Evaluation of severinghaus' equation and its modification for 2, 3-dpg

Area of Science:

• Biomedical Engineering
• Clinical Chemistry
• Respiratory Physiology

Background:

• Severinghaus' equation is standard for estimating oxygen half saturation pressure (P50) using blood gas parameters.
• This equation shows significant deviations in patients with severe injuries.

Purpose of the Study:

• To modify Severinghaus' equation for accurate P50 estimation in critically ill patients.
• To incorporate the 2,3-diphosphoglycerate to hemoglobin tetramer ratio ([DPG]) into the P50 estimation.

Main Methods:

• Analyzed 139 blood samples from 65 severely injured patients.
• Correlated P50 estimation differences with the 2,3-DPG ratio.
• Derived a modified Severinghaus' equation including the [DPG] ratio.

Main Results:

• The modified equation: deltalog Po2 = +0.48 (7.4-pH) + 0.024 (T-37) + 0.0013BE + 0.135[DPG] - 0.116.
• Achieved P50 estimation accuracy of ±2.5 mmHg and oxygen saturation accuracy of ±5%.
• Demonstrated improved indirect estimation of Po2 and oxygen saturation in most clinical cases.

Conclusions:

• The modified Severinghaus' equation provides accurate P50 and oxygen saturation estimates in critically injured patients.
• Incorporating the 2,3-DPG ratio significantly enhances the equation's clinical utility.
• The study discusses the limitations of the modified equation.