Acid-Base Imbalance

What is pH? pH is the concentration of hydrogen (H+) ions The pH of blood indicates the net result of normal acid-base regulation, any acid-base imbalance, and the body’s compensatory mechanisms The human body must maintain a very narrow pH range 7.35-7.45

What is pH? In terms of the human body: acidosis<------7.4------>alkalosis Carbon dioxide is the “acid” (CO2) Normal: 35-45 mmHg Bicarbonate is the “base” (HCO3) Normal: 22-26 mEq/L

pH in Abnormal Range Enzymes within cells do not function properly Hemoglobin does not manage oxygen properly Serious physiological problems occur, including death

How does the body maintain pH? Buffer systems Prevent major changes in pH by removing or releasing a hydrogen (H+) ion Act chemically to change strong acids into weaker acids or to bind acids to neutralize their effects Carbonic acid (H2C03) buffer system neutralized hydrochloric acid 2. Phosphate buffer system neutralizes strong acids

How does the body maintain pH? Buffer systems Intracellular and extracellular proteins act as buffer systems The cell can act as a buffer by shifting hydrogen in and out of the cell

How does the body maintain pH? Kidneys Regulate bicarbonate in the ECF The kidneys will retain or excrete H+ ions or HCO3 ions as needed Normally acidic urine Lungs Control CO2 Adjust rate and depth of ventilation in response to amount of CO2 in the blood A rise in arterial blood CO2 stimulates respiration Oxygen content of arterial blood will also stimulate respiration

Acidosis and Alkalosis Metabolic acidosis Decreased HCO3 or increase in other acids Metabolic alkalosis Increased HCO3 and excess loss of acids Respiratory acidosis Increased PaCO2 due to hypoventilation Respiratory alkalosis Decreased PaC02 due to hyperventilation

Imbalances Imbalances in PaCO2 are influenced by respiratory causes Imbalances in HCO3 are influenced by metabolic processes

Respiratory Acidosis Low pH (<7.35) High serum CO2 (>42) Body may attempt to compensate through renal retention of HCO3 (does not happen quickly - hours to days) Chronic respiratory acidosis occurs with chronic pulmonary disease (eg, emphysema, OSA) Pt. will often be asymptomatic, as the body has time to compensate Acute respiratory acidosis may be severe and will produce symptoms

Respiratory Acidosis Treatment is directed at improving ventilation --> treat the underlying cause Pulmonary hygiene to clear respiratory tract Adequate hydration to help clear secretions Supplemental oxygen Adjustment of mechanical ventilation as appropriate

Respiratory Alkalosis High pH (>7.45) Low PaCO2 (<35) Always due to hyperventilation Body may compensate through increased kidney excretion of bicarbonate (does not happen quickly - hours to days) Treatment is aimed at correcting the cause of hyperventilation If anxiety-related, may breathe into a closed system (rebreathe CO2)

Metabolic Acidosis Low pH (<7.35) Low HCO3 (<22 mEq/L) Body may attempt to compensate by increasing respirations to decrease CO2 High anion gap acidosis Results from excessive accumulation of fixed acid Normal anion gap acidosis Results from direct loss of bicarbonate

Metabolic acidosis Primary feature is decrease in serum HCO3 Hyperkalemia may also occur due to shift of potassium out of the cells Hypokalemia may occur once the acidosis is corrected Treatment is aimed at correcting the metabolic defect IV bicarbonate Potassium management Dialysis

Metabolic Alkalosis High pH (>7.45) High serum HCO3 (>26) Body may attempt to compensate by decreasing respirations to increase CO2 Treatment is aimed at treating the underlying disorder Chloride supplementation Restore normal fluid volume Maintain potassium Carbonic anhydrase inhibitor if unable to tolerate volume resuscitation

Interpreting Arterial Blood Gases pH (7.35-7.45) PaO2 (80-100 mmHg on room air) O2 saturation (95-100%) PaCO2 (35-45 mmHg) HCO3 (22-26 mEq/L) Base excess (or deficit) (+2 to -2 mEq/L) Sum of bases (alkalis)

Interpreting Arterial Blood Gases 1. Determine if acidosis or alkalosis *use 7.40 as normal in this step 2. Determine the component that caused the abnormality in step 1 3. Determine if the gas is compensated If the pH is 7.35-7.45, it is compensated If the pH is <7.35 or >7.45, it is uncompensated