Spinal anaesthesia (SA) reduces the risk of postoperative apnoea after general anaesthesia in neonates. In 30% of patients, however, the duration of anaesthesia provided does not allow completion of surgery. When compared with term infants, formerly preterm neonates experience a shorter duration of anaesthesia after SA. A difference in the cerebrospinal fluid (CSF) volume between those two populations could explain this difference, but this has never been investigated. The study was designed to evaluate the relationship between the spinal CSF volume and patient characteristics in neonates.

Sixty-seven neonates, aged 30–60 weeks postconception, were included in this study. Their spinal CSF volumes were calculated using magnetic resonance imaging, and these volumes were plotted individually against sex, term at birth, birth weight, current gestational age, civil age, and weight. Correlations between CSF volume and these variables were investigated.

Fifty-four neonates completed the study. The CSF volume was found to be closely and linearly correlated with weight and postconceptional age. The relationship between spinal CSF volume and weight can be described as follows: CSF volume (ml)=1.94 weight (kg)+0.13. The CSF volume was not correlated with sex, weight, or term at birth, nor with civil age.

The amount of spinal CSF in neonates can be estimated as 2 ml kg ⁻¹ in both term and formerly preterm neonates. A difference in the CSF volume between them does not provide an explanation for a shorter duration of SA in the latter. Our findings reinforce weight-adjusted dosage of SA in neonates.