Ventilating device for use in anesthesiology

Abstract

A patient ventilating device, for use in anesthesiology, comprises a cannula having an oxygen jet tube connected thereto so as to terminate within the lumen of the cannula and to be directed towards an outlet end thereof, the cannula being surrounded by a cuff adapted to be inflated to retain the device in position in the patient's trachea.

Description

This invention concerns a ventilating device for use in anesthesiology, and more particularly, but not exclusively for use in surgery of the larynx.

Microsurgery of the larynx, using direct laryngoscopy with or without an operating microscope, is becoming an increasingly popular technique of the armamentarium of the otorhinolaryngologist. A great variety of complementary techniques of anesthesia have been developed but these techniques all have the drawbacks that they either provide a decreased field of vision for the surgeon or require an unusual degree of surgeon-anesthesiologist co-operation for the surgical technique to be accomplished smoothly without hazard to the patient.

In order to improve both operating and anesthetic conditions, two new interesting techniques have recently been proposed. One of these employs an oxygen jet which is attached to the blade of a suspension laryngoscope and through which oxygen is administered through the vocal cords and down the trachea when the laryngoscope blade is correctly in position. This causes intermittent positive pressure ventilation of the patient's lungs with a mixture of oxygen and air because the trachea acts as a venturi tube, as the oxygen jets down into it, causing air to be entrained.

The other recently proposed technique approaches the problem in a slightly different way. It makes use of an oxygen jet placed in the trachea through the crycothyroid membrane, this jet consisting of a 16 gauge plastic cannula aimed caudally. By intermittently firing oxygen from the jet down into the trachea, positive pressure ventilation of the lungs can be accomplished as with the previously mentioned technique. Both of these techniques have drawbacks which tend to eliminate them from universal use.

An object of the present invention is to provide a ventilating device for use in anesthesiology which is particularly, but not exclusively, suitable for use in operations involving microsurgery of the larynx, whereby the above-discussed drawbacks may be avoided, the device involving either no or only an insignificant obstruction to the surgeon's view during performance of the operation.

With this object in view, the present invention provides a ventilating device, for use in anesthesiology, comprising a cannula to which is connected an oxygen jet tube, the jet tube terminating within the lumen of the cannula and being directed towards an outlet end of the cannula which is surrounded by an inflatable cuff.

The oxygen jet tube may be arranged so as to enter the lumen of the cannula by extending through the wall of the latter, in which case the arrangement may be such that the cuff serves to retain the oxygen jet tube in its position.

Preferably the outlet end of the cannula terminates obliquely to define a tip thereon the jet tube conveniently extending through the wall of the cannula at a location whose orientation, about the axis of the cannula, is approximately 90.degree. from that of the tip.

The oxygen jet tube is preferably connected by way of a blow gun incorporating an operating button depression of which permits oxygen flow to the jet tube from a pressure reducing valve, whereby oxygen can be permitted to flow intermittently to the jet tube, under manual control.

The cuff may be inflatable by way of an inflating tube which extends to the cannula alongside the oxygen jet tube, and such inflating tube may, if desired, be provided with a plug whereby it can be blanked off.

The invention will be described further, by way of example, with reference to the accompanying drawings, in which:

FIG. 1 is a diagrammatic view, illustrating a first embodiment of the device of the invention connected to a pressure regulator;

FIG. 2 is an enlarged fragmentary view of the device of FIG. 1;

FIG. 3 is a section taken on the line 3--3 of FIG. 2;

FIG. 4 is a section taken on the line 4--4 of FIG. 2, but showing the cuff inflated;

FIG. 5 is a view similar to FIG. 3 but showing a second embodiment; and

FIG. 6 is a view corresponding to FIG. 5 but showing the cuff inflated.

In relation to both the illustrated embodiments, similar reference numerals have been allocated to similar parts.

