Acid-Base Imbalance
Metropolitan Community College
Fall 2013
Acid Base Balance

Hydrogen ions - Low concentrations but highly
reactive

Concentration affects physiological functions
Alters protein and enzyme functioning
 Can cause cardiac, renal, pulmonary abnormalities
 Alters blood clotting,
 Metabolization of meds

Acid and Bases

Acids – compounds that form hydrogen ion in a
solution
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Bases – compounds that combine with
hydrogen ion in a solution
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Proton donors
Strong acids give up their hydrogen ion easily
Weak acids hold on to their hydrogen ion more tightly
Proton acceptors
Neutralizes
20:1 ratio (20 parts bicarbonate to one part
carbonic acid)
What is pH?
pH is a measurement of the acidity or alkalinity
of the blood.
 It is inversely proportional to the number of
hydrogen ions (H+) in the blood.
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The more H+ present, the lower the pH will be.
The fewer H+ present, the higher the pH will be.
Homeostasis keeps pH in a very narrow range
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7.35-7.45 for optimum functioning
6.8-7.8 compatible with life
Blood pH
Blood pH < 7.40 acidosis
Blood pH > 7.40 alkalosis
Body Acids

Respiratory Acid - CO2 – eliminated by lungs (288 L/day)
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Metabolic acids:
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Lactic acids
Pyruvic acid
Ketoacids (DKA)
Acetoatic acids
Beta-hydrobutyric acids
Very little metabolic acid is produced on a daily basis
Metabolized by the liver or eliminated by the kidneys
Four Basic Categories of Abnormalities

Respiratory acidosis
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Respiratory alkalosis
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Lower than normal level of carbon dioxide leading to an
alkaline pH
Metabolic acidosis
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Excess of carbon dioxide leading to an acid pH
Excess of hydrogen ion or a deficiency in bicarbonate leading
to an acid pH
Metabolic alkalosis

Excess of bicarbonate leading to an alkaline pH
Buffer Systems

Like a sponge
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Extracellular Buffers
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Soaks up extra ions
Squeezed when there’s not enough
Carbonic acid: controlled by respiration
Bicarbonate: controlled by excretion
Intracellular Buffers
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Phosphate Buffer System
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Dihydrogen phosphate (H2PO4) – hydrogen donor or acid
Hydrogen phosphate (HPO4) – hydrogen acceptor or base
Buffer Systems

Protein Buffers
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In the blood
Plasma Proteins
Hemoglobin: deoxygenated is better than
oxygenated at buffering
Bones
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Carbonate and phosphate salts in bone provide a
long term supply of buffer.
In acute metabolic acidosis bone takes up hydrogen
in exchange for calcium, sodium, and potassium.
Role of the Lungs

Regulate plasma pH minute to minute by
regulating the level of Carbon Dioxide (CO2)

Carbon Dioxide is measured as a partial
pressure of carbon dioxide in arterial blood
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PaCO2 35-45mmHg
Lungs alter rate and depth of ventilations in
order to retain or excrete CO2
Minute Volume – Tidal Volume

Ventilation is measured by how much air the lungs
move in one minute (minute ventilation)
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Minute Ventilation is the product of respiratory
rate and depth and is referred to as the TIDAL
VOLUME (Vt)
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Normal depth tidal volume is about 500ml
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Normal respiratory rate is 12 breaths per min
12 breaths x 500 ml = 6000 ml or 6 liters
Anatomic Dead Space
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The volume of air that doesn’t reach the alveolar
airspace
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Estimated at 1ml/lb of ideal body weight
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150lb of ideal body weight = 150ml of dead space
Tidal volume – dead space = alveolar volume
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Trachea & Bronchi
Doesn’t take part in gas exchange
500ml – 150ml = 350ml
RR x alveolar volume = minute alveolar ventilation
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12 x 350ml = 4200ml or 4.2 L/min
Hypercarbic Drive
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Respiratory center in the medulla controls the rate and depth
of ventilation
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Responds to levels of arterial CO2, denoted as PaCO2
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Chemoreceptors in the medulla come into contact with CSF
As PaCO2 rises the arterial PaCO2 reaches equilibrium with
the CO2 in the CSF
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The CO2 in the CSF dissociates into hydrogen ions
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The hydrogen ions stimulate the chemoreceptors in the
medulla which in turn stimulates the diaphragm and intercostal
muscles
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Respiratory rate and depth increase and CO2 is blown off
Hypoxic Drive
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There are also peripheral chemoreceptors
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Respond to levels of
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Carotid arteries
Bifurcation of the common carotid and arch of aorta
Oxygen in the blood or PaO2
Hydrogen ions or pH
Carbon dioxide in the blood or PaCO2
As PaO2 falls below 60 mmHg the respiratory center
is stimulated to increase rate and depth
The role of the Kidneys
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Two main functions to maintain acid/base
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Secrete hydrogen ions
Restore or reclaim bicarbonate (HCO3)
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In high metabolic acidosis, the kidneys can
excrete ammonia as a urinary buffer.
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In alkalosis - the kidneys retain hydrogen ion and
excrete bicarbonate to correct the pH.
In acidosis - the kidneys excrete hydrogen ions
and conserve bicarbonate to correct the pH.
 Very slow process
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Assessment of ACID BASE

