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Acid Base Balance
1.
2. Homeostasis
• A delicate balance of fluids, electrolytes, and acids
and bases is required to maintain good health.
• This balance is called Homeostasis.
3. Body Fluids
• Intracellular fluid (ICF)
– found within the cells of the body
– constitutes 2/3 of total body fluid in adults
– major cation is potassium
• Extracellular fluid (ECF)
– found outside the cells
– accounts of 1/3 of total body fluid
– major cation is sodium
6. pH
• The acidity or alkalinity of a solution is
measured as pH.
• The more acidic a solution, the lower the pH.
• The more alkaline a solution , the higher the pH.
• Water has a pH of 7 and is neutral.
• The pH of arterial blood is normally between
7.35 and 7.45
7.
8. Hydrogen ions
• The more Hydrogen ions, the more acidic the solution and
the LOWER the pH
• The lower Hydrogen concentration, the more alkaline the
solution and the HIGHER the pH
12. Buffer Systems
• Regulate pH by binding or releasing Hydrogen
• Most important buffer system:
– Bicarbonate-Carbonic Acid Buffer System
• (Blood Buffer systems act instantaneously and thus constitute
the body’s first line of defense against acid-base imbalance)
16. Respiratory Regulation
• Lungs
– help regulated acid-base balance by
eliminating or retaining carbon dioxide
– pH may be regulated by altering the rate and depth of
respirations
– changes in pH are rapid,
» occurring within minutes
– normal CO2 level
• 35 to 45 mm Hg
17. Renal Regulation
• Kidneys
– the long-term regulator of acid-base balance
– slower to respond
• may take hours or days to correct pH
– kidneys maintain balance by excreting or conserving
bicarbonate and hydrogen ions
– normal bicarbonate level
• 22 to 26 mEq/L.
18. Factors Affecting Balance
• Age
– especially infants and the elderly
• Gender and Body Size
– amount of fat
• Environmental Temperature
• Lifestyle
– stress
20. Respiratory Acidosis
• Mechanism
– Hypoventilation or Excess CO2Production
• Etiology
– COPD
– Neuromuscular Disease
– Respiratory Center Depression
– Late ARDS
– Inadequate mechanical ventilation
– Sepsis or Burns
– Excess carbohydrate intake
21.
22. Respiratory Acidosis (cont)
• Symptoms
– Dyspnea, Disorientation or coma
– Dysrhythmias
– pH < 7.35, PaCO2 > 45mm Hg
– Hyperkalemia or Hypoxemia
• Treatment
– Treat underlying cause
– Support ventilation
– Correct electrolyte imbalance
– IV Sodium Bicarb
23.
24. Respiratory Alkalosis
• Risk Factors and etiology
– Hyperventilation due to
» extreme anxiety, stress, or pain
» elevated body temperature
» overventilation with ventilator
» hypoxia
» hypoxemia (emphysema or pneumonia)
» CNS trauma or tumor
25. Respiratory Alkalosis (cont)
• Symptoms
– Tachypnea or Hyperpnea
– Complaints of SOB, chest pain
– Light-headedness, syncope, coma, seizures
– Numbness and tingling of extremities
– Difficult concentrating, tremors, blurred vision
– Weakness, paresthesias, tetany
– Lab findings
– pH above 7.45
– CO2 less than 35
26. Respiratory Alkalosis (cont)
• Treatment
• Monitor VS and ABGs
• Treat underlying disease
• Assist client to breathe more slowly
• Help client breathe in a paper bag
• or apply rebreather mask
• Sedation
27.
28. Metabolic Acidosis
• Risk Factors/Etiology
– Conditions that increase acids in the blood
• Renal Failure
• DKA
• Starvation
• Lactic acidosis
– Prolonged diarrhea
– Toxins (antifreeze or aspirin)
– Carbonic anhydrase inhibitors - Diamox
29. Metabolic Acidosis (cont)
• Symptoms
– Kussmaul’s respiration
– Lethargy, confusion, headache, weakness
– Nausea and Vomiting
– Lab:
• pH below 7.35
• Bicarb less than 22
• Treatment
– treat underlying cause
– monitor ABG, I&O, VS, LOC Sodium Bicarb?
30.
31. Metabolic Alkalosis
• Risk Factors/Etiology
– Acid loss due to
• vomiting
• gastric suction
– Loss of potassium due to
• steroids
• diuresis
– Antacids (overuse of)
32. Metabolic Alkalosis (cont)
• Symptoms
– Hypoventilation (compensatory)
– Dysrhythmias, dizziness
– Paresthesia, numbness, tingling of extremities
– Hypertonic muscles, tetany
– Lab: pH above 7.45, Bicarb above 26
– CO2 normal or increased w/comp
– Hypokalmia, Hypocalcemia
• Treatment
– I&O, VS, LOC
– give potassium
– treat underlying cause
33.
34. Interpreting ABGs
• 1. Look at the pH
• is the primary problem acidosis (low) or alkalosis (high)
• 2. Check the CO2 (respiratory indicator)
• is it less than 35 (alkalosis) or more than 45 (acidosis)
• 3. Check the HCO3 (metabolic indicator)
• is it less than 22 (acidosis) or more than 26 (alkalosis)
• 4. Which is primary disorder (Resp. or Metabolic)?
• If the pH is low (acidosis), then look to see if CO2 or HCO3 is acidosis
(which ever is acidosis will be primary).
• If the pH is high (alkalosis), then look to see if CO2 or HCO3 is alkalosis
(which ever is alkalosis is the primary).
• The one that matches the pH (acidosis or alkalosis), is the primary disorder.
37. Example 1
• John Doe is a 55 year-old male admitted to your nursing unit with recurring bowel
obstruction. He has been experiencing intractable vomiting for the last several hours
despite the use of antiemetics. His arterial blood gas result is as follows:
• pH 7.5
• pCO2 42
• HCO3 33
38. Example 2
• Jane Doe is a 55-year-old female admitted to your nursing unit with
sepsis. Here is her arterial blood gas result: pH 7.31, pCO2 39, HCO3
17
• pH 7.31
• PaCO2 39
• HCO3 13
39. Example 3
• Jane Doe is a 34 year-old female admitted to your
nursing unit with thyrotoxicosis. Her blood gas
results are as follows:
• pH 7.5
• pCO2 30
• HCO3 24
40. Example 4
• Jane Doe is a 19 year-old female admitted to your
nursing unit with head injury. Her blood gas results
are as follows:
• pH 7.38
• PaCO2 56
• HCO3 35
41. Compensation
• The Respiratory system and Renal systems
compensate for each other
– attempt to return the pH to normal
• ABG’s show that compensation is present when
– the pH returns to normal or near normal
• If the nonprimary system is in the normal range
(CO2 35 to 45) (HCO3 22-26), then that system is
not compensating for the primary.
• For example:
– In respiratory acidosis (pH<7.35, CO2>45), if the HCO3 is >26,
then the kidneys are compensating by retaining bicarbonate.
– If HCO3 is normal, then not compensating.
42. Example 5
• Jane Doe is admitted to your nursing unit. Her
admission labwork reveals an arterial blood gas with
the following values:
• pH 7.45
• pCO2 48
• HCO3 28
43. Example 6
• John Doe is a trauma patient with an altered mental
status. His initial arterial blood gas result is as
follows:
• pH 7.33
• pCO2 62
• HCO3 35
44. Example 7
• Jane Doe is a 54-year-old female admitted to your
nursing unit. Here are the last ABG results:
• pH 7.29
• pCO2 30
• HCO3 18
