Blood gas tension

{{short description|Partial pressure of blood gases}} <!-- {{Infobox diagnostic | name = Blood gas tension | image = SpO₂_PaO₂_Table_Excel.png | alt = SpO₂ PaO₂ Table Excel | caption = SpO₂ PaO₂ Table Excel | pronounce = | purpose = Assess blood oxygenation | test of = | based on = | synonyms = | reference_range = | calculator = | DiseasesDB = {{DiseasesDB2|numeric_id}} | ICD10 = {{ICD10|Group|Major|minor|LinkGroup|LinkMajor}} or {{ICD10PCS|code|char1/char2/char3/char4}} | ICD9 = | ICDO = | MedlinePlus = article_number | eMedicine = article_number | MeshID = | OPS301 = {{OPS301|code}} | LOINC = {{LOINC|code}} }} --> '''Blood gas tension''' refers to the partial pressure of gases in blood.<ref name="pmid9563770">{{cite journal|vauthors=Severinghaus JW, Astrup P, Murray JF | title=Blood gas analysis and critical care medicine | journal=Am J Respir Crit Care Med | year= 1998 | volume= 157 | issue= 4 Pt 2 | pages= S114-22 | pmid=9563770 | doi= 10.1164/ajrccm.157.4.nhlb1-9}}</ref> There are several significant purposes for measuring gas tension.<ref name="pmid16215371">{{cite journal|vauthors=Bendjelid K, Schütz N, Stotz M, Gerard I, Suter PM, Romand JA | title=Transcutaneous PCO2 monitoring in critically ill adults: clinical evaluation of a new sensor | journal=Crit Care Med | year= 2005 | volume= 33 | issue= 10 | pages= 2203–6 | pmid=16215371 | doi= 10.1097/01.ccm.0000181734.26070.26}}</ref> The most common gas tensions measured are oxygen tension (P_xO₂), carbon dioxide tension (P_xCO₂) and carbon monoxide tension (P_xCO).<ref name="pmid14736638">{{cite journal|vauthors=Yildizdaş D, Yapicioğlu H, Yilmaz HL, Sertdemir Y | title=Correlation of simultaneously obtained capillary, venous, and arterial blood gases of patients in a paediatric intensive care unit | journal=Arch Dis Child | year= 2004 | volume= 89 | issue= 2 | pages= 176–80 | pmid=14736638 | doi= 10.1136/adc.2002.016261| pmc=1719810 }}</ref> The subscript ''x'' in each symbol represents the source of the gas being measured: "''a''" meaning arterial, "''A''" being alveolar, "''v''" being venous, and "''c''" being capillary.<ref name="pmid14736638"/> Blood gas tests (such as arterial blood gas tests) measure these partial pressures.

==Oxygen tension== ;Arterial blood oxygen tension (normal) '''P_aO₂''' – Partial pressure of oxygen at sea level ({{convert|160|mmHg|kPa|sigfig=3|lk=on|abbr=on}} in the atmosphere, 21% of the standard atmospheric pressure of {{convert|760|mmHg|kPa|sigfig=3|abbr=on}}) in arterial blood is between {{convert|75 and 100|mmHg|kPa|sigfig=3|abbr=on}}.<ref name="pmid9390851">{{cite journal| author=Shapiro BA| title=Temperature correction of blood gas values | journal=Respir Care Clin N Am | year= 1995 | volume= 1 | issue= 1 | pages= 69–76 | pmid=9390851 }}</ref><ref name="pmid17652681">{{cite journal|vauthors=Malatesha G, Singh NK, Bharija A, Rehani B, Goel A | title=Comparison of arterial and venous pH, bicarbonate, PCO2 and PO2 in initial emergency department assessment | journal=Emerg Med J | year= 2007 | volume= 24 | issue= 8 | pages= 569–71 | pmid=17652681 | doi=10.1136/emj.2007.046979 | pmc=2660085 }}</ref><ref name="pmid14569318">{{cite journal|vauthors=Chu YC, Chen CZ, Lee CH, Chen CW, Chang HY, Hsiue TR|author-link5=Howard Y. Chang | title=Prediction of arterial blood gas values from venous blood gas values in patients with acute respiratory failure receiving mechanical ventilation | journal=J Formos Med Assoc | year= 2003 | volume= 102 | issue= 8 | pages= 539–43 | pmid=14569318 }}</ref>

