Measurement Of Tissue Oxygen Saturation Research Articles

Tissue oxygen saturation measurement in pre-hospital trauma patients—A pilot, feasibility studyCategory: Trauma/Disaster Med

Background: Major trauma is a leading cause of mortality and morbidity and a significant number of patients die from haemorrhage. Detection of active haemorrhage early can potentially reduce mortality by triggering appropriate triage, surgical expertise and transfusion protocols. The identification of actively bleeding patients with traditional physiological measurements such as pulse rate and blood pressure can be insensitive. This study evaluated the feasibility of prehospital tissue oxygen saturation (StO2) in major trauma patients.

Cerebral oxygen saturation evaluated by near‐infrared time‐resolved spectroscopy (TRS) in pregnant women during caesarean section – a promising new method of maternal monitoring

Time-resolved spectroscopy (TRS-20) measures tissue oxygen saturation (%) by evaluating the absolute concentrations of oxygenated, deoxygenated and total haemoglobin based on measurement of the transit time of individual photons through a tissue of interest. We measured tissue oxygen saturation in the prefrontal lobes of the brain by TRS-20 in eighteen pregnant women during caesarean section. In a case of placenta previa, massive bleeding immediately decreased cerebral oxygen saturation from 67·2% to 54·2%, but did not alter peripheral tissue oxygenation as measured by pulse oximetry. Four cases of pre-eclampsia revealed chronic changes in elevated base levels of cerebral oxygen saturation, though peripheral oxygen saturation was similar to that in normotensive pregnant women. Average cerebral oxygen saturation in the cases of pre-eclampsia before the introduction of anaesthesia was 73·6±4·4 (SD)% (n=4), significantly higher than in normotensive pregnant women, 67·2±4·3% (n=13, P<0·05). Z-scores of cerebral oxygen saturation prior to anaesthesia positively correlated with those of systolic or diastolic blood pressure. TRS-20 could detect acute as well as chronic changes in brain oxygen saturation in response to pregnancy-associated complications.

Effect of hyperoxia and vascular occlusion on tissue oxygenation measured by near infra‐red spectroscopy (InSpectra™): a volunteer study

Standard cardiorespiratory monitoring may fail to detect occult tissue ischaemia. This study assessed whether a near infra-red spectroscopy tissue oxygen saturation monitor (InSpectra™) could detect progressive peripheral tissue ischaemia and whether hyperoxia may confound tissue oxygen saturation measurement. Tissue oxygen and arterial oxygen saturations were measured continuously in 30 healthy volunteers, first during a period of progressive increase in inspired oxygen concentration and subsequently during two periods of low- and high-pressure limb ischaemia. Increasing inspired oxygen concentration was associated with a small increase in mean (SD) tissue oxygen saturation of 5.3 (7.1) %, reaching a plateau between 30% and 40% inspired oxygen. The rate and magnitude of decreases in tissue oxygen saturations were greater during high- than low-pressure ischaemia with a mean (SD) desaturation rate of 3.3 (0.9) vs 1.8 (0.8) %.min(-1) (p<0.01). The dose-related association and lack of confounding by hyperoxia suggest that tissue oxygen saturation monitoring may be a useful adjunct to detect occult ischaemia.

Tissue oxygen saturation measurement in prehospital trauma patients: a pilot, feasibility study

BackgroundThis study evaluated the feasibility of prehospital tissue oxygen saturation (StO2) in major trauma patients.MethodsA prospective, pilot feasibility study carried out in a physician based prehospital trauma service.ResultsPrehospital StO2 was...

