Mesquida et al. Ann. Intensive Care (2020) 10:54 https://doi.org/10.1186/s13613-020-00670-y RESEARCH Open Access Thenar oxygen saturation ­(StO2) alterations during a spontaneous breathing trial predict extubation failure Jaume Mesquida1,2* , Guillem Gruartmoner1,2, Cristina Espinal1, Jordi Masip1, Caroline Sabatier1,3, Ana Villagrá1,4, Hernando Gómez5,6, Michael Pinsky5, Francisco Baigorri1 and Antonio Artigas1,2,7 Abstract Background: Weaning from mechanical ventilation (MV) is a cardiovascular stress test. Monitoring the regional oxy- genation status has shown promising results in predicting the tolerance to spontaneously breathe in the process of weaning from MV. Our aim was to determine whether changes in skeletal muscle oxygen saturation (­ StO2) measured by near-infrared spectroscopy (NIRS) on the thenar eminence during a vascular occlusion test (VOT) can be used to predict extubation failure from mechanical ventilation. Methods: We prospectively studied 206 adult patients with acute respiratory failure receiving MV for at least 48 h from a 30-bed mixed ICU, who were deemed ready to wean by their physicians. Patients underwent a 30-min spon- taneous breathing trial (SBT), and were extubated according to the local protocol. Continuous S­ tO2 was measured non-invasively on the thenar eminence. A VOT was performed prior to and at 30 min of the SBT (­ SBT30). The rate of ­StO2 deoxygenation (­ DeO2), ­StO2 reoxygenation ­(ReO2) rate and ­StO2 hyperemic response to ischemia (HAUC​) were calculated. Results: Thirty-six of the 206 patients (17%) failed their SBT. The remainder 170 patients (83%) were extubated. Twenty-three of these patients (13.5%) needed reinstitution of MV within 24 h. Reintubated patients displayed a lower HAUC​ at baseline, and higher relative changes in their ­StO2 deoxygenation rate between baseline and ­SBT30 ­(DeO2 Ratio). A logistic regression-derived ­StO2 score, combining baseline ­StO2, HAUC​ and D ­ eO2 ratio, showed an AUC of 0.84 (95% CI 0.74–0.91) for prediction of extubation failure. Conclusions: Extubation failure was associated to baseline and dynamic ­StO2 alterations during the SBT. Monitoring ­StO2-derived parameters might be useful in predicting extubation outcome. Keywords: Near-infrared spectroscopy, Tissue oxygenation, Microcirculation, Regional blood flow, Mechanical ventilation, Weaning Background extubation occurs in up to 20% [1–5]. Importantly, failed Weaning from ventilatory support is a challenge for criti- extubation is associated with increased hospital mor- cal care clinicians. Even in those patients who succeed tality, prolonged ICU and hospital stays, and increased a spontaneous breathing trial (SBT), failure of planned need for tracheostomy [6, 7]. Despite many respiratory and hemodynamic variables for predicting weaning suc- cess have been evaluated, few parameters have substan- *Correspondence: jmesquida@tauli.cat 1 tial predictive power [7, 8], and new predictive tools are Critical Care Department, Parc Taulí Hospital Universitari. Institut d’Investigació i Innovació Parc Taulí (I3PT), Parc Taulí, 1, 08208 Sabadell, needed. Spain The SBT is a cardiovascular stress test, and failure to Full list of author information is available at the end of the article wean from mechanical ventilation (MV) often reflects © The Author(s) 2020. 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://creat​iveco​ mmons​.org/licen​ses/by/4.0/. Mesquida et al. Ann. Intensive Care (2020) 10:54 Page 2 of 7 cardiovascular insufficiency to cope with the increased criteria were considered ready to wean, and were eligible oxygen cost of breathing [9, 10]. Since the augmented for a subsequent spontaneous breathing trial. oxygen cost of breathing is met by increases in respira- Exclusion criteria included trauma in both upper limbs, tory muscle blood flow, diversion of flow away from and hematoma or skin lesions at the thenar eminence that “non-vital” tissues might occur, potentially causing could hinder placement of NIRS sensor probe. Patients hypoperfusion in areas such as the splanchnic and the with altered level of consciousness that could lead to cen- peripheral circulation [11–15]. In fact, alterations in tral hypoventilation and/or impaired secretions’ man- splanchnic and peripheral circulation, assessed by dif- agement were excluded. Patients in whom their medical ferent technologies, have been associated with failure team decided to indicate preventive non-invasive ventila- to tolerate an SBT [12–16]. In a preliminary study, our tion following extubation were also excluded. group demonstrated that changes in skeletal muscle oxy- genation ­(StO2) measured non-invasively on the thenar Study protocol eminence by near-infrared spectroscopy (NIRS) were After inclusion, patients underwent a spontaneous associated with the outcome of a 30-min SBT [16]. breathing trial (SBT) for 30 min, defined as assisted spon- In the present study, we hypothesized that regional taneous breathing with continuous positive airway pres- oxygenation alterations within the SBT would be associ- sure (CPAP) of 5 cm ­H2O, or a T-tube trial, as prescribed ated with extubation failure after a clinically successful by their medical team. Patients were in a semi-recumbent SBT. position, and ­FiO2 was kept constant during the trial. The evaluation criteria for SBT failure was defined as the presence of one or more of the following criteria Methods during the trial: respiratory rate (RR) > 35 breaths/min Setting for 5 min or longer; arterial pulse oximetry saturation This prospective observational study was conducted in ­(SpO2) < 90%, heart rate (HR) > 140 beats/min or sus- a 30-bed medical-surgical intensive care unit at a uni- tained increase or decrease in HR > 20%; systolic blood versity hospital. The local Ethics Committee (CEIC pressure > 180 mmHg or < 90 mmHg; increased anxiety 2008/554) approved the study. Informed consent was and diaphoresis. Decision to remove the endotracheal obtained from the patient or their next of kin prior to the tube was made independently of the study investigators study initiation. This study is presented according to the by the attending physicians, who did not have access to STROBE recommendations for reporting observational the ­StO2 data. Weaning success was defined as patient studies [17]. remaining free of MV for > 24 h after passing the SBT. Extubation failure was defined as the need for reinstitu- Patients and data collection tion of MV, either invasive or non-invasive, within 24 h We included adult patients (≥ 18-year old) receiving following extubation. invasive mechanical ventilatory support for > 48 h and considered ready to wean by their physicians, accord- Clinical parameters and outcomes ing to the local protocol, and who never experienced We collected demographic data: age, sex, diagnosis, and any previous attempt of separation from MV. Eligibility days on mechanical ventilation. Hemodynamic, respira- to perform a weaning trial included partial or complete tory and oxygenation variables were monitored continu- recovery from the underlying cause of acute respiratory ously and recorded just before starting and at 30 min failure; adequate gas exchange, as indicated by a partial into the SBT. HR and mean arterial pressure (MAP) were pressure of arterial oxygen (­PaO2) > 60 mmHg to a frac- recorded by routine bedside monitoring (Monitor Intel- tion of inspired oxygen (­FiO2) < 0.4, with a positive end- livue MP 70; Phillips Medizinsystems, Boeblingen, Ger- expiratory pressure (PEEP) < 5 c­ mH2O; adequate cough, many). RR, tidal volume (Vt), minute ventilation (VE), with absence of excessive tracheobronchial secretion; ­FiO2 and ­SpO2 were recorded at start and 30 min into the core temperature < 38 °C; hemoglobin > 8 g/dL; stable car- SBT. Arterial and/or central venous blood gas analyses diovascular status (heart rate < 120 beats m­ in−1, systolic were made when an arterial line and/or a central venous blood pressure 90–160 mmHg), with no need for vasoac- line was in place, respectively (ABL 700 series; Radiom- tive agents; adequate level of consciousness (awake, alert eter Medical, Copenhagen, Denmark). and aware of their surroundings), with no further need The primary outcome of interest was extubation failure. for sedative agents. Patients were also tested for adequate pulmonary function, defined as a rapid shallow breathing NIRS measurements index < 100 breaths ­min−1 ­L−1, and a maximal inspiratory Tissue oxygen saturation (­StO2) was recorded con- pressure (MIP) < − 20 ­cmH2O. Patients meeting these tinuously using the InSpectra 650 Tissue Spectrometer Mesquida et al. Ann. Intensive Care (2020) 10:54 Page 3 of 7 (Hutchinson Tech., Hutchinson, Minnessotta). This tech- slope)−1/[(THIstart + THIend)/2]. Relative changes in nology uses a wide gap 40-nm second derivative spec- ­StO2-derived parameters were calculated as the quo- troscopic method, with measurements at four different tient between values at minute 30 and baseline ­(DeO2 wavelengths (680, 720, 760 and 800 nm), and has been ratio, ­nirVO2 ratio and ­ReO2 ratio). Absolute S ­ tO2- and tra Research ­Software® v4.01 (Hutchinson Technology). previously validated for estimating local hemoglobin VOT-derived variables were obtained using the InSpec- oxygen saturation in tissues [18]. The S ­ tO2 15-mm opti- cal surface probe was placed on intact skin on the the- Two researchers (JM and JM) separately analyzed all the nar eminence never placed adjacent to the site of radial registers, and a database was constructed. When discrep- artery cannulation. The InSpectra tissue spectrometer ancies were observed, the two researchers performed a also measures relative hemoglobin concentration, pre- third joint analysis. sented as the tissue hemoglobin index (THI). Vascular Occlusion Test (VOT) The VOT was per- Sample size calculation formed as previously described [19, 20]. A blood pres- Accepting an alpha risk of 0.05 and a beta risk of 0.20 in a sure cuff (Portable Tourniquet System; Delfi Medical, two-sided test, estimating an SBT failure rate of 20%, and Vancouver) was placed on the forearm, rapidly inflated an extubation failure rate of 15%, we calculated that 200 40 mmHg above systolic pressure, and kept inflated patients were necessary to detect a positive likelihood until ­StO2 decreased to 40%. Then, the cuff was rapidly ratio (LR +) of the test equal to or greater than 5. deflated. The resulting deoxygenation ­(DeO2) and reoxy- genation ­(ReO2) slopes are reported as change in satu- Statistical analysis ration over time (Fig. 1). Hyperemic response following Statistical analysis was performed by means of IBM SPSS the reoxygenation is reported as an area under the curve statistics 20.0 software (IBM Corporation). Normal dis- (HAUC​). We performed a VOT at the beginning of the tribution of the studied variables was confirmed using SBT and again at 30 min into the SBT. NIRS-derived the Kolmogorov–Smirnov test. Accordingly, continu- thenar muscle oxygen consumption ­(nirVO2) was cal- ous variables were expressed as mean ± standard devia- culated as described by Skarda [21]: ­nirVO2 = (DeO2 tion (SD), and categorical variables were expressed as absolute number and proportions (%). Chi square and Student’s t test were used to compare extubation success and failure groups. Student’s t test for paired measure- ments was used to analyze changes over time. Bivariate logistic regression analysis was used to obtain independ- ent predictors of extubation success, and logistic regres- sion models were used to create a predictive ­StO2-score. Statistical significance was defined as p < 0.05 (two-tailed test). Results Two hundred-and-six patients were studied. Thirty-six patients (17.5%) failed the SBT, and were excluded of the final analysis. One hundred-and-seventy patients passed the SBT and were extubated. Twenty-three (13.5%) of these patients failed extubation and required re-instaura- tion of MV within 24 h. The suspected etiology of extu- bation failure was mainly increased respiratory muscle load (52%), and cardiac failure (35%) (Additional file 1: Table S1). No baseline differences in demographic, hemo- dynamic, and respiratory variables were observed when comparing extubation success and extubation failure groups (Table 1). Hemodynamic and respiratory changes Fig. 1 StO2 response to the Vascular Occlusion Test (VOT). The response to transient ischemia generates three main parameters in within the SBT were similar in both groups (Table 1). the continuous ­StO2 recording: the S­ tO2 deoxygenation rate ­(DeO2), the ­StO2 reoxygenation rate ­(ReO2), and the hyperemic response StO2 variables to ischemia, which is computed as the area under the curve of the Baseline ­ReO2 and HAUC​ values were significantly lower hyperemic response (HAUC​) as referred to steady-state ­StO2 in the extubation failure group (Table 1). The weaning Mesquida et al. Ann. Intensive Care (2020) 10:54 Page 4 of 7 Table 1 Characteristics of the patients who succeed the spontaneous breathing trial (SBT) Extubation success (n = 147) Extubation failure (n = 23) Age (years) 66 ± 14 67 ± 12 Days on MV (n) 7±5 8±6 Pre-existent comorbidities (%) Diabetes mellitus 33 35 Hypertension 57 48 Cardiac disease 23 22 COPD 16 30 Etiology of acute respiratory failure (%) Septic shock 29 26 Heart failure 17 26 Respiratory 20 26 Trauma 6 0 Other 29 22 Baseline Minute 30 Baseline Minute 30 † HR (beats/min) 88 ± 16 91 ± 16 83 ± 17 87 ± 18† † MAP (mmHg) 82 ± 13 85 ± 15 79 ± 14 80 ± 12 RR (resp/min) 19 ± 4 23 ± 5† 18 ± 3 23 ± 4† † Vt (mL) 454 ± 96 430 ± 123 438 ± 115 367 ± 132† † pH 7.46 ± 0.05 7.44 ± 0.06 7.47 ± 0.04 7.44 ± 0.04† † pCO2 (mmHg) 37 ± 6 38 ± 6 41 ± 9 42 ± 14 † Hb (g/dL) 9.9 ± 1.8 9.9 ± 1.8 10.1 ± 2 10.3 ± 2.1 SaO2 (%) 96 ± 8 97 ± 3 97 ± 3 96 ± 3 ScvO2 (%) 66 ± 9 66 ± 8 62 ± 9 61 ± 5* StO2 (%) 80 ± 6 80 ± 7 76 ± 11 77 ± 9 DeO2 (%/min) − 13.1 ± 8.4 − 13.6 ± 10.7 − 12.7 ± 7 − 17.2 ± 10.3† nirVO2 (U) 139 ± 80 159 ± 135† 129 ± 75 174 ± 97† THI (U) 10.7 ± 2.9 11.3 ± 3.1† 10.0 ± 3.9 10.5 ± 4.0 ReO2 (%/s) 4.1 ± 1.6 4.2 ± 1.8† 3.3 ± 1.9* 3.7 ± 2.0 Hyperemia AUC (U) 12.2 ± 6.5 12.9 ± 5.7 7.1 ± 4.7** 8.4 ± 4.1** DeO2 ratio 1.1 ± 0.3 1.5 ± 0.6** nirVO2 ratio 1.1 ± 0.4 1.5 ± 0.5* MV Mechanical ventilation, COPD Chronic obstructive pulmonary disease, HR heart rate, MAP mean arterial pressure, RR respiratory rate, Vt tidal volume, pCO2 arterial partial pressure of carbon dioxide, Hb Hemoglobin, SaO2 arterial oxygen saturation, ScvO2 central venous oxygen saturation, StO2 tissue oxygen saturation, DeO2 ­StO2 deoxygenation rate, nirVO2 NIRS-derived local oxygen consumption, THI tissue hemoglobin index, ReO2 ­StO2 reoxygenation rate * p < 0.05; and ** p < 0.01, as compared to success group at the same time point; †p < 0.05, as compared to baseline values within the group success group showed no significant changes in S ­ tO2, Extubation failure prediction ­DeO2, and HAUC​ after 30 min of SBT, while ­nirVO2 Univariate analysis showed that S ­ tO2, ­ReO2, and HAUC​ at and THI significantly increased. The extubation fail- baseline, ­StO2 and HAUC​ after 30 min of the SBT, ­DeO2 ure group showed a significant decrease in their D ­ eO2 ratio, and ­nirVO2 ratio were associated with extubation slope, as well as an increase in n ­ irVO2 after 30 min of failure. In a multivariate analysis, only baseline ­ StO2, SBT, while no changes in ­StO2, HAUC​ and THI were baseline HAUC​ and ­ DeO2 ratio persisted significantly observed. The D ­ eO2 ratio (represented as the ratio of associated with extubation failure (Table 2). ­DeO2 at 30 min to baseline D ­ eO2) was significantly The AUC for predicting extubation failure for base- higher in the failure group (1.5 ± 0.6 vs. 1.1 ± 0.3 in line ­StO2, baseline HAUC​, and ­DeO2 ratio are displayed the success group, p < 0.01). The n­ irVO2 ratio was also in Table 3. A logistic regression-derived S ­tO2 score, higher in the failure group (1.5 ± 0.5 vs. 1.1 ± 0.4 in the combining baseline ­StO2, baseline HAUC​ and ­DeO2 ratio, success group, p < 0.05). proved an AUC of 0.84 (95% CI 0.74–0.93, p < 0.001) for prediction of extubation failure. An S ­ tO2 score cut-off Mesquida et al. Ann. Intensive Care (2020) 10:54 Page 5 of 7 Table 2 Multivariate regression analysis monitoring in the weaning process might help prevent B ß p (95% CI) failed extubations, and therefore, the potential negative consequences on the outcome of critically ill patients. Baseline ­StO2 − 0.075 0.93 0.03 0.87–0.99 Transitioning from positive pressure ventilation to Baseline hyperemic AUC​ − 0.192 0.83 0.001 0.74–0.92 spontaneous ventilation determines an increase in the DeO2 ratio 2.849 17.3 < 0.001 4.1–72.8 work of breathing, and thus, an increase in the oxygen demand of the respiratory muscles. Such increase in the metabolic demand causes a sympathetic activation, in an Table 3 Prediction of extubation failure attempt to optimize cardiac output delivery to the meta- bolically active tissues [24], and to