Chapter 14 Assessment and Care of Patients with Acid-Base Imbalances
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Assessment and Care of Patients with Acid-Base Imbalances
Normal Blood pH
Keeping pH within the normal range involves balancing acids and bases in body fluids.
Normal pH for arterial blood
7.35 to 7.45.
Normal pH for venous blood
7.31 to 7.41.
Normal Blood pH (Cont’d)
Changes from normal blood pH interfere with many normal functions by:
Changing the shape of hormones and enzymes.
Changing the distribution of other electrolytes, causing fluid and electrolyte imbalances.
Changing of excitable membranes.
Decreasing the effectiveness of many hormones and drugs.
Introduction to Acid-Base Chemistry
Body fluid chemistry:
Relationship between carbon dioxide and hydrogen ions
Calculation of free hydrogen ion level
Sources of Acids
Incomplete breakdown of glucose
Destruction of cells
Respiratory Acid-Base Control Mechanisms
When chemical buffers alone cannot prevent changes in blood pH, the respiratory system is the second line of defense against changes:
Respiratory Acid-Base Control Mechanisms (Cont’d)
Renal Acid-Base Control Mechanisms
The kidneys are the third line of defense against wide changes in body fluid pH.
Stronger for regulating acid-base balance but take longer than chemical and respiratory mechanisms to completely respond.
Kidney movement of bicarbonate.
Formation of acids.
Formation of ammonium.
The body attempts to correct changes in blood pH.
pH below 6.9 or higher than 7.8 is usually fatal.
Respiratory system is more sensitive to acid-base changes; can begin compensation efforts within seconds to minutes.
Renal compensatory mechanisms are much more powerful and result in rapid changes in ECF composition not fully triggered unless imbalance continues for several hours to days.
Lungs compensate for acid-base imbalances of a metabolic origin.
Prolonged running causes buildup of lactic acid, hydrogen ion levels in the ECF increase, pH drops; breathing is triggered in response to the increased carbon dioxide levels to bring the pH level back to normal.
A healthy kidney can correct or compensate for changes in blood pH when the respiratory system either is overwhelmed or is not healthy.
Person has chronic obstructive pulmonary disease, retains carbon dioxide in the blood, blood pH level falls (becomes more acidic); kidney excretes more hydrogen ions and increases the reabsorption of bicarbonate back into the blood.
Combined metabolic and respiratory acidosis
Overproduction of hydrogen ions
Under-elimination of hydrogen ions
Underproduction of bicarbonate ions
Over-elimination of bicarbonate ions
Retention of CO:
Inadequate chest expansion
Reduced alveolar-capillary diffusion
Combined Metabolic and Respiratory Acidosis
Uncorrected respiratory acidosis always leads to poor oxygenation and lactic acidosis.
Combined acidosis is more severe than metabolic or respiratory acidosis alone.
Cardiac arrest is an example of a problem leading to combined metabolic and respiratory acidosis.
Bicarbonate <21 mEq/L
normal or slightly decreased
Serum potassium high
Laboratory Assessment (Cont’d)
Serum bicarbonate variable
Serum potassium levels elevated if acidosis is acute
Serum potassium levels normal or low if renal compensation is present
Insulin to treat DKA
Bicarbonate only if serum bicarbonate levels are low
Maintain a patent airway, and enhance gas exchange
Base excesses—excessive intake bicarbonates, carbonates, acetates, and citrates