Carbon-dioxide DetectionThis invention relates to carbon-dioxide detection, and more particularly although not exclusively to tracheal tube monitoring arrangements incorporating carbon-dioxide detection means.
Whenever a tracheal tube is placed via the nose or mouth into the trachea of a subject or patient in order to supply medical gases (ie oxygen with or without other gases), or air, or anaesthetics, or to protect the lower airways from aspiration of foreign material in the upper airway, it is of vital importance to ensure that the tracheal tube is, in fact, inserted correctly into the trachea and not into the oesophagus.
Whilst sophisticated equipment is known for use in operating theatres (and other areas where tracheal tubes are used) for the measurement and monitoring of the patient's exhaled carbon-dioxide, and by implication ensuring the correct location of the tracheal tube, this equipment is bulky, relatively expensive, so scarce as not to be available for use with every patient, and also not usually rapidly available and in working condition when needed in an emergency situation.
There is a real problem and risk that during any intubation, but especially in emergency situations when desperate and urgent conditions sometimes pertain, the tracheal tube can be incorrectly inserted into the oesphagus so that the patient would not, in fact, receive the intended medical gas, or air, or anaesthetic to his lungs, or have his lower airways protected. Such a situation is clearly extremely dangerous and has to be avoided.
It is an object of the present invention to provide an arrangement which enables this particular problem to be overcome or at least substantially reduced.
In accordance with the present invention there is provided an arrangement for detecting or monitoring carbon dioxide and thereby determining the presence of pulmonary ventilation in a subject (or patient) comprising means carrying a carbon dioxide indicator, of the type changing colour when exposed to the presence of carbon dioxide, said means being adapted for close association with a patients pulmonary ventilation. The indicators working principle may be to detect the presence of carbon dioxide either by means of a carbon-dioxide-specific indicator or by an indicator which detects changes in pH caused by the dissolving of carbon dioxide in water.
Carbon dioxide is present, and continues to be present, in gases that are exhaled from the lungs. Gas from the stomach may, in some circumstances, contain carbon dioxide but this is rapidly diluted by fresh gas if the trachael tube is incorrectly placed in the oesophagus and the carbon dioxide levels issuing back from the stomach rapidly decrease.
Thus, the monitoring arrangement for carbon dioxide may be located at any position that is exposed to the patient's carbon dioxide.
With trachael tube monitoring the monitoring arrangement may conveniently be located immediately between the apparatus delivering fresh gas (usually but not necessarily the breathing attachment) and the trachael tube. Note that the carbon dioxide indicator may also be associated directly with the trachael tube itself, forming a part of the trachael tube.
Note, also, that the carbon dioxide indicator can be used in situations where a tracheal tube is not used but in which it is important to monitor the presence of and/or rate of pulmonary ventilation e.g. the indicator may be applied to breathing masks used for oxygen therapy, or pharyngeal or laryngeal airways.
The carbon dioxide indicator used in association with the monitoring device is such that it can give a visible reaction when carbon dioxide is present. The physical carrier of the indicator will depend on the conditions in the equipment, and may be of any suitable gas-permeable structure e.g. of fluid or solid or gel or sponge form, or gas-porous film, paper or membrane. Any or all of the component parts of the indicator may be chemically attached or bonded to any other component part of the indicator or its supporting carrier. Any or all of the component parts of the indicator and its supporting carrier may be such that they need to be associated together before use, and in order that the indicator is able to respond to the presence of carbon dioxide. In such cases the arrangement may be such as to allow the components to be kept separate and their eventual combination before use.
An electrical or electronic method may also be used to detect the presence of carbon dioxide.
The indicator may also be designed to give a visual indication of the level of carbon dioxide to which it is exposed.
Where the indicator functions on the basis of a chemical reaction, the speed of this reaction may be assisted by the use of an appropriate catalyst (or catalyst-containing formulation) or enzyme (or enzymecontaining formulation). The indicator may contain several catalysts or enzymes or both.
