Changes In Tissue Oxygen Saturation Research Articles

Oxygen Saturation Increase in Ischemic Wound Tissues after Direct and Indirect Revascularization.

The primary approach for treating ischemic wounds is restoring oxygen supply to the ischemic region. While direct angiosomal revascularization is often associated with better post-operative wound healing and limb salvage, its superiority over non-angiosomal revascularization remains controversial. This study aimed to compare intraoperative tissue oxygen saturation changes in ischemic zones following either direct or indirect revascularization in below-the-knee arteries. This prospective observational study included patients undergoing direct and indirect below-the-knee endovascular revascularizations. Assignment to the groups was not randomized. Near-infrared spectroscopy was used to monitor rSO2 changes near the ischemic wounds intraoperatively. The changes were compared between the groups. 15 patients (50%) underwent direct angiosomal revascularization, while an equal number of patients underwent indirect revascularization. Overall, a statistically significant increase in regional oxygen saturation was observed after revascularization (p = 0.001). No statistically significant difference was found between the direct and indirect revascularization groups (p = 0.619). This study revealed a minor difference in the oxygen saturation increase between the angiosomal and non-angiosomal revascularization groups. Such a finding indicates that the clinical significance of angiosomal revascularization is negligible and might be concealed by confounding factors, such as the vessel diameter and outflow impact on the restenosis rate.

Reduced oxygen desaturation in the vastus lateralis of chronic stroke survivors during graded muscle contractions

ABSTRACT Background Few studies have examined changes in skeletal muscle physiology post-stroke. This study examined changes in tissue oxygen saturation (StO2) of the vastus lateralis (VL) muscle of stroke survivors and age-matched control participants during maximal and submaximal isometric contractions of the knee extensor muscles. Objectives We hypothesized that tissue oxygen desaturation (ΔStO2) during knee extensor muscle contractions would be less in the VL in the paretic vs. the non-paretic and control legs. Methods Ten chronic stroke survivors (>6 months post-stroke) with lower extremity muscle weakness and 10 age-matched controls completed this prospective cohort study. Maximum voluntary contractions (MVCs) of the knee extensor muscles were assessed with a Biodex dynamometer and StO2 of the VL was measured using near-infrared spectroscopy. Results In the paretic leg of the stroke survivors little change in StO2 of the VL was observed during an MVC (ΔStO2 = -1.7 ± 1.8%) compared to the non-paretic (ΔStO2 = -5.1 ± 6.1%; p < 0.05) and control legs (ΔStO2 = -14.4 ± 8.8%; p < 0.05 vs. paretic and non-paretic leg). These differences remained when normalizing for strength differences between the legs. Compared to controls, both the paretic and non-paretic VL showed pronounced reductions in ΔStO2 during ramp and hold contractions equal to 20%, 40%, or 60% of the MVC (p < 0.05 vs. controls at all load levels). Conclusions These results indicate that oxygen desaturation in response to isometric muscle contractions is impaired in both the paretic and non-paretic leg muscle of stroke survivors compared to age-matched controls, and these differences are independent of differences in muscle strength.

Cerebral near-infrared spectroscopy monitoring to predict periventricular-intraventricular haemorrhage and neurodevelopmental outcomes in preterm infants: a protocol for a systematic review and meta-analysis

IntroductionPeriventricular-intraventricular haemorrhage (PV-IVH) is one of the major cause of mortality and long-term neurodevelopmental sequela in preterm infants born at less than 32 weeks of gestation. Near-infrared spectroscopy (NIRS) monitoring...

Measurement of tissue oxygen saturation during arthroscopic surgery of knee with a tourniquet.

