celeste_acid base slides

7/30/2019 Celeste_acid Base Slides

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Facts and Definitions

1. Acid-base homeostasis - necessary tomaintain life.

2. Acid base balance must be within a definiterange for cellular function to occur.

3. The acidity of a substance, determined bythe hydrogen ion (H+) concentration; is

expressed as pH.

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pH - measures degree of acidity and

alkalinity

- indicator of H ion concentration

- Normal ph 7.35-7.45

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4. Acids

a. Release hydrogen ions into solution

b. Have pH < 7

5. Alkalines (bases)

a. Accept hydrogen ions into solutionb. Have pH > 7

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Acid- substance that can donate or releasehydrogen ions

ie Carbonic acid (H2CO3),Hydrochloric acid

** Carbon dioxide

combines with water toform carbonic acid

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Base

- substance that can accept hydrogen ions

ie Bicarbonate (HCO3)

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Body fluids

1. Normally slightly alkaline

2. Normal range is narrow: 7.35 7.45

(pH of 7 is neutral)3. Arterial blood pH < 7.35

is considered acid

4. Arterial blood pH > 7.45is considered alkaline

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Acids and Bases in the body

1. Body functions constantly produce acids

2. Most acids and bases in the body are weak

3. Acids includea. Carbonic acid, which is eliminated as a gas, carbon

dioxide

b. Lactic, hydrochloric, phosphoric, sulfuric acids,

which are metabolized or excreted as fluids

4. Bicarbonate is the major base

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Dynamics of Acid Base Balance

Acids and bases are constantly produced in the

body

They must be constantly regulated

CO2 and HCO3 are crucial in the balance

A HCO3:H2CO3 ratio of 20:1 should be

maintained

Respiratory and renal system are active inregulation

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Body regulation of acid-base balance

Constant response to changes in pH to maintainthe pH in the normal range

3 systems in the body, with various responsetimes, to maintain acid-base balance :

1. Buffers/ Chemical Buffers

2. Respiratory System

3. Renal ( metabolic) System

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A. Buffer System

1. Responds immediately, but has limited

capacity to maintain

2. Buffers: substances that bind or release

hydrogen ions

a. When body fluid becomes acid, buffers bindwith hydrogen ions to raise pH

b. When body fluid becomes alkaline, buffers

release hydrogen ions to lower pH

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Buffer systems

a. Bicarbonate-carbonic acid buffer system- blood and interstitial fluid

CO2 + H20 H2C03 H+ + HC03

weak acid weak base

Process is reversible but the ratio of 20 (bicarbonate) to

1 (hydrogen) must be maintained

b. Protein buffer system - intracellular and plasma;

hemoglobin buffer

c. Phosphates buffer system renal tubules

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B. Respiratory System

- controls CO2 and Carbonic acid content of ECF

1. Responds within minutes2. Includes respiratory center of brain stem and lungs

3. Occurs automatically, not under voluntary control

4. Adjusts the depth and frequency of respiration according to

the pH of the blood; increases or decreases the amount ofcarbon dioxide in the blood; controls the amount ofcarbonic acid formed and adjusts the pH of the blood

a. Hyperventilation: increased depth and frequency ofrespiration; blows off more CO2 in response to an acid pH

b. Hypoventilation: decreased depth and frequency ofrespiration; retains more CO2 in response to an alkaline pH

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Respiratory System

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H ions and CO2

(blood)

Stimulates theMedulla Oblongata

RR

Hyperventilation

(blows off CO2) H ions and CO2

(blood)

H ions and CO2

(blood)

Stimulates theMedulla Oblongata

RR

Hypoventilation

(retains CO2)

H ions and CO2(blood)


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C. Renal (Metabolic) System

-regulates bicarbonate level in ECF

1. Responds within hours to days

2. Adjusts the amounts of hydrogen and bicarbonate(metabolic component) ions

a. Kidneys excrete H+ ions, or generate and reabsorbbicarbonate ions, in response to an acid pH

b. Kidneys retain H+ ions, or generate and excrete bicarbonate

ions, in response to an alkaline pH

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How to obtain blood sample?

