Mitigation of Pneumatic Tube Effects on Blood Gas Measurements for pH,PO 2,and PCO 2

Abstract

Background:

Specimen transport is a pre-analytical factor that can influence the accuracy of blood gas results as gas exchange can occur between an air bubble and the sample. A literature review determined that there is no uniform consensus as to whether pneumatic tube transport is appropriate for blood gas specimens. Our study was designed to determine acceptability of pH, PCO₂ and PO₂ results for specimens transported via a pneumatic tube

Methods:

Blood gas measurements were conducted on performance comparable Siemens Rapidpoint 500 analyzers. Blood gas samples were analyzed at point-of-care then sent through the pneumatic tube system for repeat analysis. Sample integrity was evaluated prior to tube transport. All sample analysis was performed by two experienced respiratory therapists. All point of care testing was performed by one therapist and the second therapist performed the post tube transport analysis. CLIA/CAP total allowable error limits were utilized to establish acceptable limits for pH, PCO_2, and PO₂. Phase two testing introduced a rubber stopper and immobilization padding prior to specimen tube transport.

Results:

Sixty blood gas specimens were analyzed pre and post-tube transport. 96.7% of pH results, 88.3% of PCO₂ results, and 50.0% of PO₂ results were within the acceptable range. The average biases between pre and post pneumatic tube specimens were -0.0048 for pH, 1.25 mm Hg for PCO₂, and 0.99 mm Hg for PO₂. In phase two, 54 blood gas samples were measured pre- and post-tube transport utilizing the mitigation interventions, 74.1% of PO₂ results (average bias of -0.59 mm Hg). 92.6% of PCO₂ results and 100% of pH measurements were within acceptable limits. To determine the clinical significance of the PO₂ differences, data with PO₂ values outside of the reference interval (70–100 mm Hg) with the potential to impact patient management were examined. Ten specimens were <70.0 mm Hg pre-transport, all of which had a higher post transport PO₂ (average increase of 7.4 mm Hg). Importantly, 100% of these specimens remained at < 70.0 mm Hg PO₂ post transport. All samples within the normal reference range remained in range post transport. The largest variation occurred in samples with high PO₂ values.

Conclusions:

The study confirmed measurable variation in PO₂ values post tube transport. The PO₂ variability was reduced to an acceptable level by immobilizing the sample and capping the syringe with a rubber stopper. Findings support tube transport of blood gas specimens under these conditions.