Our goal was to study the impact of different ways to perform passive leg raising (PLR) on the accuracy of evaluation of fluid responsiveness.

Patients who have shock of all kinds of reasons usually need to be transferred to the Intensive Care Unit(ICU) for monitoring and treatment due to unstable vital signs and high fatal risks. The cardiac function of these patients requires special attention. Fluid responsiveness is a comprehensive reflection of preload and cardiac function, which provides guidance on how to conduct fluid replacement therapy. When patients have fluid responsiveness, it means that after fluid resuscitation therapy, the patients' cardiac output will increase and tissue perfusion will improve, bringing benefits to patients themselves. Therefore, it is of vital significance to evaluate the presence of fluid responsiveness in patients before fluid therapy in clinical practice. Passive leg raising(PLR) is a commonly used method in clinical practice to evaluate patients' fluid responsiveness. But its accuracy is affected by the way the leg lifting is performed.

This project is aimed to explore the impact of different ways to perform passive leg raising on the accuracy of evaluation of fluid responsiveness.

Inclusion Criteria:

• (1) patients who have signs of tissue hypo-perfusion (increasing lactate levels, in need of vasopressor agents to maintain blood pressure, oliguria, and weak consciousness), and need to evaluate their fluid responsiveness; (2) patients who have received Pulse indicator Continuous Cardiac Output (PiCCO) monitoring ; (3) patients who are transferred into the intensive care department.

Exclusion Criteria:

• (1) Age < 18 years old, or > 75 years old (2) pregnancy or lactation; (3) refusal to sign the informed consent form for enrollment; (4) patients who are clearly unable to perform passive leg raising (PLR) (intra-abdominal pressure ≥16cmH2O, high risk of lower limb venous thrombosis, intracranial hypertension, and recent undergone abdominal or pelvic surgery); (5) patients with the contraindications of fluid resuscitation therapy ( pulmonary edema, intracranial hypertension and so on); (6) patients clinical doctors assessed as unsuitable for PLR.