# DiCART TM device to measure capillary refill time: a validation study in patients with acute circulatory failure

Alexandre Descamps, Matthias Jacquet-Lagrèze, Thomas Aussal, Jean-Luc Fellahi, Martin Ruste

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Alexandre Descamps, Matthias Jacquet-Lagrèze, Thomas Aussal, Jean-Luc Fellahi, Martin Ruste. DiCART TM device to measure capillary refill time: a validation study in patients with acute circulatory failure. Journal of Clinical Monitoring and Computing, 2025, 39 (5), pp.831-840. 10.1007/s10877-025-01271-5 . inserm-05319096

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# DiCART™ device to measure capillary refill time: a validation study in patients with acute circulatory failure

Alexandre Descamps<fnref n="1" />,<fnref n="2" /> · Matthias Jacquet-Lagrèze<fnref n="1" />,<fnref n="2" />,<fnref n="3" /> · Thomas Aussal<fnref n="1" /> · Jean-Luc Fellahi<fnref n="1" />,<fnref n="2" />,<fnref n="3" /> · Martin Ruste<fnref n="1" />,<fnref n="2" />,<fnref n="3" /> ID

Received: 4 December 2024 / Accepted: 11 February 2025 / Published online: 26 February 2025

© The Author(s) 2025

## Abstract

Capillary Refill Time (CRT) is a valuable metric to assess cutaneous perfusion. Its prognostic value in patients with acute circulatory failure has been reported as improved when the measurement is standardized. The DiCART™ device is a fully automated CRT measurement tool requiring validation. We conducted a comparative interventional single-center study including 25 patients with acute circulatory failure, to evaluate the agreement between CRT measured by an automated measurement device (CRT<sub>DiCART</sub>) and CRT measured clinically (CRT<sub>CLIN</sub>). CRT was measured on the fingertip, chest, and knee. Three measurements were performed at each location to obtain an average for each site. The measurements were conducted both clinically and using the DiCART™ device by two different operators, each blinded to the results. Agreement was determined using intraclass correlation coefficient (ICC) and Bland and Altman analysis. The ICC between CRT<sub>CLIN</sub> and CRT<sub>DiCART</sub> was 0.46 (95% Confidence Interval (CI) 0.32, 0.59) across all measurement sites; the mean bias was 0.23s (95% CI -0.17, 0.64), with upper Limit of Agreement (LoA) 2.77s (95% CI 2.44, 3.20) and lower LoA –2.30s (-2.73, -1.97). Intra observer ICC was 0.85 (95% CI 0.74, 0.91) for CRT<sub>CLIN</sub> and 0.43 (95% CI 0.15, 0.64) for CRT<sub>DiCART</sub>. Inter observer ICC was 0.86 (95% CI 0.76, 0.92) for CRT<sub>CLIN</sub> and was 0.41 (95% CI 0.14, 0.63) for CRT<sub>DiCART</sub>. The DiCART™ device showed poor agreement with clinical CRT in patients with acute circulatory failure, which does not support its use in routine practice.

**Keywords** Capillary refill time · Acute circulatory failure · Validation, agreement · DiCART™

## 1 Introduction

The capillary refill time (CRT) is a dynamic clinical parameter of cutaneous perfusion that is used on a daily basis by emergency physicians, pediatricians, and intensivists. The measurement of this parameter has a prognostic value and is useful to guide the treatment in various contexts of acute circulatory insufficiency, such as sepsis [1] or dehydration states in children [2]. Its use is recommended by numerous scientific societies [3’5].

Nevertheless, the measurement of capillary refill time is subject to a number of limitations and remains a subjective and non-standardized evaluation. The reliability of this measurement may be influenced by various factors, including the location of the evaluation, the level and duration of the pressure applied and the training of the raters [6’8]. Furthermore, the precision of this method seems to be influenced by environmental factors such as temperature and brightness [9]. A survey among physicians reported a high rate of CRT measurement use, but through heterogeneous methods [10]; therefore, a better standardization would increase its accuracy in predicting death or adverse effects [11].

