Simultaneous multi-depth assessment of tissue oxygen saturation in thenar and forearm using near-infrared spectroscopy during a simple cardiovascular challenge

Tissue oxygen saturation is predictive of lactate clearance in patients with circulatory shock

BACKGROUND

Tissue oxygen saturation (StO₂) decrease could appear earlier than lactate alteration. However, the correlation between StO₂ and lactate clearance was unknown.

METHODS

This was a prospective observational study. All consecutive patients with circulatory shock and lactate over 3 mmol/L were included. Based on the rule of nines, a BSA (body surface area) weighted StO₂ was calculated from four sites of StO₂ (masseter, deltoid, thenar and knee). The formulation was as follows: masseter StO₂ × 9% + (deltoid StO₂ + thenar StO₂) × (18% + 27%)/ 2 + knee StO₂ × 46%. Vital signs, blood lactate, arterial and central venous blood gas were measured simultaneously within 48 h of ICU admission. The predictive value of BSA-weighted StO₂ on 6-hour lactate clearance > 10% since StO₂ initially monitored was assessed.

RESULTS

A total of 34 patients were included, of whom 19 (55.9%) had a lactate clearance higher than 10%. The mean SOFA score was lower in cLac ≥ 10% group compared with cLac < 10% group (11 ± 3 vs. 15 ± 4, p = 0.007). Other baseline characteristics were comparable between groups. Compared to non-clearance group, StO₂ in deltoid, thenar and knee were significantly higher in clearance group. The area under the receiver operating curves (AUROC) of BSA-weighted StO₂ for prediction of lactate clearance (0.92, 95% CI [Confidence Interval] 0.82-1.00) was significantly higher than StO₂ of masseter (0.65, 95% CI 0.45-0.84; p < 0.01), deltoid (0.77, 95% CI 0.60-0.94; p = 0.04), thenar (0.72, 95% CI 0.55-0.90; p = 0.01), and similar to knee (0.87, 0.73-1.00; p = 0.40), mean StO₂ (0.85, 0.73-0.98; p = 0.09). Additionally, BSA-weighted StO₂ model had continuous net reclassification improvement (NRI) over the knee StO₂ and mean StO₂ model (continuous NRI 48.1% and 90.2%, respectively). The AUROC of BSA-weighted StO₂ was 0.91(95% CI 0.75-1.0) adjusted by mean arterial pressure and norepinephrine dose.

CONCLUSIONS

Our results suggested that BSA-weighted StO₂ was a strong predictor of 6-hour lactate clearance in patients with shock.

New Hemodynamic Parameters in Peri-Operative and Critical Care-Challenges in Translation

Hemodynamic monitoring technologies are evolving continuously-a large number of bedside monitoring options are becoming available in the clinic. Methods such as echocardiography, electrical bioimpedance, and calibrated/uncalibrated analysis of pulse contours are becoming increasingly common. This is leading to a decline in the use of highly invasive monitoring and allowing for safer, more accurate, and continuous measurements. The new devices mainly aim to monitor the well-known hemodynamic variables (e.g., novel pulse contour, bioreactance methods are aimed at measuring widely-used variables such as blood pressure, cardiac output). Even though hemodynamic monitoring is now safer and more accurate, a number of issues remain due to the limited amount of information available for diagnosis and treatment. Extensive work is being carried out in order to allow for more hemodynamic parameters to be measured in the clinic. In this review, we identify and discuss the main sensing strategies aimed at obtaining a more complete picture of the hemodynamic status of a patient, namely: (i) measurement of the circulatory system response to a defined stimulus; (ii) measurement of the microcirculation; (iii) technologies for assessing dynamic vascular mechanisms; and (iv) machine learning methods. By analyzing these four main research strategies, we aim to convey the key aspects, challenges, and clinical value of measuring novel hemodynamic parameters in critical care.

