A method is provided for predicting that a patient will require a blood transfusion during a treatment. The method includes obtaining, on a processor, first data that indicates values for one or more parameters of a characteristic of a continuous photoplethysmographic (PPG) waveform collected during the treatment. The method further includes applying, on the processor, coefficients to the values for the one or more parameters. The method further includes determining, on the processor, second data that indicates a prediction that the patient will require the blood transfusion during the treatment based on applying the coefficients to the values for the one or more parameters. An apparatus is also provided for predicting that the patient will require the blood transfusion during the treatment.