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Using surface anatomy measurements to place umbilical catheters

Journal of Perinatology volume 36, pages 161–162 (2016)Cite this article

Subjects

We read with great interest the recently published study by Gupta et al.1 that analyzed umbilical catheter insertion depth based on surface anatomy compared with estimations from commonly used weight-based formulas, such as the Shukla2 and Wright3 methods. Like the authors, we have encountered plenty of mal-positioned catheters placed via Shukla calculations, and are first-hand witnesses to the subsequent adverse effects in our patients. As such, we agree that better methods of estimating insertion length are needed and praise the authors for their work in this area. We note several strengths in the study: the relatively large sample size, the inclusion of both very low birth weight (VLBW) and larger, term infants, and the authors’ clear and logical description of how they derived their measurement calculations based on surface anatomy. In addition, they provide a thoughtful discussion and an excellent breakdown of the weaknesses inherent in the Shukla and Wright formulas, as well as other previously proposed methods. We agree with the authors that the greatest limitation of their data is that they were observational and in some aspects determined retrospectively. We hope the authors proceed as planned with prospective testing of their morphometric measurements, and encourage their efforts in that regard. This would improve the level of evidence for their proposed methods by accounting for variables such as interpersonal variability in obtaining surface anatomy measurements, which could lead to less consistency and lower accuracy in estimating catheter insertion length.

The second concern we have with the study is the use of Fisher’s exact test for comparing each method’s proportion of correctly estimated insertion lengths. McNemar’s test would be more appropriate to compare methods in this situation because of the data pairing (that is, each patient is assessed by method A and method B, so the results from methods A and B are paired for each patient). When Fisher’s exact test is used to compare the proportion correct between two methods, the within-patient pairing is ignored and the methods results are incorrectly treated as two independent groups with an effective sample size that is double the actual number of patients.6

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References

  1. Gupta AO, Peesay MR, Ramsethu J . Simple measurements to place umbilical catheters using surface anatomy. J Perinatol 2015; 35: 476–480.

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  2. Shukla H, Ferrara A . Rapid estimation of insertional length of umbilical catheters in newborns. Am J Dis Child 1986; 140: 786–788.

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  3. Wright IM, Owers M, Wagner M . The umbilical arterial catheter: a formula for improved positioning in the very low birth weight infant. Pediatr Crit Care Med 2008; 9: 498–501.

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  6. Rosner B . Fundamentals of Biostatistics, 8th edn. Cengage Learning: Boston, MA, USA, 2015, pp 395–399.

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Authors and Affiliations

  1. Department of Pediatrics, Section of Neonatology, Texas Children's Hospital/Baylor College of Medicine, Houston, TX, USA

    S L Ford

  2. Research Statistician, Newborn Center, Texas Children’s Hospital, Houston, TX, USA

    J L Hagan

Authors
  1. S L Ford
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  2. J L Hagan
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Correspondence to S L Ford.

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Ford, S., Hagan, J. Using surface anatomy measurements to place umbilical catheters. J Perinatol 36, 161–162 (2016). https://doi.org/10.1038/jp.2015.159

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