Abstract:
A limb compression system for increasing the flow of venous blood in a patient comprises an inflatable cuff, a pump, a controller, and a pressure transducer. The system collects a signal from the pressure transducer indicative of the pressure in the cuff and uses the signal to determine the blood pressure of the patient. A method for providing patient cardiovascular support and monitoring of patient blood pressure is also herein disclosed.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention is related to the field of intermittent pneumatic compression (IPC) therapy. More specifically, the present invention relates to a system that provides automated non-invasive blood pressure (NIBP) monitoring support in addition to IPC therapy. 
       BACKGROUND OF THE INVENTION 
       [0002]    The application of external compression to the limbs of a patient has been used for many years to improve cardiovascular function. Researchers and clinicians have used intermittent pneumatic compression (IPC) on a patient&#39;s extremity to augment venous blood flow, which helps to prevent deep vein thrombosis (DVT) and pulmonary embolism (PE), two life threatening cardiovascular complications. 
         [0003]    IPC is a mechanical method of delivering compression to the limbs. One or more pneumatic sleeves are attached to an extremity of a patient&#39;s body. A source of pressurized gas is connected to the pneumatic sleeve and the sleeve is inflated and deflated in a cyclic fashion. This wave-like motion helps to increase the venous blood flow, thus returning the blood to the patient&#39;s heart and reducing pooling of blood in the patient&#39;s extremities. Besides the mechanical effects of enhancing venous blood flow, IPC devices have also been found to cause an increase in the body&#39;s own anti-coagulant secretions, further improving blood circulation. Deep vein thrombosis (DVT) is caused by blood clotting in a vein of the inner thigh or leg. Typically, DVT occurs when a person spends long stretches immobilized or in cramped conditions. Therefore, patients recovering from major surgery and/or leg-related surgery, such as a hip replacement, are at increased risk for DVT due to being confined in a hospital bed. Blood clots can break off from the main clot in the leg and make their way up the blood stream to the lung, resulting in a pulmonary embolism (PE) that has the potential of causing respiratory distress and failure. These conditions are exacerbated in situations where, due to excessive post-surgery bleeding, a patient is not able receive anti-coagulant drugs such as COUMADIN® to treat the DVT. 
         [0004]    Automated blood pressure monitoring has rapidly become an accepted and, in many cases, essential aspect of patient treatment. Such monitors are now a conventional part of the patient environment in emergency rooms, intensive and critical care units and in the operating theater. 
         [0005]    During the use of a conventional non-invasive blood pressure (NIBP) monitoring system, the blood pressure cuff is placed around the arm of a patient and is inflated to a supra-systolic pressure to fully occlude the brachial artery. The cuff is then progressively deflated and a pressure transducer in the cuff detects the pressure pulses as blood begins to flow past the pressure cuff. The data from the pressure sensor is used to compute the patient&#39;s systolic pressure, mean arterial pressure (MAP) and diastolic pressure. Furthermore, if blood pressures are monitored at multiple patient extremities, these blood pressures may be compared in a useful determination of arterial function. 
         [0006]    In a typical hospital setting, especially that of a patient recovering from a major surgery, the patient is surrounded by a multitude of monitoring, diagnostic, and therapeutic devices. Each of these devices is connected to the patient at one or more sites, creating a vast network of patient connections surrounding the patient. This decreases patient mobility if the patient needs to be moved to a different location within the facility and also impedes clinician access to a patient to provide care. Furthermore, due to facility resources, some machines, such as a NIBP monitoring device, do not exist in a one-to-one relationship with the patients and therefore must be moved about the facility and reconnected to each new patient to perform the diagnostic measurement. Therefore, it is desirable in the field to provide a therapeutic IPC device with an integrated NIBP monitor such that the number of connections to the patient is reduced and the number of required bedside devices is also reduced. 
       SUMMARY OF THE INVENTION 
       [0007]    The following describes an apparatus for providing intermittent pneumatic compression (IPC) that further comprises an integrated non-invasive blood pressure (NIBP) monitoring device. In a first embodiment, an inflatable cuff is removably secured to an extremity of a patient that requires IPC therapy. During the IPC therapy, a source of pressurized air will selectively inflate the inflatable cuff to a first target pressure. Then the cuff is deflated until the pressure in the cuff reaches a second, lower target pressure. The IPC therapy will continue in this cyclic fashion. A pressure transducer disposed in fluid communication with the cuff continuously monitors the pressure inside the cuff for oscillometric pulses during each deflation of the cuff. The patient&#39;s blood pressure is calculated from the characteristics of these pulses. 