Evidence that large vessels do affect near infrared spectroscopy

The influence of large vessels on near infrared spectroscopy (NIRS) measurement is generally considered negligible. Aim of this study is to test the hypothesis that changes in the vessel size, by varying the amount of absorbed NIR light, could profoundly affect NIRS blood volume indexes. Changes in haemoglobin concentration (tHb) and in tissue haemoglobin index (THI) were monitored over the basilic vein (BV) and over the biceps muscle belly, in 11 subjects (7 M - 4 F; age 31 ± 8 year) with simultaneous ultrasound monitoring of BV size. The arm was subjected to venous occlusion, according to two pressure profiles: slow (from 0 to 60 mmHg in 135 s) and rapid (0 to 40 mmHg maintained for 30 s). Both tHb and THI detected a larger blood volume increase (1.7 to 4 fold; p < 0.01) and exhibited a faster increase and a greater convexity on the BV than on the muscle. In addition, NIRS signals from BV exhibited higher correlation with changes in BV size than from muscle (r = 0.91 vs 0.55, p < 0.001 for THI). A collection of individual relevant recordings is also included. These results challenge the long-standing belief that the NIRS measurement is unaffected by large vessels and support the concept that large veins may be a major determinant of blood volume changes in multiple experimental conditions.

Comparison of Intra-operative Pressure-Controlled Ventilation and Volume-Controlled Ventilation in Bariatric Surgery: A Prospective Randomized Study

Background: Mechanical ventilation may be particularly challenging in obese patients undergoing laparoscopic bariatric surgery. The present study aimed to compare the effects of pressure-controlled ventilation (PCV) with those of volume-controlled ventilation (VCV) on peripheral tissue oxygenation (PTO), respiratory function, hemodynamic status, and ventilation-related complications in patients undergoing laparoscopic bariatric surgery.

Methods: A total of 100 patients with obesity who underwent gastric plication or sleeve gastrectomy were recruited for the study, and 60 patients (n=32, in group PCV; n=28, in group VCV) were ultimately enrolled. Data on peri-operative PTO (arterial blood gas [ABG] analysis and tissue oxygen saturation [StO₂]) and respiratory functions were recorded for each patient, along with post-operative hemodynamic status, fluid intake, urinary output, Numeric Pain Rating Scale (NPRS) score , and complications.

Results: The two groups were similar in pH, partial pressure of oxygen, partial pressure of carbon dioxide, oxygen saturation, and lactate values at baseline, intra-operative and post-operative periods. The peri-operative StO₂ values were also similar between the two groups at all times. The two groups were identical in terms of preoperative values for respiratory function tests and post-operative hemodynamic status, fluid intake, urinary output, pain scores, and complication rates.

Conclusions: In conclusion, the choice of the mechanical ventilation mode did not appear to influence oxygen delivery, respiratory function, hemodynamic status, post-operative pain, or ventilation-related complications in obese patients undergoing laparoscopic bariatric surgery.

Randomized controlled trial of regional tissue oxygenation following goal-directed fluid therapy during laparoscopic colorectal surgery

BACKGROUND

A randomized, double-blinded controlled trial was performed to evaluate how perioperative goal-directed fluid therapy (GDFT) influences tissue oxygenation in laparoscopic colorectal surgery.

METHODS

A total of 74 patients undergoing elective laparoscopic colorectal surgery were treated with GDFT (G group) guided by stroke volume variation or conventional fluid therapy (C group). Forearm, crural, and cerebral tissue oxygen saturation (rSO₂) were simultaneously measured by near-infrared spectroscopy. Parameters of hemodynamics and rSO₂ were obtained at seven time points including before induction of anesthesia (T1), 5 min after trachea cannula (T2), 5, 60, and 120 min after pneumoperitoneum in the Trendeleburg position (T3, T4 and T5, respectively), after desufflation in the Trendeleburg position (T6), and at the end of the operation in a supine position (T7). The postoperative outcomes were recorded.

