[DerangedPhysiology文章]：血气分析的误差来源
Sources of error in blood gas analysis
Esntially, this chapter is a short list of reasons as to why your ABG (or venous biochemistry) measurement may be wrong, i.e. not reflective of what is happening in the patient. In 99% of cas, it is a problem with the collection storage and transport of the sample, becau the are factors which are subject to human input and thus human error. The lf-calibrating blood gas analyr is a dutiful and dependable rvant; some sort of failure in its internal workings will only rarely contribute to the error (and usually it will be becau some idiot human has improperly calibrated it). Lastly, a tiny fraction of errors are begot by the physicochemical limitations of the measurement method (eg. when an absurdly high bromine concentration interferes with chloride measurement and returns a spuriously raid chloride concentration value). This whole thing enjoys a rich full discussion in the ction dedicated to arterial blood gas analysis.
Sources of error due to inappropriate sample collection and handling
Source of error in blood gas collection and handling
∙Sample contaminated with bubbles
∙Published information on the errors of ABG sampling arising from the prence of air bubbles comes from Biswas et al (1982). After two minutes, the prence of air bubbles or froth in the syringe had resulted in a significant increa of PaO2 and a decrea in PaCO2.
∙Sample contaminated with venous blood
∙Sample clotted
∙Sample contains too much heparin (liquid heparin dilutes the sample, and caus pH changes)
∙Haemolysis en route to the ABG analyr
赵汉奇∙Inappropriate type of syringe ud (gas-tight syringes are needed, rather than evacuated
tubes)
∙The sample contains an excessive number of leukocytes, and they have consumed all the oxygen (eg. leukaemia blasts)
老人过寿祝福语∙The sample took too long to transport, and blood cell metabolism has changed the gas concentration (e the ction on delayed processing below)
∙The sample was transported to the lab by a pressurid pneumatic system - this has the tendency to amplify errors caud by gas bubbles (Woolley and Hickling, 2003).
∙Sample was chilled with ice (and then analyd at body temperature values)
∙Low temperatures also make the ABG syringe polymer more gas-permeable, allowing gas to exchange with the atmosphere.
Sources of error in venous biochemistry sample collection and handling
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∙Clotted sample
∙Haemolyd by inappropriately small needle
∙Haemolyd by syringe vacuum
∙Inappropriate collection tube
The conquences of a delay in sample processing
Delayed venous sample processing
Question 3.2 from the cond paper of 2015 prents the candidates with a venous blood sample which demonstrates characteristic features of a delay in processing. A good reference is a 2008 paper by Tanner et al, examining the delayed processing of samples collected in rural and remote areas. The studies have discovered that over 4-24 hours of storage various changes take place. The changes (and the reasons behind them) were as follows:
Escape of cellular contents due to haemolysis
∙Potassium increas. After 24 hours, Tanner et al found the original K level of 3.8 incread to 8.0.
∙Phosphate increas. In the same study, the PO桃花髻4- went from an average value of 1.36 to 4.36.
∙Total protein increas
∙LDH increas
Compartment shift
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∙Sodium decreas
Metabolism by live cells
∙Acidosis develops (bicarbonate drops)
∙LDH increas (also becau of anaerobic metabolism)
∙Gluco decreas (consumed by RBCs)
大宇神秘惊奇∙Lactate increas (produced by RBCs)
Conquences of delay in arterial blood gas processing
An ideal reference for this exists in the Journal of Critical Care (Woolley and Hickling, 2003). It is unfortunately not available as free full text, but the author was able to get access to the article anyway, and summari its contents.
∙课题研究方法有哪些Some of the changes listed above apply:
∙pH decreas
∙HCO3-新蒜 decreas
∙SBE decreas
∙Lactate increas
∙Gluco decreas
∙PaO2 decreas and PaCO2 increas as a conquence of RBC metabolism (in the experiments by Biswas et al (1982), the PaO2 fell by up to 40% in samples which were stored at room temperature for twenty minutes. This ameliorated by storing the sample at 4°C, but all sorts of other problems develop as a conquence of this).
The actual difference in reality is not that great. It is possible to demonstrate this directly, in the following scenario. The two gas are arterial, taken at 35% FiO2 from an ICU patient; the sample was analyd once, then left next to the ABG machine for a half-hour or so, and then accidentally analyd again by someone who thought it was fresh.
The sample on the left was first, the one on the right was the thirty minute delay. The ambient temperature was probably clo to 20 degrees. As one can e, the differences are trivial. During that half hour, this anaemic patient's few remaining RBCs managed to metaboli only 0.1mmol/L of gluco, and produced a barely measurable increa in lactate and CO2.
