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A VENTILATOR FOR CARBON DIOXIDE LASER BRONCHOSCOPY
Br. J. Anaesth. (1986), 58, 663-669
A VENTILATOR FOR CARBON DIOXIDE LASER BRONCHOSCOPY M. L. PAES, I. D. CONACHER AND T. R. SNELLGROVE
M. L. PAES,
F.F.A.R.CJ.;
I. D . CONACHER,
M.R.C.P.,
F.F.A.R.C.S.; Regional CardiothoracicCentre.FreemanHospital, Freeman Road, High Heaton, Newcastle upon Tyne NE7 7DN. T. R. SNELLGROVE, B.A., PH.D., Litetechnica, Adamson House, Shambles Square, Manchester M3 IRE.
SUMMARY A jet ventilator is described. It is designed for use in patients undergoing carbon dioxide laser vaporization ofintraluminaltumours, and obstructions in the trachea and main bronchi. The ventilator overcomes two major anaesthetic problems during laser vaporization in the tracheobronchial tree. It ensures adequate alveolar ventilation and it evacuates smoke generated by the laser. The device has two modes of operation, an automatic ventilation mode and a second mode in which ventilation and suction can be alternated—laser ventilation mode.
(b) a suction system for the evacuation of smoke, and (c) the phasing of (a) and (b) to allow ventilation to occur independently of laser vaporization. An anaesthetic technique has been modified to take account of these factors (Conacher, Paes and Morritt, 1985) and the device described, the Laser Bronchoscope Ventilator (Marketed by Litetechnica Ltd, Adamson House, Shambles Square, Manchester, M3 IRE) has been developed to automate the method. MATERIALS AND METHODS
Apparatus A Wolf bronchoscope (fig. 1) was modified for laser surgery by the addition of a narrow conduit 2 mm in diameter, extending along the whole length of the outer wall and ending within the bronchoscope, 1 cm from the tip. This channel was designed to permit the extraction of smoke. Operation of the Laser Bronchoscope Ventilator converts this channel into a conduit for ventilation as well as smoke extraction. The bronchoscope has a side-arm port to which ventilation devices are
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Jet ventilation during bronchoscopy has a well proven record of ensuring adequate gas exchange (Sanders, 1967; Spoerel, 1969; Giesecke et al., 1973); the high pressure jet of oxygen at the operator end of the bronchoscope entrains additional air through the main orifice of the bronchoscope. However, during carbon dioxide laser bronchoscopy, the main orifice of the bronchoscope is occluded when the laser manipulator is in position, thus decreasing considerably the entrained volume. Patients with tracheobronchial obstruction present the anaesthetist with major problems. High ventilatory pressures are required to provide adequate alveolar ventilation in the presence of high airway impedance. Jet ventilation in the presence of high airway impedance consists initially of the jet volume with little or no entrained volume (Jardine, Harrison and Healy, 1975). As the obstruction is decreased in size by laser vaporization, entrained volume is increased with an improvement in alveolar ventilation. However, the smoke generated from laser vaporization creates further problems. It obscures the operator's view and smoke, with charred debris, is driven into the lungs if ventilation and vaporization are performed concomitantly. Thus, the requirements for laser surgery using a carbon dioxide laser in conjunction with a rigid bronchoscope for lesions in the trachea and main bronchi are: (a) a system of ventilation which can provide adequate oxygenation and removal of carbon dioxide,
BRITISH JOURNAL OF ANAESTHESIA
664 MANIPULATOR
SUCTION PORT
FIG. 2. Front panel of laser bronchoscope ventilator.
Downloaded from http://bja.oxfordjournals.org/ at University of Iowa Libraries/Serials Acquisitions on July 10, 2015
E TIP
FIG. 1. Modified Wolf bronchoscope.
