Nonlinear Imputation of Pao 2/Fio 2 From Spo 2/Fio 2 Among Mechanically Ventilated Patients in the ICU: A Prospective, Observational Study

Abstract

Objectives In the contemporary intensive care unit (ICU), mechanically ventilated patients may not have arterial blood gas (ABG) measurements available at relevant timepoints. Severity criteria often depend on ABG results. Retrospective studies suggest that non-linear imputation of PaO2/FIO2 from SpO2/FIO2 is accurate, but this has not been established prospectively among mechanically ventilated ICU patients. The objective was to validate the superiority of non-linear imputation of PaO2/FIO2 among mechanically ventilated patients and understand what factors influence the accuracy of imputation. Design Simultaneous SpO2, oximeter characteristics, receipt of vasopressors, and skin pigmentation were recorded at the time of a clinical ABG. ARDS criteria were recorded. For each imputation method, we calculated both imputation error and the area under the curve (AUC) for patients meeting criteria for ARDS (PaO2/FIO2≤300) and moderate-severe ARDS (PaO2/FIO2≤150). Setting Nine hospitals within the Prevention and Early Treatment of Acute Lung Injury network. Patients We prospectively enrolled 703 mechanically ventilated patients admitted to the emergency departments or ICUs of participating study hospitals. Interventions None. Measurements and Main Results We studied 1034 ABGs from 703 patients; 650 ABGs were associated with SpO2≤96%. Non-linear imputation had consistently lower error than other techniques. Among all patients, non-linear had a lower error (p<0.001) and higher (p<0.001) AUC (0.87; 95% CI 0.85–0.90) for PaO2/FIO2 ≤300 than linear/log-linear (0.80; 95%CI 0.76–0.83) imputation. All imputation methods better identified moderate-severe ARDS (PaO2/FIO2 ≤150); non-linear imputation remained superior (p<0.001). For PaO2/FiO2≤150, the sensitivity and specificity for non-linear imputation were 0.87 (95% CI 0.83–0.90) and 0.91 (95% CI 0.88–0.93) respectively. Skin pigmentation and receipt of vasopressors were not associated with imputation accuracy. Conclusions In mechanically ventilated patients, non-linear imputation of PaO2/FIO2 from SpO2/FIO2 appears accurate, especially for moderate-severe hypoxemia. Linear and log-linear imputation cannot be recommended.

A phase I trial of low-dose inhaled carbon monoxide in sepsis-induced ARDS

“…For the SOFA score calculation, if a value was missing, we carried forward the value from the prior measurement. For LIS and SOFA score calculations, when PaO 2 / FiO 2 was not available, the PaO 2 was estimated from the SpO 2 using nonlinear imputation, and the SpO 2 / FiO 2 equivalent was used as described previously (64,65). For the cardiovascular dysfunction component of the SOFA score, patients on phenylephrine and vasopressin were scored using estimated norepinephrine equivalences based on prior studies (66,67).…”

“…Subjects who no longer required mechanical ventilation were scored 0 for the respiratory component of the SOFA score, as the PaO 2 /FiO 2 ratio was either unavailable or could not be reliably compared with the PaO 2 /FiO 2 ratio in mechanically ventilated subjects. SpO 2 /FiO 2 was not used to impute the PaO 2 /FiO 2 ratio in subjects no longer requiring mechanical ventilation, as this methodology has only been validated in mechanically ventilated ARDS patients (64,65).…”

The Value of Oxygenation Saturation Index in Predicting the Outcomes of Patients with Acute Respiratory Distress Syndrome

“…Through the help of noninvasive pulse oximetry, clinicians can obtain SpO 2 and calculate the SpO 2 /FiO 2 ratio, which has been demonstrated to be well correlated with the PaO 2 /FiO 2 ratio among patients with mechanical ventilation and ARDS after using a nonlinear imputation strategy [ 10 , 11 ]. Moreover, DesPrez et al showed that oxygenation saturation index (OSI) combining the SpO 2 /FiO 2 ratio and mean airway pressure was well correlated with the oxygenation index (OI) and could be a reliable predictor of ARDS patients’ outcome [ 12 ].…”

Predictive performance of PiCCO system and blood gas parameters for early prognosis of patients with sepsis

“…Some pathophysiological factors, including lung resection, pulmonary vessels obstruction, and higher positive end-expiratory pressure, may potentially generate the trust-less data of EVLWI [14]. PaO2/FiO2 and Lac widely veri ed in the multiple intensive care scenarios [15][16][17], likewise present the affordable alternatives to invasive methods in our results, especially combined both themselves.…”