Continuous Muscle Tissue Oxygenation in Critically Injured Patients: A Prospective Observational Study

The role of tissue oxygenation in obesity-related cardiometabolic complications

Obesity is a complex, multifactorial, chronic disease that acts as a gateway to a range of other diseases. Evidence from recent studies suggests that changes in oxygen availability in the microenvironment of metabolic organs may exert an important role in the development of obesity-related cardiometabolic complications. In this review, we will first discuss results from observational and controlled laboratory studies that examined the relationship between reduced oxygen availability and obesity-related metabolic derangements. Next, the effects of alterations in oxygen partial pressure (pO2) in the adipose tissue, skeletal muscle and the liver microenvironment on physiological processes in these key metabolic organs will be addressed, and how this might relate to cardiometabolic complications. Since many obesity-related chronic diseases, including type 2 diabetes mellitus, cardiovascular diseases, chronic kidney disease, chronic obstructive pulmonary disease and obstructive sleep apnea, are characterized by changes in pO2 in the tissue microenvironment, a better understanding of the metabolic impact of altered tissue oxygenation can provide valuable insights into the complex interplay between environmental and biological factors involved in the pathophysiology of metabolic impairments. This may ultimately contribute to the development of novel strategies to prevent and treat obesity-related cardiometabolic diseases.

Reference ranges of peripheral-muscle oxygenation in term neonates delivered by Caesarean section during immediate transition after birth

AIM

To establish reference ranges of peripheral-muscle regional oxygen saturation (prSO2) and peripheral fractional tissue oxygen extraction (pFTOE) during the first 15 min after birth in stable term neonates.

METHODS

Secondary outcome parameters of prospective observational studies in healthy term neonates delivered by Caesarean section were analysed. prSO2 was measured on the right forearm using the INVOS 5100C monitor. pFTOE was calculated out of prSO2 and arterial oxygen saturation (SpO2). Centile charts (10th-90th) of prSO2 and pFTOE were defined during the first 15 min after birth.

RESULTS

Three-hundred-five term neonates with a mean gestational age and birth weight of 39.0 ± 0.9 weeks and 3321 ± 454 g, respectively, were included. The 50th centiles of prSO2 were 39% (minute two), 52% (minute five), 71% (minute 10), and 73% (minute 15). The 50th centiles of pFTOE were 0.529 (minute two), 0.378 (minute five), 0.237 (minute 10), and 0.231 (minute 15).

CONCLUSION

Reference ranges of prSO2 and pFTOE were established for term neonates delivered by Caesarean section during the immediate transition after birth. These reference ranges increase knowledge of physiological processes taking place immediately after birth and are necessary for possible future clinical applications.

Origins and molecular effects of hypoxia in cancer

Hypoxia (insufficient O2) is a pivotal factor in cancer progression, triggering genetic, transcriptional, translational and epigenetic adaptations associated to therapy resistance, metastasis and patient mortality. In this review, we outline the microenvironmental origins and molecular mechanisms responsible for hypoxic cancer cell adaptations in situ and in vitro, whilst outlining current approaches to stratify, quantify and therapeutically target hypoxia in the context of precision oncology.

Hypoxia enhances human myoblast differentiation: involvement of HIF1α and impact of DUX4, the FSHD causal gene

BACKGROUND

Hypoxia is known to modify skeletal muscle biological functions and muscle regeneration. However, the mechanisms underlying the effects of hypoxia on human myoblast differentiation remain unclear. The hypoxic response pathway is of particular interest in patients with hereditary muscular dystrophies since many present respiratory impairment and muscle regeneration defects. For example, an altered hypoxia response characterizes the muscles of patients with facioscapulohumeral dystrophy (FSHD).

METHODS

We examined the impact of hypoxia on the differentiation of human immortalized myoblasts (LHCN-M2) cultured in normoxia (PO2: 21%) or hypoxia (PO2: 1%). Cells were grown in proliferation (myoblasts) or differentiation medium for 2 (myocytes) or 4 days (myotubes). We evaluated proliferation rate by EdU incorporation, used myogenin-positive nuclei as a differentiation marker for myocytes, and determined the fusion index and myosin heavy chain-positive area in myotubes. The contribution of HIF1α was studied by gain (CoCl2) and loss (siRNAs) of function experiments. We further examined hypoxia in LHCN-M2-iDUX4 myoblasts with inducible expression of DUX4, the transcription factor underlying FSHD pathology.

RESULTS

We found that the hypoxic response did not impact myoblast proliferation but activated precocious myogenic differentiation and that HIF1α was critical for this process. Hypoxia also enhanced the late differentiation of human myocytes, but in an HIF1α-independent manner. Interestingly, the impact of hypoxia on muscle cell proliferation was influenced by dexamethasone. In the FSHD pathological context, DUX4 suppressed HIF1α-mediated precocious muscle differentiation.

CONCLUSION

Hypoxia stimulates myogenic differentiation in healthy myoblasts, with HIF1α-dependent early steps. In FSHD, DUX4-HIF1α interplay indicates a novel mechanism by which DUX4 could interfere with HIF1α function in the myogenic program and therefore with FSHD muscle performance and regeneration.

Peripheral muscle fractional tissue oxygen extraction in stable term and preterm neonates during the first 24 h after birth

Background

Peripheral muscle fractional tissue oxygen extraction (pFTOE) represents the relative extraction of oxygen from the arterial to venous compartment, providing information about dynamic changes of oxygen delivery and oxygen consumption. The aim of the present study was to establish reference values of pFTOE during the first 24 h after birth in stable term and late preterm neonates.

Methods

The present study is a post-hoc analysis of secondary outcome parameters of prospective observational studies. Only stable neonates without infection, asphyxia and any medical support were eligible for our analysis to obtain normal values. For measurements of peripheral muscle tissue oxygenation index (pTOI) during the first 24 h after birth in term and preterm neonates, the NIRO200/NIRO200NX was used. Arterial oxygen saturation (SpO2) was obtained by pulse oximetry. pFTOE was calculated out of pTOI and SpO2: pFTOE = (SpO2-pTOI)/SpO2. Measurements of neonates were stratified into four groups according to their respective measurement time point (6 h periods) after birth. Term and preterm neonates were analyzed separately. Mean values of measurements during the first time period (0-6 h after birth) were compared to measurements of the following time periods (second = 7-12 h, third = 13-18 h, fourth = 19-24 h after birth).

