Acid Base Balance
by: Susan Mberenga RN, BSN, MSN
Acid Base Balance
• Refers to hydrogen ions as measured by pH
• Normal range: 7.35 - 7.45
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Acidosis/acidemia: pH is less than 7.35
Alkalosis/alkalemia: pH is greater than 7.45
(McCance et al., 2008)
Acid-Base Balance
• Acids release H+ ions
• The less hydrogen ions that are present, the more acidic a solution
becomes
• Bases receive H+ ions
• The more hydrogen ions that are present, the more basic a solution
becomes
Regulators of Acid Base Balance
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Keeps everything in balance
Constantly working to prevent acidosis/alkalosis
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Buffers
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Carbonic Acid/Bicarbonate
Phosphate
Protein
Respiratory system
Renal system
(Bartelmo, 2011)
Buffers
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Maintain equilibrium by adding or
subtracting H+ ions thus regulating pH
• First responders
• Primary regulators
• Cannot maintain pH without adequate
renal and respiratory function
(Bartelmo, 2011)
Carbonic acid-bicarbonate buffer system
If there is too much acid the body will
cause the lungs to increase respirations
and blow off CO++ and H2O and the
kidneys will release H+
Carbonic acid-bicarbonate buffer system
If there isn’t enough acid the kidneys
will hang on to H ions and the lungs
will slow down respirations
Respiratory System
Lungs regulate CO2
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Respiratory center in medulla controls breathing
Responds within minutes/hours to changes in acid/base
Increased respiratory rate leads to increased CO2 –hyperventilation
elimination and decreased CO2 in blood (blowing off CO2)-hypoventilation
Renal System
Kidneys regulate bicarb (HCO3 ) by eliminating or adding H +
Re-absorption and secretion of electrolytes
• Takes the longest to respond (hours to days)
• Kidneys usually function by retaining bicarbonate and
secreting acidic urine
• Kidneys work to increase or decrease pH as a
compensatory mechanism
•
Parameter
pH
Arterial
7.35 – 7.45
PaCO2
35 - 45 mm Hg
Bicarbonate
21 - 28 mEq/L
Arterial blood gasses- laboratory sample of arterial blood that is used to
monitor a patient’s acid base status
Can be done by a respiratory therapist or an RN who has been checked off on
the competency
ABG Components and Normal Values
ABG pH
• ACIDOSIS= pH<7.35
• Remember- acidosis is
sliding on down = low pH
• Causes:
• high (CO2)hyperventilation
• Low (HCO3)
• ALKALOSIS=pH>7.45
• Remember- alkalosis is
kicking on up= high pH
• Causes:
• High (HCO3)− Low (CO2)hypoventilation
ABG Components
HCO3 – 21-28 mEq/L
• Regulated by kidneys
• Kidneys secrete H+ ions
(making acidic urine) or
retain HCO3
PaCO2 – 35-45 mm Hg
• Regulated by lungs
• lungs hyperventilate CO2
• Result: body becomes more
basic
• Lungs hypoventilate CO2
• Result: body becomes more
acidic
ABG Components
O2 saturation: infrared light
measures the % of O2
bound to Hgb molecules in
RBC.
PaO2:
Blood test that measures the
amount of oxygen molecules
dissolved in the blood which
determines how well 02 is carried
from lungs to the blood.
Discussion: Which patient is in
a better situation and why?
1. A 45-year-old male with a COPD
exacerbation. He states he has
been progressively getting worse
over the last 3 weeks and has
presented to the ED for
treatment.
2. A 22-year-old patient that
presents to the ED after a
traumatic injury with a
respiratory rate of 7.
ABG Interpretation
1.
Evaluate pH (acidosis or alkalosis)
Sliding on down, kicking up
2.
Analyze PaCO2
3.
Analyze HCO3
4.
5.
35-45
22-26
Determine if CO2 or HCO3 matches the alteration
Could be both, that’s ok… the one most imbalanced is usually
the cause
Decide if the body is attempting to compensate
The one least imbalanced is usually trying to
compensate
ABG Interpretation
ROME- respiratory is opposite metabolic is equal
Respiratory
• Arrows move in opposite direction
• ↑ pH, ↓ PaCO2 = respiratory alkalosis
• ↓ pH, ↑ PaCO2 = respiratory acidosis
•Metabolic
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•Arrows move in the same direction
• ↑ pH, ↑ HCO3 = metabolic alkalosis
• ↓ pH, ↓ HCO3 = metabolic acidosis
For compensatory mechanisms, look for the one that is the least
out of whack!
• Body attempts to correct blood pH changes
• pH <6.9 or >7.8 usually fatal
• Respiratory system more sensitive to acid-base changes; can begin
compensating in seconds to minutes
• Kidneys more powerful; result in rapid changes in ECF composition; fully
triggered for imbalance of several hours to days
Compensation
18
FYI of ABG’s
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2.
3.
4.
Evaluation of Oxygenation Status: Hypoxemia (PaO2)
Mild: PaO2 <80 mm Hg, moderate: PaO2<60 mm Hg, severe: PaO2 < 40 mm Hg
Compare to previous blood gases
Compare the results to the patient’s clinical picture and your
assessments
Report changes and new findings
Blood Gas Alterations
Microsoft Clip Art
Case Study
A 25-year-old female was admitted to the hospital for attempted
suicide. She has had a 24-hour sitter at the bedside for the last 3
days and is to be discharged today. The primary care provider
stated that she no longer needs a sitter at the bedside. When
you enter the room to give her discharge instructions, you find
an empty pill bottle laying next to her.
Case Study
Vital signs are as follows: HR 109, RR-6, Temp-98.6, BP90/52.
• What are your first actions as the primary nurse?