Referring firstly to FIGS. 1 to 4, in making the preferred embodiment illustrated therein, one starts by forming a cannula 10 from relatively stiff plastics tubing, such as is conveniently employed, for example, as endotracheal tubing, e.g., of 7 to 7.5 mm diameter. This is done by cutting a length of the tubing, of about 6 or 7 centimetres in its axial dimension, and trimming one end 11 (hereinafter referred to as the outlet end for convenience) obliquely so that such end 11 terminates in a wedge-like pointed tip 12. Then, an opening 13 is formed through the wall of the tube, at a location which is spaced between one-third and one-half of the way along the tube from the outlet end 11, and at an orientation around the axis of the tube which is approximately 90.degree. from that of the tip 12 of the outlet ends 11, as will readily be understood from comparison of FIGS. 2 and 3.

To this cannula 10 is attached an oxygen jet tube 14 formed of plastics tubing (such as that conventionally used in intravenous infusion equipment) of internal diameter approximately 2.5 mm and of external diameter approximately 3.5 mm. This tubing, which can be of any practical length, encouters the cannula 10, externally of the latter, at its end 15 (hereinafter referred to as the inlet end for convenience) remote from the outlet end 11 and extends along the outside of the cannula 10 up to the opening 13. Here, the tubing passes through the wall of the cannula to provide an inserted end 16 which extends along the lumen of the cannula 10 generally towards the outlet end 11 approximately in alignment with the tip 12. The inserted end 16 of the jet tube stops just short of the oblique outlet end 11 of the cannula 10.

The oxygen jet tube 14 having been so positioned, it is located in such position by positioning, around the cannula 10, an inflatable cuff 17 which, in its unrelaxed condition, is smaller in diameter than the outside diameter of the cannula 10, so that it has to be stretched to permit the cannula 10 to be inserted, and upon release it contracts and grips tightly around the cannula 10. This cuff 17, which is conveniently of latex, may be formed as two thin tubes 18, 19 arranged concentrically one within the other and bonded or vulcanised together over relatively wide circumferential bands 20, 21 at each axial end to define, between such bands 20, 21, an inflatable annular space 22 (see FIG. 4) of axial length approximately one-half of the overall length of the cuff 17, which in turn may have an axial length of approximately two-thirds of the length of the cannula 10.

A cuff-inflating tube 23 connects by one end to the inflatable annular space 22 and extends away from the cannula 10, past the rear end 15 thereof, alongside the oxygen jet tube 14.

The cuff-inflating tube 23 is connected to an appropriate compressed air supply (not shown) by way of a control valve (also not shown) enabling the cuff 17 to be inflated to the condition of FIG. 4 and deflated to the condition of FIGS. 1, 2 and 3 as desired.

The oxygen jet tube 14 connects, by its free end, to the outlet 24 of a so-called "blow gun" 25 which is, in effect, a shut-off valve having a body which is conveniently shaped for holding in the hand and incorporates a manually depressable button 26 depression of which opens the valve. The blow gun 25 in turn is connected by way of a high-pressure tube 27 to an oxygen supply (not shown), such as a cylinder of compressed gas, the high-pressure tube 27 incorporating a manually adjustable pressure-reducing valve 28 whereby the pressure of oxygen supplied to the blow gun 25 and through the latter to the oxygen jet tube 14 can be preset as desired.

Provided as an adjunct to the device as just described is an applicator which is not shown in the drawings. This comprises a handle from which extends a stainless steel rod of arcuate configuration, the outside diameter of the rod being such that it is a snug fit into the lumen of the cannula 10. A bulge is provided on the rod near to its free end to define a predetermined depth of insertion of the rod into the cannula 10 sufficient to ensure that the device is located reliably on the applicator whilst assuring that no damage can be done to the inserted end 16 of the oxygen jet tube 14.

In making practical use of the device as described, the cannula 10 is inserted, by means of the applicator and with the aid of an obturator, into a patient's trachea to a position approximately 15 to 25 mm below the vocal cords. The device is then located in position by inflating the cuff 17 by way of the cuff inflating tube 23 as shown in FIG. 4 and maintaining it so inflated, whereupon it is used to ventilate the patient's lungs by intermittently depressing the button 26 of the blow gun 25 to supply oxygen under pressure to the oxygen jet tube 14, thereby momentarily blowing oxygen as a high pressure jet into the patient's lungs sufficient to cause inflation thereof. Subsequent expiration from the patient's lungs can, of course, occur by way of the lumen through the cannula 10.

