A. Bhardwaj and M.A. Mirski (eds.), Handbook of Neurocritical Care: Se - PDF document

A. Bhardwaj and M.A. Mirski (eds.), Handbook of Neurocritical Care: Second EditionAcid – Base DisordersAcid – base disorders are very common in the NCCUThe normal pH range is 7.35–7.45; alkalosis is defined as pH ■7.45, and acidosis is defined as pH pH is a measure of the hydrogen ion concentration in the extracellular fluids and is determined by the pCO and HCO concentrationconcentration♦♦♦■♦2] (meq/L) = 24 × (PCOThe initial change in PCO or HCO is called the primary disorder; the subsequent change is called the or secondary disorderCompensatory changes frequently will not return the pH to the normal range but will serve to limit the effect of the primary derangementAcid – base disorders are of particular concern in neurophysiology because of their effects on cerebral blood flow (CBF)Acidosis (decrease in pH) results in cerebral vasodilation, whereas alkalosis (increase in pH) results in cerebral vasoconstrictionAs pH increases, cerebral vasoconstriction also increases, resulting in decreased CBF and therefore decreased cerebral blood volume and ICPChanges in acid – base status within the blood are transmitted across the blood-brain barrier (BBB) via CO rather than by H ions; the BBB is impermeable to , but CO crosses freelyThe subsequent change in the CSF pH is a result of the conversion of CO + O to H and HCO by carbonic anhydraseChapter 2Electrolyte and Metabolic DerangementsNikki Jaworski and Ansgar Brambrink N. Jaworski, MDDepartment of Anesthesia and Peri-operative Medicine, Oregon Health and Science University, Portland ORDepartment of Anesthesiolgy, Oregon Health and Science University, 3181 SW Sam Jackson Park Road, Portland, OR 97239, USA