Utility of Pulse Oximetry Oxygen Saturation (SpO<sub>2</sub>) with Incorporation of Positive End-Expiratory Pressure (SpO<sub>2</sub><svg xmlns:xlink="http://www.w3.org/1999/xlink" xmlns="http://www.w3.org/2000/svg" style="vertical-align:-0.06576014pt" id="M1" height="7.93416pt" version="1.1" viewBox="-0.0657574 -7.8684 10.2422 7.93416" width="10.2422pt"><g transform="matrix(.017,0,0,-0.017,0,0)"><path id="g113-43" d="M471 153C471 170 463 194 452 212C400 220 373 229 322 255C373 281 400 290 452 298C463 316 471 339 471 357C456 366 431 371 410 370C377 329 356 310 308 279C311 336 317 364 336 413C326 432 310 451 294 459C279 451 262 432 252 413C271 364 277 336 280 279C232 310 211 329 178 370C157 371 132 367 117 357C117 340 125 316 136 298C188 290 215 281 266 255C215 229 188 220 136 212C125 194 117 171 117 153C132 144 157 139 178 140C211 181 232 200 280 231C277 174 271 146 252 97C262 78 278 59 294 51C309 59 326 78 336 97C317 146 311 174 308 231C356 200 377 181 410 140C431 139 456 143 471 153Z"/></g></svg>10/FiO<sub>2</sub><svg xmlns:xlink="http://www.w3.org/1999/xlink" xmlns="http://www.w3.org/2000/svg" style="vertical-align:-0.06576014pt" id="M2" height="7.93416pt" version="1.1" viewBox="-0.0657574 -7.8684 10.2422 7.93416" width="10.2422pt"><g transform="matrix(.017,0,0,-0.017,0,0)"><use xlink:href="#g113-43"/></g></svg>PEEP) for Classification and Prognostication of Patients with Acute Respiratory Distress Syndrome

Todur, Pratibha; Nileshwar, Anitha; Chaudhuri, Souvik; Gupta, Nitin; Natarajan, Srikant; Rao, Shwethapriya

doi:https://doi.org/10.1155/2022/7871579

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Research Article | Open Access

Volume 2022 | Article ID 7871579 | https://doi.org/10.1155/2022/7871579

Utility of Pulse Oximetry Oxygen Saturation (SpO₂) with Incorporation of Positive End-Expiratory Pressure (SpO₂10/FiO₂PEEP) for Classification and Prognostication of Patients with Acute Respiratory Distress Syndrome

Pratibha Todur,¹Anitha Nileshwar,²Souvik Chaudhuri,³Nitin Gupta,⁴Srikant Natarajan,⁵and Shwethapriya Rao³

Academic Editor: Samuel A. Tisherman

Received02 Apr 2022

Revised30 Jun 2022

Accepted27 Jul 2022

Published06 Sept 2022

Abstract

Background. Conventionally, PaO₂/FiO₂ (P/F ratio) has been used to categorize severity of acute respiratory distress syndrome (ARDS) and prognostication of outcome. Recent literature has shown that incorporation of positive end-expiratory pressure (PEEP) into the P/F ratio (PaO₂10/FiO₂PEEP or P/FP10) has a much better prognostic ability in ARDS as compared to P/F ratio. The aim of this study was to correlate SpO₂10/FiO₂PEEP (S/FP10) to PaO₂10/FiO₂PEEP (P/FP10) and evaluate the utility of S/FP10 as a reliable noninvasive indicator of oxygenation in ARDS to avoid repeated arterial blood sampling. Aim. To evaluate if pulse oximetry is a reliable indicator of oxygenation in ARDS patients by calculating SpO₂10/FiO₂PEEP (S/FP10). The primary objective was to determine the correlation of S/FP10 to P/FP10 ratio in ARDS patients. The secondary objective was to determine the cut-off value of S/FP10 ratio to predict severe ARDS and survival. Methods. Patients aged 18–80 years on invasive mechanical ventilation (MV) diagnosed with ARDS as defined by the Berlin definition were included. The values of PaO₂, FiO₂, and SpO₂ were collected at three different time points. They were at baseline, i.e., after intubation and initiation of MV (within one hour of intubation), day one (1–24 hours of MV), and day three (48–72 hours of MV). The primary outcome was survival at the end of intensive care unit (ICU) stay. Results. A total of 85 patients with ARDS on invasive MV were included. The data points were obtained at baseline, day one, and day three of MV. S/FP10 ratio has an excellent correlation to P/FP10 ratio at baseline and day three of invasive MV (r = 0.831 and 0.853, respectively; ) and has a strong correlation on day one of invasive MV (r = 0.733, ). S/FP10 ratio ≤116 at baseline has excellent discriminant function to be categorized as severe ARDS as per Berlin definition (AUC: 0.925, , 90% sensitivity, 93% specificity, CI: [0.862–0.988]). The increase in S/FP10 ratio by ≥64.40 from baseline to day three of MV is a good predictor of survival (AUC: 0.877, , 73.5% sensitivity, 97% specificity, CI: [0.803–0.952]). Conclusion. S/FP10 has a strong correlation to P/FP10 in ARDS patients. S/FP10 ≤116 has an excellent discriminant function to be categorized as severe ARDS. The S/FP10 ratio on day three of MV and the change in S/FP10 ratio from baseline and day one to day three of MV are good predictors of survival in ARDS patients. This trial is registered with CTRI/2020/04/024940.

