1. Focus on Acid-Base Balance and Arterial Blood Gases
J. Brinley

2. Purpose
Maintain a steady balance between acids and bases to achieve homeostasis
Health problems lead to imbalance
Diabetes mellitus
Vomiting and diarrhea
Respiratory conditions
The kidneys are an essential buffer system for acids, and in the older adult, the kidneys are less able to compensate for an acid load. The older adult has decreased respiratory function, leading to impaired compensation for acid-base imbalances. In addition, tissue hypoxia from any cause may alter acid-base balance.

3. pH Measure of H+ ion concentration
Blood is slightly alkaline at pH 7.35 to 7.45.
<7.35 is acidosis.
>7.45 is alkalosis.

4. Range of pH
Fig The normal range of plasma pH is 7.35 to A normal pH is maintained by a ratio of 1 part
carbonic acid to 20 parts bicarbonate.

5. Regulators of Acid/Base
Metabolic processes produce acids that must be neutralized and excreted.
Regulatory mechanisms
Buffers
Respiratory system
Renal system
The regulatory mechanisms react at different speeds. Buffers react immediately; the respiratory system responds in minutes and reaches maximum effectiveness in hours; the renal response takes 2 to 3 days to respond maximally, but the kidneys can maintain balance indefinitely in chronic imbalances.

6. Regulators of Acid/Base
Buffers: Act chemically to neutralize acids or change strong acids to weak acids
Primary regulators
React immediately
Cannot maintain pH without adequate respiratory and renal function
The buffers in the body include carbonic acid–bicarbonate, monohydrogen-dihydrogen phosphate, intracellular and plasma protein, and hemoglobin buffers.
{Show examples of buffer’s actions}

7. Regulators of Acid/Base
Respiratory system: Eliminates CO2
Respiratory center in medulla
controls breathing.
Responds within minutes/hours to changes in acid/base.
Increased respirations lead to increased CO2 elimination and decreased CO2 in blood.
When released into circulation, CO2 enters RBCs and combines with H2O to form H2CO3. This carbonic acid dissociates into hydrogen ions and bicarbonate. The free hydrogen is buffered by hemoglobin molecules, and the bicarbonate diffuses into the plasma. In the pulmonary capillaries, this process is reversed, and CO2 is formed and excreted by the lungs.
As a compensatory mechanism, the respiratory system acts on the CO2 + H2O side of the reaction by altering the rate and depth of breathing to “blow off” (through hyperventilation) or “retain” (through hypoventilation) CO2. If a respiratory problem is the cause of an acid-base imbalance (e.g., respiratory failure), the respiratory system loses its ability to correct a pH alteration.

8. Regulators of Acid/Base
Renal system: Eliminates H+ and reabsorbs HCO3-
Reabsorption and secretion of electrolytes (e.g., Na+, Cl-)
Responds within hours to days
The three mechanisms of acid elimination are (1) secretion of small amounts of free hydrogen into the renal tubule, (2) combination of H+ with ammonia (NH3) to form ammonium (NH4+), and (3) excretion of weak acids.
The body depends on the kidneys to excrete a portion of the acid produced by cellular metabolism. Thus the kidneys normally excrete acidic urine (average pH equals 6). As a compensatory mechanism, the pH of the urine can decrease to 4 and increase to 8.

9. Alterations in Acid-Base Balance
Imbalances occur when compensatory mechanisms fail.
Classification of imbalances
Respiratory: Affect carbonic acid concentration
Metabolic: Affect bicarbonate
An acid-base imbalance is produced when the ratio of 1:20 between acid and base content is altered.
A primary disease or process may alter one side of the ratio (e.g., CO2 retention in pulmonary disease). The compensatory process attempts to maintain the other side of the ratio (e.g., increased renal bicarbonate reabsorption).
Acidosis can be caused by an increase in carbonic acid (respiratory acidosis) or a decrease in bicarbonate (metabolic acidosis).

10. Respiratory Acidosis Carbonic acid excess caused by Compensation
Hypoventilation
Respiratory failure
Compensation
Kidneys conserve HCO3- and secrete H+ into urine.
Hypoventilation results in a buildup of CO2; subsequently, carbonic acid accumulates in the blood. Carbonic acid dissociates, liberating H+, and a decrease in pH occurs. If CO2 is not eliminated from the blood, acidosis results from the accumulation of carbonic acid.
{See next slide for figure}
In acute respiratory acidosis, the renal compensatory mechanisms begin to operate within 24 hours. Until the renal mechanisms have an effect, the serum bicarbonate level will usually be normal.

