Tissue Hemoglobin Oxygen Saturation Research Articles

Effects of Compression on Muscle Tissue Oxygenation at the Onset of Exercise

The effects of compression on gastrocnemius medialis muscle oxygenation and hemodynamics during a short-term dynamic exercise was investigated in a sample of 15 male subjects (mean ± SD; age 25.8 ± 4.9 years; mass 70.6 ± 4.3 kg). Elastic compression sleeves were used to apply multiple levels of compression to the calf muscles during exercise, and noncompressive garments were used for the control condition. Tissue hemoglobin oxygen saturation was measured as the relative "tissue oxygen index" (TOI) with a near-infrared spectrometer. The recovery of TOI during exercise was determined from the slope of oxygenation recovery in a nonoccluded situation. The TOI recovery rate during the first 2 minutes of the exercise was 24% higher (p = 0.042) for the compression condition than for the control condition. A significant correlation (r = 0.61, p = 0.012) between the level of compression and the tissue oxygenation recovery during exercise was observed. Muscle energy use was determined from the rate of decline of TOI immediately upon arterial occlusion during early exercise. Muscle energy use measured during the occluded situation was not significantly influenced by compression. Based on these results, it was concluded that compression induced changes in tissue blood flow and perfusion appear to result in improved oxygenation during short-term exercise. Assuming that increased muscle oxygen availability positively influences performance, compression of muscles may enhance performance especially in sports that require repeated short bouts of exercise.

The Utility of near Infrared Imaging in Intra-Operative Prediction of Flap Outcome: A Reverse McFarlane Skin Flap Model Study

Skin flaps are complex procedures used extensively in reconstructive surgery that require post-operative monitoring to ensure that they do not fail. Near infrared (NIR) spectroscopic imaging is a convenient, non-invasive method for surgeons to examine flaps during surgery and in the early post-operative period. Using a reverse McFarlane skin flap model, we show that model-free chemometric methods as well as simple modified Beer-Lambert analysis of the NIR images provide insights into the blood supply to flaps and demonstrate that the technique can detect and localise perfusion-related complications as well as give real-time feedback to the surgeon as they try to resolve the complication. We also show that using estimates of tissue haemoglobin oxygen saturation, imaging measurements made during surgery and in the early post-operative period are highly predictive of the outcome of the flap tissue with specificities and sensitivities exceeding 85%.

The Use of Visible Light Spectroscopy to Measure Tissue Oxygenation in Free Flap Reconstruction

The loss of a free flap is a feared complication for both the surgeon and the patient. Early recognition of vascular compromise has been shown to provide the best chance for flap salvage. The ideal monitoring technique for perioperative free flap ischemia would be noninvasive, continuous, and reliable. Visible light spectroscopy (VLS) was evaluated as a new method for predicting ischemia in microvascular cutaneous soft tissue free flaps. In an Institutional Review Board-approved prospective trial, 12 patients were monitored after free flap reconstructions. The tissue hemoglobin oxygen saturation (StO (2)) and total hemoglobin concentration (THB) of 12 flaps were continuously monitored using VLS for 72 hours postoperatively. Out of these 12 flaps 11 were transplanted successfully and 1 flap loss occurred. The StO (2 )was 48.99% and the THB was 46.74% for the 12 flaps. There was no significant difference in these values among the flaps. For the single flap loss, the device accurately reflected the ischemic drop in StO (2) indicating drastic tissue ischemia at 6 hours postoperatively before the disappearance of implantable Doppler signals or clinical signs of flap compromise. VLS, a continuous, noninvasive, and localized method to monitor oxygenation, appeared to predict early ischemic complications after free flap reconstruction.

