AcidBase Balance

1
Acid-Base Balance
By Sr. Beverly Raway Fall 2001
2
Normal Acid-Base Balance

• Normal pH 7.35-7.45
• Narrow normal range
• Compatible with life 6.8 - 8.0
• ___/______/___/______/___
  6.8 7.35 7.45 8.0
• Acid Alkaline

3
Maintenance of Balance

• Balance maintained by
• Buffering systems
• Lungs
• Kidneys

H2CO3..HCO3

4
Buffer Systems

• Prevent major changes in pH
• Act as sponges
• 3 main systems
• Bicarbonate-carbonic acid buffer
• Phosphate buffer
• Protein buffer

H
H
H
5
Buffer Systems

• Bicarbonate buffer - most important
• Active in ECF and ICF
• Phosphate buffer
• Active in intracelluar (ICF) fluid
• Protein buffer - Largest buffer store
• Albumins and globulins (ECF)
• Hemoglobin (ICF)

6
Bicarbonate-Carbonic Acid

• Bodys major buffer
• Carbonic acid - H2CO3 (Acid)
• Bicarbonate - HCO3 (Base)
• 1 20
• pH 7.4

24 mEq/L
1.2 mEq/L
H2CO3 HCO3
7
Bicarbonate-Carbonic Acid

• Ratio important
• Not absolute values
• Person with COPD (CAL)
• 1 20
• 7.4

48 mEq/L
2.4 mEq/L
H2CO3 HCO3
8
Regulation

• Key concept
• Carbonic anhydrase equation
• CO2 H2O H2CO3 H HCO3
• Carbon Carbonic Bicarbonate
  Dioxide Acid
• (ACID) (BASE)

9

• Acid
• Substance that contains H ions that can be
  released (H2CO3)
• Carbonic acid releases H ions
• Base
• Substance that can accept H ions
• (HCO3)
• Bicarbonate accepts H ions

10

• As CO2 increases, carbonic acid increases, H
  ions increase
• pH drops.. becomes more acidic
• CO2 H2O H2CO3 H HCO3
• Carbonic Bicarbonate
• Acid
• CO2 H2CO3 H HCO3
• (pH Acidic lt7.35)

11

• As HCO3 increases, H decreases
• pH rises, becomes more alkaline
• CO2 H2O H2CO3 H HCO3
• Carbonic Bicarbonate
• Acid
• CO2 H2CO3 H HCO3
• (pH Basic gt7.45)

12
Respiratory Renal Regulation

• Lungs control CO2
• Kidneys control HCO3
• pH

kidneys (bicarbonate) lungs (carbon dioxide)
13
Respiratory Regulation

• Mechanisms of control
• Hyperventilation -- blow off CO2
• Hypoventilation -- retain CO2
• Regulation rapid...
• Seconds to minutes
• Measured by PaCO2 - Normal
• 35-45 mm Hg

14
Renal Regulation

• Mechanism of control
• Excretion or retention of
• H or HCO3
• Regulation.. Slow
• Hours to days to change pH
• Normal serum HCO3
• 22-26 mEq/L

15
Acid-Base Imbalances

• Ratio of 20 to 1 out of balance
• Acidosis (acidemia)
• pH falls below 7.35
• Increase in blood carbonic acid or
• Decrease in bicarbonate

16
Acid-Base Imbalances

• Alkalosis (alkalemia)
• pH greater than 7.45
• Increase in bicarbonate
• or
• Decrease in carbonic acid

17
Acid-Base Imbalances

• Primary cause or origin
• Metabolic
• Changes brought about by systemic alterations
  (cellular level)
• Respiratory
• Changes brought about by respiratory
  alterations

18
Acid-Base Imbalances

• Compensation
• Corrective response of kidneys and/or lungs
• Compensated
• Restoration of pH and 20 1 ratio
• Uncompensated
• Inability to adjust pH or 20 1 ratio

19
Four Basic Types of Imbalance

• Respiratory Acidosis
• Respiratory Alkalosis
• Metabolic Acidosis
• Metabolic Alkalosis

20
Respiratory Acidosis

• Carbonic acid excess
• Exhaling of CO2
• inhibited
• Carbonic acid builds up
• pH falls below 7.35
• Cause Hypoventilation (see chart)

H2CO3
21
Acid-Base Imbalances

• Normal
• 1 20
• 7.4

24 mEq/L
1.2 mEq/L
H2CO3 HCO3
22
Respiratory Acidosis

• 1 13
• 7.21

24 mEq/L
1.84 mEq/L
H2CO3 HCO3
23
Respiratory Acidosis

• Compensation How?
• Opposite regulating mechanism
• Problem depressed breathing, build up of CO2
  in blood
• Response - Kidney retains HCO3
• (Response .. Slow)

24
Respiratory Alkalosis

• Carbonic acid deficit
• Increased exhaling
• of CO2
• Carbonic acid decreases
• pH rises above 7.45
• Cause hyperventilation (see chart)