RESULTS

Compared to C group, intraoperatively, patients in the G group received more colloid (P<0.05). The stroke volume variation in G group at T5, T6 and T7 was significantly lower than that in C group (P<0.05). The cardiac index, forearm and crural rSO₂ in G group at T4, T5, T6 and T7 were significantly higher than those in C group (P<0.05). No significant differences were observed for the cerebral rSO₂ between the two groups (P > 0.05). The postoperative hospital stay and complications also showed no differences between these two groups.

CONCLUSIONS

Although the implementation of GDFT cannot increase cerebral rSO₂, the forearm and crural rSO₂ are improved during the laparoscopic colorectal surgery, which is helpful to reduce the risk of regional tissue hypoxia.

Tissue oximetry during cardiac surgery and in the cardiac intensive care unit: A prospective observational trial

Background:

Cerebral oximetry using near-infrared spectroscopy (NIRS) has well-documented benefits during cardiac surgery. The authors tested the hypothesis that NIRS technology can be used at other sites as a tissue oximeter during cardiac surgery and in the Intensive Care Unit (ICU).

Aims:

To establish feasibility of monitoring tissue oximetry during and after cardiac surgery, to examine the correlations between tissue oximetry values and cerebral oximetry values, and to examine correlations between oximetry values and mean arterial pressure (MAP) in order to test whether cerebral oximetry can be used as an index organ.

Settings and Designs:

A large, single-center tertiary care university hospital prospective observational trial of 31 patients undergoing cardiac surgery with cardiopulmonary bypass was conducted.

Materials and Methods:

Oximetry stickers were applied to both sides of the forehead, the nonarterial line forearm, and the skin above one paraspinal muscle. Data were collected from before anesthesia induction until extubation or for at least 24 h in patients who remained intubated.

Statistical Analysis:

Categorical variables were evaluated with Chi-square or Fisher's exact tests, while Wilcoxon rank-sum tests or student's t-tests were used for continuous variables.

Results:

The correlation between cerebral oximetry values and back oximetry values ranged from r = 0.37 to 0.40. The correlation between cerebral oximetry values and forearm oximetry values ranged from r = 0.11 to 0.13. None of the sites correlated with MAP.

Conclusions:

Tissue oximetry at the paraspinal muscle correlates with cerebral oximetry values while at the arm does not. Further research is needed to evaluate the role of tissue oximetry on outcomes such as acute renal failure, prolonged need for mechanical ventilation, stroke, vascular ischemic complications, prolonged ICU and hospital length of stay, and mortality in cardiac surgery.

Understanding near infrared spectroscopy and its application to skeletal muscle research

Near infrared spectroscopy (NIRS) is a powerful noninvasive tool with which to study the matching of oxygen delivery to oxygen utilization and the number of new publications utilizing this technique has increased exponentially in the last 20 yr. By measuring the state of oxygenation of the primary heme compounds in skeletal muscle (hemoglobin and myoglobin), greater understanding of the underlying control mechanisms that couple perfusive and diffusive oxygen delivery to oxidative metabolism can be gained from the laboratory to the athletic field to the intensive care unit or emergency room. However, the field of NIRS has been complicated by the diversity of instrumentation, the inherent limitations of some of these technologies, the associated diversity of terminology, and a general lack of standardization of protocols. This Cores of Reproducibility in Physiology (CORP) will describe in basic but important detail the most common methodologies of NIRS, their strengths and limitations, and discuss some of the potential confounding factors that can affect the quality and reproducibility of NIRS data. Recommendations are provided to reduce the variability and errors in data collection, analysis, and interpretation. The goal of this CORP is to provide readers with a greater understanding of the methodology, limitations, and best practices so as to improve the reproducibility of NIRS research in skeletal muscle.

Non-invasive ventilation as a strategy for weaning from invasive mechanical ventilation: a systematic review and Bayesian meta-analysis

PURPOSE

A systematic review and meta-analysis was conducted to answer the question 'In adults with respiratory failure requiring invasive ventilation for more than 24 h, does a weaning strategy with early extubation to non-invasive ventilation (NIV) compared to invasive ventilation weaning reduce all-cause hospital mortality?'