Thenar Oxygen Saturation and Invasive Oxygen Delivery Measurements in Critically Ill Patients in Early Septic Shock

This prospective study was aimed to test the hypothesis that tissue hemoglobin oxygen saturation (StO₂) measured noninvasively using near-infrared spectroscopy is a reliable indicator of global oxygen delivery (DO₂) measured invasively using a pulmonary artery catheter (PAC) in patients with septic shock. The study setting was a 26-bed medical-surgical intensive care unit at a university hospital. Subjects were adult patients in septic shock who required PAC hemodynamic monitoring for resuscitation. Interventions included transient ischemic challenge on the forearm. After blood pressure normalization, hemodynamic and oximetric PAC variables and, simultaneously, steady-state StO₂ and its changes from ischemic challenge (deoxygenation and reoxygenation rates) were measured. Fifteen patients were studied. All the patients had a mean arterial pressure above 65 mmHg. The DO₂ index (iDO₂) range in the studied population was 215 to 674 mL O₂/min per m. The mean mixed venous oxygen saturation value was 61% ± 10%, mean cardiac index was 3.4 ± 0.9 L/min per m, and blood lactate level was 4.6 ± 2.7 mmol/L. Steady-state StO₂ significantly correlated with iDO₂, arterial and venous O₂ content, and O₂ extraction ratio. A StO₂ cutoff value of 75% predicted iDO₂ below 450, with a sensitivity of 0.9 and a specificity of 0.9. In patients in septic shock and normalized MAP, low StO₂ reflects extremely low iDO₂. Steady-state StO₂ does not correlate with moderately low iDO₂, indicating poor sensitivity of StO₂ to rule out hypoperfusion.

Peripheral tissue oxygenation improves during ED treatment of acute heart failure

Objective The objective of the study was to quantitatively characterize peripheral tissue microvascular oxygenation during emergency department (ED) treatment of acute heart failure (HF). Methods This prospective, observational study enrolled acutely decompensated HF patients presenting to an urban ED and stable, asymptomatic HF patients evaluated in an outpatient cardiology clinic. Stable, pre-ED treatment, and post-ED treatment microvascular oxygen extraction ratios (OER Ms) were calculated, defined as SaO 2 − StO 2/0.8*SaO 2, where SaO 2 is pulse oximetry–derived arterial hemoglobin saturation and StO 2 is the tissue hemoglobin oxygen saturation measured with differential absorption spectroscopy. The OER M measurements were analyzed using repeated-measures analysis of variance. Pulse oximetry, patient demographics, HF etiology, serum B-type natriuretic peptide, and hemoglobin were measured along with a visual analogue scale to assess patient baseline characteristics and response to ED treatment ( P < .05 was considered significant for all testing). Results The OER M for the stable HF group (n = 45) was 0.65 (SE = 0.07). The pre- and posttreatment OER Ms for the ED HF group (n = 46) were 0.92 (SE = 0.07) and 0.75 (SE = 0.06), respectively. Whereas the pretreatment ED OER M was higher than the stable patient OER M ( P = .001), the posttreatment ED OER M was not significantly different from the stable patient measurement ( P = .271). Conclusions Oxygen extraction in acute HF is significantly increased, but approaches values found in the stable HF population after ED treatment. The OER M may deserve closer examination as a possible goal-directed variable in the treatment of acute HF.

Ascites in Adult Patients With Cyanotic Congenital Heart Disease

Hematologic, neurologic, renal, and rheumatic complications in patients with cyanotic congenital heart disease are well known. However, the effects of this condition on the liver are poorly described. Between April 2005 and April 2010, 25 adults with cyanotic congenital heart disease were studied to determine clinical history, liver ultrasonographic data, and liver histological presentation. Twenty-five patients, with a median age of 28.7 ± 8.3 years and a basal tissue hemoglobin oxygen saturation of 83.3% ± 6.8%, were studied. Liver ultrasonographic examination showed abnormalities in 10 of 20 patients (50%): 6 patients (30%) had hepatomegaly, 2 patients (10%) heterogeneous parenchyma echo pattern, and 2 patients (10%) increased portal echogenicity. Ascites was found in 7 patients (28%): 4 patients had refractory ascites and 3 patients anasarca. Patients with anasarca responded well to oral and intravenous furosemide, but those with isolated ascites did not. No data to indicate severe ventricular dysfunction or severe valve regurgitation were seen. In patients with refractory ascites who had therapeutic paracentesis, serum-ascites albumin gradient in ascites was greater than 1.1 g/dL. No significant association was found between patients with or without ascites when laboratory data and New York Heart Association functional class were compared. Liver biopsy was performed in 6 patients (24%). The most remarkable liver histological finding, in those with refractory ascites, was the existence of periportal fibrosis associated with sinusoidal dilatation. Periportal liver fibrosis associated with congestive heart failure, sepsis, or a long-term Fontan procedure can trigger refractory ascites formation.

