A VENTILATING LARYNGOSCOPE FOR INHALATION ANAESTHESIA AND AUGMENTED VENTILATION DURING LARYNGOSCOPIC PROCEDURES

Brit. J. Anaesth. (1972), 44, 874

A VENTILATING LARYNGOSCOPE FOR INHALATION ANAESTHESIA AND AUGMENTED VENTILATION DURING LARYNGOSCOPIC PROCEDURES SHAOTSU THOMAS LEE

SUMMARY

Laryngoscopic procedures have usually been performed under topical anaesthesia, and their success has depended greatly on the co-operation of the patient. For prolonged and delicate laryngoscopic procedures, or in paediatric patients, general anaesthesia is preferred and often required. General anaesthesia for laryngoscopic procedures presents the problem of maintenance of satisfactory pulmonary ventilation because both the laryngologist and the anaesthetist compete for the same anatomical area, the larynx, for examination, surgery and as an airway. General anaesthesia for laryngoscopic procedures has been managed utilizing an endotracheal tube, by insufflation, with intravenous neuroleptanaesthesia, apnoeic oxygenation, or some combination of these. During insufflation or neuroleptanaesthesia (Gordon and Sellars, 1971), with the patient spontaneously breathing, the ventilation is usually less satisfactory. The use of apnoeic oxygenation imposes a time limit because of unavoidable respiratory acidosis (Frumin, Epstein and Cohen, 1959). Augmented ventilation during laryngoscopic procedures can be accomplished with a special endotracheal tube (Pollard, 1968) or cuirass respirator. However, the first usually interferes with the procedure or obstructs a free and complete view of the larynx and the second is often found cumbersome and inefficient. An ideal situation would be to use the laryngoscope as a ventilating device, so that the laryngologist could use the instrument for brief or prolonged and delicate procedures, and the anaesthetist could use it as a ventilating device without interference with

each other's work. Such a method would provide an unobstructed view of the entire larynx and permit instrumentation without hindrance. In an attempt to approach the ideal situation, two versions of a ventilating laryngoscope using some of the principles in fluid amplification were developed and are described here. The Bernoulli theorem (1738) states that the pressure of a fluid in motion through a tube of varying cross-sectional area is least at the narrowest portion where the speed is greatest, and that the pressure is greatest at the widest portion where the speed is least. Some 60 years later, G. B. Venturi (1797) showed that in order for a stream of fluid to regain a pressure much higher than that at the constriction, it was necessary for the tube immediately distal to the constriction to open out gradually. Gases, in essence, behave like fluids but, because they are compressible, deviate somewhat from the principle. In a suitably designed tube, a marked negative pressure can be created in the region of the constriction. From these principles evolved the various types of injector with an entrainment duct. The entrainment is the result not only of the subatmospheric pressure (hence, suction effect on the fast stream of driving gas), but also of its propulsive effect on the resting gas surrounding SHAOTSU THOMAS

LEE, M.D.; Department

of

Anes-

thesiology, Kaiser Foundation Medical Center, Department of Anesthesiology and Pharmacology, University of Hawaii Medical School, Honolulu, Hawaii. Presented in part as an exhibit at the Biennial Western Conference on Anesthesiology, May 2-7, 1971, Princess Kaiulani Hotel, Honolulu, Hawaii.

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Two versions of a ventilating laryngoscope using principles of fluid amplification are described which provide means of augmented ventilation during laryngoscopic procedures under general anaesthesia and muscle relaxation with unobstructed views of the entire larynx. There is minimal attachment to the laryngoscope; in the simpler Type I venti-laryngoscope, there is only a driving gas line. For delivering inhalation anaesthetics and predetermined gas mixtures, an entrainment arm with reservoir bag is incorporated in the Type II venti-laryngoscope. Intravenous anaesthesia as well as inhalation anaesthesia can be used for laryngoscopy. Clinical experiences and laboratory data provide evidence of adequate ventilation and satisfactory anaesthesia during various laryngoscopic procedures. Flow and pressure measurements have been obtained to facilitate better understanding of the devices.

A VENTILATING LARYNGOSCOPE FOR INHALATION ANAESTHESIA

the jet (Macintosh, Mushin and Epstein, 1958). Sanders (1967) used these principles in the design of a special attachment to a bronchoscope for ventilation during bronchoscopy. Extended application of the same principles to laryngoscopy seems a natural progressive process. The following described venti-laryngoscopes provide means of augmented ventilation by incorporation of the entrainment effect into their open lumen.*

FIG. 2a. Cross-section of the venti-laryngoscope II. (1) Oxygen at 60 Lb./sq. in. (2) and (3) Controls for pressure flow and rate adjustment in Bird Mark II; and respirator to provide intermittent flow of oxygen as driving gas. (4) Driving gas inlet (Luer-Lok). (5) Entrained air at the proximal end of the laryngoscope. (6) Entrainment arm. (7) Wire embraided tube used as an extension of the entrainment arm. (8) One-way valve. (9) Reservoirbag for inhalation anaesthetics or other gases. (10) Anaesthetic vaporizer. (11) Flow meter. (12) Oxygen. • Since the completion of this paper, an application of entrainment principles for laryngoscopy, similar to that used with our Type I venu-laryngoscope, has been described by Albert (1971).

