Evaluating tissue hypoxia and the response to fluid administration in septic shock patients: a metabolic cluster analysis.

BACKGROUND: The selection of adequate indicators of tissue hypoxia for guiding the resuscitation process of septic patients is a highly relevant issue. Current guidelines advocate for the use of lactate as sole metabolic marker, which may be markedly limited, and the integration of different variables seems more adequate. In this study, we explored the metabolic profile and its implications in the response to the administration of a fluid challenge in early septic shock patients. METHODS: Observational study including septic shock patients within 24 h of ICU admission, monitored with a cardiac output estimation system, with ongoing resuscitation. Hemodynamic and metabolic variables were measured before and after a fluid challenge (FC). A two-step cluster analysis was used to define the baseline metabolic profile, including lactate, central venous oxygen saturation (ScvO2), central venous-to-arterial carbon dioxide difference (PcvaCO2), and PcvaCO2 corrected by the difference in arterial-to-venous oxygen content (PcvaCO2/CavO2). RESULTS: Seventy-seven fluid challenges were analyzed. Cluster analysis revealed two distinct metabolic profiles at baseline. Cluster A exhibited lower ScvO2, higher PcvaCO2, and lower PcvaCO2/CavO2. Increases in cardiac output (CO) were associated with increases in VO2 exclusively in cluster A. Baseline isolated metabolic variables did not correlate with VO2 response, and changes in ScvO2 and PcvaCO2 were associated to VO2 increase only in cluster A. CONCLUSIONS: In a population of early septic shock patients, two distinct metabolic profiles were identified, suggesting tissue hypoxia or dysoxia. Integrating metabolic variables enhances the ability to detect those patients whose VO2 might increase as results of fluid administration.

Peripheral microcirculatory alterations are associated with the severity of acute respiratory distress syndrome in COVID-19 patients admitted to intermediate respiratory and intensive care units.

BACKGROUND: COVID-19 is primarily a respiratory disease; however, there is also evidence that it causes endothelial damage in the microvasculature of several organs. The aim of the present study is to characterize in vivo the microvascular reactivity in peripheral skeletal muscle of severe COVID-19 patients. METHODS: This is a prospective observational study carried out in Spain, Mexico and Brazil. Healthy subjects and severe COVID-19 patients admitted to the intermediate respiratory (IRCU) and intensive care units (ICU) due to hypoxemia were studied. Local tissue/blood oxygen saturation (StO2) and local hemoglobin concentration (THC) were non-invasively measured on the forearm by near-infrared spectroscopy (NIRS). A vascular occlusion test (VOT), a three-minute induced ischemia, was performed in order to obtain dynamic StO2 parameters: deoxygenation rate (DeO2), reoxygenation rate (ReO2), and hyperemic response (HAUC). In COVID-19 patients, the severity of ARDS was evaluated by the ratio between peripheral arterial oxygen saturation (SpO2) and the fraction of inspired oxygen (FiO2) (SF ratio). RESULTS: Healthy controls (32) and COVID-19 patients (73) were studied. Baseline StO2 and THC did not differ between the two groups. Dynamic VOT-derived parameters were significantly impaired in COVID-19 patients showing lower metabolic rate (DeO2) and diminished endothelial reactivity. At enrollment, most COVID-19 patients were receiving invasive mechanical ventilation (MV) (53%) or high-flow nasal cannula support (32%). Patients on MV were also receiving sedative agents (100%) and vasopressors (29%). Baseline StO2 and DeO2 negatively correlated with SF ratio, while ReO2 showed a positive correlation with SF ratio. There were significant differences in baseline StO2 and ReO2 among the different ARDS groups according to SF ratio, but not among different respiratory support therapies. CONCLUSION: Patients with severe COVID-19 show systemic microcirculatory alterations suggestive of endothelial dysfunction, and these alterations are associated with the severity of ARDS. Further evaluation is needed to determine whether these observations have prognostic implications. These results represent interim findings of the ongoing HEMOCOVID-19 trial. Trial registration ClinicalTrials.gov NCT04689477 . Retrospectively registered 30 December 2020.

Performance Assessment of a Commercial Continuous-Wave Near-Infrared Spectroscopy Tissue Oximeter for Suitability for Use in an International, Multi-Center Clinical Trial.

