Noninvasive hypovolemia monitor

Abstract

A hypovolemia monitor comprises a plethysmograph input responsive to light intensity after absorption by fleshy tissue. A measurement of respiration-induced variation in the input is made. The measurement is normalized and converted into a hypovolemia parameter. An audible or visual indication of hypovolemia is provided, based upon the hypovolemia parameter.

1 . A method of determining a indication of blood volume in a monitored patient using a noninvasive optical sensor, the method comprising:
 receiving a plethysmograph responsive to light detected by a noninvasive optical sensor, said light being attenuated by tissue of a patient being monitored;   electronically determining variations in said plethysmograph due to respiration of said patient; and   electronically calculating a blood volume parameter responsive to said variations, said blood volume parameter indicative of blood volume of said patient at the time of said monitoring.   
     
     
         2 . The method of  claim 1 , wherein the calculating said blood volume parameter comprises normalizing said variations. 
     
     
         3 . The method of  claim 1 , wherein the calculating said blood volume parameter comprises converting said variations to a numeric value. 
     
     
         4 . The method of  claim 3 , wherein said converting comprises accessing clinical data including blood volume information. 
     
     
         5 . The method of  claim 3 , wherein said numeric value comprises a percentage of blood loss. 
     
     
         6 . The method of  claim 3 , wherein said numeric value comprises a total volume of blood. 
     
     
         7 . The method of  claim 1 , wherein the calculating said blood volume parameter comprises accessing input parameters usable in determining said blood volume parameter. 
     
     
         8 . The method of  claim 7 , wherein said input parameters include patient type. 
     
     
         9 . The method of  claim 8 , wherein said patient type includes at least two of adult, pediatric, and neonatal. 
     
     
         10 . The method of  claim 7 , wherein said input parameters include patient characteristics. 
     
     
         11 . The method of  claim 10 , wherein said patient characteristics include at least one of height, weight, and blood pressure. 
     
     
         12 . The method of  claim 1 , wherein the calculating said blood volume parameter comprises calculating using frequency domain information. 
     
     
         13 . The method of  claim 1 , wherein the calculating said blood volume parameter relies on time domain information. 
     
     
         14 . The method of  claim 1 , wherein the calculating said blood volume parameter comprises calculating a magnitude of said variations. 
     
     
         15 . The method of  claim 14 , wherein said magnitude comprises one of a variation in a minimum, a variation in a maximum, and a curve fit. 
     
     
         16 . A method of activating a blood volume alarm indicative of a blood volume needing caregiver attention, said volume detected with a noninvasive optical sensor, the method comprising:
 receiving data responsive to light detected by a noninvasive optical sensor, said light being attenuated by tissue of a patient being monitored;   electronically selecting a subset of said data responsive to respiration of said patient; and   activating a low blood volume alarm configured to attract a caregiver's attention responsive to said subset of said data.   
     
     
         17 . The method of  claim 16 , wherein said activating said alarm comprises evaluation of additional input parameters, including at least one of patient type and patient characteristic. 
     
     
         18 . The method of  claim 16 , comprising displaying a numeric value to said caregiver responsive to a blood volume of a patient being monitored. 
     
     
         19 . The method of  claim 18 , wherein said numeric value comprises at least one of a percentage of blood loss and a total volume of blood. 
     
     
         20 . A blood volume monitor comprising:
 an input configured to receive a plethysmograph responsive to light detected by a noninvasive optical sensor, said light being attenuated by tissue of a patient being monitored; and   a processor configured to electronically determine variations in said plethysmograph due to respiration of said patient, and to calculate a blood volume parameter responsive to said variations, said blood volume parameter indicative of blood volume of said patient at the time of said monitoring.