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 .
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.