European Journal of Trauma and Emergency Surgery https://doi.org/10.1007/s00068-022-02068-w ORIGINAL ARTICLE Alterations in tissue oxygen saturation measured by near‑infrared spectroscopy in trauma patients after initial resuscitation are associated with occult shock Andrea Campos‑Serra1 · Jaume Mesquida2 · Sandra Montmany‑Vioque1 · Pere Rebasa‑Cladera1 · Marta Barquero‑Lopez3 · Ariadna Cidoncha‑Secilla1 · Núria Llorach‑Perucho1 · Marc Morales‑Codina4 · Juan Carlos Puyana5 · Salvador Navarro‑Soto1 Received: 3 April 2022 / Accepted: 16 July 2022 © The Author(s) 2022 Abstract Purpose Persistent occult hypoperfusion after initial resuscitation is strongly associated with increased morbidity and mor- tality after severe trauma. The objective of this study was to analyze regional tissue oxygenation, along with other global markers, as potential detectors of occult shock in otherwise hemodynamically stable trauma patients. Methods Trauma patients undergoing active resuscitation were evaluated 8 h after hospital admission with the measure- ment of several global and local hemodynamic/metabolic parameters. Apparently hemodynamically stable (AHD) patients, defined as having SBP ≥ 90 mmHg, HR < 100 bpm and no vasopressor support, were followed for 48 h, and finally classified according to the need for further treatment for persistent bleeding (defined as requiring additional red blood cell transfusion), initiation of vasopressors and/or bleeding control with surgery and/or angioembolization. Patients were labeled as “Occult shock” (OS) if they required any intervention or “Truly hemodynamically stable” (THD) if they did not. Regional tissue oxygenation ­(rSO2) was measured non-invasively by near-infrared spectroscopy (NIRS) on the forearm. A vascular occlu- sion test was performed, allowing a 3-min deoxygenation period and a reoxygenation period following occlusion release. Minimal ­rSO2 ­(rSO2min), Delta-down (­ rSO2–rSO2min), maximal r­ SO2 following cuff-release (­ rSO2max), and Delta-up ­(rSO2max–rSO2min) were computed. The NIRS response to the occlusion test was also measured in a control group of healthy volunteers. Results Sixty-six consecutive trauma patients were included. After 8 h, 17 patients were classified as AHD, of whom five were finally considered to have OS and 12 THD. No hemodynamic, metabolic or coagulopathic differences were observed between the two groups, while NIRS-derived parameters showed statistically significant differences in Delta-down, r­ SO2min, and Delta-up. Conclusions After 8 h of care, NIRS evaluation with an occlusion test is helpful for identifying occult shock in apparently hemodynamically stable patients. Level of evidence IV, descriptive observational study. Trial registration ClinicalTrials.gov Registration Number: NCT02772653. Keywords Trauma · Occult shock · Microcirculation · Hemodynamics · Resuscitation Introduction Trauma is the most frequent cause of death among peo- ple aged between 5 and 29 years old worldwide [1], and in trauma patients, hemorrhagic shock is the first cause of preventable death [2, 3]. To increase the chances of sur- * Andrea Campos‑Serra vival, efforts must be made to rapidly detect and resusci- acampos@tauli.cat tate patients from shock [2, 4, 5]. The classical definition of Extended author information available on the last page of the article shock is the alteration of vital signs, but, after normalization 13 Vol.:(0123456789) A. Campos‑Serra et al. Table 1  Physiological and Physiological criteria Anatomical criteria anatomical prehospital triage criteria Systolic blood pressure < 90 mmHg All penetrating injuries to head, neck, torso and extremities proximal to the elbow and knee Respiratory rate < 10 or > 29 breaths/min Chest wall instability or deformity Glasgow coma scale score ≤ 13 Two or more proximal long-bone fractures Non-palpable peripheric pulses Crushed, degloved mangled or pulseless extremity Amputation proximal to wrist or ankle Pelvic fractures of these parameters, up to 85% of severely injured trauma Methods patients still have persistent hypoperfusion and ongoing tis- sue acidosis, also known as occult shock, which may lead to Design and setting organ dysfunction and death [4, 6]. Traditional markers such as blood pressure, heart rate, urine output, and mental status We conducted a prospective observational study at a are still commonly used to guide resuscitation in trauma university hospital (Parc Taulí University Hospital, patients [7, 8] but they are non-specific [9, 10]. Other mark- Sabadell, Spain). The local Ethics Committee (Comitè ers such as arterial lactate or base