Allens test - evaluatepatency of radial and ulnarartery

Heparinized syringe and ice-filled container

Pressure dressing, noactivity at the site andcheck 5 ps distal to the siteof punctured artery

Note if patient is under O2

therapy Label the sample and send

immediately to thelaboratory

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ABG Responsibilities

Arterial blood

Radial or ulnar artery

Allens test

Prepare

Heparinized (Syringe,

specimen container)

Note: 02 therapy Bring specimen to the

LAB (ice)

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After injection

Maintain extension

position, no activity 8H

Apply pressure 5-15 min

Observe the site

Distal, 5 ps

(Pulselessness, Pain,

Paresthesia,Poikilothermia, Pallor)

Radial artery

30-45 degrees

Brachial artery60 degrees

Femoral artery

90 degrees

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Handling of Specimen

Expel all air bubblesimmediately

Do not agitate the syringe

Discard frothy specimen 1:1000 U/ml HEPARIN

Place sample in ice

Cool sample to 5 C if it can

not be analyzed quickly

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Determination of Acid-Base Balance: Analysis of

Arterial Blood Gases

pH

PaCO2

HCO3

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A. pH

1. Normal: 7.35 3.45

2. Acidic: 7.45

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B. PaCO2

Partial Pressure of carbon dioxide; respiratorycomponent

1. Normal: 35-45 mm Hg

2. Acidic: > 45 mm Hg

(carbon dioxide forms carbonic acid)

Hypercapnia: elevated levels of carbon dioxide inblood

3. Alkaline: < 35 mm HgHypocapnia: decreased levels of carbon dioxide in

blood

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C. HCO3

Bicarbonate; renal or metabolic component

1. Normal: 22 26 mEq/L2. Acidic: < 22 mEq/L

3. Alkaline: > 26 mEq/L

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D. Base Excess

1. Calculated value for buffer base capacity: the

amount of acid or base added to blood to

obtain a pH of 7.4

2. Normal: -3 - +3

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E. PaO2 or pO2

Pressure of oxygen in blood

1. Gives data about level of oxygenation; notused to calculate acid-base status of blood

2. Normal: 80 100 mm Hg

3. Hypoxemia: < 80 mm Hg

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F. SaO2 oxygen saturation

95% - 100%

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Interpreting ABG results

1. Check the pH.

2. Determine the PaCO2.

3. Watch the bicarbonate.4. Look for compensation.

5. Determine PaO2 and SaO2.

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Parameter Normal Value

pH 7.357.45

PaCO2 35

45 mmHgHCO3 22-26 mEq/L

PaO2 80100 mmHg

SaO2 95100 %

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1. Check the pH.

pH = 7.35 7.45 (normal)

pH = < 7.35 (acidosis)

pH = > 7.45 (alkalosis)

compensated normal pH

uncompensated abnormal pH

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Determine primary cause of disturbance.

Figure out whether the cause is:

Respiratory (PaCO2) or

Metabolic (HCO3)

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2. Determine the PaCO2. normal or abnormal

- Respiratory component

Normal: 35-45 mm Hg

a. PaCo2 < 35 mmHg respiratory alkalosis

? pH > 7.45 hypocapnia

a. PaCo2 > 45 mm Hg respiratory acidosis

? pH < 7.35 hypercapnia

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3. Watch the bicarbonate.

renal or metabolic component

Normal: 22 26 mEq/L

HCO3 < 22 mEq/L metabolic acidosis

? pH < 7.35

HCO3 > 26 mEq/L metabolic alkalosis

? pH > 7.45

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4. Look for compensation: look at the value whichdoes not match the acid base status of thepatients pH:

a. Within normal range: NO compensation

b. Above or below normal AND the pH itself isoutside the normal range: PARTIAL

c. Above or below normal AND the pH is within thenormal range: COMPLETE

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5. Determine PaO2 and SaO2

PaO2 80100 mmHg

SaO2 95100 %

- Reflect bodys ability to pick up oxygen from the lungs

Low hypoxemia; can cause hyperventialtion

- Indicate when to make adjustments in theconcentration being administered to the patient

