Surgery – Diagnostic testing – Cardiovascular
Reexamination Certificate
2002-05-16
2004-10-19
Winakur, Eric F. (Department: 3736)
Surgery
Diagnostic testing
Cardiovascular
C600S549000
Reexamination Certificate
active
06805672
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to monitoring physiological conditions as an indicator of shock. More specifically, the invention relates to monitoring of blood flow in tissues as an indicator of shock.
BACKGROUND OF THE INVENTION
Shock is a clinical syndrome in which blood flow to the capillary beds (the perfusion) is decreased. Shock occurs in about 1 million patients/year in the United States and a total of about 3 million patients/year are at risk. Shock occurs when arterial pressure and subsequently tissue blood flow drop so low that the amount of delivered oxygen is inadequate to meet the metabolic needs of the tissue.
During shock, the body directs blood to the heart and the brain, often at the expense of “sacrificial” organs such as the liver, skin, muscle, and gut. Prolonged shock may diminish blood flow to the gut such that the normal intestinal barrier function is disrupted and gut-derived bacteria and endotoxins are translocated to other organs via the blood. This, in turn, may lead to bacteremia, sepsis, inflammatory response and ultimately multi-organ failure—one of the major causes of patient mortality.
Conventional therapy for shock involves resuscitation. Resuscitation therapy is directed toward first assuring that oxygen is being supplied to the patient and that it is being transported through the circulation to the organs to support life. Circulatory distress is addressed with the infusion of fluids and pharmacological agents (inotropes) to increase cardiac output. Therapy is typically titrated to attain a target heart rate (HR), systolic blood pressure (BP), mean arterial blood pressure (MAP), urine output, and normal arterial pH. Cardiac output (CO) may also be monitored. While these conventional parameters are thought to give an indirect indication of tissue oxygenation, they correlate poorly with survival in critically ill patients (Astiz and Rackow, 1993; Shoemaker et al., 1993).
While the global, systemic parameters (HR, BP, CO, etc.) are readily accessible, these non-specific variables cannot tell if oxygen deprivation is occurring in one or more tissue beds or organs. Given the limitations of global monitoring, a number of local tissue monitoring techniques have been proposed to detect the onset of shock and provide an optimal “end point” to guide therapy for complete resuscitation. Techniques have been proposed to monitor parameters (pO
2
, pH, pCO
2
, lactate levels, etc.) in sacrificial tissues that are susceptible to hypoperfusion, hypoxia and ischemia to provide an optimal “end point” to guide resuscitation therapy. While these parameters are an attempt to assess the local tissue blood flow, and hence the oxygen delivery, these parameters also depend on metabolism and their respective arterial blood concentrations. Since during shock the blood supply is directed to the heart and the brain, often at the expense of the liver, skin, muscle and gut, these “sacrificial” organs are thought to provide sites to monitor shock onset and resuscitation end points. The sacrificial organs are the first to develop hypoperfusion at shock onset and are the last to be restored after resuscitation. These prior methods, however, have not revealed an effective correlation between patient survival and outcome and are not well suited for rapid and simple use in a clinical setting. Therefore, a reliable monitor for gut ischemia is needed, because such measurements could significantly impact the management of shock patients.
INFORMATION DISCLSOURE
The following patents are cited as background information herein, and to the extent necessary for a full and complete understanding of this invention, these patents are hereby incorporated herein by reference: U.S. Pat. Nos. 4,059,982, 4,852,027, 6,2221,025, 6,010,455, 5,792,070, 5,771,261, 5,769,784, 5,404,881, 5,335,669, 5,205,293, 4,859,078, 4,413,633, 4,392,005, 4,306,569, 3,818,895, 3,623,473 and Design Pat. No. 384,412.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a shock monitoring apparatus. It is a particular object of certain aspects to use the shock monitoring apparatus to monitor for shock through measurement of rectal wall blood flow as a proxy for gut ischemia.
In accordance with a first aspect, a shock monitoring apparatus comprises a probe and a controller. Optionally, the apparatus comprises one or more additional probes or sensors. The probe typically functions to provide an input stimulus to an area of interest, such as to tissue in the rectum. That is, the probe transmits an input signal, e.g., heat, into the tissue region contacted by the probe. The input signal functions to perturb the tissue. The tissue functionally responds to such perturbations, and this functional response can be correlated with the physiological state of the tissue, e.g., low blood flow to the tissue, etc., as an indicator of the state-of-shock (SOS) in the patient. In certain embodiments, a reference probe is used to account for baseline fluctuations in the tissue temperature. The system measures the functional response of the tissue and transmits an output signal to a controller. The controller then typically performs one or more operations on the signal, e.g., recording, adding, subtracting, comparing, etc. In certain embodiments described here, the output signal is compared with tabulated values contained in the controller to calculate a blood flow value based on known blood flow values.
In accordance with preferred embodiments, a system for monitoring shock comprises an apparatus for supplying heat to tissue and measuring the thermal response in the tissue, which is functionally related to physiological conditions in the tissue, e.g., blood flow in the tissue, and an device for calculating a blood flow value. Optionally, the system comprises one or more additional probes or other sensors. Such apparatus for supplying heat to tissue are well known to those skilled in the art and include, but are not limited to thermistors, thermocouples, electric wires, etc.
In accordance with additional aspects, the heating apparatus may be electrically energized, or magnetically energized as the case may be, to elevate the temperature of the apparatus and/or the probe. In preferred embodiments, the heating apparatus is designed such that only the portion of the probe in contact with the tissue is heated.
The blood flow values may be representative of several indicators of shock including but not limited to blood flow in tissue, oxygen levels in the tissue, in pH, etc. In certain embodiments, the blood flow values are converted to State-Of-Shock (SOS) values to facilitate rapid clinical assessment of a patient's condition. For example, if blood flow value is between 95-100% of non-shock blood flow value, e.g. the blood flow value in the absence of shock, an SOS value of “1” may be assigned. If the blood flow is between 85-95% an SOS value of “2” may be assigned and so on. It is preferred, but not required, that the SOS values are on a scale of “1-5”, where an SOS value of “1” represents little or no shock and an SOS value of “5” represents severe shock. One skilled in the art will recognize that the scaling of blood flow values is not limited to the “1-5” scale or that the percentages of the blood flow values necessarily are limited to the scaling described here.
In accordance with a method aspect, the shock monitoring apparatus is used to input a stimulus into the tissue, measure the response of the tissue to the stimulus, transmit and record the response of the tissue in an output signal, and output or display the results of the measurement for evaluation of the patient's physiological state. The stimulus may comprise heat, an electric current, a voltage, or any other signal capable of perturbing a physiological condition indicative of blood flow, e.g., the temperature, of the tissue. The response of the tissue is typically measured using the probe itself. In other embodiments, the response of the tissue is measured using any of the sensors well known to those skilled in the art, such as tho
Bowman Harry Frederick
Martin Gregory T.
Thermal Technologies, Inc.
Winakur Eric F.
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