attached normally; with the new ventilator the side-arm port is left open to atmosphere to act as a pressure release valve and an expiratory pathway when the laser manipulator is in position. The Laser Bronchoscope Ventilator is an electrically operated jet ventilator. It is housed in a rectangular metal box 33 cm long, 12 cm high and 21 cm wide. There are front and rear panels. The front panel (fig. 2) has four control knobs and two switches. Besides an ON/OFF rocker switch, there are inspiratory and expiratory controls which enable independent variation of the duration of the inspiratory and expiratory periods. The central switch in the top half of the panel alters the ventilation sequences. When it is on "CONT", the ventilator is in the automatic ventilation mode. When it is on " INT ", the laser ventilation mode is activated. The two controls marked "BREATHS" and "VAC TIME SECS" are used in the laser ventilation mode. The vacuum control allows the duration of suction to be adjusted from 10 s to 40 s. The number of breaths per minute (3, 5, 7 or 9) required during laser ventilation are set by the "BREATHS" control. These controls are adjusted according to the adequacy of the ventilation during the laser ventilation mode. At the top of the rear panel (fig. 3) are the gas and suction connections. The connector marked "OXYGEN" is for a high pressure oxygen hose, the
VENTILATOR FOR CARBON DIOXIDE LASER BRONCHOSCOPY
665
distal end of which can be connected to an oxygen pipeline outlet or by an adaptor to an oxygen-air mixer valve. The other connector is for suction and is fitted with a short length of colour-coded vacuum hose which is connected to a suction apparatus, switched to maximum, when in use. Below these connectors are two openings to which an air filter is attached. This absorbs some of the smoke particles aspirated from the airway during laser vaporization. The outlet in the bottom right hand corner is connected to the bronchoscope by a length of flexible p.v.c. tubing and is a dual conduit for both ventilation and suction. An electric power cable and fuse holder occupy the opposite corner. The internal construction is in two parts, the pneumatic connections and an electronic control circuit. Pneumatic connections
From the gas and suction inlets on the rear of the ventilator, compressed gas lines connect to two two-way, electronically controlled solenoid gas valves (fig. 4). A T-connection, containing two
one-way valves, lies between the solenoid valves and the ventilator outlet. The one-way valve on the gas side prevents smoke and debris from contaminating the gas channel. The valve on the suction side was inserted to prevent damage in the event of a high pressure gas supply being accidentally connected to the suction side. On the low pressure, suction side an external air filter is interposed between the solenoid valve and the one-way valve, to filter out smoke particles. Electronic control circuit (fig. 5)
A variable timer initiates the suction cycle, the duration of which is set by the front panel control and has a range of 5-35 s. At the end of this cycle an audible alarm is tripped by the 5-s delay timer. While either of these timers is in operation, the gate inhibits the ventilation timer. When these timers are off, the ventilation timer functions. The inspiratory and expiratory periods of this latter timer are individually adjusted by the front panel controls. The number of ventilatory cycles (3, 5, 7 or 9) set by the "BREATHS" control, are counted by a decode counter. On completion of a sequence,
Downloaded from http://bja.oxfordjournals.org/ at University of Iowa Libraries/Serials Acquisitions on July 10, 2015
FIG. 3. Rear connections of laser bronchoscope ventilator.
BRITISH JOURNAL OF ANAESTHESIA
666
n External filter FIG. 4. Pneumatic circuit of laser bronchoscope ventilator.
the variable timer initiates the suction phase. All (e) The solenoid suction valve closes and the the main timers are reset so that the ventilation solenoid gas valve opens. timer cycles automatically for a continuous (f) The ventilation sequence is repeated for the set ventilation sequence when the switch on the front number of breaths. panel in on "CONT". RESULTS
Thus two sequences are available with the Laser Bronchoscope Ventilator: (1) Automatic ventilation mode. (a) The solenoid gas valve on the gas line opens for a preset time, enabling gas to flow to the patient. (b) The valve closes for a preset time to permit expiration to occur. (c) The sequence is repeated. (2) Laser Ventilation Mode. (a) The automatic ventilation sequence is repeated for a set number of breaths (3, 5, 7 and 9). (b) Ventilation stops and the solenoid suction valve opens for a set period (5-35 s). The surgeon utilizes this period for laser vaporization while, simultaneously, smoke is evacuated. (c) An audible alarm warns the surgeon that the suction phase is about to be terminated, and that vaporization should be discontinued. (d) Suction continues for a further 5 s to evacuate the smoke left in the tracheobronchial tree.
Laser bronchoscopy was performed on 20 patients for a total of 34 procedures, of which the ventilation technique using the Laser Bronchoscope Ventilator was used in 19 patients for 31 procedures. Fifteen patients had single procedures, three patients had two procedures each and one patient has had 11 procedures, the first of which was performed using our original technique (Conacher, Paes and Morritt, 1985). The majority of patients were premedicated with a tranquillizer and an antisialagogue. The latter avoids unnecessary absorption of laser energy by tracheobronchial secretions. Anaesthesia was induced with midazolam and etomidate, and maintained by a continuous infusion of etomidate. Muscle relaxation was provided with atracurium or pancuronium, and analgesia with phenoperidine, fentanyl or alfentanil. Methylprednisolone was usually given at induction to prevent oedema from instrumentation. Arterial blood-gas tensions were measured before, and at intervals during, the procedure.
