ASSESSMENT OF ACID-BASE STATUS

In summary, the approach to assessment of acid-base status involves four key steps (1) initial inspection of the pH,... 

Constable, P. D. 1999. Clinical assessment of acid-base status. Strong ion difference theory. Veterinary Clinics of North American Animal Practice 15 447 71. 

Abnormalities of acid-base status of the blood are always accompanied by characteristic changes in electrolyte concentrations in the plasma, especially in metabolic acid-base disorders. Hydrogen ions cannot accumulate without concomitant accumulation of anions, such as CL or lactate, or without exchange for cations, such as or NaL Consequently, electrolyte composition of blood serum or plasma is often determined along with measurements of blood gases and pH and to assess acid-base disturbances. 

The unmeasured anion is commonly known as the anion gap, which is normally 12 4 mEq/L. This value is useful in assessing the acid-base status of a patient and in diagnosing metabolic acidosis. Disorders that cause a high anion gap are metabolic acidosis, dehydration, therapy with sodium salts of strong acids, therapy with certain antibiotics (e.g., carbenicillin), and alkalosis. A decrease in the normal anion gap occurs in various plasma dilution states, hypercalcemia, hypermagnesemia, hypernatremia, hypoalbuminemia, disorders associated with hyperviscosity, some paraproteinemias, and bromide toxicity. 

The assessment o( acid-base status is carried out by measuring [H ], [HCO3 ] and PCO, the components of the bicarbonate buffer system in plasma. 

All patients with significant disturbances in their acid-base status require continuous cardiovascular and hemodynamic monitoring. Because frequent assessment of the patient s response to treatment is critical, an arterial line is often placed to minimize patient discomfort with serial ABG collections. If... 

The importance of these secondary effects on acid-base status, metal concentration, and toxicity are still being studied. The recovery from acidification has been simulated by MAGIC for many watersheds, but sufficient time has not elapsed since acid inputs declined to assess the accuracy of the model predictions (Majer et aL, in review). 

Laboratory assessment includes indicators of general operative health (e.g., electrolytes, acid-base status, clotting profile, full blood cell count, and cross-matching). In addition, full human leukocyte antigen (HLA) tissue typing is undertaken, in addition to a full screen for infectious diseases, particularly cytomegalovirus (CMV), hepatitis, herpes, and HIV status, as these infections can be activated by immunosuppressive therapy. 

A description of acid-base balance involves an accounting of the carbonic (H2C03, HCOh COa", and CO2) and noncar-bonic acids and conjugate bases in terms of input (intake plus metabolic production) and output (excretion plus metabolic conversion) over a given time interval. The acid-base status of the body fluids is typically assessed by measurements of total CO2 plasma pH and PCO2, because the bicarbonate/carbonic acid system is the most important buffering system of the plasma. Occasionally, measurement of total titratable acid or base, or other acid and base analytes (e.g., lactate and ammonia [NH3]) is necessary to determine the etiology of an acid-base disorder. 

By far the most likely diagnosis in this case is diabetic ketoacidosis. This may be precipitated by a number of conditions, such as infection. This may have caused anorexia and, thus, the patient may have omitted to take her insulin. Trauma can increase a patient s requirement for insulin but there is nothing to suggest that in this case. The blood glucose can be checked at the bedside as can a specimen of urine for the presence or absence of ketones. The laboratory tests which may be requested are urea and electrolytes to assess renal function, the presence or absence of hyperkalaemia and the serum sodium concentration. The patient s acid-base status should be assessed to quantitate the severity of the acidosis present, and the blood glucose should be accurately measured. These will influence the patient s treatment. It is essential in cases such as this that samples of blood and urine and, if appropriate, sputum are sent to the microbiological laboratory to look for the presence of infection. 

Whereas simple buffers rapidly become ineffective as the association of the hydrogen ion and the anion of the weak acid reaches equilibritim. the bictubonate system keeps working because the carbonic acid is removed as carbon dioxide. The 1 i mi I to the effect i veness of the bicarbonate system is the initial concentration of bicarbonate. Only when all the bicarbonate is used up does the system have no further buffering capacity. The acid-base status of patients is assessed by consideration of the bicarbonate system of plasma. 

Bkiw, J. E., R. J. Rose, and I. C. Martin. 1991. A comparison of simultaneously collected arterial, mixed venous, jugular venous and cephalic venous blood samples in the assessment of blood-gas and acid-base status in the dog. Journal of Veterinary Medicine 5 294-298. 

Chen, L. and Driscoll, C.T. (2005a). A regional assessment of the response of the acid-base status of lake-watersheds in the Adirondack region of New York to changes in atmospheric deposition using PnET-BGC. Environmental Science and Technology, 39, 787-794. 

Determination of plasma and urine osmolality can be useful in the assessment of electrolyte and acid-base disorders. Comparison of plasma and urine osmolalities can determine the appropriateness and status of water regulation by the kidneys in settings of severe electrolyte disturbances, as might occur in diabetes insipidus or the syndrome of inappropriate antidiuretic hormone (SIADH) (see Chapters 45 and 50). The major osmotic substances in normal plasma are Ha, Cr, glucose, and urea thus expected plasma osmolality can be calculated from the following empirical equation ... 

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