The device as described and illustrated in FIGS. 1 to 4 was tested on two dogs which had been anesthetized with intravenous Nembutal and paralyzed with succinylcholine. The cannula 10 was introduced into a position approximately 1 cm. below the cords under direct vision, using a Magill Laryngoscope blade, and with the use of an obturator. The cuff 17 was then blown up and the obturator removed. With the pressure reducing valve 28 adjusted to deliver oxygen at a pressure of 20 cm. of water at the outlet end of the cannula 10, the lungs were intermittently inflated by depressing the blow gun button 26. Arterial carbon dioxide levels on these dogs varied between 30 and 35 mm. of mercury and the oxygen levels varied between 500 and 550 mm. of mercury, samples having been taken from a peripheral artery by a percutaneous puncture into a heparintized syringe and immediately analyzed on an IL Model 113 blood gas analyzer. No untoward sequelae were found.

The device was also clinically tested on twenty-five patients having microsurgery on the larynx. The patients were premedicated with diazepam, 10 mg. intramuscularly given one hour before surgery. On the arrival at the operating room an intravenous infusion was started with an 18 gauge plastic cannula nd EKG leads connected to the chest giving an EKG readout on an oscilloscope via a VHF telemetry system as described in "Radio telemetry in anesthesia and surgery" by David A. Davis and William E. Thornton (Electronics in Anesthesiology - International Anesthesiology Clinics, 3:535-545, May 1965). Prior to induction of anesthesia in the patient, each device to be used on the patients was first tested by connecting it, by the outlet end of the cannula 10, to a Racine connector connected to a pressure gauge. Using this as a guide, the oxygen outlet pressure developed from the device was adjusted to 20 cm. of wter by adjusting the pressure reducing valve 28.

Each patient was pre-oxygenated for four minutes. Induction of anesthesia was carried out with intravenous methohexital in a dosage sufficient to ensure adequate hypnosis followed by 80 mg. of succinylcholine, intravenously. Next, under direct vision, using a McIntosh laryngoscope blade, the cannula 10, mounted on its applicator, was inserted through the cords with the aid of an obturator. Relative hereto it is to be noted that a range of the devices with different sizes of cannula 10 should be available so that there be much more distortion of the laryngeal opening than originally expected, a device having a smaller cannula 10 will always be at hand for substitution.

The cuff 17 of the device was then blown up and the applicator and obturator were removed. Immediately positive pressure ventilation was begun by intermittently pressing and releasing the blow gun button 26. The patient was then ready for the attention of the otorhinolaryngologist.

The surgeon then inserted his operating laryngoscope blade and surgery began. A succinylcholine drip of 500 mg. in 500 cc. of normal saline was begun into the infusion line to ensure relaxation. Further doses of 1 percent methohexital in 3 cc. increments were given via the same route as needed to ensure hypnosis.

The cuff inflating tube 23 and the oxygen jet tube 14 are fitted on the cannula 10 in such a way that when the cannula 10 of the device is correctly inserted, these two tubes 23, 14 leave the trachea through the cords in the posterior part of the laryngeal opening, causing little or no obstruction to the surgeon's view. In fact, in most cases when viewing the cords down the operating microscope it was impossible to see the tubes 23, 14. It was noted that at all times during both inspiratory and expiratory cycles, gas was exiting through the cords, and blood which appeared near the edges of the cords was seen to be blown out of the trachea.

When surgery had been completed, following careful suctioning of the back of the throat, the cuff 17 on the cannula 10 was allowed to deflate. The device was then withdrawn very simply by pressing the blow gun button 26. This caused a jet of oxygen to flow, which caused a positive pressure in the lungs and very simply blew the device out of the trachea through the cords. Occasionally slight traction on the oxygen jet tube 14 and cuff inflating tube 23 was needed.

