Blood flow monitoring in extracorporeal circulation and the skin microcirculation using dynamic light scattering in an in vitro calibration and clinical application study

Dynamic light scattering (DLS) is a promising but currently uncalibrated technology for non-invasive measurements of total blood flow (TBF) and relative blood velocity (RBV) at the skin surface in critically ill patients. This study aimed to calibrate DLS flow measurements against reference blood flow measured in the tubing of a heart-lung machine (HLM) during an in vitro setup and during minimally invasive cardiac surgery (MICS). For both setups, calibration curves between HLM flow and TBF and between HLM flow and RBV were described, differentiating for haemoglobin (Hb) levels. TBF and RBV values were lower at higher Hb levels and in the clinical setting. DLS parameters were not affected by ambient light or intravenous dyes, however, Hb concentration and blood temperature influenced the obtained HLM-TBF and HLM-RBV relationships. No correlation was found between HLM flow and skin TBF or RBV measurements at the lower extremities. In conclusion, a clear relation between DLS flow measurements and blood flow in an extracorporeal circulation was found. Future studies should further evaluate DLS technology in critically ill patients with a defective microcirculation.