Utility of near-infrared spectroscopy in the diagnosis of lower extremity compartment syndrome

Measurements of Electrodermal Activity, Tissue Oxygen Saturation, and Visual Analog Scale for Different Cuff Pressures

The quantification of comfort in binding parts, essential human-machine interfaces (HMI) for the functioning of rehabilitation robots, is necessary to reduce physical strain on the user despite great achievements in their structure and control. This study aims to investigate the physiological impacts of binding parts by measuring electrodermal activity (EDA) and tissue oxygen saturation (StO2). In Experiment 1, EDA was measured from 13 healthy subjects under three different pressure conditions (10, 20, and 30 kPa) for 1 min using a pneumatic cuff on the right thigh. In Experiment 2, EDA and StO2 were measured from 10 healthy subjects for 5 min. To analyze the correlation between EDA parameters and the decrease in StO2, a survey using the visual analog scale (VAS) was conducted to assess the level of discomfort at each pressure. The EDA signal was decomposed into phasic and tonic components, and the EDA parameters were extracted from these two components. RM ANOVA and a post hoc paired t-test were used to determine significant differences in parameters as the pressure increased. The results showed that EDA parameters and the decrease in StO2 significantly increased with the pressure increase. Among the extracted parameters, the decrease in StO2 and the mean SCL proved to be effective indicators. Such analysis outcomes would be highly beneficial for studies focusing on the comfort assessment of the binding parts of rehabilitation robots.

Comparison and convergence of compartment syndrome techniques: a narrative review

INTRODUCTION

Compartment syndrome (CS) continues to be a legitimate orthopedic emergency as it leads to thousands of amputations and permanent nerve and tissue damage to undiagnosed patients for more than eight hours. In CS, intracompartmental pressure is elevated, causing reduced blood flow inside the limb compartments. An erroneous diagnosis may result in unnecessary fasciotomies, the only treatment for this condition.

AREAS COVERED

This review examines the previous and current diagnostic and therapeutic practices for compartment syndrome. It also performs a comparative analysis of each diagnostic technique and its foresights.

EXPERT OPINION

Currently, most clinicians rely on a physical examination of the patient to diagnose CS. The primary reason for the physical examination is the lack of a gold-standard device. The invasive intracompartmental pressure (ICP) measurement technique is still the most commonly used. On the other hand, many non-invasive approaches have the potential to be used as diagnostic tools; however, more research is needed before they can be accepted as standard clinical approaches.

Extremity compartment syndrome: A review with a focus on non-invasive methods of diagnosis

The article deals with an overview of acute extremity compartment syndrome with a focus on the option of non-invasive detection of the syndrome. Acute extremity compartment syndrome (ECS) is an urgent complication that occurs most often in fractures or high-energy injuries. There is still no reliable method for detecting ECS. The only objective measurement method used in clinical practice is an invasive measurement of intramuscular pressure (IMP). The purpose of this paper is to summarize the current state of research into non-invasive measurement methods that could allow simple and reliable continuous monitoring of patients at risk of developing ECS. Clinical trials are currently underway to verify the suitability of the most studied method, near-infrared spectroscopy (NIRS), which is a method for measuring the local oxygenation of muscle compartments. Less explored methods include the use of ultrasound, ultrasound elastography, bioimpedance measurements, and quantitative tissue hardness measurements. Finding a suitable method for continuous non-invasive monitoring of the syndrome would greatly improve the quality of care for patients at risk. ECS must be diagnosed quickly and accurately to prevent irreversible tissue damage that can occur within hours of syndrome onset and may even warrant amputation if neglected.

Effects of upper limb ischemia-reperfusion on regional oxidative stress during aortic surgery with moderate hypothermia

INTRODUCTION

This study aims to evaluate the effect of acute, iatrogenic right arm ischemia and reperfusion (I/R) due to right axillary cannulation on regional oxidative stress using tissue perfusion markers such as central venous oxygen saturation, lactate, the difference between central venous and arterial CO₂ pressure, near-infrared spectroscopy (NIRS) measurements, and biomarkers like sialic acid, malondialdehyde, advanced oxidative protein products in aortic surgery with moderate hypothermia.

METHODS

Adult patients undergoing ascending aorta repair with antegrade cerebral perfusion via the axillary artery participated. Blood samples were collected from the internal jugular vein, right arm cubital vein, and left arm cubital vein, and analysis was performed at intraoperative time points.

RESULTS

Right-arm venous oxygen saturation levels are significantly lower than left arm and central venous, as expected in iatrogenic ischemia. Right arm lactate levels are significantly higher. Somatic right arm NIRS values are significantly lower than somatic left arm. There are no significant differences for biomarkers throughout the time points.

CONCLUSIONS

We have concluded that well-known markers reflect the results of ischemia-reperfusion more rapidly, and are more valuable than novel biomarkers. NIRS is a promising monitor in terms of providing information about tissue oxygenation. Oxidative stress biomarkers do not change quickly enough to give useful information in a short enough period of time; moreover, their costs are high and laboratory studies take time. Although axillary cannulation is controlled limb ischemia, the local effects of I/R did not completely normalize at the end of the surgery, and this regional I/R did not affect the global body organism.

Drug Overdose, Loss of Consciousness, and Compartment Syndrome: A Life-Threatening Combination

Acute extremity compartment syndrome is considered an orthopedic emergency that has serious consequences if a correct diagnosis is not made rapidly. Patients who lose consciousness due to a drug overdose are known to collapse onto their extremities. The limbs are compressed for hours, placing them at an increased risk for acute extremity compartment syndrome and its sequelae. Compartment syndrome due to a compression of a limb from loss of consciousness secondary to drug overdose, presents unique issues to health care providers. In the setting of overdose compartment syndrome, it is similar to the more common traumatic type of compartment syndrome with respect to the pathophysiology, diagnosis and treatment. However, it differs in relation to the muscles affected, physical assessment strategy, and accurately determining the amount of the time from onset of injury to the presentation of symptoms. The purpose of this article is to facilitate emergency department nurses' understanding of the complexities of overdose compartment syndrome, combined with the importance of early recognition of the condition. In addition, the authors review the pathophysiology, the traditional and innovative diagnostic techniques, and the current treatment options available for overdose compartment syndrome.