Downloaded from http://bja.oxfordjournals.org/ at University of Iowa Libraries/Serials Acquisitions on July 10, 2015
Suction inlet
VENTILATOR FOR CARBON DIOXIDE LASER BRONCHOSCOPY Suction solenoid
Alarm
5-s delay timer
Gate
Gas solenoid
Ventilation timer variable
Decode counter 3/5/7/9
FIG. 5. Electronic control circuit of laser bronchoscope ventilator.
Evacuation of smoke has been a minor but consistent problem with our technique. Although the suction is kept at maximum, we have been unable to evacuate smoke fast enough to give the operator as clear a view as we would like. This has prolonged the operating time, but has been offset by the reduction in the number of smoke particles propelled distally into the lungfields.Examination of the filters (fig. 6) showed a large amount of smoke particles lodged on the surface. Hypercarbia (Pco2 > 6.5 kPa) has occurred in 23 patients. In 22 of these, the Pco, was decreased by a period of automatic ventilation, or by connecting the ventilator directly to the oxygen pipeline outlet rather than the air mix valve, to make use of the higher driving pressure. Hypoxia(.Po, < 9 kPa) occurred in nine patients. In two the Po, was less than 6.0 kPa. Hypoxia and hypercarbia occurred in one patient with a large fleshy tumour at the lower end of the trachea and a large amount of thick secretion distal to the obstruction. The bronchoscope was manipulated past the tumour and tracheobronchial toilet was performed in conjunction with physiotherapy to both lungs. An improvement in both Po, and Pco, permitted the operation to proceed safely. DISCUSSION
Traditionally, ventilation during rigid bronchoscopy is maintained using a variety of techniques
FIG. 6. Filter from suction rhgnni-1: opened to show collection of particles of soot.
Downloaded from http://bja.oxfordjournals.org/ at University of Iowa Libraries/Serials Acquisitions on July 10, 2015
Variable timer 5-35s
667
668
and the airway impedance decreases. Usually, however, it is not sufficient to produce effective ventilation. An automatic ventilator designed for bronchoscopic ventilation (Riwomat, Wolf) proved impractical for laser work. The device, which plugged into the ventilation port of the bronchoscope, did not allow for any entrainment and the jet volume from the injector was inadequate to maintain normal gas exchange in the presence of lesions that resulted in high airway impedance. High Frequency Positive Pressure Ventilation (HFPPV) has been tried successfully for laser bronchoscopy using a Neodymium-Yag laser (Vourc'h et al., 1983a, b). In this technique, HFPPV is instituted via a rigid bronchoscope. Introduction of the fibrebronchoscope, which carries the laser fibre, to the lumen of the rigid bronchoscope will cause a decrease in entrained volume and a decrease in the elimination of carbon dioxide. In patients with airway tumours, one must be aware of the risk of gas trapping with this technique. Decreasing the inspiratory/expiratory ratio may minimize this problem. In clinical practice, the suction conduit of a laser bronchoscope can function as a conduit for ventilation, even in the absence of a port for additional entrainment of air, providing the pressure generated via the jet is adequate. At bench testing, the pressure at the outlet of the Laser Bronchoscope Ventilator when driven by pipeline oxygen supply was found to be in the region of 400 kPa. With an oxygen-air mixer unit (Medishield oxygen-air mixer unit), the pressure decreases to 330 kPa. This valve, although convenient to tailor the inspired oxygen to the needs of the patient and to reduce the degree of flaring at the operative site, acts as a flow and pressure restrictor. In some patients, particularly those with high airway impedance, it may have to be removed from the circuit because the pressure generated is inadequate to promote gas exchange. Frequent monitoring of the blood-gas tensions is essential when dealing with such patients. Hypercarbia can be corrected by a short period of automatic ventilation. Adequate oxygenation has rarely been a problem, as the oxygen concentration in the airway approximates to the oxygen concentration of the jet when the impedance to ventilation is high (Jardine, Harrison and Healy, 1975). There are several advantages to automating the ventilation of patients undergoing laser broncho-
