Articles on Medical Diseases and Conditions

Entries for the ‘Acid-Base and pH Measurements’ Category

Effect of Physiologic Patient Variation on Blood Gas Interpretation

There is a surprising degree of fluctuation in blood gas values in normal persons and in stabilized sick persons. In one study of normal persons using arterialized capillary blood, changes of at least 10% in bicarbonate or total CO2, 15% in PCO2, and 170% in base excess were required to exceed normal day-to-day variation. In […]

Newborn and Neonatal Blood Gas Measurement

A number of studies have found that umbilical cord arterial pH is the best available indicator of fetal acidosis, which would suggest intrauterine fetal hypoxia. Arterial pH was found to be more accurate than arterial PCO2, PO2, cord venous pH, or Apgar score. Although there is some disagreement regarding cord arterial pH reference range, a […]

Noninvasive Measurement of PCO2, PO2, and Oxygen Saturation

There are now several ways to measure carbon dioxide and oxygen in blood without drawing a blood sample. The two most popular methods at present are transcutaneous electrode systems and pulse oximetry. Both systems can provide continuous readings. The transcutaneous systems use PCO2 and PO2 electrodes similar to those of standard arterial blood gas analysis […]

Blood Lactate

Under conditions of adequate or near-adequate tissue oxygenation, glucose is metabolized for energy production using the aerobic metabolic pathway that converts glucose metabolic products to pyruvate that is, in turn, metabolized in the citric acid (Krebs) cycle. Under conditions of severe tissue hypoxia, aerobic metabolism cannot function properly, and glucose metabolic products at the pyruvate […]

Blood Oxygen Studies

The greatest stimulus for arterial as opposed to venous specimens for blood gas studies is to obtain measurement of blood oxygen. The usual information reported is PO2 (concentration of O2 gas measured in mm of Hg or Torr), obtained with a direct-reading PO2 electrode. PO2 represents the dissolved oxygen content of plasma, analogous to the […]

Anion Gap

Once metabolic acidosis is apparent, the problem becomes one of identifying the cause. Calculation of the anion gap may be helpful. The anion gap is the difference between the major cations (sodium, or sodium plus potassium) and the major anions (chloride and bicarbonate). The anion gap formula is: AG = Na – (C1 + HCO–3). […]

Other Comments on Acid-Base Problems

The preceding discussion applies to an acid-base problem involving a single primary metabolic or primary respiratory abnormality, with or without body attempts at compensation. Unfortunately, in some cases the laboratory picture is more complicated; for example, when there are superimposed attempts at therapy or when two different acid-base processes coexist (referred to as “mixed acid-base […]

Interpretation of Acid-Base Data

Acid-base data interpretation has always been one of the more difficult areas of laboratory medicine. In most uncomplicated untreated cases the diagnosis can be achieved with reasonable ease. There are several ways of approaching an acid-base problem. One way is to examine first the arterial PCO2 value. Since primary respiratory disorders result from hypoventilation or […]

Buffer Base and Base Excess

The concepts of buffer base and base excess form part of the Astrup acid-base system. The term buffer base refers to all substances in the buffering system of whole blood that are able to bind excess H+. Bicarbonate forms slightly more than one half of the total buffer base; hemoglobin makes up about one third […]

Acid-Base Compensation

Compensation refers to the degree of PCO2 change when there is, or has been, an abnormality in pH. An uncompensated disorder is a primary metabolic or respiratory condition that has not been altered by any significant degree of correction. In the case of a primary metabolic condition the respiratory counterbalance (change in ventilation which is […]