Near-infrared phototherapy for patient-derived orthotopic xenograft model of hepatocellular carcinoma in combination with indocyanine green

BACKGROUND

Hepatocellular carcinoma notably takes up and retains indocyanine green (ICG). Here, we investigated whether patient-derived orthotopic xenograft of hepatocellular carcinoma could accumulate ICG and show full remission via phototherapy.

METHODS

NIR light and ICG were tested for cytotoxicity in cancerous cell lines (Huh-7, Hep3B). Patient-derived orthotopic xenograft (PDoX) mice were subjected to phototherapy comprising of daily NIR exposure (0.5-1.75 W/cm²) and intravenous injection of ICG (5-20 mg/kg²). Moreover, NIR laser was flashed on individual mouse until hepatocellular carcinoma completely loss the fluorescence, as determined by NIR camera.

RESULTS

Cytotoxicity increased in response to the input energy, but insufficient energy (< 150 joule/cm²) was irresponsive at all irradiances. NIR irradiance in the range of 0.5-1.75 W/cm² took 5-7 days to elicit complete remission from PDoX mice in combination with 20 mg/kg ICG. In contrast, phototherapy could completely ablate hepatocellular carcinoma at 5-15 mg/kg ICG.

CONCLUSIONS

ICG could potentiate the tumoricidal ability of NIR light in a dose-dependent manner, and vice versa. Regardless of ICG dosage, however, phototherapy treated group showed a relatively high survival rate compared to the non-treated group. Notably, real-time phototherapy could halve the effective ICG dosage for full remission of deep-seated tumor.

Imaging-based internal body temperature measurements: The journal Temperature toolbox

Noninvasive imaging methods of internal body temperature are in high demand in both clinical medicine and physiological research. Thermography and thermometry can be used to assess tissue temperature during thermal therapies: ablative and hyperthermia treatments to ensure adequate temperature rise in target tissues but also to avoid collateral damage by heating healthy tissues. In research use, measurement of internal body temperature enables us the production of thermal maps on muscles, internal organs, and other tissues of interest. The most used methods for noninvasive imaging of internal body temperature are based on different parameters acquired with magnetic resonance imaging, ultrasound, computed tomography, microwave radiometry, photoacoustic imaging, and near-infrared spectroscopy. In the current review, we examine the aforementioned imaging methods, their use in estimating internal body temperature in vivo with their advantages and disadvantages, and the physical phenomena the thermography or thermometry modalities are based on.

Clinical and Technical Limitations of Cerebral and Somatic Near-Infrared Spectroscopy as an Oxygenation Monitor

Cerebral and somatic near-infrared spectroscopy monitors are commonly used to detect tissue oxygenation in various circumstances. This form of monitoring is based on tissue infrared absorption and can be influenced by several physiological and non-physiological factors that can induce error in the interpretation. This narrative review explores those clinical and technical limitations and proposes solutions and alternatives in order to avoid some of those pitfalls.

Use of Oxygen Tissue Monitoring in Patients With Compartment Syndrome: Two Clinical Cases and Literature Review

Compartment syndrome is defined as the pathology caused by the increase of pressure within a muscular compartment to the point where the vascular perfusion necessary for the viability of the tissues included therein is reduced. The diagnosis is established by clinical exam and pressure measurement. Measurement of intracompartmental pressure is an invasive method with no option of easy continuous monitoring. Continuous tissue oximetry, using near-infrared light spectroscopy, can estimate soft-tissue oxygenation several centimeters below the sensor placement. This method of monitoring has been used successfully in the diagnosis of compartment syndrome, presenting itself as a non-invasive method of continuous measurement that can be a very useful alternative in complex situations or doubtful cases. We present two clinical cases of patients with acute compartment syndrome, in which the use of near-infrared light spectroscopy was determinant, both for the diagnosis and to verify the surgical treatment performed.

Avoiding, diagnosing and treating well leg compartment syndrome after pelvic surgery

Background

Patients undergoing prolonged pelvic surgery may develop compartment syndrome of one or both lower limbs in the absence of direct trauma or pre‐existing vascular disease (well leg compartment syndrome). This condition may have devastating consequences for postoperative recovery, including loss of life or limb, and irreversible disability.

Methods

These guidelines represent the collaboration of a multidisciplinary group of colorectal, vascular and orthopaedic surgeons, acting on behalf of their specialty associations in the UK and Ireland. A systematic analysis of the available peer‐reviewed literature was undertaken to provide an evidence base from which these guidelines were developed.

Results

These guidelines encompass the risk factors (both patient‐ and procedure‐related), diagnosis and management of the condition. Key recommendations for the adoption of perioperative strategies to facilitate prevention and effective treatment of well leg compartment syndrome are presented.

Conclusion

All surgeons who carry out abdominopelvic surgical procedures should be aware of well leg compartment syndrome, and instigate policies within their own institution to reduce the risk of this potentially life‐changing complication.

Propagating Relationship of Cerebral Oximetric Volume and the Clinical Outcome of Recombinant Tissue Plasminogen Activator (r-TPA) Therapy on Acute Cerebral Ischemic Stroke Patients

Introduction:

Currently, the most available treatment for acute ischemic stroke (AIS) is thrombolytic therapy with recombinant tissue plasminogen activator (r-TPA). A challenge in r-TPA therapy is the prediction of recovery in each case.

Objective:

The aim was to find a possible relationship between the cerebral oximetry indexes and the clinical outcome of r-TPA therapy to assess the cerebral oximetry as a non-invasive monitoring agent for therapy.

Methods:

The inclusion criteria were all patients with AIS who received r-TPA. The neurologic status was evaluated based on the national institutes of health stroke scale (NIHSS) score at arrival, and after a period of 24 hours. In addition, the levels of brain oxygenation in both hemispheres were measured before and continuously over the first 24 hours after r-TPA injection, using an oximetric sensor in the frontal lobes. The clinical success was defined as a 4-point improvement from the baseline NIHSS.