Biomedical applications of wireless continuous wave near infrared spectroscopy

Progress in research applications of near infrared spectroscopy (NIRS) and growing clinical interest have led to significant improvements in hardware and software. Amongst continuous wave systems the use of light emitting diodes, incorporation of spatially resolved optical geometry, algorithm refinement, development of portable systems, and wireless telemetry led first to portable NIRS instruments, then wearable systems, and now miniaturized self-contained devices. Measurement of absolute tissue oxygen saturation in both muscle and brain, and mapping of event related cortical hemodynamic responses using functional NIRS (fNIRS) have added specific measurement modalities. Wireless wearable systems and self-contained devices capable of measuring such modalities in addition to providing conventional monitoring of trends in oxygenated and deoxygenated haemoglobin concentration from baseline have increased the scope of research, expanded the population readily monitored, and opened new clinical avenues for applications involving NIRS. This review explores the range of biomedical applications reported using wireless continuous wave (CW) NIRS and fNIRS systems, summarizes key elements in the specification of available devices, and outlines potential future directions for clinical use of wireless NIRS technologies.

Lower Cerebral Oxygen Saturation in Preterm Compared with Term Infants During the First 24 Hours of Life

Background and aims: Frequency-domain near-infrared spectroscopy (FD-NIRS) enables longitudinal measurements of cerebral tissue oxygen saturation (StO2). The objective was to evaluate changes in cerebral oxygenation in preterm versus term infants during the first days of life.Methods: StO2 was repeatedly measured by FD-NIRS (Oxiplex TS, ISS Inc., Champaign, IL, USA) in preterm (n=11, gestational age 34+3/7 (32+1/7-35+5/7) weeks, birth weight 2.125 (1.150-2.922) kg) and term (n=8, gestational age of 39+6/7 (37+0/7-40+6/7) weeks, birth weight 3.535 (2.360-4.390) kg) infants within the following postnatal time intervals: 0-12h, 12h-24h, 24-36h, 36-48h and 48-72h. The optode was placed over the right temporo-parietal region. For each measurement, 3 separate recordings of at least 2 minutes each at 1Hz sampling rate were combined. Median (min.-max.) p-values by Wilcoxon rank-sum test are depicted.Results: At 6h and 18h, preterm infants had lower StO2 values 55.6 (54.2-57.6)% and 60.5 (47.3-66.0)% compared to term infants (64.9 (59.4-74.8)% and 68.7 (59.3-75.8)%; p=0.004 and p=0.024). In contrast, at 42h and 60h StO2 values were similar: 63.1 (57.0-69.0)% and 60.1 (54.1-67.4)% compared with 65.1 (58.9-72.4)% and 61.4 (56.6-70.5)%; p=0.262 and p=0.358.Conclusion: These results suggest that preterm infants have lower StO2 levels compared with term infants during the first day after birth. Inadequate cardio-respiratory adaptation may contribute to this finding.Funded by AKF-Grant E.03.27025.1, Faculty of Medicine Tuebingen.

NIRS-Derived Tissue Oxygen Saturation and Hydrogen Ion Concentration following Bed Rest

Long-term bed rest (BR), a model of spaceflight, results in a decrease in aerobic capacity and altered submaximal exercise responses. The strongest BR-induced effects on exercise appear to be centrally-mediated, but longer BR durations may result in peripheral adaptations (e.g., decreased mitochondrial and capillary density) which are likely to influence exercise responses. PURPOSE: To measure tissue oxygen saturation (SO2) and hydrogen ion concentration ([H+]) in the vastus lateralis (VL) using near infrared spectroscopy (NIRS) during cycle ergometry before and after ≥ 30 d of BR. METHODS: Eight subjects performed a graded exercise test on a cycle erogmeter to volitional fatigue 7 d before (pre-BR) and at the end or 1 day after BR (post-BR). NIRS spectra were collected from a sensor adhered to the skin overlying the VL. Oxygen consumption (VO2) was measured by open circuit spirometry. Blood volume (BV) was measured before and after BR using the carbon monoxide rebreathing technique. Changes in pre- and post-BR SO2 and [H+] data were compared using mixed model analyses. BV and peak exercise data were compared using paired t-tests. RESULTS: BV (pre-BR: 4.3 ± 0.3, post-BR: 3.7 ± 0.2 L, mean ± SE, p=.01) and peak VO2 (pre-BR: 1.98 ± 0.24, post-BR: 1.48 ± 0.21 L/min, p<.01) were reduced after BR. As expected, SO2 decreased with exercise before and after BR. However, SO2 was lower post compared with pre-BR throughout exercise, including at peak exercise (pre-BR: 50± 3, post-BR: 43 ± 4%, p=.01). After BR, [H+] was higher at the start of exercise and did not increase at the same rate as pre-BR. Peak [H+] was not different from pre to post-BR (pre-BR: 36 ± 2; post-BR: 38 ± 2 nmol/L). CONCLUSIONS: Lower SO2 during exercise suggests that oxygen extraction in the VL is higher after BR, perhaps due to lower circulating blood volume. The higher [H+] after BR suggests a greater reliance upon glycolysis during submaximal exercise, although [H+] at peak exercise was unchanged. Taken together, these data suggest that longer duration BR induces a number of changes that result in peripheral adaptations which contribute to cardiovascular and muscular deconditioning as measured by NIRS-derived SO2 and [H+] in the VL and may contribute to lower post-BR exercise tolerance. Supported by the National Space Biomedical Research Institute through NASA NCC 9-58

