The Ayala Quotient (also referred to as the Ayala Index) measures the effect of removing a volume of cerebrospinal fluid (CSF) on the pressure. Its value correlates with the size of the cerebrospinal fluid reservoir. The quotient was proposed by Giuseppe Ayala.



(1) pressure of the CSF before removal of CSF, in cm H2O

(2) volume of CSF removed in mL

(3) pressure of the CSF after removal of the CSF, in cm H2O


Ayala quotient =

= (volume of CSF removed in mL) * (pressure after removal of the fluid) / (pressure before removal of the fluid)



• The normal value is 5.5 to 6.5.

• An increased value correlates with a large CSF reservoir.

• An decreased value correlates with a small CSF reservoir.

Ayala Quotient


Seen In

< 5.0


subarachnoid block or other cause of a small CSF reservoir

5 - 5.4

borderline low


5.5 to 6.5



6.6 to 7.0

borderline high


> 7.0


hydrocephalus, serous meningitis or other cause of a large CSF reservoir


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