[Comparison of pulse oxygen saturation/fraction of inhaled oxygen and arterial partial pressure of oxygen/fraction of inhaled oxygen in the assessment of oxygenation in acute respiratory distress syndrome patients at different high altitudes in Yunnan Province].

OBJECTIVE

To investigate and evaluate if pulse oxygen saturation/fraction of inhaled oxygen (SpO/FiO) can be used, as replacement of arterial partial pressure of oxygen/fraction of inhaled oxygen (PaO/FiO), to assess oxygenation in acute respiratory distress syndrome (ARDS) patients at different high altitudes in Yunnan Province, and to find a rapid and non-invasive method for the diagnosis of ARDS at different altitudes.

METHODS

Patients with ARDS at different high altitudes in Yunnan Province from January 2019 to December 2020 were enrolled. The patients were divided into three groups according to different altitudes, and received different oxygen therapies according to their respective medical conditions. Group 1 consisted of patients with moderate to severe ARDS from the department of critical care medicine of the First Affiliated Hospital of Kunming Medical University (average altitude approximately 1 800 m), and received mechanical ventilation to maintain SpO of 0.90-0.96 with a low FiO for more than 30 minutes, and SpO, FiO, PaO were recorded. Group 2 consisted of patients with moderate to severe ARDS at the department of critical care medicine of People's Hospital of Diqing Tibetan Autonomous Prefecture (mean altitude about 3 200 m), and received oxygen with an attached reservoir mask to maintain SpO of 0.90-0.96 for 10 minutes, and then SpO, FiO, and PaO were recorded. Group 3 consisted of patients with mild to moderate-severe ARDS who admitted to the emergency department of the People's Hospital of Lijiang (average altitude approximately 2 200 m); when SpO < 0.90, patients received oxygen with the oxygen storage mask, and the FiO required to maintain SpO ≥ 0.90 was recorded, and SpO, FiO, PaO were recorded after oxygen inhalation for 10 minutes. Spearman coefficient was used to analyze the correlation between SpO/FiO and PaO/FiO in each group. Linear analysis was used to derive the linear equation between SpO/FiO and PaO/FiO, and to evaluate arterial pH, arterial partial pressure of carbon dioxide (PaCO), FiO, tidal volume (VT), positive end-expiratory pressure (PEEP) and other related factors which would change the correlation between SpO/FiO and PaO/FiO. The receiver operator characteristic curve (ROC curve) was plotted to calculate the sensitivity and specificity of using SpO/FiO instead of PaO/FiO to assess oxygenation of ARDS patients.

RESULTS

Group 1 consisted of 24 ARDS patients from whom 271 blood gas analysis results were collected; group 2 consisted of 14 ARDS patients from whom a total of 47 blood gas analysis results were collected; group 3 consisted of 76 ARDS patients, and a total of 76 blood gas analysis results were collected. The PaO/FiO (mmHg, 1 mmHg = 0.133 kPa) in groups 1, 2 and 3 were 103 (79, 130), 168 (98, 195) and 232 (146, 271) respectively, while SpO/FiO were 157 (128, 190), 419 (190, 445) and 319 (228, 446) respectively. Among the three groups, patients in group 1 had the lowest PaO/FiO and SpO/FiO, while patients in group 3 had the highest. Spearman correlation analysis showed that PaO/FiO was highly correlated with SpO/FiO in groups 1, 2 and 3 (r values were 0.830, 0.951, 0.828, all P < 0.05). Regression equation was fitted according to linear analysis: in group 1 SpO/FiO = 58+0.97×PaO/FiO (R = 0.548, P < 0.001); in group 2 SpO/FiO = 6+2.13×PaO/FiO (R = 0.938, P < 0.001); in group 3 SpO/FiO = 53+1.33×PaO/FiO (R = 0.828, P < 0.001). Further analysis revealed that PEEP, FiO, and arterial blood pH could affect the correlation between SpO/FiO and PaO/FiO. ROC curve analysis showed that the area under ROC curve (AUC) was 0.848 and 0.916 in group 1 with moderate to severe ARDS; based on the regression equation, the corresponding SpO/FiO cut-off values at a PaO/FiO of 100 mmHg and 200 mmHg were 155, 252 with a sensitivity of 84.9% and 100%, specificity of 87.2% and 70.6%, respectively. Patients with moderate to severe ARDS in group 2 (AUC was 0.945 and 0.977), the corresponding SpO/FiO cut-off values at PaO/FiO of 100 mmHg and 200 mmHg were 219 and 432 with the sensitivity of 100% and 85.2%, specificity of 82.5% and 100%, respectively. Patients with mild to moderate-severe ARDS in group 3 (AUC was 0.903 and 0.936), the corresponding SpO/FiO cut-off values at a PaO/FiO of 200 mmHg and 300 mmHg were 319 and 452 with the sensitivity of 100% and 100%, specificity of 80.9% and 86.2%, respectively.

CONCLUSIONS

SpO/FiO and PaO/FiO in ARDS patients at different high altitudes in Yunnan Province have a good correlation, and non-invasive SpO/FiO can be used to replace PaO/FiO to assess the oxygenation in ARDS patients.