The DicarTech Company (Davézieux, France) is developing a medical device aiming to automatize the measurement of CRT. A clinical study demonstrated the safety and diagnostic efficacy of an initial prototype in healthy volunteers [12]. Furthermore, feedback resulted in the development of a second-generation prototype, which led to significant improvements of the device according to preliminary results [13]. The objective of this study was to assess the degree

<figure><img src="image_2.png" /></figure>

<footnote>Martin Ruste
martin.ruste@chu-lyon.fr</footnote>

<footnote n="1">¹ Service d'anesthésie-réanimation, Hôpital cardiologique Louis Pradel, Hospices Civils de Lyon, Bron, France</footnote>

<footnote n="2">² Faculté de médecine Lyon Est, Université Claude Bernard Lyon 1, Lyon, France</footnote>

<footnote n="3">³ CarMeN Laboratoire, Inserm UMR 1060, Université Claude Bernard Lyon 1, Lyon, France</footnote>
of concordance between the DiCART™ second-generation prototype device and clinically measured capillary refill time in patients presenting with acute circulatory failure.

## 2 Methods

### 2.1 Study design and settings

The study protocol was approved by an institutional review board (Centre de Protection des Personnes Sud-Med 1, 05/04/2022). Written informed consent was collected from each participant prior to their participation when their clinical condition allowed it. Otherwise, it was obtained from a family member. When the patient's clinical condition improved subsequently, their consent was sought at the earliest opportunity. This study was conducted in the Cardiothoracic and Vascular Intensive Care Unit of the Louis Pradel University Hospital, Hospices Civils de Lyon, Lyon, France. The study was registered in ClinicalTrials.gov (NCT05847998, 02/16/2022).

### 2.2 Participants

Patients aged of at least 18 years with acute circulatory failure were eligible for inclusion in the study. Acute circulatory failure was defined as a mean arterial pressure (MAP) lower than 70 mmHg or inotropic or vasopressor therapy to maintain a MAP greater than 65 mmHg, in conjunction with at least one indicator of tissue hypoperfusion, comprising mottling, hyperlactatemia greater than 2 mmol/L, oliguria, or confusion (defined with the Confusion Assessment Method [14]).

The exclusion criteria were the presence of skin lesions at the measurement site, current pregnancy or breastfeeding,

lack of effective contraception in women with childbearing potential, absence of social security coverage, legal protection measures for patients, and participation in another interventional study.

### 2.3 The DiCART™ device

The DiCART™ prototype is a fully automated device for CRT measurement (Fig. 1). The second-generation of the device has been designed and manufactured in accordance with a standardized process, enabling certification and industrial production. It has a compact design, with dimensions of 15 × 18 cm and a weight of 450 g, which allows its use with a single hand. It features a user interface comprising a 1.44-inch display, control buttons, and a joystick for navigation. It includes a temperature sensor for indicative surface temperature measurements. The device comprised a mechatronic system. The device is initially positioned on the patient's skin for use. The measurement process is initiated through a trigger mechanism. Subsequently, the piston exerts a pressure on the skin for a period of five seconds, thereby inducing a blanching effect of the skin. The pressure applied by the piston is adjusted using a precision sensor and a calibrated spring system, thereby ensuring consistent force application. The sensors provide real-time feedback to maintain the expected pressure throughout the compression period. Subsequently, the piston retracts, and a high-precision camera captures Red Green Blue (RGB) images at 30 frames per second with a resolution of 1920 × 1080 pixels and a viewing angle of 64 × 48 degrees. The image acquisition process lasts for eight seconds. To ensure standardized lighting conditions, low-intensity pure white LEDs are used. The captured images are then processed by an embedded algorithm. This algorithm first converts the images from the RGB color space to the L*a*b color space and smooths the

<figure><img src="image_3.png" /><figcaption>**Fig. 1** DiCART™ device. **A:** Spring connected to the pressure sensor; **B:** Start trigger; **C:** Screen displaying adynamic gauge of exerted pressure; **D:** Camera; **E:** Piston; **F:** Temperature sensor</figcaption></figure>
curves along the ‘a’ axis (red-green axis). It then calculates
the averages of positive and negative gradients. Finally,
the CRT is determined when the sum of positive gradients
exceeds 50% of the total gradients.