The Use of Near-Infrared Spectrometry for the Diagnosis of Lower-Extremity Compartment Syndrome

While intracompartmental pressure monitoring is a widely used diagnostic tool to measure intracompartmental pressures in the setting of compartment syndrome, its invasive nature has prompted the development of noninvasive techniques, such as near-infrared spectrometry. We prospectively assessed the association between tissue oxygen saturation measured by near-infrared spectrometry and compartment pressure measured by intracompartmental pressure monitoring in a cohort of patients with compartment syndrome of the lower extremity. We hypothesized that tissue oxygen saturation measured by near-infrared spectrometry would negatively correlate with intracompartmental pressures. Tissue oxygen saturation was determined for all 4 compartments of the lower extremity in 7 patients using near-infrared spectrometry. All patients subsequently underwent lower-extremity fasciotomies. Mechanism of injury, compartment pressures, blood pressure, near-infrared spectrometry measurement of tissue oxygen saturation, and characteristics of the muscle at the time of fasciotomy were recorded. The strength of the correlations between tissue oxygen saturation and absolute and relative compartment pressures was estimated based on mixed linear (growth) models with repeated observations nested within patients. Our analyses demonstrated no significant relationship between tissue oxygen saturation measured by near-infrared spectrometry and the absolute or relative compartment pressures. This suggests that compartment tissue oxygen saturation measurements by near-infrared spectrometry do not correlate with the diagnosis of compartment syndrome, and that near-infrared spectrometry would not serve as a reliable diagnostic tool.

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

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

Reproducibility of cerebral tissue oxygen saturation measurements by near-infrared spectroscopy in newborn infants

Early detection of cerebral hypoxemia is an important aim in neonatology. A relevant parameter to assess brain oxygenation may be the cerebral tissue oxygen saturation (StO(2)) measured by near-infrared spectroscopy (NIRS). So far the reproducibility of StO(2) measurements was too low for clinical application, probably due to inhomogeneities. The aim of this study was to test a novel sensor geometry which reduces the influence of inhomogeneities. Thirty clinically stable newborn infants, with a gestational age of median 33.9 (range 26.9 to 41.9) weeks, birth weight of 2220 (820 to 4230) g, postnatal age of 5 (1 to 71) days were studied. At least four StO(2) measurements of 1 min duration were carried out using NIRS on the lateral head. The sensor was repositioned between measurements. Reproducibility was calculated by a linear mixed effects model. The mean StO(2) was 79.99 ± 4.47% with a reproducibility of 2.76% and a between-infant variability of 4.20%. Thus, the error of measurement only accounts for 30.1% of the variability. The novel sensor geometry leads to considerably more precise measurements compared to previous studies with, e.g., ∼5% reproducibility for the NIRO 300. The novel StO(2) values hence have a higher clinical relevance.

