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Observational Study
. 2025 Feb 4;29(1):57.
doi: 10.1186/s13054-025-05285-y.

Relationship between skin microvascular blood flow and capillary refill time in critically ill patients

Alexandra Morin  1 , Louai Missri  1 , Tomas Urbina  1 , Vincent Bonny  1 , Maxime Gasperment  1 , Juliette Bernier  1 , Jean-Luc Baudel  1 , Eduardo Kattan  2 , Eric Maury  1 , Jérémie Joffre  1   3 , Hafid Ait-Oufella  4   5
Affiliations
Observational Study

Relationship between skin microvascular blood flow and capillary refill time in critically ill patients

Alexandra Morin et al. Crit Care. .

Abstract

Background: Capillary refill time (CRT) and skin blood flow (SBF) have been reported to be strong predictors of mortality in critically ill patients. However, the relationship between both parameters remains unclear.

Methods: We conducted a prospective observational study in a tertiary teaching hospital. All patients older than 18 years admitted in the intensive care unit (ICU) with circulatory failure and a measurable CRT were included. We assessed index SBF by laser doppler flowmetry and CRT on the fingertip, at T0 (Within the first 48 h from admission) and T1 (4 to 6 h later). Correlation was computed using Spearman or Pearson's formula.

Results: During a 2-month period, 50 patients were included, 54% were admitted for sepsis. At baseline median CRT was 2.0 [1.1-3.9] seconds and median SBF was 46 [20-184] PU. At baseline SBF strongly correlated with CRT (R2 = 0.89; p < 0.0001, curvilinear relationship), this correlation was maintained whether patients were septic or not (R2 = 0.94; p = 0.0013; R2 = 0.87; p < 0.0001, respectively), and whether they received norepinephrine or not (R2 = 0.97; p = 0.0035; R2 = 0.92; p < 0.0001, respectively). Between T0 and T1, changes in SBF also significantly correlated with changes in CRT (R2 = 0.34; p < 0.0001). SBF was related to tissue perfusion parameters such as arterial lactate level (p = 0.02), whilst no correlation was found with cardiac output. In addition, only survivors significantly improved their SBF between T0 and T1. SBF was a powerful predictor of day-28 mortality as the AUROC at T0 was 85% [95% IC [76-91]] and at T1 90% [95% IC [78-100]].

Conclusion: We have shown that index CRT and SBF were correlated, providing evidence that CRT is a reliable marker of microvascular blood flow. Trial registration Comité de protection des personnes Ouest II N° 2023-A02046-39.

Keywords: Blood flow; Capillary refill time; Tissue perfusion.

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Conflict of interest statement

Declarations. Ethical approval and consent to participate: The protocol was approved by a national IRB (Comité de protection des personnes Ouest II N° 2023-A02046-39). All patients were informed of the study and gave oral consent for participation. Consent for publication: Not applicable. Competing interests: The authors declare that they have no competing interests.

Figures

Fig. 1
Fig. 1
Correlation between capillary refill time and skin blood flow at baseline. A Correlation between CRT and SBF measured on the index, B in patients with (red) or without norepinephrine (blue) C in patients with (green) or without sepsis (black). Spearman test. CRT, capillary refill time; SBF, skin blood flow; PU, perfusion units
Fig. 2
Fig. 2
Correlation between capillary refill time and skin blood flow variations. Correlation of changes between T0 and T1 in CRT and SBF, ∆CRT = CRT T1–CRT T0, ∆SBF = SBF T1–SBF T0. Pearson test. CRT, capillary refill time; SBF, skin blood flow; PU, perfusion units
Fig. 3
Fig. 3
Prediction of day-28 mortality by baseline skin blood flow
Fig. 4
Fig. 4
Variations of skin blood flow in survivors and non survivors. Variations between T0 and T1 of SBF in survivors with initial CRT > 2.5 s A and in non survivors C Example of variations between T0 (blue) and T1 (red) of SBF in a survivor B and a non-survivor D. CRT, capillary refill time; SBF, skin blood flow; PU, perfusion units
See this image and copyright information in PMC

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