Despite the wide range of clinical and research applications, the reliability of the absolute oxygenation measurements of continuous wave near-infrared spectroscopy sensors is often questioned, partially due to issues of standardization. In this study, we have compared the performances of 13 units of a continuous wave near-infrared spectroscopy device (PortaMon, Artinis Medical Systems, NL) to test their suitability for being used in the HEMOCOVID-19 clinical trial in 10 medical centers around the world. Detailed phantom and in vivo tests were employed to measure the precision and reproducibility of measurements of local blood oxygen saturation and total hemoglobin concentration under different conditions: for different devices used, different operators, for probe repositioning over the same location, and over time (hours/days/months). We have detected systematic differences between devices when measuring phantoms (inter-device variability, <4%), which were larger than the intra-device variability (<1%). This intrinsic variability is in addition to the variability during in vivo measurements on the forearm muscle resulting from errors in probe positioning and intrinsic physiological noise (<9%), which was also larger than the inter-device differences (<3%) during the same test. Lastly, we have tested the reproducibility of the protocol of the HEMOCOVID-19 clinical trial; that is, forearm muscle oxygenation monitoring during vascular occlusion tests over days. Overall, our conclusion is that these devices can be used in multi-center trials but care must be taken to characterize, follow-up, and statistically account for inter-device variability.

Non-invasive tools for guiding hemodynamic resuscitation in septic shock: the perfusion vs metabolic issue.

Transcutaneous oxygen pressure reflects the balance between cardiac output, arterial oxygenation, and the metabolic rate of the tissue. In septic shock, it allows a real time assessment of the adequacy of tissue perfusion, and therefore it has been proposed as a non-invasive tool to guide the hemodynamic resuscitation process. However, its value is limited in those situations where cardiac output has been optimized, but tissue dysoxia persists as results of an impairment in oxygen utilization.

Hemodynamic support in septic shock.

PURPOSE OF REVIEW: The current article reviews recent findings on the monitoring and hemodynamic support of septic shock patients. RECENT FINDINGS: The ultimate goal of hemodynamic resuscitation is to restore tissue oxygenation. A multimodal approach combining global and regional markers of tissue hypoxia seems appropriate to guide resuscitation. Several multicenter clinical trials have provided evidence against an aggressive fluid resuscitation strategy. Fluid administration should be personalized and based on the evidence of fluid responsiveness. Dynamic indices have proven to be highly predictive of responsiveness. Recent data suggest that balanced crystalloids may be associated with less renal failure. When fluid therapy is insufficient, a multimode approach with different types of vasopressors has been suggested as an initial approach. Dobutamine remains the firs inotropic option in patients with persistent hypotension and decrease ventricular systolic function. Calcium sensitizer and phosphodiesterase inhibitors may be considered, but evidence is still limited. Veno-arterial extracorporeal membrane oxygenation may be considered in selected unresponsive patients, particularly with myocardial depression, and in a highly experienced center. SUMMARY: Resuscitation should be personalized and based on global and regional markers of tissue hypoxia as well as the fluid responsiveness indices. The beneficial effect of multimode approach with different types of vasopressors, remains to be determined.

Nursing workload and compliance with non-pharmacological measures to prevent ventilator-associated pneumonia: a multicentre study.

BACKGROUND: Ventilator-associated pneumonia is common and associated with high mortality. Nurses play a fundamental role in preventing ventilator-associated pneumonia. Evidence-based guidelines and training interventions about preventing ventilator-associated pneumonia do not ensure compliance with recommendations. AIMS AND OBJECTIVE: To evaluate the impact of nursing workload on compliance with non-pharmacological measures to prevent ventilator-associated pneumonia. DESIGN: A prospective observational study in two medical-surgical adult ICUs in Spain. METHODS: We measured nurses' knowledge about preventing ventilator-associated pneumonia through a questionnaire and workload, categorized with the Nine Equivalents of Nursing Manpower Use Score. We directly observed nurses to measure compliance with non-pharmacological measures to prevent ventilator-associated pneumonia. RESULTS: A total of 97 nurses were studied; 76 (79%) were observed. There were 327 observations (mean 4·30 observations per nurse). The questionnaire showed good baseline knowledge of preventive measures [mean score (92% ± 16%)]. Nurses complied with the preventive measures in 66% ± 15% of observations; compliance ranged from 11·9% for pre-aspiration hand washing to 99·7% for using sterile aspiration probes. Mean Nine Equivalents of Nursing Manpower Use Score for each nurse observed was 50 ± 13, without differences between centres (49 ± 14 versus 51 ± 11, p = 0·4). Overall compliance was lower in the light workload group (p = 0·02), but no significant differences in compliance between workload groups were found when each measure was analysed separately. Compliance was higher in nurses aged 31-40 years than in those aged >51 years, although workload was similar in both groups. CONCLUSIONS: Compliance with non-pharmacological measures to prevent ventilator-associated pneumonia varies widely; non-compliance is not because of increased workload. RELEVANCE TO CLINICAL PRACTICE: Most critical care nurses have good baseline knowledge of non-pharmacological measures to prevent ventilator-associated pneumonia. Failure to comply with these measures is probably more related with behavioural, structural and organizational aspects than with nursing workload. Interventions to improve compliance might be more effective if they focus on factors such as work climate and professionals' attitudes.

