult to achieve equal power densities at the point of laser strike. The experiments, therefore, should be seen as each laser assessing di#erent valves, rather than each valve being assessed by three di#erent equivalent laser energies. With each laser and valve combination, power was gradually increased and the valve reactions noted. The CO2 laser initially delivered 4 W at 0.2 s exposure, for five exposures, via a handpiece spot size of 600 m. The exposure and power were increased for the second and third set of strikes to 10 W, 0.2 s, for five exposures, and 16 W continuous, respectively. The KTP laser delivery was via a 600 m fibre, and started at 4 W for 0.2 s exposure, for five exposures. This was then increased to 10 W, 0.5 s, for five exposures, and then to 10 W continuous. The HoYAG laser was also delivered by a fibre, of 365 m and an initial exposure of 0.5 J for 2.5 s. The rate was eight pulses per second (pps) and total exposure was for 1 s. This was then increased to 1 J for 2.5 s, at 8 pps, and then 1 J for 2.5 s at 20 pps. The e#ects of the lasering were recorded photographically and by video.
RESULTS The results (Table 1.) show that the Provox valves have a greater susceptibility to all forms of laser energy tested, compared with both types of Blom–Singer valve. In particular, the Provox radiological blue ring was extremely flammable, in direct contrast to the resistance shown by the radiological marker of
159
the Blom–Singer indwelling valve (Figs 2 and 3). Admittedly, from the position of these markers, it would be di$cult to strike them with a laser clinically, but not entirely improbable. The silicone clear portion of each indwelling valve also showed marked variation in flammability, despite both being apparently very similar in the manufacturer’s description. The Blom–Singer indwelling proved much more resistant again than the Provox, which charred and melted at lower energies. The duckbill Blom–Singer showed similar resistance to its indwelling variant. Attempting to increase the absorption of the KTP laser onto the valves by adding blood pigment, made no obvious di#erence. If anything, the liquid acted as a heat sump, protecting the valve, rather than causing more damage. This is in contrast to previous experiments with the KTP laser on middle ear prostheses [11]. The e#ect of Candida plaques during lasering, was similarly limited, with no obvious di#erence.
DISCUSSION In the presence of an oxygen-rich atmosphere, as commonly exists during airway surgery under general anaesthesia, the ignition of combustible materials by a laser can be disastrous. All materials that may be present during such conditions should either be removed or rendered as non-flammable as possible. The common endotracheal tubes have been rigorously assessed for laser safety [6–10]. Unwrapped silicone-based endotracheal tubes, to which voice prostheses are most similar in material, have been shown to be vulnerable to laser energy [7–10], although, of all the materials used for tube manufacturing, there is evidence that it is relatively resistant to the CO2 laser [6,7]. However, when energy levels are high enough, ignition occurs. We found no striking di#erence between the type of laser and its e#ect on each valve. Certainly, at clinical settings, no laser appeared to be much more potent or dangerous than any other, despite the considerable variation in their modes of action, and their di#ering power densities. The CO2 laser is the commonest currently in use in otolaryngology. The CO2 laser energy is absorbed by water and tissue vaporisation is
4 10 16 4 10 10 4 10 10 0.5/8 1/8 1/20
0.2 s 0.2 s Cont 0.2 s 0.5 s Cont 0.2 s 0.5 s Cont 2.5 s 2.5s 2.5 s
Exposure time
— + + + + ++ + + ++ + + ++
Blom–Singer duckbill
Prosthesis type
Cont, continuous. —, No obvious e#ect; +, melting; + +, charring; + + +, vaporisation.
HoYAG (J/pulses/s)
KTP+blood (W)
KTP (W)
Carbon dioxide (W)
Laser type
Power/energy setting
Table 1. Results of laser treatment of voice prostheses
— + + — — + — — + + + ++
Blom–Singer indwelling — + + — + + — — + + + ++
Blom–Singer X-ray line
+ + ++ ++ ++ ++ + ++ ++ ++ ++ +++
Provox
+ + ++ ++ ++ ++ + ++ ++ ++ ++ +++
Provox +Candida
+ + ++ ++ +++ +++ ++ ++ +++ ++ +++ +++
Provox X-ray line
160 A. Murray and B.J.G. Bingham
The Safety of Common Voice Prostheses with ENT Lasers
Fig. 2. The radiological marker of the Provox value after lasering with KTP 10 W.
Fig. 3. The radiological marker of the Blom–Singer indwelling valve after lasering with KTP 10 W.