deficit (BD) are accurate Ètic d'Investigació Clínica, Institut d’Investigació i Inno- and objective but require invasive monitoring or intermit- vació Parc Taulí I­ 3PT (Reference 2,016,529) approved the tent blood sampling, and may still fail to detect regional study and it was registered at Clinicaltrials.gov (Reference hypoperfusion [9]. To improve the ability to detect ongoing NCT02772653). Informed consent was obtained from each hypoperfusion, monitoring of regional “non-vital” areas, patient or each patient’s next of kin. This study is presented such as the splanchnic area or peripheral skeletal muscle, has following the STROBE recommendations for reporting been proposed [11, 12]. It has been suggested that regional observational studies [16]. hypoperfusion should be evaluated at the end of conven- tional resuscitation, when “global” hypoperfusion markers Patients have been corrected [11]. On the whole, even though several markers of resuscitation have been described, to date, no Severely injured trauma patients with physiological or ana- gold standard has been identified [4]. tomical prehospital triage criteria (Table 1) according to During hemorrhagic shock, the activation of the sympa- ATLS [8] were included. thetic nervous system causes a redistribution of the blood Exclusion criteria were: age under 16 years old, patients flow from the periphery to the central compartment, to transferred from/to other hospitals within 24 h of the acci- maintain optimal perfusion of the vital organs [13]. Near- dent, patients with isolated neurological injury, and the infrared spectroscopy (NIRS) provides a rapid, noninvasive, impossibility of measuring NIRS-derived tissue oxygena- and continuous estimate of local tissue oximetry, also known tion parameters due to local conditions such as trauma in as regional tissue oxygen saturation ­(rSO2), and it is gener- both upper limbs, and skin and/or vascular injuries affecting ally used in peripheral areas such as the skeletal muscle [9, the thenar eminence. 14, 15]. Real-time measurements of ­rSO2 allow dynamic assessment of the patient’s response to resuscitation, and Protocol additional data can be obtained from a vascular occlusion test (VOT), a regional stress test that has repeatedly demon- Resuscitation markers were evaluated in patients undergo- strated its value in the assessment of hemodynamic altera- ing active resuscitation after 8 h of hospital care. In critical tions in several scenarios [10, 14]. care, although it is accepted that “the earlier, the better”, this The objective of this study was to establish whether initial window for achieving resuscitation goals is usually set NIRS-derived muscle r­ SO2, and the response to a VOT, were at 6–8 h [17]. In our study, we aimed at analyzing the ability associated with occult shock once conventional global resus- of regional tissue oxygenation to detect occult hypoperfu- citation was considered to be complete. To this end, other sion once the initial resuscitation process would be ideally commonly used markers of shock were compared, including complete. Therefore, we chose the 8-h time frame as a suf- vital signs, Shock Index, ROPE index, hemoglobin, natriu- ficient window to complete this initial resuscitation. Patients retic atrial peptide, arterial BD, serum lactate concentration, with SBP ≥ 90 mmHg, HR < 100 bpm and no vasopressor and coagulopathy, defined according to rotational thromboe- support were defined as apparently hemodynamically stable lastography ­(ROTEM®). 13 Alterations in tissue oxygen saturation measured by near‑infrared spectroscopy in trauma… (AHD), as opposed to hemodynamically unstable (HDU) ­rSO2min) and Delta-up (difference between ­rSO2min when at least one of the criteria was not met. AHD patients and ­rSO2max). Absolute ­rSO2 and VOT-derived vari- were later categorized into two groups according to the need ables were obtained using the INVOS Analytics Tool for additional treatment between the eighth and the 48th v1.2 (Medtronic, Essex, UK). hour after the injury: AHD patients were finally labeled as having “Occult shock” (OS) if they needed further treat- Patient demographics, prehospital triage criteria, ment for persistent bleeding, defined as requiring additional Injury Severity Score (ISS), mechanism of injury, causes transfusion, initiation of vasopressors, or needing surgery or of death, vasopressor administration, blood products, and angioembolization. Patients who did not need any additional operative and interventional radiology procedures were treatment were finally labeled as “truly HD stable” (THD). recorded. It