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From system to organ to cell: oxygenation and perfusion measurement in anesthesia and critical care.Journal of Clinical Monitoring and... Aug 2012Maintenance or restoration of adequate tissue oxygenation is a main goal of anesthesiologic and intensive care patient management. Pathophysiological disturbances which... (Review)
Review
Maintenance or restoration of adequate tissue oxygenation is a main goal of anesthesiologic and intensive care patient management. Pathophysiological disturbances which interfere with aerobic metabolism may occur at any stage in the oxygen cascade from atmospheric gas to the mitochondria, and there is no single monitoring modality that allows comprehensive determination of "the oxygenation". To facilitate early detection of tissue hypoxia (or hyperoxia) and to allow a goal directed therapy targeted at the underlying problem, the anesthesiologist and intensive care physician require a thorough understanding of the numerous determinants that influence cellular oxygenation. This article reviews the basic physiology of oxygen uptake and delivery to tissues as well as the options to monitor determinants of oxygenation at different stages from the alveolus to the cell.
Topics: Anesthesia; Blood Flow Velocity; Critical Care; Humans; Models, Biological; Oximetry; Oxygen Consumption; Rheology
PubMed: 22437884
DOI: 10.1007/s10877-012-9350-4 -
Journal of Biomedical Optics 2008The purpose of this study was to measure the hemoglobin oxygenation in retinal vessels and to evaluate the sensitivity and reproducibility of the measurement. Using a...
The purpose of this study was to measure the hemoglobin oxygenation in retinal vessels and to evaluate the sensitivity and reproducibility of the measurement. Using a fundus camera equipped with a special dual wavelength transmission filter and a color charge-coupled device camera, two monochromatic fundus images at 548 and 610 nm were recorded simultaneously. The optical densities of retinal vessels for both wavelengths and their ratio, which is known to be proportional to the oxygen saturation, were calculated. From 50-deg images, the used semiautomatic vessel recognition and tracking algorithm recognized and measured vessels of 100 microm or more in diameter. On average, arterial and venous oxygen saturations were measured at 98+/-10.1% and 65+/-11.7%, respectively. For measurements in the same vessel segments from the five images per subject, standard deviations of 2.52% and 3.25% oxygen saturation were found in arteries and veins, respectively. Respiration of 100% oxygen increased the mean arterial and venous oxygen saturation by 2% and 7% respectively. A simple system for noninvasive optical oximetry, consisting of a special filter in a fundus camera and software, was introduced. It is able to measure the oxygen saturation in retinal branch vessels with reproducibility and sensitivity suitable for clinical investigations.
Topics: Adult; Calibration; Female; Germany; Humans; Male; Oximetry; Oxygen; Reproducibility of Results; Retinal Artery; Retinal Pigments; Retinoscopy; Sensitivity and Specificity
PubMed: 19021395
DOI: 10.1117/1.2976032 -
Anesthesiology Jul 1992
Topics: Corneal Injuries; Humans; Intraoperative Complications; Oximetry
PubMed: 1610006
DOI: 10.1097/00000542-199207000-00045 -
BMJ (Clinical Research Ed.) Aug 1995
Review
Topics: Decision Making; Humans; Hyperoxia; Hypoxia; Oximetry
PubMed: 7640545
DOI: 10.1136/bmj.311.7001.367 -
Eye (London, England) Mar 2011The work described here involved the use of a modified fundus camera to obtain sequential hyperspectral images of the retina in 14 normal volunteers and in 1...
INTRODUCTION
The work described here involved the use of a modified fundus camera to obtain sequential hyperspectral images of the retina in 14 normal volunteers and in 1 illustrative patient with a retinal vascular occlusion.
METHODS
The paper describes analysis techniques, which allow oximetry within retinal vessels; these results are presented as retinal oximetry maps.
RESULTS
Using spectral images, with wavelengths between 556 and 650 nm, the mean oxygen saturation (OS) value in temporal retinal arterioles in normal volunteers was 104.3 (± 16.7), and in normal temporal retinal venules was 34.8 (± 17.8). These values are comparable to those quoted in the literature, although, the venular saturations are slightly lower than those values found by other authors; explanations are offered for these differences.
DISCUSSION
The described imaging and analysis techniques produce a clinically useful map of retinal oximetric values. The results from normal volunteers and from one illustrative patient are presented. Further developments, including the recent development of a 'snapshot' spectral camera, promises enhanced non-invasive retinal vessel oximetry mapping.