Tissue oxygenation measured with near-infrared spectroscopy during normobaric and hyperbaric oxygen breathing in healthy subjects

To evaluate the possibility of using near-infrared spectroscopy (NIRS) to measure tissue oxygenation (StO(2)) during hyperbaric oxygen (HBO) therapy. Nine healthy volunteers (1 female) age 25-37 years, breathed air or oxygen. Tissue oxygenation was measured using NIRS on the thumb. Subjects were blinded to breathing gas. A range of partial pressures of oxygen were administered in 10-min intervals: 21, 101, 21 kPa (compression to 280 kPa), 59, 280, 59 (decompression), 21 kPa. Data were averaged over last 5 min at each pressure. When switching from air to normobaric oxygen (NBO 101 kPa) StO(2) increased from 83% (82-85%, median and interquartile range) to 85% (84-87%) (P < 0.01), while when switching from air at pressure (59 kPa O(2)) to HBO (280 kPa), StO(2) increased from 85% (85-86%) to 88% (87-89%) (P < 0.001). There was no difference between baseline StO(2) while air breathing before NBO or after decompression. Values did not reach the maximal value of 100% at any point. The changes in hemoglobin oxygen saturation in tissue registered by the NIRS monitor when switching from air to oxygen followed inspired PO(2) under normobaric and hyperbaric conditions.

Mucosal and serosal changes after gastric stapling determined by a new “real-time” surface tissue oxygenation probe: a pilot study

Background Although tissue ischemia at surgical anastomoses can cause leakage, stricture, and ulceration, surgeons rely on nonquantitative measures of detecting ischemia (e.g., color changes, pulsation), which are not likely to detect transient or small degrees of ischemia. A new microvascular tissue oximeter probe (T-Stat) provides noninvasive real-time measurement of tissue hemoglobin oxygen saturation (StO 2). We measured local gastric StO 2 during stapling for transection/pouch creation to assess the reproducibility of measurements, the sensitivity of the mucosa versus serosa to ischemia, and the effect of the proximity to the staple line on the measurement. Methods Anesthetized adult swine (n = 8) underwent laparotomy to transect gastric tissue in vivo with measurements made in 2 locations using 4.8-mm staple height cartridges. Results Both mucosal and serosal StO 2 decreased significantly when measured adjacent to the staple line compared with baseline (mucosa 3.0% ± 5.6% versus 42.1% ± 13.5%, serosa 48.2% ± 15.1% versus 64.9% ± 7.6%, P <.05). No significant change was found in the mucosal or serosal StO 2 at baseline compared with 2 cm away (mucosa 42.1% ± 13.5% versus 32.3% ± 18.7%, serosa 64.9% ± 7.6% versus 59.9 ± 9.4; P >.05). No color or pulsation changes were observed. Conclusion Although significant reproducible mucosal and serosal decreases in StO 2 were seen in proximity to the gastric staple lines, the decrease in mucosal StO 2 was dramatic in the absence of any visible changes. The persistence of tissue ischemia with gastric stapling or in the creation of an anastomosis might contribute to the development of complications. The use of a real-time, noninvasive tissue probe could ultimately assist surgeons in identifying patients at risk of complications.