METHODS

We included randomised and quasi-randomised controlled trials that evaluated the use of non-invasive ventilation, compared to invasive ventilation, as a weaning strategy in adults mechanically ventilated for at least 24 h. The EMBASE, MEDLINE and Cochrane Central Register of Controlled Trials (CENTRAL) bibliographic databases were searched from inception to February 2018. Bayesian hierarchical models were used to perform the meta-analysis. The primary outcome was mortality at hospital discharge. Secondary outcomes included mortality (30, 60, 90 and 180 days), quality of life, duration of invasive ventilation, weaning failure, length of stay [intensive care unit (ICU) and hospital] and adverse events.

RESULTS

Twenty-five relevant studies involving 1609 patients were included in the quantitative analysis. Studies had moderate to high risk of bias due to risk of performance and detection bias. Mortality at hospital discharge was lower in the NIV weaning group compared to the invasive weaning group [pooled odds ratio (OR) 0.58, 95% highest density interval (HDI) 0.29-0.89]. Subgroup analyses showed lower pooled mortality at hospital discharge rates in NIV weaning than those in the control group in chronic obstructive pulmonary disease (COPD) patients (pooled OR 0.43, 95% HDI 0.13-0.81) and the effect is less certain in the mixed ICU population (pooled OR 0.88, 95% HDI 0.25-1.48). NIV weaning reduced the duration of invasive ventilation in patients [standardised mean difference (SMD) - 1.34, 95% HDI - 1.92 to - 0.77] and ICU length of stay (SMD - 0.70, 95% HDI - 0.94 to - 0.46). Reported rates of ventilator associated pneumonia (VAP) were lower in the NIV group. NIV weaning did not reduce overall hospital length of stay or long-term mortality. There were insufficient data to compare other adverse events and health-related quality of life.

CONCLUSIONS

The use of NIV in weaning from mechanical ventilation decreases hospital mortality, the incidence of VAP and ICU length of stay. NIV as a weaning strategy appears to be most beneficial in patients with COPD.

New method of extracting information of arterial oxygen saturation based on ∑|𝚫|

Noninvasive detection of oxygen saturation with near-infrared spectroscopy has been widely used in clinics. In order to further enhance its detection precision and reliability, this paper proposes a method of time domain absolute difference summation (∑|Δ|) based on a dynamic spectrum. In this method, the ratio of absolute differences between intervals of two differential sampling points at the same moment on logarithm photoplethysmography signals of red and infrared light was obtained in turn, and then they obtained a ratio sequence which was screened with a statistical method. Finally, use the summation of the screened ratio sequence as the oxygen saturation coefficient Q. We collected 120 reference samples of SpO₂ and then compared the result of two methods, which are ∑|Δ| and peak-peak. Average root-mean-square errors of the two methods were 3.02% and 6.80%, respectively, in the 20 cases which were selected randomly. In addition, the average variance of Q of the 10 samples, which were obtained by the new method, reduced to 22.77% of that obtained by the peak-peak method. Comparing with the commercial product, the new method makes the results more accurate. Theoretical and experimental analysis indicates that the application of the ∑|Δ| method could enhance the precision and reliability of oxygen saturation detection in real time.

Regional muscle tissue saturation is an indicator of global inadequate circulation during cardiopulmonary bypass: a randomized porcine study using muscle, intestinal and brain tissue metabolomics

Background:

Muscle tissue saturation (StO2) measured with near-infrared spectroscopy has generally been considered a measurement of the tissue microcirculatory condition. However, we hypothesized that StO2 could be more regarded as a fast and reliable measure of global than of regional circulatory adequacy and tested this with muscle, intestinal and brain metabolomics at normal and two levels of low cardiopulmonary bypass blood flow rates in a porcine model.