11. Types of Acid-Base Imbalances
A, Respiratory imbalances caused by carbonic acid (CA) excess and carbonic acid deficit.
B, Metabolic imbalances caused by base bicarbonate (BB) deficit and base bicarbonate excess.
Fig Kinds of acid-base imbalances. A, Respiratory imbalances caused by carbonic acid (CA) excess and
carbonic acid deficit. B, Metabolic imbalances caused by base bicarbonate (BB) deficit and base bicarbonate
excess.

12. Respiratory Alkalosis
Carbonic acid deficit caused by
Hyperventilation
Hypoxemia from acute pulmonary disorders
Compensation
Rarely occurs because of aggressive treatment of causes of hypoxemia
Anxiety, CNS disorders, and mechanical over-ventilation also increase ventilation rate and decrease the partial pressure of arterial carbon dioxide (PaCO2) level.
In acute respiratory alkalosis, aggressive treatment of the causes of hypoxemia is essential and usually does not allow time for compensation to occur. However, buffering of acute respiratory alkalosis may occur with shifting of bicarbonate (HCO3–) into cells in exchange for Cl–.

13. Metabolic Acidosis Base bicarbonate deficit caused by Ketoacidosis
Lactic acid accumulation (shock)
Severe diarrhea
Kidney disease
Metabolic acidosis (base bicarbonate deficit) occurs when an acid other than carbonic acid accumulates in the body, or when bicarbonate is lost from body fluids.

14. Metabolic Acidosis Compensatory mechanisms
Increased CO2 excretion by lungs
Kussmaul respirations (deep and rapid)
Kidneys excrete acid

15. Metabolic Alkalosis Base bicarbonate excess caused by
Prolonged vomiting or gastric suction
Gain of HCO3-

16. Metabolic Alkalosis Compensatory mechanisms
Decreased respiratory rate to increase plasma CO2
Renal excretion of HCO3-

17. Blood Gas Values
Arterial blood gas (ABG) values provide information about
Acid-base status
Underlying cause of imbalance
Body’s ability to regulate pH
Overall oxygen status

18. Interpretation of ABGs
Diagnosis in six steps:
Evaluate pH.
Analyze PaCO2.
Analyze HCO3-.
Determine if CO2 or HCO3- matches the alteration.
Decide if the body is attempting to compensate.

19. Normal Blood Gas Values
Table Normal Arterial Blood Gas Values *.

20. Sample ABG Interpretation
Table Arterial Blood Gas (ABG) Analysis.

21. Acid-Base Mnemonic—ROME
Respiratory
Opposite
Alkalosis ↑ pH ↓ PaCO2
Acidosis ↓ pH ↑ PaCO2
Metabolic
Equal
Acidosis ↓ pH ↓ HCO3
Alkalosis ↑ pH ↑ HCO3

22. Interpretation of ABGs
pH 7.36
PaCO2 67 mm Hg
PaO2 47 mm Hg
HCO3 37 mEq/L
What is this?
Respiratory acidosis

23. Interpretation of ABGs
pH 7.18
PaCO2 38 mm Hg
PaO2 70 mm Hg
HCO3- 15 mEq/L
What is this?
Metabolic acidosis

24. Interpretation of ABGs
pH 7.60
PaCO2 30 mm Hg
PaO2 60 mm Hg
HCO3- 22 mEq/L
What is this?
Respiratory alkalosis

25. Interpretation of ABGs
pH 7.58
PaCO2 35 mm Hg
PaO2 75 mm Hg
HCO3- 50 mEq/L
What is this?
Metabolic alkalosis

26. Interpretation of ABGs
pH 7.28
PaCO2 28 mm Hg
PaO2 70 mm Hg
HCO3- 18 mEq/L
What is this ?
Metabolic acidosis partial

27. Audience Response Question
A patient with an acid-base imbalance has an altered
potassium level. The nurse recognizes that the potassium
level is altered because:
1. Potassium is returned to extracellular fluid when metabolic acidosis is corrected.
2. Hyperkalemia causes an alkalosis that results in potassium being shifted into the cells.
3. Acidosis causes hydrogen ions in the blood to be exchanged for potassium from the cells.
4. In alkalosis, potassium is shifted into extracellular fluid to bind excessive bicarbonate.
Answer: 3
Rationale: Changes in pH (hydrogen ion concentration) will affect potassium balance. In acidosis, hydrogen ions accumulate in the intracellular fluid (ICF), and potassium shifts out of the cell to the extracellular fluid to maintain a balance of cations across the cell membrane. In alkalosis, ICF levels of hydrogen diminish, and potassium shifts into the cell. If a deficit of H+ occurs in the extracellular fluid, potassium will shift into the cell. Acidosis is associated with hyperkalemia, and alkalosis is associated with hypokalemia. 27