swift. Surronding tissue damage is minimal and postoperative oedema is reduced [12]. Obviously though, inorganic materials, despite having no water content, will also absorb CO2 laser energy and convert it into heat, causing melting and possible ignition [13]. This is the mechanism of injury we have demonstrated. The KTP laser is a solid state laser with a visible spectrum wavelength (green 532 nm) and is absorbed by red pigment, which may theoretically improve its haemostatic properties. KTP laser energy will pass through clear material, such as silicone, but if small particles of debris are present, ignition may follow [8]. The HoYAG is a pulsed laser (2120 nm) which has a low thermal component and removes tissue by photo-ablation [14]. It has previously been used in the aerodigestive tract [15]. Experimental evidence has shown that silicone and polyvinyl chloride endotracheal tubes can be perforated with the HoYAG laser including ‘laser safe’ tubes [10], mainly due to its distinctive mechanism of action. We have shown that all these lasers are capable of damaging voice prostheses. The most obvious finding from the experiments was the flammability of the Provox valve constituents, compared to the Blom– Singer. Manufacturing details are confidential but, although described as the same materials, it is clear from holding these valves, as well as lasering them, that their constituents are different. It is also probable that the selection of the raw materials is made on factors apart
161
from flammability. This is perhaps, an aspect which needs fuller consideration by the manufacturers concerned. The di#erence in flammability was evident across all the lasers tested. In particular, the radiological blueline of the Provox was extremely flammable, and suggests that great care should be taken when lasering around these valves, as stray hits could potentially strike this material. Our experiments were carried out in air but it is probable that the oxygen concentration in the area of a valve being lasered, would be higher, due to oxygen leakage around an anaesthetic tube, as they are often manipulated to allow access to the target tissues. This could further increase the flammability of the materials we tested, since an increase in oxygen concentration increases the likelihood of ignition. CONCLUSION If, during laser removal of granulation tissue around a voice prosthesis, the valve is accidentally struck, the consequences are much less dependent on which laser is being used, than on which valve is in place. The Blom–Singer valves appear more resistant to laser energy than the Provox, which is much more flammable, especially its radiological marker. It would seem that if granulations are a problem around valves then the simpler methods of removal, such as antibiotic treatment, silver nitrate or electrocautery, may be worth considering before resorting to a potentially dangerous laser technique. It may be safer to accept that the valve has to be removed, and then reinserted when the granulations have resolved. REFERENCES 1. Manni JJ, Van den Broek P. Surgical and prosthesis related complications using the Groningen button voice prosthesis. Clin Otolaryngol 1990; 15:515–23. 2. Van den Hoogen FJA, Oudes MJ, Hombergen G et al. The Groningen, Nijdam and Provox voice prostheses: a prospective clinical comparison based on 845 replacements. Acta Otolaryngol (Stockh) 1996; 116:119– 24. 3. Matt BH, Myer CM 3rd, Harrison CJ et al. Tracheal granulation tissue. A study of bacteriology. Arch Otolaryngol Head Neck Surg 1991; 117:538–41. 4. Brown MT, Montgomergy WW. Microbiology of tracheal granulation tissue associated with silicone airway prostheses. Ann Otol Rhinol Laryngol 1996; 105:624–7.
162 5. Punzal PA, Myers R, Ries AL, Harrell JH 2nd. Laser resection of granulation tissue secondary to transtracheal oxygen catheter. Chest 1992; 101:269– 71. 6. Ohashi N, Asai M, Ueda S et al. Hazard to endotracheal tubes by CO2 laser beam. Experimental report. ORL J OtoRhinoLaryngol Relat Spec 1985; 47:22–5. 7. Duncanavage JA, Osso# RH, Rouman WC et al. Injuries to the bronchi and lungs caused by laserignited endotracheal tube fires. Otolaryngol Head Neck Surg 1984; 92:639–43. 8. Fried MP, Mallampati SR, Caminear DS. Comparative analysis of the safety of endotracheal tubes with the KTP laser. Laryngoscope 1989; 99:748–51. 9. Simpson JI, Wolf GL, Rosen A et al. The oxygen and nitrous oxide indices of flammability of endotracheal tubes determined by laser ignition. Laryngoscope 1991; 101:981–4. 10. Kautzky M, Fitzgerald R, Dechtyar I, Schenk P. E#ects of the holmium:YAG and erbium:YAG lasers on
A. Murray and B.J.G. Bingham
11.
12.
13.
14.
15.
endotracheal tubes. ORL J OtoRhinoLaryngol Relat Spec 1993; 55:105–9. Wanamaker HH, Silverstein HS. Compatibility of the argon and KTP lasers with middle ear implants. Laryngoscope 1993; 103:609–13. Roodenburg JLN, Panders AK, Vermey A et al. Histology of lasered tissue. In: Oswal VH, Kashima HK, Flood LM (eds) The CO2 Laser in Otolaryngology and Head and Neck Surgery. John Wright (imprint of Butterworth Scientific), 1988, Ch 4. Mihashi S, Jako GJ, Incze J et al. Laser surgery in otolaryngology: interaction of CO2 laser and soft tissue. Ann NY Acad Sci 1976; 267:263–94. Kautzky M, Susani M, Steurer M, Schenk P. Soft tissue e#ects of the holmium:YAG laser: an ultrastructural study on oral mucosa. Lasers Surg Med 1997; 20:265–71. Gleich LL, Rebeiz EE, Pankratov MM, Shapsay SM. The holmium:YAG laser-assisted otolaryngologic procedures. Arch Otolaryngol Head Neck Surg 1995; 121:1162–6.
Paper received 3 January 1998; accepted after revision 25 November 1998.
![[Voice rehabilitation after laryngectomy with voice prostheses. Results of a prospective follow-up study].](/assets/img/hold.png)
