Mannitol is a monosaccharide available as 10% & 20% solutions
DURING NEUROSURGERY/ IN NEUROCRITICAL CARE:
✔️Mannitol is freely filtered in the glomerulus but won’t get reabsorbed in the tubules; so it will drive water from the interstitium which gets eliminated as urine. Hence acts as an osmotic diuretic
✔️When blood brain barrier is intact, the osmotic gradient created by mannitol will move water from the cerebral extravascular compartment to the intravascular space, reducing ICP. If blood brain barrier is not intact, it will worsen cerebral edema.
✔️The expansion of the plasma volume caused by mannitol will reduce the viscosity and improve cerebrovascular microcirculation and oxygenation. The increase in cardiac output can also cause an increase in regional blood flow which will cause a compensatory cerebrovascular vasoconstriction in areas where autoregulation is intact.
IN CRUSH INJURY / MYOGLOBINURIA
✔️Will release renal prostaglandins, which will cause renal vasodilation and increase tubular urine flow causing a solute washout and avoidance of tubular obstruction #TheLayMedicalMan
MECHANISM BEHIND ADVERSE EFFECTS
✔️The initial increase in plasma volume as a result of drawing of water into the vascular component and the resultant increase in cardiac output can precipitate heart failure in cardiac patients
✔️The osmotic diuresis can cause hypernatremia [increases urinary losses of both sodium and electrolyte-free water] , metabolic acidosis and hyperosmolarity. It has been advised that therapy should be monitored and titrated so that osmolarity doesn’t go up beyond 300 mOsm/L
✔️The rise in the plasma potassium concentration following hypertonic mannitol is due to the movement of potassium out of the cells into the extracellular fluid as the rise in cell potassium concentration induced by water loss favors passive potassium exit through potassium channels in the cell membrane
✔️Though it has been used for renal protection, the reduction in renal perfusion resulting from hypovolemia caused by diuresis can adversely affect renal function; so should be avoided in patients with renal dysfunction
#Neuroanesthesia , #Anesthesia , #Neurology , #CriticalCare