Results

Two-hundred-fourty neonates (55 term and 185 late preterm neonates) had at least one peripheral muscle NIRS measurements within the first 24 h after birth. Mean gestational age and birth weight were 39.4 ± 1.1 weeks and 3360 (2860-3680)g in term neonates and 34.0 ± 1.4 weeks and 2060 (1750-2350)g in preterm neonates, respectively. In term neonates pFTOE was 0.264 (0.229-0.300), 0.228 (0.192-0.264), 0.237 (0.200-0.274) and 0.220 (0.186-0.254) in the first, second, third and fourth time period. In preterm neonates pFTOE was 0.229 (0.213-0.246), 0.225 (0.209-0.240), 0.226 (0.210-0.242) and 0.238 (0.222-0.255) in the first, second, third and fourth time period. pFTOE did not show any significant changes between the time periods, neither in term nor in preterm neonates.

Conclusion

We provide reference values of pFTOE for stable term and late preterm neonates within the first 24 h after birth, which were stable when comparing four 6-h periods. These normal values are of great need for interpreting pFTOE in scientific context as well as for potential future clinical applications.

Peripheral fractional oxygen extraction measured with near-infrared spectroscopy in neonates-A systematic qualitative review

BACKGROUND

Peripheral fractional oxygen extraction (pFOE) measured with near-infrared spectroscopy (NIRS) in combination with venous occlusion is of increasing interest in term and preterm neonates.

OBJECTIVE

The aim was to perform a systematic qualitative review of literature on the clinical use of pFOE in term and preterm neonates and on the changes in pFOE values over time.

METHODS

A systematic search of PubMed, Embase and Medline was performed using following terms: newborn, infant, neonate, preterm, term, near-infrared spectroscopy, NIRS, oximetry, spectroscopy, tissue, muscle, peripheral, arm, calf, pFOE, OE, oxygen extraction, fractional oxygen extraction, peripheral perfusion and peripheral oxygenation. Additional articles were identified by manual search of cited references. Only studies in human neonates were included.

RESULTS

Nineteen studies were identified describing pFOE measured with NIRS in combination with venous occlusion. Nine studies described pFOE measured on the forearm and calf at different time points after birth, both in stable preterm and term neonates without medical/respiratory support or any pathological findings. Nine studies described pFOE measured at different time points in sick preterm and term neonates presenting with signs of infection/inflammation, anemia, arterial hypotension, patent ductus arteriosus, asphyxia or prenatal tobacco exposure. One study described pFOE both, in neonates with and without pathological findings.

CONCLUSION

This systematic review demonstrates that pFOE may provide additional insight into peripheral perfusion and oxygenation, as well as into disturbances of microcirculation caused by centralization in preterm and term neonates with different pathological findings.

SYSTEMATIC REVIEW REGISTRATION

[https://www.crd.york.ac.uk/prospero/], identifier [CRD42021249235].

Hypoxia and Hypoxia-Inducible Factor Signaling in Muscular Dystrophies: Cause and Consequences

Muscular dystrophies (MDs) are a group of inherited degenerative muscle disorders characterized by a progressive skeletal muscle wasting. Respiratory impairments and subsequent hypoxemia are encountered in a significant subgroup of patients in almost all MD forms. In response to hypoxic stress, compensatory mechanisms are activated especially through Hypoxia-Inducible Factor 1 α (HIF-1α). In healthy muscle, hypoxia and HIF-1α activation are known to affect oxidative stress balance and metabolism. Recent evidence has also highlighted HIF-1α as a regulator of myogenesis and satellite cell function. However, the impact of HIF-1α pathway modifications in MDs remains to be investigated. Multifactorial pathological mechanisms could lead to HIF-1α activation in patient skeletal muscles. In addition to the genetic defect per se, respiratory failure or blood vessel alterations could modify hypoxia response pathways. Here, we will discuss the current knowledge about the hypoxia response pathway alterations in MDs and address whether such changes could influence MD pathophysiology.

Hypoxia and the phenomenon of immune exclusion

Over the last few years, cancer immunotherapy experienced tremendous developments and it is nowadays considered a promising strategy against many types of cancer. However, the exclusion of lymphocytes from the tumor nest is a common phenomenon that limits the efficiency of immunotherapy in solid tumors. Despite several mechanisms proposed during the years to explain the immune excluded phenotype, at present, there is no integrated understanding about the role played by different models of immune exclusion in human cancers. Hypoxia is a hallmark of most solid tumors and, being a multifaceted and complex condition, shapes in a unique way the tumor microenvironment, affecting gene transcription and chromatin remodeling. In this review, we speculate about an upstream role for hypoxia as a common biological determinant of immune exclusion in solid tumors. We also discuss the current state of ex vivo and in vivo imaging of hypoxic determinants in relation to T cell distribution that could mechanisms of immune exclusion and discover functional-morphological tumor features that could support clinical monitoring.

Changes in peripheral muscle oxygenation measured with near-infrared spectroscopy in preterm neonates within the first 24 h after birth

BACKGROUND

Near-infrared spectroscopy (NIRS) combined with venous occlusions enables peripheral-muscle oxygenation and perfusion monitoring.

OBJECTIVE

The aim of the present exploratory observational study was to evaluate peripheral-muscle oxygenation and perfusion during the first 24 h after birth in stable preterm neonates.

APPROACH

Secondary outcome parameters of prospective observational studies were analysed. Preterm neonates with peripheral-muscle NIRS measurements combined with venous occlusion on the first day after birth were included. Neonates without circulatory support and without signs of infection/inflammation were included. Neonates were stratified in four groups according to their measurement time-point (6 h-periods) and matched 2:1 for gestational age ±1 week. For each group haemoglobin flow (Hbflow), oxygen-delivery (DO2), oxygen-consumption (VO2), fractional-oxygen-extraction (FOE), tissue-oxygenation-index (TOI) and mixed-venous-oxygenation (SvO2) were calculated. Neonates with measurements during the first 6-hour time period were compared to neonates with measurements of the following time periods.

MAIN RESULTS

40 preterm neonates (gestational age (median(IQR)): 33.5(32.5-34.1)weeks) measured during the first 6 h period after birth were compared to 20 preterm neonates measured in each of the following 6 h periods (period two: 33.7(33.1-34.3)weeks; period three: 34.1(33.2-34.6)weeks; period four: 33.8(32.6-34.6)weeks). Hbflow, DO2 and SvO2 were significantly higher in the second and third 6 h time period compared to the first 6 h period. VO2 did not change significantly during the first day after birth. FOE was significantly lower in the second, third and fourth time period compared to the first 6 h period. TOI showed a non-significant trend towards higher values in the third period compared to the first 6 h period.

SIGNIFICANCE

In preterm neonates Hbflow, DO2, SvO2 increased, FOE decreased and TOI showed a trend towards increase during the first day after birth, whereas VO2 did not change. Changes of peripheral-muscle oxygenation during the first day after birth in stable preterm neonates are different to already published changes thereafter.