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and apparatus. Spontaneous ventilation, apnoeic oxygenation, ventilating bronchoscopes, jet ventilation and venturi devices and, of late, high frequency positive pressure ventilation (HFPPV) have been used with varying degrees of success. Spontaneous ventilation would, in these patients with significant degrees of large airway obstruction, result in increased respiratory workload. The likelihood of hypoxia and hypercarbia developing under such conditions would be greatly increased by the presence of volatile agents. These latter, vaporized either by nitrous oxide or by high concentrations of oxygen are, on the whole, contraindicated in carbon dioxide laser bronchoscopy because of the duration of the operative procedure and the danger of fire. Techniques based on apnoeic oxygenation, although simple, are not recommended in situations where bronchoscopy may be prolonged (Gothard and Branthwaite, 1982). In our hands the duration of the procedure for laser vaporization of neoplastic lesions of the trachea or bronchi may be anything from 20 to 100 min. For prolonged bronchoscopy, the techniques effective in providing consistently adequate gas exchange involve the use of ventilating bronchoscopes, jet ventilators or HFPPV. Snow and colleagues (1974) successfully used a ventilating bronchoscope with a high gasflowwith manual ventilation. This form of continuous ventilation used in conjunction with laser vaporization can lead to problems from smoke and debris. This same group (Norton et al., 1976) have found, like ourselves, that with a technique in which ventilation is concurrent with vaporization, paniculate matter is propelled distally to pollute the lower respiratory tract. They suggested that this problem could be obviated to some extent by synchronization between suction and ventilation. Such a refinement can be awkward in practice. Smoke production is a prominent feature of laser vaporization. The alternate phasing of suction and ventilation means that smoke is generated during a period when it can be actively scavenged. Sander's technique of manually controlled ventilation using the venturi principle through an open-ended bronchoscope is not appropriate as the laser manipulator occupies the viewer end of the bronchoscope and prevents entrainment. In clinical practice, by putting a needle venturi device through the ventilation port of a ventilating bronchoscope, some entrainment occurs as the lesion in the airway is reduced by laser vaporization
BRITISH JOURNAL OF ANAESTHESIA
VENTILATOR FOR CARBON DIOXIDE LASER BRONCHOSCOPY
ACKNOWLEDGEMENTS We wish to thank our anaesthetic nurses and technicians for their enthusiasm and contribution to this very difficult field of respiratory therapy, David Crawford, O.DJV. for his contributions to the anaesthesia as well as for the illustrations, and Mr G. N. Morritt for his interest in this field and permission to report on his cases. Finally, we thank Miss Helen Ashford for her patience and assistance in compiling thin manuscript.
REFERENCES Conacher, I. D., Paes, M. L., and Morritt, G. N. (1985). Anaesthesia for carbon dioxide laser surgery on the trachea. Taking turns in the airway. Br. J. Anaesth., SI, 448. Giesecke, A. H., Gerbshagen, H. N., Dortman, D., and Lee, D. (1973). Comparison of the ventilating and injection bronchoscopes. Anesthesiology, 38, 298. Gothard,J. W., and Branthwaite, M. A. (1982). Anaesthesia for Thoracic Surgery, 1st Edn, p. 32. London: Blackwell. Jardine, A. D., Harrison, M. J., and Healy, T. E. J. (1975). Automatic flow interruption bronchoscope: a laboratory study. Br. J. Anaesth., 47, 385. Norton, M. L., Strong, M. S., Vaughan, C. W., Snow, J. C , and Kripke, B. J. (1976). Endobronchial intubation and venturi (jtt) ventilation for laser microsurgery of the larynx. Ann. Otol., 85, 656. Sanders, R. D. (1967). Two ventilating attachments for bronchoscopes. Del. Med. J., 39, 170. Snow, J. C , Kripke, B. J., Strong, M. S., Jako, G. J., Meyer, M. R., and Vaughan, C. W. (1974). Anaesthesia for carbon dioxide laser microsurgery of the larynx and trachea. Anesth. Analg., 53, 507. Spoerel, W. E. (1969). Ventilation through an open bronchoscope. Can. Anaesth. Soc. J., 16, 61. Vourc'h, G., Fischler, M., Michon, F., Melchior, J. C , and Seigneur,F. (1983). High frequency jet ventilation v. manual jet ventilation during bronchoscopy in patients with tracheo-bronchial stenosis. Br. J. Anaesth., 55, 969. (1983). Manual jet ventilation v. High frequency jet ventilation during laser resection of tracheobronchial stenosis. Br. J. Anaesth., 55, 973.
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scopy. The anaesthetist is freed to concentrate on other aspects of patient care. Consistent ventilation is achievable in a way that is not possible with manually operated systems, particularly if surgery is prolonged. The absence of turbulent gas flow during the suction phase avoids vibration of the tracheobronchial walls, giving the operator a quiescent field. In addition, the ventilator is not restricted to use in patients undergoing carbon dioxide laser bronchoscopy. It has been used to produce intermittent inflation of the nondependant lung during thoracic surgery (Conacher, personal communication) and has been used for prolonged bronchoscopic procedures.