## 2.4 Study protocol

At baseline, the following data were collected for each
patient: demographics, comprising age, sex, height, weight,
body mass index, and prototype (Fitzpatrick Scale I to VI);
medical history, comprising arterial hypertension, diabetes,
ischemic cardiopathy, chronic obstructive pulmonary dis-
ease, peripheral arterial disease, and chronic kidney disease;
clinical assessments, comprising shock mechanism, ventila-
tion status, presence of confusion, urine output, mean arte-
rial pressure, central venous pressure, heart rate, oxygen
saturation, peripheral perfusion index [15], cardiac index,
and mottling score [16]; medications, comprising admin-
istration of dobutamine, vasopressin, and norepinephrine;
laboratory measurements, comprising plasmatic creatinine,
arterial pH, arterial partial pressure of oxygen (PaO2), lac-
tate, difference between venous and arterial partial pressure
of carbon dioxide (pCO2 gap), transaminases, gamma-
glutamyl transferase, alkaline phosphatase, bilirubin; and
Sequential Organ Failure Assessment (SOFA) score [17].
Temperature measurements were taken for room tempera-
ture, central temperature (urinal or tympanic), and cutane-
ous temperature (measured with the DiCART™ device’s
temperature sensor). Then, CRT were measured by two
operators, both clinically and using the DiCART™ device,
with each operator blinded to their own results. To estimate
clinical CRT, the operator applied a firm pressure (charac-
terized by the observer’s tip of the nail turning white) at

the measurement site, for a duration of five seconds, which
aligns with the compression time used by the DiCART™
device. Subsequently, the CRT was assessed using a chro-
nometer. In order to be blinded to the result of the clinical
CRT, the observer performing it gave a vocal signal ('top')
at the moment of releasing the compression and another sig-
nal when he considered that the skin color had returned to its
baseline state, allowing the second observer to start and stop
the chronometer accurately. Each operator performed two
series of three consecutive clinical measurements (CRT-
CLIN) and with the DiCART™ device (CRT<sub>DiCART</sub>) on the
fingertip. Then, one operator performed a train of three mea-
surements on the knee and on the chest (Fig. 2). CRT<sub>CLIN</sub>
and CRT<sub>DiCART</sub> were carried out alternatively to enhance
the comparability between the two methods. To finish, skin
integrity was checked in the areas where the device was
applied, and discomfort as well as pain were assessed using
a numeric rating scale (range 0–10) when the patient was
able to cooperate. At day 30, the following characteristics
were collected: vital status and need for renal replacement
therapy, length of stay in intensive care unit, duration of
mechanical ventilation, and vasopressor support.

## 2.5 Endpoints

The primary endpoint was the concordance between CRT
measured clinically and using the DiCART™, assessed by
the intraclass correlation coefficient (ICC). Secondary end-
points were: the diagnostic performance of the DiCART™
in detecting a CRT>3 s established by the reference clinical
test and expressed by the area under the receiver operating
characteristic curve (ROC<sub>AUC</sub>); the inter and intra observer
reproducibility of CRT<sub>CLIN</sub> and CRT<sub>DiCART</sub> (ICC and least

<figure><img src="image_4.png" /><figcaption>**Fig. 2** Experimental design of the study. CRT: Capillary refill time, CRT<sub>CLIN</sub>: Clinical measurement of CRT, CRT<sub>DiCART</sub>: CRT measured with the DiCART™ automated device. Each measurement was per-</figcaption></figure>