An airway was then inserted into the patient's mouth, the succinylcholine drip turned off, and the patient was then gently ventilated via a mask with 100 percent oxygen in a 5.degree. Trendelenberg position until spontaneous respiration started again.

During one of the surgical procedures, (a teflon injection of a non-functioning vocal cord), the patient, although still asleep under the influence of methohexital, was allowed to regain functioning of the vocal cords by switching off the succinylcholine drip so that the surgeons could see how much telfon to inject to allow correct approximation of the cords. The oxygen jet tube 14 and cuff inflating tube 23 coming out through the cords seemed to not interfere with the movement of the free cord at all.

By use of the device of the invention, very adequate pressures can be produced, enabling positive pressure ventilation to be accomplished easily.

With a maximum available oxygen pressure of 20 cm. of water, an inspiratory rate of approximately 35 litres per minute was initially available and this is quite adequate. With a higher maximum pressure, of the order of 30 cm. of water, the initial flow rate was 48 litres per minute. This, of course, is the oxygen flow, and does not include any air which may be entrained. Under clinical conditions, however, virtually no air entrainment occurs, and at nearly all times of the inspiratory cycle oxygen is blowing back from the device out through the cords, as will be the case during expiration. Blood gas results obtained from the patients were very adequate and oxygen levels were exceedingly high indicating ventilation of the patient with 100 percent oxygen or very near it. This means that during ventilation the patient is extremely well oxygenated, but (and this is far more important) at the end of ventilation the patient's lungs were full of oxygen. Accordingly, the patient can theoretically be apneic for 5 minutes without the arterial PaO.sub.2 falling below 100 mm. of mercury.

The device ensures very adequate minute volumes going through the patient's lungs, but possibly more important is the fact that should the patient suffer bronchospasm or for some reason become difficult to ventilate, this can, in many instances be overcome by increasing the pressure delivered to the device from the pressure reducing valve 28 to blow gas into the patient's lungs. Difficulties hitherto experienced as a result of laryngeal spasm are minimised by use of the device of the invention. It is well known that when laryngeal spasm occurs, it is impossible to ventilate the patient from above the cords using a mask or some other form of positive pressure applied to the upper airway. This is because the larynx is shaped in such a way that pressure from above tends to close the cords tightly together. However, pressure from below tends to below the cords apart, and in fact, theoretically it should be possible for the patient to be ventilated with an adequate minute volume, even though the cords have gone into spasm, using the device of the invention because the pressure from below tends to blow the cords apart and permits gas to escape from the lungs. Of course, gas can get into the lungs very easily through the oxygen line leading down into the device, which is positioned below the larynx. Constant monitoring of the degree of relaxation of the cords is carried out by the surgeon and if the relaxant is allowed to wear off for a short time as noted in the earlier mentioned case, ventilation is stopped momentarily until the cords are paralyzed again or continued at a lower pressure allowing longer for respiration to occur.

Apneic techniques and the use of the venturi principles have the hazard of inhalation of blood and debris. With the use of the device of the invention, for practically the whole inspiratory cycle, gas is blowing out through the cords and, as was noted by the surgeons operating on the patients above referred to, blood around the cords was seen to be blown out and away from the cords rather than trickling down into the trachea. It was found that the optimum way to ventilate the patients, during the time that blood or debris were in the area of the cords, was to follow expiration by the inspiratory phase without any appreciable pause, in order to continue the flow of gas out through the cords and so stop inhalation of blood or other debris.

Operating conditions are generally found to be extremely good because of complete relaxation and the lack of obstruction to the surgeon's operating field. If the surgeon wished to operate on the posterior part of the cords, then it was a very simple matter to put the device into position with the cannula 10 rotated through 180.degree.. The oxygen jet tube 14 and cuff inflating tube 23 then leave the cords through the anterior part, thereby leaving the posterior part of the cords completely clear. Due to the already-mentioned fact that blood and debris is continuously being blown away from the cords, the surgeon does not have to use suction as often as hitherto, and, therefore, can work more rapidly.