Methods:

Twelve 80 kg pigs were connected to normothermic cardiopulmonary bypass with a blood flow of 60 mL/kg/min for one hour, reduced randomly to 47.5 mL/kg/min (Group I) or 35 mL/kg/min (Group II) for one hour followed by one hour of 60 mL/kg/min in both groups. Regional StO2 was measured continuously above the musculus gracilis (non-cannulated leg). Metabolomics were obtained by brain tissue oxygen monitoring system (Licox) measurements of the brain and microdialysis perfusate from the muscle, intestinal mucosa and brain. A non-parametric statistical method was used.

Results:

The systemic parameters showed profound systemic ischaemia during low CPB blood flow. StO2 did not change markedly in Group I, but in Group II, StO2 decreased immediately when blood flow was reduced and, furthermore, was not restored despite blood flow being normalized. Changes in the metabolomics from the muscle, colon and brain followed the changes in StO2.

Conclusion:

We found, in this experimental cardiopulmonary bypass model, that StO2 reacted rapidly when the systemic circulation became inadequate and, furthermore, reliably indicate insufficient global tissue perfusion even when the systemic circulation was restored after a period of systemic hypoperfusion.

Rapid assessment of shock in a nonhuman primate model of uncontrolled hemorrhage: Association of traditional and nontraditional vital signs to mortality risk

BACKGROUND

Heart rate (HR), systolic blood pressure (SBP) and mean arterial pressure (MAP) are traditionally used to guide patient triage and resuscitation; however, they correlate poorly to shock severity. Therefore, improved acute diagnostic capabilities are needed. Here, we correlated acute alterations in tissue oxygen saturation (StO2) and end-tidal carbon dioxide (ETCO2) to mortality in a rhesus macaque model of uncontrolled hemorrhage.

METHODS

Uncontrolled hemorrhage was induced in anesthetized rhesus macaques by a laparoscopic 60% left-lobe hepatectomy (T = 0 minute). StO2, ETCO2, HR, as well as invasive SBP and MAP were continuously monitored through T = 480 minutes. At T = 120 minutes, bleeding was surgically controlled, and blood loss was quantified. Data analyses compared nonsurvivors (expired before T = 480 minutes, n = 5) with survivors (survived to T = 480 minutes, n = 11) using repeated-measures analysis of variance with Bonferroni correction. All p < 0.05 was considered statistically significant. Results were reported as mean ± SEM.

RESULTS

Baseline values were equivalent between groups for each parameter. In nonsurvivors versus survivors at T = 5 minutes, StO2 (55% ± 10% vs. 78% ± 3%, p = 0.02) and ETCO2 (15 ± 2 vs. 25 ± 2 mm Hg, p = 0.0005) were lower, while MAP (18 ± 1 vs. 23 ± 2 mm Hg, p = 0.2), SBP (26 ± 2 vs. 34 ± 3 mm Hg, p = 0.4), and HR (104 ± 13 vs. 105 ± 6 beats/min, p = 0.3) were similar. Association of values over T = 5-30 minutes to mortality demonstrated StO2 and ETCO2 equivalency with a significant group effect (p ≤ 0.009 for each parameter; R(2) = 0.92 and R(2) = 0.90, respectively). MAP and SBP associated with mortality later into the shock period (p < 0.04 for each parameter; R(2) = 0.91 and R(2) = 0.89, respectively), while HR yielded the lowest association (p = 0.8, R(2) = 0.83).

CONCLUSION

Acute alterations in StO2 and ETCO2 strongly associated with mortality and preceded those of traditional vital signs. The continuous, noninvasive aspects of Food and Drug Administration-approved StO2 and ETCO2 monitoring devices provide logistical benefits over other methodologies and thus warrant further investigation.

