Normovolemia

The presence of a normal amount of body fluids, normal blood volume.

Fluid management is an important component of perioperative care for patients undergoing neurosurgery. The primary goal of fluid management in neurosurgery is the maintenance of normovolemia and prevention of serum osmolarity reduction. To maintain normovolemia, it is important to administer fluids in appropriate amounts following appropriate methods, and to prevent a decrease in serum osmolarity, the choice of fluid is essential. There is considerable debate about the choice and optimal amounts of fluids administered in the perioperative period. However, there is little high-quality clinical research on fluid therapy for patients undergoing neurosurgery. A review of Ryu discussed the choice and optimal amounts of fluids in neurosurgical patients based on the literature, recent issues, and perioperative fluid management practices ¹⁾.

It is essential in patients admitted to the intensive care unit (ICU) with traumatic brain injury. Wiegers et al. aimed to quantify the variability in fluid management policies in patients with traumatic brain injury and to study the effect of this variability on patients' outcomes.

They did a prospective, multicentre, comparative effectiveness study of two observational cohorts: CENTER-TBI in Europe and OzENTER-TBI in Australia. Patients from 55 hospitals in 18 countries, aged 16 years or older with traumatic brain injury requiring a head CT, and admitted to the ICU were included in this analysis. We extracted data on demographics, injury, and clinical and treatment characteristics, and calculated the mean daily fluid balance (difference between fluid input and loss) and mean daily fluid input during ICU stay per patient. We analysed the association of fluid balance and input with ICU mortality and functional outcome at 6 months, measured by the Glasgow Outcome Scale Extended (GOSE). Patient-level analyses relied on adjustment for key characteristics per patient, whereas centre-level analyses used the centre as the instrumental variable.

2125 patients enrolled in CENTER-TBI and OzENTER-TBI between Dec 19, 2014, and Dec 17, 2017, were eligible for inclusion in this analysis. The median age was 50 years (IQR 31 to 66) and 1566 (74%) of patients were male. The median of the mean daily fluid input ranged from 1·48 L (IQR 1·12 to 2·09) to 4·23 L (3·78 to 4·94) across centres. The median of the mean daily fluid balance ranged from -0·85 L (IQR -1·51 to -0·49) to 1·13 L (0·99 to 1·37) across centres. In patient-level analyses, a mean positive daily fluid balance was associated with higher ICU mortality (odds ratio [OR] 1·10 [95% CI 1·07 to 1·12] per 0·1 L increase) and worse functional outcome (1·04 [1·02 to 1·05] per 0·1 L increase); higher mean daily fluid input was also associated with higher ICU mortality (1·05 [1·03 to 1·06] per 0·1 L increase) and worse functional outcome (1·04 [1·03 to 1·04] per 1-point decrease of the GOSE per 0·1 L increase). Centre-level analyses showed similar associations of higher fluid balance with ICU mortality (OR 1·17 [95% CI 1·05 to 1·29]) and worse functional outcome (1·07 [1·02 to 1·13]), but higher fluid input was not associated with ICU mortality (OR 0·95 [0·90 to 1·00]) or worse functional outcome (1·01 [0·98 to 1·03]).

In critically ill patients with traumatic brain injury, there is significant variability in fluid management, with more positive fluid balances being associated with worse outcomes. These results, when added to previous evidence, suggest that aiming for neutral fluid balances, indicating a state of normovolemia, contributes to improved outcome ²⁾.