Tourniquets provide better tissue visibility during arthroscopic surgery. However, multiple postoperative adverse events associated with ischemia may be caused by excessive inflation pressure and duration. We aimed to evaluate the degree of tourniquet-induced ischemia using a noninvasive continuous real-time monitoring method and the relationship between changes in tissue oxygen saturation (StO2) and blood biochemical markers of ischemic injuries in patients undergoing arthroscopic knee surgery. This was a prospective observational study using near-infrared spectroscopy (NIRS). Data were collected from 29 consecutive patients who underwent arthroscopic procedures. Twenty-five patients underwent anterior cruciate ligament reconstruction, and four underwent meniscal repair. We investigated tourniquet-induced changes in StO2, monitored using NIRS, and blood biochemical markers of ischemic injuries. A significant decrease in the mean StO2 from the baseline was observed during tourniquet inflation in the operative legs. The average decrease in the mean StO2 was 58%. A comparison of mean StO2 between the nonoperative and operative legs before tourniquet deflation showed that mean values of StO2 in the operative legs were significantly lower than those in the nonoperative legs. No significant clinical relationships were observed between changes in StO2 and blood biochemical markers of ischemic injuries (creatine kinase) (p = 0.04, r = 0.38) or tourniquet duration (p = 0.05, r = 0.366). Our results demonstrated that StO2 could be used to evaluate tissue perfusion in real time but did not support the hypothesis that StO2 is a useful method for predicting the degree of tourniquet-induced injury during arthroscopic knee surgery.

Evaluation of distal skin temperature and tissue oxygen saturation determined by near-infrared spectroscopy for predicting ultrasound-guided lateral infraclavicular block success.

Changes in tissue oxygen saturation determined by near-infrared spectroscopy (NIRS) may help predict and determine the success of a lateral infraclavicular (LIC) block.We investigated whether evaluation of tissue oxygen saturation determined by NIRS couldbe an indicator of LIC block success. Forty patients scheduled for hand or forearm surgery under LIC block were studied. NIRS sensors were placed on the ventral aspect of both mid-forearms, and the contralateral hand was used as the control group. NIRS values were recorded before the block andat regular intervals during the following 30 min. NIRS values were significantly higher in the successfully blocked patients whencompared to the complete failure, partial failure, and contralateral hand groups at the 10thmin. In the successfully blocked patients, NIRS values (mean ± SD [change in %]) increasedby 11.09 ± 4.86 (16.03%), 15.00 ± 4.53 (21.76%), 16.35 ± 5.14 (23.77%), 16.38 ± 4.88(23.85%), 16.67 ± 5.04 (24.29%), and 16.96 ± 5.71 (24.78%), respectively, from baselineto 5, 10, 15, 20, 25, and 30 min. ΔTs values were significantly higher in the successfullyblocked patients than in the complete failure patients and contralateral hand at the 30thmin. However, there was no statistically significant difference when comparing ΔTs values ofsuccessful block and partial failure block patients at the 30th min. We conclude that measurement of tissue oxygen saturation by NIRS withinthe scope of evaluation of the lateral infraclavicular block is a rapid, effective, and applicabletechnique.

The Effects Of Acute Consumption Of A Brewed Cocoa Beverage On Endothelial Function

Previous studies have shown that the polyphenol components of cocoa can improve the health and function of blood vessels. It is currently unknown whether consuming a brewed drink made from roasted cocoa beans has the same beneficial effects on blood vessel function. PURPOSE: The purpose of this study was to assess the acute effects of consuming brewed cocoa on resting blood pressure and endothelial function using near-infrared spectroscopy (NIRS) to evaluate changes in tissue oxygen saturation (StO2) following blood vessel occlusion. METHODS: A total of 15 healthy college-aged adults participated in this study. StO2 levels were monitored continuously throughout the test using a NIRS device placed on the flexor digitorum profundus of the dominant arm. Baseline StO2 levels were measured for 5 minutes following 10 minutes of supine rest, after which blood flow to the forearm was occluded for 3 minutes using a blood pressure cuff inflated to 50mmHg above resting systolic pressure, followed by a 5-minute period of reperfusion following release of the cuff. Subjects then consumed either plain water, or the cocoa treatment (40g of roasted cocoa brewed for 10 minutes), and all testing was repeated 90 minutes later. Subjects returned to the lab on a separate day to repeat the test using the opposite beverage. RESULTS: The change from baseline was not significantly different between water (W) and cocoa (C) for resting heart rate (C= -6.6+6.5 bpm, W= -4.4+7.0 bpm; p=0.29), resting systolic blood pressure (C= 0.9+4.5 mmHg, W= -2.2+7.4 mmHg; p=0.10), resting diastolic blood pressure (C= -1.1+6.7 mmHg, W= 0.8+4.5 mmHg; p=0.39), pre-occlusion StO2 (C= 1.6+5.6 %, W= -1.9+6.9%; p=0.06), minimum StO2 during occlusion (C= -0.6+10.5 %, W= -0.7+12.8%; p=0.98), reperfusion maximum StO2 (C= 0.5+3.6 %, W= -0.8+5.0 %; p=0.40), or reperfusion rate quantified as the slope of the StO2 during the first 10 seconds of reperfusion (C= 0.1+0.4 % s-1, W= 0.06+0.4 % s-1; p=0.79). CONCLUSION: Consumption of a brewed cocoa drink does not significantly affect markers of endothelial function or blood pressure in healthy college-aged adults.

