GB2318518A - Micro ventilation anaesthetic circuit - Google Patents

Abstract

The circuit comprises an inspiratory limb 1, an expiratory limb and a double lumen tracheal tube having a small, inspiratory lumen 2 for continuous fresh gas flow and a larger lumen 3 for interrupted expiratory flow, such interruption being accomplished by means of an electronically controlled occluder valve 12 in the expiratory limb. An air suction valve 11, expiratory valve 13 and reservoir bag 14 may also be provided. Operation of the circuit is based on double current (current and counter-current) "microloop" flow and enables lung ventilation at minimal positive intrapulmonary pressure with relatively small tidal volumes and higher frequencies.

Description

MiCRO VENTILATION ANAESTHETIC CIRCUIT This invention relates to micro ventilation anaesthetic circuit.

In controlled ventilation using IPPV (intermittent positive pressure ventilation) the positive intra pulmonary pressure which is initiated is significantly affecting the haemodynamics of pulmonary and systemic circulation.

According to the present invention the lung can be ventilated with a minimal positive intra pulmonary pressure by small tidal volumes and relatively high frequencies, avoiding the complications of IPPV which are mentioned above.

The circuit is composed of:1. Inspiratory limb 2. Double tracheal tubes incorporated together in a single tube, one is small for continuous fresh gas flow which is connected to the inspiratory limb. The other is large for expiratory flow. This flow is interrupted by an occluder valve (solenoid) placed at:3. The expiratory limb which is connected to the expiratory tube.

A specific embodiment of the invention will now be described by way of example with reference to the accompanying drawing in which: Figure 1 shows in perspective, the components of the circuit.

Figure 2 illustrates the detail of the electronic compartment of the solenoid valve.

Figure 3 shows the details of the double tubes which are incorporated together as if they are a single endotracheal tube.

Figure 4 shows the possible incorporation of the inspiratory limb with the expiratory limb of the circuit.

The FGF (fresh gas flow) comes through the inspiratory limb 1 passing via the inspiratory tube 2 into the trachea (at a flow range similar to what is used in oxygen tracheal Insufflation e.g. lOL/min). Accordingly oxygenation is secured. The best way to washout CO2 at this level of microloop ventilation is to initiate lung movement.

The expiratory flow moving through the expiratory tube 3 is interrupted by an electronically working solenoid valve 12 at frequencies (up to 100/min). The solenoid valve in Sheffield paediatric ventilator mark 4, was used.

A tidal volume as low as 50ml is used i.e. + 1 cm HzO increase in intra pulmonary pressure which is usually zero at FRC (functional residual capacity), providing the benefit of relative motionless field and reduced need to use of muscle relaxants.

The endotracheal tube is sealed by the cuff 4. Its pressure is controlled by the balloon 5. It can be connected to a pressure manometer. The pressure needed to seal the trachea is less than that used in IPPV because this circuit is low pressure one reducing the possibility of sloughing to the tracheal mucosa. Cobb's suction connector 6 helps to suck the bronchial tree, through, while fresh gas flow is continuous giving enough time for suction. The Connection piece 7 connects the expiratory limb to the capnograph 8 which measures the pCO2 of the expired flow. It is connected to the pressure transducer 9 as well, which measures the pressure inside the expiratory limb at a point nearby the patient. A manometer gauge can be added.

The corrugated tube 10 is long enough and non expanding to avoid wasting.

The air suction valve 11 opens when the patient takes a breath against closed solenoid valve during recovery or weaning. It opens at a few negative cms H20 pressure.

The solenoid valve 12 is opened and closed electronically and controlled by the electronic compartment 15.

The expiratory valve 13 is used as PEEP valve as well as expiratory valve.

The reservoir bag 14 is used:1. To control ventilation manually in long time electrical failure.

2. At weaning.

3. As a visual monitor for the pressure inside the circuit.

4. To assess compliance and resistance manually on need and to check the endotracheal intubation and in doubtful endobronchial intubation.

The face mask 16 has two ways connection, the small one is for the inspiratory limb and the big one is to be connected to the expiratory limb.

This face mask is used during induction and recovery of anaesthesia.

Figure 2 shows the components of the electronic compartment of the solenoid valve: The inspiratory time control a is working at a range of 0.2-1.2 seconds.

The expiratory time control b is working at a range of 0.4-1.4 seconds.

