Caudal anaesthesia for upper abdominal surgery in infants and children: a simple calculation of the volume of local anaesthetic.

Where the use of non-depolarizing muscle relaxants and antagonists is undesirable in infants and children undergoing abdominal surgery, caudal anaesthesia is frequently adopted, combined with light general anaesthesia. A simple calculation has been derived to determine the volume of local anaesthetic needed to obtain a higher effective anaesthetic level (up to T4-5) for upper abdominal operations using caudal anaesthesia. Clinically, a linear correlation was found between an empirically injected volume of local anaesthetic and the distance from C7 to the sacral hiatus in 21 infants and children. A similar relationship was also demonstrated radiographically in 16 cadavers by studying the spread of radio-opaque solution in the epidural space introduced by the caudal technique. From both statistical studies, a simple formula to determine the required volume of local anaesthetic for upper abdominal surgery was derived: V = D-13, where V is the volume of local anaesthetic in ml and D is the distance from C7 to the sacral hiatus in cm.