formed 3 times to determine a mean CRT. Fingertip CRT assessments
were carried out alternately by observer 1 and 2 in the shortest possible
time
<table><caption>**Table 1** Patients characteristics at baseline</caption><thead><tr><th></th><th></th></tr></thead><tbody><tr><td>Median age, years [25th – 75th percentile]</td><td>64 [60, 74]</td></tr><tr><td>Sex, female, n (%)</td><td>5 (20)</td></tr><tr><td>Mean Body Mass Index, kg/m² (SD)</td><td>27.4±3.9</td></tr><tr><td>Phototype, n (%)</td><td></td></tr><tr><td>II</td><td>13 (52)</td></tr><tr><td>III</td><td>6 (24)</td></tr><tr><td>IV</td><td>6 (24)</td></tr><tr><td>Medical history, n (%)</td><td></td></tr><tr><td>Arterial hypertension</td><td>9 (36)</td></tr><tr><td>Diabetes</td><td>4 (16)</td></tr><tr><td>Ischemic cardiopathy</td><td>10 (40)</td></tr><tr><td>Chronic obstructive pulmonary disease</td><td>2 (8)</td></tr><tr><td>Peripheral arterial disease</td><td>2 (8)</td></tr><tr><td>Chronic kidney disease</td><td>3 (12)</td></tr><tr><td>Shock mechanism, n (%)</td><td></td></tr><tr><td>Cardiogenic</td><td>17 (68)</td></tr><tr><td>Septic</td><td>4 (16)</td></tr><tr><td>Hypovolemic</td><td>2 (8)</td></tr><tr><td>Non-septic vasoplegic</td><td>1 (4)</td></tr><tr><td>Mixed</td><td>1 (4)</td></tr><tr><td>Mean SOFA score±SD</td><td>8±4</td></tr><tr><td>Mechanical ventilation, n (%)</td><td>4 (16)</td></tr><tr><td>Confusion, n (%)</td><td>5 (13)</td></tr><tr><td>Median urinary output, ml/kg/h [25th – 75th percentile]</td><td>0.5 [0.3, 1.0]</td></tr><tr><td>Mean arterial pressure, mmHg±SD</td><td>73±9</td></tr><tr><td>Mean central venous pressure, mmHg±SD</td><td>11±6</td></tr><tr><td>Mean heart rate, /min±SD</td><td>94±17</td></tr><tr><td>Mean SpO2, %±SD</td><td>95±3</td></tr><tr><td>Median peripheral perfusion index, [25th – 75th percentile]</td><td>0.7 [0.2, 1.7]</td></tr><tr><td>Median mottling score, [25th – 75th percentile]</td><td>1 [1, 2]</td></tr><tr><td>Dobutamine administration, n (%)</td><td>12 (48)</td></tr><tr><td>Vasopressin administration, n (%)</td><td>2 (8)</td></tr><tr><td>Norepinephrine administration, n (%)</td><td>19 (76)</td></tr><tr><td>Median norepinephrine dosage, µg/kg/min [25th – 75th percentile]</td><td>0.13 [0.03, 0.24]</td></tr><tr><td>Median plasmatic creatinine, µmol/L [25th – 75th percentile]</td><td>124 [107, 196]</td></tr><tr><td>Mean arterial lactate, mmol/L±SD</td><td>2.4±1</td></tr><tr><td>Mean pCO2 gap, mmHg±SD</td><td>6.2±3.9</td></tr><tr><td>Mean room temperature, °C±SD</td><td>22.7±1.1</td></tr><tr><td>Mean patient central temperature, °C±SD</td><td>37.2±0.5</td></tr><tr><td>Median patient cutaneous, °C [25th – 75th percentile]</td><td>30.1 [29.2, 31.3]</td></tr></tbody></table>

SD: Standard Deviation, SOFA score: Sequential Organ Failure Assessment score, SpO2: blood oxygen saturation by pulse oximetry; pCO2 gap: difference between venous and arterial partial pressure of carbon dioxide. Patient's central temperatures were either urinary or tympanic temperature

significant change); and the clinical tolerance (skin lesions, pain, itching) of the DiCART™ device.