increase vasomotor AUC​ p (95% CI) tone, redistributing blood flow away from the periphery StO2 at baseline 0.57 ns 0.43–0.72 toward the respiratory muscles [10, 25]. The ability of the DeO2 ratio 0.72 < 0.01 0.58–0.85 cardiovascular system to meet this increased demand nirVO2 ratio 0.69 0.02 0.56–0.81 might be closely related to the ability of the patient to Hyperemia AUC​0 0.73 0.01 0.58–0.88 tolerate spontaneously breathing. Therefore, when the Hyperemia AUC​30 0.74 < 0.01 0.62–0.87 cardiovascular performance is limited, and/or the cost of StO2 score 0.84 < 0.001 0.74–0.93 breathing excessive, extubation failure will be more likely ScvO2 at min 30 0.72 0.04 0.58–0.85 to occur. In these situations, the increase in sympathetic % change in S­ cvO2 0.59 ns tone might be more accentuated, as the cardiovascular system continues to attempt to match cardiac output to DeO2 ratio quotient between ­StO2-deoxygenation rate at the end of SBT and at baseline, nirVO2 ratio quotient between NIRS-derived local oxygen consumption an increasing metabolic demand. Indeed, clinical crite- at the end of SBT and at baseline, HAUC​ area under the curve of the hyperemic ria for determining the success of the SBT are essential response, StO2 tissue oxygen saturation, ScvO2 central venous oxygen saturation, % change in S­ cvO2 refers to the % change in S­ cvO2 at min 30 of the SBT as symptoms of excessive sympathetic activity (i.e., tachy- compared to baseline ­ScvO2 cardia, hypertension, agitation). A subclinical manifesta- tion of the sympathetic activation would be the degree of peripheral vasoconstriction and/or the increase in the value of − 1.23 showed an LR + of 7 for predicting extu- metabolic rate, and this is the basis for regional oxygena- bation failure (Additional file 2: Figure S1). tion measurements with NIRS. Discussion Increased local oxygen extraction rate Our study demonstrates that alterations in S ­ tO2-derived Our data confirmed that relative increases in ­DeO2 dur- parameters were predictive of extubation failure after a ing a 30-min SBT are associated with extubation failure, clinically successful SBT. independent of other respiratory and hemodynamic To our knowledge, this is the first study showing that parameters. The observed increases in D ­ eO2 within the regional oxygenation parameters are associated with SBT might be explained by two different, but potentially extubation outcome. The peripheral circulation has been concurrent, pathophysiological mechanisms: (1) local previously studied in the setting of a cardiovascular stress supply–demand dependency in low or inadequate blood test such as the SBT. Several studies showed that changes flow states, such as blood flow diversion from the periph- in gastric mucosal pH within the SBT were predictive of ery; and (2) increase in local metabolic rate. the clinical outcome of such SBT [12–15]. Similar results The increase in oxygen demand of the respiratory mus- were obtained when assessing the peripheral circulation cles during an SBT may lead to blood flow redistribu- by means of NIRS, non-invasively monitoring oxygena- tion via activation of the sympathetic–adrenal system. tion of the skeletal muscle within the SBT [16, 22, 23]. When accentuated, this compensatory mechanism might However, they were all small studies, and never explored cause a stealing effect from the periphery [10]. Accord- the ability to predict the outcome of the overall weaning ingly, one would expect decreases in blood content of process. In this prospective study, we analyzed the util- the sensed area [19, 26], along with relative increases in ity of S­tO2-derived parameters in the extubation pro- the ­DeO2 rate (either due to the decreased Hb content or cess, after a clinically successful SBT. Our results add to the sympathetically driven increase in the metabolic new evidence on the usefulness of regional non-invasive rate). In our population, extubation failure was associ- parameters as a complimentary tool in monitoring the ated with significant increases in ­DeO2, but no change cardiovascular performance of critically ill patients. in THI. Conversely, the success group showed no change Indeed, our data suggest that the inclusion of ­ StO2 in ­DeO2, with significant