Toward early identification of acute lung injury in the emergency department

Abstract

Background: There are no studies evaluating the epidemiology of pediatric acute lung injury (ALI) in the emergency department (ED), where early identification and interventions are most likely to be helpful. The purpose of this study was to describe the epidemiology of the ALI precursor acute hypoxemic respiratory failure (AHRF) in the ED.

Methods: We analyzed 11,664 pediatric patient records from 16 EDs. Records were selected if oxygen saturation (SpO(2)) was recorded during the visit. Virtual partial pressure of oxygen (pO(2)) was calculated from SpO(2), thus allowing calculation of ratios of pO(2) to fraction of inspired oxygen (FiO(2)) (PFRs). Patients with a PFR < 300 were classified as having AHRF. Univariate analyses and logistic regression were used to test the association of clinical factors with the presence of AHRF and intubation.

Results: AHRF criteria (ie, PFR < 300) were met in 121 (2.9%) of the 4,184 patients with an oxygenation measurement. The following variables were independently associated with ALI: higher Pediatric Risk of Admission II score (adjusted odds ratio [95% confidence interval (CI)] = 1.12 [1.08-1.16]; p < .001), higher heart rate (1.02 [1.01-1.03]; p = .009), a positive chest radiograph (2.35 [1.02-5.43]; p = .045), and lower temperature (0.49 [0.36-0.68]; p < .001).The final model had an R(2) = .20.

Conclusion: We found nonintubated AHRF to be prevalent in the ED. The low R(2) for the regression model for AHRF underscores the lack of criteria for early identification of patients with respiratory compromise. Our findings represent an important first step toward establishing the true incidence of ALI in the pediatric ED.

Figure 1

Scatterplots were used to test the validity of the assumption that underrecognizing acidosis and hypercarbia would bias our results toward the null hypothesis. We generated scatterplots for a range of carbon dioxide partial pressure (pCO₂) values and their calculated partial pressure of oxygen (pO₂) to fraction of inspired oxygen (FiO₂) ratios (PFRs) as well as for a range of pH values and their corresponding PFRs while holding all other values constant (ie, FiO₂ = 0.5, temperature = 37°C, and either pCO₂ = 40 or pH = 7.4). The effect of pH on PFR was much larger than that of pCO₂ and the data trends confirmed that overestimating pCO₂ and underestimating pH would result in higher than true PFRs, thus leading to an underestimation of acute hypoxemic respiratory failure.

Figure 2

Bland-Altman plot of pO₂ versus SpO₂ in patients with simultaneously measured values.