Impact of Pleth Variability Index-Guided Acute Normovolemic Hemodilution on Intraoperative Fluid Management and Postoperative Complications in Cardiac Surgery

Acute normovolemic hemodilution (ANH) is a blood conservation strategy used to reduce intraoperative blood loss and minimize the need for allogeneic blood transfusion. The technique involves withdrawing a predetermined volume of whole blood from the patient before surgery and replacing it with crystalloid or colloid solutions to maintain intravascular volume. Consequently, blood lost during surgery contains a lower hemoglobin concentration due to hemodilution, and the patient's hemoglobin level is subsequently restored through reinfusion of the collected autologous blood after the surgical procedure [1]. Based on available evidence, the European Society of Anaesthesiology recommends the use of ANH in perioperative bleeding management guidelines to reduce the need for allogeneic blood transfusion [2].

Although ANH is generally considered a safe technique, inadequate or excessive intravenous fluid replacement may lead to several potential adverse effects, including hemodynamic instability, anemia, increased myocardial oxygen consumption due to high cardiac output, dilutional coagulopathy, electrolyte imbalance, and renal dysfunction [3].

The Pleth Variability Index (PVI) is a noninvasive monitoring parameter derived from pulse oximetry that evaluates fluid responsiveness by analyzing respiratory variations in the plethysmographic waveform amplitude [4]. Particularly in patients receiving positive pressure ventilation, PVI can serve as a useful indicator for assessing intravascular volume status. As a dynamic and continuously monitored parameter, PVI has been shown to predict fluid responsiveness and facilitate goal-directed fluid therapy. Studies have demonstrated that PVI-guided fluid management may reduce the total volume of administered fluids compared with conventional fluid administration strategies [5].

Currently, no standardized protocol exists for the implementation of ANH, and its application often depends on institutional or local procedural guidelines [6]. Traditionally, ANH is performed using a 1:3 fluid replacement ratio during acute blood withdrawal, and the amount of blood to be collected is calculated using the formula:

ANH volume = (patient Hb - target Hb) / mean Hb × blood volume,