## 2.6 Statistical analysis

The sample size calculation was based on the primary endpoint to detect an ICC of at least 0.6 with a power of 0.9 and an alpha risk of 0.05. We calculated a sample size of 23 patients, round to 25 [18]. The variable distribution was explored with the analysis of skewness and kurtosis, and with the Shapiro-Wilk test. No imputation was used for missing data (which are reported in Additional File, Table 1), variables with more than 25% of missing values were not analyzed. As DiCART™ devices are limited to estimate CRT≤8 s, all the couple of measurements with a CRT<sub>CLIN</sub> > 8 s were excluded from the analysis. For the whole analysis, 3 measurements were averaged to define CRT<sub>CLIN</sub> and CRT<sub>DiCART</sub>. To describe the variability of the CRT<sub>CLIN</sub> and CRT<sub>DiCART</sub>, the least significant change was calculated as previously described [19]. Agreement between CRT<sub>CLIN</sub> and CRT<sub>DiCART</sub> was estimated with ICC (model: two-way random effects; type: single rater; definition: consistency) [20] and Bland and Altman approach with confidence interval (CI) estimation by the MOVER approach to take into account for multiple observations per individual [21]. Thresholds for ICC interpretation defined a priori were based on the literature [20], and we defined acceptable limits of agreement (LoA) as ±1 s as it is a threshold higher than the least significant changes previously described [22, 23] and that allows to discriminate patients with a normal from those with a high CRT. To analyze the intra and inter observer reproducibility of the two methods in the fingertip, we calculated the respective ICC between the two series of CRT measurements carried out by the same operator and between the measurements of the two operators. Receiver operating characteristic curves were constructed to evaluate the diagnostic performances of the DiCART™ device to detect an abnormal clinical CRT on the fingertip, defined as CRT>3 s. ROC<sub>AUC</sub>, sensitivity, specificity, and best threshold were determined, with 95% CI by bootstrap analysis with 2000 repetitions. Renal replacement therapy and vital status at day 30 were compared in high CRT<sub>DiCART</sub> versus low, separated by the median value on the fingertip of CRT<sub>DiCART</sub> in the present population, and compared using Fisher's exact tests. Statistical analysis was performed using R software with the packages *pROC* and *SimplyAgree*. All tests were two-sided, and a P-value<0.05 was considered statistically significant.
## 3 Results

Twenty-five patients were enrolled between April and October 2023. The study population was predominantly male (80%) and the median age was 64 [60, 74] years. The mechanism of shock was mainly cardiogenic (68%) and septic (16%). Mean SOFA score was 8±4 (Table 1). The use of DiCART™ device did not encounter any mechanical issues and all measurements could be carried out. The median overall CRT<sub>CLIN</sub> was 4.3s [2.4, 6.1]; 4.1s [1.6, 5.5] on the fingertip, 7.4s [4.2, 10.3] on the knee, and 3.9s [3.6, 4.4] on the chest. The median overall CRT<sub>DiCART</sub> was 3.8s [2.7, 4.7]; 3.3s [2.5, 4.3] on the fingertip, 5.1s [3.5, 5.6] on the knee, and 4.5s [4.3, 4.8] on the chest. Twenty-two (15%) CRT paired measurements were excluded from the analysis due to an averaged CRT<sub>CLIN</sub> > 8 s; 9 (9%) on the fingertip, 11 (44%) on the knee, and 2 (8%), on the chest. The ICC between CRT<sub>DiCART</sub> and CRT<sub>CLIN</sub> was 0.46 (95% CI 0.32, 0.59) overall, 0.5 (95% CI 0.32, 0.59) for the fingertip, 0.12 (95% CI -0.42, 0.60) for the knee, and 0.05 (95% CI -0.36, 0.45) for the chest (Table 2). Bland and Altman analysis is reported in Fig. 3; the mean bias was 0.23s (95% CI -0.17, 0.64), with upper LoA 2.77s (95% CI 2.44, 3.20) and lower LoA -2.30s (-2.73, -1.97; Table 2). LoA calculation were corrected for proportional bias (Additional File, Fig. 1). Diagnostic performance of the DiCART™ to detect a CRT>3 s had a ROC<sub>AUC</sub> of 0.79 (95% CI 0.69, 0.88), with a sensitivity of 79 (95% CI 67, 90) %, a specificity of 76% (95% CI 63, 90) %, a positive predictive value of 71% (95% CI 62, 82), and a negative predictive value of 83% (95% CI 74, 91) for a best threshold of 3.1s (95% CI 2.8, 3.3; Fig. 4). Intra observer ICC on fingertip was 0.85 (95% CI 0.74, 0.91) for CRT<sub>CLIN</sub> and 0.43 (95% CI 0.15, 0.64) for CRT<sub>DiCART</sub>. Inter observer ICC was 0.86 (95% CI 0.76, 0.92) for CRT<sub>CLIN</sub> and was 0.41 (95% CI 0.14, 0.63) for CRT<sub>DiCART</sub>. CRT measurement variability was significantly lower for CRT<sub>CLIN</sub> compared to CRT<sub>DiCART</sub>; least significant change 31% (95% CI 28, 35) versus 65% (95% CI 59, 72), p value<0.001. No skin lesion was observed at the different measurement sites. All patients reported no discomfort or pain (median numeric rating scale value 0 [0, 0]). There was no significant difference regarding the need for renal

