CSF formation/inhibition

1. CSF absorption is a sensitive function of intracranial pressure; absorption increases at pressures above the threshold for absorption and no absorption occurs below this threshold pressure (a linear fashion even in hydrocephalics who have the same relationship but at a reduced pressure/volume slope)
   1. absorption of CSF appears to be limited to the arachnoid villi
2. CSF production is thought to be relatively insensitive to pressure
3. CSF production is mainly in the choroid plexus although not entirely since fourth ventricle tumors that preclude communication between the ventricle and the thecal sac do not create a dry thecal sac; similarly, removing the choroid plexus of hydrocephalic patients does not cure hydrocephalus; thus epenymal cells also contribute to CSF production
   1. drugs that inhibit Na transport or carbonic anhydrase activity also inhibit CSF production; with various drug combinations, CSF production can be reduced to 60% of baseline
   2. Agents affecting CSF production – in general what increases CBF increases CSF production
      1. Anesthetic agents
         1. Halothane, ketamine – increase CSF production
         2. thiopental – decreases CSF production, decreases CBF, CMRO2 and is a cardiovascular depressant
      2. Active transport inhibitors
         1. Acetazolaminde, furosemide – reduce CSF production
      3. Hormones
         1. Angiotensin, vasopressin – reduce CSF production
      4. Others
         1. CO2 – increase CSF production
         2. Glycerol – reduces CSF production
         3. Norepinephrine – reduces CSF production
         4. CSF infection – reduces CSF production
         5. Aging – reduces CSF production
         6. Prolonged hypocapnia – no effect CSF production
         7. Hydrocephalus – no effect on CSF production