Fluid management of the neurological patient: a concise review

Maintenance fluids: how much?

The current guidelines on fluid management in brain injury recommend using fluid balances to guide volume status (Table 1). A non-systematic overview of pertinent contemporary studies in brain-injured patients is provided in Additional file 1 [3, 23–45]. Not all of the reports in this overview studied fluid balance or fluid intake as the primary aim, but because fluid amounts were clearly reported some relevant information could be extracted.

The mean fluid intake was around 3–4 L/day in SAH patients who were treated with normovolemia or received fluid management based on volumetric haemodynamic monitoring versus 4–5 L/day in patients managed with hypervolemic treatment which often included CVP or pulmonary artery occlusion pressure (PAOP)-directed management. Fluid balances generally did not differ between both treatment groups and varied around neutral balance (?0.5 to +1 L) even in a study where mean daily fluid intake was 8 L [28]. Only one study [30] included weight-normalized fluid intake (ml/kg/day). Positive fluid balances have been associated with (angiographic) vasospasm, longer hospital length of stay and poor functional outcomes [27, 37] (see Additional file 1). Higher fluid intake has been associated with more cardiovascular side effects and DCI/delayed ischaemic neurologic deficit (DIND)/infarctions [25, 27, 28, 30, 31, 34, 35]. One may argue that the adverse prognostic value of aggressive fluid loading may reflect more intense treatments in more severely affected patients rather than causal associations because many of these studies are observational cohort studies undoubtedly prone to confounding.

In the trial on prophylactic hypervolemia after aneurysm clipping after SAH by Lennihan et al. [46] the hypervolemic group had a mean fluid intake of up to 4.5 L/day versus around 3.7 L/day in the normovolemia group, with similar daily net fluid balances in both groups (between +0.7 and ?0.7 L/day). Hypervolemia did not confer any benefit with regard to CBF or clinical outcomes. The trial by Egge et al. [47] randomized SAH patients between prophylactic hypertensive hypervolemic haemodilution (triple-H) and normovolemia, and reported fluid intake of approximately 3 L/day in the normovolemic group versus 4–5 L/day in the triple-H group (no exact data were provided in the publication). There were no differences in clinical endpoints, but more complications with triple-H (extradural haematoma, haemorrhagic diathesis, congestive heart failure and arrhythmia). For fluid balances (in contrast to fluid intake) such a trend for DCI/DIND/vasospasm was less clear, although two studies reported more adverse outcomes (not restricted to DCI) associated with positive versus negative fluid balances. Data from three other RCTs (of which two were by the same group) [25, 34, 35], a propensity matched analysis on prospective data from a RCT in SAH patients [31] and a RCT on echocardiography-guided fluid resuscitation in trauma patients [43] corroborated the association between more aggressive fluid loading and adverse outcomes (DCI/DIND, cardiovascular side effects, pulmonary oedema, functional outcome and mortality) in both SAH and TBI patients. In addition, a population-based study (n?=?5400) reported a temporal association between increased fluid intake and mortality when administered in the pre-DCI period in SAH patients (days 1–3 after the bleed), although it seemed to be beneficial in the DCI risk period (days 4–14) [30]. The data from the RCTs, the propensity matched analysis and the population-based study suggest that there may indeed be a causal link between aggressive fluid loading beyond euvolemia and adverse neurological outcomes, since major confounding is much less likely in these studies. However, tailoring treatment in individual patients remains important, which is exemplified by an investigation in SAH patients showing that increased fluid intake was associated with DIND whereas net negative fluid balances seemed harmful, but only in patients with severe vasospasm [31]. In line with this study and the fact that frank hypovolemia is to be avoided in brain-injured patients, a study in TBI patients found an association of negative fluid balances ( ?594 ml) with poor outcome [42]. The ICP and CPP values did not differ between outcome groups, which may indicate that fluid management might impact on outcomes despite successful pressure-targeted management in TBI [42]. Studies showing harm from more positive fluid balances and higher fluid intake and studies specifically targeting fluid management with isotonic fluids are scarce in TBI compared with SAH [42, 45, 48].