Tissue oxygen saturation changes and postoperative complications in cardiac surgery: a prospective observational study

BackgroundCardiac surgery with extracorporeal circulation (ECC) can induce microvascular dysfunction and tissue hypoperfusion. We hypothesized that the alterations in near-infrared spectroscopy (NIRS)-derived parameters would be associated with post-operative complications in cardiac surgery patients.MethodsProspective observational study performed at two University Hospitals. Ninety patients undergoing cardiac surgery with ECC were enrolled. The NIRS sensor was applied on the thenar eminence. A vascular occlusion test (VOT, 3-min ischemia) was performed at baseline (t0), at Intensive Care Unit (ICU) admission (t1), 3 (t2) and 6 (t3) hours later. Baseline tissue oxygen saturation (StO2), oxygen extraction rate and microvascular reactivity indices were calculated.ResultsIn the first hours after cardiac surgery, StO2 tended to increase (86% [80–89] at T3 versus 82% [79–86] at T0, p = ns), while both tissue oxygen extraction and microvascular reactivity tended to decrease, as indicated by increasing occlusion slope (− 8.1%/min [− 11.2 to − 7] at T3 versus − 11.2%/min [− 13.9 to − 7.9] at T0, p = ns) and decreasing recovery slope (1.9%/sec [1.1–2.9] at T3 versus 3.1%/sec [2.3–3.9] at T0, p = ns). No substantial differences were found in NIRS-derived variables and their changes over time between patients with complications and those without complications.ConclusionsPeripheral tissue oxygen extraction and microvascular reactivity were reduced during the first hours after cardiac surgery. NIRS-derived parameters were not able to predict complications in this population of cardiac surgery patients.

Hyperspectral near-infrared spectroscopy assessment of the brain during hypoperfusion.

.Two-thirds of out-of-hospital cardiac arrest patients, who survive to hospital admission, die in the hospital from neurological injuries related to cerebral hypoperfusion. Therefore, noninvasive real-time monitoring of the cerebral oxygen metabolism in cardiac arrest patients is extremely important. Hyperspectral near-infrared spectroscopy (hNIRS) is a noninvasive technique that measures concentrations of the key chromophores in the brain, such as oxygenated hemoglobin, deoxygenated hemoglobin, and cytochrome C oxidase (CCO), an intracellular marker of oxygen consumption. We tested hNIRS on 10 patients undergoing transcatheter aortic valve insertion, where rapid ventricular pacing (RVP) is required to temporarily induce sudden hypotension and hypoperfusion that mimic cardiac arrest. Using multidistance hNIRS, we found that tissue oxygen saturation changes in the cerebral tissue were lower than those in the scalp during RVP. CCO redox changes were detected in cerebral tissue but not in the scalp during RVP. We have demonstrated that hNIRS is feasible and can detect sudden changes in cerebral oxygenation and metabolism in patients during profound hypotension.

Assessing changes in tissue oxygenation by near-infrared spectroscopy following brachial plexus block for arteriovenous fistula surgery: A prospective observational pilot study.