Results:

Total 44 patients with the mean age of 58.2 ± 2.18 years were enrolled, of whom 68.18% were male. Twenty-eight patients remained clinically unimproved and 16 patients were improved. A significant difference was found in the mean surface area under the brain oximetric curve in the 24 hour, in the affected hemisphere in the improved group, compared to the unimproved group (P = 0.007). There was a significant difference between the mean increase in brain oxygenation within 24 hours in the improved and unimproved groups (P = 0.002).

Conclusion:

It is likely that, The cerebral oximetry could contribute to predict the likelihood of r-TPA prognosis in patients with AIS.

Monitoring of limb perfusion after vascular surgery in critical limb ischemia using near-infrared spectroscopy: A prospective observational study

Background:

Intra and postoperative perfusion monitoring should be used in critical limb ischemia patients undergoing vascular surgery to improve outcomes and reduce costs. While a pulse oximeter can be applied on the affected limb to monitor the arterial saturation of the limb, thus reflecting flow in that limb, we need to focus on other important parameters like muscle oxygen consumption and regional blood flow for a good outcome. Near-infrared spectroscopy (NIRS) can be used in such patients to monitor regional and tissue oxygenation.

Methodology:

In this prospective observational study, 30 adult patients undergoing infra-inguinal bypass were recruited. All these patients were given combined spinal-epidural anesthesia. In addition to routine monitoring, a pulse oximeter and NIRS electrodes were applied on the affected limb. rsO2, limb spO2, and Doppler signals were noted before the induction of anesthesia (baseline) and postoperatively at 0, 6, and 12 h. Improvement in rsO2 and limb spO2 values after surgery was noted and fall in these values was evaluated. Pearson correlation between rsO2 and limb spO2 was assessed. The data was analyzed using repeated-measures ANOVA.

Results:

Pearson correlation between rsO2 and limb spO2 was r > 0.8. Two patients had a fall in rsO2 in postoperative period, which co-related with a fall in limb spO2 and decreased/absent Doppler signals.

Conclusion:

NIRS represents a noninvasive and reliable means to monitor limb perfusion in patients undergoing vascular surgery for rest pain.

Noninvasive diagnostics for extremity compartment syndrome following traumatic injury: A state-of-the-art review

Acute compartment syndrome (ACS) is a serious medical condition that can occur following traumatic injury to an extremity. If left undiagnosed, ACS can eventuate in amputation of the limb or even death. Because of this, fasciotomy to release the pressure within the muscle and restore tissue perfusion is often performed upon suspicion of ACS, as the sequelae to fasciotomy are less severe than those associated with not performing the fasciotomy. Currently, the "gold standard" of diagnosis is based on clinical assessment of such symptoms as pain out of proportion to the injury, obvious high pressure and swelling, pain on passive stretch of the muscles in the affected compartment, and deficits in sensory and/ormotor functions. Diagnosis is often confirmed using invasive measurements of intramuscular pressure (IMP); however, controversy exists as to how direct IMP measurement should be accomplished and threshold pressures for accurate diagnosis. Because of this and the attendant issues with invasive measurements, investigators have been searching over the last 25 years for a noninvasive means to quantitatively measure IMP or perfusion to the limb. The purpose of this review is to summarize the current state of the art of noninvasive devices that could potentially be used to diagnose ACS accurately and objectively. To do this, we divide the discussion into those medical devices that primarily measure mechanical surrogates of IMP (e.g., tissue hardness or myofascial displacement) and those that primarily measure indices of tissue perfusion (e.g., tissue oxygen saturation via near-infraredspectroscopy). While near-infrared spectroscopy-basedtechnologies have shown the most promise, whether such technologies will be of diagnostic benefit await the completion of ongoing clinical trials. LEVEL OF EVIDENCE: Systematic Review, level II.

Feasibility of ultrasound measurement in a human model of acute compartment syndrome

Background

Early diagnosis of acute compartment syndrome (ACS) of the leg is essential to improve the outcome. Direct invasive measurement is currently recommended to measure intracompartmental pressure. A non-invasive and reproducible means of making the diagnosis would be a step forward. The purpose of this exploratory study was to investigate the feasibility of non-invasive ultrasound-guided angle measurement as a surrogate of increased pressure in a model of ACS.

Methods

A model of ACS was generated by infusion of saline into the anterior compartment of the leg of human cadavers to incrementally increase the intracompartmental pressure from 10 to 100 mmHg. In 40 legs (20 cadavers), the angle (TFA, tibia-fascia angle) between the anterolateral cortex of the tibia and the fascia of the anterior compartment was measured at each 10 mmHg pressure increase using ultrasound in a standardized transversal plane. A multilevel linear regression model was used to estimate intracompartmental pressure from delta TFA (ΔTFA).

Results

TFA (mean [± SD]) increased from 61.0° (± 12.0°) at 10 mmHg up to 81.1° (± 11.1°) at 100 mmHg compartment pressure. Each increase ΔTFA by one degree was associated with an increase in pressure by 3.9 mmHg (95% CI, 3.8–4.0, p < 0.001).

Conclusions

We found that intracompartmental pressure of the anterior compartment of the calf can be well estimated by ultrasound-based ΔTFA in this post mortem experiment. Our findings indicate that non-invasive TFA measurement is feasible and it is reasonable that this will hold true in real life, but the findings are too preliminary to be used in clinical practice now.

Continuous Near-Infrared Spectroscopy Demonstrates Limitations in Monitoring the Development of Acute Compartment Syndrome in Patients with Leg Injuries

BACKGROUND

We recorded measurements of muscle perfusion using near-infrared spectroscopy (NIRS) and intramuscular pressure (IMP) in a study designed to develop a decision rule for predicting acute compartment syndrome (ACS). The purpose of this study was to report our experience measuring NIRS data in the context of this broader investigation and to explore factors related to variations in data capture.

