Comparison of Pulse Pressure Variation and Central Venous Pressure for Fluid Management Guidance in Intracranial Tumor Surgery

To prevent fluid losses secondary to surgery, fluid therapy should be administered to patients during the preoperative, intraoperative, and postoperative periods. The goal of perioperative fluid therapy is to maintain adequate circulating volume and pressure, avoid dehydration and the adverse effects of excessive fluid administration, and optimize oxygen delivery to tissues to ensure sufficient perfusion. Inadequate fluid administration can result in hypovolemia, leading to complications such as hypotension, tissue hypoperfusion, ischemia, arrhythmias, and renal damage. Conversely, excessive fluid administration can cause hypervolemia-related issues, including fluid accumulation in tissues (especially in the lungs), impaired tissue perfusion, prolonged mechanical ventilation, anastomotic leaks, delayed wound healing, and infections. Postoperative complications can also increase morbidity, mortality, and healthcare costs. Therefore, achieving normovolemia in patients during the perioperative period is of paramount importance.

In traditional fluid therapy, hourly fluid requirements for maintenance and fasting-related deficits are calculated using the '4-2-1' rule (4 mL/kg/hour for the first 10 kg, 2 mL/kg/hour for the next 10 kg, and 1 mL/kg/hour for each kilogram thereafter). Estimated fluid losses from surgical bleeding and evaporation are added to these calculations for replacement. In traditional fluid therapy, intravascular volume is estimated using parameters such as arterial blood pressure, heart rate (HR), and urine output. However, these parameters are influenced by many factors and do not always accurately reflect intravascular volume. Managing patients using these parameters, especially in high-risk surgeries, can result in complications related to hypovolemia and hypervolemia. The lack of an optimal perioperative fluid therapy approach in high-risk surgeries has led to new explorations, including personalized, goal-directed fluid therapy facilitated by advanced technological devices. Studies have shown that personalized, goal-directed fluid therapy improves postoperative outcomes.

Various static parameters have been used to guide fluid therapy to date, one of which is CVP (central venous pressure), commonly employed in clinical practice. The normal range of CVP in the supine position is 0-6 mmHg. A CVP below this range indicates hypovolemia, while a CVP above it suggests hypervolemia. Recent studies have shown that CVP's sensitivity and specificity in detecting fluid deficits are insufficient.

In recent years, dynamic parameters with high sensitivity and specificity, such as PPV (pulse pressure variation) and SVV (stroke volume variation), have been increasingly utilized to assess fluid deficits. Changes in arterial pressure waveforms during respiration are used to evaluate the response to fluid administration. These changes occur during controlled mechanical ventilation. Positive pressure ventilation increases intrathoracic pressure during inspiration, reducing venous return, right ventricular filling volume, and left ventricular stroke volume. During expiration, the effects are reversed. If arterial vasomotor tone and cardiac function remain constant, these changes in stroke volume during positive pressure ventilation are reflected in pulse pressure and systolic blood pressure. In fluid-nonresponsive patients, variations in these dynamic parameters are less than 10%.

In mechanically ventilated, hemodynamically stable, and intubated patients with a tidal volume ≥8 mL/kg, a stroke volume variation (SVV) >10% and a pulse pressure variation (PPV) >13% indicate a fluid deficit.