Tissue Oxygenation Monitoring in the Field: A New EMS Vital Sign

A tissue hemoglobin oxygen saturation (STO2) monitor was created to assess the perfusion status of a peripheral muscle bed using near infrared light to directly measure oxygen saturation in the microcirculation. Hypoperfusion has been noted when the STO2 is <75%. The use of this technology has not been tested in the prehospital setting. This pilot study was performed to assess the technology's ease of use in the field and to correlate STO2 readings with patient outcomes. Hospital-based transport vehicles were equipped with STO2 monitors and personnel were asked to evaluate the functionality of the technology. Initial, average, and minimal STO2 values were collected and compared with data of the trauma registry. Forty five of 55 surveys were returned with 100% reporting ease of use and no reports of interference with monitors or avionics. Monitoring length averaged 16.9 minutes +/- 6.9 minutes. Forty-one patients had complete data sets and five deaths were reported for a mortality rate of 12%. STO2 endpoints revealed and increased risk of death for every 10% decrease in STO2. The STO2 monitor can easily be used in the prehospital environment. In addition, initial recordings were significantly different between survivors and nonsurvivors with every 10% decrease in STO2 increasing mortality threefold. This monitor seems to give the prehospital provider a noninvasive tool for assessment of hypoperfusion in the field and may allow for earlier resuscitative efforts to commence.

Real-time probe measurement of tissue oxygenation during gastrointestinal stapling: mucosal ischemia occurs and is not influenced by staple height

Tension, ischemia, and technical error are factors leading to anastomotic complications such as leak, stricture, and ulceration with bleeding. Currently, surgeons evaluate tissue ischemia without any simple routine measurement technique. A new tissue surface probe, T-Stat 303, provides continuous measurement of tissue hemoglobin oxygen saturation (StO(2)) and may have clinical utility for intraoperative assessment of blood flow in areas of surgical anastomosis. This pilot study aimed to determine local StO(2) during gut stapling using various staple sizes for the purpose of assessing the tool's ability to measure changes and the reproducibility of those changes with stapling. Measurements were made in nine anesthetized adult swine during laparotomy. Various staple heights were used to transect small bowel and colon. Serosal and mucosal surface measurements were obtained at baseline and on each side of the transection using the T-Stat device adjacent to the staple line and 2 cm away from it. Both small bowel and colon mucosal StO(2) adjacent to the staple line showed significant ischemia compared with baseline (p < 0.001) and 2 cm away from the staple line (p < 0.001) using all staple heights. The serosa of both small bowel and colon adjacent to the staple line was not significantly different from baseline serosa (p > 0.11) except when the grey stapler was used (baseline, 58 +/- 6.6 vs. staple line, 51 +/- 15.1; p = 0.022). The baseline mucosa of the small bowel and colon did not differ from mucosa 2 cm away from the staple line (p > 0.08). The small bowel serosa 2 cm away from the staple line did not differ from baseline mucosa, whereas the colon serosa 2 cm away significantly increased after stapling compared with baseline mucosa (p < 0.012). No statistically significant StO(2) difference was found between the various staple load sizes. Mucosal ischemia occurs after gastrointestinal stapling and is not affected by various staple heights. The T-Stat probe provides a real-time method for assessment of gut ischemia by surgeons during surgical procedures.

Monitoring trauma and intensive care unit resuscitation with tissue hemoglobin oxygen saturation

IntroductionThe purpose of the present review is to review our experience with near-infrared spectroscopy (NIRS) monitoring in shock resuscitation and predicting clinical outcomes.MethodsThe management of critically ill patients with goal-oriented intensive care unit (ICU) resuscitation continues to evolve as our understanding of the appropriate physiologic targets improves. It is now recognized that resuscitation to achieve supranormal indices is not beneficial in all patients and may precipitate abdominal compartment syndrome.ResultsOver the years, ICU technology has provided physicians with specific physiologic parameters to guide shock resuscitation. Throughout this time, the tissue hemoglobin oxygen saturation (StO2) monitor has emerged as a non-invasive means to obtain reliable physiologic parameters to guide clinicians' resuscitative efforts. StO2 monitors have been shown to aid in early identification of nonresponders and to predict outcomes in hemorrhagic shock and ICU resuscitation. These data have also been used to better understand and refine existing resuscitation protocols. More recently, use of NIRS technology to guide resuscitation in septic shock has been shown to predict outcomes in high-risk patients.ConclusionsStO2 is an important tool in identifying high-risk patients in septic and hemorrhagic shock. It is a non-invasive means of obtaining vital information regarding outcome and adequacy of resuscitation.