METHODS

One hundred and eighty-five patients with lower-leg injuries had data consisting of continuous NIRS measurement of the O2 saturation in the anterior compartment of the injured limb and the contralateral (control) limb, and continuous IMP recording in the anterior and deep posterior compartments of the injured leg as part of their participation in an institutional review board-approved multicenter trial. All monitoring was done for a prescribed period of time. For both types of data, the percentage of valid data capture was defined as the ratio of the minutes of observed data points within a physiological range to the total minutes of expected data points. Clinically useful NIRS data required simultaneous data from the injured and control limbs to calculate the ratio. Statistical tests were used to compare the 2 methods as well as factors associated with the percent of valid NIRS data capture.

RESULTS

For the original cohort, clinically useful NIRS data were available a median of 9.1% of the expected time, while IMP data were captured a median of 87.6% of the expected time (p < 0.001). Excluding 46 patients who had erroneous NIRS data recorded, the median percentage was 31.6% for NIRS compared with 87.4% for IMP data (p < 0.00001). Fractures with an associated hematoma were less likely to have valid data points (odds ratio [OR], 0.53; p = 0.04). Gustilo types-I and II open fractures were more likely than Tscherne grades C0 and C1 closed fractures to have valid data points (OR, 1.97; p = 0.03).

CONCLUSIONS

In this study, NIRS data were not collected reliably. In contrast, IMP measurements were collected during >85% of the expected monitoring period. These data raise questions about the utility of current NIRS data capture technology for monitoring oxygenation in patients at risk of ACS.

Perspective review on solid-organ transplant: needs in point-of-care optical biomarkers

Solid-organ transplant is one of the most complex areas of modern medicine involving surgery. There are challenging opportunities in solid-organ transplant, specifically regarding the deficiencies in pathology workflow or gaps in pathology support, which may await alleviations or even de novo solutions, by means of point-of-care, or point-of-procedure optical biomarkers. Focusing the discussions of pathology workflow on donor liver assessment, we analyze the undermet need for intraoperative, real-time, and nondestructive assessment of the donor injuries (such as fibrosis, steatosis, and necrosis) that are the most significant predictors of post-transplant viability. We also identify an unmet need for real-time and nondestructive characterization of ischemia or irreversible injuries to the donor liver, earlier than appearing on morphological histology examined with light microscopy. Point-of-procedure laparoscopic optical biomarkers of liver injuries and tissue ischemia may also facilitate post-transplant management that is currently difficult for or devoid of pathological consultation due to lack of tools. The potential and pitfalls of point-of-procedure optical biomarkers for liver assessment are exemplified in breadth for steatosis. The more general and overarching challenges of point-of-procedure optical biomarkers for liver transplant pathology, including the shielding effect of the liver capsule that was quantitated only recently, are projected. The technological and presentational benchmarks that a candidate technology of point-of-procedure optical biomarkers for transplant pathology must demonstrate to motivate clinical translation are also foreseen.

Predicting Acute Compartment Syndrome (PACS): The Role of Continuous Monitoring

The diagnosis of acute compartment syndrome (ACS) is a common clinical challenge among patients who sustain high-energy orthopaedic trauma, largely because no validated criteria exist to reliably define the presence of the condition. In the absence of validated diagnostic standards, concern for the potential clinical and medicolegal impact of a missed compartment syndrome may result in the potential overuse of fasciotomy in "at-risk" patients. The goal of the Predicting Acute Compartment Syndrome Study was to develop a decision rule for predicting the likelihood of ACS that would reduce unnecessary fasciotomies while guarding against potentially missed ACS. Of particular interest was the utility of early and continuous monitoring of intramuscular pressure and muscle oxygenation using near-infrared spectroscopy in the timely diagnosis of ACS. In this observational study, 191 participants aged 18-60 with high-energy tibia fractures were prospectively enrolled and monitored for up to 72 hours after admission, then followed for 6 months. Treating physicians were blinded to continuous pressure and oxygenation data. An expert panel of 9 orthopaedic surgeons retrospectively assessed the likelihood that each patient developed ACS based on data collected on initial presentation, clinical course, and known functional outcome at 6 months. This retrospectively assigned likelihood is modeled as a function of clinical data typically available within 72 hours of admission together with continuous pressure and oxygenation data. This study will improve our understanding of the natural history of compartment syndrome and examine the utility of early and continuous monitoring of the physiologic status of the injured extremity in the timely diagnosis of ACS.

Compartment syndrome in infants and toddlers

PURPOSE

To study the cause, diagnosis, treatment and outcome of acute compartment syndrome in infants and toddlers aged <3 years.

METHODS

Fifteen patients aged <3 years with acute compartment syndrome were identified from two large pediatric trauma centers over a fifteen-year period. All children underwent fasciotomy. The mechanism of injury, time of injury, time to diagnosis, compartment pressures, time to fasciotomy, and outcome at the time of the latest follow-up were recorded.

RESULTS

Nine (60 %) of fifteen patients developed compartment syndrome secondary to trauma, four (4/15, 27 %) due to infection, and two (2/15, 13 %) due to intravenous infiltration. The average time from injury or hospital admission to fasciotomy was 31.8 h (range 2.9-136.3 h). In general, the functional outcome was excellent at the latest follow-up with thirteen (13/15, 87 %) patients having an excellent outcome. No cases of Volkmann's ischemia were noted at the time of fasciotomy, even when performed as late as 5 days after injury.

CONCLUSIONS

Compared to the general pediatric population, the diagnosis of compartment syndrome in infants and toddlers may be further delayed, i.e., >24 h after injury. Despite delays in diagnosis and time to treatment, the present study shows that outcomes in infants and toddlers remain favorable even when fasciotomy is performed 48-72 h after injury.

LEVEL OF EVIDENCE

Case series, level IV.

Ambulatory diffuse optical tomography and multimodality physiological monitoring system for muscle and exercise applications

Ambulatory diffuse optical tomography (aDOT) is based on near-infrared spectroscopy (NIRS) and enables three-dimensional imaging of regional hemodynamics and oxygen consumption during a person’s normal activities. Although NIRS has been previously used for muscle assessment, it has been notably limited in terms of the number of channels measured, the extent to which subjects can be ambulatory, and/or the ability to simultaneously acquire synchronized auxiliary data such as electromyography (EMG) or electrocardiography (ECG). We describe the development of a prototype aDOT system, called NINscan-M, capable of ambulatory tomographic imaging as well as simultaneous auxiliary multimodal physiological monitoring. Powered by four AA size batteries and weighing 577 g, the NINscan-M prototype can synchronously record 64-channel NIRS imaging data, eight channels of EMG, ECG, or other analog signals, plus force, acceleration, rotation, and temperature for 24+ h at up to 250 Hz. We describe the system’s design, characterization, and performance characteristics. We also describe examples of isometric, cycle ergometer, and free-running ambulatory exercise to demonstrate tomographic imaging at 25 Hz. NINscan-M represents a multiuse tool for muscle physiology studies as well as clinical muscle assessment.

