Noninvasive detection of symptomless blood loss

During a surgical operation it is usually easy to measure the extent of blood loss and to compensate it. So, at the end of the operation the blood volume of a person is normal. After every operation there is, depending on the state and medication of the patient and the type of the operation, at least some blood loss. Mostly this blood loss is so slight that no actions are needed. Postoperatively, in the recovery room, it is not easy to estimate a possible decrease in blood volume. At present, in most recovery rooms, a nurse measures the blood pressure and the heart rate of the patient for instance every 15 minutes. This takes quite a lot of time, and more personnel are needed. On the other hand, it is well known that blood pressure and heart rate are normal when the blood volume loss is not more than 10 percent of the normal blood volume. About 10 percent of the normal blood volume of a person may be removed with almost no effect on either arterial pressure or cardiac output, and most people may lose 1000 – 1500 ml blood before remarkable symptoms or changes in blood volume or heart rate. In blood donation, about 500 ml of blood is removed with no harm to the donor. For a man weighing 70 kg this means 10 percent of his total blood volume.

It is desirable to detect a blood loss condition while still at the early stage, because such an early detection would give hospital personnel more time for corrective actions. A problem is, however, that there is virtually nothing that would serve as an indicator of such early phase blood loss. After an accident the magnitude of the possible blood loss before the start of the monitoring is usually not known, however, during the monitoring the magnitude of the possible ongoing blood loss can be estimated like in postoperative patients. It has been shown that a major determinant of the amplitude of T wave, caused by repolarization of the heart, is left ventricular cavity size which is directly dependent on left ventricular end-diastolic volume, reflecting blood volume. We, at BIOPOTENTIAL have developed a method and apparatus to enable easy and noninvasive monitoring of also relatively small (10 % or less) blood volume decrease in a person using changes in T wave amplitude and T/R amplitude ratio of the heart wherein T and R wave amplitudes are measured using standardized electrode placement.

The method is based on our hypothesis according to which, in acute blood volume loss, T wave amplitudes and T/R amplitude ratios in humans decrease earlier than QRS amplitudes do. This hypothesis was studied and confirmed in a pilot study of quantitative influence of acute blood volume loss of 500 ml on QRS and T wave amplitudes and T/R amplitude ratios. T wave amplitude is expressed in percentage of the amplitude at the beginning of the postoperative monitoring.

Every 5 % decrease in T wave amplitude, that means about 5 % decrease in blood volume, raises an alert conditioning. The method and apparatus help the nurse of the postoperative recovery room to oversee better the condition of the patient. Hence the nurse has more time for the care of other patients. In practice, the monitoring is performed by monitoring the magnitude of the repolarization amplitude (T wave) measured by the unipolar electrode corresponding to ECG coupling V4. The position of the electrode is determined by standardized measurement, rather than visually, as is usually the case. The nurse of the recovery room knows that if the percentage reading of the blood volume is greater than 90 %, the blood volume is large enough. If the blood volume drops to 90 %, the practitioner may, at her/his discretion, consult a physician responsible for the department.

The method and apparatus have been patented in US and Finland.

Essential references

1. Nadler R, Convertino VA, Gendler S. The value of noninvasive measurement on the compensatory reserve index in monitoring and triage of patients experiencing minimal blood loss. Shock 2014; 42: 93-98.

2. Stewart CL, Mulligan J, Grudic GZ et al. Detection of low-volume blood loss. J Trauma Acute Care Surg 2014; 77: 892-898.

3. Moulton SL, Mulligan J, Grudic GZ et al. The compensatory reserve index. J Trauma Acute Care Surg 2013; 75: 1053-1059.

4. Epstein D, Guinzburg A, Sharon S et al. A noninvasive stroke volume monitoring for early detection of minimal blood loss: a pilot study. Shock 2021; 55: 230-235.

5. Feldman T, Childers RW, Borow KM et al. Change in ventricular cavity size: differential effects on QRS and T wave amplitude. Circulation 1985; 72: 495-501.

6. Hall JE. Guyton et Hall textbook of medical physiology. 12th ed. Philadelphia RA: Saunders 2011; 274.

7. Riekkinen H. Method and apparatus for noninvasive detection of potential symptomless blood loss. United States Patent 2019; US 10,292,627 B2. Kuopio 28.02.2023 Heikki Riekkinen