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Adequate oxygen delivery to a tissue depends on sufficient oxygen content in arterial blood and blood flow to the tissue. Oximetry is a technique for the assessment of blood oxygenation by measurements of light transmission through the blood, which is based on the different absorption spectra of oxygenated and deoxygenated hemoglobin. Oxygen saturation in arterial blood provides information on the adequacy of respiration and is routinely measured in clinical settings, utilizing pulse oximetry. Oxygen saturation, in venous blood (SvO 2 ) and in the entire blood in a tissue (StO 2 ), is related to the blood supply to the tissue, and several oximetric techniques have been developed for their assessment. SvO 2 can be measured non-invasively in the fingers, making use of modified pulse oximetry, and in the retina, using the modified Beer-Lambert Law. StO 2 is measured in peripheral muscle and cerebral tissue by means of various modes of near infrared spectroscopy (NIRS), utilizing the relative transparency of infrared light in muscle and cerebral tissue. The primary problem of oximetry is the discrimination between absorption by hemoglobin and scattering by tissue elements in the attenuation measurement, and the various techniques developed for isolating the absorption effect are presented in the current review, with their limitations.

Background: To assess changes in clinical condition and oxygenation in neonates after rewarming following moderate therapeutic hypothermia (MTH) for neonatal encephalopathy., Methods: Retrospective study of 28 neonates receiving MTH in a tertiary neonatal intensive care unit in Israel. We compared pre-and 24 h post-rewarming arterial oxygen saturation (SaO 2 ) as measured by the blood gases analyzer, pulse-oximetry saturation (SpO 2 ), and cardio-respiratory condition., Results: The SpO 2 declined from 96.9% (±2.9) before rewarming to 95.2% (±2.6) after rewarming (p < 0.001). Twelve neonates (42.9%) had clinical respiratory impairment (needing higher respiratory support or had new onset desaturations). In 16 neonates (57.1%) with no change in respiratory support after rewarming, SpO 2 decreased from 98.3 ± 1.9% to 95.6 ± 3.0% (p < 0.001) and SaO 2 decreased from 97.1 ± 1.7% to 96.0 ± 2.3% (p = 0.002). The mean SpO 2 decrease was greater than mean SaO 2 decrease (2.63 ± 1.8 and 1.1 ± 1.3 respectively, p = 0.021)., Conclusion: Neonates who underwent MTH showed reduction in oxygenation after rewarming either by decreasing SpO 2 or increasing FiO 2 requirements. The SpO 2 decline was larger than the SaO 2 decline. We suggest careful monitoring of neonates after rewarming., (Copyright © 2018. Published by Elsevier B.V.)

Objective: To assess the effect of blood transfusions in neonates on partial pressure of oxygen in arterial blood (PaO 2 ), arterial hemoglobin oxygen saturation (SaO 2 ) and arterial hemoglobin oxygen saturation as measured by pulse oximetry (SpO 2 )., Study Design: Retrospective study of neonates that received a first blood transfusion while having an indwelling arterial line. We compared PaO 2 , SaO 2, SpO 2, SaO 2 /PaO 2 ratio and fraction of inspired oxygen (FiO 2 ) 12 h before and after blood transfusion., Results: Post-transfusion neonates had higher PaO 2 and SaO 2 , had lower SaO 2 /PaO 2 ratio, and received higher FiO 2 with no change in SpO 2 ., Conclusions: Post-transfusion, neonates had lower hemoglobin oxygen affinity. They received higher FiO 2 and had higher PaO 2 at the same SpO 2 . We speculate that FiO 2 was increased in order to maintain SpO 2 . Larger prospective trials are needed to confirm our findings.

The oxygen saturation of the systemic arterial blood is associated with the adequacy of respiration, and can be measured non-invasively by pulse oximetry in the systemic tissue. The oxygen saturation of the blood in the pulmonary artery, the mixed venous blood, reflects the balance between oxygen supply to the systemic tissues and their oxygen demand. The mixed venous oxygen saturation has also clinical significance because it is used in Fick equation for the quantitative measurement of cardiac output. At present the measurement of the mixed venous oxygen saturation is invasive and requires insertion of a Swan-Ganz catheter into the pulmonary artery. We suggest a noninvasive method for the measurement of the mixed venous oxygen saturation in infants, pulmonary pulse oximetry. The method is similar to the systemic pulse oximetry, which is based on the different light absorption curves of oxygenated and deoxygenated hemoglobin and on the analysis of photoplethysmographic curves in two wavelengths. The proposed pulmonary pulse oximeter includes light-sources of two wavelengths in the infrared, which illuminate the pulmonary tissue through the thoracic wall. Part of the light which is scattered back from the pulmonary tissue and passes through the thoracic wall is detected, and for each wavelength a pulmonary photoplethysmographic curve is obtained. The pulmonary photoplethysmographic curves reflect blood volume increase during systole in the pulmonary arteries in the lung tissue, which contain mixed venous blood. The ratio R of the amplitude-to-baseline ratio for the two wavelengths is related to the mixed venous oxygen saturation through equations derived for the systemic pulse oximetry. The method requires the use of extinction coefficients values for oxygenated and deoxygenated hemoglobin, which can be found in the literature., (Copyright © 2013 Elsevier Ltd. All rights reserved.)