Disclosed herein are methods, systems and devices to monitor vascular volume status during renal replacement therapy utilizing at least one oximetryphotoplethysmography sensor. Reaction solution is delivered to and withdrawn from the one or more cells when the electrochemical power source is in a standby mode of operation. Depending on the dive opening’s location in the boat hull, the passageway may or may not be enclosed on all sides. Based on the result of the judgment, the motor is driven and controlled.