Near-infrared spectroscopy (NIRS) can be used to measure tissue oxygen saturation (StO2) in different sites and in a wide range of clinical scenarios. Peripheral regional anaesthesia induces vascular changes causing increased arterial blood flow and venodilatation, but its effect on StO2 is still under debate. This is especially so for patients undergoing arteriovenous fistula surgery, wherein latest data suggest an improved outcome under brachial plexus block (BPB) compared with local anaesthesia, but no data are available. The aim of this study was to investigate changes in StO2 following BPB prior to arteriovenous fistula surgery using NIRS. A prospective observational study. A secondary teaching hospital from August 2016 to March 2017. Fifteen patients undergoing arteriovenous fistula surgery. Ultrasound-guided BPB in 15 patients undergoing arteriovenous fistula surgery. StO2 at baseline and compared with baseline and the contralateral arm following BPB measured using NIRS of the thenar eminence (NIRSth). Baseline values of StO2 assessed by NIRSth were 42.6 ± 7.7% in the arteriovenous fistula arm and 42.7 ± 9.7% in the contralateral arm. There was no significant difference between the two. Five minutes after BPB, there was a significant increase in StO2 of the blocked arm, compared with the control arm expressed as difference of absolute values (7.1 ± 9.7%). At 60 min, an absolute difference of 21.0 ± 13.5% was reached. The absolute increase in StO2 of the blocked arm compared with baseline reached significance after 5 min (8.8 ± 4.6%) and increased up to 23.2 ± 8.2% after 60 min. NIRSth indicates that BPB significantly increases StO2 of the arteriovenous fistula arm in patients undergoing haemodialysis. Clinicaltrials.gov: NCT03044496.

Regional cerebral tissue oxygen saturation changes following blood transfusion in neuro-intensive care unit patients-a pilot observational study.

Although central venous oxygen saturation (ScvO2 ) is used to decide on red blood cell (RBC) transfusion, whether its improvement is associated with parallel improvement in cerebral oxygenation is not adequately studied. This study looked at changes in regional cerebral tissue oxygen saturation (rSO2 ) following RBC transfusion in neuro-intensive care unit (ICU) patients. In this prospective observational pilot study, rSO2 was measured in adult neuro-ICU patients before RBC transfusion, at the end and at 6, 12, 18 and 24 h after RBC transfusion. rSO2 measurements were taken using cerebral oximetry on both sides of the hemicraniums. Haemoglobin, central venous pressure, ScvO2 and temperature were recorded during the study period. Arterial oxygen content, central venous oxygen content and cerebral fractional oxygen extraction were calculated. Mann Whitney U test was used to study the changes in variables at baseline and at 24 h following RBC transfusion. Friedman's test was used to study changes in parameters from baseline to 24 h post-transfusion. A P value of <0·05 was considered to be significant. The data from 13 subjects were analysed. rSO2 increased significantly following RBC transfusion on both sides of the brain (P = 0·002, P = 0·007), with a corresponding decrease in cerebral fractional oxygen extraction (P = 0·001, P = 0·007). RBC transfusion increased rSO2 significantly on both sides of the brain. As patients' outcomes were not studied, whether this increase in regional cerebral oxygen saturation is beneficial or if it is because of excess DO2 is still unclear. Further studies are required to clarify this issue.

Changes in Tissue Oxygen Saturation with Well- and Tight-Fitted Compression Sleeves During an Incremental Exercise on Treadmill

Background: Effects of lower-limb compression garments on hemodynamics during walking or running remain unclear. Objectives: The purpose was to examine the changes in tissue oxygen saturation (StO2) with well- and tight-fitted compression sleeves - before, during and after an exercise on treadmill. Methods: 14 athletes came to the laboratory three times to complete the same session with or without well- (COMP) and tight-fitted (COMP+) calf compression sleeves. The session included an incremental exercise on treadmill: 2 min at each intensity - 1, 2, 3, 4, 5, 6 and 7 km/h - each was preceded and followed by a 10-minute rest in a seated position. Calf StO2 was recorded using near infrared spectroscopy before, during and after the exercise. Results: StO2 significantly increased with COMP and COMP+ before (+ 25.2 ± 2.7 % and +22.5 ± 2.7 %) and after the exercise (+ 11.0 ± 1.5 % and +10.2 ± 1.7 %). StO2 also increased while walking but declined as the intensity progressed (+ 14.6 ± 1.9 %, +11.7 ± 1.7 %, +8.5 ± 1.8 %, +8.1 ± 1.8 %, + 5.2 ± 1.7, +3.1 ± 2.0 % and -1.3 ± 4.0 % with COMP vs. +11.3 ± 2.0 %, +8.5 ± 1.7 %, +6.0 ± 1.9 %, +5.9 ± 1.7 %, + 2.9 ± 1.6 %, -0.2 ± 2.2 % and -6.5 ± 3.6 % with COMP+). With COMP+ the significance phased out earlier (2 km/h vs. 4 km/h with COMP) and was altered at 7 km/h (while the effects were trivial with COMP). The differential was considered small compared to without (Cohen’s d = - 0.38; 95 % CI -5.46 to 4.69) and COMP (d = 0.27; 95 % CI -5.30 to 5.84). Conclusions: This study gives ground to the hypothesis that wearing calf compression sleeves may be useful during prolonged efforts involving sections of low-velocity walks (i.e. < 6 km/h such as Nordic walking or ultra-trail races), by virtue of their effect on StO2. It also appears that compression sleeves could be useful in re-oxygenating tired muscles after exercise. Finally this work provides information about the modalities for using compression garments. Indeed, using very tight-fitted compression garments may alter the hemodynamics and potentially jeopardize performances.

