Base excess

The base excess is the change from normal of the sum of the concentration of bicarbonate and non-bicarbonate buffer base ([HCO3 ]-K [Pr ]). The steps involved in the measurement are shown in Table 4.2B. The first step is to take a measured volume of the patient s blood and to equilibrate it at 37°C with a gas mixture containing carbon dioxide at a partial pressure of 40 mmHg. This removes any respiratory component of the acid base disorder. 

Base excess the change from normal of ([HCO3-] + [Pr-]). Measurement  

Equilibrate the sample of arterial blood with gas containing CO2 at Pco2 = 40mmHg. 

The base excess is an estimate of the magnitude of the non-respiratory component of an acid-base disturbance. In a population of normal individuals with no disturbance of acid-base physiology, the base excess is normally in the range of +/—2.5mM. 

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Schlichtig R, Grogono A, Severinghaus J. Human PaC02 and standard base excess for compensation of acid-base imbalances. Crit Care Med 1998 26 1173-1179. 

Benzenechromium tricarbonyl 371 is deprotonated by BuLi in EtiO-THF at —40 °C in a reaction that needs carefnl control for good yields . The prodnct 372 can be sily-lated to give 373 in 60% yield (Scheme 158). Toluenechrominm tricarbonyl lithiates non-regioselectively on the ring (bnt at the benzylic position with Na or K bases). Excess base can lead to polylithiation . 

If heparin comprises 10% or more of the total volume of a sample for blood gas analysis, errors in measurements of carbon dioxide pressure, bicarbonate concentration, and base excess may occur. 

A 15-year-old girl took 38 g of metformin (135). Her pH was 7.29, bicarbonate 17 mmol/1, base excess -10 mmol/1, and blood glucose 9.2 mmol/1 after receiving glucose from the rescue team. Her condition worsened—the bicarbonate fell to 15 mmol/1, the pH to 7.2, and the blood glucose to 2.7 mmol/1 the lactate rose to 8.7 mmol/1. The lactate concentration subsequently peaked at 21 mmol/1. 

For slow, bad mixing there will be local acid and base excesses [36], The excess of the acid can promote the redox reaction mentioned above. This acid-catalyzed reaction is much faster than the redox reaction without acid. Thus measurable contents of iodine are formed. These quantities can be detected photometrically using a UV-Vis spectrometer. 

In cases of incomplete C,H acid deprotonation, an excess of base can be employed to increase the enolate fraction. According to the principle of Le Chatelier, the base excess increases the enolate fraction by a factor that equals the square root of the number of mole equivalents of the base employed. 

The panned heavy mineral concentrates have not generally been analysed unless follow-up work has been carried out. However, all are inspected at site and observed minerals and contaminants are recorded. The samples are an excellent resource for identifying drainage catchment mineralisation and lithologies as well as anthropogenic contamination (Fig. 4.8). Indeed, all the G-BASE excess samples are stored at the National Geological Data Centre, Keyworth, UK, and are available for further study. The value of excess sample powders in research should not be underestimated. 

What is the base excess in meq/L in a patient with fully compensated respiratory acidosis having an initial pH of 7.2 and [HC03 ] = 28 meq/L ... 

The treatment of acid-base disturbances should be directed at the imderlying cause and the specific plasma constituent imbalance. It is possible to determine the relative contributions of sodium, chloride, unidentified anions (principally lactate in horses) and protein to the metabolic component of acid-base disturbances by the use of equations based on the calculated base excess (Corley Marr 1998, Whitehair et al 1995). However, decisions on treatment can often be based on the absolute values of these blood constituents and it is only in complex disturbances, with changes in multiple plasma constituents, that the equations are usually necessary. 

The pH of the plasma may be considered to be a function of two independent variables (1) the PCO2, which is regulated by the lungs and represents the acid component of the carbonic acid/bicarbonate buffer system, and (2) the concentration of titratable base (base excess or deficit, which is defined later), which is regulated by the kidneys. The plasma bicarbonate concentration is generally taken as a measure of the base excess or deficit in plasma and ECF, although it is recognized tliat conditions exist in which bicarbonate concentration may not accurately reflect the true base excess or deficit. 

Plasma Protein Buffer System and Plasma Base Excess The buffer value (p) of the nonbicarbonate buffers of plasma is about 7.7 mmol/L at pH 7.40 and a normal plasma protein concentration of 72 g/L. Proteins, especially albumin, account for the greatest portion (95%) of the nonbicarbonate buffer value of the plasma. The most important buffer groups of proteins in the physiological pH range are the imidazole groups of histidines (pimolecule contains 16 histidines. 

Plasma base excess is defined as the initial concentration of titratable base when titrating the plasma with strong acid or base to pH (Std) - 7.4 at PCO2 = 40 mm Hg and 37 °C. The equation for the CO2 equilibration curve of plasma and calculation of plasma base excess can be written ... 

As in plasma, CO2 equilibration of whole blood depends on the buffer value of nonbicarbonate buffers. Thus CO2 equilibration in whole blood is dependent on hemoglobin concentration and also on pH and oxygenation status. It is possible to derive an approximate equation for whole blood CO2 equilibration and calculation of whole blood base excess as follows ... 

ApH = measured pH - the standard pH of 7.40 AcB (B) the whole blood base excess (i.e., the concentration of titratable base when titrating the blood with strong acid or base to pH = 7.40 at PCO2 IStd] and 37 C)... 

This equation for whole blood base excess (Icnown as the Van Slyke equation ), together with the Henderson-Hasselbalch equation, provides the simplest algorithm for calculation of the various acid-base variables. The buffer... 

Metabolic acidosis is readily detected by decreased plasma bicarbonate (or a negative extracellular base excess), the primary perturbation in this acid-base disorder. Bicarbonate is lost in the buffering of excess acid. Causes include the foUowing ... 

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