ABSTRACT
BACKGROUND: Administration of oxygen in the delivery room is informed by oxygen saturation (SpO2). An oxygen saturation range of 60%-70% is the threshold for administering oxygen in the first minutes after birth. The accuracy of newer generation oximeters to measure SpO2 has not been compared against the 'gold standard', direct arterial blood oxygen saturation (SaO2) when SaO2 is low. The aim of this study was to determine the accuracy and precision of Nellcor and Masimo oximeters to measure SpO2 when SaO2 <70%. METHOD: Prospective observational study in ventilated anaesthetised newborn lambs with an indwelling carotid artery catheter. Ventilation was adjusted to achieve hypoxaemia. Nellcor (Oxi-Max 600 with Max-N sensor) and Masimo (Rad 4 with low noise optical probe (LNOP) sensor) sensors were applied to the right forelimb (preductal). An arterial blood sample was collected at 1-5 min intervals when the animal was hypoxic. The displayed SpO2 was recorded. We used Bland-Altman analysis to determine precision and accuracy of each oximeter when SaO2 <70%. RESULTS: 17 lambs were studied, 165 measurements were obtained, 123 were SaO2 <70%. The mean difference (±1.96 SD) Nellcor SpO2-SaO2 when SaO2 <70% was 17% (-12% to 46%). The mean difference (±1.96 SD) Masimo SpO2-SaO2 when SaO2 <70% was 13% (-19% to 45%). CONCLUSIONS: At SaO2<70%, both monitors overestimated oxygen saturation (SpO2) compared with the gold standard. Both oximeters were equally inaccurate when SaO2 was low.
Subject(s)
Hypoxia/diagnosis , Oximetry/instrumentation , Oxygen/blood , Animals , Animals, Newborn , Disease Models, Animal , Hypoxia/blood , Hypoxia/therapy , Oximetry/methods , Oximetry/standards , Oxygen Inhalation Therapy , Reproducibility of Results , Sheep, DomesticABSTRACT
Phase contrast x-ray imaging can provide detailed images of lung morphology with sufficient spatial resolution to observe the terminal airways (alveoli). We demonstrate that quantitative functional and anatomical imaging of lung ventilation can be achieved in vivo using two-dimensional phase contrast x-ray images with high contrast and spatial resolution (<100 microm) in near real time. Changes in lung air volume as small as 25 microL were calculated from the images of term and preterm rabbit pup lungs (n = 28) using a single-image phase retrieval algorithm. Comparisons with plethysmography and computed tomography showed that the technique provided an accurate and robust method of measuring total lung air volumes. Furthermore, regional ventilation was measured by partitioning the phase contrast images, which revealed differences in aeration for different ventilation strategies.