;Venous blood oxygen tension (normal) '''P_vO₂''' – Oxygen tension in venous blood at sea level is between {{convert|30 and 40|mmHg|kPa|sigfig=3|abbr=on}}.<ref name="pmid14569318"/><ref name="pmid20018607">{{cite journal|vauthors=Walkey AJ, Farber HW, O'Donnell C, Cabral H, Eagan JS, Philippides GJ | title=The accuracy of the central venous blood gas for acid-base monitoring | journal=J Intensive Care Med | year= 2010 | volume= 25 | issue= 2 | pages= 104–10 | pmid=20018607 | doi=10.1177/0885066609356164 }}</ref>

==Carbon dioxide tension== Carbon dioxide is a by-product of food metabolism and in high amounts has toxic effects including: dyspnea, acidosis and altered consciousness.<ref name="pmid2535633">{{cite journal|vauthors=Adrogué HJ, Rashad MN, Gorin AB, Yacoub J, Madias NE | title=Assessing acid-base status in circulatory failure. Differences between arterial and central venous blood | journal=N Engl J Med | year= 1989 | volume= 320 | issue= 20 | pages= 1312–6 | pmid=2535633 | doi=10.1056/NEJM198905183202004 }}</ref>

;Arterial blood carbon dioxide tension '''P_aCO₂''' – Partial pressure of carbon dioxide at sea level in arterial blood is between {{convert|35 and 45|mmHg|kPa|abbr=on}}.<ref name="pmid9794863">{{cite journal| author=Williams AJ| title=ABC of oxygen: assessing and interpreting arterial blood gases and acid-base balance | journal=BMJ | year= 1998 | volume= 317 | issue= 7167 | pages= 1213–6 | pmid=9794863 | doi= 10.1136/bmj.317.7167.1213| pmc=1114160 }}</ref>

;Venous blood carbon dioxide tension '''P_vCO₂''' – Partial pressure of carbon dioxide at sea level in venous blood is between {{convert|40 and 50|mmHg|kPa|sigfig=3|abbr=on}}.<ref name="pmid9794863"/>

==Carbon monoxide tension== ;Arterial carbon monoxide tension (normal) '''P_aCO''' – Partial pressure of CO at sea level in arterial blood is approximately {{convert|0.02|mmHg|kPa|sigfig=3|abbr=on}}. 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.<ref name="pmid2661120">{{cite journal| author=Hansen JE| title=Arterial blood gases | journal=Clin Chest Med | year= 1989 | volume= 10 | issue= 2 | pages= 227–37 | doi=10.1016/S0272-5231(21)00624-9 | pmid=2661120 }}</ref> When used alongside the pH balance of the blood, the P_aCO₂ and {{chem|H|C|O|3|-}} (and lactate) suggest to the health care practitioner which interventions, if any, should be made.<ref name="pmid2661120"/><ref name="pmid3144222">{{cite journal| author=Tobin MJ| title=Respiratory monitoring in the intensive care unit | journal=Am Rev Respir Dis | year= 1988 | volume= 138 | issue= 6 | pages= 1625–42 | pmid=3144222 | doi= 10.1164/ajrccm/138.6.1625}}</ref>

== Equations ==

=== Oxygen content === :<math chem>C_a \ce{O2} = 1.36 \cdot \ce{Hgb} \cdot \frac{S_a \ce{O2}}{100} + 0.0031 \cdot P_a \ce{O2}</math> 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. S_aO₂ 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 P_aO₂ (as in a hyperbaric chamber) or in severe anemia.<ref>{{cite web|title=Oxygen Content|url=https://www-users.med.cornell.edu/~spon/picu/calc/oxycont.htm|accessdate=October 7, 2014}}</ref>

=== Oxygen saturation === :<math chem> \ce{SO2} = \left(\frac{23,400}{\ce{PO2}^3 + 150 \ce{PO2}} +1\right)^{-1}</math> This is an estimation and does not account for differences in temperature, pH and concentrations of 2,3 DPG.<ref>{{cite journal|author=Severinghaus, J. W.|title=Simple, accurate equations for human blood O₂ dissociation computations|journal=J Appl Physiol|volume=46|issue=3|pages=599–602|year=1979|pmid=35496|url=https://www.nickalls.org/dick/papers/anes/JWSrevised2007.pdf|doi=10.1152/jappl.1979.46.3.599}}</ref>

==See also== * Alveolar air equation * Fick's laws of diffusion * Fraction of inspired oxygen

==References== {{reflist}}

Category:Hematology Category:Respiratory therapy Category:Pulmonology