<table><caption>**Table 2** Agreement analysis</caption><thead><tr><th></th><th></th></tr></thead><tbody><tr><td colspan="2">Intra class correlation coefficients (95% CI)</td></tr><tr><td>Overall</td><td>0.46 (0.32, 0.59)</td></tr><tr><td>Fingertip</td><td>0.50 (0.32, 0.64)</td></tr><tr><td>Knee</td><td>0.12 (-0.42, 0.60)</td></tr><tr><td>Chest Sternum</td><td>0.05 (-0.36, 0.45)</td></tr><tr><td colspan="2">All sites Bland and Altman analysis (90% CI)</td></tr><tr><td>Mean Bias, s</td><td>0.23 (-0.17, 0.64)</td></tr><tr><td>Mean Upper limit of agreement, s</td><td>2.77 (2.44, 3.20)</td></tr><tr><td>Mean Lower limit of agreement, s</td><td>-2.30 (-2.73, -1.97)</td></tr></tbody></table>

replacement and vital status at day 30 between patients with a CRT<sub>DiCART</sub> > 3.3s compared to the others (Table 3).

## 4 Discussion

The present study demonstrated a poor agreement between CRT<sub>CLIN</sub> and CRT<sub>DiCART</sub> in patients with acute circulatory failure. Furthermore, the device exhibited lower intra and interobserver reproducibility compared to the clinically measured CRT.

This study provided several insights into the current DiCART™ prototype. Firstly, the agreement between clinical CRT and CRT measured using the DiCART™ device was poor, with an ICC lower than 0.5. The Bland and Altman analysis also suggested that the DiCART™ device may not provide reliable measurements (i.e. consistent with the clinical method). The LoA were significantly greater than the a priori defined acceptable limits of -1 and +1 s, indicating a high variability in the differences between the two methods. The agreement was reasonable when the difference was within one second to distinguish a normal CRT from an abnormal one with a 3-second threshold, which is a good predictor of poor outcome in critically ill patients [24]. The present results highlighted a systematic bias, using the DiCART™ method, which tended to record greater CRT compared to the clinical method. Additionally, there was a proportional bias, with a noticeable trend toward increased differences in measurements with greater ranges. In the validation study of the first DiCART™ prototype in healthy volunteers, concordance was also reported as poor, within the same range as herein [12]. The authors identified the pressure performed on the skin by the crown of the device, which appeared to alter the capillary refill time, as a significant problem. To develop the second-generation prototype, a spring connected to a pressure sensor was added to the device, allowing the user to control the pressure performed on the skin. However, this addition did not improve the reliability of the device.