28. Question 1. Warm, flushed skin. 2. Respiratory rate of 36.
A patient has the following arterial blood gas (ABG) results: pH 7.48, PaO2 86 mm Hg, PaCO2 44 mm Hg, HCO3 29 mEq/L. When assessing the patient, the nurse would expect the patient to experience:
1. Warm, flushed skin.
2. Respiratory rate of 36.
3. Blood pressure of 94/52.
4. Hypertonic muscles with cramping.
Answer: 4
Rationale: The patient is experiencing metabolic alkalosis (elevated pH and elevated HCO3). Clinical manifestations of metabolic alkalosis include hypertonic muscles and cramping and reduced respiratory rate. Hypotension and warm, flushed skin may occur with respiratory acidosis. 28

29. Copyright © 2011, 2007 by Mosby, Inc., an affiliate of Elsevier Inc.
Case Studies
Copyright © 2011, 2007 by Mosby, Inc., an affiliate of Elsevier Inc. 29

30. Case Study 1: Jeri Jeri’s been on a 3-day party binge.
Friends are unable to awaken her.
Assessment reveals level of consciousness difficult to arouse. 30

31. Case Study 1: Jeri Respiratory rate 8 Shallow breathing pattern
Diminished breath sounds 31

32. Case Study 1: Jeri What ABGs do you expect? What is your treatment?
Respiratory acidosis reflected by pH <7.35 and PCO2 >45 mm Hg. The HCO3 will be normal (20-30 mEq/L) if her respiratory depression has lasted less than 24 hours; if longer than 24 hours, the HCO3 may be elevated as the result of compensation. The PaO2 may be <80 mm Hg because of respiratory depression leading to hypoxemia.
2. What is your treatment?
Determine the cause of the respiratory depression. If induced by opioids or benzodiazepines, treat with appropriate antagonists. If induced by alcohol or other CNS depressants, breathing must be stimulated until the effects of drugs have worn off. Mechanical ventilation may be necessary to increase respiratory rate and depth, increasing oxygenation and promoting excretion of carbon dioxide.

33. Case Study 2: Mayna Presented to the ED after a sexual assault
Examination reveals hysteria and emotional distress.

34. Case Study 2: Mayna
Respiratory rate 38
Lungs clear
O2 sat 96%

35. Case Study 2: Mayna What ABGs do you expect? What is your treatment?
Respiratory alkalosis indicated by pH >7.45 and PCO2 <35 mm Hg. The HCO3 will be normal (20-30 mEq/L) because compensation will not occur in this acute event.
2. What is your treatment?
Relieve her anxiety and coax her to take slow breaths. Carbon dioxide may be administered by mask, or she may be asked to breathe into a paper bag placed over her nose and mouth.

36. Case Study 3: Glen History of fever, aches, and chills
Generally feeling ill
Cough productive of yellow, thick sputum for the past 4 days

37. Case Study 3: Glen Examination reveals temp 38.4° C
Respiratory rate 20
Lungs with crackles in left lower lobes

38. Case Study 3: Glen What ABGs do you expect? What is your treatment?
A possible pneumonia in this case may cause a hypoxemia with the PaO2 <80 mm Hg. If untreated, the patient could trend to respiratory acidosis with decreasing pH and increasing PCO2.
2. What is your treatment?
Promoting coughing to clear the lungs, administering oxygen, and treating the underlying infection.

39. Case Study 4: Alan 17 years old History of Feeling bad Fatigue
Constant thirst
Frequent urination

40. Case Study 4: Alan Blood sugar is 484 mg/dL.
Respirations are 28 and deep.
Breath has a fruity odor.
Lungs are clear.