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Interpreting ABG results Exercises

ACIDIC

dec pH

inc PaCO2 or pCO2

dec HCO3

ALKALINE/ BASIC

inc pH

dec PaCO2 or pCO2

inc HCO3

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1. pH 7.20 dec acidic

2. pCO2 60 inc acidic

3. HCO3 24 normal normal*

RESPIRATORY ACIDOSIS

no/ absent compensation

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3. HCO3 30 inc alkaline*

RESPIRATORY ACIDOSISpartial compensation

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1. pH 7.40* normal acidic*

2. pCO2 48 inc acidic3. HCO3 24 normal normal*

RESPIRATORY ACIDOSISno/ absent compensation

NOTE: If pH is normal but PaCO2 or HCO3 is abnormal,

use 7.4 as a cut off point

7.35 - 7.40 acidosis

7.40 - 7.45 alkalosis

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1. pH 7.60 inc alkaline

2. pCO2 20 dec alkaline

3. HCO3 18 dec acidic

RESPIRATORY ALKALOSIS

partial compensation

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1. pH 7.50 inc alkaline


3. HCO3 34 inc alkaline

METABOLIC ALKALOSIS

partial compensation

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1. pH 7.36* normal acidic

2. pCO2 30 dec alkaline


METABOLIC ACIDOSIS

complete/ full compensation

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2. pCO2 40 normal normal


METABOLIC ACIDOSIS

no/ absent compensation

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Acid-Base Imbalance

Classifications

1. Acidosis or alkalosis

a. Acidosis: Hydrogen ion concentration in bloodincreases above normal and pH is below 7.35

b. Alkalosis: Hydrogen ion concentration in blooddecreases below normal and pH is above 7.45

2. Origin of the problema. From the respiratory system

b. From the metabolic system

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Disorders: Simple or Combined

1. Primary disorders

a. Simple

b. One cause, either respiratory or metabolic

2. Combined disorders

a. More severeb. Both the respiratory and metabolic systems are the

cause of the same imbalance

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Compensation

1. Only occurs with primary disorders

2. Response by the system not causing the imbalanceto correct the pH

Example: with respiratory acidosis, the kidneys wouldeliminate hydrogen ions in urine to offset the

acidosis caused by hypoventilation of lungs.3. Complete Compensation occurs if the pH is corrected

to the normal range (7.35 7.45)

4. Partial Compensation occurs if there is improvement

in the pH but not to the normal range.5. Compensation can be determined by analysis of the

arterial blood gas results.

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Treatment

1. Urgency

a. Mental ability and level of consciousness is

often affectedb. Brain function usually affected; brain cells

need proper conditions to perform cellularfunctions

c. Cells cannot function properly if significantacidosis or alkalosis occurs

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2. Indirect treatment

a. Treating and correcting the precipitating condition

often corrects the acid-base imbalanceb. Directly treating the acid-base imbalance, by

adding or removing hydrogen or bicarbonate ions,

may lead to further imbalances

c. Not usually first line of treatment

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Types of Acid-Base Imbalances

A. Respiratory Acidosis

pH < 7.35

pCO2 > 45 mm Hg (excess carbon dioxide in the

blood)