Towards monitoring dysplastic progression in the oral cavity using a hybrid fiber-bundle imaging and spectroscopy probe

Intraepithelial dysplasia of the oral mucosa typically originates in the proliferative cell layer at the basement membrane and extends to the upper epithelial layers as the disease progresses. Detection of malignancies typically occurs upon visual inspection by non-specialists at a late-stage. In this manuscript, we validate a quantitative hybrid imaging and spectroscopy microendoscope to monitor dysplastic progression within the oral cavity microenvironment in a phantom and pre-clinical study. We use an empirical model to quantify optical properties and sampling depth from sub-diffuse reflectance spectra (450–750 nm) at two source-detector separations (374 and 730 μm). Average errors in recovering reduced scattering (5–26 cm⁻¹) and absorption coefficients (0–10 cm⁻¹) in hemoglobin-based phantoms were approximately 2% and 6%, respectively. Next, a 300 μm-thick phantom tumor model was used to validate the probe’s ability to monitor progression of a proliferating optical heterogeneity. Finally, the technique was demonstrated on 13 healthy volunteers and volume-averaged optical coefficients, scattering exponent, hemoglobin concentration, oxygen saturation, and sampling depth are presented alongside a high-resolution microendoscopy image of oral mucosa from one volunteer. This multimodal microendoscopy approach encompasses both structural and spectroscopic reporters of perfusion within the tissue microenvironment and can potentially be used to monitor tumor response to therapy.

The prognostic value of muscle regional oxygen saturation index in severe community-acquired pneumonia: a prospective observational study

Background

Community-acquired pneumonia (CAP) mortality exceeds 20 % in critical care patients despite appropriate antibiotic therapy. Regional tissue oxygen saturation index (rSO2) measured with near-infrared spectroscopy (NIRS) might facilitate early detection for patients at risk of serious complications. Our objectives were to determine the relationship between early determination of rSO2 and mortality and to compare discrimination power for mortality of rSO2 and other resuscitation variables in critically ill CAP patients.

Methods

This is a prospective observational study. Patients with CAP were enrolled within 6 h to intensive care admission. Demographics and clinical variables were recorded. rSO2 was determined using NIRS in brachioradialis muscle. All variables were determined at baseline and 24 h after admission.

Results

Forty patients were enrolled. Fourteen patients (35 %) had a baseline rSO2 < 60 % and 7 of them died (50 %). Only 1 of 26 (3.8 %) patients with rSO2 ≥ 60 % died (p = 0.007). The area under ROC curve (AUROC) showed consistent mortality discrimination at baseline (0.84, p = 0.03) and at 24 h (0.86, p = 0.006) for rSO2 values. Cox regression analysis showed that “low” rSO2 at ICU admission (hazard ratio (HR) = 8.99; 95 % confidence interval (CI) 1.05–76.8; p = 0.045) and “low” rSO2 at 24 h (HR = 13.18; 95 % CI 1.52–113.6; p = 0.019) were variables independently associated with mortality. In contrast, other variables such as Acute Physiology and Chronic Health Evaluation (APACHE II) score (HR = 1.09; 95 % CI 0.99–1.19; p = 0.052) were not associated with mortality.

Conclusions

Our findings suggest that forearm skeletal muscle rSO2 differs in patients with severe CAP according to outcome and might be an early prognosis tool.

Regional oxygen saturation index (rSO2) in brachioradialis and deltoid muscle. Correlation and prognosis in patients with respiratory sepsis

OBJECTIVE

To compare oxygen saturation index (rSO2) obtained simultaneously in two different brachial muscles.

DESIGN

Prospective and observational study.

SETTING

Intensive care unit.

PATIENTS

Critically ill patients with community-acquired pneumonia.

INTERVENTIONS

Two probes of NIRS device (INVOS 5100) were simultaneously placed on the brachioradialis (BR) and deltoid (D) muscles.

VARIABLES

rSO2 measurements were recorded at baseline (ICU admission) and at 24h. Demographic and clinical variables were registered. Pearson's correlation coefficient was used to assess the association between continuous variables. The consistency of the correlation was assessed using the intraclass correlation coefficient (ICC) and Bland-Altman plot. The predictive value of the rSO2 for mortality was calculated by ROC curve.

