PaO2 – Partial pressure of oxygen at sea level (160mmHg (21.3kPa) in the atmosphere, 21% of the standard atmospheric pressure of 760mmHg (101kPa)) in arterial blood is between 75 and 100mmHg (10.0 and 13.3kPa).[4][5][6]
Venous blood oxygen tension (normal)
PvO2 – Oxygen tension in venous blood at sea level is between 30 and 40mmHg (4.00 and 5.33kPa).[6][7]
PaCO2 – Partial pressure of carbon dioxide at sea level in arterial blood is between 35 and 45mmHg (4.7 and 6.0kPa).[9]
Venous blood carbon dioxide tension
PvCO2 – Partial pressure of carbon dioxide at sea level in venous blood is between 40 and 50mmHg (5.33 and 6.67kPa).[9]
Carbon monoxide tension
Arterial carbon monoxide tension (normal)
PaCO – Partial pressure of CO at sea level in arterial blood is approximately 0.02mmHg (0.00267kPa). It can be slightly higher in smokers and people living in dense urban areas.
Significance
The partial pressure of gas in blood is significant because it is directly related to gas exchange, as the driving force of diffusion across the blood gas barrier and thus blood oxygenation.[10] When used alongside the pH balance of the blood, the PaCO2 and HCO− 3 (and lactate) suggest to the health care practitioner which interventions, if any, should be made.[10][11]
Equations
Oxygen content
The constant, 1.36, is the amount of oxygen (ml at 1 atmosphere) bound per gram of hemoglobin. The exact value of this constant varies from 1.34 to 1.39, depending on the reference and the way it is derived. SaO2 refers to the percent of arterial hemoglobin that is saturated with oxygen. The constant 0.0031 represents the amount of oxygen dissolved in plasma per mm Hg of partial pressure. The dissolved-oxygen term is generally small relative to the term for hemoglobin-bound oxygen, but becomes significant at very high PaO2 (as in a hyperbaric chamber) or in severe anemia.[12]
Oxygen saturation
This is an estimation and does not account for differences in temperature, pH and concentrations of 2,3 DPG.[13]
↑ Severinghaus JW, Astrup P, Murray JF (1998). "Blood gas analysis and critical care medicine". Am J Respir Crit Care Med. 157 (4 Pt 2): S114-22. doi:10.1164/ajrccm.157.4.nhlb1-9. PMID9563770.
↑ Bendjelid K, Schütz N, Stotz M, Gerard I, Suter PM, Romand JA (2005). "Transcutaneous PCO2 monitoring in critically ill adults: clinical evaluation of a new sensor". Crit Care Med. 33 (10): 2203–6. doi:10.1097/01.ccm.0000181734.26070.26. PMID16215371.
1 2 Chu YC, Chen CZ, Lee CH, Chen CW, Chang HY, Hsiue TR (2003). "Prediction of arterial blood gas values from venous blood gas values in patients with acute respiratory failure receiving mechanical ventilation". J Formos Med Assoc. 102 (8): 539–43. PMID14569318.
↑ Walkey AJ, Farber HW, O'Donnell C, Cabral H, Eagan JS, Philippides GJ (2010). "The accuracy of the central venous blood gas for acid-base monitoring". J Intensive Care Med. 25 (2): 104–10. doi:10.1177/0885066609356164. PMID20018607.
↑ Adrogué HJ, Rashad MN, Gorin AB, Yacoub J, Madias NE (1989). "Assessing acid-base status in circulatory failure. Differences between arterial and central venous blood". N Engl J Med. 320 (20): 1312–6. doi:10.1056/NEJM198905183202004. PMID2535633.
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