In one embodiment of the invention the carbon dioxide indicating means may comprise an appropriate chemical indicator (or indicators) of the type that changes colour according to, and relative to, the presence of and the absence of carbon dioxide. Where the indicator changes colour when a pH change occurs (e.g. with the chemical reactions that occur when carbon dioxide dissolves or comes out of solution), the colour being related to the pH, an appropriate enzyme to speed up the reaction would be Carbonic Anhydrase. This catalyses the reaction of carbon dioxide with water to form carbonic acid, and the reverse direction of the reaction in which carbon dioxide is liberated from carbonic acid.This enzyme will therefore speed up the rates of pH change (lower pH when carbon dioxide dissolves, higher pH when carbon dioxide comes out of solution) and thus speed up the respective colour changes. Thus, if the indicator is exposed to both fresh and exhaled gases an alternating colour will be apparent between each inspiration and exhalation giving continued evidence of correct tracheal tube placement and also continued pulmonary ventilation. If the indicator is only ever exposed to exhaled gas it will give continuous evidence of correct tracheal tube placement and will remain an appropriate colour according to the level of carbon dioxide to which it is exposed.
Generally the indicator may be such as to change colour between two definite colours depending on the presence of carbon dioxide or may be such as to colour and decolour, or may pass through a range of colours between two principal colours.
In one embodiment the chemical indicator or indicators change colour according to the presence and level of carbon dioxide, with or without the use of catalysts or enzymes, such that the level of carbon dioxide can be ascertained by the colour change that has taken place. The actual colour being related to the carbon dioxide level.
In one embodiment a chemical indicator may be stored in a container such that prior to use it can be sprayed or applied onto the surface of a device that will be exposed to the patients carbon dioxide.
In one embodiment of the present invention there is provided an arrangement for monitoring the disposition of the tracheal tube immediately after insertion into a patient in such circumstances as mentioned above comprising tubular means for providing gas to the tracheal tube via a non-rebreathing arrangement of valves and a carbon-dioxide indicator attached to an outlet port of the tubular means.
The non-rebreathing arrangement of valves may incorporate uni-directional valves which direct fresh gas to the patient's lungs and the exhaled gases to an outlet port preventing exhalation of gases into the breathing attachment and contamination of fresh gas with exhaled gas.
The apparatus delivering fresh gases may connect directly to the inspiratory port of the valve assembly.
In one form of the embodiment, on the fresh gas supply side of the uni-directional valve in the inspiratory port is a second side port venting again to a carbon-dioxide indicator to determine whether the incoming fresh gas contains carbon-dioxide.
By this embodiment, it will be immediately apparent to the operator whether the tracheal tube is correctly inserted in the trachea if, on the first few breathing cycles, it is found that the carbon-dioxide indicator on the tracheal side of the valve assembly indicates the continued presence of carbon-dioxide, whilst the indicator on the gas supply side does not.
It will be appreciated that the non-rebreathing arrangement of valves, the input carbon-dioxide monitoring outlet and output monitoring outlet can be comprised within a single unitary assembly connectable into equipment for patient ventilation already in place.
In another embodiment of the present invention there is provided an arrangement for monitoring the disposition of the tracheal tube immediately after and following the insertion into a patient in such circumstances as mentioned above comprising a non-return valve located in a breathing attachment leading from an anaesthetic gas supply to the tracheal tube arranged to prevent exhalation of gas from the patient's lungs through the breathing attachment, and, on the tracheal tube side of the nonreturn valve, a side port to the breathing attachment venting to a carbon-dioxide indicator.
In yet another embodiment of the present invention there is provided an arrangement for monitoring the disposition of a tracheal tube immediately after and following insertion into a patient in such circumstances as mentioned above comprising tubular means for providing fresh gas to the tracheal tube and for carrying exhaled gases out from the patient's lungs, and carbon-dioxide indicating means associated with either the tubular means or with the tracheal tube and arranged in use to make intimate contact with the fresh and exhaled gases.
The carbon-dioxide indicating means may comprise an appropriate chemical indicator and the indication means may be carried within the tubular means or tracheal tube, such as being applied to a portion of the inside wall thereof.
The carbon dioxide indicating means may be indirectly or directly associated with other equipment already known and used e.g. a chemical carbon dioxide indicator may be combined with, or applied to, a heat and moisture exchange filter, or cricothyroid membrane puncturing device, or nasogastric tube. It may also be incorporated with other devices which indicate the presence of other gases and vapours of medical use e.g. oxygen, nitrous oxide, anaesthetic vapours. A chemical indicator may be associated with electrical, electronic or optical devices which can detect changes in pH or depth of quality of colour so as to provide an additional manner of representing the presence of carbon dioxide e.g. audible tones, flashing lights, numerical readout or carbon dioxide level.When a colour indicator is used equipment may be designed to magnify or enhance the colour changes taking place e.g. a magnifying portion or white background.
