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Venous Blood Gas Versus Arterial Blood Gas Analysis Ping-Wei Chen PGY-2 Emergency Medicine.

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Presentation on theme: "Venous Blood Gas Versus Arterial Blood Gas Analysis Ping-Wei Chen PGY-2 Emergency Medicine."— Presentation transcript:

1 Venous Blood Gas Versus Arterial Blood Gas Analysis Ping-Wei Chen PGY-2 Emergency Medicine

2 Its Go Time… 25 yo female Single vehicle rollover near Sundre Intubated for deteriorating GCS In the ED: – BP 70 palp, HR 122 – Not responding to painful stimuli 01:23 - VBG ordered as part of workup 01:41 – ABG ordered as part of workup

3 Objectives Controversy Can VBGs replace ABGs? When are VBGs and ABGs different? When might I want an ABG? NOT covered – Electrolytes – Lactate

4 Whats all the fuss about? Arterial Blood Gas PAINFUL Arterial injury Thrombosis with distal ischemia Hemorrhage/hematoma Aneurysm formation Median nerve damage Infection Needlestick injury Reflex sympathetic dystrophy Venous Blood Gas Samples can be drawn simultaneously at time of venipuncture Should be done without tourniquette More difficult to obtain in pulseless patients Controversy regarding level of agreement with arterial values

5 Prospective, observational study 218 subjects, ED population dyspnea, DKA, renal failure, seizures, LOC, ingestions, ischemic colitis A priori definition of clinically important difference Pearson correlation coefficient Bland-Altman plots Rang et al Can J Emerg Med 4(1):7

6 Results Excellent correlation pH (r= 0.913) pCO 2 (r=0.921) calculated HCO 3 (r=0.953)

7 Results Clinically Important Differences 26/45 physicians responded

8 Result Mean Differences pH ( ) pCO mm Hg ( ) HCO mEq/L ( )

9 Prospective, observational study 246 subjects, ED population acute respiratory disease, suspected metabolic disorder pH only Results: Excellent correlation r=0.92 Mean difference: 0.04 pH units (-0.11 to +0.04) Kelly et al Emerg Med J. 18:340

10 Prospective, observational study 95 patients, ED population AECOPD, pneumonia, sepsis, ARF/CRF, DKA, ACS, acute gastroenteritis, SLE, toxic ingestion Bland-Altman Analysis Results: ABG compared to VBG Mean Difference 95% Limits of Agreement pH to 0.13 PCO to 6.8 HCO to 4.3 PO to 145.3

11 Review article: 6 studies pH and HCO 3 Results: – Mean difference pH: 0.02 ( to 0.021), n=258, DKA patients only pH: (-0.11 to 0.04), n =763, respiratory/metabolic illness HCO 3 : mEq/L (N/A), n =21, DKA patients only HCO 3 : mEq/L (-2.73 to 5.13), n=763, respiratory/metabolic illness

12 When are they different? Weil et al Difference in acid-base state between venous and arterial blood during cardiopulmonary resuscitation. NJEM. 315: – Prospective, observational study (n=16) – ICU/CCU patients – Arteriovenous gradient Pre-ArrestArrest pH0.06± ±0.05 pCO 2 11±2 mmHg36±6mmHg

13 So when might I want an ABG? Unable to establish IV access Inability to obtain sample Inability to obtain O 2 saturation by pulse oximeter – Peripheral vasoconstriction – Abnormal hemoglobins Carboxyhemoglobin Methemoglobin Sickle hemoglobin

14 N = 1 VBG at 01:32 – pH 7.11/pCO 2 41/HCO 3 14/lactate 6.6 ABG at 01:41 – pH 7.12/pCO 2 34/HCO 3 11/lactate 6.1

15 Conclusions VBGs not interchangeable with ABGs BUT – Excellent correlation with ABG values – Reasonable agreement on VBG for clinical decision making in ED pH lower PCO mmHg higher HCO 3 essentially the same Consider ABG in: – Inability to obtain sample – Inability to utilize pulse oximeter

16 Questions?


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