FIG. lb and 2b. Assembly of venti-laryngoscopes I and II. (1) Oxygen at 60 Lb./sq. in. (2) Adjustable pressure regulator. (3) Speedaire blowgun to provide intermittent oxygen at 20-60 Lb./sq. in. as driving gas. (4) Driving gas inlet (Luer-Lok). (5) Entrained air at the proximal end of the laryngoscope. (6) Entrainment arm. (7) Wire embraided tube used as an extension of the entrainment arm. (8) One-way valve. (9) Reservoir bag for inhalation anaesthetics or other gases. (10) Inlet for inhalation anaesthetics or other gases.

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FIG. la. Cross-section of the venti-laryngoscope I. (1) Oxygen at 60 Lb./sq. in. (2) Adjustable pressure regulator. (3) Speedaire blowgun to provide intermittent flow of oxygen at 20-60 Lb./sq. in. as driving gas. (4) Driving gas inlet (Luer-Lok). (5) Entrained air at the proximal end of the laryngoscope.

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Construction of the venti-laryngoscope. Two versions of the venti-laryngoscope are constructed by use of a similar principle! in fluid amplification as described above:

f Correspondingly, two versions of a venti-bronchoscope have also been constructed. These create less problem during bronchoscopic procedures than during laryngoscopy since there is less gas leakage due to the well established airway in the trachea. 450

90

400

80

350

70

300

60

Venti-laryngoscopes CD

50 E

E 250 o

,

x VL-I flow _.

VL-I pressure

«

VL-II flow'

A

Entrainment arm flqw

x

No. 15 needle flow

40

200

150

30

100

20

50

10

10 15

20 25 30 35 40

45

Driving pressure (Lb./sq.in.)

50

55

60

FIG. 3. Flow l./min) and pressure (mm Hg) measurements of the venti-laryngoscopes at various driving pressures (Lb./sqan.). VL-I Venti-laryngoscope I (17GH, 17 cm X 1.2X1.7). VL-II Venti-laryngoscope II (17H, 17 cm X 1.2X1.6).

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Type I. A simpler form (figs, la, b) is for ventilation during laryngoscopy with pressurized oxygen as the driving gas which entrains air. Intravenous anaesthesia is used. A No. 15 metal needle is soldered to the proximal end of the laryngoscope as an injector, or the driving gas inlet (4). This driving gas inlet is built with the sharpest angle possible (<10°) toward the main lumen of the instrument, i.e., the entrainment duct and the diffuser, so they are almost parallel to each other, thus creating a maximal possible entrainment, and it does not inter-

fere with vision or instrumentation. There is no other extra attachment except the driving gas line (4). The amplified gas mixture with its force is used to ventilate the patient's lungs. Type II. The universal form is designed for use with inhalation anaesthetics (figs. 2a, b and 3). It has the driving gas inlet (4) in a specially designed entraining gas inlet, the entraining arm (6), which runs into the proximal end of the laryngoscope and has the same internal diameter as the laryngoscope. This entraining arm provides a means of delivering predetermined gas or vapour, which might be inhalation anaesthetics, anaesthetic vapours, oxygen, etc. (9). Thus, intravenous anaesthesia and/or inhalation anaesthesia can be used. Controlled ventilation can be carried out. The special entraining arm (6) with the driving gas inlet (4) is positioned in the sharpest angle possible toward the main lumen of the laryngoscope. The driving gas inlet (4) is parallel to the lumen of the special entrainment

A VENTILATING LARYNGOSCOPE FOR INHALATION ANAESTHESIA arm (6) and located at its most distal end closest to but not into the lumen of the laryngoscope. During anaesthesia a reservoir bag is needed for the measured gases and vapours (9), and a one-way valve (8) is required between the reservoir bag (9) and the special entrainment arm (6) to prevent rebreathing. The reservoir bag deflates passively during inspiration and gas entrainment, and refills during expiration.

* Speedaire Blowgun, Model 2X492, Inhalation Therapy Supply Co., 25 Ralph Street, San Francisco, California 94112; Regulator, RO4-20O-RGEA, C A. Norgren Co., U.S.A.

