Volumes of the spinal canal and caudal space in children zero to three years of age assessed by magnetic resonance imaging: implications for volume dosage of caudal blockade.

Background: The primary aim of this study was to objectively assess the different spinal and caudal volumes that are of interest for caudal block volume dosing.

Methods: Three directly assessed (volume of spinal canal/caudal space, volume of the dural sac and volume of spinal cord) and two derived volumes (volume of the epidural space and cerebrospinal fluid volume) were determined from magnetic resonance images (MRI) in 20 children (zero - three yr of age). The assessed volumes were correlated to age, height and weight. Furthermore, the volumes of the epidural space from caudal canal to three different clinically relevant target levels (L 1, Th 10 and Th 6) and the epidural volume of each individual spinal segment at the caudal, lumbar and thoracic levels were calculated.

Results: All volumes correlated in a linear manner to length and weight (R2 0.614 - 0.867) whereas a curvilinear correlation was associated with best curve fit for age (R2 0.696 - 0.883). The median volumes of the epidural space from caudal canal to L 1, Th 10 and Th 6 were 1.30 ml kg-1 (95%CI 1.08-1.51), 1.57 ml kg-1 (95%CI 1.29-1.81) and 1.78 ml kg-1 (95%CI 1.52-2.08), respectively. The median volumes of the epidural space per vertebral segment were Thoracic: 0.60 ml (95%CI 0.38-0.75); Lumbar: 1.18 ml (95%CI 0.94-1.43) and Caudal: 0.85 ml (95%CI 0.56-1.18).

Conclusions: The spinal volumes of interest show a linear correlation to height and weight whereas a curvilinear correlation was found for age. The volume of the epidural space per segment was found to be significantly higher at the lumbar level compared with the caudal and thoracic levels.