On the other hand, the previous validation study demonstrated the device's ability to diagnose tissue hypoperfusion during an upper limb arterial occlusion test, with both sensitivity and specificity exceeding 90% [12]. In the present study, these results were not confirmed in patients with acute circulatory failure. An explanation could be that a vascular occlusion test is a caricature of cutaneous ischemia whereas cutaneous microcirculatory impairment in patients with acute circulatory failure can be much more heterogeneous. While reporting significant improvements of the device, the previous bench and in silico study has shown a decrease in reliability and reproducibility when random perturbations (brightness, contrast, saturation) were applied to
<figure><img src="image_5.png" /><figcaption>**Fig. 3** Bland and Altman plot assessing the agreement between the DiCART™ device and clinical measurement for capillary refill time (all measurement sites). LoA: limit of agreement, represented with their 95% confidence interval; x: capillary refill time measured with</figcaption></figure>

clinical method; y: capillary refill time measure with DiCART™ method. Dashed lines represent the acceptable limits of agreement defined a priori in the study

videos originating from healthy volunteers, also highlight-
ing some limitations of the device’s algorithm [13].

Several studies have assessed CRT measurement devices
that used various technologies. While some of them have
yielded promising results, they have been conducted mostly
on healthy volunteers under experimental conditions, with a
particular focus on cutaneous cooling [25'27]. Shavit et al.
measured CRT using a digital camera and custom software
that compares each frame after the release of a 5-second fin-
gertip compression with the initial pre-compression frame,
calculating CRT when an exact color match is achieved
[28]. In children suffering from gastroenteritis, the use of a
digital camera with custom software to analyze cutaneous
recoloration had shown excellent diagnostic performance to

detect significant dehydration (AUC 0.99) as well as high
intra observer reliability (ICC 0.99), but the application
of the compression in the skin was not controlled by the
device, potentially leading to variability. The Digital Cap-
illary Refill (DCR) device, developed by ProMedix Inc.
(Portland, OR, USA) is a compact handled prototype that
consists in a finger sensor applied on the fingertip. The CRT
is measured using light reflectance technology following
manual compression. Correlation coefficient range between
the device estimated CRT and the clinically measured CRT
ranged from 0.69 to 0.91 [29, 30], and a prolonged CRT
estimated by the device was associated with the diagnosis
of sepsis [31]. However, these studies were not designed to
<figure><img src="image_6.png" /><figcaption>**Fig. 4** Receiver operating characteristic curve of the DiCART™ diagnostic performance to detect a capillary refill time higher than 3 s. ROC-AUC: area under the receiver characteristic curve, with its 95% confidence interval</figcaption></figure>

<table><caption>**Table 3** 30-day outcomes based on high or low value of capillary refill time measured with the DiCART™ device</caption><thead><tr><th>Variables</th><th>DiCART<sub>LOW</sub><br>(n=12)</th><th>DiCART<sub>HIGH</sub><br>(n=13)</th><th>p<br>value</th></tr></thead><tbody><tr><td>RRT status, n (%)</td><td></td><td></td><td></td></tr><tr><td>No</td><td>10 (83.3)</td><td>10 (76.9)</td><td></td></tr><tr><td>Current</td><td>1 (8.3)</td><td>0 (0)</td><td>0.375</td></tr><tr><td>Withdrawal</td><td>1 (8.3)</td><td>3 (23.1)</td><td></td></tr><tr><td>Vital status, n (%)</td><td></td><td></td><td></td></tr><tr><td>Deceased</td><td>3 (25.0)</td><td>3 (23.1)</td><td>1.000</td></tr><tr><td>Alive</td><td>9 (75.0)</td><td>10 (76.9)</td><td></td></tr></tbody></table>

RRT: Renal Replacement Therapy, No: RRT was not needed, Current: RRT is ongoing, Withdrawal: RRT is weaned off

Capillary refill time values used for the analysis were the average of the means of the two observers' first measurement series on finger tip. DiCART<sub>LOW</sub>: Means of capillary refill time measured with the DiCART™ device < 3.3 s. DiCART<sub>HIGH</sub>: Means of capillary refill time measured with the DiCART™ device > 3.3 s

evaluate the agreement of the methods nor the diagnostic performance of the device.

