Acid-Base Imbalances

pH< 7.35 acidosis pH > 7.45 alkalosis The body response to acid-base imbalance is called compensation May be complete if brought back within normal limits Partial compensation if range is still outside norms. 2

Compensation If underlying problem is metabolic, hyperventilation or hypoventilation can help : respiratory compensation. If problem is respiratory, renal mechanisms can bring about metabolic compensation. 3

Acid-Base Disturbances When compensation is appropriate Metabolic acidosis (↓ HCO 3, ↓ pCO 2 ) Metabolic alkalosis (↑ HCO 3, ↑ pCO 2 ) Respiratory acidosis (↑ pCO 2, ↑ HCO 3 ) Respiratory alkalosis (↓ pCO 2, ↓ HCO 3 )

Stepwise Approaches 1.History & physical examination 2.Arterial blood gas for pH, pCO 2, (HCO 3 ) Use the HCO 3 from ABG to determine compensation 3.Serum Na, K, Cl, CO 2 content Use CO 2 content to calculate anion gap 4.Calculate anion gap Anion gap = {Na + K - (Cl + HCO3-)} 5.Determine appropriate compensation 6.Determine the primary cause

1. Respiratory Acidosis Carbonic acid excess caused by blood levels of CO 2 above 45 mm Hg. Hypercapnia – high levels of CO 2 in blood Causes: Chronic conditions: Depression of respiratory center – drugs or head trauma Paralysis of respiratory or chest muscles Emphysema 6

Respiratory Acidosis cont. Acute conditions: Adult Respiratory Distress Syndrome Pulmonary edema Pneumothorax Compensation for Respiratory Acidosis: the kidneys eliminate hydrogen ion and retain bicarbonate ion (metabolic alkalosis) 7

Signs and Symptoms of Respiratory Acidosis Breathlessness Restlessness Lethargy and disorientation Tremors, convulsions, coma Respiratory rate rapid, then gradually depressed Skin warm and flushed due to vasodilation caused by excess CO 2 8

Treatment of Respiratory Acidosis Treat underlying dysfunction or disease Caution should be exercised in the correction of chronic hypercapnia: too-rapid correction of the hypercapnia can result in metabolic alkalosis. Alkalization of the cerebrospinal fluid (CSF) can result in seizures. Admit to intensive care unit (ICU) if pH (< 7.25) Oxygen therapy should be used with caution because it may worsen hypercapnia 9

Restore ventilation: invasive or non invasive ventilation Bicarbonate: Infusion of sodium bicarbonate is rarely indicated. This measure may be considered after cardiopulmonary arrest with an extremely low pH (< ). In most other situations, sodium bicarbonate has no role in the treatment of respiratory acidosis.

2. Respiratory Alkalosis Carbonic acid deficit pCO 2 less than 35 mm Hg (hypocapnea) Most common acid-base imbalance Primary cause is hyperventilation 11

Respiratory Alkalosis Conditions that stimulate respiratory center: Oxygen deficiency at high altitudes Pulmonary embolism Acute anxiety Fever, anemia Early salicylate intoxication Cirrhosis Gram-negative sepsis Compensation of Respiratory Alkalosis Kidneys conserve hydrogen ion Excrete bicarbonate ion (metabolic acidosis) 12

Treatment of Respiratory Alkalosis The treatment of respiratory alkalosis is primarily directed at correcting the underlying disorder. Respiratory alkalosis itself is rarely life threatening. Therefore, emergent treatment is usually not indicated unless the pH level is greater than 7.5. Breathe into a paper bag, beta blocker or sedatives can be helpful in anxiety attacks 13

3. Metabolic Acidosis Bicarbonate deficit - blood concentrations of bicarbonate drop below 22mEq/L Causes: Loss of bicarbonate through diarrhea or renal dysfunction Accumulation of acids (lactic acid or ketones) Failure of kidneys to excrete H+ 14

Symptoms of Metabolic Acidosis Headache, lethargy Nausea, vomiting, Diarrhea Coma Death Compensation for Metabolic Acidosis Increased ventilation (respiratory alkalosis) Renal excretion of hydrogen ions if possible K + exchanges with excess H + in ECF ( H + into cells, K + out of cells) 15

Treatment of Metabolic Acidosis Treating the underlying conditions in high AG states usually is sufficient in reversing the acidosis. Treatment with bicarbonate is unnecessary, except in extreme cases of acidosis when the pH is less than HCO 3 - can be administered intravenously to raise the serum HCO 3 - level adequately to increase the pH to greater than

4. Metabolic Alkalosis Bicarbonate excess - concentration in blood is greater than 26 mEq/L Causes: Excess vomiting = loss of stomach acid Excessive use of alkaline drugs Certain diuretics Endocrine disorders Heavy ingestion of antacids Severe dehydration 17

Symptoms of Metabolic Alkalosis Respiration slow and shallow Hyperactive reflexes ; tetany often related to depletion of electrolytes Dysrhythmias Compensation for Metabolic Alkalosis Alkalosis most commonly occurs with renal dysfunction, so can’t count on kidneys Respiratory compensation difficult – hypoventilation limited by hypoxia 18

Treatment of Metabolic Alkalosis Treat underlying disorder Replace electrolytes loss IV sodium chloride in volume depleted patients often need to add potassium Hydrochloric acid: Intravenous HCl is indicated in severe metabolic alkalosis (pH >7.55) or when sodium or potassium chloride cannot be administered because of volume overload or advanced renal failure. Dialysis: Both peritoneal dialysis and hemodialysis can be used with certain modifications of the dialysate to correct metabolic alkalosis 19