669
A VENTILATOR FOR CARBON DIOXIDE LASER BRONCHOSCOPY M. L. PAES, I. D. CONACHER AND T. R. SNELLGROVE
M. L. PAES,
F.F.A.R.CJ.;
I. D . CONACHER,
M.R.C.P.,
F.F.A.R.C.S.; Regional CardiothoracicCentre.FreemanHospital, Freeman Road, High Heaton, Newcastle upon Tyne NE7 7DN. T. R. SNELLGROVE, B.A., PH.D., Litetechnica, Adamson House, Shambles Square, Manchester M3 IRE.
SUMMARY A jet ventilator is described. It is designed for use in patients undergoing carbon dioxide laser vaporization ofintraluminaltumours, and obstructions in the trachea and main bronchi. The ventilator overcomes two major anaesthetic problems during laser vaporization in the tracheobronchial tree. It ensures adequate alveolar ventilation and it evacuates smoke generated by the laser. The device has two modes of operation, an automatic ventilation mode and a second mode in which ventilation and suction can be alternated—laser ventilation mode.
(b) a suction system for the evacuation of smoke, and (c) the phasing of (a) and (b) to allow ventilation to occur independently of laser vaporization. An anaesthetic technique has been modified to take account of these factors (Conacher, Paes and Morritt, 1985) and the device described, the Laser Bronchoscope Ventilator (Marketed by Litetechnica Ltd, Adamson House, Shambles Square, Manchester, M3 IRE) has been developed to automate the method. MATERIALS AND METHODS
Apparatus A Wolf bronchoscope (fig. 1) was modified for laser surgery by the addition of a narrow conduit 2 mm in diameter, extending along the whole length of the outer wall and ending within the bronchoscope, 1 cm from the tip. This channel was designed to permit the extraction of smoke. Operation of the Laser Bronchoscope Ventilator converts this channel into a conduit for ventilation as well as smoke extraction. The bronchoscope has a side-arm port to which ventilation devices are
Downloaded from http://bja.oxfordjournals.org/ at University of Iowa Libraries/Serials Acquisitions on July 10, 2015
Jet ventilation during bronchoscopy has a well proven record of ensuring adequate gas exchange (Sanders, 1967; Spoerel, 1969; Giesecke et al., 1973); the high pressure jet of oxygen at the operator end of the bronchoscope entrains additional air through the main orifice of the bronchoscope. However, during carbon dioxide laser bronchoscopy, the main orifice of the bronchoscope is occluded when the laser manipulator is in position, thus decreasing considerably the entrained volume. Patients with tracheobronchial obstruction present the anaesthetist with major problems. High ventilatory pressures are required to provide adequate alveolar ventilation in the presence of high airway impedance. Jet ventilation in the presence of high airway impedance consists initially of the jet volume with little or no entrained volume (Jardine, Harrison and Healy, 1975). As the obstruction is decreased in size by laser vaporization, entrained volume is increased with an improvement in alveolar ventilation. However, the smoke generated from laser vaporization creates further problems. It obscures the operator's view and smoke, with charred debris, is driven into the lungs if ventilation and vaporization are performed concomitantly. Thus, the requirements for laser surgery using a carbon dioxide laser in conjunction with a rigid bronchoscope for lesions in the trachea and main bronchi are: (a) a system of ventilation which can provide adequate oxygenation and removal of carbon dioxide,
BRITISH JOURNAL OF ANAESTHESIA
664 MANIPULATOR
SUCTION PORT
FIG. 2. Front panel of laser bronchoscope ventilator.
Downloaded from http://bja.oxfordjournals.org/ at University of Iowa Libraries/Serials Acquisitions on July 10, 2015
E TIP
FIG. 1. Modified Wolf bronchoscope.
