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Semin Respir Crit Care Med 2025; 46(02): 221-232
DOI: 10.1055/a-2618-7422
Review Article

Nocturnal Hypoxemia in Respiratory Medicine: Pathophysiology, Measurement, and Association with Outcomes

Mohammadreza Hajipour
1   Department of Medicine, University of British Columbia, Vancouver, BC, Canada
,
Gonzalo Labarca
2   Department of Respiratory Diseases, School of Medicine, Pontificia Universidad Católica de Chile, Santiago, Chile
3   Division of Respiratory, Critical Care and Sleep Medicine, Mayo Clinic, Jacksonville, Florida
,
Najib Ayas
1   Department of Medicine, University of British Columbia, Vancouver, BC, Canada
,
Ali Azarbarzin
4   Sleep Apnea Health Outcomes Research Group, Brigham and women's Hospital, Harvard Medical School, Boston, Massachusetts
› Author Affiliations
Funding M.H. reports support from the Canadian Institutes of Health Research (CIHR), Canadian Lung Association (CLA), and Mitacs through the Mitacs Accelerate program. N.A. reports funding from Vancouver Coastal Health Research Institute Innovation. G.L. reports grant support from the American Academy of Sleep Medicine, Sleep Research Societe, CHEST Foundation, American Thoracic Society, and Agencia Nacional de Investigacion y Desarrollo (Chile). A.A. reports funding from NIH (fund nos.: R01HL153874, R01 HL158765, and R21 HL161766) AHA (fund no.: 19CDA34660137), and the American Academy of Sleep Medicine (fund no.: 188-SR-17, SR-2217).
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Abstract

Nocturnal hypoxemia is a prevalent feature of various respiratory diseases, significantly impacting patient outcomes and therapeutic strategies. Oximetry, a noninvasive and widely accessible tool, enables the measurement of nocturnal hypoxemia through oxyhemoglobin saturation (SpO2)-derived metrics such as the oxygen desaturation index, percentage of sleep time with SpO2 below 90%, mean SpO2, and measures of the area under the desaturation curve (e.g., sleep apnea-specific hypoxic burden). While these metrics are well established in obstructive sleep apnea (OSA), their application in other respiratory conditions, including chronic obstructive pulmonary disease, pulmonary hypertension, obesity hypoventilation syndrome, heart failure, neuromuscular disorders, pregnancy, and high-altitude residents, remains an area of active investigation. This review explores the pathophysiology of hypoxemia in these conditions and evaluates the role of SpO2-derived metrics in risk stratification beyond OSA. We also discuss the challenges of interpreting SpO2 data, particularly the difficulty differentiating disease-related hypoxemia from comorbid OSA. Additionally, we examine the limitations of oximetry, including sensor inaccuracies, motion artifacts, and skin pigmentation. Finally, we emphasize the need for further research to standardize these metrics across diverse conditions and advocate for their integration into clinical practice to enhance patient management and outcomes.

Keywords

nocturnal hypoxemia - pulse oximetry - respiratory disease - hypoxic burden - OSA

Authors' Contributions

M.H. and A.A. contributed to data extraction and manuscript drafting. All authors contributed to interpreting the findings and critically revising the manuscript. All authors have approved the manuscript in its final form.




Publication History

Accepted Manuscript online:
22 May 2025

Article published online:
11 June 2025

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