J Crit Care. 2013 Feb 7. pii: S0883-9441(12)00497-2. PMID: 23395312

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PURPOSE: Oxygen saturation as measured by pulse oximetry (Spo(2))/fraction of inspired oxygen (Fio(2)) (SF) ratio has demonstrated to be an adequate marker for lung disease severity in children under mechanical ventilation. We sought to validate the utility of SF ratio in a population of critically ill children under mechanical ventilation, noninvasive ventilation support, and breathing spontaneously.

MATERIALS AND METHODS: A retrospective database study was conducted in a pediatric intensive care unit of a university hospital. Children with Spo(2) less than or equal to 97% and an indwelling arterial catheter were included. Simultaneous blood gas and pulse oximetry were collected in a database. Derivation and validation data sets were generated, and a linear mixed modeling was used to derive predictive equations. Model performance and fit were evaluated using the validation data set.

RESULTS: Three thousand two hundred forty-eight blood gas and Spo(2) values from 298 patients were included. 1/SF ratio had a strong linear association with 1/Pao(2)/Fio(2) (PF) ratio in both derivation and validation data sets, given by the equation 1/SF = 0.00164 + 0.521/PF (derivation). Oxygen saturation as measured by pulse oximetry/Fio(2) values for PF criteria of 100, 200, and 300 were 146 (95% confidence interval [CI], 142-150), 236 (95% CI, 228-244), and 296 (95% CI, 285-308). Areas under receiver operating characteristic curves for diagnosis of PF ratio less than 100, 200, and 300 with the SF ratio were 0.978, 0.952, and 0.951, respectively, in the validation data set. CONCLUSIONS: Oxygen saturation as measured by pulse oximetry/Fio(2) ratio is an adequate noninvasive surrogate marker for PF ratio. Oxygen saturation as measured by pulse oximetry/Fio(2) ratio may be an ideal noninvasive marker for patients with acute hypoxemic respiratory failure.

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