Broadband diffuse optical spectroscopy assessment of hemorrhage- and hemoglobin-based blood substitute resuscitation

Hemoglobin-based oxygen carriers (HBOCs) are solutions of cell-free hemoglobin (Hb) that have been developed for replacement or augmentation of blood transfusion. It is important to monitor in vivo tissue hemoglobin content, total tissue hemoglobin [THb], oxy- and deoxy-hemoglobin concentrations ([OHb], [RHb]), and tissue oxygen saturation (S(t)O(2)=[OHb][THb]x100%) to evaluate effectiveness of HBOC transfusion. We designed and constructed a broadband diffuse optical spectroscopy (DOS) prototype system to measure bulk tissue absorption and scattering spectra between 650 and 1000 nm capable of accurately determining these tissue hemoglobin component concentrations in vivo. Our purpose was to assess the feasibility of using DOS to optically monitor tissue [OHb], [RHb], S(t)O(2), and total tissue hemoglobin concentration ([THb]=[OHb]+[RHb]) during HBOC infusion using a rabbit hypovolemic shock model. The DOS prototype probe was placed on the shaved inner thigh muscle of the hind leg to assess concentrations of [OHb], [RHb], [THb], as well as S(t)O(2). Hemorrhagic shock was induced in intubated New Zealand white rabbits (N=6) by withdrawing blood via a femoral arterial line to 20% blood loss (10-15 cckg). Hemoglobin glutamer-200 (Hb-200) 1:1 volume resuscitation was administered following the hemorrhage. These values were compared against traditional invasive measurements, serum hemoglobin concentration (sHGB), systemic blood pressure, heart rate, and blood gases. DOS revealed increases of [THb], [OHb], and tissue hemoglobin oxygen saturation after Hb-200 infusion, while blood total hemoglobin values continued did not increase; we speculate, due to hyperosmolality induced hemodilution. DOS enables noninvasive in vivo monitoring of tissue hemoglobin and oxygenation parameters during shock and volume expansion with HBOC and potentially enables the assessment of efficacy of resuscitation efforts using artificial blood substitutes.

Tissue hemoglobin index: a non-invasive optical measure of total tissue hemoglobin

IntroductionThe tissue hemoglobin index (THI) is a hemoglobin signal strength metric provided on the InSpectra™ StO2 Tissue Oxygenation Monitor, Model 650. There is growing interest regarding the physiologic meaning of THI and whether a clinically useful correlation between THI and blood hemoglobin concentration exists. A series of in vitro and in vivo experiments was performed to evaluate whether THI has potential utility beyond its primary purpose of helping InSpectra™ device users optimally position a StO2 sensor over muscle tissue.MethodsThe THI and tissue hemoglobin oxygen saturation (StO2) were measured using the InSpectra™ StO2 Tissue Oxygenation Monitor, Model 650, with a 15 mm optical sensor. A THI normal reference range was established in the thenar eminence (hand) for 434 nonhospitalized human volunteers. In 30 subjects, the thenar THI was also evaluated during 5-minute arterial and venous blood flow occlusions, and with blood volume exsanguination in the hand induced with an Esmarch bandage. In addition, correlation of the THI to blood total hemoglobin concentration (Hbt) was studied in five pigs whose Hbt was isovolumetrically diluted from 13 to 4 g/dl systemically and 0.5 g/dl locally in the hind limb. The sensitivity and specificity of the THI to measure tissue hemoglobin concentration (THC) were characterized in vitro using isolated blood tissue phantoms.ResultsIn human thenar tissue, the average THI was 14.1 ± 1.6 (mean ± standard deviation). The THI extrapolated to 100% blood volume exsanguination was 3.7 ± 2.0 units presumably from myoglobin. On average, the THI increased 1.5 ± 1.0 units with venous occlusion and decreased 4.0 ± 2.0 units with arterial occlusion. In porcine hind limbs, the THI weakly correlated with Hbt (r2 = 0.26) while ΔTHI during venous occlusion had a stronger correlation (r2 = 0.62). In vitro tests indicated that THI strongly correlated (r2 > 0.99) to phantom THC and was insensitive to StO2 changes.ConclusionsSteady-state THI values do not reliably indicate Hbt. The THI is a reproducible quantitative index for THC, and THI trends can discriminate between arterial or venous blood flow occlusions. The THI magnitude permits the estimation of myoglobin's contribution to StO2.