\\

centration of the entrained gas, vapour, etc., from the entrainment arm (e.g., inhalation anaesthetics) is halved at the distal end of the laryngoscope and eventually goes into the lungs. The entrainment is greatest when the driving gas injector is centred in axial alignment with the diffuser. With a suitably designed injector and diffuser, the driving gas may entrain as much as twenty times its own volume (Macintosh, Mushin and Epstein, 1958). In the venti-laryngoscope the injector nozzle is on the perimeter of the diffuser, in the wall of the laryngoscope. Thus, the entrainment is considerably less than that of a suitably designed injector and diffuser in an ideal entrainment duct. However, the flow and the resulting pressure are more than adequate for clinical purposes (fig. 3). Although the simple form of the Type I ventilaryngoscope described above has been proved very TABLE I. Blood gases measured before, during and after laryngoscopic procedures using the venti-laryngoscope. Case

No.

Time of blood samples related to laryngoscopy

1 Male 41 140 kg 2 Female 54 72 kg 3 Female 66 78 kg 4 Male 59 102 kg 5 Female 44 59 kg 6 Female 31 54 kg 7 Male 61 96 kg

PAGO,

PH

PAO,

(mm Hg) (mm Hg)

Before During After

7.38 7.45 7.39

41 36 39

98 280* 120

Before During After

7.45 7.41 7.45

22 21.2 18

280f 246.2* 262f

During

7.41

38.5

101

During

7.46

22.5

220

During

7.41

40

298*

During

7.38

43

180

During

7.36

45

162

Before: Before induction of anaesthesia. During: 10 to 25 minutes after induction of anaesthesia. After: 15 to 30 minutes after termination of anaesthesia. 'Oxygen at 10-12 L/min flows into the reservoir bag and hence into the entrainment arm.

fO, by mask.

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These venti-laryngoscopes permit the performance of prolonged or brief delicate procedures under general anaesthesia and controlled ventilation with a Bird Mark II ventilator or a blowgun type device with a pressure regulator* or any other device to interrupt the driving gas, oxygen, intermittently. Adequate ventilation can be provided during intravenous as well as in inhalation anaesthesia with muscle relaxation. There is minimal attachment to hinder the laryngoscopist when using Type I ventilaryngoscope, although for inhalation anaesthesia the entrainment arm with the reservoir bag of the Type LI laryngoscope might be used. There is no endotracheal tube to obstruct the view of the entire larynx or to hinder the use of instruments. The lumen of the laryngoscope and the larynx are free of obstruction during the laryngoscopic procedure. The ventilation under such conditions has been excellent even with an open and unsealed connection between venti-laryngoscope and larynx. Flow measurements were carried out in the laboratory with calibrated Fleisch pneumotachographs mounted at the distal end of both types of ventilaryngoscopes and at the proximal end of the entrainment arm in the Type II model and using pressurized oxygen inflow at various pressures (p.s.i.) as the driving gas. Pressure measurements were carried out with a Statham P23 transducer mounted at the distal end of the laryngoscope. The results of the flow and pressure measurements were recorded using a Grass Model 7 Polygraph. These results are shown in figure 3. With the Type II venti-laryngoscope it can be made so that approximately 50 per cent of the total gas volume flow at the distal end of the laryngoscope is entrained from the special entrainment arm, while the remaining 50 per cent consists of the driving gas and the entrained air from the proximal inlet of the instrument. Thus, the con-

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dans le venti-laryngoscope Type 1 plus simple, il n'y a que la conduite de gaz. Au venti-laryngoscope Type 2 est incorpord un bras avec sac-reservoir pour l'administration d'anesth^siques par inhalation et de melanges prctJetermines. Unc anesthesie intraveineuse ou par inhalation peut £tre utilised pour la laryngoscopie. Les experiences cliniques et les donnees de laboratoire prouvent une ventilation adequate et une anesthesie satisfaisantes durant diverses procedures de laryngoscopie. Des mesures du flux et de la pression ont iii obtenues pour permettre de mieux comprendre le fonctionnement des appareils.