         [0008]    In another embodiment of the present invention, the apparatus of the present invention operates in two modes. In a first mode, the inflatable cuff cyclically inflates to a target pressure and deflates from the target pressure to provide IPC therapy to the patient. In the second mode, in a single cycle the apparatus of the present invention inflates the cuff to a second target pressure suitable for the determination of the patient&#39;s blood pressure and releases the pressure within the cuff in a suitable fashion for the determination of the patient&#39;s blood pressure. While the pressure is being released from the inflatable cuff, the pressure transducer detects the oscillometric pulses within the cuff and the apparatus of the present invention determines the patient&#39;s blood pressure. 
     
     
       BRIEF DESCRIPTION OF THE DRAWING 
         [0009]    The drawings illustrate the best mode presently contemplated of carrying out the invention. In the drawings: 
           [0010]      FIG. 1  depicts an embodiment of the present invention; 
           [0011]      FIG. 2  depicts another embodiment of the present invention; 
           [0012]      FIG. 3  depicts a schematic diagram of the operation of an embodiment of the present invention; 
           [0013]      FIG. 4  depicts a schematic diagram of the operation of an embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0014]      FIG. 1  generally depicts a patient connected to an embodiment of the system of the present invention. The system comprises an apparatus  12  which may comprise, as depicted in  FIG. 3 , a CPU  14  and an air pump  16 . The air pump  16  is connected to the patient interface, which in a preferred embodiment is an inflatable cuff  18 , via an air hose  20 . The inflatable cuff  18  may be placed on the upper arm, as depicted in  FIG. 1 , or, as depicted in  FIG. 2 , may be a thigh cuff  22  or a calf cuff  24 . 
         [0015]    A pressure transducer (not pictured) is associated with each cuff  18  used in the system. The pressure transducer may be disposed inside the cuff  18  and a lead  26  connects the pressure transducer to the CPU  14  of the apparatus  12 , as depicted in  FIG. 3 . It is understood that this connection may be done in a variety of ways including using wireless technology such as WIFI, RF, and infrared communication systems. Alternatively, as depicted in  FIG. 4 , the pressure transducer  28  may be a part integral with the apparatus  12  disposed in such fluid communication with the air hose  20  to measure the pressure within the cuff  18 . 
         [0016]    The apparatus  12  is further connected to a display  30  which may comprise a user interface such that measured patient data can be displayed to a clinician, and a clinician may modify the treatment and/or monitoring provided to the patient  10  by the apparatus  12 . 
         [0017]    The operation of the embodiment of the system depicted in  FIGS. 1 and 3  is described herein. The CPU  14  in the apparatus  12  directs the air pump  16  to deliver a target pressure of air via the air hose  20  to the cuff  18 . This air pressure inflates the cuff  18  to the target pressure. When the target pressure within the cuff  18  has been achieved, a pressure release valve  32  releases the pressure in cuff  18 . This process is performed in a cyclical fashion as controlled by the CPU  14  to provide IPC to the patient. As in accordance with an embodiment of the present invention, when the cuff  18  has reached the target pressure, the pressure transducer (not pictured) begins to monitor the pressure in the cuff  18  and send this signal via lead  26  back to the CPU. Typically, the IPC cycle lasts between 10 and 20 seconds with the target pressure ranging between 40 and 140 mmHg. The pressure signal received by the CPU contains minute fluctuations based upon the flow of the patient&#39;s blood through the arm as it is enclosed in the cuff  18 . By analyzing these fluctuations, the CPU  14  is able to determine the systolic and diastolic blood pressures of the patient as is well known in the art. 