Near-infrared tissue oximetry of beef longissimus muscle for the improvement of meat color and meat color stability (2009)

Introductioncolor as perceived by consumers serves as a valuable guide for assessing overall quality and wholesomeness of meat. The bright cherry-red color of beef is influenced by tissue oxygen consumption, obstacles to oxygen diffusion, and thickness of the oxymyoglobin layer. The dynamics of meat color depend on several physical properties of muscle including myoglobin redox status and concentration. Physical, chemical, and anatomical differences in muscles cause large variations in color from cut to cut, within a cut, and in cuts made parallel or perpendicular to muscle fibers. Clearly, muscle fiber orientation affects measurements of tenderness and cooking yields; however, variations in myoglobin redox dynamics, oxygen penetration, and color stability due to muscle fiber orientation (parallel or perpendicular) are not well documented. Among the various meat color measurement techniques available, near-infrared (NIR) methods have the advantages of being nondestructive, rapid, inexpensive, and adaptable for online measurements. The NIR tissue oximeter is a relatively new biomedical device that has been used in exercise physiology and in medicine to measure hemoglobin and myoglobin oxygen saturation in brain tissue and cardiac and skeletal muscle. This instrument seems to have promise for use in measuring inherent properties of meat that are related to meat color stability. NIR tissue oximetry may provide continuous real-time measurements of changes in myoglobin oxygen status, thus providing information on tissue oxygenation and hemodynamics. The unique feature of the tissue oximeter is that it uses the theory of photon migration through tissue, allowing for absolute measurement of absorption in, for example, human or animal tissue. If the NIR absorption properties of any chromophore are known, quantitative analysis of color compounds is possible without constant calibration and validation. We are not aware of any research in which NIR tissue oximetry has been used to evaluate color of post-rigor meat. This study was designed to evaluate whether NIR tissue oximetry has promise for measuring meat properties related to meat color. Specific objectives were to determine: (1) effects of parallel vs. perpendicular muscle fiber orientation of meat cuts on NIR measurements, (2) amounts of deoxymyoglobin (DMb), oxymyoglobin (OMb), and total myoglobin (TMb) in the superficial and subsurface layers of beef muscle (longissimus) stored in several packaging formats, and (3) tissue oximeter responses to post-rigor muscle fiber orientation and surface measures of color.

Is thenar tissue hemoglobin oxygen saturation in septic shock related to macrohemodynamic variables and outcome?

IntroductionThe study objectives were to evaluate septic shock-induced alterations in skeletal muscle hemoglobin oxygenation saturation (StO2) using near-infrared spectroscopy (NIRS) and forearm skin blood flow velocity using laser Doppler (LD) to determine the relationship of macroperfusion and microperfusion parameters, and to test the relationship of the worst NIRS parameters during the first 24 hours of shock with 28-day prognosis.MethodsA prospective, observational study was performed in a 21-bed university hospital surgical intensive care unit. Forty-three septic shock patients with at least another organ failure underwent a 3-minute, upper arm (brachial artery) vascular occlusion test (VOT). Microperfusion parameters (thenar eminence StO2 and forearm LD skin blood flow) were collected on days 1, 2 and 3, before (baseline StO2 and LD values) and during the 3-minute VOT with calculation of occlusion and reperfusion slopes for StO2 and LD. Daily Sequential Organ Failure Assessment (SOFA) score, macrohemodynamic parameters (systolic arterial blood pressure, cardiac output (pulmonary artery catheter or transesophageal Doppler), mixed venous oxygen saturation (pulmonary artery or superior vena cava catheter)) and metabolic parameters (pH, base excess, lactate) were determined.ResultsBaseline StO2 (82% (75 to 88) vs. 89% (85 to 92), P = 0.04) and reperfusion slope (2.79%/second (1.75 to 4.32) vs. 9.35%/second (8.32 to 11.57), P < 0.0001) were lower in septic shock patients than in healthy volunteers. StO2 reperfusion slope correlated with occlusion slope (P < 0.0001), cardiac output (P = 0.01) and LD reperfusion slope (P = 0.08), and negatively with lactate level (P = 0.04). The worst StO2 reperfusion slope during the first day of shock was lower in nonsurvivors than in survivors (P = 0.003) and improved significantly the predictive value of Simplified Acute Physiology Score II and SOFA scores.ConclusionsThe alteration of StO2 reperfusion slope in septic shock patients compared with healthy volunteers was related with macrohemodynamic, microhemodynamic and metabolic parameters. The addition of the worst value of the day 1 StO2 reperfusion slope improved the outcome prediction of Simplified Acute Physiology Score II and SOFA scores.