EIN SAUERSTOFF ZUFUHRENDES LARYNGOSKOP FOR DIE INHALATIONSNARKOSE UND FUR VERSTARKTE BEATMUNG WAHREND DER MANIPULATION MIT DEM LARYNGOSKOP ZUSAMMENFASSUNG

Es werden zwei Typen eines Beatmungs-Laryngoskopes, die auf dem Grundsatz der FlQssigkeitsausdehnung beruhen, beschrieben; sie erlauben cine verstarkte Beatmung wahrend der Manipulation mit dem Laryngoskop in Allgemein-Narkose und bei Muskelrelaxation bei freier Sicht des gesamten Larynx. Das Laryngoskop hat REFERENCES eine minimale Zusatzvorrichtung; beim einfacheren Typ 1 Venti-Laryngoskop ist es nur ein durchlaufender Albert, S. N. (1971). The Albert-Sanders adaptor for Schlauch. Das Typ 2 Venti-Laryngoskop hat einen ventilating anaesthetized patients for micro-laryngeal eingebauten Zufuhrhebel mit Reservebeutel, um die surgery. Brit. J. Anaesth., 43, 1098. Inhalationsanaesthetica und bestimmte Gasgemische Frumin, M. J., Epstein, R. M., and Cohen, G. (1959). einzuleiten. Die Laryngoskopie kann in intravenOser Anesthesie und in Inhalationsanaesthesie durchgefuhrt Apneic oxygenation in man. Anesthesiology, 20, 789. Gordon, M., and Sellers, S. (1971). Anaesthesia for micro- werden. KJinische Erfahrungen und Laborwene beweisen, dass bei verschiedenen laryngoskopischen Untersuchungen surgery of the larynx. Anaesthesia, 26, 199. die Beatmung ausreichend und die Narkose zufriedenHill, D. W. (1967). Physics applied to anaesthesia. stellend waren. Es wurden Stromung- und DruckmessButterworth: London. ungen angestellt, um das Verstandnis der Gerate zu Kleinsasser, O. (1968). Microlaryngoscopy and endolaryn- erleichtern. geal microsurgery. Philadelphia: W. B. Saunders Company, and Stuttgart: F. K. Schattauer-Verlag. Macintosh, R. R., Mushin, W. W., and Epstein, H. G. (1958). Physics for the anaesthetist. 2nd edn. Oxford: UN LARINGOSCOPIC VENTILADOR PARA LA Blackwell. ANESTESIA POR INHALACION Y AUMENTO DE Pollard, B. J. (1968). Anaesthesia for laryngeal microLA VENTILACION DURANTE LOS surgery. Anaesthesia, 23, 534. PROCEDIMIENTOS LARINGOSCOPICOS Sanders, R. D. (1967). Two ventilating attachments for bronchoscopies. Delaware St. med. J., 39, 170. RESUMEN Spoerel, W. E., and Grant, P. A. (1971). Ventilation dur- Son descritas dos versiones de una laringoscopic ventilaing bronchoscopy. Canad. Anaesth. Soc. J., 18, 178. dor utilizando los principios de la amplificaci6n de fluidos que permiten un aumento de la yentilacion durante los procedimientos Iaringosc6picos bajo anestesia general y relajamiento muscular con vistas completes de toda la UN LARYNGOSCOPE VENTILANT POUR laringe. El laringoscopic posee un dispositivo anexo L'ANSTHESIE PAR INHALATION ET LA mlnimo; en el tipo I del ventilaringoscopio, mas simple, VENTILATION AUGMENTEE DURANT LES solamente hay un conducto para el gas. En el ventiLARYNGOSCOPIES laringoscopio tipo II se ha incorporado un brazo de conducci6n con una bolsa respiratoria. Se puede utilizar SOMMAIRE para la laringoscopia anestesia por inhalacion o anestesia Deux versions sont decrites d'un laryngoscope ventilant, intravenosa. La experiencia clinica y los analisis de utilisant les principes de l'amplification liquide, qui laboratorio demuestran que durante los diversos procedifoumissent les possibility d'une ventilation augmentee mientos Iaringosc6picos hay una ventilaci6n adecuada y durant la laryngoscopie sous anesthesie generale et anestesia stificiente. Han sido obtenidas medidas del flujo relachement musculaire avec vue parfaite du larynx com- y de la presi6n para facilitar un mejor entendimiento de plet. II y a un minimum d'attachements au laryngoscope: estos dispositivos.

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satisfactory with intravenous anaesthesia in most of the adult patients, inhalation anaesthesia and means of providing higher concentration of oxygen are often required or necessary in other situations. Therefore, the universal Type II venti-laryngoscope is designed as a means for augmenting ventilation as well as for delivering inhalation anaesthetics and other gases. Since September 1970, these instruments have been used routinely at Kaiser Foundation Medical Center in Honolulu, Hawaii. The clinical use of these venti-laryngoscopes on more than 100 occasions is to form the subject of a separate report. They have been found especially useful in routine laryngoscopic examination, microlaryngeal surgery and laryngoscopic procedures where a paralyzed patient or prolonged time is desired. Blood gas measurements were made on 7 subjects. The results are listed in table I and provide evidence of adequate ventilation during various laryngoscopic procedures.

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