Optical Measurement of Tissue Oxygen Saturation

Advances in opto-electronic systems have meant that optical spectroscopy can now be used for noninvasive measurements in tissue in patients. A number of techniques have evolved over the last 15 years that make use of the characteristic differences in the absorption spectrum of deoxygenated and oxygenated hemoglobin to measure oxygen saturation. This article summarizes, in particular, those techniques that may prove to be applicable to measurements relating to lower extremity wounds. A short introduction is given about existing electrode methods before describing applications of near infrared and visible wavelength spectroscopy to measurements in tissue. The advantages and limitations of these methods are discussed. An example of an area where tissue spectroscopy is now in routine clinical use for tissue healing viability assessment is presented.

A systematic review of human and veterinary applications of noninvasive tissue oxygen monitoring

OBJECTIVE

To describe the methodology for and utilization of tissue oxygen monitoring by near infrared spectroscopy, and to review the current literature on the use of this monitoring modality in human and veterinary settings.

DATA SOURCES

Scientific reviews and original research found using the PubMed and CAB Abstract search engines with the following keywords: "tissue oxygen monitoring," "near-infrared tissue spectroscopy," and "tissue oxygen saturation (StO2 )."

HUMAN DATA SYNTHESIS

Tissue oxygen monitors have been evaluated in a wide variety of human clinical applications including trauma and triage, surgery, sepsis, and septic shock, and early goal-directed therapy. StO2 more rapidly identifies occult shock in human patients compared to traditional methods, which can lead to earlier intervention in these patients.

VETERINARY DATA SYNTHESIS

Veterinary studies involving tissue oxygen monitoring are limited, but the technology may have utility for identification of hemorrhagic shock earlier than changes in base excess, blood lactate concentration, or other traditional perfusion parameters.

CONCLUSION

Tissue oxygen monitoring is most commonly performed utilizing a noninvasive, portable monitor, which provides real-time, continuous, repeatable StO2 measurements. A decline in StO2 is an early indicator of shock in both human and veterinary patients. Low StO2 values in human patients are associated with increased morbidity, mortality, and length of hospitalization, as well as the development of multiple organ system dysfunction and surgical site infections.

Spectroscopic limb monitoring in peripheral extracorporeal membrane oxygenation

Limb-related complications are major contributors to extracorporeal membrane oxygenation-associated complications. Early detection of limb ischemia and or compartment syndrome is paramount to minimizing the adverse effects. With the absence of pulsatile flow, bedside Doppler examination of distal arterial waveforms is an impractical and an unreliable method of monitoring limb perfusion. We describe a new application of near-infrared spectroscopy monitoring of tissue oxygenation for the early detection of limb complications in extracorporeal membrane oxygenation.

Correlation of near-infrared spectroscopy and direct pressure monitoring in an acute porcine compartmental syndrome model

OBJECTIVE

To correlate near-infrared spectroscopy (NIRS) and the tibial intracompartmental perfusion pressure (TIPP) in an acute limb compartmental syndrome.

METHODS

Landrace swine were subdivided into 2 groups: plasma infusion (n = 16) and blunt trauma plus plasma infusion (n = 15). NIRS sensors were placed over the craniolateral muscle compartment of proximal both tibiae. Albumin infusion elevated tibial intracompartmental pressures (TICP). Time-synchronized measures of systolic, diastolic, and mean arterial pressures, TICP, and percent oxygenation from each leg were collected. For the blunt trauma group, trauma was induced by dropping a 2-kg weight 30 times from 100 cm directly on the muscle compartment. For each group, a repeated-measures analysis of variance model was used to test differences in the TICP, TIPP, and oxygenation values. Pearson correlations were calculated between TICP and oxygenation and between TIPP and oxygenation.

RESULTS

Both models created reproducible increases in TICP and decreases in TIPP. Trauma did not alter TICP, TIPP, or percent oxygenation in the model. NIRS was able to detect significant changes in tissue oxygenation at all the same time points. NIRS was able to detect decreased oxygenation at every TIPP decrease and subsequent increase after fasciotomies. An increase in percent oxygenation was seen in all cases once fasciotomy was performed and TICP was reduced.

CONCLUSIONS

NIRS provided a sensitive measure correlating to both an increase and decrease in TICP and TIPP, respectively, in this infusion model. The addition of blunt trauma to the model did not alter the correlations of NIRS values with TICP and TIPP. Fasciotomy produced a rebound in oxygenation values.

Near-infrared spectroscopy assessment of tissue saturation of oxygen in torsed and healthy testes

OBJECTIVES

The objective was to assess whether testicular torsion is associated with low testicular tissue saturation of oxygen (StO2 ) as measured by transscrotal near-infrared spectroscopy (NIRS) and to compare the differences in NIRS values between testicles of the same patient, both in patients with testicular torsion and in healthy controls.

METHODS

This was an observational study of healthy controls and patients with surgically confirmed testicular torsion who were recruited from males under 30 years of age presenting to the emergency department (ED). The hypothesis was that the difference in NIRS values for the control's two testicles would be zero, and that the difference between the torsed and healthy testicles on an individual patient would not be zero. Based on animal data, the study was powered to detect an absolute difference of StO2 of 47%.

