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 (SvO2) and in the entire blood in a tissue (StO2), is related to the blood supply to the tissue, and several oximetric techniques have been developed for their assessment. SvO2 can be measured non-invasively in the fingers, making use of modified pulse oximetry, and in the retina, using the modified Beer–Lambert Law. StO2 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.

Oxygen saturation in arterial blood (SaO2) provides information about the performance of the respiratory system. Non-invasive measurement of SaO2 by commercial pulse oximeters (SpO2) make use of photoplethysmographic pulses in the red and infrared regions and utilizes the different spectra of light absorption by oxygenated and de-oxygenated hemoglobin. Because light scattering and optical path-lengths differ between the two wavelengths, commercial pulse oximeters require empirical calibration which is based on SaO2 measurement in extracted arterial blood. They are still prone to error, because the path-lengths difference between the two wavelengths varies among different subjects. We have developed modified pulse oximetry, which makes use of two nearby infrared wavelengths that have relatively similar scattering constants and path-lengths and does not require an invasive calibration step. In measurements performed on adults during breath holding, the two-infrared pulse oximeter and a commercial pulse oximeter showed similar changes in SpO2. The two pulse oximeters showed similar accuracy when compared to SaO2 measurement in extracted arterial blood (the gold standard) performed in intensive care units on newborns and children with an arterial line. Errors in SpO2 because of variability in path-lengths difference between the two wavelengths are expected to be smaller in the two-infrared pulse oximeter.

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There appears to be an overall stepwise progression in the incidence of poor outcome parameters from "closed" to "borderline" to "hemodynamically significant" PDA. Both the El-Khuffash and Shaare Zedek scores are predictive of PDA-associated morbidities.

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Post-transfusion, neonates had lower hemoglobin oxygen affinity. They received higher FiO and had higher PaO at the same SpO. We speculate that FiO was increased in order to maintain SpO. Larger prospective trials are needed to confirm our findings.

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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 cardiorespiratory condition. Results: The SpO 2 declined from 96.9% (AE2.9) before rewarming to 95.2% (AE2.6) 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 AE 1.9% to 95.6 AE 3.0% (p < 0.001) and SaO 2 decreased from 97.1 AE 1.7% to 96.0 AE 2.3% (p Z 0.002). The mean SpO 2 decrease was greater than mean SaO 2 decrease (2.63 AE 1.8 and 1.1 AE 1.3 respectively, p Z 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.