Impact of positive fluid balance on ICU outcome is influenced by the severity of illness

Introduction

Less fluid gain has been suggested to be associated with better survival of ICU patients. We investigated whether the positive fluid balance itself or rather the severity of illness is the major determinant of ICU mortality.

Materials and methods

Four hundred and seventeen medical and surgical adult patients admitted to the general ICU of Tartu University Clinics during 2004 and 2005 were retrospectively studied. Eighty patients were excluded due to missing data.

Results

The total ICU mortality was 29%. The survivors had significantly smaller fluid gain during the admission day than nonsurvivors (2.6 ± 3.3 l vs 4.7 ± 6.4 l; P < 0.001). The fluid gain was significantly smaller in survivors who had SOFA score >10 (2.4 ± 3.3 l vs 3.8 ± 5.6 l in nonsurvivors; P = 0.026), but not for those with SOFA score >10 (4.3 ± 3.7 l vs 5.3 ± 6.9 l; P = 0.525). The fluid balance had no impact on the outcome of the latter subgroup of patients, having lactate >4 mmol/l. However, if these patients had lactate <4 mmol/ they significantly benefit from positive fluid gain (Table 1).

Table 1 Fluid gain on the day of admission to the ICU in subgroups of patients (liters)

Conclusion

The fluid gain during the admission day is associated with increased mortality of ICU patients. Subgroup analysis revealed that this was true for less severely ill patients (SOFA score ≤ 10), but not for patients with SOFA score >10. The positive fluid balance per se is not necessarily fatal and its effect on outcome is mainly dependent on the severity of illness.