H2CO3
25
Acid-Base Imbalances

• Normal
• 1 20
• 7.4

24 mEq/L
1.2 mEq/L
H2CO3 HCO3
26
Respiratory Alkalosis

• 1 40
• 7.70

0.6 mEq/L
24 mEq/L
H2CO3 HCO3
27
Respiratory Alkalosis

• Compensation
• Problem excess blowing off of CO2
• Result decrease in carbonic acid and increase
  in HCO3
• Response Kidney excretes excess bicarbonate

28
Metabolic Acidosis

• Base-bicarbonate deficit
• Low pH (lt 7.35)
• Low plasma bicarbonate (base)
• Cause relative gain in H (lactic acidosis,
  ketoacidosis)
• or actual loss of HCO3
• (renal failure, diarrhea)

29
Acid-Base Imbalances

• Normal
• 1 20
• 7.4

24 mEq/L
1.2 mEq/L
H2CO3 HCO3
30
Metabolic Acidosis

• Kidney failure (decrease in bicarbonate)
• 1 10
• 7.10

12 mEq/L
1.2 mEq/L
H2CO3 HCO3
31
Metabolic Acidosis

• Lactic acidosis, keto acidosis (increase acid no
  change in bicarbonate)
• 1 10
• 7.10

24 mEq/L
2.4 mEq/L
H2CO3 HCO3
32
Metabolic Acidosis

• Compensation
• Problem low HCO3 (base) or high H ion (acid)
• Response Lungs hyperventilate
• Get rid of CO2
• (decrease PaCO2 and therefore raise level of
  HCO3)

33
Metabolic Alkalosis

• Bicarbonate excess
• High pH (gt 7.45)
• Loss of H ion or gain of HCO3
• Most common causes vomiting, gastric suctioning
  (NG tube)
• Other Abuse of antacids, K wasting diuretics

34
Acid-Base Imbalances

• Normal
• 1 20
• 7.4

24 mEq/L
1.2 mEq/L
H2CO3 HCO3
35
Metabolic Alkalosis

• 1 30 7.58

1.2 mEq/L
36 mEq/L
H2CO3 HCO3
36
Metabolic Alkalosis

• Compensation
• Problem too much base
• Response Lungs compensate by hypoventilating
• Retain CO2, increase PaCO2
• Increase acid level in blood

37
Assessing ABGs

• pH 7.35 - 7.45
• PaCO2 35 - 45 mmHg
• HCO3 22 - 26 mEq/L
• Base Excess -2 - 2 mEq/L
• PaO2 80 - 100 mm Hg
• O2 saturation 95 - 100

38
Interpreting ABGs

• 1. Start with pH
• Normal?
• Acidosis?
• Alkalosis?
• ___/______/___/______/___
  6.8 7.35 7.45 8.0
• Acidosis Alkalosis

39
Interpreting ABGs

• 2. Assess PaCO2
• (respiratory value)
• _____/________/______
• 35 45
• Respiratory Respiratory
• Alkalosis Acidosis (Note reversal)
• (See Chart)

40
Interpreting ABGs

• 3. Evaluate metabolic indicators
• Bicarbonate (HCO3) 22-26
• and
• Base excess (-2 to 2)

41
Interpreting ABGs

• HCO3
• _______/_______/________
• 22 26
• BE ______/_______/_________
• -2 2
• Metabolic Metabolic
• acidosis alkalosis

42
Interpreting ABGs

• 4. Determine level of compensation
• Has the body tried to readjust the pH?
• Uncompensated
• Partly compensated
• Compensated

43
Interpreting ABGs

• Uncompensated
• pH abnormal (high or low)
• One component abnormal (high or low CO2 or HCO3)
• The other component is normal
• (The component not causing the acid-base
  imbalance is still normal)

44

• Partly compensated
• pH not normal (but moving toward normal)
• Both CO2 and HCO3 are outside normal range
• The component that was normal is changing in
  order to compensate

45
Interpreting ABGs

• Compensated
• pH normal
• Other values abnormal in opposite directions
• One is acidotic the other alkaline

46
Interpreting ABGs

• Determine amount of hypoxemia present
• Normal PaO2 (adults - room air)
• lt 70 years 80-100 mm Hg
• 70-79 70-100 mm Hg
• Drops 10 mm Hg for each decade

47
Interpreting ABGs

• Hypoxemia lt 70 mm Hg
• (for adult lt 70 years old)
• Mild 60-80 mm Hg
• Moderate 40-60 mm Hg
• Severe lt 40 mm Hg

48
Interpreting ABGs

• Oxygen saturation (pulse oximetry)
• 95-100
• lt 91 confusion
• lt 70 life threatening

49
Practice Problem

• 80 year old female with severe pneumonia, fever
• pH 7.25
• PaCO2 55 mm Hg
• HCO3 24 mEq/L
• PaO2 65 mm Hg
• O2 sat 80

50
Practice Problems

• What is the problem?
• Acidosis or alkalosis?
• Respiratory or metabolic?
• Compensated or not?
• Level of hypoxemia?
• Diagnoses? Interventions?

