Case scenario: respiratory variations in arterial pressure for guiding fluid management in mechanically ventilated patients.

M AINTAINING perioperative optimal cardiac preload in surgical patients is paramount for precise hemodynamic management. Hypovolemia may result in tissue hypoperfusion and worsened organ dysfunction, whereas fluid overload appears to impede oxygen delivery and compromise patient outcome. Several clinical and experimental studies have demonstrated the usefulness of dynamic indices based on heart–lung interactions for guiding volume resuscitation. Mechanical ventilation induces cyclic changes in intrathoracic and transpulmonary pressures that transiently affect left ventricular preload, resulting in cyclic changes in stroke volume that are more pronounced in preload-dependent, but not in preload-independent, patients. These cyclic changes in left ventricular stroke volume induce cyclic changes in arterial pressure waveform. Schematically, systolic pressure variations, pulse pressure variations, stroke volume variations, and deltadown ( Down) are dynamic indicators of preload dependence that can be obtained from arterial pressure waveform. They have been extensively studied in different clinical settings and are robust indicators of fluid responsiveness. The authors present a patient with hypovolemia and hemodynamic instability during emergency abdominal surgery. Hemodynamic optimization is detailed before, during and after surgery using or not using arterial pressure waveform. In addition, the physiologic basis for these dynamic indices, their use in clinical practice, recent progress, and future perspectives are discussed.