1. Introduction

The severity, oxygenation status, and extent of lung injury in acute respiratory distress syndrome (ARDS) have traditionally been assessed by the ratio of partial pressure of arterial oxygen to fraction of inspired oxygen (PaO₂/FiO₂ or P/F ratio) as per the Berlin definition [1]. However, the P/F ratio is often misleading in predicting the extent of lung injury [2, 3]. Two different mechanically ventilated patients with the same P/F ratio may have different positive end-expiratory pressures (PEEP). As the application of PEEP will improve the PaO₂, calculating a P/F ratio without taking PEEP into account may be misleading [2]. A recent study has shown that PaO₂10/FiO₂PEEP (P/FP10 ratio) has a significantly better predictive ability for mortality in ARDS patients when compared to P/F ratio alone [2]. However, as these values change dynamically during the course of mechanical ventilation (MV) in a patient, repeated arterial sampling is required which is associated with increased chances of infection, blood loss, patient discomfort, and costs [4, 5].

2. Aim

The aim of this study is to evaluate oxygen saturation by pulse oximetry (SpO₂) as an alternative noninvasive reliable indicator of oxygenation by calculating SpO₂10/FiO₂PEEP (S/FP10) ratio. SpO₂ measurement is widely available, is conducive to use, enables continuous monitoring, and is reliable [6]. To the best of our knowledge, this is the first study that has incorporated the concept of PEEP into SpO₂/FiO₂ (S/F) to evaluate its accuracy in predicting severe ARDS and survival. The primary objective of the study was to determine the correlation of the S/FP10 ratio to P/FP10 in patients with ARDS. The secondary objective was to determine the cut-off value of the S/FP10 ratio to predict severe ARDS and survival.

3. Materials and Methods

3.1. Study Setting and Approvals

It was a single-centre prospective observational study conducted at the level III intensive care units (ICUs) of a tertiary care medical college from September 2020 to September 2021. This data was a secondary analysis of an ongoing prospective observational study approved by the Institutional Ethics Committee (IEC: 765/2019) and is registered in India's Clinical Trial Registry (CTRI/2020/04/024940).

3.2. Inclusion Criteria

The inclusion criteria were as follows: all patients between the ages of 18 and 80 years with ARDS, as defined by the Berlin definition, and on invasive mechanical ventilation.

3.3. Exclusion Criteria

The exclusion criteria were as follows:(i)Patients with COVID-19.(ii)Patients with documented barotrauma (air leak syndromes).(iii)Patients with penetrating chest injuries.(iv)Patients planned for palliative care.

3.4. Sample Size

The sample size was based on the primary objective of assessment of correlation between two quantitative variables considering the expected correlation coefficient between PaO₂10/FiO₂PEEP (P/FP10) and SpO₂10/FiO₂PEEP (S/FP10) as at least 0.3, with power of 80% and alpha error of 5%. The following formula was used to calculate sample size (n):where r is the correlation coefficient, Z_1−α/2 is the desired confidence level, and 1 − β is the power; thus, n = 85.

3.5. Methodology

All patients admitted to the ICU were screened daily for eligibility. Those who met the inclusion criteria were enrolled, after obtaining written informed consent from the legally authorized representatives.

The flowchart depicting the methodology is shown in Figure 1.

In Figure 1, ABG = arterial blood gas, MV = mechanical ventilation, PaO₂ = partial pressure of arterial oxygen, SpO₂ = pulse oximetry oxygen saturation, FiO₂ = fraction of inspired oxygen, PEEP = positive end-expiratory pressure, P/FP10 = (PaO₂10)/(FiO₂PEEP), S/FP10 = (SpO₂10)/(FiO₂PEEP), P/FP10 (B) = the value obtained at one hour after intubation and initiation of MV, S/FP10 (B) = corresponding values obtained at one hour after intubation and MV, P/FP10 (D1) = worst values of P/FP10 day 1 (within 1–24 hours of intubation), S/FP10 (D1) = corresponding values of S/FP10 on day 1, P/FP10 (D3) = worst values of P/FP10 day 3 (within 48–72 hours of intubation), S/FP10 (D3) = corresponding values of S/FP10 on day 3 (within 48–72 hours of intubation), S/FP (D3–B) = change in S/FP10 from baseline to day three, S/FP (D3–D1) = change in S/FP10 from day one to day three, P/FP (D3-B) = change in P/FP10 from baseline to day three, and P/FP (D3-D1) = change in S/FP10 from day one to day three.