Vascular Occlusion Test to Dynamically Assess Microcirculation During Normothermic Pulsatile Cardiopulmonary Bypass.

To evaluate parameters of the vascular occlusion test (VOT) before, during, and after pulsatile cardiopulmonary bypass (CPB). Prospective, observational study. Single-center university hospital. Adult patients undergoing elective cardiac surgery with pulsatile CPB. An oximeter sensor and adult-sized pneumatic tourniquet were positioned at the right forearm. A VOT with a predefined ischemic time of 3 minutes was performed before, during, and after CPB. Changes in tissue oxygen saturation were recorded. Thirty-four patients who underwent cardiac surgery were enrolled in the study. The lowest tissue oxygen saturation measured during the ischemic challenge differed among all 3 stages of surgery, with median values of 62.9% before, 57.5% during, and 59.3% after perfusion (p<0.05). Both occlusion (p<0.001) and reperfusion (p<0.05) slopes were steeper after bypass compared with before initiating bypass, whereas the reperfusion time remained constant among the different time points. The microcirculatory function as demonstrated by changes in VOT parameters was enhanced during and after normothermic pulsatile CPB. Clinical relevance, however, needs to be further explored.

Monitoring mesenteric tissue oxygenation with near-infrared spectroscopy during packed red blood cell transfusion in preterm infants.

To monitor altered mesenteric tissue oxygen saturation (StO2) before and after blood transfusion. We placed a 4-wavelength NIRS sensor (FORE-SIGHT, CASMED, Branford, CT USA) on the right lower abdominal quadrant prior to transfusion and measured StO2 for up to 48 hours post transfusion. Pulse oximetry (SpO2) data was collected simultaneously, with fractional tissue oxygen extraction (FTOE) and the [SpO2-StO2] difference calculated to normalize for hypoxic episodes. All data was combined and averaged in 30 minute windows for events before, during, and post transfusion to determine long term trends and analyzed using Repeated Measures ANOVA. 24 infants were enrolled in this study with 36 hours of data collected for 23 subjects and 48 hours for 16 subjects. We found no significant differences in any of the parameters when compared pre and post transfusion values at 3, 6, 12, 24 and 36 hours post transfusion. For the 16 subjects monitored to 48 hours, there was a significant decrease in FTOE and near significant increase in StO2 and reciprocal decrease in [SpO2 - StO2] at 48 hours post transfusion. There are several plausible mechanisms that may explain the relationship between necrotizing enterocolitis and PRBC transfusion; however, mesenteric tissue oxygen saturation changes did not clearly show that ischemia or re-perfusion injury to be one of the potential mechanisms.

Changes in Tissue Oxygen Saturation in Response to Different Calf Compression Sleeves.

Aim. The purpose was to examine the changes in tissue oxygen saturation (StO2) in response to the application of different commercially available calf compression sleeves. Methods. Eight subjects came to the laboratory to complete a session in seated position including 10 min of quiet rest followed by 3 min measuring calf StO2 without compression sleeves and then alternating of 3 min of passive rest and 3 min measuring StO2 with calf compression sleeves. A total of 15 different commercially available compression sleeves were studied in a randomized order. Calf StO2 was recorded using near-infrared spectroscopy. Results. StO2 was significantly increased with all compression sleeves (p < 0.05) compared with no compression (from +6.9% for the least effective to +22.6% for the most effective). Large differences were observed between compression sleeves (p < 0.05). StO2 was positively correlated with compression pressure (p < 0.05; r = 0.84). Conclusion. This study shows that wearing compression sleeves from various brands differently affects tissue oxygen saturation. Differences were linked to the compression pressure: higher compression pressures were associated with higher StO2.