[Diagnosing acute organ ischemia : A practical guide for the emergency and intensive care physician]

Ischemia refers to a reduction or interruption of the blood flow to one or more organs. Early recognition of shock, a global ischemic state of the body, is of key importance in emergency and intensive care medicine. The physical examination and point-of-care laboratory diagnostics (i.e. lactate, base deficit, central/mixed venous oxygen saturation, venous-arterial carbon dioxide partial tension) are the methods of choice to diagnose shock in clinical practice. Importantly, a state of shock can also be present in patients with normo- or hypertensive arterial blood pressures. In shock, hypoperfusion of vital and visceral organs occurs. In the second part of this article, physical examination techniques, laboratory and diagnostic methods to detect shock-related hypoperfusion of the brain, heart, kidney and gastrointestinal tract are reviewed.

Oxygenation strategies for encapsulated islet and beta cell transplants

Human allogeneic islet transplantation (ITx) is emerging as a promising treatment option for qualified patients with type 1 diabetes. However, widespread clinical application of allogeneic ITx is hindered by two critical barriers: the need for systemic immunosuppression and the limited supply of human islet tissue. Biocompatible, retrievable immunoisolation devices containing glucose-responsive insulin-secreting tissue may address both critical barriers by enabling the more effective and efficient use of allogeneic islets without immunosuppression in the near-term, and ultimately the use of a cell source with a virtually unlimited supply, such as human stem cell-derived β-cells or xenogeneic (porcine) islets with minimal or no immunosuppression. However, even though encapsulation methods have been developed and immunoprotection has been successfully tested in small and large animal models and to a limited extent in proof-of-concept clinical studies, the effective use of encapsulation approaches to convincingly and consistently treat diabetes in humans has yet to be demonstrated. There is increasing consensus that inadequate oxygen supply is a major factor limiting their clinical translation and routine implementation. Poor oxygenation negatively affects cell viability and β-cell function, and the problem is exacerbated with the high-density seeding required for reasonably-sized clinical encapsulation devices. Approaches for enhanced oxygen delivery to encapsulated tissues in implantable devices are therefore being actively developed and tested. This review summarizes fundamental aspects of islet microarchitecture and β-cell physiology as well as encapsulation approaches highlighting the need for adequate oxygenation; it also evaluates existing and emerging approaches for enhanced oxygen delivery to encapsulation devices, particularly with the advent of β-cell sources from stem cells that may enable the large-scale application of this approach.

Transient HIF2A inhibition promotes satellite cell proliferation and muscle regeneration

The remarkable regeneration capability of skeletal muscle depends on the coordinated proliferation and differentiation of satellite cells (SCs). The self-renewal of SCs is critical for long-term maintenance of muscle regeneration potential. Hypoxia profoundly affects the proliferation, differentiation, and self-renewal of cultured myoblasts. However, the physiological relevance of hypoxia and hypoxia signaling in SCs in vivo remains largely unknown. Here, we demonstrate that SCs are in an intrinsic hypoxic state in vivo and express hypoxia-inducible factor 2A (HIF2A). HIF2A promotes the stemness and long-term homeostatic maintenance of SCs by maintaining their quiescence, increasing their self-renewal, and blocking their myogenic differentiation. HIF2A stabilization in SCs cultured under normoxia augments their engraftment potential in regenerative muscle. Conversely, HIF2A ablation leads to the depletion of SCs and their consequent regenerative failure in the long-term. In contrast, transient pharmacological inhibition of HIF2A accelerates muscle regeneration by increasing SC proliferation and differentiation. Mechanistically, HIF2A induces the quiescence and self-renewal of SCs by binding the promoter of the Spry1 gene and activating Spry1 expression. These findings suggest that HIF2A is a pivotal mediator of hypoxia signaling in SCs and may be therapeutically targeted to improve muscle regeneration.

Tissue Oxygenation Monitoring as a Guide for Trauma Resuscitation

Hypoperfusion is the most common event preceding the onset of multiple organ dysfunction syndrome during trauma resuscitation. Detecting subtle changes in perfusion is crucial to ensure adequate tissue oxygenation and perfusion. Traditional methods of detecting physiological changes include measurements of blood pressure, heart rate, urine output, serum levels of lactate, mixed venous oxygen saturation, and central venous oxygen saturation. Continuous noninvasive monitoring of tissue oxygen saturation in muscle has the potential to indicate severity of shock, detect occult hypoperfusion, guide resuscitation, and be predictive of the need for interventions to prevent multiple organ dysfunction syndrome. Tissue oxygen saturation is being used in emergency departments, trauma rooms, operating rooms, and emergency medical services. Tissue oxygen saturation technology is just as effective as mixed venous oxygen saturation, central venous oxygen saturation, serum lactate, and Stewart approach with strong ion gap, yet tissue oxygen saturation assessment is also a direct, noninvasive microcirculatory measurement of oxygen saturation.

Low near infrared spectroscopic somatic oxygen saturation at admission is associated with need for lifesaving interventions among unplanned admissions to the pediatric intensive care unit

To investigate the association between low near infrared spectroscopy (NIRS) somatic oxygen saturation (<70%) at admission and the need for lifesaving interventions (LSI) in the initial 24 h of a PICU admission. Retrospective chart review of all unplanned admissions to the pediatric intensive care unit (PICU) with NIRS somatic oxygen saturation data available within 4 h of admission, excluding admissions with a cardiac diagnosis. LSI data were collected for the first 24 h after admission. Hemodynamic parameters, laboratory values, illness severity scores and diagnoses were collected. Included PICU admissions were stratified by lowest NIRS value in the first 4 h after admission: low NIRS (<70%) and normal NIRS (≥70%) groups. Rate of LSI from 4 h to 24 h was compared between the two groups. Association of LSI with NIRS saturation and other clinical and laboratory parameters was measured by univariate and multivariate methods. We reviewed 411 consecutive unplanned admissions to the PICU of which 184 (44%) patients underwent NIRS monitoring. A higher proportion of patients who underwent somatic NIRS monitoring required LSIs compared to those without NIRS monitoring (36.4 vs 5.7% respectively, p < 0.0001). The proportion of patients who required LSI was higher in the group with low NIRS (<70%) within the first 4 h compared to those with normal NIRS (≥70%) (77.1 vs 22.1%, p < 0.0001). Fluid resuscitation, blood products and vasoactive medications were the most common LSIs. Multivariable modeling showed NIRS < 70% and heart rate > 2SD for age to be associated with LSIs. ROC curve analysis of the combination of NIRS < 70% and HR >2SD for age had an area under the curve of 0.79 with 78% sensitivity and 76% specificity for association with LSI. Compared to the normal NIRS group, the low NIRS group had higher mortality (10.4 vs 0.7%, p = 0.005) and longer median hospital length of stay (2.9 vs 1.6 days, p < 0.0001). Low somatic NIRS oxygen saturation (<70%) in the first 4 h of an unplanned PICU admission is associated with need for higher number of subsequent lifesaving interventions up to 24 h after admission. Noninvasive, continuous, somatic NIRS monitoring may identify children at high risk of medical instability.