Sequential Organ Failure Assessment (SOFA) score on ICU admission was noted. PaO₂ values were noted using the worst ABG during three defined time periods. The three time periods taken for the study were as follows: baseline (B: within one hour of intubation), day 1 (D1: 1–24 hours after intubation), and day 3 (D3: 48–72 hours after intubation). The FiO₂, SpO₂, and corresponding PEEP value set on the ventilator were also noted. The difference between day three and day S/FP∗10 values [S/FP (D3-D1] as well as the difference between the values of S/FP∗10 between that of day 3 and baseline [S/FP (D3-B)] were also calculated. Similarly, the difference between day three and day one P/FP∗10 values [P/FP (D3-D1] as well as the difference the values of P/FP∗10 between that of day three and baseline [P/FP (D3-B)] were also calculated. MV days, length of stay in ICU (ICU LOS), and outcomes in terms of survival at the end of ICU stay were also noted.

4. Statistical Analysis

The analysis of data was done using SPSS (Statistical Package for the Social Sciences) software (IBM Corp. Released 2012. IBM SPSS Statistics for Windows, version 22.0 Armonk, NY: IBM). Mean and standard deviation (SD) for the variables following parametric distribution were calculated. The analysis was performed for the three unique data points (baseline, day one, and day three of MV), and repeated data points were not aggregated for the purpose of analysis.

For correlation of the variables P/FP10 and S/FP10, the Pearson correlation test was used, and the correlation coefficient r was calculated. Pearson's correlation coefficient r <0.4 was considered as weak correlation, 0.4–0.59 was considered moderate correlation, r within 0.6–0.79 was considered as strong correlation, and r >0.8 was considered as excellent correlation. Additionally, the correlation analysis was also conducted for those patients with high PEEP (≥10 cm H₂O). The main correlation analysis of S/FP10 and P/FP10 included patients at all PEEP levels (PEEP <10 cm H₂O as well as PEEP ≥10 cm H₂O). However, we separately did a sub-analysis of the correlation of S/F to P/F and S/FP10 to P/FP10 at the three time points. This separate sub-analysis was done because clinicians often repeat ABG for patients with higher PEEP levels, and thus it is this category of patients that is likely to benefit the most if the noninvasively determined S/FP10 correlated to P/FP10 at all the three time points.

A receiver operating characteristic (ROC) was plotted for the ability of the P/FP10 (B, D1, D3) and S/FP10 (B, D1, D3) to predict survival. Similarly, ROC curves were plotted for S/FP (D3-B), S/FP (D3-D1), P/FP (D3-B), and P/FP (D3-D1) to predict survival. Area under curve (AUC) within 0.91–1.0 was considered excellent, 0.81–0.90 was considered good, and 0.71–0.80 was considered fair. A value <0.05 was taken as statistically significant and value <0.001 as statistically highly significant.

To compare the reliability of S/FP to predict outcomes as compared to P/FP, the comparison of the ROC curves was done using the DeLong test using MedCalc software version 20.111 (Ostend, Belgium).

5. Results

A total of 85 patients with ARDS receiving invasive mechanical ventilation were included in the study. Six patients died between day one and day three. At the end of the ICU stay, 49 (58%) patients survived. The demographic characteristics and values of the variables of the 85 ARDS patients are depicted in Table 1.

The correlation of P/FP10 and S/FP10 at baseline, day one, and day three of MV was stronger than the correlation of P/F and S/F on the respective days (Table 2). For the subgroup of patients with PEEP ≥10 cm H₂O, the same correlation was observed as in all patients (Table 2). The scatterplot depicting correlation of S/FP10 and P/FP10 at all levels of PEEP at all the three time points is shown in Figure 2. P/FP10 (B) = (PaO₂10)/(FiO₂PEEP) at baseline (the value obtained at one hour after intubation and initiation of MV); S/FP10 (B) = (SpO₂10)/(FiO₂PEEP) at baseline (the corresponding values obtained at one hour after intubation and MV). P/FP10 (D1) = (PaO₂10)/(FiO₂PEEP) at day 1 (worst values of P/FP10 within 1–24 hours of intubation); S/FP10 (B) = (SpO₂10)/(FiO₂PEEP) at day 1 (the corresponding values of S/FP10 within 1–24 hours of intubation). P/FP10 (D3) = (PaO₂10)/(FiO₂PEEP) at day 3 (worst values of P/FP10 within 48–72 hours of intubation); S/FP10 (D3) = (SpO₂10)/(FiO₂PEEP) at day 3 (the corresponding values of S/FP10 within 48–72 hours of intubation). PEEP: positive end-expiratory pressure.

(a)

(b)

(c)

Among all the P/FP10 and S/FP10 ratios at baseline, day one, and day three and the changes in the ratios from baseline and day one to day three of MV, the change in P/FP10 (D3-B) has the best ability to predict survival in ARDS patients, with AUC of 0.902 and a cut-off ≥34.25 (Table 3). Among the S/FP10 ratios, the S/FP10 (D3-B) has the highest AUC and specificity to predict survival (AUC: 0.877, , sensitivity: 73.5%, specificity: 97%, CI: 0.803–0.952, cut-off ≥64.40). The AUC values of the P/FP10 (B), P/FP10 (D1), P/FP10 (D3), P/FP (D3-B), P/FP (D3-D1), S/FP10 (B), S/FP10 (D1), S/FP10 (D3), S/FP (D3-B), and S/FP (D3-D1) with their respective cut-off values are depicted in Table 3.

