Description

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 50 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), 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]PLR.

If patients were treated with norepinephrine, the dose remained unchanged from before volume expansion until all hemodynamic measurements were complete.