How I personalize fluid therapy in septic shock?

Abstract

During septic shock, fluid therapy is aimed at increasing cardiac output and improving tissue oxygenation, but it poses two problems: it has inconsistent and transient efficacy, and it has many well-documented deleterious effects. We suggest that there is a place for its personalization according to the patient characteristics and the clinical situation, at all stages of circulatory failure. Regarding the choice of fluid for volume expansion, isotonic saline induces hyperchloremic acidosis, but only for very large volumes administered. We suggest that balanced solutions should be reserved for patients who have already received large volumes and in whom the chloremia is rising. The initial volume expansion, intended to compensate for the constant hypovolaemia in the initial phase of septic shock, cannot be adapted to the patient's weight only, as suggested by the Surviving Sepsis Campaign, but should also consider potential absolute hypovolemia induced by fluid losses. After the initial fluid infusion, preload responsiveness may rapidly disappear, and it should be assessed. The choice between tests used for this purpose depends on the presence or absence of mechanical ventilation, the monitoring in place and the risk of fluid accumulation. In non-intubated patients, the passive leg raising test and the mini-fluid challenge are suitable. In patients without cardiac output monitoring, tests like the tidal volume challenge, the passive leg raising test and the mini-fluid challenge can be used as they can be performed by measuring changes in pulse pressure variation, assessed through an arterial line. The mini-fluid challenge should not be repeated in patients who already received large volumes of fluids. The variables to assess fluid accumulation depend on the clinical condition. In acute respiratory distress syndrome, pulmonary arterial occlusion pressure, extravascular lung water and pulmonary vascular permeability index assess the risk of worsening alveolar oedema better than arterial oxygenation. In case of abdominal problems, the intra-abdominal pressure should be taken into account. Finally, fluid depletion in the de-escalation phase is considered in patients with significant fluid accumulation. Fluid removal can be guided by preload responsiveness testing, since haemodynamic deterioration is likely to occur in patients with a preload dependent state.

Keywords: Cardiac output; Fluid balance; Fluid challenge; Passive leg raising; Tidal volume; Volume expansion.

Fig. 1

Criteria to customize the fluid strategy at different steps of septic shock. ARDS acute respiratory distress syndrome, CO cardiac output, C(O₂) oxygen content, CRT capillary refill time, CVP central venous pressure, EEXPO end-expiratory occlusion, HR heart rate, ICU intensive care unit, MAP mean arterial pressure, P/F ratio ratio of the arterial oxygen partial pressure to the inspired oxygen fraction, PAOP pulmonary artery occlusion pressure, PCO₂ carbon dioxide partial pressure, PLR passive leg raising, PPV pulse pressure variation, PI perfusion index, RR: respiratory rate, RV right ventricular, SvO₂ mixed, venous oxygen saturation, ScvO₂ central venous oxygen saturation, SVV stroke volume variation, Vt tidal volume

Fig. 2

Means for reducing the cumulative fluid balance depending on the stage of resuscitation of septic shock. CVP central venous pressure, PAOP pulmonary artery occlusion pressure