
==== Front
Indian J Crit Care Med
Indian J Crit Care Med
IJCCM
Indian Journal of Critical Care Medicine : Peer-reviewed, Official Publication of Indian Society of Critical Care Medicine
0972-5229
1998-359X
Jaypee Brothers Medical Publishers

10.5005/jp-journals-10071-24724
Letter to the Editor
The Evolution of Central Venous-to-arterial Carbon Dioxide Difference (pCO2 Gap) during Resuscitation Affects ICU Outcomes: A Prospective Observational Study
Sundarsingh Vijay 1https://orcid.org/0009-0009-3303-2328

Kumar Manoj 2https://orcid.org/0000-0002-4990-3708

Rodrigues Pramela R 3https://orcid.org/0009-0009-4128-7654

1 Department of Critical Care Medicine, Father Muller Medical College, Mangaluru, Karnataka, India
2 Department of Anaesthesiology, Father Muller Medical College, Mangaluru, Karnataka, India
3 Department of Anaesthesiology, Father Muller Medical College, Mangaluru, Karnataka, India
Vijay Sundarsingh, Department of Critical Care Medicine, Father Muller Medical College, Mangaluru, Karnataka, India, Phone: +91 8072952625, e-mail: vijayss87pm@gmail.com
7 2024
29 6 2024
28 7 709709
Copyright © 2024; The Author(s).
2024
https://creativecommons.org/licenses/by-nc/4.0/ © The Author(s). 2024 Open Access. This article is distributed under the terms of the Creative Commons Attribution 4.0 International License (https://creativecommons.org/licenses/by-nc/4.0/), which permits unrestricted use, distribution, and non-commercial reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The Creative Commons Public Domain Dedication waiver (http://creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated.
How to cite this article: Sundarsingh V, Kumar M, Rodrigues PR. The Evolution of Central Venous-to-arterial Carbon Dioxide Difference (pCO2 Gap) during Resuscitation Affects ICU Outcomes: A Prospective Observational Study. Indian J Crit Care Med 2024;28(7):709.

Keywords

Circulatory shock
Correlation
pCO2 gap
==== Body
pmcTo the Editor,

We read with immense interest the article by Zirpe et al. addressing the role of central venous-to-arterial carbon dioxide difference (pCO2 gap) during resuscitation in outcomes of ICU patients.1 We congratulate the authors for their excellent work. There are a few comments regarding the study that we want to highlight.

2D Echocardiography was conducted to measure the cardiac index, which is susceptible to interobserver variability. Was it performed by a single observer or multiple observers?

All patients in this study were resuscitated according to Surviving sepsis guidelines but a significant proportion (60%) of patients with shock due to other causes (hypovolemic, neurogenic, and combined) were included in this study.

After 6 hours of resuscitation, patients were categorized into high and low pCO2 gap groups. What were the respective patient counts in the high and low pCO2 groups?

Authors have compared high pCO2 and low pCO2 groups in terms of mortality, ICU length of stay, and organ support requirements. However, if they had included a comparison of data regarding differences in the severity of illness, vasopressor requirements, type of shock, and acid-base status between the two groups, it would have offered more insights into the utility of the pCO2 gap.

While correlating pCO2 gap with lactate and cardiac index, we observed a stronger focus on statistical significance rather than on the strength of the observed correlations. The strength of correlation is crucial for evaluating the pCO2 gap's validity. The significance of Spearman's coefficient is assessed through a significance test. However, it's crucial to understand that the p value derived from this test does 'not indicate the magnitude of the correlation between two variables. In reality, with a sufficiently large sample size, the statistical test will consistently show significance, regardless of the strength of the correlation. Rather than presenting p-values, we propose that the authors report the confidence intervals around Spearman's coefficients. This approach would redirect the reader's attention from statistical testing of the null hypothesis toward estimating the strength of the observed correlations.2,3

We commend Zirpe et al. for their insightful study on the role of central venous-to-arterial carbon dioxide difference (pCO2 gap) during resuscitation in ICU patients. More data on the differences in clinical characteristics, organ supports, and etiology of shock between the two pCO2 gap groups would have made this data on the pCO2 gap more applicable and externally valid. We also emphasize that the strength of correlation to be focused more rather than the p value.

Orcid

Vijay Sundarsingh https://orcid.org/0009-0009-3303-2328

Manoj Kumar https://orcid.org/0000-0002-4990-3708

Pramela R Rodrigues https://orcid.org/0009-0009-4128-7654

Source of support: Nil

Conflict of interest: None
==== Refs
References

1. Zirpe KG Tiwari AM Kulkarni AP Vaidya HS Gurav SK Deshmukh AM et al. The evolution of central venous-to-arterial carbon dioxide difference (pCO2 gap) during resuscitation affects ICU outcomes: A prospective observational study Indian J Crit Care Med 2024 28 4 349 354 10.5005/jp-journals-10071-24680 38585325
2. Her QL Wong J Significant correlation versus strength of correlation Am J Health Syst Pharm 2020 77 2 73 75 10.1093/ajhp/zxz280 31876930
3. Schober P Boer C Schwarte LA Correlation coefficients: Appropriate use and interpretation Anesth Analg 2018 126 5 1763 1768 10.1213/ANE.0000000000002864 29481436