41. Case Study 4: Alan What ABGs do you expect? What is your treatment?
A diabetic ketoacidosis is a metabolic acidosis indicated by a pH <7.35 and a HCO3 <20 mEq/L. The PCO2 will be within the normal range if the acidosis is uncompensated, but will be <35 mm Hg if compensation has occurred. The PaO2 will not be affected.
2. What is your treatment?
Administration of insulin to promote normal glucose metabolism and administration of fluids and electrolytes to replace those lost because of the hyperglycemia.

42. Case Study 5: Anthony History of nausea and vomiting for the past week
Has been self-medicating himself with baking soda to control his abdominal discomfort

43. Case Study 5: Anthony What ABGs do you expect? What is your treatment?
The metabolic alkalosis in this case would be reflected by a pH >7.45 and a HCO3 >30 mEq/L. Because of the duration of this condition, compensation may be indicated by a PCO2 >45 mm Hg.
2. What is your treatment?
Determine the underlying cause of the vomiting if possible, and stop the use of baking soda (sodium bicarbonate). Antiemetic drugs and nasogastric intubation may help relieve the vomiting, and IV replacement of fluids and electrolytes may be necessary.

44. Case Study 6: Susan ABG results are as follows: pH 7.20 PaCO2 58 mm Hg
PaO2 59 mm Hg
HCO3- 24 mEq/L
1. Describe a patient who would have these ABGs, including history and assessment.
These ABGs reflect an uncompensated respiratory acidosis with hypoxemia. This could occur with a respiratory infection causing an exacerbation in a patient with COPD. The hypoxemia may be reflected by restlessness, confusion, or stupor. Respiratory and cardiac findings could include rapid, shallow breathing, rhonchi, crackles, diminished breath sounds, increased work of breathing with use of accessory muscles, orthopnea, tachycardia, and arrhythmias.
2. What is the treatment?
Treatment includes treatment of any underlying respiratory infections, bronchodilator therapy, corticosteroids, hydration therapy, chest PT and postural drainage, breathing exercises, low-flow oxygen therapy, and mechanical ventilation if the patient continues to deteriorate.

45. Case Study 6: Susan
Describe a patient who would have these ABGs, including history and assessment.
What is the treatment?
1. Describe a patient who would have these ABGs, including history and assessment.
These ABGs reflect an uncompensated respiratory acidosis with hypoxemia. This could occur with a respiratory infection causing an exacerbation in a patient with COPD. The hypoxemia may be reflected by restlessness, confusion, or stupor. Respiratory and cardiac findings could include rapid, shallow breathing, rhonchi, crackles, diminished breath sounds, increased work of breathing with use of accessory muscles, orthopnea, tachycardia, and arrhythmias.
2. What is the treatment?
Treatment includes treatment of any underlying respiratory infections, bronchodilator therapy, corticosteroids, hydration therapy, chest PT and postural drainage, breathing exercises, low-flow oxygen therapy, and mechanical ventilation if the patient continues to deteriorate.

46. Case Study 7: Fernando ABG results are as follows: pH 7.39
PaCO2 38 mm Hg
PaO2 44 mm Hg
HCO3- 24 mEq/L

47. Case Study 7: Fernando
Describe a patient who would have these ABGs, including history and assessment.
What is the treatment?
1. Describe a patient who would have these ABGs, including history and assessment.
These ABGs indicate a hypoxemic respiratory failure because all ABGs are within normal range except for the PaO2. Patients experiencing hypoxemic respiratory failure may include those with pneumonia, shock, pulmonary embolism, acute respiratory distress syndrome, or pulmonary edema. The patient’s history would include an underlying organ damage or assault. Respiratory symptoms include dyspnea, tachypnea, accessory muscle use, and late cyanosis. The patient may experience decreased level of consciousness, restlessness, tachycardia, and late arrhythmias and hypotension.
2. What is the treatment?
In addition to treating the underlying cause, oxygen therapy and mobilization of secretions are used to correct the hypoxemia. Positive-pressure ventilation via endotracheal intubation may be necessary. Maintaining adequate cardiac output with IV fluids and medications is also necessary.