Guiding Management in Severe Trauma: Reviewing Factors Predicting Outcome in Vastly Injured Patients

Trauma is one of the leading causes of death worldwide, with road traffic collisions, suicides, and homicides accounting for the majority of injury-related deaths. Since trauma mainly affects young age groups, it is recognized as a serious social and economic threat, as annually, almost 16,000 posttrauma individuals are expected to lose their lives and many more to end up disabled. The purpose of this research is to summarize current knowledge on factors predicting outcome - specifically mortality risk - in severely injured patients. Development of this review was mainly based on the systematic search of PubMed medical library, Cochrane database, and advanced trauma life support Guiding Manuals. The research was based on publications between 1994 and 2016. Although hypovolemic, obstructive, cardiogenic, and septic shock can all be seen in multi-trauma patients, hemorrhage-induced shock is by far the most common cause of shock. In this review, we summarize current knowledge on factors predicting outcome - more specifically mortality risk - in severely injured patients. The main mortality-predicting factors in trauma patients are those associated with basic human physiology and tissue perfusion status, coagulation adequacy, and resuscitation requirements. On the contrary, advanced age and the presence of comorbidities predispose patients to a poor outcome because of the loss of physiological reserves. Trauma resuscitation teams considering mortality prediction factors can not only guide resuscitation but also identify patients with high mortality risk who were previously considered less severely injured.

Transfusion Decision Making in Pediatric Critical Illness

Transfusion decision making (TDM) in the critically ill requires consideration of: (1) anemia tolerance, which is linked to active pathology and to physiologic reserve, (2) differences in donor RBC physiology from that of native RBCs, and (3) relative risk from anemia-attributable oxygen delivery failure vs hazards of transfusion, itself. Current approaches to TDM (e.g. hemoglobin thresholds) do not: (1) differentiate between patients with similar anemia, but dissimilar pathology/physiology, and (2) guide transfusion timing and amount to efficacy-based goals (other than resolution of hemoglobin thresholds). Here, we explore approaches to TDM that address the above gaps.

Monitoring Acute Myocardial Infarction Complicated with Cardiogenic Shock — from the Emergency Room to Coronary Care Units

Cardiogenic shock remains the leading cause of death in patients hospitalized for acute myocardial infarction, despite many advances encountered in the last years in reperfusion, mechanical, and pharmacological therapies addressed to stabilization of the hemodynamic condition of these critical patients. Such patients require immediate initiation of the most effective therapy, as well as a continuous monitoring in the Coronary Care Unit. Novel biomarkers have been shown to improve diagnosis and risk stratification in patients with cardiogenic shock, and their proper use may be especially important for the identification of the critical condition, leading to prompt therapeutic interventions. The aim of this review was to evaluate the current literature data on complex biomarker assessment and monitoring of patients with acute myocardial infarction complicated with cardiogenic shock in the Coronary Care Unit.

Comparative and Experimental Studies on the Genes Altered by Chronic Hypoxia in Human Brain Microendothelial Cells

Background : Hypoxia inducible factor 1 alpha (HIF1A) is a master regulator of acute hypoxia; however, with chronic hypoxia, HIF1A levels return to the normoxic levels. Importantly, the genes that are involved in the cell survival and viability under chronic hypoxia are not known. Therefore, we tested the hypothesis that chronic hypoxia leads to the upregulation of a core group of genes with associated changes in the promoter DNA methylation that mediates the cell survival under hypoxia. Results : We examined the effect of chronic hypoxia (3 days; 0.5% oxygen) on human brain micro endothelial cells (HBMEC) viability and apoptosis. Hypoxia caused a significant reduction in cell viability and an increase in apoptosis. Next, we examined chronic hypoxia associated changes in transcriptome and genome-wide promoter methylation. The data obtained was compared with 16 other microarray studies on chronic hypoxia. Nine genes were altered in response to chronic hypoxia in all 17 studies. Interestingly, HIF1A was not altered with chronic hypoxia in any of the studies. Furthermore, we compared our data to three other studies that identified HIF-responsive genes by various approaches. Only two genes were found to be HIF dependent. We silenced each of these 9 genes using CRISPR/Cas9 system. Downregulation of EGLN3 significantly increased the cell death under chronic hypoxia, whereas downregulation of ERO1L, ENO2, adrenomedullin, and spag4 reduced the cell death under hypoxia. Conclusions : We provide a core group of genes that regulates cellular acclimatization under chronic hypoxic stress, and most of them are HIF independent.

Molecular targeting of hypoxia in radiotherapy

Hypoxia (low O₂) is an essential microenvironmental driver of phenotypic diversity in human solid cancers. Hypoxic cancer cells hijack evolutionarily conserved, O₂- sensitive pathways eliciting molecular adaptations that impact responses to radiotherapy, tumor recurrence and patient survival. In this review, we summarize the radiobiological, genetic, epigenetic and metabolic mechanisms orchestrating oncogenic responses to hypoxia. In addition, we outline emerging hypoxia- targeting strategies that hold promise for individualized cancer therapy in the context of radiotherapy and drug delivery.

Direct Measurement of Tissue Oxygenation as a Method of Diagnosis of Acute Compartment Syndrome

OBJECTIVE

The aim of this study was to investigate the utility of direct measurement of tissue oxygenation during compartment syndrome (CS) and tourniquet-induced ischemia in a large animal model. We hypothesize that as compartment pressure (CP) rises, circulation within the compartment will decrease resulting in a decreased level of oxygen in the muscle.

METHODS

This study used a dog model of both CS- and tourniquet-based ischemia. In 15 animals, CS was induced in 1 hind limb with varying degrees of severity using an infusion model. Tourniquet ischemia was induced in the contralateral hind limb for varying durations. The partial pressure of oxygen (PmO2) was continuously monitored using a polarographic oxygen probe in the muscle of both hind limbs. CP was monitored in the CS limb. PmO2 and CP were analyzed after fasciotomy, performed after approximately 7 hours of warm ischemia, or release of tourniquet.

RESULTS

With the application of tourniquet ischemia, PmO2 fell from 38.40 to 1.30 mm Hg (P < 0.001) and subsequently rose after release of the tourniquet to 39.81 mm Hg (P < 0.001). Elevated CP induced by infusion was relieved by fasciotomy (52.04-11.37 mm Hg postfasciotomy, P < 0.001). PmO2 readings in the infusion model were significantly higher in pre-CS than during CS (31.77 mm Hg vs. 3.88 mm Hg, P < 0.001) and rebounded after fasciotomy (50.24 mm Hg, P < 0.001), consistent with hyperemic response.

