Chapter 14 Assessment and Care of Patients with Acid-Base Imbalances
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Slide1
Chapter 14
Assessment and Care of Patients with Acid-Base Imbalances
Slide2
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.
Slide3
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.
Slide4
Introduction to Acid-Base Chemistry
Acids
Bases
Buffers
Body fluid chemistry:
Bicarbonate ions
Relationship between carbon dioxide and hydrogen ions
Calculation of free hydrogen ion level
Slide5
Sources of Acids
Incomplete breakdown of glucose
Destruction of cells
Bicarbonate
Slide6
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:
Hyperventilation
Hypoventilation
Slide7
Respiratory Acid-Base Control Mechanisms (Cont’d)
Slide8
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.
Slide9
Compensation
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.
Slide10
Respiratory Compensation
Lungs compensate for acid-base imbalances of a metabolic origin.
Example:
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.
Slide11
Renal Compensation
A healthy kidney can correct or compensate for changes in blood pH when the respiratory system either is overwhelmed or is not healthy.
Example:
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.
Slide12
Acid-Base Imbalances
Metabolic acidosis
Respiratory acidosis
Combined metabolic and respiratory acidosis
Metabolic alkalosis
Respiratory alkalosis
Slide13
Metabolic Acidosis
Overproduction of hydrogen ions
Under-elimination of hydrogen ions
Underproduction of bicarbonate ions
Over-elimination of bicarbonate ions
Slide14
Respiratory Acidosis
Retention of CO:
Respiratory depression
Inadequate chest expansion
Airway obstruction
Reduced alveolar-capillary diffusion
Slide15
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.
Slide16
Collaborative Care
History
CNS changes
Neuromuscular changes
Cardiovascular changes
Respiratory changes:
Kussmaul respiration
Skin changes
Psychosocial assessment
Slide17
Laboratory Assessment
Metabolic acidosis:
pH <7.35
Bicarbonate <21 mEq/L
PaO
2
normal
PaCO
2
normal or slightly decreased
Serum potassium high
Slide18
Laboratory Assessment (Cont’d)
Respiratory acidosis:
pH <7.35
PaO
2
low
PaCO
2
high
Serum bicarbonate variable
Serum potassium levels elevated if acidosis is acute
Serum potassium levels normal or low if renal compensation is present
Slide19
Interventions—Metabolic Acidosis
Hydration
Drugs:
Insulin to treat DKA
Antidiarrheal drugs
Bicarbonate only if serum bicarbonate levels are low
Slide20
Interventions—Respiratory Acidosis
Maintain a patent airway, and enhance gas exchange
Drug therapy
Oxygen therapy
Pulmonary hygiene
Ventilation support
Prevent complications
Slide21
Alkalosis
Metabolic alkalosis:
Base excesses—excessive intake bicarbonates, carbonates, acetates, and citrates
