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. 2024 Mar 13;11(1):e002250.
doi: 10.1136/bmjresp-2023-002250.

Characteristics of pulse oximetry and arterial blood gas in patients with fibrotic interstitial lung disease

Mira A Donaldson  1 , Kathryn Donohoe  2 , Deborah Assayag  3 , Celine Durand  4 , Jolene H Fisher  5 , Kerri Johannson  6 , Martin Kolb  7 , Stacey D Lok  8 , Hélène Manganas  4 , Veronica Marcoux  8 , Bohyung Min  6 , Julie Morisset  4 , Daniel-Costin Marinescu  1   9 , Christopher J Ryerson  10   9
Affiliations

Characteristics of pulse oximetry and arterial blood gas in patients with fibrotic interstitial lung disease

Mira A Donaldson et al. BMJ Open Respir Res. .

Abstract

Background: Fibrotic interstitial lung disease (ILD) is frequently associated with abnormal oxygenation; however, little is known about the accuracy of oxygen saturation by pulse oximetry (SpO2) compared with arterial blood gas (ABG) saturation (SaO2), the factors that influence the partial pressure of carbon dioxide (PaCO2) and the impact of PaCO2 on outcomes in patients with fibrotic ILD.

Study design and methods: Patients with fibrotic ILD enrolled in a large prospective registry with a room air ABG were included. Prespecified analyses included testing the correlation between SaO2 and SpO2, the difference between SaO2 and SpO2, the association of baseline characteristics with both the difference between SaO2 and SpO2 and the PaCO2, the association of baseline characteristics with acid-base category, and the association of PaCO2 and acid-base category with time to death or transplant.

Results: A total of 532 patients with fibrotic ILD were included. Mean resting SaO2 was 92±4% and SpO2 was 95±3%. Mean PaCO2 was 38±6 mmHg, with 135 patients having PaCO2 <35 mmHg and 62 having PaCO2 >45 mmHg. Correlation between SaO2 and SpO2 was mild to moderate (r=0.39), with SpO2 on average 3.0% higher than SaO2. No baseline characteristics were associated with the difference in SaO2 and SpO2. Variables associated with either elevated or abnormal (elevated or low) PaCO2 included higher smoking pack-years and lower baseline forced vital capacity (FVC). Lower baseline lung function was associated with an increased risk of chronic respiratory acidosis. PaCO2 and acid-base status were not associated with time to death or transplant.

Interpretation: SaO2 and SpO2 are weakly-to-moderately correlated in fibrotic ILD, with limited ability to accurately predict this difference. Abnormal PaCO2 was associated with baseline FVC but was not associated with outcomes.

Keywords: interstitial fibrosis.

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Conflict of interest statement

Competing interests: MAD reports no conflicts of interest relevant to this manuscript. KD reports no conflicts of interest relevant to this manuscript. DA reports grants and personal fees from Boehringer Ingelheim, grants from Canadian Institute for Health Research and from Fonds de Recherche du Quebec en Santé. CD reports no conflicts of interest relevant to this manuscript. JHF reports personal fees from AstraZeneca and Boehringer Ingelheim. KJ reports grants from Boehringer Ingelheim, Pulmonary Fibrosis Society of Calgary, University of Calgary School of Medicine; personal fees from Boehringer Ingelheim, Roche, Three Lakes Foundation, Pliant Therapeutics, Theravance, Blade Therapeutics. MK reports grants from Canadian Institute for Health Research, Roche, Boehringer Ingelheim, Pieris, Prometic; personal fees from Boehringer Ingelheim, Roche, European Respiratory Journal, Belerophon, United Therapeutics, Nitto Denko, MitoImmune, Pieris, AbbVie, DevPro Biopharma, Horizon, Algernon, CSL Behring. SDL reports consulting/personal fees and moderator honoraria from Boehringer-Ingelheim, honoraria from Hoffman-La Roche Ltd, grants from AstraZeneca and the University of Saskatchewan. HM reports grants from Boehringer Ingelheim and Gilead. VM reports grants from Boehringer Ingelheim, AstraZeneca, and Roche; personal fees from Boehringer Ingelheim and Roche. BM reports no conflicts of interest relevant to this manuscript. JM reports personal fees from Boehringer Ingelheim and Roche. D-CM reports personal fees from Boehringer Ingelheim. CJR reports grants from Boehringer Ingelheim; personal fees from AstraZeneca, Boehringer Ingelheim, Roche, Pliant Therapeutics, Cipla, Veracyte.

Figures

Figure 1
Figure 1
(A) Histogram of SaO2 values with a reference line at the boundary of normal. (B) Histogram of SpO2 values with a reference line at the boundary of normal. (C) Histogram of PaCO2 values with reference lines at boundaries of normal (35 and 45 mmHg). (D) Histogram of pH values with reference lines at boundaries of normal (7.35 and 7.45). Abnormal values are shown in light blue.
Figure 2
Figure 2
(A) Scatter plot of room air SaO2 and paired room air SpO2 measured within 30 days of each other. (B) Scatter plot comparing paired SaO2 from room air arterial blood gas (ABG) and room air SpO2 taken within 30 days of each other. Red lines indicate mean difference and the corresponding 95% CI. (C) Scatter plot comparing paired SaO2 and PaO2 from room air ABG. Red line indicates the curve of best fit. A minor jitter function was added to all graphs to better display overlapping data points.
Figure 3
Figure 3
(A) Scatter plot of PaCO2 and baseline FVC percent. (B) Scatter plot of PaCO2 and baseline FEV1 percent. (C) Scatter plot of PaCO2 and smoking pack years. FEV1, forced expiratory volume in one second; FVC, forced vital capacity.
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