Metabolic Acidosis

pH is the measure of how acidic or alkaline (basic) a substance is. Urine with abnormally high or low pH can contribute to the formation of certain types of kidney or bladder diseases. In dogs, the normal pH level should be between 7.0 and 7.5.

Acidosis is an abnormal increase in hydrogen ion concentration in the body, resulting from an accumulation of acid or the loss of the base. It is indicated by a blood pH below the normal range. The various forms of acidosis are named for their causes.

Role of Buffer System in Blood pH

The pH of the blood is maintained within the normal range by its buffer system, of which the bicarbonate system is most important. The addition of relatively large amounts of acid or alkali to the blood is necessary before its buffering capacity is exhausted and its pH is changed. The proportion of the dissolved carbon dioxide and the bicarbonate ion, which form the components of the buffer system, is maintained at a constant level either by increased pulmonary ventilation and discharge of carbon dioxide or by increased urinary excretion of the bicarbonate radical. Changes from normal acid-based balance towards either alkalosis or acidosis make significant contributions to ill-health and to clinical signs observed.

Causes of Acidosis

The general causes of acidosis can be divided into three categories:

1. Excessive loss of base (bicarbonate)
2. Accumulation of acid
3. Combination of both

Some common specific causes include acute diarrhea in newborn animals an acute enteritis. Metabolic acidosis also occurs where there is retention of carbon dioxide in the blood due to interference with normal respiratory exchange. Thus pneumonia, severe depression of the respiratory center and congestive heart failure may all be accompanied by acidosis.

Acidosis occurs in newborns during birth if this is prolonged and difficult. It also occurs in shock with circulatory failure.

A decrease of acid excretion by kidneys in renal insufficiency or renal failure also contributes to acidosis. The administration of excessive quantities of acidifying solutions for the treatment of alkalosis also may cause acidosis.

Metabolic Acidosis

Metabolic acidosis is characterized by a low arterial blood pH and a reduced plasma bicarbonate concentration, following the loss of bicarbonate or the addition of the hydrogen ion. Extra- and intracellular buffering and respiratory compensation minimize the change in pH until the kidney can excrete sufficient hydrogen ion to correct the acid-base imbalance. In general, a body will tolerate a pH range of 7.0-7.8, although survival has been reported at pH values beyond these limits for short periods.

The major clinical manifestation of metabolic acidosis is mental depression and varying degrees of muscular weakness.

Signs of Metabolic Acidosis in Diabetic Dogs

In dogs with diabetes mellitus, a total lack of insulin may yield an extremely high level of keton bodies. This pathological ketosis causes metabolic acidosis resulting in loss of appetite, decreased water intake and depression. especially when vomiting develops, the situation may deteriorate rapidly and when left untreated, death may occur.

Treatment of Metabolic Acidosis

Alkali therapy for severe acidemia which has its benefits and risks.

The source of protein in a dog's diet is considered important as it has been found that dogs fed low protein diets where the sole source of protein was egg albumen had a more severe metabolic acidosis.³

Uremia is a complex systemic disease brought about by decreased renal glomerular filtration and by other kidney abnormalities. As renal tubules fail to reabsorb water, urine volumes may remain large until shortly before death and failure of the kidneys to secrete ammonia and to absorb N₊ ions leads to progressive metabolic acidosis.⁴

References

1. Otto M. Radostits. Veterinary Medicine: A Textbook of the Diseases of Cattle, Sheep, Pigs, Goats and Horses
2. Jill E. Maddison, Stephen W. Page, David Church. Small Animal Clinical Pharmacology
3. John Henry Lewington. Ferret Husbandry, Medicine and Surgery
4. Norman F. Cheville. Introduction to Veterinary Pathology