Blood loss volume prediction from arterial waveform

Description (excerpt)

BLOOD LOSS VOLUME PREDICTION FROM ARTERIAL WAVEFORM CROSS-REFERENCE TO RELATED APPLICATIONS [0001] This application claims benefit of Provisional Appln. 63/532,529, filed August 14, 2023, the entire contents of which are hereby incorporated by reference as if fully set forth herein, under 35 U.S.C. § 119(e). STATEMENT OF GOVERNMENTAL INTEREST [0002] Under paragraph 1(a) of Executive Order 10096, the conditions under which this invention was made entitle the Government of the United States, as represented by the Secretary of the Army, to an undivided interest therein on any patent granted thereon by the United States. This and related patents are available for licensing to qualified licensees. BACKGROUND [0003] Hemorrhagic shock is a type of shock that is caused by heavy blood loss, which can be caused by internal or external bleeding. Hemorrhagic shock can be life threatening and needs to be treated as a medical emergency. Hemorrhagic shock can be characterized by class: Class 1 represents volume loss up to 15% of total blood volume; Class 2 represents volume loss from 15% to 30% of total blood volume; Class 3 represents volume loss from 30% to 40% of total blood volume; and Class 4 represents volume loss over 40% of total blood volume. In the acute phase of traumatic hemorrhagic shock, the therapeutic priority is to stop the bleeding. As long as such bleeding is not controlled, the physician must manage fluid resuscitation, vasopressors, and blood transfusion to prevent or treat acute coagulopathy of trauma. [0004] Compensatory Reserve Metric (CRM) for trauma victims suffering from hypovolemia (decreased circulating blood volume) is a single health indicator value that ranges from 100% for healthy individuals, down to 0% at hemodynamic decompensation - when the body can no longer compensate for blood loss. However, identifying the point of decompensation needed for developing CRM can be subjective, often relying on qualitative observations made by the patient. [0005] Canines, horses and other animals operating in hazardous situations, such as search and rescue or battlefield conditions, can also suffer from hemorrhagic shock and should be monitored for the severity of blood volume loss. SUMMARY [0006] Techniques are provided for determining quantitative metrics predictive of hemorrhagic shock based on objective measurements from arterial waveform sensors monitoring a subject, such as a human or other animal. The arterial waveforms can be obtained in any known manner, including obtained via an indwelling arterial cannula transducer and displayed on a monitor providing a beat-to-beat estimate of the systolic, diastolic, and mean arterial pressures (MAPs), or from optical transmission or electrical voltage measurements. [0007] These techniques are based on machine learning on animal training data sets obtained through controlled exsanguination of laboratory animals, including animals that are surrogates for humans. [0008] In a first set of embodiments, a method for monitoring blood loss in a subject animal includes collecting arterial pressure waveform measurements of the subject animal. The arterial pressure waveform measurements are collected by a pressure waveform sensor during an observation period spanning several heartbeats. The method also includes processing the arterial pressure waveform measurements of the subject animal to extract one or more blood pressure features. The method further includes outputting a value of at least one objective blood loss metric for the subject animal by providing the one or more extracted blood pressure features as input to one or more machine learning (ML) models. Still further the method includes presenting the value of the at least one objective blood loss metric. The one or more machine learning models are trained on multiple historical instances. Each instance includes historical arterial pressure waveform measurements for an animal of a related species over a historical observation period spanning a laboratory exsanguination experiment. The historical arterial pressure waveform measurements are associated with at least one historical objective blood loss metric value determined from directly-measured blood loss during the laboratory exsanguination experiment. [0009] In some embodiments of the first set, the at least one objective blood loss metric includes a blood loss volume metric (BLVM) based on a ratio of a shed blood volume over a maximum shed blood volume that the subject animal can survive. In some of these embodiments, the at least one objective blood loss metric includes a hemorrhage area (HemArea) or mean arterial pressure area (MAP Area) or both derived from the BLVM. [0010] In some embodiments of the first set, the at least one objective blood loss metric includes a percent estimated blood loss (PEBL) based on a ratio of a shed blood volume over a total blood volume for the subject animal. In some of these embodiments, the total blood volume for the subject animal is based on a height or weight,