The lamp c indicates main electricity connection. The visual alarm e and the audible alarm d are working when the pressure inside the expiratory limb is at zero level for more than five minutes remembering that bronchial suction better not to be delayed more than S minutes.

Dangerous CO2 accumulation needs more time provided that the fresh gas flow is continuous through the inspiratory tube.

During electrical failure the solenoid valve works on chargeable batteries for about 2hrs.

Thereafter, ventilation should be assisted manually by the use of the reservoir bag. Figure 3 shows the incorporated expiratory tube 3 with the inspiratory tube 2 as if they are one endotracheal tube. The inspiratory tube 2 is small and crescentic in shape as seen in cross section 17 while the expiratory tube is larger and almost round or oval in shape.

The c.s.a. (cross sectional area) of the usual single lumen tube no. 7.5 is about 44mm2 while the c.s.a. of the tube no. 2.5 is about 4mm2. Furthermore the difference between tube no. 8 and 8.5 in c.s.a. is (5.6mm2) more than c.s.a. of tube no. 2.5. The tube no. 2.5 can transmit more than 20L/min flow at usual clinical circumstances i.e. from the FGF outlet of the anaesthetic machine which is enough to be used as an inspiratory tube to ventilate adult patients while the expiratory tube can be used as large as possible.

From what is mentioned above there are no problems seen regarding the tube sizes.

It is shown in figure 4 that the inspiratory and expiratory limbs can be incorporated together for the sake of heat conservation in anaesthesia. The corrugated tube 10 can be transparent and the inspiratory limb I can be anti static. In apnoeic oxygenation technique, if the size of the catheter starts to be reduced and the flow starts to be increased by applying more pressure, the velocity will be increased according to the equation Flow rate = velocity x cross sectional area. This velocity represents the momentum (driving force) of the molecules flowing because the mass is negligible according to the following equation: Momentum = velocity x mass on applying excessive pressure e.g. 4-5 atmospheres across a small cannula e.g. SGW 16., the micro loops will be inside or nearby the alveoli. Accordingly, apnoeic oxygenation technique is the beginning of micro ventilation while high frequency ventilation is its practical end.

MICRO LOOP FLOW PHENOMENON This invention relates to the discovery of micro loop flow phenomenon.

Flow known to be of two types a laminar and turbulent flow, through tubes and pipes which are opened from both ends.

Venturi principle indicates air suction at the maximum point of velocity due to the negative pressure developed around the tip of the source.

Nobody mentioned what happened to the flow when the distal end of the tube is occluded.

According to the present invention there is provided a current (inflow) and counter current (outflow) i.e. double current flow with loop formation, within the same tube which is occluded distally at atmospheric pressure provided that the outflow is free and not interfered with. This type of flow is involved in micro ventilation phenomenon in concern to gases instead of fluids.

A specific embodiment of the invention will now be described by the way of example with reference to the accompanying drawing in which Figure 1 shows venturi principle.

Figure 2 illustrates the homogenous mixing induced by laminar flow.

Figure 3 shows the current-counter current flow with loop formation once the velocity of the inflow is increased changing the flow from laminar to turbulent flow.

Figure 4 shows the flat flow profile of the turbulent flow.

Figure 5 shows the resisting compression waves against the lower end of the micro loop.

Figure 6 shows the change in direction of the compression waves once the inflow is stopped.

Figure 7 shows oscillations of the end of the loop once the inflow is stopped.

Figure 8 show a source of vibrations is initiated due to (on and off) inflow, shaking the resonant structure which is the tube representing the bronchiole.

Figure 9 shows the addition of larger outflow tube in addition to the smaller inflow tube.

Figure 10 shows the stoppage of the out flow leading to positive pressure distension of the balloon at the end of the tube, abolishing the loop flow.

Figure 11 shows the recurrence of micro loop double current flow once the outflow becomes free under atmospheric pressure, moving the ink inside the balloon to the outside with the outflow (ink represents CO2 accumulated in alveolus).

Refering to the drawing venturi principle shown in figure 1 is clearly seen through a tube or a cylinder which has two openings. Air suction is a must due to a negative pressure initiated at the tip of inflow source.

