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Observational Study
. 2017 Aug;45(8):1317-1324.
doi: 10.1097/CCM.0000000000002514.

Nonlinear Imputation of PaO2/FIO2 From SpO2/FIO2 Among Mechanically Ventilated Patients in the ICU: A Prospective, Observational Study

Samuel M Brown  1 , Abhijit Duggal, Peter C Hou, Mark Tidswell, Akram Khan, Matthew Exline, Pauline K Park, David A Schoenfeld, Ming Liu, Colin K Grissom, Marc Moss, Todd W Rice, Catherine L Hough, Emanuel Rivers, B Taylor Thompson, Roy G Brower; National Institutes of Health (NIH)/National Heart, Lung, and Blood Institute (NHLBI) Prevention and Early Treatment of Acute Lung Injury (PETAL) Network
Collaborators, Affiliations
Observational Study

Nonlinear Imputation of PaO2/FIO2 From SpO2/FIO2 Among Mechanically Ventilated Patients in the ICU: A Prospective, Observational Study

Samuel M Brown et al. Crit Care Med. 2017 Aug.

Abstract

Objectives: In the contemporary ICU, mechanically ventilated patients may not have arterial blood gas measurements available at relevant timepoints. Severity criteria often depend on arterial blood gas results. Retrospective studies suggest that nonlinear 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 nonlinear 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 arterial blood gas. Acute respiratory distress syndrome criteria were recorded. For each imputation method, we calculated both imputation error and the area under the curve for patients meeting criteria for acute respiratory distress syndrome (PaO2/FIO2 ≤ 300) and moderate-severe acute respiratory distress syndrome (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 1,034 arterial blood gases from 703 patients; 650 arterial blood gases were associated with SpO2 less than or equal to 96%. Nonlinear imputation had consistently lower error than other techniques. Among all patients, nonlinear had a lower error (p < 0.001) and higher (p < 0.001) area under the curve (0.87; 95% CI, 0.85-0.90) for PaO2/FIO2 less than or equal to 300 than linear/log-linear (0.80; 95% CI, 0.76-0.83) imputation. All imputation methods better identified moderate-severe acute respiratory distress syndrome (PaO2/FIO2 ≤ 150); nonlinear imputation remained superior (p < 0.001). For PaO2/FIO2 less than or equal to 150, the sensitivity and specificity for nonlinear 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, nonlinear imputation of PaO2/FIO2 from SpO2/FIO2 seems accurate, especially for moderate-severe hypoxemia. Linear and log-linear imputations cannot be recommended.

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Conflict of interest statement

Conflicts of Interest: The author(s) declare that they have no competing interests.

Dr. Duggal disclosed that he does not have any potential conflicts of interest.

Figures

Figure 1
Figure 1. Bland-Altman plots of imputed vs. measured PaO2:FIO2 ratios
Bland-Altman plot of the difference between measured and imputed PaO2/FIO2 ratios. Black represents non-linear, red linear, and blue log-linear imputation results.
See this image and copyright information in PMC

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