Venous blood gas - Revision history

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Background

Chungirv: Created page with "==Background== The '''venous blood gas''' ('''VBG''') is a multi-component serum assessment of pH, blood gas tensions (P_vO₂ and P_vCO_{2
2017-08-03T15:15:26Z
Created page with "==Background== The '''venous blood gas''' ('''VBG''') is a multi-component serum assessment of pH, blood gas tensions (PvO2 and PvCO2</su..."
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==Background==

The '''venous blood gas''' ('''VBG''') is a multi-component serum assessment of pH, blood gas tensions (PvO2 and PvCO2), bicarbonate (HCO3), and the base excess.

can be drawn from a an IV catheter along with other bloodwork, unlike an arterial blood gas ([[ABG]]),

does not accurately reflect (PaO2)

arterial values of pH, CO2, and HCO3 can be extrapolated with varying levels of accuracy <ref>Byrne AL, Bennett M, Chatterji R, Symons R, Pace NL, Thomas PS. Peripheral venous and arterial blood gas analysis in adults: are they comparable? A systematic review and meta-analysis. Respirology. 2014 Feb;19(2):168-75. doi: 10.1111/resp.12225. Epub 2014 Jan 3. Review. PubMed PMID: 24383789.</ref> <ref>Malatesha G, Singh NK, Bharija A, Rehani B, Goel A. Comparison of arterial and venous pH, bicarbonate, Pco2 and Po2 in initial emergency department assessment. Emergency Medicine Journal : EMJ. 2007;24(8):569-571. doi:10.1136/emj.2007.046979.</ref><ref>McCanny P, Bennett K, Staunton P, McMahon G. Venous vs arterial blood gases in the assessment of patients presenting with an exacerbation of chronic obstructive pulmonary disease. Am J Emerg Med. 2012;30(6):896-900.</ref>

==Components==

===pH===

measurement of acidity/alkalinity: normal range 7.37-7.45

pH > 7.45 = alkalosis

pH< 7.35 = acidosis

correlates well with arterial pH <ref>1: 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 Apr;31(4):459-65. PubMed PMID: 9546014.</ref>

===PvO2===

measures the partial pressure of oxygen dissolved in the serum; that is, the dissolved oxygen ''not'' carried by hemoglobin

significantly lower than and nonindicative of arterial oxygen pressure (PaO2)

===PvCO2===

The amount of carbon dioxide dissolved in arterial blood. The normal range is 35 to 45 mm Hg.

PvCO2 >45 = primary respiratory acidosis

PvCO2 <35 = primary respiratory alkalosis

correlates with controversial accuracy with PaCO2: see discussion below

===HCO3===

calculated from PvCO2 and pH with Henderson-Hasselbalch equation

correlates well with serum HCO3 <ref>Nargis W, Rahman AS, Ahamed BU, Hossain MZ. Comparison of values of traditionally measured venous bicarbonate with calculated arterial bicarbonate in intensive care unit patients of a hospital in a third-world country. Nigerian Medical Journal : Journal of the Nigeria Medical Association. 2014;55(4):285-288. doi:10.4103/0300-1652.137186.</ref>

===Base Excess===

an estimation of the metabolic component of acid/base status: how much "extra base" there is in the system

the theoretical number of H+ needed to bring pH to 7.40 at pCO2=40

reference range -2 to +2

**positive in metabolic alkalosis, negative in metabolic acidosis

*can be expressed as "base deficit", with the same but opposite values

**e.g. base excess=-8 in a case of lactic acidosis; base deficit=+8

==Comparison with ABG==

===Disadvantages===

no information about PaO2

poor correlation with PaCO2

one study in COPDers shows PvCO2 exceeds PaCO2 by 5.4, but only unreliably so with 95%i nterval -8.8 to +20.5 mmHg<ref>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 Jan;22(1):15-9. PubMed PMID: 11809551.</ref>

*sensitivity for elevated arterial hypercapnea was 100% in this study with PvCO2>45; authors suggest that PvCO2 can be used to screen for hypercapnea

**metaanalysis shows 95% prediction interval PvCO2 of -10.7 mm Hg to +2.4 mm Hg <ref>Byrne AL, Bennett M, Chatterji R, Symons R, Pace NL, Thomas PS. Peripheral venous and arterial blood gas analysis in adults: are they comparable? A systematic review and meta-analysis. Respirology. 2014 Feb;19(2):168-75. doi: 10.1111/resp.12225. Epub 2014 Jan 3. Review. PubMed PMID: 24383789.</ref>

===Advantages===

convenience

no extra, painful radial artery access to draw ABG

can be easily obtained with IV access

pH very reliable

some studies do show

in the era of continuous pulse ox, meaningful information about oxygenation is always available

*the PvCO2 is internally consistent

**can trend CO2 response to treatment; just don't know exact starting point

==External Links==

http://www.clinicalcorrelations.org/?p=5608

https://lifeinthefastlane.com/ccc/vbg-versus-abg/

==References==

<references/>

[[Category:EBQ]]}