Sources of error in alveolar-arterial po2 difference calculated
from blood stored in plastic and glass syringes.
Wu, Eugene Y., Khalid W. Barazanji, and Robert L. Johnson, Jr.
Department of Internal Medicine, University of Texas Southwestern
Medical Center, Dallas, TX 75235
APStracts 3:0433A, 1996.
We studied the effects of time delay on blood gases, pH, and base
excess in blood stored in glass and plastic syringes on ice and the
effects of resulting errors on calculated alveolar-arterial PO2
difference (). Matched samples of dog whole blood were tonometered
with gas mixtures of 5% CO2 and 12% O2 (mixture A), 10% CO2 and 5% O2
(mixture B), and 2.88% CO2 and 4% O2 (mixture C). Tonometered blood
samples were transferred to 5 ml glass (5G), 5 ml plastic (5P), and 3
ml plastic (3P) syringes and stored on ice. Blood gases were measured
every hour up to six hours. In 5G syringes, oxygen tension (PO2)
progressively decreased in blood tonometered with A but rose in blood
tonometered with mixture B and C. Oxygen saturation (SO2)
progressively fell in all cases. In 5G syringes blood CO2 tension
(PCO2) progressively rose regardless of which gas mixture was used
and pH as well as base excess (SBE) progressively fell. The rise in
PO2 was faster in plastic than that in glass syringes and SO2 always
rose in plastic syringes. Differences between storage in plastic and
glass syringes on PO2 change were greatest when the initial blood PO2
was highest (mixture A). At the highest PO2 oxygen exchange was
faster in 3P than in 5P syringes. The rise of PCO2 was just as fast
in plastic as in glass syringes but in both the rise in PCO2 was
faster at a higher initial PCO2 (mixture B) than at lower initial
PCO2's (mixtures B and C). Rates of PO2 and PCO2 change in matched
samples were significantly faster in 3P than those in 5P syringes.
Errors due to rises in PCO2 and PO2 cause additive errors in
calculated and when blood is stored in plastic syringes for more than
1 hour significant errors in result. Errors are greater in normoxic
than in hypoxic blood where estimated decreased more than 10 mmHg in
normoxic blood after six hours stored on ice in plastic syringes.
Received 20 November 1995; accepted in final form 30 August 1996.
APS Manuscript Number A1210-5.
Article publication pending Journal of Applied Physiology.
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 7 October 1996