RESULTS

Nineteen patients were included with an ICU mortality of 21.1%. The rSO2 values at baseline and at 24h were significantly higher in D than in BR muscle. Values obtained simultaneously in both limbs showed a strong correlation and adequate consistency: BR (r=0.95; p<0.001; ICC=0.94; 95% CI: 0.90-0.96; p<0.001), D (r=0.88; p=0.01; ICC=0.88; 95% CI: 0.80-0.90; p>0.001) but a wide limit of agreement. Non-survivors had rSO2 values significantly lower than survivors at all times of the study. No patient with rSO2 >60% in BR died, and only 17.6% died with an rSO2 value >60% in D. Both muscles showed consistent discriminatory power for mortality.

CONCLUSION

Both BR and D muscles were appropriate for measuring rSO2.

Comparison of two different generations of "NIRS" devices and transducers in healthy volunteers and ICU patients

The purpose of this study is to compare Near Infrared Spectroscopy (NIRS) thenar eminence parameters obtained with 2 different devices from the same manufacturer (InSpectra Models 325 and 650, Hutchinson Tech, Min USA), and 2 different probes (15 vs. 25 mm spacing), in healthy volunteers (HV) and ICU patients. Prospective, observational study in ICU setting. Simultaneous, cross over NIRS inter-device comparison and comparison between different probes (25 vs. 15 mm spacing) were done at baseline and during vascular occlusion tests (VOTs). Forty patients (19 septic shock, 21 trauma), and 29 HV were included. NIRS inter-device comparison showed similar baseline StO(2) values in HV and patients. The VOT result were significantly different for minimal StO(2) value reached during VOT (StO(2min)) (intraclass concordance coefficient (ICC) = 0.18), the occlusion slope (ICC = 0.16) and the reperfusion slope (StO(2reperf)) (ICC = 0.26). The probe comparison was also significantly different for VOT parameters (StO(2min) (ICC = 0.43), occlusion (ICC = 0.50) and StO(2reperf) (ICC = 0.48). The low concordance, poor agreement and large bias (ICC and Bland & Altman) observed, were related both to the device used and the probe spacing. StO(2) data obtained with NIRS model 650 and 15 mm probe differ from values obtained with the previous device (325 and probe spacing 25 or 15 mm). This difference is not related to the population tested, but to the device and probe spacing. As a consequence, despite similar trends for variations between HV and patients during VOT, threshold and predictive values for outcome should be revisited with the new device before the acceptance for routine clinical use.

Monitoring tissue oxygenation by near infrared spectroscopy (NIRS): background and current applications

Conventional cardiovascular monitoring may not detect tissue hypoxia, and conventional cardiovascular support aiming at global hemodynamics may not restore tissue oxygenation. NIRS offers non-invasive online monitoring of tissue oxygenation in a wide range of clinical scenarios. NIRS monitoring is commonly used to measure cerebral oxygenation (rSO(2)), e.g. during cardiac surgery. In this review, we will show that tissue hypoxia occurs frequently in the perioperative setting, particularly in cardiac surgery. Therefore, measuring and obtaining adequate tissue oxygenation may prevent (postoperative) complications and may thus be cost-effective. NIRS monitoring may also be used to detect tissue hypoxia in (prehospital) emergency settings, where it has prognostic significance and enables monitoring of therapeutic interventions, particularly in patients with trauma. However, optimal therapeutic agents and strategies for augmenting tissue oxygenation have yet to be determined.

Mortality and regional oxygen saturation index in septic shock patients: a pilot study

BACKGROUND

Peripheral muscle tissue oxygenation determined noninvasively using near-infrared spectroscopy may help to identify tissue hypoperfusion in septic patients. The aim of this study was to investigate regional oxygen saturation index (rSO2) in the brachioradialis (forearm) muscle by comparing measurements in healthy subjects and in intensive care unit (ICU) septic shock patients, and determine whether brachioradialis muscle rSO2 is associated with poor outcome in ICU septic shock patients.