The embodiment above described is not the only form the device of the invention may take, and other constructions are possible. One such other construction is shown in FIGS. 5 and 6 in which the cannula 10 is formed over about one half of its length, terminating at its rear end 15, with a groove 29 in its inner surface and leading up to a radial port 30 opening into interior space 22 of a cuff 17 consisting of a single circumferential tube 31 around the cannula 10 and bonded thereto at bands 32 and 33 at its axial ends. The groove 29 accommodates that portion 34 of the cuff inflating tube 23 which is secured to the cannula 10 with its end registering with the port 30, so it will be understood that the cuff inflating tube 23 does not produce any bulge on the exterior of the cannula 10 as is the case with the embodiment of FIGS. 1 to 4. For the same reason, the oxygen jet tube 14, instead of extending partially along the exterior of the cannula 10, is adhered to the interior of the cannula 10, to extend substantially parallel to the axis thereof, in correspondence with the cuff inflating tube 17.

The oxygen jet tube 14 is shown in these figures as being provided with a connector 35 for connecting it to the outlet 24 of the blow gun 25. Furthermore, the cuff inflating tube 23 is shown as being provided with a respective connector 36 to enable it to be connected to its source of compressed air. Attached to the connector 36 by a pliable tongue 37 is a blanking plug 38. This enables the cuff 17 to be maintained in its inflated condition whilst the cuff inflating tube 23 is disconnected from its source of compressed air. Blanking-off of the tube 23 by inserting the plug 37 into the connector 36, is effected, of course, whilst the cuff inflating tube 23 is squeezed to close it, thereby to prevent deflation of the cuff upon disconnection of the connector 36 from the compressed air supply.

In this embodiment, as in the case of the embodiment of FIGS. 1 to 4, the device is preferably made of soft silicone elastomer, which is non-toxic and substantially chemically-inert under practical conditions of use whilst being quite soft and therefore unliketly to cause unintentional damage.

Other variations are, of course, possible. Thus, the nature of and materials employed for the cannula, oxygen jet tube and cuff can differ from what is above described. Although, in the FIGS. 1 to 4 embodiment, it is convenient for the arrangement to be such that the cuff serves to retain the oxygen jet tube in position, this is not essential and the latter tube could, if desired, be located in position by adhesion or welding to the cannula where it passes through the wall of the latter or adhesion to the inside wall of the cannula without having to pass through the wall. If desired, a suture or the like can be connected to the cannula to enable it to be withdrawn from the trachea without tension having to be applied to either the cuff inflation tube or the oxygen jet tube. The cannula may, if desired, be gently curved.

Naturally, the device can be employed in relation to surgical operations, particularly those of an otorhinolaryngological nature, other than those mentioned above.

Claims

I claim:

1. A ventilating device connected to a supply of high pressure oxygen for use in anaesthesiology comprising:

a cannula having a lumen approximately 6.5 cm. in axial length,

an oxygen jet tube disposed within and connected to the cannula and terminating within the lumen thereof, the jet tube being directed toward an outlet end of the cannula,

the oxygen jet tube being of a smaller diameter than the diameter of the lumen,

an inflatable cuff circumscribing the cannula with the axial length of the cannula being slightly in excess of the length of the cuff, the supply of high pressure oxygen communicating with the jet tube for facilitating respiration in a patient.

2. A device as claimed in claim 1 wherein the oxygen jet tube extends along the interior of and substantially parallel to the axis of the cannula.

3. A device as claimed in claim 2 wherein the cannula terminates obliquely to define a tip thereon.

4. A device as claimed in claim 3 wherein the jet tube extends through the wall of the cannula at a location whose orientation, about the axis of the cannula, is approximately 90.degree. from that of the tip.

5. A device as claimed in claim 1 wherein the oxygen jet tube is connected by way of a blow gun incorporating a depressible operating button for permitting oxygen flow to the jet tube from a pressure reducing valve and oxygen flow intermittently to the jet tube under manual control.

6. A device as claimed in claim 1 wherein the cuff is inflatable by way of an inflating tube which extends to the cannula alongside the oxygen jet tube.

7. A device as claimed in claim 6 wherein the inflating tube is provided with a plug whereby it may be blanked off.