Passive leg raising for assessment of volume responsiveness: a review.

PURPOSE OF REVIEW: To evaluate the existing evidence on the passive leg raising (PLR) test for fluid responsiveness prediction. RECENT FINDINGS: It has been well established that either insufficient or excessive fluid administration derives in worse outcomes in critically ill patients, highlighting that a more accurate assessment of fluid management is required. Accordingly, several cardiovascular indices have been tested to improve our ability to predict patients' response to fluid loading at the bedside, the so-called functional hemodynamic monitoring. The standardized PLR is a relatively novel maneuver that, over the past 10 years, has repeatedly demonstrated high sensitivity and specificity for fluid responsiveness prediction. SUMMARY: The current review underlines that PLR is an easy-to-perform and reliable method to assess fluid responsiveness. Its excellent performance is maintained even in many situations in which other dynamic predictive indices are not consistent and represents a valid alternative to the fluid challenge to avoid unnecessary volume administration.

Central venous-to-arterial carbon dioxide difference combined with arterial-to-venous oxygen content difference is associated with lactate evolution in the hemodynamic resuscitation process in early septic shock.

INTRODUCTION: Since normal or high central venous oxygen saturation (ScvO2) values cannot discriminate if tissue perfusion is adequate, integrating other markers of tissue hypoxia, such as central venous-to-arterial carbon dioxide difference (PcvaCO2 gap) has been proposed. In the present study, we aimed to evaluate the ability of the PcvaCO2 gap and the PcvaCO2/arterial-venous oxygen content difference ratio (PcvaCO2/CavO2) to predict lactate evolution in septic shock. METHODS: Observational study. Septic shock patients within the first 24 hours of ICU admission. After restoration of mean arterial pressure, and central venous oxygen saturation, the PcvaCO2 gap and the PcvaCO2/CavO2 ratio were calculated. Consecutive arterial and central venous blood samples were obtained for each patient within 24 hours. Lactate improvement was defined as the decrease ≥ 10% of the previous lactate value. RESULTS: Thirty-five septic shock patients were studied. At inclusion, the PcvaCO2 gap was 5.6 ± 2.1 mmHg, and the PcvaCO2/CavO2 ratio was 1.6 ± 0.7 mmHg · dL/mL O2. Those patients whose lactate values did not decrease had higher PcvaCO2/CavO2 ratio values at inclusion (1.8 ± 0.8vs. 1.4 ± 0.5, p 0.02). During the follow-up, 97 paired blood samples were obtained. No-improvement in lactate values was associated to higher PcvaCO2/CavO2 ratio values in the previous control. The ROC analysis showed an AUC 0.82 (p < 0.001), and a PcvaCO2/CavO2 ratio cut-off value of 1.4 mmHg · dL/mL O2 showed sensitivity 0.80 and specificity 0.75 for lactate improvement prediction. The odds ratio of an adequate lactate clearance was 0.10 (p < 0.001) in those patients with an elevated PcvaCO2/CavO2 ratio (≥1.4). CONCLUSION: In a population of septic shock patients with normalized MAP and ScvO2, the presence of elevated PcvaCO2/CavO2 ratio significantly reduced the odds of adequate lactate clearance during the following hours.

Evaluating tissue oxygenation at the bedside: global, regional, or both?