Topics: Adult; Aged; Female; Humans; Male; Middle Aged; Oximetry; Photography; Regional Blood Flow; Retinal Vessels
PubMed: 21390065
DOI: 10.1038/eye.2010.222 -
Advances in Experimental Medicine and... 2017Clinical EPR spectroscopy is emerging as an important modality, with the potential to be used in standard clinical practice to determine the extent of hypoxia in tissues... (Review)
Review
UNLABELLED
Clinical EPR spectroscopy is emerging as an important modality, with the potential to be used in standard clinical practice to determine the extent of hypoxia in tissues and whether hypoxic tissues respond to breathing enriched oxygen during therapy. Oximetry can provide important information useful for prognosis and to improve patient outcomes. EPR oximetry has many potential advantages over other ways to measure oxygen in tissues, including directly measuring oxygen in tissues and being particularly sensitive to low oxygen, repeatable, and non-invasive after an initial injection of the EPR-sensing material is placed in the tumor. The most immediately available oxygen sensor is India ink, where two classes of carbon (carbon black and charcoal) have been identified as having acceptable paramagnetic properties for oximetry. While India ink has a long history of safe use in tattoos, a systematic research search regarding its safety for marking tissues for medical uses and an examination of the evidence that differentiates between ink based on charcoal or carbon black has not been conducted.
METHODS
Using systematic literature search techniques, we searched the PubMed and Food and Drug Administration databases, finding ~1000 publications reporting on adverse events associated with India/carbon based inks. The detailed review of outcomes was based on studies involving >16 patients, where the ink was identifiable as carbon black or charcoal.
RESULTS
Fifty-six studies met these criteria. There were few reports of complications other than transient and usually mild discomfort and bleeding at injection, and there was no difference in charcoal vs. carbon black India ink.
CONCLUSIONS
India ink was generally well tolerated by patients and physicians reported that it was easy to use in practice and used few resources. The risk is low enough to justify its use as an oxygen sensor in clinical practice.
Topics: Animals; Biosensing Techniques; Carbon; Coloring Agents; Electron Spin Resonance Spectroscopy; Humans; Oximetry
PubMed: 28685459
DOI: 10.1007/978-3-319-55231-6_40 -
Chest Feb 2021Millions of smartphones contain a photoplethysmography (PPG) biosensor (Maxim Integrated) that accurately measures pulse oximetry. No clinical use of these embedded...
BACKGROUND
Millions of smartphones contain a photoplethysmography (PPG) biosensor (Maxim Integrated) that accurately measures pulse oximetry. No clinical use of these embedded sensors is currently being made, despite the relevance of remote clinical pulse oximetry to the management of chronic cardiopulmonary disease, and the triage, initial management, and remote monitoring of people affected by respiratory viral pandemics, such as severe acute respiratory syndrome coronavirus 2 or influenza. To be used for clinical pulse oximetry the embedded PPG system must be paired with an application (app) and meet US Food and Drug Administration (FDA) and International Organization for Standardization (ISO) requirements.
RESEARCH QUESTION
Does this smartphone sensor with app meet FDA/ISO requirements? Are measurements obtained using this system comparable to those of hospital reference devices, across a wide range of people?
STUDY DESIGN AND METHODS
We performed laboratory testing addressing ISO and FDA requirements in 10 participants using the smartphone sensor with app. Subsequently, we performed an open-label clinical study on 320 participants with widely varying characteristics, to compare the accuracy and precision of readings obtained by patients with those of hospital reference devices, using rigorous statistical methodology.
RESULTS
"Breathe down" testing in the laboratory showed that the total root-mean-square deviation of oxygen saturation (Spo) measurement was 2.2%, meeting FDA/ISO standards. Clinical comparison of the smartphone sensor with app vs hospital reference devices determined that Spo and heart rate accuracy were 0.48% points (95% CI, 0.38-0.58; P < .001) and 0.73 bpm (95% CI, 0.33-1.14; P < .001), respectively; Spo and heart rate precision were 1.25 vs reference 0.95% points (P < .001) and 5.99 vs reference 3.80 bpm (P < .001), respectively. These small differences were similar to the variation found between two FDA-approved reference instruments for Spo: accuracy, 0.52% points (95% CI, 0.41-0.64; P < .001) and precision, 1.01 vs 0.86% points (P < .001).
INTERPRETATION
Our findings support the application for full FDA/ISO approval of the smartphone sensor with app tested for use in clinical pulse oximetry. Given the immense and immediate practical medical importance of remote intermittent clinical pulse oximetry to both chronic disease management and the global ability to respond to respiratory viral pandemics, the smartphone sensor with app should be prioritized and fast-tracked for FDA/ISO approval to allow clinical use.
TRIAL REGISTRY
ClinicalTrials.gov; No.: NCT04233827; URL: www.clinicaltrials.gov.
Topics: Adolescent; Adult; Aged; Aged, 80 and over; Biosensing Techniques; Device Approval; Female; Humans; Male; Middle Aged; Mobile Applications; Oximetry; Photoplethysmography; Smartphone; United States; United States Food and Drug Administration; Young Adult
PubMed: 32926871
DOI: 10.1016/j.chest.2020.08.2104 -
Eye (London, England) Aug 2023Clinical methods examining oxygenation parameters in humans have been used in many different care settings, but concerns have been raised regarding their clinical...