should be taken into consideration that elective surgical interventions were not considered to be interventions for bleeding control. On the other hand, patients who had semi- Normal data set with healthy volunteers elective surgical interventions between the 8th and the 48th hours after the accident had no active bleeding that needed To determine the normal range of forearm muscle ­rSO2 surgical control and did not need any red blood cell transfu- and the normal response to VOT, forearm muscle ­rSO2 and sion (RBCT) nor vasopressors administration, which could VOT readings were taken from healthy volunteers whose age have been considered a cause of bias interpreting the results and sex were similar to the patients analyzed for this study. of this study. Generally, these individuals were hospital and university Hemodynamic, metabolic, coagulopathy, and microcircu- staff and medical students. Additional parameters recorded latory parameters were measured simultaneously. included individual’s age, sex, blood pressure, and comor- bidities. Exclusion criteria were consumption of caffeine Measured variables within the previous 8 h before the test, taking medications with cardiovascular effects, and/or previous known periph- (1) Hemodynamic variables included: systolic blood pres- eral vascular disease. sure (SBP), diastolic blood pressure (DBP), heart rate (HR), Shock Index (SI) [HR/SBP] and ROPE Index [HR/(SBP-DBP)]. Statistical analysis (2) Blood samples included: hemoglobin, natriuretic atrial peptide (NAP), base deficit and serum lactate concen- Statistical analysis was performed by means of IBM SPSS tration. statistics v25 software (SPSS Inc, Chicago, IL, USA). The (3) Coagulopathy was assessed with R ­ OTEM® and clas- normal distribution of the variables studied was confirmed sified in five phenotypes, according to the degree of using the Kolmogorov–Smirnov test. Accordingly, continu- abnormality observed: 0 = normal; 1 = fibrinogen defi- ous variables were expressed as means ± standard deviation ciency; 2 = hypocoagulability; 3 = platelet deficiency; (SD), and categorical variables were expressed as abso- 4 = global deficiency; 5 = global deficiency and hyper- lute numbers and proportions (%). A descriptive analysis fibrinolysis. was performed. Differences between groups were assessed (4) Regional oxygen saturation ­(rSO2) was recorded con- using the Chi-squared test for categorical variables, and the tinuously using the INVOS™ 5100C Cerebral/Somatic Kruskal–Wallis test, Mann–Whitney’s U-test or Student’s Oximeter (Medtronic, Essex, UK). The ­rSO2 15 mm t-test for continuous variables, as appropriate. A two-tailed optical surface probe was placed on intact skin on the p value of less than 0.05 was taken to indicate statistical forearm muscle. In addition to the steady-state ­rSO2 significance. value, the response to a transient ischemic challenge was also computed. The ischemic challenge consisted in a standardized Vascular Occlusion Test (VOT), and was performed as previously described in the literature Results [18]. Briefly, a blood pressure cuff was placed on the arm and rapidly inflated at 50 mmHg above systolic Healthy volunteers pressure and kept inflated for a three-minute period. Then, the cuff was rapidly deflated and the minimum From December 2019 to March 2020, basal ­rSO2 and VOT- ­rSO2 ­(rSO2min) and maximum ­rSO2 ­(rSO2max) val- derived variables were obtained from 48 healthy volunteers. ues were recorded. VOT-derived variables included Main characteristics of the sample population and NIRS- Delta-down (difference between basal ­rSO 2 and related results are shown in Table 2. 13 A. Campos‑Serra et al. Table 2  Demographics, and N 48 NIRS-related results of healthy volunteers Age (years) 43 ± 16 Sex Male (n, %) 37 (77%) Female (n, %) 11 (23%) Absolute ­rSO2 (%) 71 ± 7 Minimum ­rSO2 (%) 43 ± 15 Maximum ­rSO2 (%) 86 ± 8 Delta-down (%) 28 ± 12 Delta-up (%) 43 ± 16 NIRS near-infrared spectros- copy, rSO2 regional oxygen saturation Trauma patients From May 2016 to March 2019, 66 consecutive trauma patients with eligible criteria for this study were admit- ted to our hospital. Mean age was 42 ± 15 years old, 80% were males and median injury severity score (ISS) was 25.5 (IQR 8–68). The characteristics of AHD and HDU patients are shown in Table 3. Three patients (5%) died Fig. 1  Flow chart illustrating the study recruitment and the final cat- within the initial hours of admission, and six patients (9%) egorization ofapparently HD stable patients died of severe brain injury later in the course of the ini- tial care and were excluded from the final