Respiratory system impaired and retaining CO2;causing acidosis

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Etiology: pulmonary edema, aspiration,

atelectasis, pneumothorax, sleep apnea

syndrome, pneumonia, asthma,bronchiectasis, overdose of medications

(sedatives, narcotics, anesthetics),

neuromuscular d/o ( Guillain Barre),hypoventilation

s/sx: sudden hypercapnia produces incPR, RR, inc BP, mental cloudinesss,

feeling of fullness in head, papilledema

and dilated conjunctival blood vessels


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Respiratory Acidosis

Common Stimuli

a. Acute respiratory failure from airwayobstruction

b. Over-sedation from anesthesia or narcoticsc. Some neuromuscular diseases that affect

ability to use chest muscles

d. Chronic respiratory problems, such as ChronicObstructive Lung Disease

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Signs and Symptoms

a. Compensation: kidneys respond by generating andreabsorbing bicarbonate ions, so HCO3 >26 mm Hg

b. Respiratory: hypoventilation, slow or shallowrespirations

c. Neuro: headache, blurred vision, irritability,confusion

d. Respiratory collapse leads to unconsciousness andcardiovascular collapse

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Collaborative Care

a. Early recognition of respiratory status and treatcause

b. Restore ventilation and gas exchange; CPR forrespiratory failure with oxygen supplementation;intubation and ventilator support if indicated

c. Treatment of respiratory infections with

bronchodilators, antibiotic therapyd. Reverse excess anesthetics and narcotics with

medications such as naloxone (Narcan)

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e. Chronic respiratory conditions

a. Breathe in response to low oxygen levels

b. Adjusted to high carbon dioxide level through metaboliccompensation (therefore, high CO2 not a breathing trigger)

c. Cannot receive high levels of oxygen, or will have notrigger to breathe; will develop carbon dioxide narcosis

d. Treat with no higher than 2 liters O2 per cannula

f. Continue respiratory assessments, monitor further arterialblood gas results

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Nursing Diagnoses

a. Impaired Gas Exchange

b. Ineffective Airway Clearance

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B. Respiratory Alkalosis

pH > 7.45

pCO2 < 35 mm Hg.

Carbon dioxide deficit, secondary to

hyperventilation

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Etiology: extreme anxiety, hypoxemia,

Fever, hyperventilation, hysteria, hypoxia,

Salicycates (early)

s/sx: lightheadednes, inability to

concentrate, numbness, tingling, loss of

consciousness


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Respiratory Alkalosis

Common Stimuli

a. Hyperventilation with anxiety from

uncontrolled fear, pain, stress (e.g. women in

labor, trauma victims)

b. High fever

c. Mechanical ventilation, during anesthesia

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Signs and Symptoms

a. Compensation: kidneys compensate by eliminatingbicarbonate ions; decrease in bicarbonate HCO3 < 22 mm Hg.

b. Respiratory: hyperventilating: shallow, rapid breathing

c. Neuro: panicked, light-headed, tremors, may develop tetany,numb hands and feet (related to symptoms of hypocalcemia;with elevated pH more Ca ions are bound to serum albuminand less ionized active calcium available for nerve andmuscle conduction)

d. May progress to seizures, loss of consciousness (when normalbreathing pattern returns)

e. Cardiac: palpitations, sensation of chest tightness

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Collaborative Care

a. Treatment: encourage client to breathe slowly in apaper bag to rebreathe CO2

b. Breathe slowly; breathe with the patient; provideemotional support and reassurance, anti-anxietyagents, sedation

c. On ventilator, adjustment of ventilation settings

(decrease rate and tidal volume)d. Prevention: pre-procedure teaching, preventative

emotional support, monitor blood gases as indicated

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C. Metabolic Acidosis

pH


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Etiology: diarrhea, fistulas, diuretics, TPN

w/o Bicarbonate, lactic acidosis, DM,DKA, excessive ingestion of salicylates

(late)- aspirin, high fat diet, malnutrition,

renal insufficiency/ failure

S/sx: headache, confusion, drowsiness,

inc RR, dec BP, cold clammy skin,

dysrythmia, shock


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Metabolic Acidosis

Common Stimuli

a. Acute lactic acidosis from tissue hypoxia (lactic acid producedfrom anaerobic metabolism with shock, cardiac arrest)

b. Ketoacidosis (fatty acids are released and converted toketones when fat is used to supply glucose needs as inuncontrolled Type 1 diabetes or starvation)

c. Acute or chronic renal failure (kidneys unable to regulateelectrolytes)

d. Excessive bicarbonate loss (severe diarrhea, intestinal suction,bowel fistulas)