321 Reproducibility of Cerebral Tissue Oxygen Saturation Measurements by Near Infrared Spectroscopy in Newborn Infants

Objectives: Cerebral tissue oxygen saturation (StO2) may be a relevant parameter to assess brain oxygenation in intensive care. Near infrared spectroscopy (NIRS) is able to measure this parameter, but so far the reproducibility of such measurements has been too low due to inhomogeneities. The aim of this study was to test a novel sensor geometry, which is based on two source and two detector locations, which are arranged symmetrically to reduce the influence of superficial inhomogeneities.Methods: Thirty clinically stable, spontaneously breathing newborn infants with a gestational age of 34.2±3.1 weeks, birth weight of 2295±970g and postnatal age of 10.2±14.9 days were measured four times for one minute by NIRS on the lateral head. Between measurements the sensor was replaced. The reproducibility was calculated by a linear mixed effects model.Results: The mean StO2 was 79.99±4.47% with a reproducibility of 2.76% and a variability of 4.20% between infants. The error of measurement only accounts for 30% of the variability.Conclusions: The novel sensor geometry leads to much more precise measurements compared to previous studies (e.g. ∽5% reproducibility for the NIRO 300). For this reason the measured StO2 values do not require averaging and are therefore more clinically relevant.

Near-Infrared Tissue Oximetry: A Pilot Study for Intraoperative Monitoring and Quantitation of Renal Ischemia During Partial Nephrectomy

Introduction: There are currently no good real-time methods to measure renal ischemic damage during hilar clamping. In this video we describe a novel technique for monitoring renal ischemia during hilar clamping using near-infrared tissue oximetry. Materials and Methods: After obtaining approval from the Institutional Animal Care and Use Committee, we performed continuous tissue oxygen measurements on six renal units of Yorkshire swine per protocol. Pneumoperitoneum to 10 mm Hg was achieved, three trocars were placed, and the kidney was mobilized laparoscopically. The ViOptix T.Ox™ Tissue Oximeter (ViOptix Inc., Fremont, CA) probe was secured to the kidney using a harness fashioned from umbilical tape. A clamp was used to occlude the renal artery and vein. Local tissue oxygen saturation measurements were obtained (up to a depth of 10 mm) and recorded at 4-sec intervals at baseline, during hilar clamping, and for 5 min after unclamping the renal vasculature. Clamp times and sequence were varied in each renal unit. Results: Near-infrared tissue oximetry reflected baseline tissue oxygen saturation levels followed by an ischemic drop levels during hilar clamping and then a return to pre-clamp levels. Conclusions: This video demonstrates a novel technique for monitoring renal ischemia during hilar clamping in a porcine model. Tissue oximetry may be a useful tool for assessing intraoperative renal ischemia during partial nephrectomy. Further studies are necessary to determine if local tissue oximetry correlates with long-term renal function. No competing financial interests exist. Runtime of video: 4 mins

Near-Infrared Spectroscopy Measurement of Sacral Tissue Oxygen Saturation in Healthy Volunteers Immobilized on Rigid Spine Boards

Introduction. Immobilization of patients utilizing rigid spine boards (RSBs) is standard practice in the management of trauma patients. Pressure ulcers have been associated with prolonged immobilization, and the possibility exists that formation may begin when the patient is initially immobilized on the RSB. The effects may not be fully recognized because of limited research on the direct tissue effects of prolonged immobilization. Near-infrared spectroscopy is an emerging tool to measure peripheral tissue oxygen saturation (StO2). The purpose of this research was to study the effects of prolonged spinal immobilization on an RSB on sacral tissue oxygenation of healthy volunteers. Methods. This experimental study measured StO2 in healthy volunteers at baseline and again after 30 minutes of immobilization on an RSB at two sites: the sacral area (intervention) and 8–10 cm above the buttocks (control). Tissue oxygenation was measured with the InSpectra Tissue Oxygenation Monitor (Hutchinson Technology, Hutchinson, MN) by placing the probe at the measurement site and waiting for 15 seconds for equilibration prior to recording StO2. Data were analyzed utilizing mixed-model and within-subjects analysis of variance (ANOVA), chi-square, and t-tests. Results. Seventy-three participants were included in the analysis. A slight majority of participants were female (55%), the average age was 38 years, the average height was 170 cm, and the average weight was 82 kg. There was a significant increase in the StO2 percentage at the sacral (intervention) area following immobilization, p < 0.001, point biserial correlation (rpb) = 0.48. Significant changes in oxygenation were not noted at the control site. Conclusion. An increase in sacral tissue oxygenation following immobilization was a finding consistent with other research. This is likely a result of initial, rapid tissue reperfusion at the time of pressure release. Rapid reperfusion indicates that a period of previous hypoperfusion has occurred. This research indicates that there are detrimental effects of spine board immobilization in healthy volunteers, which suggests that pressure ulcer formation may begin prior to hospital admission with immobilization on an RSB.

