Optical Measurement of Tissue Oxygen Saturation

Long-Term In Vivo Oxygen Sensors for Peripheral Artery Disease Monitoring

Tracking of tissue oxygenation around chronic foot wounds may help direct therapy decisions in patients with peripheral artery disease (PAD). Novel sensing technology to enable such monitoring was tested over 9 months in a Sinclair mini-pig model. No adverse events were observed over the entire study period. Systemic and acute hypoxia challenges were detected during each measurement period by the microsensors. The median time to locate the sensor signal was 13 s. Lumee Oxygen microsensors appear safe for long-term repeated oxygen measurements over 9 months.

Hematopoietic Stem Cells: Normal Versus Malignant

SIGNIFICANCE

The long-term hematopoietic stem cell (LT-HSC) demonstrates characteristics of self-renewal and the ability to manage expansion of the hematopoietic compartment while maintaining the capacity for differentiation into hematopoietic stem/progenitor cell (HSPC) and terminal subpopulations. Deregulation of the HSPC redox environment results in loss of signaling that normally controls HSPC fate, leading to a loss of HSPC function and exhaustion. The characteristics of HSPC exhaustion via redox stress closely mirror phenotypic traits of hematopoietic malignancies and the leukemic stem cell (LSC). These facets elucidate the HSC/LSC redox environment as a druggable target and a growing area of cancer research. Recent Advances: Although myelosuppression and exhaustion of the hematopoietic niche are detrimental side effects of classical chemotherapies, new agents that modify the HSPC/LSC redox environment have demonstrated the potential for protection of normal HSPC function while inducing cytotoxicity within malignant populations.

CRITICAL ISSUES

New therapies must preserve, or only slightly disturb normal HSPC redox balance and function, while simultaneously altering the malignant cellular redox state. The cascade nature of redox damage makes this a critical and delicate line for the development of a redox-based therapeutic index.

FUTURE DIRECTIONS

Recent evidence demonstrates the potential for redox-based therapies to impact metabolic and epigenetic factors that could contribute to initial LSC transformation. This is balanced by the development of therapies that protect HSPC function. This pushes toward therapies that may alter the HSC/LSC redox state but lead to initiation cell fate signaling lost in malignant transformation while protecting normal HSPC function. Antioxid. Redox Signal.

Low tissue oxygen saturation is associated with requirements for transfusion in the rural trauma population

BACKGROUND

Tissue O2 saturation (StO2) is a measure of tissue perfusion and should decrease during active hemorrhage. An initial StO2 value upon trauma center arrival measured concurrently with or prior to vitals, may predict hemorrhagic shock, requiring early blood product transfusion. Our aim was to identify the early StO2 threshold associated with a greater volume of packed red blood cell (PRBC) transfusion 24 h after injury.

METHODS

All highest tier triage trauma patients from January 2011 to July 2012 were included in this study. The initial StO2 value upon arrival was used for comparison.

RESULTS

A total of 632 patients were considered, 74% of them male with a mean age of 46 years. Initial StO2 values were available for 325 patients. An StO2 value of 65% was determined as the cutoff due to the marked increase in PRBC consumption in 24 h. There were 23 patients (7%) with an StO2 reading <65% compared to 302 patients with values ≥65%. Both groups had similar systolic blood pressure (118 vs. 126) and heart rate (99 vs. 95) in the trauma bay. In addition, there was no difference in the initial hemoglobin, pH, or base deficit. An early StO2 value <65% also led to a greater number of PRBC transfused in 24 h (6.4 vs. 1.7). Regression analysis demonstrated that an StO2 <65% was the only variable associated with a higher PRBC transfusion volume in 24 h (p = 0.01).

CONCLUSIONS

An StO2 value <65% correlates with greater requirement for PRBC transfusion 24 h after injury. This suggests that StO2 can be used as an early marker of hemorrhage which may be superior to traditional vital signs in the trauma population.

A pilot study of a new spectrophotometry device to measure tissue oxygen saturation

Tissue oxygen saturation (SO2) measurements have the potential for far wider use than at present but are limited by device availability and portability for many potential applications. A device based on a small, low-cost general-purpose spectrophotometer (the Harrison device) might facilitate wider use. The aim of this study was to compare the Harrison device with a commercial instrument, the LEA O2C.Measurements were carried out on the forearm and finger of 20 healthy volunteers, using a blood pressure cuff on the upper arm to induce different levels of oxygenation. Repeatability of both devices was assessed, and the Bland-Altman method was used to assess agreement between them.The devices showed agreement in overall tracking of changes in SO2. Test-retest agreement for the Harrison device was worse than for O2C, with SD repeatability of 10.6% (forearm) or 18.6% (finger). There was no overall bias between devices, but mean (SD) difference of 1.2 (11.8%) (forearm) or 4.4 (11.5%) (finger) were outside of a clinically acceptable range.Disagreements were attributed to the stability of the Harrison probe and the natural SO2 variations across the skin surface increasing the random error. Therefore, though not equivalent to the LEA O2C, a probe redesign and averaged measurements may help establish the Harrison device as a low cost alternative.

Techniques to assess tissue oxygenation in the clinical setting

The microcirculation plays an essential role in health and disease. Microvascular perfusion can be assessed directly using laser Doppler flowmetry and various imaging techniques or indirectly using regional capnometry and measurement of indicators of mismatch between oxygen delivery and oxygen consumption or indices of disturbed cellular oxygen utilization. Assessment of microvascular oxygen availability implies measurement of oxygen pressure or measurement of hemoglobin oxygen saturation. Microvascular function is assessed using other methods, including venous plethysmography. In this paper, I review current knowledge concerning assessment of the microcirculation with special emphasis on methods that could be used at the bedside.

Optical Measurements of Tissue Oxygen Saturation in Lower Limb Wound Healing

This review has highlighted the role of oxygen in wound healing and in the mechanism of preventing infection. Optical measurements of tissue SO2 in wounds can provide valuable information, not only about the inflammatory state of the wound, but also about healing potential in ulcers and critical limb ischaemia. The technique is fast, non-invasive and can be used without the necessity for contact with the skin.