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Metabolic Acidosis

e. Usually results from some other disease and is

often accompanied by electrolyte and fluid

imbalances

f. Hyperkalemia often occurs as the hydrogenions enter cells to lower the pH displacing the

intracellular potassium; hypercalcemia and

hypomagnesemia may occur

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Metabolic Acidosis

f. Respiratory: tries to compensate by

hyperventilation: deep and rapid respirations

known as Kussmauls respirations

g. Diagnostic test findings:

1. ABG: pH < 7.35, HCO3 < 22

2. Electrolytes: Serum K+ >5.0 mEq/L

3. Serum Ca+2 > 10.0 mg/dL

4. Serum Mg+2 < 1.6 mg/dL

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Metabolic Acidosis

Collaborative Carea. Medications: Correcting underlying cause will often improve

acidosis

b. Restore fluid balance, prevent dehydration with IV fluids

c. Correct electrolyte imbalances

d. Administer Sodium Bicarbonate IV, if acidosis is severe anddoes not respond rapidly enough to treatment of primarycause. (Oral bicarbonate is sometimes given to clients withchronic metabolic acidosis) Be careful not to overtreat andput client into alkalosis

e. As acidosis improves, hydrogen ions shift out of cells andpotassium moves intracellularly. Hyperkalemia may becomehypokalemia and potassium replacement will be needed.

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Metabolic Acidosis

f. Assessment

1. Vital signs

2. Intake and output

3. Neuro, GI, and respiratory status;

4. Cardiac monitoring

5. Reassess repeated arterial blood gases andelectrolytes

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Metabolic Acidosis

Nursing Diagnoses

a. Decreased Cardiac Output

b. Risk for Excess Fluid Volume

c. Risk for Injury

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D. Metabolic Alkalosis

pH >7.45

HCO3 > 26 mEq/L

Caused by a bicarbonate excess, due to loss of

acid, or a bicarbonate excess in the body

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Etiology: excessive vomiting, diuretic,

hyperaldosteronism, hypokalemia, excessive

alkali ingestion, ingestion of excess sodium

bicarbonate/ antacids, massive transfusion ofwhole blood

s/sx: tingling of toes, dizziness, dec RR, inc PR,ventricular disturbances

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Metabolic Alkalosis

Common Stimuli

a. Loss of hydrogen and chloride ions through

excessive vomiting, gastric suctioning, or

excessive diuretic therapy

b. Response to hypokalemia

c. Excess ingestion of bicarbonate rich antacids

or excessive treatment of acidosis with

Sodium Bicarbonate

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Metabolic Alkalosis

Signs and Symptoms

a. Compensation: Lungs respond by decreasing the

depth and rate of respiration in effort to retain

carbon dioxide and lower pHb. Neuro: altered mental status, numbness and tingling

around mouth, fingers, toes, dizziness, muscle

spasms (similar to hypocalcemia due to less ionized

calcium levels)

c. Respiratory: shallow, slow breathing

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Metabolic Alkalosis

d. Diagnostic test findings

1. ABGs: pH> 7.45, HCO3 >26

2. Electrolytes: Serum K+ < 3.5 mEq/L

3. Electrocardiogram: as with hypokalemia

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Metabolic Alkalosis

Collaborative Care

a. Correcting underlying cause will often improve

alkalosis

b. Restore fluid volume and correct electrolyte

imbalances (usually IV NaCl with KCL).

c. With severe cases, acidifying solution may be

administered.

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Metabolic Alkalosis

d. Assessment

1. Vital signs

2. Neuro, cardiac, respiratory assessment

3. Repeat arterial blood gases and electrolytes

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Metabolic Alkalosis

Nursing Diagnoses

a. Impaired Gas Exchange

b. Ineffective Airway Clearance

c. Risk for Injury

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