Role of near infrared spectroscopy in pediatric cardiac surgery

Initial interest in near infrared spectroscopy for the prevention of neurological injury during cardiac surgery focused on intra-operative cerebral oximetry monitoring to minimize the potential negative impact of cardiopulmonary bypass and various perfusion strategies. However, it has become increasingly apparent, over the past decade, that neurological function can be impacted throughout the peri-operative period, particularly in the intensive care unit environment (Ballweg et al., 2007 [1]). As a result, the application of near infrared spectroscopy has expanded beyond the operating room to a variety of clinical arenas, including the intensive care unit and even the outpatient setting. In addition, the clinical indications have expanded to include multi-site, continuous monitoring for detection of low cardiac output states and regional tissue hypoxia of tissue beds other than the cerebral circulation. The precise role for near infrared spectroscopy in the pediatric cardiac surgery population remains unclear. While there is a growing body of evidence demonstrating its correlation with other physiologic markers, such as SvO 2, currently there are limited data to support that clinical decision-making based on near infrared spectroscopy improves patient outcomes. In assessing the potential role of near infrared spectroscopy monitoring in congenital heart disease, it is important to emphasize its unique qualities, including noninvasive, continuous, and real-time measurement of regional tissue oxygen saturation, and its potential earlier, faster and more accurate physiologic assessments to direct patient care, monitor response to therapeutic intervention, and ultimately to improve long term outcomes.

Measuring Tissue Oxygen Saturation via Spectrometer in Children

: Near-infrared spectroscopy is a new noninvasive method of monitoring oxygen saturation at a tissue level. The purpose of this study was to evaluate new near-infrared tissue spectrometer InSpectra (Hutchinson Technology Inc.) in children and to determine preferable areas of the body to measure tissue oxygen saturation (StO2). : Prospective study at a pediatric emergency department. Children aged 0 years to 17 years with no respiratory distress participated in this study. StO2 on deltoid muscle, thenar eminence, forearm, calf, bicep, and tricep was measured at triage with a 25-mm probe. : A total of 310 patients were recruited. The mean age of participants was 6.8 years +/- 4.4 years and 53% were males. Average StO2 was 84% (95% confidence interval, 81-87%) on the bicep muscle, 83.5% (95% confidence interval, 82-85%) on the deltoid muscle and significantly (p < 0.05) lower on other areas. Variation of StO2 was lower on the bicep, deltoid, and thenar muscles. Regression analysis showed significant linear relationship between patients' age and StO2 measured on the thenar eminence (beta = 0.3, R = 0.08, p < 0.001) and between patients' weight and StO2 on the thenar eminence (beta = 0.3, R = 0.07, p < 0.001). StO2 in febrile patients was similar to afebrile children, except thenar eminence where StO2 was significantly lower (p = 0.002). Less than 5% reported any type of pain or cried during StO2 measurement, which did not differ from pulse oximetry. : Bicep and deltoid muscles are the most appropriate areas to measure StO2 using the 25-mm transducer in children of different ages. The use of near-infrared spectroscopy on the thenar eminence, which is usually used for measurement in adults, has varied results in children depending on the age, weight, and presence of fever.