CONCLUSIONS

Increased CP caused an observable decrease in PmO2 that was reversed by fasciotomy. PmO2 can be directly measured in real time with a polarographic tissue pO2 probe. This study is the first step of evaluating an alternative method for diagnosing acute CS.

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.

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

Background

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

Methods

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

Results

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

Conclusions

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

Tissue oxygen saturation as an early indicator of delayed lactate clearance after cardiac surgery: a prospective observational study

Background

In this observational study near infrared spectroscopy (NIRS) was evaluated as a non-invasive monitor of impaired tissue oxygenation (StO₂) after cardiac surgery. StO₂, cardiac output, mixed venous oxygen saturation and mean arterial pressure were compared with lactate clearance as established measure for sufficient tissue perfusion and oxygen metabolism.

Methods

Forty patients after cardiac surgery (24 aortocoronary bypass grafting, 5 heart valve, 3 ascending aorta and 8 combined procedures) were monitored until postoperative day 1 with NIRS of the thenar muscle (InSpectra™ StO₂-monitor, Hutchinson Technology), a pulmonary-artery catheter and intermittent blood gas analyses for the assessment of lactate clearance.

Results

StO₂ was reduced 4 h after surgery (75 ± 6 %), but recovered at day 1 (84 ± 5 %), while lactate concentration remained increased. Using uni- and multivariate regression analysis, minimum StO₂ (r = 0.46, p <0.01) and cardiac index (r = 0.40, p <0.05) correlated with lactate clearance at day 1, while minimum mixed venous saturation and mean arterial pressure did not. In a receiver-operating characteristics (ROC) analysis, minimum StO₂ (with a threshold of 75 %) predicted a lactate clearance <10 % at day 1 with an area under the ROC-curve of 0.83, a sensitivity of 78 % and a specificity of 88 %. In the subgroup with StO₂  <75 %, troponin and creatine kinase MB were significantly increased at day 1.

Conclusions

StO₂ below 75 % in the first hours after surgery was a better early indicator of persistent impaired lactate clearance at day 1 than cardiac index, mixed venous oxygen saturation or mean arterial pressure.

Tissue oxygen tension monitoring of organ perfusion: rationale, methodologies, and literature review

Tissue oxygen tension is the partial pressure of oxygen within the interstitial space of an organ bed. As it represents the balance between local oxygen delivery and consumption at any given time, it offers a ready monitoring capability to assess the adequacy of tissue perfusion relative to local demands. This review covers the various methodologies used to measure tissue oxygen tension, describes the underlying physiological and pathophysiological principles, and summarizes human and laboratory data published to date.

Association of low non-invasive near-infrared spectroscopic measurements during initial trauma resuscitation with future development of multiple organ dysfunction

BACKGROUND

Near-infrared spectroscopy (NIRS) non-invasively monitors muscle tissue oxygen saturation (StO2). It may provide a continuous noninvasive measurement to identify occult hypoperfusion, guide resuscitation, and predict the development of multiple organ dysfunction (MOD) after severe trauma. We evaluated the correlation between initial StO2 and the development of MOD in multi-trauma patients.

METHODS

Patients presenting to our urban, academic, Level I Trauma Center/Emergency Department and meeting standardized trauma-team activation criteria were enrolled in this prospective trial. NIRS monitoring was initiated immediately on arrival with collection of StO2 at the thenar eminence and continued up to 24 hours for those admitted to the Trauma Intensive Care Unit (TICU). Standardized resuscitation laboratory measures and clinical evaluation tools were collected. The primary outcome was the association between initial StO2 and the development of MOD within the first 24 hours based on a MOD score of 6 or greater. Descriptive statistical analyses were performed; numeric means, multivariate regression and rank sum comparisons were utilized. Clinicians were blinded from the StO2 values.

RESULTS

Over a 14 month period, 78 patients were enrolled. Mean age was 40.9 years (SD 18.2), 84.4% were male, 76.9% had a blunt trauma mechanism and mean injury severity score (ISS) was 18.5 (SD 12.9). Of the 78 patients, 26 (33.3%) developed MOD within the first 24 hours. The MOD patients had mean initial StO2 values of 53.3 (SD 10.3), significantly lower than those of non-MOD patients 61.1 (SD 10.0); P=0.002. The mean ISS among MOD patients was 29.9 (SD 11.5), significantly higher than that of non-MODS patients, 12.1 (SD 9.1) (P<0.0001). The mean shock index (SI) among MOD patients was 0.92 (SD 0.28), also significantly higher than that of non-MODS patients, 0.73 (SD 0.19) (P=0.0007). Lactate values were not significantly different between groups.

CONCLUSION

Non-invasive, continuous StO2 near-infrared spectroscopy values during initial trauma resuscitation correlate with the later development of multiple organ dysfunction in this patient population.

Peripheral Muscle Near-Infrared Spectroscopy in Neonates: Ready for Clinical Use? A Systematic Qualitative Review of the Literature

BACKGROUND

Peripheral muscle near-infrared spectroscopy (NIRS) measurements are of increasing interest especially in the care of critically ill patients.

OBJECTIVE

The aim was to perform a systematic qualitative review on peripheral muscle NIRS measurements in the clinical care of term and preterm neonates.

METHODS

A systematic search of PubMed and Ovid Embase was performed using the following terms: neonate, neonates, newborn, newborns, infant, infants, near-infrared spectroscopy, NIRS, oxygenation, perfusion, oxygen extraction, peripheral, tissue, muscle, calf, forearm and thigh. Additional articles were identified by a manual search of the cited references. Only human studies were included.

RESULTS

Twenty-one studies were identified to use peripheral muscle NIRS measurements as a single method, 17 studies combined cerebral and peripheral muscle NIRS measurements and 1 study used multi-site NIRS measurements in human neonates. Two randomized studies were identified. Two additional publications were included because they provided important general information about peripheral muscle NIRS measurements.

CONCLUSION

In the care of critically ill neonates peripheral muscle NIRS measurements alone or in combination with cerebral or multi-site NIRS measurements provide useful additional information about peripheral circulation and oxygenation. This method is a promising tool in the recognition of early states of centralization (compensated shock) in this vulnerable group of patients. However, before this method can be used in the clinical routine it has to be tested as monitoring to guide interventions in further studies.

