The Contribution of Plasma Urea to Total Osmolality During Iatrogenic Fluid Reduction in Critically Ill Patients.

Hyperosmolality is common in critically ill patients during body fluid volume reduction. It is unknown whether this is only a result of decreased total body water or an active osmole-producing mechanism similar to that found in aestivating animals, where muscle degradation increases urea levels to preserve water. We hypothesized that fluid volume reduction in critically ill patients contributes to a shift from ionic to organic osmolytes similar to mechanisms of aestivation. We performed a post-hoc analysis on data from a multicenter observational study in adult intensive care unit (ICU) patients in the postresuscitative phase. Fluid, electrolyte, energy and nitrogen intake, fluid loss, estimated glomerular filtration rate (eGFR), and estimated plasma osmolality (eOSM) were registered. Contributions of osmolytes Na+, K+, urea, and glucose to eOSM expressed as proportions of eOSM were calculated. A total of 241 patients were included. eOSM increased (median change 7.4 mOsm/kg [IQR-1.9-18]) during the study. Sodium's and potassium's proportions of eOSM decreased (P < .05 and P < .01, respectively), whereas urea's proportion increased (P < .001). The urea's proportion of eOSM was higher in patients with negative vs. positive fluid balance. Urea's proportion of eOSM increased with eOSM (r = 0.63; adjusted for eGFR r = 0.80), but not nitrogen intake. In patients without furosemide and/or renal replacement therapy (n = 17), urea's proportion of eOSM and eOSM correlated strongly (r = 0.92). Urea's proportion of eOSM was higher in patients not surviving up to 90 d. In stabilized ICU patients, the contribution of urea to plasma osmolality increased during body water volume reduction, statistically independently of nitrogen administration and eGFR. The shift from ionic osmolytes to urea during body fluid volume reduction is similar to that seen in aestivating animals. ClinicalTrials.org Identifier: NCT03972475.

Hidden sources of fluids, sodium and potassium in stabilised Swedish ICU patients: A multicentre retrospective observational study.

BACKGROUND: Fluid overload in ICU patients is associated with increased morbidity and mortality. Although studies report on optimisation of resuscitation fluids given to ICU patients, increasing evidence suggests that maintenance fluids and fluids used to administer drugs are important sources of fluid overload. OBJECTIVES: We aimed to evaluate the volume of maintenance fluids and electrolytes on overall fluid balance and their relation to mortality in stabilised ICU patients. DESIGN: Multicentre retrospective observational study. SETTING: Six mixed surgical and medical ICUs in Sweden. PATIENTS: A total of 241 adult patients who spent at least 7 days in the ICU during 2018. MAIN OUTCOME MEASURES: The primary endpoint was the volume of maintenance, resuscitation and drug diluent fluids administered on days 3 to 7 in the ICU. Secondary endpoints were to compare dispensed amounts of maintenance fluids and electrolytes with predicted requirements. We also investigated the effects of administered fluids and electrolytes on patient outcomes. RESULTS: During ICU days 3 to 7, 56.4% of the total fluids given were maintenance fluids, nutritional fluids or both, 25.4% were drug fluids and 18.1% were resuscitation fluids. Patients received fluids 1.29 (95% confidence interval 1.07 to 1.56) times their estimated fluid needs. Despite this, 93% of the cohort was treated with diuretics or renal replacement therapy. Patients were given 2.17 (1.57 to 2.96) times their theoretical sodium needs and 1.22 (0.75 to 1.77) times their potassium needs. The median [IQR] volume of fluid loss during the 5-day study period was 3742 [3156 to 4479] ml day-1, with urine output the main source of fluid loss. Death at 90 days was not associated with fluid or electrolyte balance in this cohort. CONCLUSION: Maintenance and drug fluids far exceeded resuscitative fluids in ICU patients beyond the resuscitative phase. This excess fluid intake, in conjunction with high urinary output and treatment for fluid offload in almost all patients, suggests that a large volume of the maintenance fluids given was unnecessary. TRIAL REGISTRATION: ClinicalTrials.org NCT03972475.