analysis. After 8 h of hospital admission, 40 patients were considered intervention between the 8th and 48th hour. On the con- to be HDU, (37 patients had a HR ≥ 100 bpm; 9 patients trary, two patients of the THS group did undergo semi- had a SBP < 90 mmHg and 32 patients were under vaso- elective surgical interventions between the 8th and 48th pressor support) and 17 patients were classified as AHD hour, but neither needed surgical bleeding control, RBCT (Fig. 1). In the HDU group, three patients died after 8 h of nor vasopressor administration: one had a laparoscopic hospital admission (7.5%) while in the AHD group there exploration of a penetrating diaphragmatic injury needing were no deaths. After 48 h of follow-up, five of the 17 suture and the other was operated for an open abdomen AHD patients were classified as OS: three patients needed closure. RBCT, one needed vasoactive drug administration plus Comparison between healthy volunteers and trauma RBCT, and one patient needed surgery to control per- patients is presented in Table 4. Age and gender of healthy sistent bleeding plus RBCT. The patient with persistent volunteers and trauma patients did not show significant dif- bleeding needing surgery had a penetrating injury to the ferences. With regard to NIRS-related variables included stomach with persistent bleeding of the posterior gastric in the protocol, there were no statistically significant dif- wall, he presented hematemesis in the 14th hour of hos- ferences between healthy volunteers and trauma patients, pital stay and was re-operated in the 16th hour. None of except for lower r­ SO2-max values in trauma patients (86 ± 8 the OS patients did undergo any semi-elective surgical vs 80 ± 7, p 0.02). No differences between volunteers and THD were observed, while OS patients showed alterations in Table 3  Main characteristics of AHD and HDU trauma patients ­rSO2-min, Delta-down, and Delta-up as compared to healthy controls. HDU only differed from healthy subjects in terms AHD HDU p of their ­rSO2-max following the VOT. N 17 40 The Kruskal–Wallis test showed different distributions of Age (years) (mean ± SD) 41 ± 17 43 ± 13 0.6 the NIRS-related variables among the three trauma groups. Sex male (n, %) 14 (82%) 35 (88%) 0.5 While no significant differences were detected between Prehospital physiological (n, %) 6 (35%) 30 (75%) 0.004 HDU and THD patients, OS patients differed from the rest criteria anatomical (n, %) 11 (65%) 10 (25%) of the groups (Table 4). Mechanism blunt (n, %) 14 (82%) 36 (90%) 0.4 Table 5 shows the relationship between all the resuscita- penetrating (n, %) 3 (18%) 4 (10%) tion markers analyzed and the identification of occult shock ISS (mean ± SD) 17 ± 8 29 ± 13 < 0.001 in AHD stable trauma patients. Only NIRS VOT-derived 13 Alterations in tissue oxygen saturation measured by near‑infrared spectroscopy in trauma… Table 4  Comparison of Healthy volunteers Trauma patients HDU AHD variables between healthy volunteers and trauma patients THD Occult shock N = 48 N = 57 N = 40 N = 12 N=5 Mean ± SD Mean ± SD Mean ± SD Mean ± SD Mean ± SD NIRS absolute ­rSO2 71 ± 7 68 ± 8 68 ± 8 68 ± 10 72 ± 11 NIRS delta-down 28 ± 12 31 ± 13 31 ± 12 23 ± 12 48 ± 11* NIRS delta-up 43 ± 16 43 ± 13 43 ± 16 35 ± 17 60 ± 10 NIRS ­rSO2 min 43 ± 15 37 ± 16 36 ± 18 45 ± 13 24 ± 2** NIRS ­rSO2 max 86 ± 8 80 ± 7** 79 ± 4** 80 ± 11 84 ± 10 Mann–Whitney U-test for comparisons between healthy volunteers and trauma patients NIRS near-infrared spectroscopy, HDU hemodynamically unstable, AHD apparently hemodynamic stable, THD truly hemodynamically stable * p < 0.05, **p < 0.01 Table 5  Associations between resuscitation markers and occult shock under-resuscitated. These findings are relevant, since altera- after 8 h of hospital admission tions in NIRS parameters can provide clinicians with impor- Truly HD stable Occult shock tant information regarding the evaluation of otherwise clini- N = 12 (70%) N = 5 (30%) cally stable patients. Occult shock, defined as persistent hypoperfusion with Mean ± SD Mean ± SD p normal vital signs, remains a controversial entity [5], and Heart rate (bpm) 80 ± 10.6 82 ± 12 0.7 its definition has evolved along with the appearance of Systolic blood pressure 118 ± 18.7 115 ± 13.6 0.7 new metabolic and perfusion parameters. In recent years, (mmHg) regional parameters have demonstrated their additional value Shock index 0.69 ± 0.2 0.72 ± 0.1 0.7 compared with global metabolic parameters [5, 12, 19, 20] ROPE index 1.6 ± 0.6 2.2 ± 1.3 0.2 such as lactate, thus further stressing the importance of the Hemoglobin (g/L) 110 ± 17.4 94 ± 0.85 0.2 concept