51
Tic-Tac-Toe Method

• ACID NORMAL ALKALINE
• _pH__________________________
• _PaCO2_______________________
• HCO3
• Problem _Respiratory acidosis___
• Compensated? _Uncompensated_____

52

• Level of hypoxemia?
• mild to normal.
• Diagnosis?
• Impaired gas exchange
• R/T lung congestion Dx pneumonia AMB CO2,
  acid pH, low PaO2, crackles, rapid resp rate and
  HR etc.

53
Nursing Management

• Assessment of breath sounds and respiratory rate
• Maintain patent airway
• Oxygen support, ventilation
• Positioning/turning q 2 hrs good lung?
• Pulmonary hygiene
• POEs, IV antibiotic

54
More Practice Problems

• Handout and Transparencies
• Phipps, p. 441 Critical Thinking

55
Collaborative Management

• Identifying clients at risk
• Pulmonary, renal, CV disease
• Fever, sepsis, burns
• TPN, tube feedings
• Mechanical ventilation
• Diabetes (insulin dependent)

56

• Vomiting, diarrhea, enteric drainage
• Elderly (limited ability to compensate)

57
Assessment

• Comprehensive physical assessment (Phipps, p.
  437-441)
• Fluid balance - often disturbed
• CV function - HR, BP, ECG (decreased K)
• Ventilatory status - always changes

58

• Breathing
• Respiratory acidosis - variable,
• usually shallow/rapid
• Respiratory alkalosis - increased rate, depth
• Metabolic acidosis - air hunger
• deep/rapid (Kussmaul) resp

59
Assessment

• CNS function -
• Acidosis - depressed activity
• Alkalosis - stimulated
• Neuromuscular function -
• Acidosis - weak, flaccid
• Alkalosis - cramps, twitching

60
Assessment (cont.)

• Skin -
• Respiratory acidosis -
• pale to cyanotic
• Metabolic acidosis -
• warm, dry, pink

61
Assessment (cont.)

• Lab values
• ABGs - interpretation critical, reported first
  to nursing staff then to doctor
• Electrolytes - coexisting imbalance almost
  always present (Na, K, Ca)
• BUN, Creatinine, serum lactate

62
Diagnoses

• Ineffective breathing pattern
• Impaired gas exchange
• Altered tissue perfusion (cerebral)
• Activity intolerance
• Altered thought processes
• Risk for injury

63
Goals/Outcomes

• Client experiences
• improved pulmonary ventilation
• adequate gas exchange and oxygenation of tissues

64
Outcome Criteria

• ...evidenced by absence of symptoms of
  respiratory distress
• (R rate decreases to ____)
• ...evidenced by ABGs within normal limits (list
  specifics)
• by ______ (specify time)

65
Goals/Outcomes

• Protection of client from injury
• Client experiences no physical injury
• Confusion decreases.
• Oriented x 3 (to person, place, time)

66
Interventions

• Monitor /interpret ABGs
• Correction of underlying problem
• Administer O2 as appropriate
• Positioning, pulmonary hygiene
• Hydration, appropriate IV solutions, electrolytes
  (bicarbonate, KCl)
• Medications (antibiotics, bronchodilators,
  mucolytics, diuretics)
• Reorientation
• Protection of client from injury
• See Table 16-4 p. 437 and pp. 437-441

67
Evaluation

• Frequency depends on severity
• Goals met
• ABGs - normal limits /compensation
• Patent airway
• Minimization of respiratory effort
• Increased activity tolerance
• Oriented x 3

68
Nursing ManagementRespiratory Acidosis

• Assessment of breath sounds and respiratory rate
• Maintain patent airway
• Oxygen support, ventilation
• Positioning/turning q 2 hrs
• Pulmonary hygiene (postural drainage, chest
  clapping)
• POEs

69
Nursing ManagementRespiratory Alkalosis

• Teach how to relieve/ prevent anxiety
• Calm environment
• Positioning for comfort
• Assist with relaxation techniques
• Reorientation
• Protection from injury
• Education re drug overdose, esp aspirin

70
Nursing ManagementMetabolic Acidosis

• Frequent assessment of vital signs esp
  respiratory rate and rhythm (compensatory
  mechanisms)
• Reorientation
• Safety precautions for confusion
• For ketoacidosis, sodium bicarbonate IV
• Education about diabetes

71
Nursing ManagementMetabolic Alkalosis

• Monitoring LOC and confusion
• Reorientation, protection from harm
• Monitor serum electrolytes, ABGs
• Administer K and Cl replacement as ordered
• Antiemetics to relieve vomiting
• Seizure precautions
• Teaching/monitoring of diuretic therapy
• Referrals re eating disorders