Tissue oxygen saturation changes during intramedullary nailing of lower-limb fractures

The systemic complications of acute intramedullary nailing (IMN) in trauma patients are well known. There are no reliable methods available to predict these adverse outcomes. Noninvasive near-infrared spectroscopy (NIRS) allows measurement of oxygen saturation within muscle tissue (StO2) and quantification of the potential metabolic and microcirculatory effects of IMN in real time. The aim of this study was to characterize tissue oxygenation changes occurring during reamed IMN. Patients undergoing reamed IMN for fixation of a tibia or femur fracture and patients having an open reduction and internal fixation of the ankle (to control for potential effects of anesthesia) had a noninvasive NIRS probe attached to the thenar eminence of the hand. Tissue oxygenation was monitored continuously throughout the operation and digitally recorded for later analysis. Vascular occlusion tests, an established technique with the NIRS device, were performed before canal opening and after nail insertion (at equivalent times in the control group), to establish the presence and nature of changes in systemic microcirculation occurring during the duration of the operation. Tissue oxygenation data were collected on 23 patients undergoing 26 IMN. (mean [SD] age, 36 [19] years; median Injury Severity Score [ISS], 9; interquartile range, 9-12). The control group consisted of 19 patients (mean [SD] age, 41 [18] years; ISS, 4). Remote muscle tissue desaturated significantly faster after IMN compared with the control operation (mean [SD] difference in IMN desaturation rate, 1.8% per minute [2.6% per minute]; mean [SD] difference in control group desaturation rate, -0.6% per minute [1.5% per minute]; p = 0.014). Near infrared-derived muscle oxygen consumption (NIR VO(2)) was significantly increased during the course of IMN compared with the control (mean [SD] difference in IMN NIR VO(2), 19.9 [32.1]; mean [SD] difference in control NIR VO(2), -4.2 [17.9]; p = 0.041). IMN causes significant remote microcirculatory changes. The responsiveness of the microcirculation could be a predictor of secondary organ dysfunction. Epidemiologic study, level III.

Noninvasive tissue oxygen saturation determined by near‐infrared spectroscopy following peripheral nerve block

Noninvasive physiologic measurement of cutaneous tissue oxygenation using near-infrared spectroscopy (NIRS) has become increasingly common in cardiovascular and plastic surgery. The aim of this study was to determine whether clinically available NIRS-based monitors could detect changes in tissue oxygen saturation (rSO(2)) following a variety of peripheral nerve blocks. We hypothesize that peripheral nerve blocks will produce detectable changes in cutaneous tissue oxygenation levels that can be measured by noninvasive NIRS-based oximetry. Forty adult patients scheduled for pre-operative peripheral nerve block placement were enrolled. Prior to block placement, NIRS sensors were placed on the operative and nonoperative (control) limb. Baseline tissue oxygen saturation values were obtained prior to dosing of the nerve block, and measurements were recorded every 5 min thereafter. Initial rSO(2) values were higher in the operative vs. control limbs prior to nerve block placement. Tissue oxygen saturation increased in the blocked, but not control, limbs with time. Subgroup analysis suggested statistically significant differences in rSO(2) values in blocked vs. control limbs for cervical paravertebral, infraclavicular, and femoral nerve blocks. Our results demonstrated sustained increases in tissue rSO(2) values following peripheral nerve block placement, in addition to higher initial rSO(2) values in operative limbs prior to block placement. Further investigations are necessary to define the expected baseline rSO(2) values in operative and control limbs. Future efforts utilizing NIRS-based detection of tissue ischemia should consider the small but significant changes in rSO(2) resulting from a successful nerve block.

