Related Experiment Video
Updated: Sep 23, 2026

Expired CO2 Measurement in Intubated or Spontaneously Breathing Patients from the Emergency Department
Published on: January 29, 2011
Loss of carbon dioxide from serum samples exposed to air. Effect on blood gas parameters and strong ions
1Department of Medicine, Division of Nephrology, Medical College of Virginia, Virginia Commonwealth University, P.O. Box 980160, Richmond, VA 23298, USA. bkirschb@hsc.vcu.edu
Background:
The acid-base status of patients is frequently inferred from the concentration of total carbon dioxide in a venous blood sample. Prior studies of hemodialysis patients have reported lower values for tCO(2) when blood is shipped to a distant central laboratory compared to samples assayed at a local laboratory. Loss of tCO(2) from the sample after exposure of the blood to room air was postulated as the predominant factor.
Methods:
Serum samples were assayed on-site before and at varying intervals after removing the tube stopper on an AVL OPTI Critical care Analyzer using E-Cl cuvettes.
Results:
A rapid and progressive decline in pCO(2) and increase in pH was documented over a 2 h period. However, the change in tCO(2) during this time period was small and not significant. There were no changes in the concentrations of strong ions.
Conclusions:
The discrepancy in tCO(2) reported previously cannot be attributed solely to rapid loss of CO(2) unless assay conditions greatly enhance the rate of loss compared to the experimental conditions used in this study.
Related Concept Videos
Carbon Dioxide Transport in the Blood
Forms of CO2 Transport
1. Dissolved in plasma: A small percentage (7-10%) of CO2 is transported and dissolved directly in the plasma.
2. Carbaminohemoglobin: Just over 20% of CO2 is chemically bound to...
Diagnosing Acidosis and Alkalosis
First, the pH level is assessed to determine whether the blood pH is normal (7.35–7.45), low (acidosis), or high (alkalosis).
Next, the PCO2 and HCO3− values are examined to...
Oxygen Transport in the Blood
Blood Studies I: ABG and VBG
Arterial Blood Gas (ABG)
Arterial Blood Gas (ABG) studies are crucial for assessing the lungs' ability to supply oxygen and remove carbon dioxide, reflecting the patient's ventilation status. They also help understand the kidneys' capacity to reabsorb or...
Bicarbonate-Carbonic Acid Buffer
Assessment of Diffusion and Perfusion
The Role of Diffusion in Respiration
Diffusion is the process by which molecules move from an area of higher concentration to an area of lower concentration. In the respiratory system, this principle...

