Fundamentals of Arterial Blood Gas Interpretation

Abstract

Acid-base disturbances in patients with cardiopulmonary or other disorders are common and are often misinterpreted or interpreted incompletely. Treating acid-base disorders in greater detail facilitates pathophysiologic understanding and improved therapeutic planning. Understanding the ratiometric relationship between the lungs, which excrete volatile acid as carbon dioxide, and the kidneys, which contribute to maintenance of plasma bicarbonate, allows precise identification of the dominant acid-base disturbance when more than a simple disorder is present and aids in executing a measured treatment response. Concordantly, mapping paired values of the partial pressure of carbon dioxide (PCO2) and the bicarbonate concentration ([HCO3-]) on a Cartesian coordinate system visually defines an acid-base disorder and validates the ratiometric methodology. We review and demonstrate the algebraic and logarithmic methods of arterial blood gas analysis through the example of a complex acid-base disorder, emphasizing examination of the PCO2-to-[HCO3-] ratio.

Hidden Acid Retention with Normal Serum Bicarbonate Level in Chronic Kidney Disease

“…Under stable clinical conditions, the difference between venous tCO 2 and arterial [HCO 3 - ] levels is usually no greater than 2-4 mEq/L. This difference is mainly attributed to the dissimilarities between venous and arterial blood and the buffering effect of hemoglobin on CO 2 -mediated H + buffering, with a negligible contribution from erythrocyte carbamino-CO 2 18) . Not all cases with low tCO 2 are indicative of metabolic acidosis, as serum HCO 3 - levels can also decrease in respiratory alkalosis 19) .…”

Effect of different hypoxic and hypobaric interventions on blood gas and erythrocyte-related indicators in rats

“…急性高原病的主要诱因是缺氧，动脉血血气分析可以快速准确地检测动脉血中酸碱度、血氧、电解质及代谢物等变化，有利于指导缺氧早期的诊断、治疗及远期的预后 ［ 9 - 10 ］ 。然而人体血气指标非常敏感，极易受到体内外众多因素的影响，临床血气测定具有严格的操作规范。缺氧大鼠进行动脉血气测定时需要降低海拔，或者脱离缺氧环境，再进行麻醉采集动脉血。由于氧气和二氧化碳的扩散速度极快，仅需0.3 s左右即可完成肺部气体交换 ［ 11 ］ ，故从出舱到采血测定间复氧时间的长短对PO 2 、PCO 2 、酸碱度等血气指标可能会造成影响。本研究通过模拟高原低压低氧大鼠模型，比较不同缺氧时间、不同缺氧模式、缺氧后常氧恢复、缺氧预适应等干预对模型大鼠血气指标检测值的影响，以期为正确测定及解读模拟高原缺氧大鼠血气指标提供参考。…”