BACKGROUND
Clinical methods examining oxygenation parameters in humans have been used in many different care settings, but concerns have been raised regarding their clinical utility when assessing people with darker skin pigmentation. While saturation values can be crucial in emergency medicine, they are equally valuable in assessing disease mechanisms and monitoring change in disease progression. Retinal pigmentation varies across individuals and hence, can impact on retinal oxygen parameters. The objective of this study was to quantify and eliminate the impact of retinal pigmentation on retinal vessel oxygen saturation parameters measured in the superficial retinal arterioles and venules.
METHODS
105 healthy individuals of varying skin colour, iris colour and heritage were included. Following a full eye exam to exclude any ocular abnormality, all participants underwent intraocular pressure, systemic blood pressure measurements and dilated dual wavelength retinal photography. Rotation matrices were employed to minimise the dependency of retinal pigmentation on arterial and venous oxygen saturation measurements determined in a concentric measurement annulus.
RESULTS
Retinal oxygen saturation in venules showed a linear correlation with retinal pigmentation (y = 0.34 × x + 38.598), whereas arterial saturation followed a polynomial pattern (y = 0.0089 × x + 0.7499 × x + 85.073). Both arterial and venous saturation values were corrected using local fundus pigmentation. Pre-correction retinal arterial and venous oxygen saturation were 89.0% (±13.1) and 43.7% (±11.5), respectively, and post- correction values were 94.8% (±8.7) for arteries and 56.3% (±7.0) veins.
CONCLUSIONS
When assessing multi-ethnic cohorts, it is important to consider the impact of pigmentation on imaging parameters and to account for it prior to clinical interpretation.
Topics: Humans; Oximetry; Retinal Vessels; Oxygen; Retina; Fundus Oculi; Oxygen Consumption
PubMed: 36460856
DOI: 10.1038/s41433-022-02325-7 -
Advances in Physiology Education Sep 2022Pulse oximetry has become the standard of care in operating rooms, intensive care units, and hospitals worldwide. A pulse oximeter continuously and noninvasively...
Pulse oximetry has become the standard of care in operating rooms, intensive care units, and hospitals worldwide. A pulse oximeter continuously and noninvasively monitors the functional oxygen saturation of hemoglobin in arterial blood ([Formula: see text]). [Formula: see text] is so important in medical care that it is often regarded as a fifth vital sign. Before pulse oximetry, arterial puncture for blood gas analysis was the only method available to determine [Formula: see text] and to identify the presence of hypoxemia. Pulse oximetry is based on the principle that oxygenated hemoglobin (OHb) absorbs more near-infrared light than deoxyhemoglobin (HHb) and HHb absorbs more red light than OHb. It is important to understand the principles of pulse oximetry, how the equipment works, and its limitations to interpret the information it provides. Accordingly, we used colored balloons to introduce the physics of how a pulse oximeter detects and measures oxyhemoglobin and deoxyhemoglobin in pulsatile (arterial) and nonpulsatile (venous and capillary) blood. The foundations of oximetry started in the 1700s with Johann Lambert (1728-1777). We approached this complex physics in a straightforward way while still providing an understanding of the fundamental concepts developed by Johann Lambert in 1760. Educators must go beyond teaching the facts and encourage students to think, investigate, and appreciate the subject matter in a broader framework. To achieve these goals, we used a simple and inexpensive experimental approach to introduce the physics of how a pulse oximeter detects and measures oxyhemoglobin and deoxyhemoglobin in blood. We approached this complex physics in a straightforward way while still providing an understanding of the fundamental concepts developed by Johann Lambert in 1760.
Topics: Hemoglobins; Humans; Oximetry; Oxygen; Oxyhemoglobins; Veins
PubMed: 35759527
DOI: 10.1152/advan.00093.2022 -
Anaesthesia Mar 1991The published studies of pulse oximeter performance under conditions of normal, high and low saturation, exercise, poor signal quality and cardiac arrhythmia are... (Comparative Study)
Comparative Study Review
The published studies of pulse oximeter performance under conditions of normal, high and low saturation, exercise, poor signal quality and cardiac arrhythmia are reviewed. Most pulse oximeters have an absolute mean error of less than 2% at normal saturation and perfusion; two-thirds have a standard deviation (SD) of less than 2%, and the remainder an SD of less than 3%. Some pulse oximeters tend to read 100% with fractional saturations of 97-98%. Pulse oximeters may be suitable hyperoxic alarms for neonates if the alarm limit chosen is directly validated for each device. Pulse oximeters are poorly calibrated at low saturations and are generally less accurate and less precise than at normal saturations; nearly 30% of 244 values reviewed were in error by more than 5% at saturations of less than 80%. Ear, nose and forehead probes respond more rapidly to rapid desaturation than finger probes, but are generally less accurate and less precise. Ear oximetry may be inaccurate during exercise. Low signal quality can result in failure to present a saturation reading, but data given with low signal quality warning messages are generally no less accurate than those without. Cardiac arrhythmias do not decrease accuracy of pulse oximeters so long as saturation readings are steady.
Topics: Animals; Arrhythmias, Cardiac; Exercise; Humans; Oximetry; Oxygen; Partial Pressure
PubMed: 2014899
DOI: 10.1111/j.1365-2044.1991.tb09411.x