This document discusses the use of venous blood gas measurements compared to arterial blood gas measurements. It finds that central venous blood gases most closely correlate with arterial measurements, while peripheral venous measurements vary more. Specifically, venous pH is typically 0.02-0.05 lower, PCO2 is typically 3-8 mmHg higher, and bicarbonate may be up to 2 mEq/L higher compared to arterial values. Venous measurements can be used for monitoring patients without arterial access, but arterial measurements are still preferred, especially for hypotensive patients. Periodic correlation of venous and arterial values is recommended when using venous measurements serially.

1. R. Amin Nejad; MD.
Anesthesiologist.

2.  Peripheral venous sample (obtained by
venipuncture),
 Central venous sample (obtained from a
central venous catheter), or a
 Mixed venous sample (obtained from the
distal port of a pulmonary artery catheter)

3.  Central venous blood gases have been preferred
because their correlation with arterial blood
gases is the most well-established by research
and clinical experience.
 Peripheral venous blood gases have been
studied in critically ill patients as an alternative
for patients who do not have central venous
access.
 Tavakol K, Ghahramanpoori B, Fararouei M. Prediction of Arterial Blood pH and Partial Pressure of
Carbon dioxide from Venous Blood Samples in Patients Receiving Mechanical Ventilation. J Med Signals
Sens 2013; 3:180.
 Byrne AL, Bennett M, Chatterji R, et al. Peripheral venous and arterial blood gas analysis in adults: are
they comparable? A systematic review and meta-analysis. Respirology 2014.
 Kelly AM, Klim S, Rees SE. Agreement between mathematically arterialised venous versus arterial blood
gas values in patients undergoing non-invasive ventilation: a cohort study. Emerg Med J 2013.

4. Cengiz M, Ulker P, Meiselman HJ, Baskurt OK. Influence of tourniquet application on
venous blood sampling for serum chemistry, hematological parameters, leukocyte
activation and erythrocyte mechanical properties. Clin Chem Lab Med 2009; 47:769.

5.  Venous oxygen tension (PvO2)
 Carbon dioxide tension (PvCO2)
 Acidity (pH)
 Oxyhemoglobin saturation (SvO2)
 Serum bicarbonate (HCO3) concentration

6. ●PvCO2, venous pH, and venous serum HCO3
concentration are used to assess ventilation and/or
acid-base status.
●SvO2 is used to guide resuscitation during severe
sepsis or septic shock, a process called early goal-directed
therapy.
●PvO2 has no practical value at this time. It is not
useful in assessing oxygenation because oxygen
has already been extracted by the tissues by the
time the blood reaches the venous circulation.

9.  The pH is usually 0.03 to 0.05 pH units lower
 The PCO2 is usually 4 to 5 mmHg higher and
 Little or no increase in serum HCO3
than the arterial one
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monitoring. J Intensive Care Med 2010; 25:104.

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venous-arterial carbon dioxide tension gradient with cardiac output during neurosurgical
procedures in the sitting position. Eur JAnaesthesiol 2010; 27:882.

11.  The pH is approximately 0.02 to 0.04 pH units
lower
 The venous serum HCO3 concentration is
approximately 1 to 2 meq/L higher
 The venous PCO2 is approximately 3 to 8
mmHg higher
than the arterial one
Gokel Y, Paydas S, Koseoglu Z, et al. Comparison of blood gas and acid-base measurements in arterial and venous blood samples in patients with uremic acidosis and diabetic ketoacidosis in the emergency room. Am J Nephrol 2000; 20:319.
Brandenburg MA, Dire DJ. Comparison of arterial and venous blood gas values in the initial emergency department evaluation of patients with diabetic ketoacidosis. Ann Emerg Med 1998; 31:459.
Malatesha G, Singh NK, Bharija A, et al. Comparison of arterial and venous pH, bicarbonate, PCO2 and PO2 in initial emergency department assessment. Emerg Med J 2007; 24:569.
Chu YC, Chen CZ, Lee CH, et al. Prediction of arterial blood gas values fromvenous blood gas values in patients with acute respiratory failure receivingmechanical ventilation. J Formos Med Assoc 2003; 102:539.
Kelly AM, Kyle E, McAlpine R. Venous pCO(2) and pH can be used to screen for significant hypercarbia in emergency patients with acute respiratory disease. J Emerg Med 2002; 22:15.
Kelly AM, McAlpine R, Kyle E. Venous pH can safely replace arterial pH in the initial evaluation of patients in the emergency department. Emerg Med J 2001; 18:340.

12. ABG pH PCO2 HCO3
VBG (CVC) + (0.03-0.05) - (4-5 mmHg) No change
VBG (MVC) + (0.03-0.05) - (4-5 mm Hg) No change
VBG (PVC) + (0.02-0.4) - (3-8 mm Hg) - (1-2 meq/L)

14.  Clinicians should be wary of VBG results and
preferentially obtain an ABG in hypotensive
patients.
 Periodic correlation of the venous
measurements with arterial measurements
should be performed whenever venous
measurements are used for serial monitoring.

15. Richard Treger, Shahriar Pirouz, Nader Kamangar, Dalila
Corry; Arterial vs venous blood gas differences during
hemorrhagic shock; World J Crit Care Med. May 4, 2014;
3(2): 55–60.

16. Peripheral or central venous pH, PCO2 and
bicarbonate can replace their arterial
equivalents in many clinical contexts that are
encountered in the ICU.