OBJECTIVE

To explore the feasibility of using pulse oxygen saturation (SpO) to evaluate the condition of patients with acute respiratory distress syndrome (ARDS) in the Lijiang region.

METHODS

Patients with ARDS who visited the department of emergency of People's Hospital of Lijiang from August to December 2020 were selected as study subjects. Patients were divided by severity into mild ARDS group [200 mmHg (1 mmHg = 0.133 kPa) ≤ oxygenation index (PaO/FiO, P/F) ≤ 300 mmHg] and moderate to severe ARDS group (P/F ≤ 200 mmHg). The general condition, clinical diagnosis, arterial blood gas analysis results of the patients were recorded, and the differences of the above indexes between the two groups of ARDS were compared. Spearman correlation analysis was used to analyze the correlation between SpO and arterial oxygen saturation (SaO). SpO was carried into the Ellis equation and the Rice equation to calculate the derived P/F and analyze the correlation between the derived P/F and the P/F measured in arterial blood gas analysis; receiver operator characteristic curve (ROC curves) were plotted, the sensitivity and specificity of SpO/fraction of inspiration oxygen (SpO/FiO, S/F) instead of P/F to assess oxygenation in patients with ARDS was calculated. To evaluate the feasibility of SpO for the condition evaluation of patients with ARDS in the Lijiang region.

RESULTS

Compared with the mild ARDS group, the arterial partial pressure of oxygen (PaO), SaO and hemoglobin (Hb) were significantly decreased in the moderate to severe ARDS group [PaO (mmHg): 50.5 (39.3, 56.5) vs. 60.0 (55.0, 67.5), SaO: 0.86 (0.73, 0.91) vs. 0. 93 (0.90, 0.96), Hb (g/L): 142±27 vs. 156±24, respectively, all P < 0.05]. Correlation analysis revealed a significant positive correlation between SpO and SaO in ARDS patients residing at high altitude (R = 0.650, P = 0.000). The P/F derived by the Rice formula was significantly and positively correlated with the P/F derived from arterial blood gas analysis (R = 0.802, P = 0.000). The deduced P/F in mild and moderate to severe ARDS groups were all significantly correlated with the measured P/F (R values were 0.562, 0.647, both P = 0.000). The P/F derived using the Ellis formula showed a significant positive correlation with the P/F derived from arterial blood gas analysis (R = 0.822, P = 0.000). The deduced P/F of mild ARDS group and moderate to severe ARDS group were all positively correlated with the measured P/F (R values were 0.556, 0.589, P values were 0.000, 0.010). There was a significant positive correlation between S/F and P/F in ARDS patients (R = 0.828, P = 0.000), and the regression equation was S/F = 1.33 P/F+52.41. ROC curve analysis showed that S/F had some predictive value for patients with mild and moderate to severe ARDS, and area under ROC curve (AUC) and 95% confidence interval (95%CI) were 0.903 (0.829-0.977), 0.936 (0.870-1.000), both P = 0.000. When the cut-off value was 452 mmHg, S/F had a sensitivity of 100% and a specificity of 80.9% for predicting mild ARDS. When the cut-off value was 319 mmHg, S/F predicted moderate to severe ARDS with 95.1% sensitivity and 86.2% specificity.

CONCLUSIONS

At high altitude, SpO and SaO have been correlated in patients with ARDS, and P/F derived using SpO and measured P/F were significantly correlated in patients with ARDS, especially in those with moderate to severe ARDS. SpO may be useful in the assessment of severity of illness in patients with ARDS at high altitude.