RESULTS

The mean StO2 for the left control patients' testicles was 73.6% (95% confidence interval [CI] = 68.0% to 79.1%) and the mean StO2 for the right controls' testicles for controls was 73.6% (95% CI = 66.9% to 80.4%; n = 17). The absolute difference in NIRS StO2 for left minus right for each individual was 3.5% (95% CI = 1.8% to 5.4%), which was significantly different (p = 0.0007), and refuted the hypothesis that there was no significant difference in StO2 between left and right testes in healthy patients. In the testicular torsion group, the torsed side had a mean StO2 of 82.8% (95% CI = 68.7% to 96.9%), and the contralateral nontorsed testes had a mean of 85.8% (95% CI = 72.3% to 99.3%). The mean StO2 difference, nontorsed minus torsed was 3.0% (range = -1% to 9%, 95% CI = -2% to 8%; p = 0.174), refuting the hypothesis that torsed testes would demonstrate significantly lower values for StO2 .

CONCLUSIONS

While pilot animal investigations support a potential role for transscrotal NIRS for the detection of testicular torsion, this first clinical translation of animal findings reveals that the investigated, transcutaneous, reflectance geometry NIRS device failed to demonstrate symmetric oxygenation of left and right testes in healthy controls and also failed to demonstrate depressed tissue saturation of oxygen values in patients with confirmed testicular torsion. While limited by a small sample size, other problems such as inability to calibrate depth of measurement of StO2 may have led to falsely elevated readings in patients with torsion.

Comparison of tissue oxygenation and compartment pressure following tibia fracture

OBJECTIVE

We investigated the ability of direct continuous measurement of intramuscular tissue oxygenation (PmO(2)) to detect acute ischaemia in the leg in patients at risk for acute extremity compartment syndrome. Following tibia fracture treated by intramedullary nailing, we compared the proportions of PmO(2) and compartment pressure (CP) measurements that met the warning criteria for compartment syndrome.

METHODS

Participants included 10 patients sustaining acute isolated closed tibia shaft fractures treated by intramedullary nailing. A tissue oxygenation probe and a CP probe were percutaneously placed into the anterior compartment of the leg. PmO(2) and CP in the anterior compartment were measured in the injured leg for 48 h postoperatively. Measurements meeting the warning criteria were defined as PmO(2) < 10 mmHg, CP > 30 mmHg and perfusion pressure ΔP < 30 mmHg.

RESULTS

None of the patients developed compartment syndrome. Comparison of CP and PmO(2) showed a CP > 30 mmHg in 50.39% of CP measurements in all patients and a PmO(2) < 10 mmHg in 0.75% of PmO(2) measurements in two patients (P = 0.005). Comparison of ΔP and PmO(2) showed a ΔP < 30 mmHg in 31.01% of ΔP measurements in nine patients and a PmO(2) < 10 mmHg in 0.76% of PmO(2) measurements in one patient (P = 0.01).

CONCLUSION

In the absence of compartment syndrome, pressure measurements following tibia fracture treated with intramedullary nailing often met the warning criteria, whereas PmO(2) did not, suggesting that measurement of intramuscular tissue oxygenation may represent a potential method for the identification of acute compartment syndrome that deserves continued investigation.

Near infrared spectroscopy: clinical and research uses

BACKGROUND

Pulse oximetry is routinely used to measure hemoglobin saturation and is currently the gold standard to assess oxygenation in patients. Due to attenuation of infrared light by skin, bone, and other organs, pulse oximetry cannot assess end-organ tissue oxygenation (StO(2)). Near infrared spectroscopy (NIS) penetrates a broad range of tissues and utilizes reflection rather than direct transmission between an emitter and receiver pair. NIS is able to measure StO(2) and assess end-organ perfusion in a variety of applications.

STUDY DESIGN AND METHODS

A retrospective review of recent animal and human StO(2) studies was undertaken. StO(2) measurements and outcomes were assessed.

RESULTS

StO(2) measurements identified visceral organ ischemia in animal hemorrhage models. These measurements were also able to guide optimization of resuscitation and end-organ oxygenation. Human studies demonstrated StO(2) changes preceded those seen in traditionally measured parameters such as blood pressure, heart rate, base deficit, serum lactate, and mental status. Additionally, StO(2) thresholds identified trauma patients who required massive transfusions, developed multiple organ dysfunction syndrome, or experienced lower extremity compartment syndrome. StO(2) measurements also demonstrated a benefit in selecting resuscitation fluids, assessing end-organ oxygenation during blood transfusion, and quantifying the oxygen-carrying deficit secondary to the blood storage lesion.

CONCLUSION

StO(2) measurements have been used to guide resuscitation efforts in trauma patients. This technology and its applications continue to evolve and represent a novel change in patient care.

Acute compartment syndrome: obtaining diagnosis, providing treatment, and minimizing medicolegal risk

Acute compartment syndrome (ACS) is a surgical emergency. Diagnosis depends on a high clinical suspicion and an understanding of risk factors, pathophysiology and subtle physical exam findings. The typical high risk scenario for ACS is a male patient younger than 35 years of age, involved in a high energy sport or roadway collision, resulting in a tibial shaft fracture. He will go on to develop acute compartment syndrome of the leg in less than 10 hours and require emergent fasciotomy. Diagnosis of ACS in this patient is primarily a clinical one but can be confirmed with invasive intracompartmental pressure monitoring or non-invasive near infrared spectroscopy (NIRS). Delaying the diagnosis will likely result in some degree of permanent disability and places the surgeon at high risk for litigation. This article reviews the salient features of acute compartment syndrome that should be understood by all orthopaedic residents and surgeons.

Near-infrared spectroscopy in the critical setting

Near-infrared spectroscopy is a noninvasive means of determining real-time changes in regional oxygen saturation of cerebral and somatic tissues. Hypoxic neurologic injuries not only involve devastating effects on patients and their families but also increase health care costs to the society. At present, monitors of cerebral function such as electroencephalograms, transcranial Doppler, jugular bulb mixed venous oximetry, and brain tissue oxygenation monitoring involve an invasive procedure, are operator-dependent, and/or lack the sensitivity required to identify patients at risk for cerebral hypoxia. Although 20th century advances in the understanding and management of resuscitation of critically ill and injured children have focused on global parameters (ie, pulse oximetry, capnography, base deficit, lactate, etc), a growing body of evidence now points to regional disturbances in microcirculation that will lead us in a new direction of adjunctive tissue monitoring and response to resuscitation. In the coming years, near-infrared spectroscopy will be accepted as a way for clinicians to more quickly and noninvasively identify patients with altered levels of cerebral and/or somatic tissue oxygenation and, in conjunction with global physiologic parameters, guide efficient and effective resuscitation to improve outcomes for critically ill and injured pediatric patients.