Near-Infrared Spectroscopy in Patients with Severe Sepsis: Correlation with Invasive Hemodynamic Measurements

Clinicians have begun using near-infrared spectroscopy (NIRS) to monitor tissue perfusion in hemorrhagic shock, as the technique allows continuous noninvasive monitoring of tissue hemoglobin oxygen saturation (StO(2)) and the tissue hemoglobin index (THI). We hypothesized that StO(2) measurements in patients with severe sepsis would be associated with the severity of their illness and would correlate with invasive hemodynamic measurements. We measured mean arterial pressure (MAP), serum lactate concentration, blood hemoglobin concentration, StO(2), and THI in nine healthy volunteers and ten patients with septic shock in a surgical intensive care unit (ICU). Enrolled patients had a pulmonary artery catheter, and had family able to give informed consent. The average Acute Physiology and Chronic Health Evaluation (APACHE) II score at enrollment for the patients was 19 +/- 5 (standard deviation) points. Volunteers and patients were similar with respect to age and sex. To collect NIRS data, we used the InSpectra Tissue Spectrometer, Model 325 (Hutchinson Technology, Inc., Hutchinson, MN). For three consecutive days, we obtained invasive hemodynamic measurements three times daily, simultaneously with NIRS measurements, and metabolic cart measurements once daily. Patients with severe sepsis had significantly lower thenar muscle StO(2) values (p = 0.031) than healthy volunteers. Near-infrared spectroscopy-derived mixed venous oxygen saturation (NIRSvO(2)) and StO(2) measured from the thenar eminence in patients with severe sepsis correlated with SvO(2) from the pulmonary artery catheter (p < 0.05). In this group of patients, StO(2) did not correlate significantly with lactate concentration, base deficit, or APACHE II score. Near-infrared spectroscopic measurements of StO(2) correlated with invasive hemodynamic measurements in patients with severe sepsis but did not correlate with severity of illness. These findings suggest that NIRStO(2) may be a clinically useful measurement in monitoring patients with severe sepsis. Further study of this device in early resuscitation of patients with sepsis is necessary.

P17: Mucosal and serosal ischemia after gastric stapling as determined by a new ‘real time' non-invasive tissue surface probe measuring tissue oxygenation

Although tissue ischemia at surgical anastomoses may cause leak, stricture, and ulceration, surgeons rely on non-quantitative measures of detecting ischemia (e.g. color change, pulsation), not likely to detect transient or small degrees of ischemia. A microvascular tissue oximeter probe (T-STAT, Spectros, CA) provides non-invasive real-time measurement of tissue hemoglobin oxygen saturation (StO2). We measured local gastric StO2 during stapling for transection/pouch creation to assess the reproducibility of measurements, sensitivity of the mucosa versus serosa to ischemia, and the impact of proximity to the staple line.

