A New Formula for Estimating Insertion Length of Umbilical Catheters in Neonates: An Observational Study

Objective: Current formulae used by clinicians to estimate the insertion length of umbilical catheters are inaccurate. We aimed to derive a new model that could improve accuracy in estimating the insertion length of umbilical catheters. Study design: This was a multi-centre prospective observational study of neonates admitted to neonatal units and needing umbilical line(s) inserted for clinical reasons. Demographic data, catheter-related measurements and a new external length measurement—sternal notch to the umbilicus, were collected at three tertiary-level neonatal units in South Wales, UK. Generalised linear models were used to estimate the fit of the external length, birthweight, gestation and head circumference with catheter length and to derive a formula. The best fit was estimated by comparing r 2 values for each equation. Results: Data from 113 infants for each venous and arterial line were analysed for the new mathematical formulae. For both umbilical arterial catheterisation [[Formula: see text] and umbilical venous catheter (UVC) [[Formula: see text]], a quadratic model based on birthweight was found to have the best fit for predicting the insertion length of the catheters. However, the overall fit for UVCs was poorer for all explanatory variables ( y = estimated insertion length of the umbilical catheter in cm, x = birthweight in kg). Conclusion: Our prospective multi-centre observational study identified a quadratic model based on birthweight as the best fit for estimating the insertion length of umbilical lines in neonates. This is a new finding and further development on earlier birthweight-based linear models.