Early recognition of tissue hypoperfusion, and monitoring tissue response to resuscitation interventions, are key points in the management of critically ill patients. In the present issue of J Clin Monit Comput, Dr. Koch and coworkers present the results of a study evaluating regional and global markers of tissue perfusion in a population of septic shock patients. We propose an integrative approach to tissue perfusion assessment, where combining both, global and regional variables, might account for a better understanding of tissue oxygenation status, and might prove useful for septic shock patients' management.

Thenar oxygen saturation during weaning from mechanical ventilation: an observational study.

Our aim was to determine whether thenar tissue oxygen saturation (S(tO2)), measured by noninvasive near-infrared spectroscopy, and its changes derived from an ischaemic challenge are associated with weaning outcome. Our study comprised a prospective observational study in a 26-bed medical-surgical intensive care unit. Patients receiving mechanical ventilation for >48 h, and considered ready to wean by their physicians underwent a 30-min weaning trial. S(tO2) was measured continuously on the thenar eminence. A transient vascular occlusion test was performed prior to and at the end of the 30-min weaning trial, in order to obtain S(tO2) deoxygenation and reoxygenation rates, and estimated local oxygen consumption. 37 patients were studied. Patients were classified as weaning success (n=24) or weaning failure (n=13). No significant demographic, respiratory or haemodynamic differences were observed between the groups at inclusion. Patients who failed the overall weaning process showed a significant increase in deoxygenation and in local oxygen consumption from baseline to 30 min of weaning trial, whereas no significant changes were observed in the weaning success group. Failure to wean from mechanical ventilation was associated with higher relative increases in deoxygenation after 30 min of spontaneous ventilation.

Erratum: Assessment of power spectral density of microvascular hemodynamics in skeletal muscles at very low and low-frequency via near-infrared diffuse optical spectroscopies: erratum.

[This corrects the article on p. 5994 in vol. 14, PMID: 38021143.].

Non-Invasive Monitoring of Microvascular Oxygenation and Reactive Hyperemia using Hybrid, Near-Infrared Diffuse Optical Spectroscopy for Critical Care.

The detection of levels of impairment in microvascular oxygen consumption and reactive hyperemia is vital in critical care. However, there are no practical means for a robust and quantitative evaluation. This paper describes a protocol to evaluate these impairments using a hybrid near-infrared diffuse optical device. The device contains modules for near-infrared time-resolved and diffuse correlation spectroscopies and pulse-oximetry. These modules allow the non-invasive, continuous, and real-time measurement of the absolute, microvascular blood/tissue oxygen saturation (StO2) and the blood flow index (BFI) along with the peripheral arterial oxygen saturation (SpO2). This device uses an integrated, computer-controlled tourniquet system to execute a standardized protocol with optical data acquisition from the brachioradialis muscle. The standardized vascular occlusion test (VOT) takes care of the variations in the occlusion duration and pressure reported in the literature, while the automation minimizes inter-operator differences. The protocol we describe focuses on a 3-min occlusion period but the details described in this paper can readily be adapted to other durations and cuff pressures, as well as other muscles. The inclusion of an extended baseline and post-occlusion recovery period measurement allows the quantification of the baseline values for all the parameters and the blood/tissue deoxygenation rate that corresponds to the metabolic rate of oxygen consumption. Once the cuff is released, we characterize the tissue reoxygenation rate, magnitude, and duration of the hyperemic response in BFI and StO2. These latter parameters correspond to the quantification of the reactive hyperemia, which provides information about the endothelial function. Furthermore, the above-mentioned measurements of the absolute concentration of oxygenated and deoxygenated hemoglobin, BFI, the derived metabolic rate of oxygen consumption, StO2, and SpO2 provide a yet-to-be-explored rich data set that can exhibit disease severity, personalized therapeutics, and management interventions.

Alterations in tissue oxygen saturation measured by near-infrared spectroscopy in trauma patients after initial resuscitation are associated with occult shock.

PURPOSE: Persistent occult hypoperfusion after initial resuscitation is strongly associated with increased morbidity and mortality 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 measurement 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 occlusion test was performed, allowing a 3-min deoxygenation period and a reoxygenation period following occlusion release. Minimal rSO2 (rSO2min), Delta-down (rSO2-rSO2min), maximal rSO2 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, rSO2min, 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.

In vivocharacterization of the optical and hemodynamic properties of the human sternocleidomastoid muscle through ultrasound-guided hybrid near-infrared spectroscopies.

