Caudal block is commonly used technique in all types of surgery below the umbilicus  for postoperative analgesia in paediatric patients because of its safety and efficacy 

Unfused sacral hiatus allows for easy and safe access into the epidural space. However, caudal epidural Has its own advantages and disadvantages. The main disadvantages of block include urinary retention , excessive motor blockade especially if higher volume and concentration of local anaesthetic drug  has been used. 

Therefore, Different volumes according to surgical procedures has been advocated for caudal epidural analgesia..

The optic nerve sheath diameter (ONSD) is a measure of diameter of the protective sheath surrounding the optic nerve. Studies suggest that ultrasonographic measurements of optic nerve sheath diameter  correlate with signs of raised  intracranial pressure.  Hansen and Helmke showed that intrathecal infusion of lactated ringer’s solution leads to an increase in ONSD measured by ultrasonography^.[2]

ONSD  is measured at three millimetres  behind the ocular globe , as the optic nerve is surrounded by fat and  the dural sheath is distensible within its fatty environment, particularly in case of raised  pressure in the cerebrospinal fluid.^[3]

A study by Gautam et al. (2019) Conducted a study  wherein  use of caudal block and its effect on ONSD in  children of various age groups were recorded  and compared . He found that there was  high success rate with the technique especially in children younger than 5 years of age 

A study by lee et al. found that caudal block with a high volume of local anaesthetic can cause greater increase in Intra Cranial Pressure than caudal block with low volume of local anaesthetic 

There has been ultrasonographic evidence of bidirectional movement of CSF, coined  as the “CSF rebound mechanism”. When a considerable volume is shifted from spinal canal  to intracranial space, this volume should increase ICP to such a degree that it affects cerebral perfusion. As CSF is rebounded from intra cranial space to the spinal canal,  the cerebral perfusion should return towards baseline. Thus, helping  us in investigate  whether such changes in cerebral perfusion are associated with high volume caudal block. As ONSD is the direct reflection of intra cranial pressure, we decided  to use it as a marker.

As all these  studies suggest that the use of caudal block can lead to a increase in ONSD in children, but the effect may vary depending on the volume and concentration of local anaesthetic used and the age of child. Therefore, we decided to compare the effect of high volume and low volume Bupivacaine on intra cranial pressure after giving caudal block in paediatric  population.