Bedside assessment of tissue oxygen saturation monitoring in critically ill adults: an integrative review of the literature

Objective. Tissue oxygen saturation (StO2) monitoring is a noninvasive technology with the purpose of alerting the clinician of peripheral hypoperfusion and the onset of tissue hypoxia. This integrative review examines the rigor and quality of studies focusing on StO2 monitoring in adult critically ill patients. Background. Clinicians must rapidly assess adverse changes in tissue perfusion while minimizing potential complications associated with invasive monitoring. The noninvasive measurement of tissue oxygen saturation is based on near-infrared spectroscopy (NIRS), an optical method of illuminating chemical compounds which absorb, reflect, and scatter light directed at that compound. Methods. An integrative review was conducted to develop a context of greater understanding about complex topics. An Integrative review draws on multiple experimental and nonexperimental research methodologies. Results. Fourteen studies were graded at the C category. None reported the use of probability sampling or demonstrated a cause-and-effect relationship between StO2 values and patient outcomes. Conclusions. Future research should be based on rigorous methods of sampling and design in order to enhance the internal and external validity of the findings.

Low StO2 measurements in surgical intensive care unit patients is associated with poor outcomes

BACKGROUND

Near-infrared spectroscopy-derived tissue hemoglobin saturation (StO2) is a noninvasive measurement that reflects changes in microcirculatory tissue perfusion. Previous studies in trauma patients have shown a correlation between low StO2 levels and mortality, organ failure, and severity of injury. The goals of this study were to identify the incidence of low StO2 in the critically ill patient population of a surgical intensive care unit (SICU) and evaluate the relationship of low StO2 and clinical outcomes.

METHODS

We conducted a prospective cohort study at the University of Minnesota Medical Center. After institutional review board approval, 620 patients admitted to the SICU between July 2010 and July 2011 were screened for enrollment. Patients with an expected ICU length of stay of less than 24 hours were excluded. In the 490 patients who met inclusion criteria, StO2 measurements were obtained from the thenar eminence one to three times daily for the length of the ICU stay, up to 14 days. Outcome data included 28-day hospital mortality; ICU readmission; ventilator-free, ICU-free, and hospital-free days; and the need for lifesaving interventions.

RESULTS

The overall incidence of low StO2 (<70%) was 11% of the patients per day. Patients with at least 1 day in the SICU with an StO2 measurement of less than 70% had higher rates of ICU readmission and fewer ventilator-free, ICU-free, and hospital-free days compared with those who did not. Mortality (28-day in-hospital) trended higher for these patients but was not statistically significant. An increase in the number of days with StO2 less than 70% was also associated with fewer ventilator-free, ICU-free, and hospital-free days.

CONCLUSION

Low StO2 (<70%) is common and associated with poor outcomes in SICU patients. Near-infrared spectroscopy represents a potentially useful, noninvasive adjunct to monitoring of critically ill patients.

LEVEL OF EVIDENCE

Prognostic study, level II.

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

OBJECTIVE

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

DESIGN

Prospective and observational study.

SETTING

Intensive care unit.

PATIENTS

Critically ill patients with community-acquired pneumonia.

INTERVENTIONS

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

VARIABLES

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

RESULTS

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

CONCLUSION

Both BR and D muscles were appropriate for measuring rSO2.

Skeletal muscle oxygen saturation (StO2) measured by near-infrared spectroscopy in the critically ill patients

According to current critical care management guidelines, the overall hemodynamic optimization process seeks to restore macrocirculatory oxygenation, pressure, and flow variables. However, there is increasing evidence demonstrating that, despite normalization of these global parameters, microcirculatory and regional perfusion alterations might occur, and persistence of these alterations has been associated with worse prognosis. Such observations have led to great interest in testing new technologies capable of evaluating the microcirculation. Near-infrared spectroscopy (NIRS) measures tissue oxygen saturation (StO₂) and has been proposed as a noninvasive system for monitoring regional circulation. The present review aims to summarize the existing evidence on NIRS and its potential clinical utility in different scenarios of critically ill patients.

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.

Venous and arterial base deficits: do these agree in occult shock and in the elderly? A Bland-Altman analysis

BACKGROUND

Trauma centers are increasingly advocating the replacement of arterial blood gas measurements with venous blood gas measurements for simplification of base deficit (BD) determination. These values have never been demonstrated to agree in important trauma populations, such as for patients in occult shock (OS) or the elderly. The goal of this study was to investigate the level of agreement between venous and arterial BDs from blood gases in critically ill or injured patients, specifically in OS and the elderly.

METHODS

This is a retrospective, consecutive, cohort study using matched pairs of venous and arterial blood gases from patients admitted to the Trauma and Neurosurgery Intensive Care Unit in a Level I trauma center in Toronto, Ontario, Canada. Agreement between near simultaneous arterial and venous BD was calculated using the Bland-Altman method. McNemar's test was used for differences in BDs in the presence or absence of OS and in elderly patients.

RESULTS

BDs for 466 arterial and venous samples from 72 patients were compared pairwise. There was no significant difference between samples (p = 0.88). Ninety-eight percent of samples were within 3.0 mmol/L of each other. No significant differences were detected between venous and arterial BD in the presence of OS or in the elderly (p = 0.72 and p = 0.25, respectively).

CONCLUSION

Arterial and venous BDs agree, including in the presence of OS and in the elderly. Consideration may be given to venous sampling both in the intensive care unit or in other areas of care, such as the trauma bay.

LEVEL OF EVIDENCE

Diagnostic study, level III.

The influence of perinatal asphyxia on peripheral oxygenation and perfusion in neonates

BACKGROUND

Perinatal asphyxia influences peripheral oxygenation and perfusion in neonates.

OBJECTIVES

The aim was to investigate the influence of perinatal asphyxia on peripheral oxygenation and perfusion in neonates by using near-infrared spectroscopy (NIRS).

METHODS

Prospective observational study. Neonates with gestational age >34 weeks and birth weight >2000 g without infection or congenital malformations were included. Peripheral muscle NIRS measurements in combination with venous occlusion were performed once in the first 48 h of life. Tissue oxygenation index (TOI), mixed venous oxygenation (SvO2), fractional oxygen extraction (FOE), haemoglobin flow (Hbflow), oxygen delivery (DO2) and oxygen consumption (VO2) were assessed. Furthermore arterial oxygen saturation, heart rate, blood pressure and temperatures were measured. Neonates with a UapH≤7.15 and an Apgar 5≤6 were compared to neonates with a UapH≥7.15, an Apgar 5≥7 (control group) and a UapH was correlated to NIRS parameters.

RESULTS

8 asphyxiated neonates were compared to 30 neonates in the control group. TOI (67.7±5.5%) and DO2 (29.0±14.2 μmol/100 mL/min) were significantly lower in asphyxiated neonates compared to the controls (TOI 71.8±4.9%, p=0.045; DO2 43.9±16.9 μmol/100 mL/min, p=0.028) and FOE was significantly higher (0.33±0.05) compared to the controls (0.28±0.06, p=0.028). Furthermore significant correlations between UapH and DO2 (r=0.78, p=0.022), VO2 (r=0.80, p=0.018) and FOE (r=-0.75, p=0.034) in the asphyxiated group were found.

