DESCRIPTION
A Device to Improve Brain and Heart Blood Flow and Aid Transportation of patients in states of Shock and Cardiac Arrest Background:
Medical Shock is defined as the inability to perfuse tissues (most importantly the brain and heart) with oxygenated blood. Its principal characteristic is low blood pressure. Its causes can be divided into:
Hypovolaemic - ("lack of blood") due to internal or external bleeding Cardiogenic - heart (pump) failure - e.g. cardiac arrest Septic - where infection makes peripheral blood vessels dilate reducing resistance for the heart to pump against and hence reducing blood pressure.
Spinal - where spinal injury causes loss of control of peripheral vasculature tone with resultant dilatation of blood vessels and hence reduction of blood pressure.
Anaphylactic - where an allergic reaction causes peripheral vasculature to dilate, again reducing blood pressure.
In all of these conditions blood pressure is reduced and perfusion of the brain and heart can be seriously compromised.
In cardiac arrest (an extreme form of "shock") there is complete failure of the heart to pump blood. With cardiopulmonary resuscitation (CPR) around 10-15% of the normal blood supply to the brain can be achieved. Out of hospital cardiac arrest currently has only a 5% survival rate. If better perfusion of the brain and heart could be achieved with CPR, these terrible survival figures could be improved.
Currently there is no simple technique that is practical.
Scientific Method:
Basic Physiology:
Ohm's law states that:
V=IR
(where V=voltage i.e. the potential difference, I = current (rate of flow) and R = resistance) The same equation applies to human physiology. The body can be thought of as an electrical circuit where the heart is the battery and there are a parallel resistances coming from it. Increasing the resistance of some resistors will force more current through those of lower resistance.
In human physiology - V becomes the blood pressure, I the cardiac output (the amount of blood the heart pumps out) and R the total peripheral resistance. In all causes of shock V (the blood pressure) is reduced. In Hypovolaemic and Cardiogenic Shock there is a reduction in I (the cardiac output) - due to the lack of blood and the heart not working properly respectively. In Anaphylactic, Spinal and Septic the problem is a reduction in R (the total peripheral resistance).
By applying pressure over an area that can survive with reduced blood supply (the abdomen and legs), there is increased resistance to blood flowing through these areas and comparatively less resistance to blood flowing towards the heart and brain. Blood will therefore preferentially flow to these areas. It is simpler to think that if the aorta (the main vessel from you heart) is blocked in you abdomen, blood will only be able to circulate the top half of your body, none being "wasted" in supplying your legs. This diversion of blood is especially important when the amount pumped out by the heart is dramatically reduced (e.g. during CPR following cardiac arrest). There would also be a translocation of blood from the venous pool back into the central circulation.
Shock (reduced blood pressure, V) can be caused by a reduction in either I (Cardiac Output) or R (Total Peripheral Resistance). In either case, blood pressure (V) and hence cerebral and coronary perfusion can be maintained by increasing the resistance. The device of this patent is concerned with increasing this value.
Current techniques include:
Pharmacological (e.g. drugs such as epinephrine) which cause a constriction of some blood vessels (arterioles). This however, requires the drug to reach these tissues (a time which is very prolonged in cardiac arrest) and does not compress larger arteries or veins. These pharmacological methods, while increasing the pressure in the arteries supplying the brain, may actually reduce brain blood flow by causing them to constrict.
Military Anti Shock Trousers (MAST) were designed to be put on following trauma (U.S. Pat. No. 4,577,622). They consist of a series of leg and abdominal bladders that are inflated with a foot pump. They have not been shown to be of benefit in treating shock in trauma, principally because of the time taken to put them on (each leg is wrapped separately then an abdominal component is fastened). A number of modifications of MAST have been put forward, many of these relate to the sequential filling of lower body air bladders to pump blood back towards the heart (e.g. U.S. Pat. No. 3,866,604; U.S. Pat. No. 2,495,316, U.S. Pat. No 6,010,470). Anti-G-suits have been used for decades in the air force (U.S. Pat. No. 4,583,522). Many of these devices require complicated pieces of equipment and are not practical for use outside of a hospital setting.None of these devices address the principle problem in cardiac arrest and other forms of shock. Time is of the essence. A device is needed that can be applied in seconds, switched on and forgotten about. A device is also needed that can still be used during and even aid the transfer of the patient from ambulance to hospital trolley. The device proposed in this patent addresses all of these issues.
What the Device Does:
The device provides a method of rapidly applying pressure over the lower half of the body while also acting as a transporting device. It is designed to rapidly improve cerebral and coronary circulation in states of shock especially during cardiopulmonary resuscitation.
Essential Features:
Accordingly, this invention provides a carrying device (analogous to a stretcher), which incorporates a simple, rapid to apply lower body positive pressure device that, in a single action, encompasses the lower body of a patient between inflatable components with the intention of improving cerebral and coronary perfusion during states of shock, in particular during cardiac arrest.
Important Features:
The device comprises a carrying device and a lower body positive pressure device that encompasses the entire lower body in one action.
The device can be made of any materials or combination of materials though preferably the device is made of plastic components. These could be designed to be either reusable or disposable and various sizes could be produced.
The device can be made from any number of components. An example is given later in this document of how the bulk of the device can, if desired, be made from a single sheet of material.
