The Science Journal of the American Association for Respiratory Care

2001 OPEN FORUM Abstracts

PCO2AND PO2 VARIABILITY IN CAPILLARY TUBE BLOOD DUE TO HANDLING TECHNIQUES

By Robert CroninRRT and David Kissin RRT Maine Medical Center, Portland, Maine

Neonatal patients whohave compromised ventilation and lack arterial lines are typically managed onthe basis of capillary blood gas analysis. Capillary blood gas samples are routinelyin the 80 to 175 micro-liter range. Many blood gas analyzers have the capacityto measure micro-samples in the order of 30 micro-liters. To prevent this smallamount of blood from clotting before analysis, therapists typically agitatecapillary samples. We studied the effects of different agitation techniqueson PcCO2 and PcO2. We took left over arterial blood gasblood taken from adults and analyzed the blood to establish a baseline. We thenused that blood to fill capillary tubes and subjected full tubes (150 to 165micro-liters) and micro samples (30┬▒ micro-liters) to two tr├╝atments. One samplewas twirled, i.e. it was rotated about the long axis of the capillary tube priorto analysis for 30 seconds. A second sample was ?rocked? about the center ofthe tube in approximately 60 degree arc, allowing the blood to flow to theends of the capillary tube. Both samples were then analyzed. Micro-samples werethen collected and given the same treatments. Finally the original syringe wasre-analyzed to see there the action of collecting the capillary samples changedthe partial pressures in the syringe from the baseline. The samples and baselineswere then compared. We found that full capillary twirled samples had a lowerPcCO2 by 9.1% (standard deviation 4.1%) and that a rocked full samplehad a lower PcCO2 by 13.5% (standard deviation 8.2 %) from baseline.Twirled micro samples had a lower PcCO2 by 13.6 % (standard deviation13%) and rocked micro samples had a lower PcCO2 by 45.4% with a standarddeviation of 4%. When the source syringe was reanalyzed, PCO2 hadfallen by an average of 1%. PcO2, which in the age of widespreaduse of pulse oximetry is less relevant, rose above or fell below baseline dependingwhether the original sample PO2 was supra or sub atmospheric. Inthe case of sub atmospheric PO2, the PcO2 rose by 7.7%when full capillary tubes were twirled and 3.4% when rocked. Micro-samples withsubatmospheric PcO2 rose by 7.6% when twirled and 28% when rocked.Supra atmospheric O2 full capillary samples (PO2 160-220torr) dropped by an average of 4.6% when twirled and by 6.4% when rocked. Micro-samplePcO2 dropped by an average 5.7% when twirled and 5.7% when rocked.We recommend minimal agitation of capillary blood samples and only with twirlingwhen necessary.

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