VBG or ABG

Case#1: 26 y/o type I diabetic in ED with "high" finger stick at home.

VBG: pH 7.24, HCO3 12, pCO2 35, Lactate 3.2, K+ 5.8

Case #2: 64 y/o male with COPD in ED with acute respiratory distress.

Vitals: BP 140/90, HR 115, O2 Sat 85% on RA

VBG: pH 7.34 pCO2 45, HCO3 25, CO 8.1

Blood gases

The Basics

• Establish acid - base status
• Measure electrolytes
• Measure respiratory function

AMS

COPD/Asthma

- ABG

* Painful

* New Stick

* Risk of thrombosis

* Allows for calculation of the A-a gradient

- VBG

* easier

* tells you almost the same information

* less complications

ABG

- PaO2 80 - 100

- PCO2 40

- pH 7.35-7.45

VBG

- PaO2 40

- PCO2 46

- pH 7.32 - 7.42

CO

Sepsis

DKA

Basic Steps to Understanding the ABG

Basic Steps to Understanding the ABG

1. Acidotic? or Alkalotic?

2. PC02? > 45 mm Hg? < 35 mm Hg?

3. HCO3? < 22 mm Hg? > 26 mm Hg?

4. Match PCO2/HCO3 with ph

5. PCO2 or HCO3 in opposite direction of pH change?

ABG #1

- pH:7.55

- CO2: 37

- HCO3: 31

1. Acidotic? or Alkalotic?

2. PC02?

> 45 mm Hg?

< 35 mm Hg?

3. HCO3?

< 22 mm Hg?

> 26 mm Hg?

4. Match PCO2/HCO3 with ph

5. PCO2 or HCO3 in opposite direction of

pH change?

ABG #2

- pH:7.29

- CO2:58.9

- HCO3:25

Basic Steps to Understanding the ABG1. Acidotic? or Alkalotic?

2. PC02? > 45 mm Hg? < 35 mm Hg?

3. HCO3? < 22 mm Hg? > 26 mm Hg?

4. Match PCO2/HCO3 with ph

5. PCO2 or HCO3 in opposite direction of pH change?

ABG #3

- pH:7.30

- CO2: 30

- HCO3:14

48 y/o male with hx of COPD in the ED. He's hypoxic to 83% on room air, looks like he's having a COPD exacerbation. I've done x,y,z and I think he needs to come in.

"Can you please obtain an ABG and call me back?"

- Your friendly internal medicine colleague

ABG vs VBG

Objectives

• To understand differences between ABG's and VBG's.
• Briefly review how to interpret results.
• Review literature

Understanding Blood Gases and More

Shaneen Doctor, MD

Lavery RF, Livingston DH, Tortella BJ, Sambol JT, Slomovitz BM, Siegel JH. The utility of venous lactate to triage injured patients in the trauma center. J Am Coll Surg. 2000;190(6):656-664.

Acad Emerg Med 2007;14:587

And finally...the Lactate

- Normal venous lactate rules out arterial lactic acidosis

- Elevated does venous not equal elevated arterial

- Tourniquets have no effect

- Venous Lactate ~ Arterial Lactate

pH- ?

HCO3 - ?

pCO2 - ?

CO - ?

Lactate - ?

Can we use venous blood gas values as clinical equivalents to arterial values?

Conclusions

- 206 critically ill patients

- VBG good enough for pH, HCO3, K+

Comparison of arterial and venous pH, bicarbonate, PCO2 and PO2 in initial ED assessment

- 95 patients

- pH, PCO2, PO2 show narrow limits of agreement

- PO2 not as much

- 61 patients

- carboxyhaemoglobin levels

- mean (SD):

arterial sample- 7.2% (8.5%)

venous sample- 6.9% (8.2%)

mean difference - 0.30% (95% CI -2.7% to3.3%)

correlation coefficient between arterial and venous CO Hb: 0.99 (95% CI: 0.99 to 0.99)

Touger M. Relationship between venous and arterial carboxyhaemoglobin levels in patients with suspected carbon monoxide poisoning. Annals of Emergency Medicine 1995; 25: 481-483

Venous vs arterial blood gases in the assessment of patients presenting with exacerbation of COPD

- 94 patients

- CO2 in ABG vs VBG

- 100% sensitivity for hypercarbia at PCO2 of 45 mm hg

- Insufficient evidence for vbg to replace abg