venous blood gas versus arterial blood gas analysis ping-wei chen pgy-2 emergency medicine
Post on 31-Mar-2015
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Venous Blood Gas Versus
Arterial Blood GasAnalysis
Ping-Wei ChenPGY-2
Emergency Medicine
It’s 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
Objectives
• Controversy• Can VBGs replace ABGs?• When are VBGs and ABGs different?• When might I want an ABG?• NOT covered– Electrolytes– Lactate
What’s 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
• 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. 2002. Can J Emerg Med 4(1):7
Results
• Excellent correlation pH (r= 0.913) pCO2 (r=0.921) calculated HCO3 (r=0.953)
Results• Clinically Important Differences
26/45 physicians responded
Result
• Mean Differences pH 0.036 (0.030-0.042) pCO2 6.0 mm Hg (5.0-7.0)
HCO3 1.5 mEq/L (1.3-1.7)
• 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. 2001. Emerg Med J. 18:340
• 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 0.015 -0.1 to 0.13
PCO2 -3 -7.6 to 6.8
HCO3 -0.74 -5.8 to 4.3
PO2 65 -32.9 to 145.3
• Review article: 6 studies• pH and HCO3
• Results:– Mean difference • pH: 0.02 (-0.009 to 0.021), n=258, DKA patients only• pH: 0.037 (-0.11 to 0.04), n =763, respiratory/metabolic
illness• HCO3: -1.88 mEq/L (N/A), n =21, DKA patients only• HCO3: -0.99 mEq/L (-2.73 to 5.13), n=763,
respiratory/metabolic illness
When are they different?
• Weil et al. 1986. Difference in acid-base state between venous and arterial blood during cardiopulmonary resuscitation. NJEM. 315:153-6.– Prospective, observational study (n=16) – ICU/CCU patients – Arteriovenous gradient
Pre-Arrest Arrest
pH 0.06±0.02 0.30±0.05
pCO2 11±2 mmHg 36±6mmHg
So when might I want an ABG?
• Unable to establish IV access• Inability to obtain sample• Inability to obtain O2 saturation by pulse
oximeter– Peripheral vasoconstriction– Abnormal hemoglobins • Carboxyhemoglobin• Methemoglobin• Sickle hemoglobin
N = 1
• VBG at 01:32– pH 7.11/pCO2 41/HCO3 14/lactate 6.6
• ABG at 01:41– pH 7.12/pCO2 34/HCO3 11/lactate 6.1
Conclusions
• VBGs not interchangeable with ABGs BUT– Excellent correlation with ABG values– Reasonable agreement on VBG for clinical
decision making in ED• pH 0.02-0.04 lower• PCO2 3-6 mmHg higher
• HCO3 essentially the same
• Consider ABG in: – Inability to obtain sample– Inability to utilize pulse oximeter
Questions?
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