In order that the invention may be more readily understood one embodiment thereof will now be described by way of example with reference to its use in anaesthetic practice with reference to the accompanying drawings in which:Figure 1 is a schematic side view of an anaesthetic providing assembly incorporating a tracheal tube carbon dioxide arrangement according to the invention;Figure 2 is an enlarged schematic side view of part of the arrangement of Figure 1.
Referring now to Figure 1 of the drawings it will be seen that the assembly comprises a breathing attachment 1 of a kind that can be used in providing anaesthetics to patients. A normal form of gas bag 2 is shown attached thereto, and it is provided with an expiratory valve 3 of normal form. In practise anaesthetics comprising the anaesthetic gas together with the appropriate quantity of oxygen and/or air is passed as at 4 into the free end of the breathing attachment. Between the breathing attachment and a standard tracheal tube 5 disposed a carbon dioxide monitoring arrangement 6 in accordance with the invention. This is insertable into the assembly for monitoring purposes after inserting a tracheal tube 5 into the patient's trachea.
The monitoring arrangement, as previously described, is intended to give an immediate indication as to whether the tracheal tube is correctly placed in the trachea or has inadvertently been disposed in the oesophagus. The monitoring arrangement, as shown in Figure 2, comprises a single transparent tubular device incorporating a chemical indicator 7 on the inner surface. The indicator illustrated is of a microporous solid form, but could equally well be of any other suitable medium such as fluid, gel, sponge, electrical or electronic. If other forms of indicator are used, the design of the device will be appropriate for their nature and form.
In this case the moist solid indicator comprises pH indicators (Bromthymol blue and Phenol red) in a 1 mM sodium carbonate solution with carbonic anhydrase all supported in a moist inert gas impermeable matrix and incorporated into the inner surface of the tubular device. The indicator is purple when exposed to fresh gas and turns rapidly yellow when exposed to the levels of carbon dioxide in exhaled gas. The indicator in turn recolorises to purple when again exposed to fresh gas at the next inspiratory phase. It is to be understood that instead of a carbonate solution, a bicarbonate solution may be used.
In practical anaesthetic use, the procedure is that on deciding to intubate an anaesthetised patient, the patient is paralysed, and the tracheal tube is inserted through his mouth or nose and into his trachea. Having done this, the tracheal tube monitoring device is connected between the free end of the tracheal tube, and the downstream end of the breathing attachment.
Fresh aneasthetic gas mixture is then passed onto the breathing attachment at the flow rate required and the revervoir bag 2 fills. Positive pressure is provided by squeezing the bag 2 attached into the breathing attachment. When the pressure in the system is positive, and the aneasthetic gas mixture passes into the tracheal tube 5 and the patient's lungs constituting inspiration.
The indicator is purple at this stage.
When bag compression stops, the pressure in the system becomes atmospheric and the patient exhales. On exhalation, the outgoing gas passes over the carbon dioxide indicator with which it changes from purple to yellow. Then it is manifest that carbon dioxide is being expired through the tracheal tube by the patient. If the yellow colour does not appear then the anaesthetist has a clear indication that the tracheal tube is probably incorrectly inserted into the oesophagus.
If the tracheal tube is in the trachea the indicator recolorises and decolorises with successive breathing cylces indicating the continued correct placement of the tracheal tube and also the continued presence of pulmonary ventilation at an observable ventilation rate.
If the tracheal tube is in the oesophagus and the stomach also happens to contain carbon dioxide (not a common situation) this will be revealed by the failure, after several ventilations, to observe an alternating colour change; the indicator will remain purple.
The above enables clear indication of successful tracheal intubation.
By means of the invention as hereinabove described we have provided an arrangement enabling a quick and certain determination and detection of carbon dioxide of wide usefulness such as in the determination as to whether a tracheal tube has been correctly located within a patient at the time of intubation for airway control, or artificial ventilation of the lungs, and also/or in some embodiments a continuous indicator of the presence and rate of pulmonary ventilation.
It is to be understood that the foregoing is merely exemplary of apparatus for detecting carbon dioxide in accordance with the invention and that modifications can readily be made thereto without departing from the true scope of the invention. Thus, for example, the apparatus may be incorporated into resuscitation apparatus (which may be disposable) to enable a check to be made for life in the patient. Again, the apparatus may be incorporated in apparatus for naso-gastric use, this time to check for the absence of carbon dioxide and that the relevant tube has not entered the trachea.