Subarachnoid haemorrhage(SAH) is an important disease, corresponding to one in twenty strokes around the world (1). The vast majority of SAH (85%) are secondary to a ruptured aneurysm within a cerebral artery (1). SAH is associated with a poor prognosis. The overall mortality rate is around 60% either immediately (12% will die before reaching the hospital), or later within the first 6 months (2). During hospital management, numerous complications can occur such as rebleeding (50% cumulative risk in 1 year), vasospasm and delayed ischemic events (DIE), hydrocephalus, high fever, seizure, electrolyte disturbances such as hyponatremia, as well as complications of therapeutic interventions (surgical or endovascular).
Brain parenchymal oxygen tension (PbtO2) is a measure of brain tissue oxygenation. It can be obtained thanks to a specific catheter inserted directly into brain parenchyma(3). Although not fully validated, it is used to guide clinical management and as a research tool in the University’s hospital of Lausanne (CHUV)’s Intensive Care Unit (ICU). It is inserted in some patients with SAH and prolonged coma on their admission in ICU. PbtO2 can be used as an indirect indicator of cerebral brain flow (CBF) and intra cerebral pressure (ICP) monitoring. Low PbtO2 (< 20mmHg) is associated with cerebral ischemia and poor neurological outcome (4). Management of a low PbtO2 includes vasoconstrictors to increase systemic blood pressure, volume expansion, intracranial pressure (ICP) management and blood transfusions. The main limitations of PbtO2 are related its invasiveness and the fact that the measured values are potentially not representative of the whole brain (5).
Fluid management is of particular importance in patients with cerebral insults. Indeed, among many other elements of care, adequate intravascular volemia, plasma osmolarity and composition must be maintained to minimize secondary cerebral insults. Indeed, those parameters are major determinants of extracellular fluid composition, which in turn influences cerebral cells volume and perfusion. Briefly, hypotonic fluids tend to be led to some degree of cerebral cells swelling while hypertonic fluids tend to lead to cerebral cells shrinking. Extracellular volume expansion also leads to impaired oxygen diffusion and perfusion.
Hence, the volume and composition of fluids administered to a critically ill patient with SAH is of paramount importance. Guidelines in SAH management recommends the use of saline isotonic solution, but more balanced solutions could produce less activation of pituitary axis and of stress hormone (4,5) so fluid composition is also questionable.
However, to our knowledge, the effect of fluids volume and composition on PbtO2 has not been studied. In this study, we aimed to research a possible relationship between fluid volume and PbtO2 and between fluid composition (namely daily sodium and chloride administration) and PbtO2. We also searched for relationship between fluid balance, sodium and chloride administration with Lactate pyruvate ratio and a new marker, the PbtO2 burden.