The diagnosis of acute lower limb compartment syndrome: Applications of near infrared spectroscopy

Acute compartment syndrome of the lower limb is a significant problem in surgical practice, the successful management of which depends upon swift diagnosis and intervention.

Conventionally, diagnosis has been based upon clinical assessment; however, this can be unreliable and the potential for missed compartment syndrome remains. The supplementary use of compartment pressure monitoring has addressed some of these issues, but it remains an invasive technique, the exact role of which is still debated in the literature.

Near infrared spectroscopy (NIRS) is an emerging technique in medical practice which provides a non-invasive, continuous and real time measure of local tissue oxygenation. Early experimental work and subsequent clinical studies have demonstrated that NIRS provides an accurate means of detecting compartment syndrome, and that its sensitivity in some circumstances may exceed that of monitoring compartment pressures. Despite this promise, limitations of the technique, such as difficultly monitoring the deep posterior compartment of leg using current systems, and the relative expense of the equipment, have hindered broader adoption.

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.

Advancing critical care: joint combat casualty research team and joint theater trauma system

Despite the severity and complexity of injuries, survival rates among combat casualties are equal to or better than those from civilian trauma. This article summarizes the evidence regarding innovations from the battlefield that contribute to these extraordinary survival rates, including preventing hemorrhage with the use of tourniquets and hemostatic dressings, damage control resuscitation, and the rapid evacuation of casualties via MEDEVAC and the US Air Force Critical Care Air Transport Teams. Care in the air for critically injured casualties with pulmonary injuries and traumatic brain injury is discussed to demonstrate the unique considerations required to ensure safe en route care. Innovations being studied to decrease sequelae associated with complex orthopedic and extremity trauma are also presented. The role and contributions of the Joint Combat Casualty Research Team and the Joint Theater Trauma System are also discussed.

500 ml of blood loss does not decrease non-invasive tissue oxygen saturation (StO2) as measured by near infrared spectroscopy - A hypothesis generating pilot study in healthy adult women

Background

The goal when resuscitating trauma patients is to achieve adequate tissue perfusion. One parameter of tissue perfusion is tissue oxygen saturation (StO₂), as measured by near infrared spectroscopy. Using a commercially available device, we investigated whether clinically relevant blood loss of 500 ml in healthy volunteers can be detected by changes in StO₂ after a standardized ischemic event.

Methods

We performed occlusion of the brachial artery for 3 minutes in 20 healthy female blood donors before and after blood donation. StO₂ and total oxygenated tissue hemoglobin (O₂Hb) were measured continuously at the thenar eminence. 10 healthy volunteers were assessed in the same way, to examine whether repeated vascular occlusion without blood donation exhibits time dependent effects.

Results

Blood donation caused a substantial decrease in systolic blood pressure, but did not affect resting StO₂ and O₂Hb values. No changes were measured in the blood donor group in the reaction to the vascular occlusion test, but in the control group there was an increase in the O₂Hb rate of recovery during the reperfusion phase.

Conclusion

StO₂ measured at the thenar eminence seems to be insensitive to blood loss of 500 ml in this setting. Probably blood loss greater than this might lead to detectable changes guiding the treating physician. The exact cut off for detectable changes and the time effect on repeated vascular occlusion tests should be explored further. Until now no such data exist.

Screening Tools in the Diagnosis of Acute Compartment Syndrome

Acute compartment syndrome (ACS) is a surgical emergency requiring urgent fasciotomy to save the limb. However, time is of the essence and diagnostic uncertainty can lead to unnecessary surgery. Measurement of intracompartmental pressure (ICP) to aid decision making is becoming commonplace, particularly in unconscious or confused patients. However, inaccurate readings can result from misplacement of the probe, subjecting patients to a needless fasciotomy in the event of an overreading. Similarly, underestimated readings create a false sense of security. Screening tools, criteria-led systems of clinical decision making, are used by some to assist in diagnosis and management planning, but do they work? Here, we review current diagnostic strategies and question whether screening tools can make rapid diagnosis more accurate. Furthermore, in the absence of a standardized tool, we analyze the practice of a sample of vascular surgeons with the aim of moving toward a management consensus useful to junior doctors.

Correlation between muscle oxygenation and compartment pressures in acute compartment syndrome of the leg

BACKGROUND

Near-infrared spectroscopy estimates soft-tissue oxygenation approximately 2 to 3 cm below the skin. The purpose of the present study was to evaluate muscle oxygenation in the setting of an acute compartment syndrome of the leg and to determine if near-infrared spectroscopy is capable of detecting perfusion deficits.

METHODS

Fourteen patients with unilateral lower extremity trauma were enrolled after the diagnosis of an acute compartment syndrome was made clinically and confirmed with intracompartmental pressure measurements. Lower extremity muscle compartments were evaluated with near-infrared spectroscopy, and near-infrared spectroscopy values of the uninjured, contralateral leg of each patient were used as internal reference values. The compartment perfusion gradient was calculated as the diastolic blood pressure minus the intracompartmental pressure.

RESULTS

Intracompartmental pressures ranged from 21 to 176 mm Hg (mean, 79 mm Hg) and exceeded 30 mm Hg in all compartments but two (both in the same patient). Thirty-eight compartments had a perfusion gradient of < or = 10 mm Hg (indicating ischemia). Among ischemic compartments, near-infrared spectroscopy values in the anterior, lateral, deep posterior, and superficial posterior compartments of the injured limbs were decreased by an average 10.1%, 10.1%, 9.4%, and 16.3% in comparison with the corresponding compartments of the uninjured leg. Differences in near-infrared spectroscopy values (the near-infrared spectroscopy value for the injured leg minus the near-infrared spectroscopy value for the uninjured leg) were positively correlated with compartment perfusion gradient within each compartment (r = 0.82, 0.65, 0.67, and 0.62, for the anterior, lateral, deep posterior, and superficial posterior compartments, respectively; p < 0.05 for all).