The ROC curves of the P/FP10 (B), P/FP10 (D1), P/FP10 (D3), S/FP10 (B), S/FP10 (D1), and S/FP10 (D3) to predict survival are depicted in Figure 3.

In Figure 3, PaO₂ = partial pressure of arterial oxygen, SpO₂ = pulse oximetry oxygen saturation, FiO₂ = fraction of inspired oxygen, PEEP = positive end-expiratory pressure, P/FP10 (B)= (PaO₂10)/(FiO₂PEEP) (the value obtained at one hour after intubation and initiation of mechanical ventilation), S/FP10 (B) = (SpO₂10)/(FiO₂PEEP) (the corresponding values obtained at one hour after intubation and mechanical ventilation), P/FP10 (D1) = worst values of P/FP10 day 1 (within 1–24 hours of intubation), S/FP10 (D1) = corresponding values of S/FP10 on day 1, P/FP10 (D3) = worst values of P/FP10 day 3 (within 48–72 hours of intubation), and S/FP10 (D3) = corresponding values of S/FP10 on day 3 (within 48–72 hours of intubation.

The ROC of the changes in oxygenation as depicted by P/FP (D3-B), P/FP (D3-D1), S/FP (D3-B), and S/FP (D3-D1) to predict survival is displayed in Figure 4.

In Figure 4, S/FP (D3–B) change in S/FP10 from baseline to day three, S/FP (D3–D1) change in S/FP10 from day one to day three, P/FP (D3-B) change in P/FP10 from baseline to day three, P/FP (D3-D1) change in S/FP10 from day one to day three. AUC = area under curve.

The S/FP10 (B) has excellent discrimination ability to predict severe ARDS category and revealed an AUC of 0.925, , 90% sensitivity, 93% specificity, cut-off value ≤116, and CI of [0.862–0.988]. The ROC of the S/FP10 (B) discriminant function to predict severe ARDS is depicted in Figure 5.

S/FP (B) also had fair discrimination ability to predict mild ARDS category and revealed an AUC of 0.773, , sensitivity of 69%, specificity of 74%, and 95% CI of [0.672–0.875] with a cut-off value ≥190. The ROC of the S/FP10 (B) discriminant function to predict mild ARDS is depicted in Figure 6.

Thus, as per our results, the moderate ARDS category will be S/FP10 (B) ≥116 and ≤190.

In order to compare the reliability of S/FP to predict outcomes as compared to P/FP, the comparison of the ROC curves was done using the DeLong test using MedCalc software version 20.111. The ROC of the S/FP10 to P/FP10 at three time points (baseline, day one, and day three) to predict outcome in terms of survival was calculated. It showed that the null hypothesis was acceptable, and there was no statistically significant difference in the AUC between the ROC curves of S/FP10 (B) and P/FP10 (B), S/FP10 (D1) and P/FP10 (D1), and S/FP10 (D3) to P/FP10 (D3) for survival outcome prediction (, , and , respectively). Similarly, there was no difference in the AUC of the ROC curves between S/FP (D3-D1) and P/FP (D3-D1) as well as S/FP (D3-B) and P/FP (D3-B) to predict survival (and 0.463, respectively).

6. Discussion

A recent study has concluded that in ARDS patients, when PEEP is integrated into the P/F ratio, the validity to predict hospital mortality is amplified [2]. The authors stated that the incorporation of PEEP into the P/F ratio enables the reflection of lung compliance and lung recruitment during the evaluation of the severity of ARDS [2]. The setting of PEEP in most cases of severe ARDS has been said to be approximately 8 cm H₂O, which is low [2, 7]. In the above-mentioned study, the AUC for prediction of mortality in cases of PEEP of about 8 cm H₂O was higher for P/FP10 (0.775) as compared to AUC of 0.691 for P/F ratio [2]. The sensitivity to predict mortality was also higher for P/FP10 (84.3%) compared to 65% for P/F [2]. The authors of the study included a correction factor of 10 for the P/FP as a PEEP of about 10 cm H₂O is commonly set as the initial ventilator setting [2, 8]. The other reason why factor 10 was chosen was that a regression line plotted in the study between P/F ratio and PEEP intersected the P/F of value 150 mmHg (which usually discriminates the survivors and non-survivors) at a PEEP of 10 cm H₂O [2]. We used the same factor (10) to be multiplied by the S/FP ratio as was done in the previous study [2]. For our study, we wanted to use a noninvasive, easily plausible, and continuous oxygen monitoring method such as SpO₂ after incorporating the PEEP into S/F ratio for correlation to the P/FP10. The P/FP10 ratio has now proven to be more pertinent as compared to the P/F ratio for prognostication of outcomes in ARDS patients [2]. Thus, we evaluated the correlation of S/FP10 to P/FP10 in ARDS patients at baseline, day one, and day three of MV. The reason for selecting the baseline and the worst values of S/FP10 up to day one of MV for correlation to P/FP10 was based on previous ARDS studies that demonstrated that compared to baseline oxygenation, values at 24 hours are more significant to predict outcomes [9–11]. Another study concluded that 6–12 hours of ARDS onset accurately predicted outcomes and was the optimal time for recruitment of patients into clinical research [12]. Thus, we selected the time interval between one hour and 24 hours of MV as day one. After initiation of MV, an ABG done within one hour has been proven to improve mechanical ventilation intervention and monitoring, by significantly detecting respiratory acidosis [13]. Thus, we chose the S/FP10 and P/FP10 values within one hour of MV initiation as baseline for correlation analysis. The strength of correlation between S/FP10 and P/FP10 in our study was more than the correlation between P/F and S/F at the respective time intervals. A study comparing the correlation between only SpO₂ and PaO₂ was done previously, which showed that the Pearson correlation coefficient was 0.423 only [14]. If FiO₂ is incorporated in the correlation, the strength of the correlation improves to about 0.580–0.766 as we found in our study. However, if PEEP is incorporated, the strength of correlation increases and is highly significant (0.733–0.853) as we found in our study. Moreover, in patients with PEEP ≥10 cm H₂O, there is a good correlation of S/FP10 and P/FP10, which is excellent on day three (0.881). This is clinically very significant because it is in this group of ARDS patients who require a higher PEEP that frequent ABG is ordered to evaluate the P/F ratios. Often as the days of MV progress from day one to day three, the need for placing an invasive arterial catheter for repeated ABG is often contemplated upon. The findings of the excellent correlation between S/FP10 and P/FP10 on day three in our study shows that the need for invasive arterial catheter placement for the purpose of frequent ABG monitoring as days of MV progress, can be avoided. Even though previous literature shows a good correlation between S/F ratio and P/F ratio, PEEP component which is so crucial was not incorporated previously [15].