Once the tube becomes occluded distally by a balloon, new things happen. When the inflow source 1 in figure 2 pushes a laminar flow there is a homogenous movement pushing the ink 10 which is present inside the balloon 7 to the outside of the tube. Once the velocity is increased i.e. the flow becomes turbulent instead of the laminar flow, the ink 10 starts to be isolated and incarcerated inside the balloon as illustrated in figure 3, showing that the inflow was faced by an opposing force making the current of the inflow reflected back forming a counter-current flow moving in the opposite direction. Part of this outflow 8 is circulated again due to the suction effect of venturi at the tip of the inflow source 1, making the double current loop flow 9. This turbulent inflow current has got a flat flow profile 11 as shown in figure 4 which is forced by opposing compression waves 12. They are cushion like waves of the medium in which the inflow current is passing (penetrating) as shown in figure 5. Once the inflow current is stopped the waves move in the opposite direction 13 that is because the compression effect is released, as shown in figure 6. According to this oscillation, a source of vibration 14 is initiated as shown in figure 7. These vibrations are transmitted to the resonant structure (the tube which represents the bronchiole) forming the phenomenon of resonance.

This type of resonance can be called as reversed resonance because it ascends up toward the trachea. This resonance is of no significance in relation to ventilation of the lungs.

Ventilation is dependent on the depth of the loop inside the bronchial tree which is a velocity dependent. It depends as well on the efficiency of the circulation of the loop.

Velocity (distance/unit time) reflects the momentum because the mass is negligible (Momentum=Velocity x Mass).

The thickness of the loop is determined by the flow (volume/unit time) which increases its efficiency as well.

Micro ventilation depends on the intact mechanism of the loop circulating movement which is at its maximum efficiency when the pressure is atmospheric and the outflow is free i.e. the trachea is connected freely to the outside at the same time of inflow continuity. Once this outflow is interfered with, the phenomenon is interfered with accordingly and the balloon (represents the alveolus) starts to distend.

Gases move between the loop and the medium according to their partial pressure gradients by simple diffusion at which the driving force (momentum ) of the inflow is around zero at that point.

Efficient movement of CO2 which accumulates inside the alveolus because of its relative heaviness can be established either by pushing the loops inside the bronchial tree (using high pressures to produce higher velocity across a fixed size (anilula) according to the following equation: Flow rate = Velocity x cross sectional area.

This washout can be established also by interrupting the outflow by using a relatively large tube 16 for the outflow in figure 9 in addition to the small inflow tube 1.

This interruption, interrupts the loop mechanism leading to distension of the balloon caused by the continuous inflow (micro IPPV like). Once the occlusion is released, the balloon returns to its original size and the loop mechanism returns while the ink starts to move out through the out flow tube 16 as seen in figure 11. This coupling between micro ventilation and micro-lPPV gives a practical method to ventilate the lung at a minimal intrapulmonary pressure and at a small tidal volumes with a relative high frequency. That is because the fresh gas flow in this mode of ventilation is very near to the alveoli.

Interference to the outflow can be done by:1. Increasing the inflow. In such a case the free outflow will be interfered with by the thick inflow leading to distension of the balloon. Frequencies seen in high frequency ventilation or venturi type of ventilation is done by this method. Increasing velocity and flow while the loops are inside the alveoli initiate an interference to the outflow leading to distension of the alveoli. Therefore any interruption to the inflow will create lung movement (tidal movement). This interruption will subject the loop mechanism to a significant interference to this mode of ventilation. These drawbacks are encountered by the beneficial effect of lung movement.

2. Direct interference to the outflow as mentioned above using double tubes, a small ore for inflow and a large one for outflow. These facts form the basis of the invention of the micro ventilation anaesthetic circuit which is essentially based on the use of double tubes incorporated together as if they are a single endotracheal tube and an occluder valve (solenoid) which is placed at the expiratory limb which is attached to the large expiratory tube. An inspiratory limb is attached to the small inspiratory tube pushing the continuous fresh gas flow inside the trachea.

The following methods of ventilation can be explained by the phenomenon of microventilation:1. Insufflation tracheal oxygenation (apnoiec oxygenation technique).

2. Venturi type of ventilation e.g. venturi Sander injector use.

3. High frequency ventilation.

Frequencies used in these methods are arbitrary and they are not significant to ventilation as far as the micro loops are inside the alveoli at a certain velocity induced by a certain pressure (e.g. 4-5 atmospheres) through a certain cannula e.g. SGW 16 cannula). At high frequency ventilation they started with for example a frequency of 150/min and a tidal volume of 100ml.