attached normally; with the new ventilator the side-arm port is left open to atmosphere to act as a pressure release valve and an expiratory pathway when the laser manipulator is in position. The Laser Bronchoscope Ventilator is an electrically operated jet ventilator. It is housed in a rectangular metal box 33 cm long, 12 cm high and 21 cm wide. There are front and rear panels. The front panel (fig. 2) has four control knobs and two switches. Besides an ON/OFF rocker switch, there are inspiratory and expiratory controls which enable independent variation of the duration of the inspiratory and expiratory periods. The central switch in the top half of the panel alters the ventilation sequences. When it is on "CONT", the ventilator is in the automatic ventilation mode. When it is on " INT ", the laser ventilation mode is activated. The two controls marked "BREATHS" and "VAC TIME SECS" are used in the laser ventilation mode. The vacuum control allows the duration of suction to be adjusted from 10 s to 40 s. The number of breaths per minute (3, 5, 7 or 9) required during laser ventilation are set by the "BREATHS" control. These controls are adjusted according to the adequacy of the ventilation during the laser ventilation mode. At the top of the rear panel (fig. 3) are the gas and suction connections. The connector marked "OXYGEN" is for a high pressure oxygen hose, the
VENTILATOR FOR CARBON DIOXIDE LASER BRONCHOSCOPY
665
distal end of which can be connected to an oxygen pipeline outlet or by an adaptor to an oxygen-air mixer valve. The other connector is for suction and is fitted with a short length of colour-coded vacuum hose which is connected to a suction apparatus, switched to maximum, when in use. Below these connectors are two openings to which an air filter is attached. This absorbs some of the smoke particles aspirated from the airway during laser vaporization. The outlet in the bottom right hand corner is connected to the bronchoscope by a length of flexible p.v.c. tubing and is a dual conduit for both ventilation and suction. An electric power cable and fuse holder occupy the opposite corner. The internal construction is in two parts, the pneumatic connections and an electronic control circuit. Pneumatic connections
From the gas and suction inlets on the rear of the ventilator, compressed gas lines connect to two two-way, electronically controlled solenoid gas valves (fig. 4). A T-connection, containing two
one-way valves, lies between the solenoid valves and the ventilator outlet. The one-way valve on the gas side prevents smoke and debris from contaminating the gas channel. The valve on the suction side was inserted to prevent damage in the event of a high pressure gas supply being accidentally connected to the suction side. On the low pressure, suction side an external air filter is interposed between the solenoid valve and the one-way valve, to filter out smoke particles. Electronic control circuit (fig. 5)
A variable timer initiates the suction cycle, the duration of which is set by the front panel control and has a range of 5-35 s. At the end of this cycle an audible alarm is tripped by the 5-s delay timer. While either of these timers is in operation, the gate inhibits the ventilation timer. When these timers are off, the ventilation timer functions. The inspiratory and expiratory periods of this latter timer are individually adjusted by the front panel controls. The number of ventilatory cycles (3, 5, 7 or 9) set by the "BREATHS" control, are counted by a decode counter. On completion of a sequence,
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FIG. 3. Rear connections of laser bronchoscope ventilator.
BRITISH JOURNAL OF ANAESTHESIA
666
n External filter FIG. 4. Pneumatic circuit of laser bronchoscope ventilator.
the variable timer initiates the suction phase. All (e) The solenoid suction valve closes and the the main timers are reset so that the ventilation solenoid gas valve opens. timer cycles automatically for a continuous (f) The ventilation sequence is repeated for the set ventilation sequence when the switch on the front number of breaths. panel in on "CONT". RESULTS
Thus two sequences are available with the Laser Bronchoscope Ventilator: (1) Automatic ventilation mode. (a) The solenoid gas valve on the gas line opens for a preset time, enabling gas to flow to the patient. (b) The valve closes for a preset time to permit expiration to occur. (c) The sequence is repeated. (2) Laser Ventilation Mode. (a) The automatic ventilation sequence is repeated for a set number of breaths (3, 5, 7 and 9). (b) Ventilation stops and the solenoid suction valve opens for a set period (5-35 s). The surgeon utilizes this period for laser vaporization while, simultaneously, smoke is evacuated. (c) An audible alarm warns the surgeon that the suction phase is about to be terminated, and that vaporization should be discontinued. (d) Suction continues for a further 5 s to evacuate the smoke left in the tracheobronchial tree.
Laser bronchoscopy was performed on 20 patients for a total of 34 procedures, of which the ventilation technique using the Laser Bronchoscope Ventilator was used in 19 patients for 31 procedures. Fifteen patients had single procedures, three patients had two procedures each and one patient has had 11 procedures, the first of which was performed using our original technique (Conacher, Paes and Morritt, 1985). The majority of patients were premedicated with a tranquillizer and an antisialagogue. The latter avoids unnecessary absorption of laser energy by tracheobronchial secretions. Anaesthesia was induced with midazolam and etomidate, and maintained by a continuous infusion of etomidate. Muscle relaxation was provided with atracurium or pancuronium, and analgesia with phenoperidine, fentanyl or alfentanil. Methylprednisolone was usually given at induction to prevent oedema from instrumentation. Arterial blood-gas tensions were measured before, and at intervals during, the procedure.
