Fluid challenge is frequently used in fluid management of critically ill patients. Assessing whether there is a preload reserve that can be used to increase the stroke volume by delivering a small amount of fluid in a short period of time. Optimization of fluid therapy is very important in intensive care patients. Inappropriate fluid therapy can cause significant morbidity and even mortality. Increased intracranial pressure is one of these important complications. In the present study, we planned to evaluate the effect of a fluid challenge on intracranial pressure by measuring the optic nerve sheath diameter (ONSD).

The fluid challenge is a simple volume resuscitation evaluation method that provides an indication of the patient's likelihood of benefiting from an increase in the intravenous fluid volume. Both the fluid challenge and fluid responsiveness are evaluated by interpreting the change in hemodynamic parameters after 500 mL of crystalloid (or 250 mL of colloid) solution is infused over 10-15 min. This is done in an attempt to regulate the fluid therapy of hemodynamically unstable patients in order to prevent fluid overload. In the present study, we aim to investigate the effect of the fluid challenge maneuver on intracranial pressure in ICU patients with hemodynamic instability through measuring the optic nerve sheath diameter by ultrasonography.

Patients in the intensive care unit undergoing a fluid challenge were included in this prospective observational study. A fluid challenge is defined as a 500 mL crystalloid infusion administered over 10 min, and fluid responsiveness is defined as a subsequent increase in stroke volume of at least 15%. The ONSD and hemodynamic variables will be measured by ultrasonography before (T0), at the end (T1), and 30 min after the fluid challenge (T2). The primary outcome of the study is the change in intracranial pressure associated with the fluid challenge, and the secondary outcome is the relationship between fluid responsiveness and the change in ONSD.

Inclusion Criteria:

1. Patients with no known intracranial pathology.
2. Patients with systolic blood pressure < 90 mmHg
3. Patients with mean blood pressure < 65 mmHg
4. Patients with tachycardia (heart rate 100 beats/min)
5. Patients with mottled skin, oliguria (diuresis of less than 20 ml/hr or 0.5 ml/kg/hr for two hours), and acute renal failure.
6. Patients with arterial lactate concentration > 2 mmol/L

Exclusion Criteria:

1. Patients with known intracranial hypertension
2. Patients in the early postpartum period
3. Patients with severe mitral or aortic regurgitation
4. Patients with cardiac arrhythmia
5. Patients unable to be evaluated due to poor echogenicity

Primary and secondary study outcomes