Massive Transfusion in Trauma Patients: Tissue Hemoglobin Oxygen Saturation Predicts Poor Outcome

Severely bleeding trauma patients requiring massive transfusion (MT) often experience poor outcomes. Our purpose was to determine the potential role of near infrared spectrometry derived tissue hemoglobin oxygen saturation (StO2) monitoring in early prediction of MT, and in the identification of those MT patients who will have poor outcomes. Data from a prospective multi-institution StO2 monitoring study were analyzed to determine the current epidemiology of MT (defined as transfusion volume >/=10 units packed red blood cells in 24 hours of hospitalization). Multivariate logistic regression was used to develop prediction models. Seven US level I trauma centers (TC) enrolled 383 patients. 114 (30%) required MT. MT progressed rapidly (40% exceeded MT threshold 2 hours after TC arrival, 80% after 6 hours). One third of MT patients died. Two thirds of deaths were due to early exsanguination and two thirds of early exsanguination patients died within 6 hours. One third of the early MT survivors developed multiple organ dysfunction syndrome. MT could be predicted with standard, readily available clinical data within 30 minutes and 60 minutes of TC arrival (area under the receiver operating characteristic curve = 0.78 and 0.80). In patients who required MT, StO2 was the only consistent predictor of poor outcome (multiple organ dysfunction syndrome or death). MT progresses rapidly to significant morbidity and mortality despite level I TC care. Patients who require MT can be predicted early, and persistent low StO2 identifies those MT patients destined to have poor outcome. The ultimate goal is to identify these high risk patients as early as possible to test new strategies to improve outcome. Further validation studies are needed to analyze appropriate allocation and study appropriate use of damage control interventions.

Tissue hemoglobin monitoring of progressive central hypovolemia in humans using broadband diffuse optical spectroscopy

We demonstrate noninvasive near-infrared diffuse optical spectroscopy (DOS) measurements of tissue hemoglobin contents that can track progressive reductions in central blood volume in human volunteers. Measurements of mean arterial blood pressure (MAP), heart rate (HR), stroke volume (SV), and cardiac output (Q) are obtained in ten healthy human subjects during baseline supine rest and exposure to progressive reductions of central blood volume produced by application of lower body negative pressure (LBNP). Simultaneous quantitative noninvasive measurements of tissue oxyhemoglobin (OHb), deoxyhemoglobin (RHb), total hemoglobin concentration (THb), and tissue hemoglobin oxygen saturation (S(t)O(2)) are performed throughout LBNP application using broadband DOS. As progressively increasing amounts of LBNP are applied, HR increases, and MAP, SV, and Q decrease (p<0.001). OHb, S(t)O(2), and THb decrease (p<0.001) in correlation with progressive increases in LBNP, while tissue RHb remained relatively constant (p=0.378). The average fractional changes from baseline values in DOS OHb (fOHb) correlate closely with independently measured changes in SV (r(2)=0.95) and Q (r(2)=0.98) during LBNP. Quantitative noninvasive broadband DOS measurements of tissue hemoglobin parameters of peripheral perfusion are capable of detecting progressive reductions in central blood volume, and appear to be sensitive markers of early hypoperfusion associated with hemorrhage as simulated by LBNP.

Diffuse optical imaging of the healthy and diseased breast: A systematic review

Screening X-ray mammography is limited by false positives and negatives leading to unnecessary physical and psychological morbidity. Diffuse Optical Imaging using harmless near infra red light, provides lesion detection based on functional abnormalities and represents a novel diagnostic arm that could complement traditional mammography. Reviews of optical breast imaging have not been systematic, are focused mainly on technological developments, and have become superseded by rapid technological advancement. The aim of this study is to review clinically orientated studies involving approximately 2,000 women in whom optical mammography has been used to evaluate the healthy or diseased breast. The results suggest that approximately 85% of breast lesions are detectable on optical mammography. Spectroscopic resolution of tissue haemoglobin composition and oxygen saturation may improve the detectability of breast diseases. Results suggest that breast lesions contain approximately twice the haemoglobin concentration of background tissue. Current evidence suggests that it is not possible to distinguish benign from malignant disease using optical imaging techniques in isolation. Methods to improve the performance of Diffuse Optical Imaging, such as better spectral coverage with additional wavelengths, improved modelling of light transport in tissues and the use of extrinsic dyes may augment lesion detection and characterisation. Future research should involve large clinical trials to determine the overall sensitivity and specificity of optical imaging techniques as well as to establish patient satisfaction and economic viability.