A recent study on 1034 ARDS patients concluded that mortality prediction from oxygenation could be more conclusively done on day three (after 48 hours) of ARDS onset [16]. As the most common cause of mortality in ARDS is multi-organ dysfunction, which evolves and progresses over time, oxygenation values on the third day (after 48 hours) are likely to have a better predictive value for mortality [16–18]. Therefore, we selected the P/FP10 and S/FP10 values at day three (48–72 hours after MV), apart from baseline (0-1 hour after MV) and day one (1–24 hours after MV), to predict survival. The S/F ratio complements the P/F ratio; thus, S/F has also been incorporated to reflect respiratory status in the modified Sequential Organ Failure Assessment (mSOFA) score [19]. Similar to the manner in which a change of SOFA score during the first 48 hours of ICU stay has been shown to predict mortality, we also hypothesized that change of S/FP10 from initiation of MV to day three of MV may predict survival in a more clinically significant and validated manner [20]. We found that as compared to the P/FP10 and S/FP10 values at baseline and day one, the values on day three were more significant for predicting survival. Both the change in P/FP10 and the change in S/FP10 values between the baseline and day three values had one of the highest AUCs to predict survival. Previous research has shown that SpO₂/FiO₂ classification (≥190 or <190) along with PEEP categorization (≥10 cm H₂O or <10 cm H₂O) was useful for predicting mortality in moderate-severe ARDS at 24 hours of ARDS onset [21]. However, the results of our study were different as compared to the previous research, and we did not find S/FP10 (D1) to be a predictor of survival in ARDS patients. This difference in finding could be due to the fact that, in our study, we took the worst values of P/F within 1–24 hours after initiation of MV, and then the corresponding value of S/FP10 (D1) was calculated. Thus, the worst value of P/F and the corresponding S/FP(10) within 1–24 hours of MV could have been even after just few hours of the baseline time point and not exactly at 24 hours of MV initiation. Thus, the S/FP10 (D1) was probably not able to predict outcomes, as it may not exactly represent the 24-hour time point values, and could have represented values much closer to baseline. However, the S/FP10 (D3), S/FP10 (D3-B), and S/FP10 (D3-D1) were able to reliably predict outcomes in ARDS patients, showing that as compared to the baseline values, the improvement or deterioration in S/FP10 values over a certain time period is more helpful in predicting outcomes. This finding was in agreement with those of a recent study on ARDS patients [16].

In a previous study on P/FP10, Palanidurai et al. studied its utility for predicting mortality in ARDS only on the day of intubation [2]. However, the authors concluded in their hypothesis that the predictive ability of P/FP10 to predict mortality will improve over 24–72 hours [2]. This is exactly what we found in our study. Not only did the P/FP10 have an excellent predictive value for survival at 48–72 hours, but S/FP10 also had a good predictive ability for survival at 48–72 hours, as compared to baseline and day one.

Thus, clinicians may use the S/FP10 parameters in a mechanically ventilated ARDS patient, rather than repeated ABGs to predict survival. However, the S/FP10 values at baseline or on day one were not able to predict survival. Our findings were like the results of the trial by Chiu et al., where the authors concluded that the change in oxygenation status over 48 hours of ARDS onset, rather than baseline values, is significant [16]. The change in oxygenation as depicted by S/FP10 change in our study being an important predictor of survival is also theoretically validated by previous studies [22, 23]. In situations when a patient’s oxygenation improves after prone position ventilation, the change in oxygenation will be significant in 48 hours after a single proning session [22]. Such patients are more likely to survive as compared to those in whom there is no significant improvement in oxygenation over a period of MV.