The device can be inflated by any known technique but it could preferably be inflated using a compressed gas (for example from an air cylinder or piped compressed gas). Alternatively a manual inflating device (such as a foot pump) could be used. An automatic pump or self-inflating mechanism (as used in life vests) could be incorporated instead. It could inflate to a set or variable pressure and a device for reading that pressure could also be incorporated. Although a gas (of any temperature e.g. air) is ideal for inflating the device, in some circumstances a liquid may be considered appropriate (e.g. to cool the patient). Ideally the device should be able to inflate to the desired pressure extremely rapidly. The device could additionally be inflated and deflated on a cyclical basis to form a pump.
The inflating device can be connected to the inflatable components in a number of ways including the use of a valve. This could be a high pressure, one way valve for example.
The device could compress the lower body in either an anterior/posterior direction (with the inflatable components above and below the lower body) or in a side-to side direction (with the inflatable components on either side of the lower body). In the later case, the fastening device would be on the top of the device, in or near the centre.
Preferably the device components should be transparent to enable viewing of the patient's lower body though this is not necessary.
The device can be fitted with a variable number of fastening devices (e.g. buckles), holding devices (e.g. handles) or straps that may further aid transportation of the patient.
The device could be made in various sizes though one size should fit all. The feet could either be contained or left out of the inflatable area.
The device can have the addition of other features such as a space for the placement of a rigid material (for example a clear rigid sheet of plastic) that can act to immobilise the spine of the patient. It could also incorporate cervical spine stabilising devices.
The device can have writing on it (for example indicating how to use it and when it should not be used).
The device can be deflated in any number of ways but a simple plug or valve mechanism would be suitable. A valve that opened above a set pressure could be used to control pressure within the device.
The hands can either be placed under the inflatable component(s) of the device or held on with another strapping mechanism.
Detailed Description:
A preferred embodiment of the invention will now be described with reference to a number of drawings:
Introduction to the Drawings:
The basic design is as follows: Figure 1: Is a simplified diagram in perspective with a patient in place and the device closed. It demonstrates the ideal positioning of the patient in the device. Figure 2: Is a schematic diagram of the open device in perspective without the patient present. Figure 3: Is a schematic diagram of the open device from above, from the side and from the end. Figure 4: Is an exploded diagram demonstrating an example of how the device can be made from a single sheet of material Figure 5: Is a diagram demonstrating how the continuation of folding of the material in Figure 4 produces the device. Fixtures such as holding devices and fasteners have not been included to keep the diagram simple.
As shown in figures 1 and 2, the device comprises a base (1) which can either run the length of the device or just to the inflatable components. Here it runs the length of the device. It can be made of either rigid (e.g. plastic) or flexible (e.g. cloth) material and could incorporate a head holding device (e.g. pillow or cervical spine stabilising device - not shown). (The base can also form the rest of the device as demonstrated in figure 4) To this base (1) a number of handles/buckles/straps/clips can be fitted. Figure 1 shows three carrying handles on each side (2). Any number of holding devices (here three clips) holds the inflatable components shut (3) Figure 2 shows the mechanism for closing the device. The top is brought over the patient (a) and then the buckles (3) brought up (b) and fastened.Figure 3 demonstrates an arrangement for the lower body positive pressure components. In this diagram there are two inflatable components (4). This could be replaced with one inflatable unit (figure 4) that folds in the middle. In figure 3 the two units are connected via the tubing that is subsequently connected to the inflating device (5); they could alternatively have separate connections to the inflating components. Here there is a small hole in the base layer (1) through which the pressure tubing passes.
The inflatable components (4) are shown each connected to the underlying base (1). This base can either extend around to provide a top cover or a separate material can be attached to it to provide this cover. Alternatively, the inflatable component alone can form the base and top cover (figure 4).
The two inflatable components (4) could be permanently fixed to the under structures or temporarily fixed (e.g. with Velcro ) to enable removal and cleaning. In this example they are permanently fixed (with, for example, glue).
The inflatable components (4) themselves would ideally be made of a strong but soft plastic though any gas/liquid tight material could be used. They would ideally be transparent.
There are a number of different fastening devices that could be used to keep the lower body positive pressure sandwich closed. A variable number of simple clips (3) as shown here could be used. Alternatively, buckles, straps or zips could be fitted.
The inflation tubing (5) connects to the inflatable components (4) by a valve. Any type of valve could be used for this though it should have to withstand relatively high pressures.
The inflating device (not shown) could either be automatic running on compressed gas (e.g. air), electric (e.g. electric pump) or manual (e.g. foot pump). A self inflating device (as used in life jackets) is another alternative.
Figure 4: Gives a simple example of how a single sheet of material can be folded and sealed to provide the device as described above. The arrows show the direction of the folds. The sides a should be sealed to a, b to b, c to c etc. Any technique can be used to join them but if made of plastic, heat sealing or glue may be appropriate. The edges can be reinforced (e.g. with the addition of tape). Edge C can have any number of fastening devices (3) to hold the device shut when inflated. Figure 5 shows the device folded and sealed. The long base folds back on itself to provide a compartment (6) into which a rigid material (e.g. transparent plastic or a spinal board) can be placed. This provides a mechanism for maintaining spinal stability of the patient and a mechanism for removing the board without having to roll the patient.Holding devices (not shown) can be attached to this layer and/or the layer above to enable movement of the device.