They continued to increase frequencies and to reduce the tidal volumes until they reach e.g. to a frequency of 3000/min and a tidal volume of Sml and the end results regarding ventilation are the same. Practically such a tidal volume (sol) when added to the Functional residual capacity (FRC =2300ml in adult female and 3300ml in adult male) is really negligible.

And at such a high frequencies (3000/min) the inflow is practically regarded as continuous.

Therefore this indicates that if frequency is stopped leaving the inflow continuously flowing, ventilation will be at its optimum if the lower ends of the loops are inside the alveoli and their mechanism is not interfered with. Accordingly, the lung can be ventilated efficiently at Zero intrapulmonary pressure and at FRC (without tidal volumes). During apnoiec oxygenation technique any increase in flow is accompanied by a relative increase in CO2 washout indicating that the micro loops being deeper and more efficient although they are still far away from the alveoli to perform a good COz washout.

By increasing the flow through the same catheter this means that we are increasing the velocity according to the equation (Flow rate = velocity x cross sectional area), so that the depth of the loops are increased. The inflow will split at each bronchial level of division.

Air entrainment will not happen if the outflow is continuous and the tip of the catheter inside the trachea. During high frequency ventilation the outflow is continuous, practically.

Therefore no air entrainment happens. While with venturi injector the frequency used is very slow giving good time for outflow to be ceased until the next cycle started, so air entrainment occurs, completing the circle of the loop.

Claims (8)

1. The microventilation anaesthetic circuit comprising a double incorporated tracheal tubes, a small one for continuous fresh gas flow and a large one for interrupted expiratory flow. This interruption is accomplished by a solenoid valve placed at the expiratory limb of the circuit. The inspiratory limb is attached to the anaesthetic machine fresh gas flow outlet at one end and to the inspiratory tube with the other end.

This invention based on the discovery of the double current micro loop flow phenomenon.

2. The micro ventilation anaesthetic circuit as claimed in Claim 1 means that we can ventilate the lungs at a minimal positive intra pulmonary pressure with the use of small tidal volumes at a relative high frequencies, avoiding the drawbacks of IPPV on haemodynamics of pulmonary and systemic circulation.

3. The micro ventilation anaesthetic circuit as claimed in claim 2 can provide a motionless field and can save in the use of muscle relaxants providing the good criteria of high frequency ventilation.

4. The micro ventilation anaesthetic circuit as claimed in Claim 3 can provide a low pressure circuit avoiding the use of high inflation pressure for the tube cuff, reducing the possibility of sloughing to the tracheal mucosa.

5. The micro ventilation anaesthetic circuit as claimed in Claim 4 permits a good time for suction of the bronchial tree through the expiratory tube as far as the FGF is continuous through the inspiratory tube.

6. The micro ventilation anaesthetic circuit can permit a suitable period of apnoea to increase arterial pC02 to stimulate the respiratory centre during recovery from anaesthesia or at weaning in I.C.U. uses.

7. The micro ventilation anaesthetic circuit as claimed in previous claims, is a low pressure circuit and free of hazardous complications including barotrauma or pneumothorax.

8. The micro ventilation anaesthetic circuit as claimed in previous claims can be modified to be used in: a. Intensive care unit for long term ventilation. Humidifiers, nebulizers, capnographs and other essential equipment can be added.

b. In thoracic anaesthesia by manufacturing four lumen tubes.

c. In spontaneous anaesthesia by connecting the expiratory valve 13 directly to the corrugated tube 10 excluding the air suction valve 11 and the solenoid valve 12.

d. Modified for paediatric use.

e. In bronchoscopy, rigid and fibroptic.

f. Any single lumen tube can be modified to be used with this circuit, including plastic tracheotomy tube.

AMENDMENTS TO THE CLAIMS HAVE BEEN FILED AS FOLLOWS Amicro ventilation anaesthetic circuit comprising an inspiratory limb , an expiratory limb , and a double lumen tracheal tube having a small lumen for continuous fresh gas flow , and a larger lumen for interrupted expiratory flow , such interruption being effected by means of an occluder valve positioned in the expiratory limb of the circuit ,the inspiratory limb being attached to the anaesthetic machine fresh gas flow outlet at one end , and to the inspiratory tube at its other end