Objective.In this paper, we present a detailedin vivocharacterization of the optical and hemodynamic properties of the human sternocleidomastoid muscle (SCM), obtained through ultrasound-guided near-infrared time-domain and diffuse correlation spectroscopies.Approach.A total of sixty-five subjects (forty-nine females, sixteen males) among healthy volunteers and thyroid nodule patients have been recruited for the study. Their SCM hemodynamic (oxy-, deoxy- and total hemoglobin concentrations, blood flow, blood oxygen saturation and metabolic rate of oxygen extraction) and optical properties (wavelength dependent absorption and reduced scattering coefficients) have been measured by the use of a novel hybrid device combining in a single unit time-domain near-infrared spectroscopy, diffuse correlation spectroscopy and simultaneous ultrasound imaging.Main results.We provide detailed tables of the results related to SCM baseline (i.e. muscle at rest) properties, and reveal significant differences on the measured parameters due to variables such as side of the neck, sex, age, body mass index, depth and thickness of the muscle, allowing future clinical studies to take into account such dependencies.Significance.The non-invasive monitoring of the hemodynamics and metabolism of the sternocleidomastoid muscle during respiration became a topic of increased interest partially due to the increased use of mechanical ventilation during the COVID-19 pandemic. Near-infrared diffuse optical spectroscopies were proposed as potential practical monitors of increased recruitment of SCM during respiratory distress. They can provide clinically relevant information on the degree of the patient's respiratory effort that is needed to maintain an optimal minute ventilation, with potential clinical application ranging from evaluating chronic pulmonary diseases to more acute settings, such as acute respiratory failure, or to determine the readiness to wean from invasive mechanical ventilation.

Assessment of power spectral density of microvascular hemodynamics in skeletal muscles at very low and low-frequency via near-infrared diffuse optical spectroscopies.

In this work, we used a hybrid time domain near-infrared spectroscopy (TD-NIRS) and diffuse correlation spectroscopy (DCS) device to retrieve hemoglobin and blood flow oscillations of skeletal muscle microvasculature. We focused on very low (VLF) and low-frequency (LF) oscillations (i.e., frequency lower than 0.145 Hz), that are related to myogenic, neurogenic and endothelial activities. We measured power spectral density (PSD) of blood flow and hemoglobin concentration in four muscles (thenar eminence, plantar fascia, sternocleidomastoid and forearm) of 14 healthy volunteers to highlight possible differences in microvascular hemodynamic oscillations. We observed larger PSDs for blood flow compared to hemoglobin concentration, in particular in case of distal muscles (i.e., thenar eminence and plantar fascia). Finally, we compared the PSDs measured on the thenar eminence of healthy subjects with the ones measured on a septic patient in the intensive care unit: lower power in the endothelial-dependent frequency band, and larger power in the myogenic ones were observed in the septic patient, in accordance with previous works based on laser doppler flowmetry.

Physiologic responses to severe hemorrhagic shock and the genesis of cardiovascular collapse: can irreversibility be anticipated?

BACKGROUND: The causes of cardiovascular collapse (CC) during hemorrhagic shock (HS) are unknown. We hypothesized that vascular tone loss characterizes CC, and that arterial pulse pressure/stroke volume index ratio or vascular tone index (VTI) would identify CC. METHODS: Fourteen Yorkshire-Durock pigs were bled to 30 mmHg mean arterial pressure and held there by repetitive bleeding until rendered unable to compensate (CC) or for 90 min (NoCC). They were then resuscitated in equal parts to shed volume and observed for 2 h. CC was defined as a MAP < 30 mmHg for 10 min or <20 mmHg for 10 s. Study variables were recorded at baseline (B0), 30, 60, 90 min after bleeding and at resuscitation (R0), 30, and 60 min afterward. RESULTS: Swine were bled to 32% ± 9% of total blood volume. Epinephrine (Epi) and VTI were low and did not change in NoCC after bleeding compared with CC swine, in which both increased (0.97 ± 0.22 to 2.57 ± 1.42 mcg/dL, and 173 ± 181 to 939 ± 474 mmHg/mL, respectively), despite no differences in bled volume. Lactate increase rate (LIR) increased with hemorrhage and was higher at R0 for CC, but did not vary in NoCC. VTI identified CC from NoCC and survivors from non-survivors before CC. A large increase in LIR was coincident with VTI decrement before CC occurred. CONCLUSIONS: Vasodilatation immediately prior to CC in severe HS occurs at the same time as an increase in LIR, suggesting loss of tone as the mechanism causing CC, and energy failure as its probable cause.