In a study done by Fukuda et al. on hypoxemic respiratory failure patients who had bilateral lung field opacities, the AUC of S/F ratio at 24 hours of ICU admission to predict mortality of ICU stay was 0.784 [24]. However, we found that, rather than the P/FP10 and S/FP10 at baseline or at day one, it is the change in P/FP10 and S/FP10 from baseline to day three of MV that has the highest AUC to predict survival (AUC of 0.902 and 0.877, respectively). In our study, the S/FP (D3-B) ≥64 and S/FP (D3-D1) ≥75 have good validity for predicting survival with AUC of 0.877 and 0.821, respectively. Other than PEEP, indices of ventilator parameters such as mean airway pressure and plateau pressure have also been incorporated into P/F ratio for better predictor of outcomes, but these require paralyzing the patient for accurate measurement [2]. Thus, incorporation of PEEP into S/F ratio and assessing the change may be a practical yet reliable predictor of outcome in ARDS patients.

Apart from the correlation to the P/FP ratio and prediction of survival, we felt that another utility of S/FP10 that should be examined is its discriminating ability to predict severe ARDS category as per Berlin criteria. The discrimination ability should also be examined early, after intubation (baseline), so that clinicians may plan interventions in severe ARDS patients accordingly. We found that the S/FP10 (B) ≤116 has excellent discrimination ability to predict severe ARDS category with an AUC of 0.925 and 90% sensitivity along with 93% specificity. This was much higher than the AUC of 0.839 for S/F to predict P/F >200 as per recently concluded study results [25]. However, the study included hypoxemic patients, and not patients with ARDS [25].

We evaluated the ability of S/FP10 (B) to predict severe ARDS, as these patients require early assiduous treatment planning and interventions such as lung-protective ventilation, prone ventilation, neuromuscular blockade, and a targeted negative fluid balance and are at greater risk of multiple organ dysfunction [26].

The correlation between S/FP10 and P/FP10 at baseline (r 0.831), day one (r 0.733), and day three (r 0.853) in our study was much higher compared to the correlation between S/F ratio and P/F ratio in the above-mentioned study (r 0.66). Thus, the consideration of PEEP applied strengthens the correlation between S/FP10 and P/FP10 ratios.

In the study done by Pandharipande et al., the authors concluded that the correlation of S/F and P/F was unaffected by the various levels of PEEP (<8 cm H₂O, 8–12 cm H₂O, and >12 cm H₂O) [27]. The results of our study were similar in the aspect that we found that, even in the subgroup of patients with higher PEEP ≥10 cm H₂O, the correlation of P/F and S/F and P/FP and S/FP was similar to that of the entire group of patients with various PEEP levels. Furthermore, in the above-mentioned study, when the contribution of PEEP was accounted for, the correlation between S/F and P/F was stronger as compared to the correlation between S/F and P/F without contribution of PEEP, as we found in our study [27].

The study’s strengths are that it has incorporated the concept of PEEP into a noninvasive method of oxygenation assessment (S/FP10) in ARDS patients to predict survival. The need for doing repeated ABGs may be avoided. This is important as, apart from the risk of infection and costs, arterial cannulation may even lead to devastating complications such as symmetrical peripheral gangrene [28]. The excellent correlation of S/FP10 to P/FP10 at higher PEEP on day three may help avoid arterial cannulation for repeated P/F or P/FP assessment in patients with PEEP ≥10 cm H₂O, as the days of MV progress in ICU. Similar to the manner in which a change in SOFA scores predicts mortality, the study could validate that the change in P/FP10 as well as S/FP10 ratio over 48 hours after intubation is a reliable predictor of survival. The study could also conclude that S/FP10 is able to predict severe ARDS category patients early after intubation, with an excellent discriminant function.

The study has certain limitations. It was a single-centre study. In addition, we did not plot the ROC of S/FP10 to predict survival at different levels of PEEP as done by Palanidurai et al. in their study on P/FP10 [2]. We assessed the discriminant function of S/FP10 to predict only severe ARDS, and not mild or moderate ARDS. The limitations of pulse oximetry use like poor waveform, hypothermia, shock, and methemoglobinemia decreases the utility of S/FP ratio as compared to P/FP ratio [25].

7. Conclusions

S/FP10 has a strong correlation to P/FP10 in ARDS patients at baseline, day one, and day three of MV, which is stronger than the correlation between S/F and P/F ratios at the respective time intervals. S/FP10 (B) ≤116 has an excellent discriminant function to predict severe ARDS category. On day three after initiation of MV, S/FP10 ≥244 has a good predictive ability for survival, whereas an increase in S/FP (D3-B) by ≥64 and increase in S/FP (D3-D1) by ≥75 also have good predictive ability for survival.

