Blood Gas Analysis and Sample Preparation in Controlled Desaturation Studies: Ensuring Accuracy in Pulse Oximetry

Introduction: The Foundation of Reliable Oxygenation Research 

Controlled desaturation studies are central to validating pulse oximeters. These studies, performed in specialized hypoxia laboratories such as PRL, safely lower arterial oxygen saturation (SaO₂) to predefined plateaus, typically from %100 to 70% SaO₂, generating reference data used to calibrate or verify pulse oximeters. 

At the core of this process lies one indispensable element: accurate blood gas analysis. The precision of a pulse oximeter’s validation depends directly on the quality of the blood gas reference, which in turn is determined by sample collection and preparation. 

Why Blood Gas Analysis Is Critical in Controlled Desaturation Studies 

In a typical pulse oximetry study, arterial blood samples are drawn at steady-state oxygenation plateaus and analyzed using regulatory-grade blood gas analyzers to obtain arterial oxygen saturation (SaO₂) via co-oximetry. 

This laboratory-measured SaO₂ serves as the ground truth against which the device under test’s functional oxygen saturation (SpO₂) is compared. Even minor errors in sample handling or analysis can introduce bias. 

Key Parameters: 

• SaO₂ (arterial oxygen saturation) - the definitive arterial blood gas reference 

• SpO₂ (oxygen saturation derived from pulse oximetry) - the functional oxygen saturation reported by a pulse oximeter 

• Total hemoglobin concentration and dyshemoglobins - ISO 80601-2-61 excludes participants with anemia or elevated dyshemoglobins 

• Carboxyhemoglobin (COHb): COHb absorbs light like oxyhemoglobin, causing two-wavelength pulse oximeters to overestimate SpO₂ 

• Methemoglobin (MetHb): MetHb absorbs red and infrared light nearly equally, impacting the pulse oximeter’s measurement ratio between its two two-wavelength  

Blood Sample Preparation: Precision from Collection to Analysis 

Sample Collection 

Arterial sampling is typically performed via radial arterial catheterization. The sampling protocol must ensure: 

• Rapid collection and minimal delay between draw and analysis  

• Dry heparin syringes to prevent clotting 

• Removal of air bubbles to prevent increasing SaO₂ and measurement errors 

• Precise synchronization with the blood sample to the pulse oximeter reading 

Sample Handling 

Immediately after draw: 

• Samples are gently mixed to prevent microclot formation and ensure homogeneity 

• They are kept anaerobic, sealed, and all air bubbles are removed 

• Blood is aspirated directly from syringe into the co-oximeter 

• Samples are analyzed within 2-10 minutes, but no longer than 30 minutes following standard guidelines 

The Role of Blood Gas Analyzers in Regulatory-Grade Studies 

Co-oximeters directly measure light absorbance at multiple wavelengths to quantify hemoglobin species. This method provides a true SaO₂ measurement, essential for optical sensor validation where spectral precision matters. ISO-aligned SpO₂ accuracy studies, laboratory blood gas analyzers serve as the reference, reporting both functional SaO₂ and fractional species (O₂Hb, HHb, COHb, MetHb) to verify accuracy and report exclusions for anemia or elevated dyshemoglobins. 

All results must be time-synchronized with the device under test and PRL’s reference data acquisition systems. Automated data capture minimizes transcription errors and ensures traceable, regulator-ready data integrity. 

Challenges and Best Practices in Desaturation Protocols 

Controlled desaturation studies are technically demanding. Maintaining precise SaO₂ plateaus across participants requires coordinated control of inspired gas and continuous physiological monitoring. 

Best Practices: 

• Use of standardized desaturation protocols aligned with ISO 80601-2-61  

• Integration of real-time logging and electronic traceability 

• Inclusion of participants with diverse skin tones (Monk Skin Tone scale) to ensure inclusive validation and mitigate optical bias. 

From Sample to Submission: Ensuring Regulator-Ready Data 

In regulatory submissions, credible data is built on precise physiological control and analytically traceable workflows. Rigorous blood sample preparation and analysis preserve the integrity of device accuracy results—helping streamline and support timely FDA review or CE mark approval. 

By adhering to ISO 80601-2-61, ISO 14155, FDA Guidance, and GCP compliance research organizations like PRL ensure that every data point is accurate, traceable, and regulator-ready. The result: a dataset that not only supports device performance claims but also withstands regulatory scrutiny. 

Conclusion: Analytical Precision Defines Validation Integrity 

In controlled desaturation research, blood gas analysis is the benchmark—the anchor that defines device accuracy and confidence in pulse oximeter performance.  

When handled under rigorous protocols, analyzed with calibrated instrumentation, and documented with transparency, these samples become more than data—they become the foundation of clinical trust in pulse oximetry and oxygenation technology validation. 

Ready to talk about your controlled desaturation study? Contact us today!

*See Disclaimer regarding AI-generated content