Tissue Oxygen Saturation and Outcome after Cardiac Surgery

Cardiopulmonary bypass during cardiac surgery can result in a shortfall in oxygen delivery relative to demand, marked by a decrease in muscle tissue oxygen saturation as blood flow is redistributed to vital organs. Such "tissue shock" might impair postoperative recovery. To determine the association of changes in tissue oxygen saturation with postoperative outcome in cardiac surgery patients. In 74 adults undergoing cardiac surgery, tissue oxygen saturation in the thenar eminence was recorded using near-infrared spectroscopy before and during induction of anesthesia, throughout surgery, and in the intensive care unit until extubation or for a maximum monitoring time of 24 hours. The measurements were related to postoperative outcome. Mean tissue oxygen saturation increased from 81.7% to 88.5% with induction of anesthesia and decreased to 78.9% and 69.9% during surgery and on arrival in the intensive care unit, respectively. Saturation increased to 77.8% by 6 hours after surgery and remained stable. Mean saturation during the first minutes of anesthesia and 20 minutes in the intensive care unit was lower in patients with a postoperative morbidity than in patients without such morbidity on day 15 (81.1% vs 87.6%; P = .04) and on day 3 (72.9% vs 85.5%; P = .009). No associations with other outcome measures were observed. In patients undergoing cardiac surgery, reduced tissue oxygen saturation in the thenar eminence may be associated with poor postoperative outcome. Further studies are needed to confirm these findings and to determine whether measures to improve the balance between oxygen delivery and consumption might improve both tissue oxygen saturation and outcome.

Monitoring of Free Flaps Using Near-Infrared Spectroscopy: A Systematic Review of the Initial Trials

Sir: Free tissue transfer is now a routine procedure in reconstructive surgery. Arterial and venous occlusions are common complications requiring revision surgery and flap salvage. Flap salvage rates remain approximately 50 percent,1 and salvage of the affected tissue depends largely on the time to reexploration. Assessing the viability of tissues by monitoring circulatory changes during harvesting and following transfer of free flaps is essential. Devices designed to augment clinical assessment (standard method) could lead to prompt surgical intervention and improved salvage rates. Popular adjuvant techniques include external and implantable Doppler monitoring and laser Doppler flowmetry.2 However, no method has proven to be more reliable than clinical assessment, and this supports the need to seek alternatives.1 Near-infrared spectroscopy exploits the relative transparency of biological tissue in the near-infrared wavelength range. Near-infrared light is capable of penetrating tissue and can still be detected on remission, following absorption by the primary light-absorbing molecules (chromophores) in biological tissues, oxyhemoglobin and deoxyhemoglobin. These chromophores have different absorption spectra in the near-infrared wavelength range (600 to 900 nm). Provided that at least two wavelengths are used, it is possible to resolve changes in oxyhemoglobin and deoxyhemoglobin, and their sum, total hemoglobin based on the amount of light absorption. Near-infrared spectroscopy is capable of noninvasively monitoring and differentiating between venous, arterial, and total occlusion of a skin flap.1 The parameters most commonly reported in the literature are tissue oxygen saturation, which represents oxygen delivery and consumption, and total hemoglobin, which reflects changes in blood tissue volume and tissue perfusion. We recently reviewed the literature systematically to determine whether near-infrared spectroscopy responses differ between successful and failing tissue flaps.1–8Figure 1 illustrates the difference between successful and failing tissue flaps in terms of longitudinal changes in tissue oxygen saturation measured using near-infrared spectroscopy. In successful flaps, an initial increase in tissue oxygen saturation is observed in the first 2 hours postoperatively, following which levels return to preoperative values. This can be explained by two mechanisms: (1) the autonomic denervation of cutaneous vessels during skin flap dissection and (2) the inflammatory reaction at the wound margin. Both result in local vasodilation.7 Several studies7,8 report an increase in total hemoglobin following successful free flap surgery, maintained up to 48 hours postoperatively, with subsequent recovery of levels toward preoperative values thereafter.Fig. 1.: Tissue hemoglobin oxygen concentration (StO2) in surviving and failing flaps. The data represent the mean preoperative and postoperative tissue oxygen saturation levels.It remains unclear whether increases or decreases in tissue oxygen saturation are more predictive of a failing flap. There appears to be little difference between preoperative and postoperative tissue oxygen saturation levels in flaps that ultimately fail. The early rise in tissue oxygen saturation levels observed in successful flaps is not observed in failing flaps. Postoperative increases in total hemoglobin occur in almost all breast flaps that ultimately fail.7 Failing flaps demonstrate a greater total hemoglobin increase than surviving flaps. The most likely explanation for excessive increases in total hemoglobin in failing flaps is associated venous congestion. Near-infrared spectroscopy is capable of providing useful information regarding tissue hemodynamics, especially with respect to the measure of tissue oxygen saturation in surviving flaps. However, there is limited current evidence that near-infrared spectroscopy is able to differentiate the specific cause for flap failure. However, near-infrared spectroscopy has been used successfully to guide early reoperation, at which point the source of flap failure can be determined. Further validation studies are necessary to determine sensitivity, specificity, and the differences in tissue hemodynamics between various tissue flaps, before the use of near-infrared spectroscopy can be fully endorsed as a clinical tool. Ali Najefi, B.Sc. Royal Wolfson Image Computing Laboratory and Department of Bio Surgery and Surgical Technology Imperial College London Daniel R. Leff, M.B.B.S. Royal Wolfson Image Computing Laboratory and Department of Bio Surgery and Surgical Technology Imperial College London Biomedical Optics Research Laboratory Department of Medical Physics and Bioengineering University College London Marios Nicolaou, Ph.D. Biomedical Optics Research Laboratory Department of Medical Physics and Bioengineering University College London Charles Nduka, M.A., M.D. Queen Victoria Hospital East Grinstead, West Sussex, United Kingdom Guang-Zhong Yang, Ph.D. Biomedical Optics Research Laboratory Department of Medical Physics and Bioengineering University College London Ara W. Darzi, F.R.C.S., F.A.C.S. Royal Wolfson Image Computing Laboratory and Department of Bio Surgery and Surgical Technology Imperial College London London, United Kingdom DISCLOSURE The authors have no financial interest to declare in relation to the content of this article.