[Haemodynamic monitoring in sepsis and septic shock]. / Monitorización hemodinámica en la sepsis y el shock séptico.

Cardiovascular disturbances associated with sepsis cause hypoperfusion situations, which will negatively impact these patients' prognosis. The aim of haemodynamic monitoring is to guide the detection and correction of this hypoperfusion, and assist in decision making in optimising oxygen transport to tissues, primarily by manipulating cardiac output. This review seeks to summarise the different parameters of haemodynamic monitoring, the objectives of resuscitation, the physiological parameters, and the tools available to us for appropriate cardiac output manipulation.

Optical imaging and spectroscopy for the study of the human brain: status report.

This report is the second part of a comprehensive two-part series aimed at reviewing an extensive and diverse toolkit of novel methods to explore brain health and function. While the first report focused on neurophotonic tools mostly applicable to animal studies, here, we highlight optical spectroscopy and imaging methods relevant to noninvasive human brain studies. We outline current state-of-the-art technologies and software advances, explore the most recent impact of these technologies on neuroscience and clinical applications, identify the areas where innovation is needed, and provide an outlook for the future directions.

Thenar oxygen saturation (StO2) alterations during a spontaneous breathing trial predict extubation failure.

BACKGROUND: Weaning from mechanical ventilation (MV) is a cardiovascular stress test. Monitoring the regional oxygenation 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 spontaneous breathing trial (SBT), and were extubated according to the local protocol. Continuous StO2 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 DeO2 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.

Characterization of tissue oxygen saturation and the vascular occlusion test: influence of measurement sites, probe sizes and deflation thresholds.

INTRODUCTION: Tissue oxygen saturation (StO2) and the vascular occlusion test (VOT) can identify tissue hypoperfusion in trauma and sepsis. However, the technique is neither standardized nor uses the same monitoring site. We hypothesized that baseline and VOT StO2 would be different in the forearm (F) and thenar eminence (TH) and that different minimal StO2 values during the VOT would result in different reoxygenation rates (ReO2). METHODS: StO2 and its change during the VOT were simultaneously measured in the F and TH, with 15 mm and 25 mm probes, using the 325 InSpectra monitor in 18 healthy, adult volunteers. Two VOTs were done to a threshold thenar StO2 of 40% interchanging the 15 mm and 25 mm probes between sites. Two additional VOTs were done to thresholds of 50% and 30%. Baseline StO2 (BaseO2), the deoxygenation rate (DeO2) and ReO2 were compared between sites, probes and (%O2/minute) thresholds. Results are presented as the median (interquartile range), P-value. RESULTS: BaseO2, DeO2, ReO2, area under the curve and hyperemia duration values were different when comparing TH vs. F and 15 mm vs. 25 mm probes. ReO2 was different between different thresholds for the TH and 15 mm probes. TH15 mm vs. F15 mm: BaseO2, 90.4 (85.2, 93.5) vs. 85.2 (80.7, 90.2), P = 0.031; DO2, -12.1 (-16.2, -11.3) vs. -8.5 (-10.3, -7.8), P = 0.011; ReO2, 297.2 (213.7, 328.6), P < 0.0001; 15 mm vs. 25 mm probe: BaseO2, 97.2 (89.4, 94.7) vs. 87.3 (81.7, 90.9), P = 0.016; DeO2, -18.0 (-24.1, -14.8) vs. -9.9 (-15.3, -6.5), P < 0.0001; and ReO2, 401.6 (331.7, 543.2) vs. 160.5 (132.3, 366.9), P = 0.012, respectively. TH15 mm vs. TH25 mm: BaseO2, P = 0.020; DeO2, P < 0.0001; and ReO2, P < 0.0001. Threshold StO2 values (15 mm probe only): ReO2, P = 0.003; DeO2, P = 0.60. ReO2 at 40% and 50% StO2 thresholds, P = 0.01. CONCLUSIONS: BaseO2, DeO2 and ReO2 were different when measured in different anatomical sites (F and TH) and with different probe sizes, and ReO2 was different with differing VOT release StO2 threshold values. Thus, standardization of the site, probe and VOT challenge need to be stipulated when reporting data.