One of the difficulties in studying CRT is the absence of a well-defined gold standard method for its measurement. Numerous techniques to clinically measure CRT were described in the literature [32]. Measuring CRT after a 5-second compression using a stopwatch and averaging the results of three measurements allowed to achieve herein good inter and intra observer agreement. Similar concordance results have already been published, such as in

patients with septic shock for whom a similar inter observer agreement was already observed using a 15-second time of compression on the fingertip, averaged over two measurements [33, 34]. Conversely, using a single, non-timed measurement, performed by a heterogeneous population of investigators comprising nurses, medical students, residents, and senior physicians led to only a moderate inter observer agreement [7].

The present study has however limitations. The generalizability is limited by the single-center design the small sample size of the study that included a high proportion of patients who experienced cardiogenic shock. One can argue that assessing a new version of the DiCART™ was premature despite the encouraging preliminary results; the modifications performed on the device were likely insufficient, focusing more on the structure. Another issue inherent to the metric assessed (CRT) is the difficulties to determine a reference method. However, the method used herein for CRT<sub>CLIN</sub> was supported by a recent meta-analysis [11], and the variability of the measure estimated by the least significant change is similar to previous studies [22, 23]. By analogy with the vascular occlusion test, the repetition of CRT assessment in the present study may have introduced a systematic bias in CRT estimation. A recent study showing that the interval between different CRT assessments does not affect the CRT value does not support this assumption [35]. However, randomization of the starting technique in the protocol would have further mitigated this potential bias.

Although the results provided by the DiCART™ were not sufficient, the study has been conducted with: (1) a strict experimental protocol with repeated measurements on various sites and blinding of the observers; (2) a strict statistical analysis to assess the agreement according to the suggestions of a dedicated recent review [36]; and (3) in a population in whom CRT assessment could be challenging but useful as a monitoring tool to guide resuscitation strategies [37] or to help to assess prognosis [38].

## 5 Conclusion

The DiCART™ device showed poor agreement with clinical CRT in patients with acute circulatory failure, which does not support its use in routine practice.

**Supplementary Information** The online version contains supplementary material available at https://doi.org/10.1007/s10877-0-25-01271-5.

**Acknowledgements** Not applicable.

**Author contributions** Study concept and design: MJL, MR Acquisition and interpretation of data: AD, MJL, MR Interpretation of data: AD, MJL, MR, JLF, TADrafting of manuscript: AD, MJL, MR Statistical
analysis: MRStudy supervision: MJLCritical revision of the manu-
script for important intellectual content: AD, MJL, MR, JLF, TA.All
authors read and approved the final manuscript and agreed to be ac-
countable for all aspects of the work. All authors ensured that ques-
tions related to the accuracy or integrity of any part of the work are
appropriately investigated and resolved.

**Funding** Open access funding provided by Hospices Civils de Lyon.
The clinical investigation was funded by the DicarTech Company.

**Data availability** Data is available from the corresponding author upon
reasonable request.

Declarations

**Ethical approval and consent to participate** The study protocol was registered in Clinicaltrials.gov (NCT05847998). The institutional review board, *Comité de protection des personnes Sud-Méditerranée I* (IRB: N° ID-RCB 2021-A02595-36) approved the study protocol. In agreement with the French law n° 2012-300 of March 5, 2012, informed consent of the patients (or their support person when the patient could not be informed) was systematically obtained before the inclusion.

**Consent for publication** Not applicable.

**Take home message** DiCART™ is a full automatized handled device to assess capillary refill time. Its agreement with clinical evaluation of capillary refill time is poor. Its reproducibility is lower than clinical evaluation of capillary refill time.

**Competing interests** MJL is cofounder and shareholder of the Di-CARTECH company that has been created to build and sell a device that measures capillary refill time. AD, TA, JF, MR have no conflicts of interest related to the study to declare.

**Open Access** This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if changes were made. The images or other third party material in this article are included in the article's Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is not included in the article's Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this licence, visit http://creativecommons.org/licenses/by/4.0/.

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