METHODS

We conducted a prospective observational study in healthy volunteers (n = 50) and ICU septic shock patients (n=19). Brachioradialis (forearm) rSO2 measurements in healthy volunteers at rest and in ICU septic shock patients were compared. Pulmonary artery catheter monitoring was used in ICU patients.

RESULTS

Significant differences in rSO2 were observed between healthy volunteers and ICU septic shock patients at ICU admission (68.7±4.9 vs. 55.0±13.0; p<0.001). When comparing septic shock survivors and nonsurvivors, significant differences were observed in rSO2 at baseline (64.5±8.9 vs. 47.5±10.7; p<0.01), 12 hours (67.3±9.6 vs. 45.0±14.9; p<0.01), and 24 hours (65.7±7.0 vs. 50.1±10.3; p<0.01). Lactate concentration was lower in survivors than nonsurvivors at 24 hours (12.0±7.5 mmol/L vs. 23.2±12.5 mmol/L; p<0.04). Cardiac index was greater in nonsurvivors than survivors at baseline (4.6+1.9 L/min/m vs. 3.0+0.9 L/min/m; p<0.05) and 12 h (3.9+0.5 L/min/m vs. 3.1+0.3 L/min/m; p<0.05).

CONCLUSIONS

We observed that septic shock patients with forearm skeletal muscle rSO2≤60% throughout first 24 hours after ICU admission had significantly greater mortality rate than patients with forearm skeletal muscle rSO2>60% throughout this critical time.

Multi-site and multi-depth near-infrared spectroscopy in a model of simulated (central) hypovolemia: lower body negative pressure

Purpose

To test the hypothesis that the sensitivity of near-infrared spectroscopy (NIRS) in reflecting the degree of (compensated) hypovolemia would be affected by the application site and probing depth. We simultaneously applied multi-site (thenar and forearm) and multi-depth (15–2.5 and 25–2.5 mm probe distance) NIRS in a model of simulated hypovolemia: lower body negative pressure (LBNP).

Methods

The study group comprised 24 healthy male volunteers who were subjected to an LBNP protocol in which a baseline period of 30 min was followed by a step-wise manipulation of negative pressure in the following steps: 0, −20, −40, −60, −80 and −100 mmHg. Stroke volume and heart rate were measured using volume-clamp finger plethysmography. Two multi-depth NIRS devices were used to measure tissue oxygen saturation (StO2) and tissue hemoglobin index (THI) continuously in the thenar and the forearm. To monitor the shift of blood volume towards the lower extremities, calf THI was measured by single-depth NIRS.

Results

The main findings were that the application of LBNP resulted in a significant reduction in stroke volume which was accompanied by a reduction in forearm StO2 and THI.

Conclusions

NIRS can be used to detect changes in StO2 and THI consequent upon central hypovolemia. Forearm NIRS measurements reflect hypovolemia more sensitively than thenar NIRS measurements. The sensitivity of these NIRS measurements does not depend on NIRS probing depth. The LBNP-induced shift in blood volume is reflected by a decreased THI in the forearm and an increased THI in the calf.

Electronic supplementary material

The online version of this article (doi:10.1007/s00134-010-2128-6) contains supplementary material, which is available to authorized users.

[Near-infrared spectroscopy in the postanesthesia recovery care unit: noninvasive monitoring of peripheral perfusion]

Clinical signs of recovery, such as blood pressure or heart rate, do not accurately reflect the perfusion of organs and tissues in patients in critical condition. Of the various means for monitoring perfusion, regional monitors are the most sensitive. Near-infrared spectroscopy (NIRS), which analyzes infrared light detected after it has passed through red blood cells in tissues, provides a measure of oxygen saturation that is the most appropriate method for clinical situations. In patients with sepsis or multiple injuries, tissue oxygen saturation can be useful as an early indicator of shock, as a marker of recovery or need for transfusion, or as a prognostic factor. In spite of widespread interest in NIRS, however, there are gaps to fill in our understanding of clinical signs and physiology in relation to this technique before peripheral tissue monitoring can become routine in postanesthesia recovery care units.