of occult shock. In the present study, occult shock Serum lactate (mg/dL) 21.4 ± 12.1 25.8 ± 9.0 0.5 was defined as the need for additional blood cell transfusion, Base deficit (mmol/L) -1.5 ± 2.0 -0.5 ± 1.5 0.4 use of vasopressors or need for surgery or angioembolization Natriuretic atrial peptide 2.4 ± 0.8 6.7 ± 8.0 0.3 in trauma patients, whose vital signs were normal, between (nmol/L) the 8th and 48th hour of hospital admission. Our results ROTEM coagulopathy 0.5 ± 0.8 0.2 ± 0.5 0.5 suggest that regional tissue oxygenation parameters play a NIRS absolute ­rSO2 68.4 ± 9.6 72.0 ± 11.1 0.6 key role in the detection of occult shock and in the need for NIRS delta-down 23.3 ± 11.5 48.3 ± 10.5 0.016 further resuscitation interventions. NIRS delta-up 34.7 ± 16.8 60.3 ± 9.5 0.047 Our findings are consistent with previous data on NIRS NIRS ­rSO2 min 44.8 ± 13.1 23.7 ± 1.5 0.010 monitoring, and are based on a strong pathophysiological NIRS ­rSO2 max 79.5 ± 11.3 84.0 ± 10.1 0.1 rationale. We observed that, in apparently stable patients, Bold values indicate statistical significance of p values of less than higher rates of desaturation following a VOT were associ- 0.05 ated with the need for further resuscitation interventions to HD hemodynamically, NIRS near-infrared spectroscopy, rSO2 control bleeding in the following 48 h. These higher ­rSO2 Regional oxygen saturation desaturation rates can only be attributed to two underlying mechanisms, or a combination of them: (a) diminished local variables showed statistically significant differences between blood flow, and (b) increased local metabolic rate. In situa- THDs and OS patients. tions of hypovolemia, blood flow is diverted from the periph- ery to the central compartment, causing a “stealing effect” of blood from these peripheral or non-vital areas. This com- Discussion pensatory mechanism is mainly driven by the activation of the sympathetic system, which also increases the metabolic Our data suggest that, after 8 h of active treatment, alter- rate, as a result of the effect of the release of catecholamines ations in ­rSO 2-related parameters may help to detect [13]. Regrettably, our study does not allow us to separate apparently hemodynamically stable patients who are still these two phenomena, but our results are consistent with 13 A. Campos‑Serra et al. those of other authors who have shown that alterations in normalization. Our study adds to the current evidence and VOT-derived parameters are associated with the redistribu- underlines the value of regional tissue oxygenation as part tion of the blood flow towards the central compartment and of the monitoring tool kit for the hemodynamic resuscitation sympathetic activation [19, 20]. Interestingly, VOT-derived of trauma patients. parameters are useful in situations where the compensa- The predictive power of non-NIRS-related variables tory mechanisms are subclinical and are not detected by the was very limited except for lactate and BD, two parameters standard hemodynamic monitoring tools. that have classically been related to occult shock detection Previous studies have already described NIRS technol- [4–6, 23–26]. However, some publications such as James ogy as a useful tool for detecting tissue hypoperfusion in et al. [27] reject the relationship between tissue acidosis and trauma patients [4, 14, 15, 21, 22]. The results of our study lactate, considering that lactate elevation is related to the coincide with those of Guyette et al. [10] which obtained catecholaminergic response to trauma. Other authors such a prehospital absolute r­ SO2 and performed a VOT in 150 as Pal et al. [23] and Petrosoniak et al. [5] have associated trauma patients, and concluded that, even though r­ SO2 had persistent elevation of lactate with occult shock; Abramson prognostic value for mortality and multiple organ failure, it et al. [24] considered that patients with pathologic lactate did not identify occult shock states. This was considered an and normalized vital signs needed more aggressive moni- inherent limitation of the technology, insofar as peripheral toring. Brohi et al. [25] stated that lactate and BD can be vasoconstriction associated with compensated shock states considered equivalent and that lactate alteration is an indica- may be accompanied by a reduction in regional tissue oxy- tor of hypoperfusion, while Guyette et al. [26] recommend gen demand and compromised supply. However, stressing prehospital lactate evaluation to identify occult shock in the system by producing a vascular occlusion yielded param- patients with normalized vital signs. eters such as