Downloaded from http://bja.oxfordjournals.org/ at University of Iowa Libraries/Serials Acquisitions on July 10, 2015
Suction inlet
VENTILATOR FOR CARBON DIOXIDE LASER BRONCHOSCOPY Suction solenoid
Alarm
5-s delay timer
Gate
Gas solenoid
Ventilation timer variable
Decode counter 3/5/7/9
FIG. 5. Electronic control circuit of laser bronchoscope ventilator.
Evacuation of smoke has been a minor but consistent problem with our technique. Although the suction is kept at maximum, we have been unable to evacuate smoke fast enough to give the operator as clear a view as we would like. This has prolonged the operating time, but has been offset by the reduction in the number of smoke particles propelled distally into the lungfields.Examination of the filters (fig. 6) showed a large amount of smoke particles lodged on the surface. Hypercarbia (Pco2 > 6.5 kPa) has occurred in 23 patients. In 22 of these, the Pco, was decreased by a period of automatic ventilation, or by connecting the ventilator directly to the oxygen pipeline outlet rather than the air mix valve, to make use of the higher driving pressure. Hypoxia(.Po, < 9 kPa) occurred in nine patients. In two the Po, was less than 6.0 kPa. Hypoxia and hypercarbia occurred in one patient with a large fleshy tumour at the lower end of the trachea and a large amount of thick secretion distal to the obstruction. The bronchoscope was manipulated past the tumour and tracheobronchial toilet was performed in conjunction with physiotherapy to both lungs. An improvement in both Po, and Pco, permitted the operation to proceed safely. DISCUSSION
Traditionally, ventilation during rigid bronchoscopy is maintained using a variety of techniques
FIG. 6. Filter from suction rhgnni-1: opened to show collection of particles of soot.
Downloaded from http://bja.oxfordjournals.org/ at University of Iowa Libraries/Serials Acquisitions on July 10, 2015
Variable timer 5-35s
667
668
and the airway impedance decreases. Usually, however, it is not sufficient to produce effective ventilation. An automatic ventilator designed for bronchoscopic ventilation (Riwomat, Wolf) proved impractical for laser work. The device, which plugged into the ventilation port of the bronchoscope, did not allow for any entrainment and the jet volume from the injector was inadequate to maintain normal gas exchange in the presence of lesions that resulted in high airway impedance. High Frequency Positive Pressure Ventilation (HFPPV) has been tried successfully for laser bronchoscopy using a Neodymium-Yag laser (Vourc'h et al., 1983a, b). In this technique, HFPPV is instituted via a rigid bronchoscope. Introduction of the fibrebronchoscope, which carries the laser fibre, to the lumen of the rigid bronchoscope will cause a decrease in entrained volume and a decrease in the elimination of carbon dioxide. In patients with airway tumours, one must be aware of the risk of gas trapping with this technique. Decreasing the inspiratory/expiratory ratio may minimize this problem. In clinical practice, the suction conduit of a laser bronchoscope can function as a conduit for ventilation, even in the absence of a port for additional entrainment of air, providing the pressure generated via the jet is adequate. At bench testing, the pressure at the outlet of the Laser Bronchoscope Ventilator when driven by pipeline oxygen supply was found to be in the region of 400 kPa. With an oxygen-air mixer unit (Medishield oxygen-air mixer unit), the pressure decreases to 330 kPa. This valve, although convenient to tailor the inspired oxygen to the needs of the patient and to reduce the degree of flaring at the operative site, acts as a flow and pressure restrictor. In some patients, particularly those with high airway impedance, it may have to be removed from the circuit because the pressure generated is inadequate to promote gas exchange. Frequent monitoring of the blood-gas tensions is essential when dealing with such patients. Hypercarbia can be corrected by a short period of automatic ventilation. Adequate oxygenation has rarely been a problem, as the oxygen concentration in the airway approximates to the oxygen concentration of the jet when the impedance to ventilation is high (Jardine, Harrison and Healy, 1975). There are several advantages to automating the ventilation of patients undergoing laser broncho-