CONCLUSION

Peripheral oxygenation and perfusion measured with NIRS are compromised in neonates with perinatal asphyxia with worsening of parameters and degree of acidosis in the umbilical cord blood.

Altering physiological networks using drugs: steps towards personalized physiology

Background

The rise of personalized medicine has reminded us that each patient must be treated as an individual. One factor in making treatment decisions is the physiological state of each patient, but definitions of relevant states and methods to visualize state-related physiologic changes are scarce. We constructed correlation networks from physiologic data to demonstrate changes associated with pressor use in the intensive care unit.

Methods

We collected 29 physiological variables at one-minute intervals from nineteen trauma patients in the intensive care unit of an academic hospital and grouped each minute of data as receiving or not receiving pressors. For each group we constructed Spearman correlation networks of pairs of physiologic variables. To visualize drug-associated changes we split the networks into three components: an unchanging network, a network of connections with changing correlation sign, and a network of connections only present in one group.

Results

Out of a possible 406 connections between the 29 physiological measures, 64, 39, and 48 were present in each of the three component networks. The static network confirms expected physiological relationships while the network of associations with changed correlation sign suggests putative changes due to the drugs. The network of associations present only with pressors suggests new relationships that could be worthy of study.

Conclusions

We demonstrated that visualizing physiological relationships using correlation networks provides insight into underlying physiologic states while also showing that many of these relationships change when the state is defined by the presence of drugs. This method applied to targeted experiments could change the way critical care patients are monitored and treated.

Serial lactate and admission SOFA scores in trauma: an analysis of predictive value in 724 patients with and without traumatic brain injury

OBJECTIVE

Arterial lactate, base excess (BE), lactate clearance, and Sequential Organ Failure Assessment (SOFA) score have been shown to correlate with outcome in severely injured patients. The goal of the present study was to separately assess their predictive value in patients suffering from traumatic brain injury (TBI) as opposed to patients suffering from injuries not related to the brain.

MATERIALS AND METHODS

A total of 724 adult trauma patients with an Injury Severity Score (ISS) ≥ 16 were grouped into patients without TBI (non-TBI), patients with isolated TBI (isolated TBI), and patients with a combination of TBI and non-TBI injuries (combined injuries). The predictive value of the above parameters was then analyzed using both uni- and multivariate analyses.

RESULTS

The mean age of the patients was 39 years (77 % males), with a mean ISS of 32 (range 16-75). Mortality ranged from 14 % (non-TBI) to 24 % (combined injuries). Admission and serial lactate/BE values were higher in non-survivors of all groups (all p < 0.01), but not in patients with isolated TBI. Admission SOFA scores were highest in non-survivors of all groups (p = 0.023); subsequently septic patients also showed elevated SOFA scores (p < 0.01), except those with isolated TBI. In this group, SOFA score was the only parameter which showed significant differences between survivors and non-survivors. Receiver operating characteristic (ROC) analysis revealed lactate to be the best overall predictor for increased mortality and further septic complications, irrespective of the leading injury.

CONCLUSION

Lactate showed the best performance in predicting sepsis or death in all trauma patients except those with isolated TBI, and the differences were greatest in patients with substantial bleeding. Following isolated TBI, SOFA score was the only parameter which could differentiate survivors from non-survivors on admission, although the SOFA score, too, was not an independent predictor of death following multivariate analysis.

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

BACKGROUND

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.

METHODS

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.

RESULTS

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).

CONCLUSION

IMN causes significant remote microcirculatory changes. The responsiveness of the microcirculation could be a predictor of secondary organ dysfunction.

LEVEL OF EVIDENCE

Epidemiologic study, level III.

Bladder tissue oxygen tension monitoring in pigs subjected to a range of cardiorespiratory and pharmacological challenges

PURPOSE

A fall in tissue oxygen tension (tPO(2)) is an early indicator of organ hypoxia in both patients and animal models. We previously demonstrated the utility of bladder tPO(2) in various rodent shock models. As a prelude to clinical testing, we aimed to provide further validation of bladder tPO(2) monitoring in a large animal model undergoing a range of cardiorespiratory insults and vasoactive drug interventions.

METHODS

Anaesthetized, mechanically ventilated, instrumented female pigs (n = 8) were subjected to a range of short-term cardiorespiratory (changes in inspired oxygen concentration (FiO(2)), haemorrhage, positive end-expiratory pressure) and pharmacologic (inotrope, pressor) challenges. Global haemodynamics, arterial and pulmonary blood gases and bladder tPO(2) were measured before and after each challenge.

RESULTS

Bladder tPO(2) values fell in line with increasing degrees of hypoxaemia and haemorrhage, and were restored during resuscitation. These changes often preceded those seen in global haemodynamics, arterial base excess and lactate. The rise in bladder tPO(2) with hyperoxia, performed as an oxygen challenge test, was incrementally blunted by progressive haemorrhage. Dobutamine and norepinephrine both increased cardiac output and global O(2) delivery, but had no effect on bladder tPO(2) or lactataemia in these healthy pigs.

CONCLUSIONS

In this pig model bladder tPO(2) provides a sensitive indicator of organ hypoxia compared to traditional biochemical markers during various cardiorespiratory challenges. This technique offers a potentially useful tool for clinical monitoring.

Change in regional (somatic) near-infrared spectroscopy is not a useful indicator of clinically detectable low cardiac output in children after surgery for congenital heart defects

OBJECTIVE

Near-infrared spectroscopy correlation with low cardiac output has not been validated. Our objective was to determine role of splanchnic and/or renal oxygenation monitoring using near-infrared spectroscopy for detection of low cardiac output in children after surgery for congenital heart defects.

DESIGN

Prospective observational study.

SETTING

Pediatric intensive care unit of a tertiary care teaching hospital.