Abbreviations

ARDS:	Acute respiratory distress syndrome
PaO₂:	Partial pressure of arterial oxygen
FiO₂:	Fraction of inspired oxygen
PEEP:	Positive end-expiratory pressure
P/F ratio:	PaO₂/FiO₂, partial pressure of arterial oxygen to inspiratory oxygen fraction ratio
P/FP10:	PaO₂10/FiO₂PEEP
SpO₂:	Pulse oximetric oxygen saturation
S/F ratio:	SpO2/FiO2, partial pressure of arterial oxygen to inspiratory oxygen fraction ratio
S/FP10:	SpO₂10/FiO₂PEEP
ICU LOS:	Length of stay in intensive care unit
MV:	Mechanical ventilation
CI:	Confidence interval
APACHE II:	Acute physiology and chronic health evaluation II
SOFA score:	Sequential Organ Failure Assessment score.

Data Availability

The data sets used and analyzed during the current study are available from the first and corresponding author upon reasonable request. The data are not publicly available due to them containing information that could compromise research participant privacy/consent.

Conflicts of Interest

The authors declare that they have no conflicts of interest.

Acknowledgments

The authors Ms. Pratibha Todur (Principal Investigator), Dr. N. Anitha (Co-principal investigator), and Dr. Souvik Chaudhuri (Coinvestigator) thank Indian Council for Medical Research (ICMR), Ministry of Health and Family Welfare, Government of India, for the extramural ad hoc grant (IRIS/Proposal No. 2020 1322, No. 5/8–4/13/Env/2020-NCD-II) for financial support. The authors also appreciate the dedicated healthcare professionals and staff who provide care for critically ill patients in the unit where the study was conducted. In addition, the authors are thankful to Ms. Kavana for helping with data extraction.

