Messmer AS, Zingg C, Muller M, Gerber JL, Schefold JC, Pfortmeuller CA. Fluid Overload and Mortality in Adult Critical Care Patients - A Systematic Review and Meta-Analysis of Observational Studies. Crit Care Med. 2020;Oct. 1. Online ahead of print. DOI:10.1097/CCM. 0000000000004617.
Authors reviewed literature to determine the extent that fluid overload in critically ill patients affects mortality.
Critically ill patients manifest physiologic derangements, such as capillary leakage, that render common treatments with isotonic fluids only transiently effective. The downstream effect of fluid therapy results in third-spacing and sequestration of fluids in the interstitial space. In situations where patients have renal, cardiac, and pulmonary dysfunction, commonly seen in intensive care units, large volume fluid therapy can have adverse effects. Authors note that a growing body of literature points towards increased mortality in critically ill patients who become fluid overloaded.
Fluid overload has not been clearly defined in the critical care arena. Due to the nature of how studies have reported on fluid overload, authors split the meaning of the term in two: fluid overload + cumulative fluid balance. For the purposes of this review, fluid overload refers to patients whose body weight increased by > 5% since admission. Cumulative fluid balance (CFB) is measured as the net change in fluid ins and outs during their hospital stay.
Systematic review and meta-analysis of observational studies
- Study must investigate impact of fluid overload in adult critical care patients
- Animal studies
- Patients < 1 year old
- Pregnant women
- Noncritically ill patients
- Evaluate the impact of fluid overload during the first 3 days after ICU admission on mortality in the critically ill patient
- Association of fluid overload with mortality during any point of ICU admission
- Association of fluid overload with mortality in patients with:
- sepsis/septic shock
- respiratory disease
- acute kidney injury
- recent surgery
- patient centered outcomes including renal replacement therapy, infections, mechanical ventilation, length of ICU stay
7894 studies were screened for inclusion; 46 met inclusion criteria and 34 (74%) of them (which reported on 31,076 patients) were included. Of the 34 included, 23 provided data for analysis and 11 were reviewed in narrative form.
Regarding pooled mortality risk:
- The adjusted RR [aRR] for fluid overload was 83 [95% CI, 4.03–19.33; n = 1].
- The aRR for (+) cumulative fluid balance was 15 [95% CI, 1.51–3.07; n = 4]).
Regarding (+) CFB, every 1L increase in fluid balance resulted in an increase in adjusted risk of mortality by a factor of 1.19 [95% CI,, 1.11-1.28].
Fluid overload and a (+) CFB may also be associated with mortality in patients with sepsis/septic shock, AKI, respiratory failure, or after surgery.
Randomized, double blinded, multicenter
- Heavy reliance on observational studies
- Majority of studies evaluated used metric of CFB which may be inaccurate
- Studies using 5% weight gain since admission rely on possibly inaccurate admission weights
- Absence of well-defined subgroups
Fluid resuscitation is foundational to emergency medicine. The complex physiology in the critically ill patient requires that EM providers acknowledge fluids need to be used carefully. While the data regarding fluid overload and a positive cumulative fluid balance are associated with increased mortality stem from observational studies, there is some sentiment that more is not always better. Admission fluid balance begins in the ED - give it carefully and remember to always think, "Does this patient need these fluids?" because they are not benign.