Tissue saturation measurement - exciting prospects, but standardisation and reference data still needed

Sepsis and shock result in disturbances in microcirculatory perfusion and tissue oxygen utilisation that may not be reflected in global measures of haemodynamics. Near-infrared spectroscopy enables measurement of tissue oxygen saturation (StO2) and provides information on local microvascular and mitochondrial function. This measure could be incorporated with existing targets of goal-directed therapy to provide an integrated approach to haemodynamic resuscitation of both the macro- and microcirculation in various shock states. However, key methodological factors must be addressed before widespread clinical application.

The Effect on Cerebral Tissue Oxygenation Index of Changes in the Concentrations of Inspired Oxygen and End-Tidal Carbon Dioxide in Healthy Adult Volunteers

A variety of near-infrared spectroscopy devices can be used to make noninvasive measurements of cerebral tissue oxygen saturation (ScO2). The ScO2 measured by the NIRO 300 spectrometer (Hamamatsu Photonics, Japan) is called the cerebral tissue oxygenation index (TOI) and is an assessment of the balance between cerebral oxygen delivery and utilization. We designed this study to investigate the effect of systemic and intracranial physiological changes on TOI. Fifteen healthy volunteers were studied during isocapneic hyperoxia and hypoxemia, and normoxic hypercapnea and hypocapnea. Absolute cerebral TOI and changes in oxy- and deoxyhemoglobin concentrations were measured using a NIRO 300 spectrometer. Changes in arterial oxygen saturation (SaO2), ETCO2, heart rate, mean arterial blood pressure (MBP), and middle cerebral artery blood flow velocity (Vmca) were also measured during these physiological challenges. Changes in cerebral blood volume (CBV) were subsequently calculated from changes in total cerebral hemoglobin concentration. Baseline TOI was 67.3% with an interquartile range (IQR) of 65.2%-71.9%. Hypoxemia was associated with a median decrease in TOI of 7.1% (IQR -9.1% to -5.4%) from baseline (P < 0.0001) and hyperoxia with a median increase of 2.3% (IQR 2.0%-2.5%) (P < 0.0001). Hypocapnea caused a reduction in TOI of 2.1% (IQR -3.3% to -1.3%) from baseline (P < 0.0001) and hypercapnea an increase of 2.6% (IQR 1.4%-3.7%) (P < 0.0001). Changes in SaO2 (P < 0.0001), ETCO2 (P < 0.0001), CBV (P = 0.0003), and MBP (P = 0.03) were significant variables affecting TOI. Changes in Vmca (P = 0.7) and heart rate (P = 0.2) were not significant factors. TOI is an easy-to-monitor variable that provides real-time, multisite, and noninvasive assessment of the balance between cerebral oxygen delivery and utilization. However, TOI is a complex variable that is affected by SaO2 and ETCO2, and, to a lesser extent, by MBP and CBV. Clinicians need to be aware of the systemic and cerebral physiological changes that can affect TOI to interpret changes in this variable during clinical monitoring.

A New Diagnostic Algorithm for Early Prediction of Vascular Compromise in 208 Microsurgical Flaps Using Tissue Oxygen Saturation Measurements

The purpose of the study was to evaluate the detection of vascular complications earlier than clinical evidence using a noninvasive near-infrared tissue oximeter monitor. Early detection of circulatory compromise allows for earlier re-exploration and better outcomes. The monitoring method studied was the ViOptix T.Ox Tissue Oximeter (ViOptix Inc., Fremont, CA). The device uses an optical tissue characterization based on measuring scattering and absorption of near infrared light. Tissue oxygen saturation and its derivates were evaluated as candidates for a more sensitive algorithm to predict vascular flap complications. Criteria studied in various combinations were the absolute value of tissue oxygen saturation (StO2), the amount of its change (DeltaStO2) and the rate of its change (DeltaStO2/Deltat). There were 208 monitored breast flaps in 145 patients (62 bilateral and 83 unilateral). In 1 patient, 2 flaps were used to make a single breast. Patients were monitored intraoperatively and postoperatively for 36 hours. No flap being monitored was lost. Among the 208 flaps monitored, 5 patients exhibited complications that were predicted by the tissue oximeter before clinical signs were evident. If blood flow was completely occluded by either venous or arterial thrombosis, the tissue oximeter provided information that enabled diagnosis to be made in about 1 hour. The drop rate indicator DeltaStO2/Deltat, when it is equal to or greater than 20% per hour sustained more than 30 minutes predicted vascular complications. The use of the new diagnostic algorithm with the T.Ox Tissue Oximeter monitor was successful in predicting flap complication within 1 hour of the onset of the occlusive event with a high diagnostic accuracy in the 208 flap procedures.

