Background:~Intravascular volume expansion is a common intervention in critically ill patients with acute circulatory failure. Nevertheless, approximately 50% of critically ill patients will not benefit from an intravascular volume expansion, since they are in the horizontal portion of the Frank-Starling curve.~Thus, an accurate assessment of fluid responsiveness prior to volume expansion is mandatory to avoid fluid overload, which has been associated with increased morbidity and mortality in critically ill patients.~Fluid challenge, which consists of administering fluid to assess volume responsiveness, is widely performed. However, repeated fluid challenges, several times a day, can be harmful Indeed, if cardiopulmonary function cannot compensate for the increase in preload, fluid loading can compromise micro-vascular perfusion and oxygen delivery or aggravate peripheral and pulmonary oedema.~For many years, spontaneous breathing was considered a major limitation to assess fluid responsiveness in critically ill patients .~Nevertheless, Guinot et al has shown that an increase in stroke volume of over 7% accurately predicted fluid responsiveness in spontaneously breathing patients under spinal anaesthesia, using a 100 ml fluid infusion.~In this study, the investigator test the hypothesis that a mini-bolus fluid challenge, of either 50 ml or 100 ml, can predict fluid responsiveness in spontaneously breathing patients with hemodynamic instability.~Passive leg raising technique: Initially, the patient is placed semi-recumbent with the head of the bed at 45°. After recording baseline measurement, the head of the bed is lowered and the legs are elevated to 45° for 2 minutes.~Fluid challenge responsiveness:~Fluid responsiveness is defined as an increase in the cardiac output measured using FloTrac-Vigileo monitor (∆CO-PLR > 10%) after the PLR, separating the studied population into responders and non-responders.~Measurements:~Patients characteristics, including age and sex, are recorded at admission. The aetiology of acute circulatory failure, the inotropic and/or vasopressor support (epinephrine, norepinephrine and dobutamine) and the APACHE II score are recorded.~The following hemodynamic variables are recorded: heart rate (beats per minute), systolic blood pressure (mmHg), diastolic blood pressure (mmHg), and mean arterial blood pressure (mmHg). These variables are collected at baseline (T0), immediately before mini-bolus infusion (T50b, T50a, T100b and T100a), and immediately before the PLR manoeuvre (TPLRb and TPLRa).~Cardiac output (CO) and stroke volume (SV) are measured using both an EsCCO monitor (COescco and SVescco) and a FloTrac transducer connected to a Vigileo monitor (COflotrac and SVflotrac). CO and SV are measured at baseline, before and after each mini-bolus infusion, and before and after passive leg raising. They are recorded at the moment when they plateau. The hemodynamic variables cited above are also recorded at that time.~Changes -induced by the mini-boluses and by the PLR- in all parameters were measured; these were referred to as ∆[parameter]50 and ∆[parameter]100, and ∆[parameter]PLR.~If patients were treated with norepinephrine, the dose remained unchanged from before volume expansion until all hemodynamic measurements were complete.
Intravascular volume expansion is a common intervention in critically ill patients with acute circulatory failure.we test the hypothesis that a mini-bolus fluid challenge, of either 50 ml or 100 ml, can predict fluid responsiveness in spontaneously breathing patients with hemodynamic instability.