ABL9 blood gas analyser

Potential of hydrogen

The degree of acidity or alkalinity of any liquid (including blood) is a function of its hydrogen ion concentration [H⁺], and pH is simply a way of expressing hydrogen ion activity. The relationship between pH and hydrogen ion concentration is described thus:

pH = -log aH⁺
where aH⁺ is hydrogen ion activity.

Low pH is associated with acidosis and high pH with alkalosis [1,2].

1. CLSI. Blood gas and pH analysis and related measurements; Approved Guidelines. CLSI document CA46-A2, 29, 8. Clinical and Laboratory Standards Institute, 940 West Valley Road, Suite 1400, Wayne, Pennsylvania 19087-1898 USA, 2009
2. Acute care testing handbook. Radiometer Medical ApS, 2700 Brønshøj, Denmark, 2014. As accessed on https://www.radiometer.com/en/knowledge-center/handbooks/acute-care-testing-handbook

Partial pressure of carbon dioxide

Carbon dioxide (CO₂) is an acidic gas; the amount of CO₂ in blood is largely controlled by the rate and depth of breathing or ventilation. pCO₂ is the partial pressure of CO₂ in blood. It is a measure of the pressure exerted by that small portion (~5 %) of total CO₂ that remains in the gaseous state, dissolved in the blood plasma. pCO₂ is the respiratory component of acid-base balance and reflects the adequacy of pulmonary ventilation. The severity of ventilator failure as well as the chronicity can be judged by the accompanying changes in acid-base status [1,2].

1. Higgins C. Parameters that reflect the carbon dioxide content of blood. www.acutecaretesting.org Oct 2008.
2. Acute care testing handbook. Radiometer Medical ApS, 2700 Brønshøj, Denmark, 2014

Partial pressure of oxygen

The amount of oxygen in blood is controlled by many variables, e.g. ventilation/perfusion. pO₂ is the partial pressure of oxygen in a gas phase in equilibrium with the blood. pO₂ only reflects a small fraction (1 – 2 %) of total oxygen in blood that is dissolved in blood plasma [1]. The remaining 98 – 99 % of oxygen present in blood is bound to the hemoglobin in the erythrocytes. pO₂ primarily reflects the oxygen uptake in the lungs. [2]

1. Wettstein R, Wilkins R. Interpretation of blood gases. In: Clinical assessment in respiratory care, 6th ed. St. Louis: Mosby, 2010.

2. Acute care testing handbook. Radiometer Medical ApS, 2700 Brønshøj, Denmark, 2014. As accessed on https://www.radiometer.com/en/knowledge-center/handbooks/acute-care-testing-handbook.

Hematocrit

Hematocrit, the ratio between the volume of erythrocytes and the volume of whole blood. [1]

1. Acute care testing handbook. Radiometer Medical ApS, 2700 Brønshøj, Denmark, 2014. As accessed on https://www.radiometer.com/en/knowledge-center/handbooks/acute-care-testing-handbook.

Calsium

The calcium ion (Ca²⁺) is one of the most prevalent cations in the body, where approximately 1 % is present in the extracellular fluid of blood. Ca²⁺ plays a vital role for bone mineralization and many cellular processes, e.g. contractility of the heart and the skeletal musculature, neuromuscular transmission, hormone secretion and action in various enzymatic reactions such as, e.g. blood coagulation. [1]

1. Acute care testing handbook. Radiometer Medical ApS, 2700 Brønshøj, Denmark, 2014. As accessed on https://www.radiometer.com/en/knowledge-center/handbooks/acute-care-testing-handbook.

Chloride

Chloride (Cl^-) is the major anion in the extracellular fluid and one of the most important anions in blood. The main function of Cl^- is to maintain osmotic pressure, fluid balance, muscular activity, ionic neutrality in plasma, and help elucidate the cause of acid-base disturbances. [1]

1. Acute care testing handbook. Radiometer Medical ApS, 2700 Brønshøj, Denmark, 2014. As accessed on https://www.radiometer.com/en/knowledge-center/handbooks/acute-care-testing-handbook.

Potassium

Potassium (K⁺) is the major cation in the intracellular fluid, where it has a 25 - 37-fold higher concentration (∼150 mmol/L in tissue cells, ∼105 mmol/L in erythrocytes) than in the extracellular fluid (∼4 mmol/L) [1, 2]. K⁺ has several vital functions in the body, e.g. regulation of neuromuscular excitability, regulation of heart rhythm, regulation of intracellular and extracellular volume and acid-base status. [3]

1. Burtis CA, Ashwood ER, Bruns DE. Tietz textbook of clinical chemistry and molecular diagnostics. 5th ed. St. Louis: Saunders Elsevier, 2012.
2. Engquist A. Fluids/Electrolytes/Nutrition. 1st ed. Copenhagen: Munksgaard, 1985.
3. Acute care testing handbook. Radiometer Medical ApS, 2700 Brønshøj, Denmark, 2014. As accessed on https://www.radiometer.com/en/knowledge-center/handbooks/acute-care-testing-handbook.

Sodium

Sodium (Na⁺) is the dominant cation in the extracellular fluid, where it has a 14-fold higher concentration (∼140 mmol/L) than in the intracellular fluid (∼10 mmol/L). Na⁺ is a major contributor of the osmolality of the extracellular fluid and its main function is largely in controlling and regulating water balance, and maintaining blood pressure. Na⁺ is also important for transmitting nerve impulses and activating muscle concretion. [1]

1. Acute care testing handbook. Radiometer Medical ApS, 2700 Brønshøj, Denmark, 2014. As accessed on https://www.radiometer.com/en/knowledge-center/handbooks/acute-care-testing-handbook.