Chapter 14 Assessment and Care of Patients with Acid-Base Imbalances
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Chapter 14 Assessment and Care of Patients with Acid-Base Imbalances

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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

Acid deficit—prolonged vomiting, excess cortisol, hyperaldosteronism, thiazide diuretics, prolonged NG suction

Slide22

Alkalosis (Cont’d)

Respiratory alkalosis:

Hyperventilation—anxiety, fear, improper vent settings, stimulation of central respiratory center due to fever, DNS lesion, and salicylates

Slide23

Collaborative Care

Assessment

CNS changes—positive Chvostek’s and Trousseau’s signs

Neuromuscular changes—tetany

Cardiovascular changes

Respiratory changes

Slide24

Interventions

Prevent further losses of hydrogen, potassium, calcium, and chloride ions.

Restore fluid balance.

Monitor changes.