the ­rSO2 de-saturation and re-saturation slopes, Blow et al. [6] defined occult shock as the presence of which distinguished between patients requiring bleeding lactate > 25 mg/dL in patients with SBP > 100 mmHg, HR control maneuvers and those that did not. Additionally, the < 120 mmHg and diuresis > 1 ml/kg/h. Patients who met the analysis of lactate and SBP found no statistical relationship inclusion criteria received intensive resuscitation to normal- for these variables, and the authors concluded that VOT- ize lactate values during the first 24 h of hospital stay, and derived variables were capable of detecting occult shock showed reduced mortality when normalization was achieved. when vital signs and lactate were normal. NIRS technology In contrast, our study did not detect a statistically signifi- has also been recommended in AHD patients before starting cant relationship between lactate or BD and occult shock. resuscitation maneuvers [15] or when “global” resuscitation This absence of a statistical relation might be attributable, on maneuvers have finished, to identify patients with persistent the one hand, to the small sample size, as we compared 12 microcirculatory hypoperfusion [14, 21]. The second case THD patients with five OS patients. On the other hand, most coincides with the moment when occult shock was evaluated authors associate lactate and BD with mortality [4, 6, 24, 25, in this study, after 8 h of hospital admission. Conversely, 28] and multiple organ failure [4, 6, 25, 28] considering it to Crookes et al. [9] found a statistically significant relationship be secondary to tissue hypoperfusion; however, in our study, only between absolute r­ SO2 and severe shock, and not with NIRS VOT-derived variables showed a higher capacity to mild or moderate shock. It should be stressed that no VOT detect microcirculation alterations, even though the sample was performed; therefore, in situations of severe shock abso- of patients analyzed was small. lute ­rSO2 is altered, but in states of moderate or occult shock A previous study by our group considered the Shock it remains normal while VOT-derived variables are altered. Index (SI) as a marker of occult shock when it was ≥ 0.8 In general, we can infer that absolute ­rSO2 values may be [29] because patients subsequently needed maneuvers to capable of detecting overt shock, and that VOT-derived control surgical bleeding or activation of a massive transfu- parameters are useful in situations where the hemodynamic sion protocol. It has also been considered as an occult shock status is apparently compensated and provide additional help marker with scores ≥ 0.9 [30, 31], in relation to multiple in the detection of tissue hypoperfusion. When analyzing organ failure or mortality in patients with previously normal the HDU group, one would expect HDU patients to show vital signs. lower regional oxygenation parameters. However, the lack of In contrast, our study did not find a statistically significant differences might derive from our definition of HDU, includ- relationship between the SI and occult shock. This may have ing those patients who were hypotensive, tachycardic, and/ been due to the moment in time when the SI was evaluated. or requiring vasopressors. In fact, 27 patients were classi- Generally, the studies that associate the SI with bleeding fied as HDU because they were on vasopressors. 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Authors and Affiliations Andrea Campos‑Serra1 · Jaume Mesquida2 · Sandra Montmany‑Vioque1 · Pere Rebasa‑Cladera1 · Marta Barquero‑Lopez3 · Ariadna Cidoncha‑Secilla1 · Núria Llorach‑Perucho1 · Marc Morales‑Codina4 · Juan Carlos Puyana5 · Salvador Navarro‑Soto1 Jaume Mesquida Ariadna Cidoncha‑Secilla jmesquida@tauli.cat acidoncha@tauli.cat Sandra Montmany‑Vioque Núria Llorach‑Perucho smontmany@tauli.cat nllorach@tauli.cat Pere Rebasa‑Cladera Marc Morales‑Codina prebasa@tauli.cat marcmoralescodina@gmail.com Marta Barquero‑Lopez Juan Carlos Puyana marta_barquero@hotmail.com puyajc@upmc.edu 13 Alterations in tissue oxygen saturation measured by near‑infrared spectroscopy in trauma… 3 Salvador Navarro‑Soto Anesthesiology Department, Parc Taulí Hospital Universitari, snavarro@tauli.cat Sabadell, Spain 4 1 Critical Care Department, Hospital Universitari Josep Trueta, Department of Surgery, Universitat Autònoma de Barcelona, Girona, Spain Parc Taulí Hospital Universitari, Parc del Taulí 1, 08208 5 Sabadell (Barcelona), Spain Department of Surgery, University of Pittsburgh, Pittsburgh, 2 USA Critical Care Department, Parc Taulí Hospital Universitari, Sabadell, Spain 13