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The possibility to monitor blood-pH has long been acknowledged to provide significant information for the diagnosis, management and treatment of a variety of diseases and it would be of considerable support for the administration of several treatments such as, for example, extracorporeal (blood) circulation (ECC). During ECC, the patient’s blood flows outside the body in disposable bloodlines and devices for treatments such as blood purification or circulation/ventilation/oxygenation support. Although blood-pH can be measured since the early twentieth century by using ion-selective electrodes (ISEs) and, more recently, also by using point-of-care testing (POCT) instruments, nowadays no measurement method has fully succeeded in providing a cost-effective, reliable and accurate estimate of the blood-pH to be routinely used for its real-time monitoring. In a recent paper, we have proposed and demonstrated a measuring instrument for the in-line and real-time monitoring of blood-pH during ECC. Such a measuring system consists of a low-cost fluorescent disposable sensor that can be integrated into the bloodline and, of a non-disposable reading system that interrogates the sensor without contacting the patient’s blood. In this paper, we investigated the robustness of such a measuring system to variations of blood parameters such as blood flow and hematocrit. The obtained results demonstrate that, although during the tests the pH, flow, and hematocrit values were significantly varied — pH from ≈ 6.8 pH, to ≈ 7.4 pH; hematocrit from 32%, to 40%; flow from 250 ml/min, to 400 ml/min, — the measuring system continued to guarantee a measurement error inferior to ±0.04 pH, thus complying with the metrological requirements for in-line and real-time monitoring of blood-pH during ECC
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