Measurement of pressure-displacement kinetics of hemoglobin in normal breast tissue with near-infrared spectral imaging

Applying localized external displacement to the breast surface can change the interstitial fluid pressure such that regional transient microvascular changes occur in oxygenation and vascular volume. Imaging these dynamic responses over time, while different pressures are applied, could provide selective temporal contrast for cancer relative to the surrounding normal breast. In order to investigate this possibility in normal breast tissue, a near-infrared spectral tomography system was developed that can simultaneously acquire data at three wavelengths with a 15 s time resolution per scan. The system was tested first with heterogeneous blood phantoms. Changes in regional blood concentrations were found to be linearly related to recovered mean hemoglobin concentration (Hb(T)) values (R(2)=0.9). In a series of volunteer breast imaging exams, data from 17 asymptomatic subjects were acquired under increasing and decreasing breast compression. Calculations show that a 10 mm displacement applied to the breast results in surface pressures in the range of 0-55 kPa depending on breast density. The recovered human data indicate that Hb(T) was reduced under compression and the normalized change was significantly correlated to the applied pressure with a p value of 0.005. The maximum Hb(T) decreases in breast tissue were associated with body mass index (BMI), which is a surrogate indicator of breast density. No statistically valid correlations were found between the applied pressure and the changes in tissue oxygen saturation (S(t)O(2)) or water percentage (H(2)O) across the range of BMI values studied.

Monitoring muscle oxygenation after eccentric exercise-induced muscle damage using near-infrared spectroscopy

Eccentric exercise (EE), a common type of muscular activity whereby muscles lengthen and contract simultaneously, is associated with higher levels of force but may also evoke muscle damage. We investigated the hypothesis that unaccustomed EE might impair muscle oxygenation and muscle blood flow in healthy adults. Ten healthy males performed a bout of 70 maximal eccentric contractions of the elbow flexors. Before and after EE on day 1 and over the next 6 days, maximum voluntary isometric torque (MVT), serum creatine kinase (CK), and the changes in muscle oxygen saturation, blood flow, and oxygen uptake (using near-infrared spectroscopy) within the biceps brachii were assessed. MVT decreased, whereas muscle soreness and CK increased after EE (p < 0.05). Mean resting oxygen saturation increased by 22% after acute EE, and remained elevated by 5%-9% for the following 6 days. During isometric contractions, significant decreases were observed in oxygen desaturation and re-saturation kinetics after EE and these declines were also significantly prevalent over the following 6 days. Both muscle blood flow and oxygen uptake increased significantly after acute EE, but recovered on the next day. This study revealed some prolonged alterations in muscle oxygenation at rest and during exercise after EE, which might be due to a decrease in muscle oxygen consumption, an increase in oxygen delivery, and (or) a combination of both. However, both oxygen consumption and blood flow recovered within 24 h after the eccentric exercise session, and therefore, the reason(s) for the changes in tissue oxygen saturation remain unknown.