         [0018]    In an alternative embodiment of the present invention, the system  12  provides IPC support to the patient  10  as described above inflating the inflatable cuff  18  to a target pressure and then releasing the pressure within the cuff in a cyclical fashion. However, when a clinician desires to obtain a measurement of NIBP, the clinician activates the CPU  14  to record an NIBP measurement. To obtain an NIBP measurement, the CPU  14  directs the air pump  16  to inflate the cuff  18  to a second target pressure that is targeted for obtaining a quality measurement of NIBP. This pressure may be typically on the range of 120 mmHg to 200 mmHg. Upon achieving the second target pressure, the pressure release valve  32  releases the pressure in the cuff in a manner suitable for the detection of NIBP. This pressure release may be continuous deflation while the pressure transducer (not pictured) detects for the oscillations in the pressure inside the cuff  18 . Alternatively, the pressure release valve  32  may release the pressure in the cuff  18  in a series of incremental steps while waiting to detect the pressure oscillations at each step, thus facilitating the detection of the patient&#39;s blood pressure. The calculation of the blood pressure can be determined in accordance with the teachings of Medero et al in U.S. Pat. No. 4,543,962, of Medero in U.S. Pat. No. 4,546,775, of Hood, Jr. et al in U.S. Pat. No. 4,461,266, of Ramsey, III et al in U.S. Pat. No. 4,638,810, of Ramsey III et al in U.S. Pat. No. 4,754,761, of Ramsey III et al in U.S. Pat. No. 5,170,795, of Ramsey III et al in U.S. Pat. No. 5,052,397, of Medero in U.S. Pat. No. 5,577,508 and of Hersh et al in U.S. Pat. No. 5,590,662, all of which are commonly assigned herewith and the disclosures of which are hereby incorporated by reference. In any event, it is desirable to use any of the known techniques to determine the quality of the oscillation complexes received at each cuff pressure so that the blood pressure determination is made using the physiological relevant cuff pressure oscillations from each heart beat and not artifacts. 
         [0019]    In a still further embodiment of the present invention, as depicted in  FIG. 2 , multiple inflatable cuffs may be applied to the patient  10 . These cuffs may be an arm cuff  18 , a thigh cuff  22 , a calf cuff  24 , or an ankle cuff (not pictured). An embodiment of the present invention utilizes the thigh cuff  22  and the calf cuff  24 , in a typical arrangement for the application of IPC to a patient&#39;s leg. It is contemplated within the present invention that a thigh cuff  22  and calf cuff  24  may be also applied to the patient&#39;s other leg at the same time. In an arrangement comprising a thigh cuff  22  and a calf cuff  24 , the system of the present invention can monitor the blood pressure at two points in a single patient extremity. These two blood pressure measurements can be compared to determine blood pressure difference within the single extremity. This indication may provide useful information to a clinician in monitoring the progression of an IPC treatment. 
         [0020]    Alternatively, arm cuff  18  may be used in conjunction with calf cuff  24 . It is also contemplated within this embodiment that arm cuff  18  may be utilized with thigh cuff  22 , thigh cuff  22  and calf cuff  24 , or the ankle cuff. In this embodiment of the present invention, the blood pressure in both the arm and the leg are collected by the CPU  14 . The comparison of these pressures detected from two different extremities of the patient  10  provides an indication of patient arterial function and cardiac health that is useful to the clinician in monitoring the treatment and progression of the patient  10 . One such indication is the ankle-brachial index wherein a determination of the presence of blood clots in the patient&#39;s leg is made by comparing the patient&#39;s blood pressure at the arm versus at the ankle while the patient is lying down. A lower blood pressure in the ankle than the arm is indicative of blood vessel blockage. 
         [0021]    The presently disclosed invention provides the advantage that it combines a system for providing a commonly used patient therapy, with a system for providing a commonly used patient monitoring process. This reduces the number of machines that must be in place in a single room and furthermore reduces the total number of patient connections that are required to provide treatment and monitoring to a patient in recovery from surgery. Furthermore, the advantage of collecting blood pressure measurements at multiple extremities provides the clinician with a useful diagnostic tool that under current systems was not available. Therefore, the present embodiment increases the quality of information provided to a clinician to aid in the clinician&#39;s monitoring and treatment decisions surrounding the patient. 
         [0022]    This written description uses examples to disclose the invention, including the best mode, and also to enable any person skilled in the art to make and use the invention. The patentable scope of the invention is defined by the claims and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they have structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements of insubstantial difference from the literal language of the claims. 
         [0023]    Various alternatives and embodiments are contemplated as being with in the scope of the following claims, particularly pointing out and distinctly claiming the subject matter regarded as the invention.