Arterial Blood Gases (ABG) most often and the
most accurate to assess acid base balances.
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Serum Electrolytes can help fine tune acid base
analysis
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NORMAL ABG VALUES:
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pH = 7.35 to 7.45
PaCO2 = 35 – 45 mEq/L
HCO3 = 22 – 28 mEq/L
Steps to Interpret ABG’s
1.
2.
3.
4.
Assess the pH
Assess the respiratory component – PaCO2
Assess the metabolic component – HCO3, base excess
Evaluate compensation
Compensation
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Once the primary cause is identified look at
the other value
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If the value is abnormal but moving in the right direction to
bring pH back to normal compensation is occuring
If the pH value is normal than compensation is complete
Because renal compensation is slower you can
infer whether respiratory abnormalities are
acute or chronic
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If kidneys have had time to compensate is chronic
If the kidneys have not had time to compensate its acute
Respiratory Acidosis
Respiratory system fails to keep up with the
body’s CO2 production
 Causes (pg. 442)
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Acute: drug overdose, head trauma, spinal cord injury, upper
airway obstruction, pneumothorax
Chronic: obesity, MS, emphysema, spinal cord injury
Clinical Manifestations
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Anxiety, irritability, confusion, lethargy, increased heart rate,
warm flushed skin
Mainly seen with acute causes because chronic patients have
compensated
Respiratory Acidosis
 Medical treatment
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Treat the underlying problem
Increase ventilation
BiPAP
Intubation
Supplemental oxygen (care must be taken with chronic pts)
Nursing care
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Assess PaCO2 levels and pH.
Observe for signs of respiratory distress: restlessness, anxiety,
confusion, tachycardia
Encourage fluid intake
Position patients with head elevated 30 degrees
Administer oxygen with care
Respiratory Alkalosis
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Most common cause is hyperventilation caused by
anxiety, panic, or pain
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Stroke
Meningitis
Head trauma
Clinical Manifestations
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Anxious
Tachycardia
Tachypnea
Vertigo
Forgetfulness
Respiratory Alkalosis
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Medical treatment
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Treat underlying cause of condition
Sedation may be needed
Nursing care
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Administer sedatives or pain medications
Provide emotional support
Encourage patient to breathe slowly, which will retain
carbon dioxide in the body
Breath into a paper bag
Metabolic Acidosis
Increase in total body acid
 Causes (pg. 442)
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Starvation
Diarrhea
Renal failure
Diabetic ketoacidosis
Signs and symptoms
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Kussmaul respirations
Altered LOC
Headache
V tach
Metabolic Acidosis
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Medical treatment
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Treat the underlying disorder
Nursing care
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Monitor VS & ECG
Assess neurological status
Provide emotional support
Metabolic Alkalosis
 An accumulation of base or a loss of acid in the
ECF
 Causes (pg. 442)
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Prolonged nasogastric suctioning or excessive vomiting
Diuretics
Electrolyte disturbances
Large volume blood transfusions, increased citrate
Clinical Manifestations
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Lethargy
Altered LOC
Tetany
ECG changes
Metabolic Alkalosis
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Medical Treatment
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Treat the underlying disorder
Nursing care
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Monitor VS & ECG
Monitor labs
Accurate I&O including the amount of fluid removed by
suction
Provide emotional support
Use isotonic saline solutions rather than water for irrigating
NG tubes because the use of water can result in a loss of
electrolytes

A client’s blood gas results are pH 7.36, PaCO2
50, HCO3 30. What do these results indicate
to the nurse?
A.
B.
C.
D.
Respiratory acidosis, compensated
Metabolic acidosis, compensated
Metabolic acidosis, uncompensated
Respiratory acidosis, uncompensated
Reference
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Osborn, Wraa, & Watson chapter 19