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Background: Diagnosis of lung injury requires invasive blood draws to measure oxygen tension in blood. This capability is nonexistent in austere settings and during prolonged field care (PFC), that is, medical care characterized by inability to evacuate casualties from the point of injury for up to 72 hours. We analyzed pulse-oximeter-derived noninvasive SpO2 and assessed the SpO2/FiO2 ratio (SFR) as a surrogate for the PaO2/FiO2 ratio (PFR), an accepted marker of lung function. We hypothesized that SFR is a suitable surrogate for PFR in a data set from animal models of combat-relevant trauma, PFC, and aeromedical evacuation., Methods: Data from anesthetized swine (N = 30) subjected to combat relevant trauma, resuscitation, and critical care interventions were analyzed. Pairwise correlations and Bland-Altman and regression analyses were performed to compare PFR and SFR, based on averaged SpO2 values obtained from two monitoring devices., Results: We performed 683 pairwise correlations. SpO2/FiO2 ratio was numerically higher than PFR with a 313 cutoff values for acute respiratory distress syndrome (ARDS) (PFR ≥300). Sensitivity/specificity for detection of mild ARDS was 75%/73% with a 200 to 300 PFR range corresponding to 252 to 312 SFR range. For moderate ARDS, sensitivity/specificity was 61%/93% with a 100 to 200 PFR range corresponding to 191 to 251 SFR range. For severe ARDS, sensitivity/specificity was 49%/97% with a 0 to 100 PFR range corresponding to 0 to 190 SFR range. For all groups, areas under the receiver operating characteristic curves ranged from 0.76 to 0.98., Conclusion: SpO2/FiO2 ratio is a useful surrogate for PFR when arterial blood gas testing is not available during dynamically changing physiologic conditions, for example, during austere conditions, PFC, or aeromedical evacuation, and may permit early detection of casualties in need of lung-specific life-saving interventions. Studies in critically ill humans are warranted.

Inhalation injury commonly accompanies thermal injury, increasing the likelihood of mortality and multiple organ dysfunction (MOD). Large animal models have given important insight into the pathophysiology of this injury; however recapitulating late MOD has remained difficult. The current report describes experiments using a smoke inhalation and burn model, with follow-up of ambulatory swine for 14days with bronchoscopy, CT scanning, and bronchoalveolar lavage fluid (BALF)/blood collection. Clinically, animals cleared airway damage in the first several days after-injury. This was mirrored with erythematous airways on day 2 after-injury, which resolved by the end of the experiment, as did parenchymal damage seen on CT. An initial rise in the protein content of BALF immediately after-injury was followed by a dramatic increase in the concentration of leukocytes. Circulating neutrophils increased while lymphocytes decreased; both correlated with cell counts in BALF. IL8 levels in BALF increased 30-fold and remained elevated throughout the experiment. IL1ra increased circulation immediately after-injury, and afterwards in BALF. Other cytokines (TNFα, IL12) transiently increased in BALF (and decreased in circulation) on day 2. Taken together, these results display a remarkable capability for the lungs to recover in the absence of intubation, with further evidence of the role of cytokines such as IL8 and IL1ra. The possible exacerbating effects of clinical practices such as ventilation and bronchoscopies should be considered., (Published by Elsevier Ltd.)