Assessment of tissue oxygen saturation during a vascular occlusion test using near-infrared spectroscopy: the role of probe spacing and measurement site studied in healthy volunteers

IntroductionTo assess potential metabolic and microcirculatory alterations in critically ill patients, near-infrared spectroscopy (NIRS) has been used, in combination with a vascular occlusion test (VOT), for the non-invasive measurement of tissue oxygen saturation (StO2), oxygen consumption, and microvascular reperfusion and reactivity. The methodologies for assessing StO2 during a VOT, however, are very inconsistent in the literature and, consequently, results vary from study to study, making data comparison difficult and potentially inadequate. Two major aspects concerning the inconsistent methodology are measurement site and probe spacing. To address these issues, we investigated the effects of probe spacing and measurement site using 15 mm and 25 mm probe spacings on the thenar and the forearm in healthy volunteers and quantified baseline, ischemic, reperfusion, and hyperemic VOT-derived StO2 variables.MethodsStO2 was non-invasively measured in the forearm and thenar in eight healthy volunteers during 3-minute VOTs using two InSpectra tissue spectrometers equipped with a 15 mm probe or a 25 mm probe. VOT-derived StO2 traces were analyzed for base-line, ischemic, reperfusion, and hyperemic parameters. Data were categorized into four groups: 15 mm probe on the forearm (F15 mm), 25 mm probe on the forearm (F25 mm), 15 mm probe on the thenar (T15 mm), and 25 mm probe on the thenar (T25 mm).ResultsAlthough not apparent at baseline, probe spacing and measurement site significantly influenced VOT-derived StO2 variables. For F15 mm, F25 mm, T15 mm, and T25 mm, StO2 ownslope was -6.4 ± 1.7%/minute, -10.0 ± 3.2%/minute, -12.5 ± 3.0%/minute, and -36.7 ± 4.6%/minute, respectively. StO2 upslope was 105 ± 34%/minute, 158 ± 55%/minute, 226 ± 41%/minute, and 713 ± 101%/minute, and the area under the hyperemic curve was 7.4 ± 3.8%·minute, 10.1 ± 4.9%·minute, 12.6 ± 4.4%·minute, and 21.2 ± 2.7%·minute in these groups, respectively. Furthermore, the StO2 parameters of the hyperemic phase of the VOT, such as the area under the curve, significantly correlated to the minimum StO2 during ischemia.ConclusionsNIRS measurements in combination with a VOT are measurement site-dependent and probe-dependent. Whether this dependence is anatomy-, physiology-, or perhaps technology-related remains to be elucidated. Our study also indicated that reactive hyperemia depends on the extent of ischemic insult.

Assessment of tissue oxygen saturation during a vascular occlusion test using near-infrared spectroscopy: role of the probe spacing and measurement site studied in healthy volunteers

To assess potential metabolic and microcirculatory alterations in critically ill patients, near-infrared spectroscopy (NIRS) has been used, in combination with a vascular occlusion test (VOT), for the noninvasive measurement of tissue oxygen saturation (StO2), oxygen consumption, and microvascular reperfusion and reactivity. However, the methodologies for assessing StO2 are very inconsistent in the literature and results vary from study to study. In this study we investigated the effects of the probe spacing and measurement site, using both a 15 mm and a 25 mm probe spacing on the thenar and the forearm, in healthy volunteers.