CONCLUSIONS

Normalized near-infrared spectroscopy values decrease significantly with decreasing lower limb perfusion pressures. Near-infrared spectroscopy may be capable of differentiating between injured patients with and without an acute compartment syndrome.

Near-infrared spectroscopy in lower extremity trauma

BACKGROUND

Near-infrared spectroscopy measures the percentage of hemoglobin oxygen saturation in the microcirculation of tissue up to 3 cm below the skin. The purpose of this study was to describe the measurable response of normal tissue oxygenation in the leg after acute trauma with use of this technique.

METHODS

Twenty-six patients with acute unilateral tibial fractures and twenty-five uninjured volunteer control subjects were enrolled. Near-infrared spectroscopy measurements were obtained for both legs in all four compartments: anterior, lateral, deep posterior, and superficial posterior. The twenty-six injured legs were compared with twenty-five uninjured legs (randomly selected) of the volunteer control group, with the contralateral limb in each patient serving as an internal control.

RESULTS

The mean tissue oxygenation for each compartment in the injured legs was 69% (anterior), 70% (lateral), 74% (deep posterior), and 70% (superficial posterior). In the control (uninjured) legs, the average tissue oxygenation percentage in each compartment was 54%, 55%, 60%, and 57%, respectively. Repeated-measures analysis revealed that near-infrared spectroscopy values averaged 15.4 percentage points (95% confidence interval, 12.2 to 18.6 percentage points) higher for injured legs than for uninjured legs, controlling for the value of the contralateral limb (p < 0.0001).

CONCLUSIONS

Tibial fracture produces a predictable increase in tissue oxygenation as measured by near-infrared spectroscopy. The corresponding compartment of the contralateral leg can provide strong utility as an internal control value when evaluating the hyperemic response to injury.

Hemodynamic changes in rat leg muscles during tourniquet-induced ischemia-reperfusion injury observed by near-infrared spectroscopy

In this study, we hypothesized that non-invasive continuous wave near-infrared spectroscopy (CWNIRS) can determine the severity or reversibility of muscle damage due to ischemia/reperfusion (I/R), and the results will be highly correlated with those from physical examination and histological analysis. To test this hypothesis, we performed CWNIRS measurements on two groups of male Sprague-Dawley rats ( approximately 400 g) that underwent 2 h (n = 6) or 3 h (n = 7) of pneumatic tourniquet application (TKA). Tissue oxyhemoglobin [HbO(2)] and deoxyhemoglobin [Hb] concentration changes were monitored during the 2 h or 3 h of 250 mmHg TKA and for an additional 2 h post-TKA. Rats were euthanized 24 h post-TKA and examined for injury, edema and viability of muscles. Contralateral muscles served as controls for each animal. In both groups, [HbO(2)] dropped immediately, then gradually decreased further after TKA and then recovered once the tourniquet was released. However, releasing after 2 h of TKA caused [HbO(2)] to overshoot above the baseline during reperfusion while the 3 h group continued to have lower [HbO(2)] than baseline. We found a significant correlation between the elapsed time from tourniquet release to the first recovery peak of [HbO(2)] and the muscle weight ratio between tourniquet and contralateral limb muscles (R = 0.86). Hemodynamic patterns from non-invasive CWNIRS demonstrated significant differences between 2 h and 3 h I/R. The results demonstrate that CWNIRS may be useful as a non-invasive prognostic tool for conditions involving vascular compromise such as extremity compartment syndrome.

Noninvasive monitoring of elevated intramuscular pressure in a model compartment syndrome via quantitative fascial motion

Compartment syndromes, conditions of elevated intramuscular pressure (IMP) resulting from trauma or chronic overuse, frequently require invasive IMP monitoring for accurate diagnosis. Our objective was to test a noninvasive ultrasound technique for estimating IMP based on fascial displacement waveforms from arterial blood pressure pulses. IMP was increased in the legs of 23 healthy adult subjects up to 80 mmHg using two blood pressure cuffs covering the region from the knee to the ankle. Receiver operator characteristic curves and recursive partitioning were used to determine the sensitivity and specificity of diagnosing elevated IMP using fascial displacement. For one curve, in which several ultrasonic measurement parameters were used along with subject body mass index and blood pressure, the sensitivity and specificity for diagnosing normal IMP (below 30 mmHg) from elevated IMP (30 mmHg and up) was 0.61 and 0.94, respectively. Recursive partitioning, in which IMP was divided into three ranges (normal <30 mmHg, midrange of 30-40 mmHg, and elevated >or=50 mmHg), resulted in improved diagnostic sensitivity (0.77) with almost no change in specificity (0.93).

Diagnostic techniques in acute compartment syndrome of the leg

OBJECTIVES

To review the efficacy of the current diagnostic methods of acute compartment syndrome (ACS) after leg fractures.

DATA SOURCES

A Medline (PubMed) search of the English literature extending from 1950 to May 2007 was performed using "compartment syndromes" as the main key word. Also a manual search of orthopaedic texts was performed.

STUDY SELECTION AND EXTRACTION

The results were limited to articles involving human subjects. Of 2605 primary titles, 489 abstracts limited to compartment syndromes in the leg and 577 articles related to the diagnosis of compartment syndromes were identified and their abstracts reviewed. Further articles were identified by reviewing the references. Sixty-six articles were found to be relevant to diagnostic techniques for compartment syndrome in the leg and formed the basis of this review.

CONCLUSIONS

Early diagnosis of an ACS is important. Despite its drawbacks, clinical assessment is still the diagnostic cornerstone of ACS. Intracompartmental pressure measurement can confirm the diagnosis in suspected patients and may have a role in the diagnosis of this condition in unconscious patients or those unable to cooperate. Whitesides suggests that the perfusion of the compartment depends on the difference between the diastolic blood pressure and the intracompartmental pressure. They recommend fasciotomy when this pressure difference, known as the Delta p, is less than 30 mm Hg. Access to a precise, reliable, and noninvasive method for early diagnosis of ACS would be a landmark achievement in orthopaedic and emergency medicine.