increases in THI. Such obser- vations suggest that cardiac output increased in those Mesquida et al. Ann. Intensive Care (2020) 10:54 Page 6 of 7 patients who succeeded the weaning process. In those patients should behave similarly, weaning approaches patients who failed, since we did not measure stroke vol- may vary across centers affecting the predictive value of ume, the interpretation of the lack of changes in THI is these ­StO2-derived parameters. Thus, this study needs more complex. In a model of simulated hypovolemia, to be duplicated across other centers. Second, we did Bartels et al. reported that THI measured on the thenar not determine the cause of weaning failure in patients eminence detected slight decreases in stroke volume, but who were considered to fail. We merely identified that changes were minimal, as compared to measurements they did fail. We can expect different behaviors of S ­ tO2 on the forearm [26]. Therefore, we cannot exclude some parameters in patients who fail because of limited car- degree of stealing effect as results of a limited sensitivity diovascular reserve from patients who fail because of of the technology. Finally, a balanced effect of increased upper airway obstruction and/or impaired secretions’ cardiac output and peripheral vasoconstriction, resulting management. This issue must be taken into account in in no changes in THI, cannot be excluded. future studies. Finally, we studied a heterogeneous ICU NirVO2, an estimation of local oxygen consumption population. Since the observed predictive value of S­ tO2 [20, 21], increased in both groups during the SBT, but might vary across populations, further studies includ- the magnitude of this increase was significantly higher in ing selected homogeneous critically ill patients are the extubation failure group. ­NirVO2 differences might required. reflect dissimilar degrees in sympathetic activation in the setting of inadequate cardiovascular response. This hypothesis is supported by studies that showed signifi- Conclusions cant increases in plasma catecholamines during the SBT, In a mixed ICU population, non-invasive ­StO2-derived especially in patients who failed an SBT [27, 28]. Overall, parameters at baseline, and within a 30-min SBT, our data suggest that the increase in D­ eO2 in the extuba- were predictive of extubation outcome. Therefore, tion failure group might be mainly related to an increase ­StO2-derived parameters may be used as indicators in local oxygen consumption, although some degree of of global ­ VO2/DO2 balance when facing a cardiovas- blood flow diversion cannot be ruled out. cular stress test, such as liberation from mechanical ventilation. Local hyperemic response after transient ischemia We also observed that baseline endothelial perfor- Supplementary information mance, as measured by the S ­ tO2 hyperemic response, Supplementary information accompanies this paper at https​://doi. org/10.1186/s1361​3-020-00670​-y. was independently associated with extubation outcome. Our findings on the predictive value of the ­StO2 hyper- Additional file 1: Table S1. Suspected etiology of extubation failure. emic response are not surprising. Activation of the sym- pathetic nervous system is a major component of the Additional file 2: Figure S1. ­StO2-derived score according to extubation outcome. The cut-off value of − 1.23 is also represented. neurohumoral response to the increased oxygen cost of breathing. Catecholamine release mediates vasoconstric- Abbreviations tion of peripheral vascular beds, and also, via ß-adreno- DeO2: VOT-derived ­StO2 deoxygenation rate; FiO2: Fraction of inspired oxygen; ceptors, promotes vasodilation of the coronary arteries, HAUC​: StO2 hyperemic response; HR: Heart rate; MAP: Mean arterial pres- and improves contractility. The functional impairment of sure; MV: Mechanical ventilation; NIRS: Near-infrared spectroscopy; nirVO2: NIRS-derived thenar muscle oxygen consumption; PaCO2: Arterial carbon the endothelium has been associated not only with poor dioxide tension; PEEP: Positive end-expiratory pressure; ReO2: VOT-derived peripheral response, but also with diminished ß-adreno- ­StO2 reoxygenation rate; RR: Respiratory rate; SBT: Spontaneous breathing ceptor