References

ARDS Definition Task Force, V. M. Ranieri, G. D. Rubenfeld et al., “Acute respiratory distress syndrome: the Berlin definition,” JAMA, vol. 307, no. 23, pp. 2526–2533, 2012.
View at: Google Scholar
S. Palanidurai, J. Phua, Y. H. Chan, and A. Mukhopadhyay, “P/FP ratio: incorporation of PEEP into the PaO₂/FiO₂ ratio for prognostication and classification of acute respiratory distress syndrome,” Annals of Intensive Care, vol. 11, no. 1, p. 124, 2021.
View at: Publisher Site | Google Scholar
J. Villar, L. Perez-Mendez, and R. M. Kacmarek, “The Berlin definition met our needs: no,” Intensive Care Medicine, vol. 42, no. 5, pp. 648–650, 2016.
View at: Publisher Site | Google Scholar
T. Andrews, H. Waterman, and V. Hillier, “Blood gas analysis: a study of blood loss in intensive care,” Journal of Advanced Nursing, vol. 30, no. 4, pp. 851–857, 1999.
View at: Publisher Site | Google Scholar
S. Sriram, J. Chandran, S. Sriram, and B. Krishna, “Clinical utility of arterial blood gas test in an intensive care unit: an observational study,” Indian Journal of Critical Care Medicine, vol. 25, no. 2, pp. 172–175, 2021.
View at: Publisher Site | Google Scholar
A. Pluddemann, M. Thompson, C. Heneghan, and C. Price, “Pulse oximetry in primary care: primary care diagnostic technology update,” British Journal of General Practice, vol. 61, no. 586, pp. 358-359, 2011.
View at: Publisher Site | Google Scholar
G. Bellani, J. G. Laffey, T. Pham et al., “Epidemiology, patterns of care, and mortality for patients with acute respiratory distress syndrome in intensive care units in 50 countries,” JAMA, vol. 315, no. 8, pp. 788–800, 2016.
View at: Publisher Site | Google Scholar
J. Villar, L. Perez-Mendez, J. Blanco et al., “A universal definition of ARDS: the PaO2/FiO2 ratio under a standard ventilatory setting—a prospective, multicenter validation study,” Intensive Care Medicine, vol. 39, no. 4, pp. 583–592, 2013.
View at: Publisher Site | Google Scholar
N. Yehya, S. Servaes, and N. J. Thomas, “Characterizing degree of lung injury in pediatric acute respiratory distress syndrome,” Critical Care Medicine, vol. 43, no. 5, pp. 937–946, 2015.
View at: Publisher Site | Google Scholar
K. Parvathaneni, S. Belani, D. Leung, C. J. L. Newth, and R. G. Khemani, “Evaluating the performance of the pediatric acute lung injury consensus conference definition of acute respiratory distress syndrome,” Pediatric Critical Care Medicine, vol. 18, no. 1, pp. 17–25, 2017.
View at: Publisher Site | Google Scholar
Y. Lopez-Fernandez, A. Martínez-de Azagra, P. de la Oliva et al., “Pediatric acute lung injury Epidemiology and natural history study: incidence and outcome of the acute respiratory distress syndrome in children,” Critical Care Medicine, vol. 40, no. 12, pp. 3238–3245, 2012.
View at: Publisher Site | Google Scholar
N. Yehya, N. J. Thomas, and R. G. Khemani, “Risk stratification using oxygenation in the first 24 hours of pediatric acute respiratory distress syndrome,” Critical Care Medicine, vol. 46, no. 4, pp. 619–624, 2018.
View at: Publisher Site | Google Scholar
R. A. McConnell, M. P. Kerlin, W. D. Schweickert, F. Ahmad, M. S. Patel, and B. D. Fuchs, “Using a post-intubation checklist and time out to expedite mechanical ventilation monitoring: observational study of a quality improvement intervention,” Respiratory Care, vol. 61, no. 7, pp. 902–912, 2016.
View at: Publisher Site | Google Scholar
S. Sembiring, “Correlation oxygen saturation in pulse oximetry with partial pressure oxygen in the arteries (PaO₂) on blood gas analysis examination in patient hypovolemic shock,” International Journal of Innovative Science and Research Technology, vol. 5, no. 9, pp. 363–365, 2020.
View at: Publisher Site | Google Scholar
T. W. Rice, A. P. Wheeler, G. R. Bernard et al., “Comparison of the SpO₂/FIO₂ ratio and the PaO₂/FIO₂ ratio in patients with acute lung injury or ARDS,” Chest, vol. 132, no. 2, pp. 410–417, 2007.
View at: Publisher Site | Google Scholar
L. C. Chiu, S. W. Lin, P. H. Liu et al., “Reclassifying severity after 48 hours could better predict mortality in acute respiratory distress syndrome,” Therapeutic Advances in Respiratory Disease, vol. 14, Article ID 175346662093687, 12 pages, 2020.
View at: Publisher Site | Google Scholar
B. T. Thompson, R. C. Chambers, and K. D. Liu, “Acute respiratory distress syndrome,” New England Journal of Medicine, vol. 377, no. 6, pp. 562–572, 2017.
View at: Publisher Site | Google Scholar
F. Madotto, T. Pham, G. Bellani et al., “Resolved versus confirmed ARDS after 24 h: insights from the LUNG SAFE study,” Intensive Care Medicine, vol. 44, no. 5, pp. 564–577, 2018.
View at: Publisher Site | Google Scholar
C. K. Grissom, S. M. Brown, K. G. Kuttler et al., “A modified sequential organ failure assessment score for critical care triage,” Disaster Medicine and Public Health Preparedness, vol. 4, no. 4, pp. 277–84, 2010.
View at: Publisher Site | Google Scholar
F. L. Ferreira, D. P. Bota, A. Bross, C. Mélot, and J. Vincent, “Serial evaluation of the SOFA score to predict outcome in critically ill patients,” JAMA, vol. 286, no. 14, pp. 1754–1758, 2001.
View at: Publisher Site | Google Scholar
L. Pisani, J. P. Roozeman, F. D. Simonis et al., “MARS consortium. Risk stratification using SpO₂/FiO₂ and PEEP at initial ARDS diagnosis and after 24 h in patients with moderate or severe ARDS,” Annals of Intensive Care, vol. 7, no. 1, p. 108, 2017 Oct 25.
View at: Publisher Site | Google Scholar
G. Scaramuzzo, L. Gamberini, T. Tonetti et al., “Sustained oxygenation improvement after first prone positioning is associated with liberation from mechanical ventilation and mortality in critically ill COVID-19 patients: a cohort study,” Annals of Intensive Care, vol. 11, no. 1, p. 63, 2021.
View at: Publisher Site | Google Scholar
J. Y. Adams, A. J. Rogers, A. Schuler et al. et al., “Association between peripheral blood oxygen saturation (SpO₂)/Fraction of inspired oxygen (FiO₂) ratio time at risk and hospital mortality in mechanically ventilated patients,” The Permanente Journal, vol. 24, no. 2, pp. 19–113, 2020.
View at: Publisher Site | Google Scholar
Y. Fukuda, A. Tanaka, T. Homma et al., “Utility of SpO2/FiO2 ratio for acute hypoxemic respiratory failure with bilateral opacities in the ICU,” PLoS One, vol. 16, no. 1, Article ID e0245927, 2021.
View at: Publisher Site | Google Scholar
M. Gowri, S. Babu, S. Kandasamy, and M. Gowri, “Association between SpO₂/FiO₂ ratio and PaO₂/FiO₂ ratio in different Modes of oxygen Supplementation,” Indian Journal of Critical Care Medicine, vol. 25, no. 9, pp. 1001–1005, 2021.
View at: Publisher Site | Google Scholar
M. A. Matthay, J. M. Aldrich, and J. E. Gotts, “Treatment for severe acute respiratory distress syndrome from COVID-19,” The Lancet Respiratory Medicine, vol. 8, no. 5, pp. 433-434, 2020.
View at: Publisher Site | Google Scholar
P. P. Pandharipande, A. K. Shintani, H. E. Hagerman et al., “Derivation and validation of SpO2/FiO2 ratio to impute for PaO₂/FiO₂ ratio in the respiratory component of the Sequential Organ Failure Assessment score,” Critical Care Medicine, vol. 37, no. 4, pp. 1317–21, 2009.
View at: Publisher Site | Google Scholar
N. M. Srinivasan and S. Chaudhuri, “Arterial cannulation can hasten the onset of symmetrical peripheral gangrene,” Anesthesia: Essays and Researches, vol. 5, no. 1, pp. 102–4, 2011.
View at: Publisher Site | Google Scholar

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Copyright © 2022 Pratibha Todur et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

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