The purpose of this study is to verify the accuracy and applicability of predictors of fluid administration efficacy in hypotensive critically ill patients.

Severe hypotension is a common life-threatening conditions in critically ill patients. Discriminating between the need for volume expansion or inotropic/vasoactive support is a main clinical goal. Pulse pressure variation are an accurate index of fluid responsiveness, but it needs controlled mechanical ventilation with a tidal volume of at least 8 ml/kg and absence of arrhythmias. This could limit its clinical applicability. Moreover pulse pressure variation accurately predicted cardiac output increment. However the cardiac output increase is not a clinically relevant target in absence of low cardiac output.

The objectives of the present protocol are: 1) to calculate the accuracy of cardiovascular and renal variables to predict either arterial pressure increase or clinically relevant improvement after fluid administration and 2) to verify how often dynamic indices could be applied in clinical practice.

Arterial pressure increase is defined by mean arterial pressure above 65 mmHg or an increment greater than 20 % respect to basal value. Clinically relevant improvement is defined by restoring adequate values of arterial pressure or cardiac index or diuresis or central venous saturation if they are inadequate before fluid administration. These adequate values are 65 mmHg for mean arterial pressure, 2.5 l.min-1.m-2 for cardiac index, 0.5 ml.kg-1.h-1 for the diuresis, 70 % for central venous saturation.

Inclusion Criteria:

• mean arterial pressure lower than 65 mmHg

Exclusion Criteria:

• fluid overload
• mean arterial pressure lower than 45 mmHg and mandatory immediate treatment
• active bleeding
• hemoglobin lower than 8 g.dl-1

Hypotensive patients in a General Intensive Care Unit of a University-affiliated hospital. Patients can be recruited only if they have both arterial and central venous catheters