sensitivity, limiting the cardiac response [29]. trial; SaO2: Arterial oxygen saturation; ScvO2: Central venous oxygen saturation; SpO2: Pulse-oxymetry saturation; StO2: Tissue oxygen saturation; THI: Tissue Therefore, endothelial dysfunction might be a poten- hemoglobin index; VO2: Global oxygen consumption; VOT: Vascular occlusion tial marker of the ability of the patient to respond to the test; Vt: Tidal volume. hemodynamic changes produced by the discontinuation of ventilatory support. According to our observations, Acknowledgements we might hypothesize that vascular endothelial integrity, The authors thank David Suarez for his statistical assistance. We also thank evaluated in peripheral skeletal muscle, might be relevant all the Critical Care Department staff of the Parc Taulí Hospital Universitari for their enthusiasm and teamwork. when facing a cardiovascular stress test such as transi- tioning from MV to spontaneously breathing. Authors’ contributions JM, GG, AV, HG, MP, FB and AA were involved in the conception and the design of the study. JM, GG, CE, JM and CS collected the data. JM and JM analyzed the Study limitations ­StO2 records. JM performed the statistical analysis. JM, GG, AV, HG, MP, FB and Our study has relevant limitations. First, it was car- AA discussed the results. All authors reviewed the manuscript and agreed with ried out in a single center. Albeit we expect that similar its final version. All authors read and approved the final manuscript. Mesquida et al. Ann. Intensive Care (2020) 10:54 Page 7 of 7 Funding 12. Mohsenifar Z, Hay A, Hay J, Lewis MI, Koerner SK. Gastric intramural pH The present study was supported by a Grant from the European Society of as a predictor of success or failure in weaning patients from mechanical Intensive Care Medicine (ECCRN Clinical Research Award 2009), and a Grant ventilation. Ann Intern Med. 1993;119(8):794–8. from the Instituto de Salud Carlos III (FIS PS PI09/01000). 13. Bouachour G, Guiraud MP, Gouello JP, Roy PM, Alquier P. Gastric intramu- cosal pH: an indicator of weaning outcome from mechanical ventilation Availability of data and materials in COPD patients. Eur Respir J. 1996;9(9):1868–73. The datasets used and/or analyzed during the current study are available from 14. Hurtado FJ, Berón M, Olivera W, Garrido R, Silva J, Caragna E, et al. Gastric the corresponding author on reasonable demand. intramucosal pH and intraluminal ­PCO2 during weaning from mechanical ventilation. Crit Care Med. 2001;29(1):70–6. Ethics approval and consent to participate 15. Bocquillon N, Mathieu D, Neviere R, Lefebvre N, Marechal X, Wattel F. The local Ethics Committee (CEIC 2008/554) approved the study. Informed Gastric mucosal pH and blood flow during weaning from mechanical consent was obtained from the patient or their next of kin prior to the study ventilation in patients with Chronic Obstructive Pulmonary Disease. Am J initiation. Respir Crit Care Med. 1999;160:1555–61. 16. Gruartmoner G, Mesquida J, Masip J, Martinez ML, Villagra A, Baigorri F, Consent for publication et al. Thenar oxygen saturation ­(StO2) during weaning from mechanical Not applicable. ventilation: an observational study. Eur Respir J. 2014;43:213–20. 17. von Elm E, Altman DG, Egger M, Pocock SJ, Gøtzsche PC, Vandenbroucke Competing interests JP. STROBE Initiative. The strengthening the reporting of observational The authors declare that they have no conflict of interest. studies in epidemiology (STROBE) statement: guidelines for reporting observational studies. Int J Surg. 2014;12(12):1495–9. Author details 18. Myers DE, Anderson LD, Seifert RP, Ortner JP, Cooper CE, Beilman GJ, 1 Critical Care Department, Parc Taulí Hospital Universitari. Institut Mowlem JD. Noninvasive method for measuring local hemoglobin oxy- d’Investigació i Innovació Parc Taulí (I3PT), Parc Taulí, 1, 08208 Sabadell, Spain. gen saturation in tissue using wide gap second derivative near-infrared 2 Departament de Medicina, Universitat Autònoma de Barcelona, Bellaterra, spectroscopy. J Biomed Opt. 2005;10(3):034017. Spain. 3 Réanimation Polyvalente, Centre Hospitalier de Pau, Pau, France. 19. Gómez H, Torres A, Polanco P, Kim HK, Zenker S, Puyana JC, et al. 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