48. Case Study 8: Brianna ABG results are as follows: pH 7.36
PaCO2 58 mm Hg
PaO2 50 mm Hg
HCO3- 33 mEq/L

49. Case Study 8: Brianna
Describe a patient who would have these ABGs, including history and assessment.
What is the treatment?
1. Describe a patient who would have these ABGs, including history and assessment.
These ABGs indicate a hypercapnic respiratory failure indicated by decreased PaO2 and increased PaCO2. Elevated HCO3 and (low) normal pH indicate compensation of a respiratory acidosis. Common causes of hypercapnic respiratory failure include any of the obstructive respiratory diseases (asthma, cystic fibrosis, COPD), central nervous system–induced respiratory depression such as head injury, spinal cord injury, brainstem infarction, sedative and narcotic overdose, and neuromuscular diseases such as myasthenia gravis, ALS, Guillain-Barré syndrome, and multiple sclerosis. Assessment findings include dyspnea, decreased respiratory rate or increased shallow respirations, and decreased tidal volume. Cerebral symptoms include disorientation and progressive somnolence. The patient may also have tachycardia, bounding pulse, arrhythmias, and hypertension.
2. What is the treatment?
Treatment of the underlying condition is necessary. In addition, oxygen therapy, mobilization of secretions, positive-pressure ventilation, and drug therapy are used. Commonly used drugs include bronchodilators, corticosteroids, diuretics, antibiotics, sedatives, and analgesics.

50. Case Study 9: Monica ABG results are as follows: pH 7.50
PaCO2 28 mm Hg
PaO2 85 mm Hg
HCO3- 24 mEq/L

51. Case Study 9: Monica
Describe a patient who would have these ABGs, including history and assessment.
What is the treatment?
1. Describe a patient who would have these ABGs, including history and assessment.
In this case, the decreased pH and decreased HCO3 indicate a metabolic acidosis. The decreased PaCO2 reflects compensation for the acidosis. Metabolic acidosis most commonly occurs in uncontrolled diabetes, but may also be caused by lactic acidosis, starvation, severe diarrhea, renal failure, or shock. Assessment findings may include drowsiness and confusion leading to coma; deep, rapid respirations (compensation); hypotension and arrhythmias; warm, dry, flushed skin; and nausea, vomiting, and abdominal pain.
2. What is the treatment?
Determination of the underlying cause is necessary to treat the acidosis. Diabetic acidosis is treated with insulin to normalize glucose metabolism, and carbohydrate (glucose) is provided in the case of starvation. Dialysis may be used to treat renal failure, and other underlying causes are treated as appropriate.

52. Case Study 10: Mike ABG results are as follows: pH 7.20 PaCO2 28 mm Hg
PaO2 81 mm Hg
HCO3- 18 mEq/L

53. Case Study 10: Mike
Describe a patient who would have these ABGs, including history and assessment.
What is the treatment?
1. Describe a patient who would have these ABGs, including history and assessment.
In this case, the decreased pH and decreased HCO3 indicate a metabolic acidosis. The decreased PaCO2 reflects compensation for the acidosis. Metabolic acidosis most commonly occurs in uncontrolled diabetes, but may also be caused by lactic acidosis, starvation, severe diarrhea, renal failure, or shock. Assessment findings may include drowsiness and confusion leading to coma; deep, rapid respirations (compensation); hypotension and arrhythmias; warm, dry, flushed skin; and nausea, vomiting, and abdominal pain.
2. What is the treatment?
Determination of the underlying cause is necessary to treat the acidosis. Diabetic acidosis is treated with insulin to normalize glucose metabolism, and carbohydrate (glucose) is provided in the case of starvation. Dialysis may be used to treat renal failure, and other underlying causes are treated as appropriate.

54. Case Study 11: Jeremy ABG results are as follows: pH 7.57
PaCO2 46 mm Hg
PaO2 87 mm Hg
HCO3- 38 mEq/L

55. Case Study 11: Jeremy
Describe a patient who would have these ABGs, including history and assessment.
What is the treatment?
1. Describe a patient who would have these ABGs, including history and assessment.
These ABG results indicate a metabolic alkalosis: the pH and HCO3 are elevated. The slightly elevated PaCO2 indicates some compensation for the alkalosis. The history of a patient with metabolic alkalosis may include severe vomiting or excessive gastric suctioning, diuretic therapy, potassium deficit, excessive intake of sodium bicarbonate (baking soda), or excessive mineralocorticoid therapy. Assessment findings may include nervousness and confusion, tachycardia and arrhythmias, nausea and vomiting, tremors, hypertonic muscles, tetany, and tingling of the fingers and toes.
2. What is the treatment?
As in all acid-base imbalances, determination and treatment of the underlying cause is necessary. The potassium that is lost in an alkalosis must be replaced to prevent arrhythmias, and contributing drugs must be discontinued. Vomiting with bicarbonate is treated as in Case Study 5.