Fluid Management During Craniotomy

We start this chapter by reviewing the concepts of osmolality and oncotic pressure of solutions as relates to their effect on the movement of fluid between the vasculature and tissues. We then specifically examine how fluid moves between cerebral capillaries and the brain in context of the blood-brain barrier, which acts as a semipermeable membrane. There are numerous fluids that can be administered perioperatively; we examine the properties of various crystalloid and colloid solutions and we delve into ongoing research surrounding the question of whether colloids provide any clinical benefit over crystalloids and the difficulties in translating preclinical data into the clinical setting of the neurosurgical population. Hyperosmolar solutions such as hypertonic saline and mannitol can be used to lower intracranial pressure by virtue of creating osmotic shifts of water from central nervous system tissue into the intravascular space; they appear to be equivalent in terms of the beneficial effect on intracranial hypertension, but whether there are differences in long-term outcomes await further investigation. Careful attention must be given to the neurosurgical patient to accurately assess intravascular status, and the selection of perioperative fluids should take into account the patient’s underlying neurological pathology along with comorbidities, with the goals of achieving euvolemia and avoiding hyperglycemia. Ideal hemoglobin thresholds are not well-established in the neurosurgical population: anemia is associated with worse outcome but evidence of whether transfusion of red blood cells improve outcome is lacking thus far.