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and apparatus. Spontaneous ventilation, apnoeic oxygenation, ventilating bronchoscopes, jet ventilation and venturi devices and, of late, high frequency positive pressure ventilation (HFPPV) have been used with varying degrees of success. Spontaneous ventilation would, in these patients with significant degrees of large airway obstruction, result in increased respiratory workload. The likelihood of hypoxia and hypercarbia developing under such conditions would be greatly increased by the presence of volatile agents. These latter, vaporized either by nitrous oxide or by high concentrations of oxygen are, on the whole, contraindicated in carbon dioxide laser bronchoscopy because of the duration of the operative procedure and the danger of fire. Techniques based on apnoeic oxygenation, although simple, are not recommended in situations where bronchoscopy may be prolonged (Gothard and Branthwaite, 1982). In our hands the duration of the procedure for laser vaporization of neoplastic lesions of the trachea or bronchi may be anything from 20 to 100 min. For prolonged bronchoscopy, the techniques effective in providing consistently adequate gas exchange involve the use of ventilating bronchoscopes, jet ventilators or HFPPV. Snow and colleagues (1974) successfully used a ventilating bronchoscope with a high gasflowwith manual ventilation. This form of continuous ventilation used in conjunction with laser vaporization can lead to problems from smoke and debris. This same group (Norton et al., 1976) have found, like ourselves, that with a technique in which ventilation is concurrent with vaporization, paniculate matter is propelled distally to pollute the lower respiratory tract. They suggested that this problem could be obviated to some extent by synchronization between suction and ventilation. Such a refinement can be awkward in practice. Smoke production is a prominent feature of laser vaporization. The alternate phasing of suction and ventilation means that smoke is generated during a period when it can be actively scavenged. Sander's technique of manually controlled ventilation using the venturi principle through an open-ended bronchoscope is not appropriate as the laser manipulator occupies the viewer end of the bronchoscope and prevents entrainment. In clinical practice, by putting a needle venturi device through the ventilation port of a ventilating bronchoscope, some entrainment occurs as the lesion in the airway is reduced by laser vaporization
BRITISH JOURNAL OF ANAESTHESIA
VENTILATOR FOR CARBON DIOXIDE LASER BRONCHOSCOPY
ACKNOWLEDGEMENTS We wish to thank our anaesthetic nurses and technicians for their enthusiasm and contribution to this very difficult field of respiratory therapy, David Crawford, O.DJV. for his contributions to the anaesthesia as well as for the illustrations, and Mr G. N. Morritt for his interest in this field and permission to report on his cases. Finally, we thank Miss Helen Ashford for her patience and assistance in compiling thin manuscript.
REFERENCES Conacher, I. D., Paes, M. L., and Morritt, G. N. (1985). Anaesthesia for carbon dioxide laser surgery on the trachea. Taking turns in the airway. Br. J. Anaesth., SI, 448. Giesecke, A. H., Gerbshagen, H. N., Dortman, D., and Lee, D. (1973). Comparison of the ventilating and injection bronchoscopes. Anesthesiology, 38, 298. Gothard,J. W., and Branthwaite, M. A. (1982). Anaesthesia for Thoracic Surgery, 1st Edn, p. 32. London: Blackwell. Jardine, A. D., Harrison, M. J., and Healy, T. E. J. (1975). Automatic flow interruption bronchoscope: a laboratory study. Br. J. Anaesth., 47, 385. Norton, M. L., Strong, M. S., Vaughan, C. W., Snow, J. C , and Kripke, B. J. (1976). Endobronchial intubation and venturi (jtt) ventilation for laser microsurgery of the larynx. Ann. Otol., 85, 656. Sanders, R. D. (1967). Two ventilating attachments for bronchoscopes. Del. Med. J., 39, 170. Snow, J. C , Kripke, B. J., Strong, M. S., Jako, G. J., Meyer, M. R., and Vaughan, C. W. (1974). Anaesthesia for carbon dioxide laser microsurgery of the larynx and trachea. Anesth. Analg., 53, 507. Spoerel, W. E. (1969). Ventilation through an open bronchoscope. Can. Anaesth. Soc. J., 16, 61. Vourc'h, G., Fischler, M., Michon, F., Melchior, J. C , and Seigneur,F. (1983). High frequency jet ventilation v. manual jet ventilation during bronchoscopy in patients with tracheo-bronchial stenosis. Br. J. Anaesth., 55, 969. (1983). Manual jet ventilation v. High frequency jet ventilation during laser resection of tracheobronchial stenosis. Br. J. Anaesth., 55, 973.
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scopy. The anaesthetist is freed to concentrate on other aspects of patient care. Consistent ventilation is achievable in a way that is not possible with manually operated systems, particularly if surgery is prolonged. The absence of turbulent gas flow during the suction phase avoids vibration of the tracheobronchial walls, giving the operator a quiescent field. In addition, the ventilator is not restricted to use in patients undergoing carbon dioxide laser bronchoscopy. It has been used to produce intermittent inflation of the nondependant lung during thoracic surgery (Conacher, personal communication) and has been used for prolonged bronchoscopic procedures.
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