• What acid base imbalance would you expect to see
with this patient and why?
Respiratory Acidosis
↓pH and ↑pCO2
Lower pH due to CO2 accumulation in the blood greater than the normal value
PaCO2 greater than 45mmHg
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Causes
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Depression of respiratory center
Respiratory muscle paralysis
Chest wall disorders
Disorders of lung parenchyma
Respiratory Acidosis
↓pH and ↑pCO2
Patients may present with:
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Bradypnea
CNS depression
Dysrhythmias
Muscle twitching
Electrolyte abnormalities
Compensation:
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Kidneys increase excretion of H+ and retain HCO3HCO3- may be normal or elevated, depending on whether the condition is acute or chronic
ABGs = high PaCO2 and near normal pH
Respiratory Acidosis
↓pH and ↑pCO2
• Treatment:
• Physical stimulation
–Turn cough and deep breathe, incentive
spirometer, bronchodilators
• Medical
–Mechanical ventilation
–Reversal of sedatives or narcotics
Case Study
Microsoft Clip Art
Case Study
Your patient, Ms. C, was just told she has 6
months to live by her oncologist. She rings
the call bell for assistance. She is talking
very quickly and you can barely understand
her.
When you enter the room, you see that your patient is
diaphoretic and unable to speak.
Vital signs are: HR-115, RR- 50, Temp-99.0, BP- 128/92.
What acid base imbalance would you expect to see and
why?
Respiratory Alkalosis
↑pH and ↓pCO2
• Blood contains too little carbonic acid
• CAUSES:
• Hypermetobolic states
–Fever, sepsis
• Hypoxia
–Heart failure, pneumonia, pulmonary embolism
• Anxiety-hyperventilation
• Psychogenic
• CNS stimulation
• Incorrect ventilator settings
Respiratory Alkalosis
↑pH and ↓pCO2
Patients may present with:
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Headache
Vertigo
Paresthesia
Tinnitus
Electrolyte abnormalities
Respiratory Alkalosis
↑pH and ↓pCO2
• TREATMENT:
• Identify and treat underlying cause: pain or
anxiety, fever, medical problems etc.
• Correct hypoxia
−Diuretics
−Mechanical ventilation
• Compensation
− Kidneys will excrete bicarbonate
− ABGs = low HCO3- and near normal pH
−
Case Study
Microsoft Clip Art
Case Study
A 70-year-old patient with a history of insulin dependent diabetes
and congestive heart failure is admitted to your unit for nausea
and vomiting.
Upon entry to the room, he is extremely confused and does not know
where he is. You check a blood glucose, and the glucometer states
that his blood sugar is greater than 600 and his urine tests positive for
ketones.
What acid base imbalance do you think you will find and why?
Metabolic Acidosis
↓pH and ↓ HCO3
• pH is low (less than 7.35) due to decrease in bicarbonate and/or
increase in acids
• pCO2 is normal or decreased
• HCO3- less than 22mEq/L
Metabolic Acidosis
↓pH and ↓ HCO3
• CAUSES:
• Overproduction of organic acids
• Ketoacidosis and starvation -DKA
• Impaired renal excretion of acid
• Abnormal loss of HCO3• Diarrhea and vomiting
• Ingestion of acid
• ASA overdose, antifreeze ingestion
• Anaerobic metabolism
Metabolic Acidosis
↓pH and ↓ HCO3
Patient may present with:
• Cardiac arrhythmias
• Electrolyte abnormalities
• Increased calcium and chloride may appear
• The serum potassium level is often high in acidosis as the body attempts to
maintain electroneutrality during buffering
• Flushed skin
• Nausea
Metabolic Acidosis
↓pH and ↓ HCO3
Compensation:
• Respiratory system attempts to blow off CO2 by hyperventilation to
increase pH
• When the body tries to compensate using respirations, a typical
pattern of breathing is Kussmaul’s respirations
https://www.youtube.com/watch?v=TG0vpKae
3Js
Metabolic Acidosis
↓pH and ↓ HCO3
Treatment - Dependent on cause:
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Administer fluids and insulin
Dialysis
Treat infection
Improve nutritional intake
Rehydration
Support of respiratory and cardiac functions
Case Study
Microsoft Clip Art
Case Study
A 22-year-old patient has been sick with the flu for the past
4 days. She states she has had fever and body aches and
complains that she has been vomiting 5 times a day and
been unable to hold anything down for the last 4 days.
What acid base imbalance would you expect to see
and why?
Metabolic Alkalosis
↑pH and ↑ HCO3
• pH is increased and HCO3 level is high or an excessive loss of acids has
occurred
(pH greater than 7.45)
• PaCO2 normal or increased
• HCO3- greater than 28 mEq/L
• CAUSES
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Large loss of gastric contents
Loss of potassium
Ingestion of large amounts of bicarbonate
Prolonged use of diuretics
Patient may present with:
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Diaphoresis
Shallow breathing
Nausea and vomiting
ECG changes
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Tachycardia
• LOC changes
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Confusion, lethargy, weakness
• Electrolyte abnormality
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Decreased Ca, lowe K and increased HCO3
Metabolic Alkalosis
↑pH and ↑ HCO3
Metabolic Alkalosis
↑pH and ↑ HCO3
Treatment
• Underlying cause must be corrected
− Replace KCL losses
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Nursing care
− Monitor neurological status
− Implement seizure precautions
− Reorient patient as needed
Metabolic Alkalosis
↑pH and ↑ HCO3
Compensation:
• Hypoventilation limited to ceiling of 50-60 mm Hg CO2, then hypoxic drive will kick in
• Kidneys will attempt to correct by increasing excretion of HCO3• ABGs = Decreased HCO3 and near normal pH