PATIENTS

Children admitted to the pediatric intensive care unit after surgery for congenital heart defects.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

We hypothesized that splanchnic and/or renal hypoxemia detected by near-infrared spectroscopy is a marker of low cardiac output after pediatric cardiac surgery. Patients admitted after cardiac surgery to the pediatric intensive care unit over a 10-month period underwent serial splanchnic and renal near-infrared spectroscopy measurements until extubation. Baseline near-infrared spectroscopy values were recorded in the first postoperative hour. A near-infrared spectroscopy event was a priori defined as ≥20% drop in splanchnic and/or renal oxygen saturation from baseline during any hour of the study. Low cardiac output was defined as metabolic acidosis (pH <7.25, lactate >2 mmol/L, or base excess ≤-5), oliguria (urine output <1 mL/kg/hr), or escalation of inotropic support. Receiver operating characteristic analysis was performed using near-infrared spectroscopy event as a diagnostic test for low cardiac output. Twenty children were enrolled: median age was 5 months; median Risk Adjustment for Congenital Heart Surgery category was 3 (1-6); median bypass and cross-clamp times were 120 mins (45-300 mins) and 88 mins (17-157 mins), respectively. Thirty-one episodes of low cardiac output and 273 near-infrared spectroscopy events were observed in 17 patients. The sensitivity and specificity of a near-infrared spectroscopy event as an indicator of low cardiac output were 48% (30%-66%) and 67% (64%-70%), respectively. On receiver operating characteristic analysis, neither splanchnic nor renal near-infrared spectroscopy event had a significant area under the curve for prediction of low cardiac output (area under the curve: splanchnic 0.45 [95% confidence interval 0.30-0.60], renal 0.51 [95% confidence interval 0.37-0.65]).

CONCLUSIONS

Splanchnic and/or renal hypoxemia as detected by near-infrared spectroscopy may not be an accurate indicator of low cardiac output after surgery for congenital heart defects.

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

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

Peripheral vasoconstriction influences thenar oxygen saturation as measured by near-infrared spectroscopy

Purpose

Near-infrared spectroscopy has been used as a noninvasive monitoring tool for tissue oxygen saturation (StO₂) in acutely ill patients. This study aimed to investigate whether local vasoconstriction induced by body surface cooling significantly influences thenar StO₂ as measured by InSpectra model 650.

Methods

Eight healthy individuals (age 26 ± 6 years) participated in the study. Using a cooling blanket, we aimed to cool the entire body surface to induce vasoconstriction in the skin without any changes in central temperature. Thenar StO₂ was noninvasively measured during a 3-min vascular occlusion test using InSpectra model 650 with a 15-mm probe. Measurements were analyzed for resting StO₂ values, rate of StO₂ desaturation (RdecStO₂, %/min), and rate of StO₂ recovery (RincStO₂, %/s) before, during, and after skin cooling. Measurements also included heart rate (HR), mean arterial pressure (MAP), cardiac output (CO), stroke volume (SV), capillary refill time (CRT), forearm-to-fingertip skin-temperature gradient (Tskin-diff), perfusion index (PI), and tissue hemoglobin index (THI).

Results

In all subjects MAP, CO, SV, and core temperature did not change during the procedure. Skin cooling resulted in a significant decrease in StO₂ from 82% (80–87) to 72% (70–77) (P < 0.05) and in RincStO₂ from 3.0%/s (2.8–3.3) to 1.7%/s (1.1–2.0) (P < 0.05). Similar changes in CRT, Tskin-diff, and PI were also observed: from 2.5 s (2.0–3.0) to 8.5 s (7.2–11.0) (P < 0.05), from 1.0°C (−1.6–1.8) to 3.1°C (1.8–4.3) (P < 0.05), and from 10.0% (9.1–11.7) to 2.5% (2.0–3.8), respectively. The THI values did not change significantly.

Conclusion

Peripheral vasoconstriction due to body surface cooling could significantly influence noninvasive measurements of thenar StO₂ using InSpectra model 650 with 15-mm probe spacing.

Why is the partial oxygen pressure of human tissues a crucial parameter? Small molecules and hypoxia

Oxygen supply and diffusion into tissues are necessary for survival. The oxygen partial pressure (pO₂), which is a key component of the physiological state of an organ, results from the balance between oxygen delivery and its consumption. In mammals, oxygen is transported by red blood cells circulating in a well-organized vasculature. Oxygen delivery is dependent on the metabolic requirements and functional status of each organ. Consequently, in a physiological condition, organ and tissue are characterized by their own unique ‘tissue normoxia’ or ‘physioxia’ status. Tissue oxygenation is severely disturbed during pathological conditions such as cancer, diabetes, coronary heart disease, stroke, etc., which are associated with decrease in pO₂, i.e. ‘hypoxia’. In this review, we present an array of methods currently used for assessing tissue oxygenation. We show that hypoxia is marked during tumour development and has strong consequences for oxygenation and its influence upon chemotherapy efficiency. Then we compare this to physiological pO₂ values of human organs. Finally we evaluate consequences of physioxia on cell activity and its molecular modulations. More importantly we emphasize the discrepancy between in vivo and in vitro tissue and cells oxygen status which can have detrimental effects on experimental outcome. It appears that the values corresponding to the physioxia are ranging between 11% and 1% O₂ whereas current in vitro experimentations are usually performed in 19.95% O₂, an artificial context as far as oxygen balance is concerned. It is important to realize that most of the experiments performed in so-called normoxia might be dangerously misleading.

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

BACKGROUND

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

Femoral nailing during serum bicarbonate-defined hypo-perfusion predicts pulmonary organ dysfunction in multi-system trauma patients

OBJECTIVE

To assess the value of venous serum bicarbonate as an endpoint of resuscitation and guide to timing of femoral nailing in multi-system trauma patients.

DESIGN

Retrospective cohort study.

SETTING

Academic Level 1 Trauma Centre.

PATIENTS

Seventy-two consecutive adult multi-system trauma patients (Injury Severity Score≥15) with femoral shaft fracture (Orthopaedic Trauma Association Class 32-A to 32-C) treated with reamed medullary nail fixation.

INTERVENTION

Femoral nailing in the setting of hypo-perfusion defined by venous serum bicarbonate (SB). Threshold values of SB were determined first by correlating SB and simultaneously drawn arterial base deficit (BD). Then, corresponding values of SB to previously defined thresholds of hypo-perfusion based on BD were identified using regression analysis.

MAIN OUTCOME MEASUREMENT

Pulmonary organ dysfunction (POD) component of the Denver Multiple Organ Failure scoring system.

RESULTS

Simultaneous admission SB and BD values were correlated (r=-0.43, p=0.001). Adjusting for age, ISS and baseline POD, patients with SB<24.7 mequiv./L within 6 h of treatment had a 12-fold increase in POD (OR 12.2, 95% CI 1.5-98.6, p=0.019). This association was diminished, but still significant with hypo-perfusion present within 12 h prior to treatment (OR 5.6, 95% CI 1.0-29.1, p=0.042) and 24 h prior to treatment (OR 5.9, 95% CI 1.1-30.7, p=0.037).

CONCLUSIONS

Medullary fixation of femoral shaft fracture in the setting of serum bicarbonate-defined hypo-perfusion is associated with increased morbidity. Appropriate damage-control measures and aggressive resuscitation prior to definitive fracture care are advised and physiologic markers such as serum bicarbonate should guide clinical decision making rather than temporal distinctions.