EFFECTS OF POSTURAL CHANGE ON OXYGEN SATURATION
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Oxygen Saturation
Saturation (graph theory)
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Saturation (graph theory)
Pulse Oximetry
Arterial blood
Oxygen Saturation
Venous blood
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A case of aniline-induced methemoglobinemia is reported. When the pulse oximeter reading (SpO2) was 80%, the oxygen saturation measured by a co-oximeter (SaO2) was 61.2%, the oxygen saturation calculated from PaO2 values was 98.9% and methemoglobin level was 38.8%. After methylene blue injection, methemoglobin level decreased gradually. With a decrease of methemoglobin level, SpO2 approached SaO2. If disparity between SpO2 and the oxygen saturation calculated from PaO2 values is noted, the presence of methemoglobinemia must be suspected. In clinical situations, the pulse oximeter permits the continuous noninvasive monitoring of oxygen saturation. It is necessary, however, to consider the potential errors in pulse oximetry.
Methemoglobinemia
Pulse Oximetry
Methemoglobin
Methylene blue
Oxygen Saturation
Saturation (graph theory)
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Saturation (graph theory)
Oxygen Saturation
Pulse Oximetry
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Introduction: Pulse oximetry is commonly used in critical care to monitor changes in arterial oxygen saturation (SpO2). However, studies have reported that decreases in SpO2 may lag behind the actual clinical event. Previous studies have demonstrated that cerebral oxygenation monitoring using near-infrared spectroscopy (NIRS) can detect alterations in oxygenation earlier than pulse oximetry. Here, we compare responses of NIRS monitoring of spinal cord tissue oxygenation (TOI) to pulse oximetry SpO2 during hypoxia. Methods: During a study on optical monitoring of spinal cord hemodynamics in an animal model of spinal cord injury (SCI), episodes of acute (70-80% SpO2) hypoxia were induced. Six anesthetized Yucatan miniature pigs were studied. A standard pulse oximeter was attached to the ear of the animal and a custom-made NIRS sensor was placed extradurally on the spinal cord. Hypoxia was induced by removing the ventilator from the animal and reattaching it once SpO2 reached 70% or 80% as reported by the pulse oximeter. Results: 21 episodes of acute hypoxia were analyzed. Upon the start of hypoxia, NIRS TOI responded in 1.8 ± 0.5 seconds, while pulse oximetry SpO2 responded in 11.4 ± 0.6 seconds (p > 0.0001). Conclusion: NIRS can detect the effects of hypoxia on spinal cord tissue earlier than pulse oximetry can detect arterial oxygenation changes in the periphery. The NIRS sensor may be used as an earlier detector of oxygen saturation changes in the clinical setting than the standard pulse oximeter.
Pulse Oximetry
Hypoxia
Blood oxygenation
Oxygen Saturation
Hypoxic hypoxia
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Oxygen Saturation
Saturation (graph theory)
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Pulse Oximetry
Oxygen Saturation
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Oxygen Saturation
Saturation (graph theory)
Pulse Oximetry
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Pulse oximeters monitor non-invasively the haemoglobin oxygen saturation. Light of two specific wavelengths, red and infrared light, is shined through a tissue, usually the finger, and the intensity of the light transmitted is measured. Oxyhaemoglobin absorbs the light differently when compared to reduced haemoglobin. The light transmission is measured on the pulse beat. It is therefore possible to calculate and display the arterial oxygen saturation. Pulse oximeters are primatily calibrated on healthy humans during transient mild hypoxia. Severe hypoxia is not extensively studied. Furthermore, the influence of alterations in blood flow and haematocrit has not been sufficiently investigated. The aims of this study were therefore to evaluate the accuracy of pulse oximetry during severe hypoxia and assess the influence of haematocrit and blood flow changes on the pulse oximeter readings. An animal- and an in vitro model have been developed, and to be able to assess the influences of blood flow a pulse oximeter probe was attached to the foot of volunteers during limb elevation. In addition, a developed prototype of a fibre optic sensor, measuring heart and respiratory rates using pulse oximeter technique, was compared with visual observation, capnography.impedance plethysmography and an acoustic sensor. Results from the animal model showed a reduced pulse oximeter accuracy when the invasive oxygen saturation was below approximately 85 %, and that the light absorption characteristics for the two wavelengths used in pulse oximetry (660 nm and 940 nm) were similar for rabbit- and human haemoglobin. After haemodilution, an increase in the pulse oximeter readings was found, resulting in an increased accuracy when the invasive oxygen saturation was over 85 %. The results from the in vitro model showed a strong dependency of the pulse oximeter accuracy on the haematocrit value and indicated that the pulse oximeter mainly measures the oxygen saturation in smaller pulsating vessels. During limb elevation in humans, resulting in reduced blood flow, the quotient between red and infrared light was changed resulting in a falsely low pulse oximeter reading. The new fibre optic sensor correlated well with the other methods monitoring respiratory rate. During apnoea the fibre optic sensor detected the event correctly. In conclusion, pulse oximetry correlated well with invasively measured oxygen haemoglobin saturation values when SaO2 > 85 %. Overestimation by the pulse oximeter was found during severe hypoxia. A dependence on the haematocrit value was found in studies using an in vitro- and an animal model. During reduction of blood perfusion in humans, the pulse oximeter readings varied with changes in blood flow. The new fibre optic sensor technique to measure respiratory rate, correlated well with other techniques measuring respiratory rate. The fibre optic technique may have several clinical advantages.
Pulse Oximetry
Plethysmograph
Photoplethysmogram
Oxygen Saturation
Hypoxia
Capnography
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The use of pulse oximeters for sickle cell patients has not been reported and therefore its validity is currently unknown. In vivo patient studies are difficult to perform because of the vaso-occlusive dangers of compromised oxygen saturation. To assess the ability of pulse oximeters to monitor sickle blood accurately, the authors used whole sickle and normal blood samples in a pulsating cuvette to compare the Nellcor pulse oximeter to the IL co-oximeter. The results show (for 100-70% saturation range) that the Nellcor does measure sickle blood saturation within 1.8%.< >
Pulse Oximetry
Oxygen Saturation
Saturation (graph theory)
Cuvette
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