acid base physiology

1. Acid-Base Balance
Dr. Radhwan Hazem Alkhashab
Consultant anaesthesia & ICU
Aljamhori teaching hospital
2020

2.  Arterial blood gas analysis is an essential part of
diagnosing and managing a patient’s oxygenation
status and acid-base balance.
Introduction

3.  Oxygenation (PaO2). The PaO2 is the amount of oxygen
dissolved in the blood and therefore provides initial information
on the efficiency of oxygenation.
 Ventilation (PaCO2). The adequacy of ventilation is inversely
proportional to the PaCO2 .so that, when ventilation increases,
PaCO2 decreases, and when ventilation decreases, PaCO2
increases.
 Acid-base status (pH, HCO3, and base deficit [BD]). A plasma pH
of >7.4 indicates alkalemia, and a pH of <7.35 indicates acidemia.
Despite a normal pH, an underlying acidosis or alkalosis may still
be present.
Arterial blood gas (ABG) provides an
assessment of the following:

4.  The 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. The more H+
present, the lower the pH will be.
 Likewise, the fewer H+ present, the higher the pH
will be. The pH of a solution is measured on
a scale from 1 (very acidic) to 14 (very alkalotic).

5.  A liquid with a pH of 7, such as water, is neutral
(neither acidic nor alkalotic).

6.  Acids & Bases
 An acid is usually defined as a chemical species that
can act as a proton (H + ) donor, whereas a base is a
species that can act as a proton acceptor (Brönsted–
Lowry definitions).
Acids

7.  A strong acid is a substance that readily and almost
irreversibly gives up an H + and increases [H + ],
whereas a strong base avidly binds H + and decreases
[H + ].
Strong acids& base

8.  In contrast, weak acids reversibly donate H + ,
whereas weak bases reversibly bind H + ; both weak
acids and bases tend to have less of an effect on [H +
] (for a given concentration of the parent compound)
than do strong acids and bases.

9.  these are compounds that are only partially ionized in solution
 Physiologically important acids include:
 Carbonic acid (H2CO3)
 Phosphoric acid (H3PO4)
 Pyruvic acid (C3H4O3)
 Lactic acid (C3H6O3)
 These acids are dissolved in body fluids.
 Physiologically important bases include:
 Bicarbonate (HCO3
- )
 Biphosphate (HPO4
-2 )
Weak Acids and Bases:

10.  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
Normal Acid-Base Balance

11.  pH is the negative logarithm of the hydrogen
ion concentration ([H]). pH is a convenient
descriptor for power of hydrogen. Normally
the [H] in extacellular fluid is 40 nmol/L, a very
small number. By taking the negative log of
this value we obtain a pH of 7.4.
pH SCALE
pH = -log10(H+)

12. Low pH values = high H+ concentrations
Unit changes in pH represent a tenfold
change in H+ concentrations
 Nature of logarithms
pH SCALE

13.  pH = 4 is more acidic than pH = 6
 pH = 4 has 10 times more free H+ concentration
than pH = 5 and 100 times more free H+
concentration than pH = 6
pH SCALE
ACIDOSIS ALKALOSISNORMAL
DEATH DEATH
Venous
Blood
Arterial
Blood
7.3 7.57.46.8 8.0

14. pH SCALE

15.  Severe acidemia is defined as blood pH <7.20 and is associated
with the following major effects:
1) Impairment of cardiac contractility, cardiac output, and the
response to catecholamines.
2) Susceptibility to recurrent arrhythmias and lowering the
threshold for ventricular fibrillation.
3) Arteriolar vasodilation resulting in hypotension
Major consequences of acidemia.

16. 4) Vasoconstriction of the pulmonary vasculature,
leading to increased pulmonary vascular resistance
5) Hyperventilation (a compensatory response)
6) Confusion, and coma
7) Insulin resistance
8) Inhibition of glycolysis and adenosine triphosphate
synthesis
9) Hyperkalemia as potassium ions are shifted
extracellularly

17. Severe alkalemia is defined as blood pH >7.60 and is
associated with the following major effects:
1. Increased cardiac contractility until pH >7.7, when a
decrease is seen.
2. Refractory ventricular arrhythmias.
3. Coronary artery spasm/vasoconstriction.
4. Vasodilation of the pulmonary vasculature, leading
to decreased pulmonary vascular resistance
Major consequences of alkalemia

18. 5. Hypoventilation (which can frustrate efforts to wean
patients from mechanical ventilation).
6. Cerebral vasoconstriction
7. Neurologic manifestations such as headache,
lethargy, delirium, stupor, tetany, and seizures
8. Hypokalemia, hypocalcemia, hypomagnesemia, and
hypophosphatemia
9. Stimulation of anaerobic glycolysis and lactate
production

19.  pH changes have dramatic effects on normal cell
function
 1) Changes in excitability of nerve and muscle cells
 2) Influences enzyme activity
 3) Influences K+ levels
ACIDOSIS / ALKALOSIS

20.  pH decrease (more acidic) depresses the
central nervous system
 Can lead to loss of consciousness
 pH increase (more basic) can cause over-
excitability
 Tingling sensations, nervousness, muscle twitches
CHANGES IN CELL EXCITABILITY

21.  pH increases or decreases can alter the shape of the
enzyme rendering it non-functional
 Changes in enzyme structure can result in accelerated
or depressed metabolic actions within the cell
INFLUENCES ON ENZYME ACTIVITY

22.  When reabsorbing Na+ from the filtrate of the renal
tubules K+ or H+ is secreted (exchanged)
 Normally K+ is
secreted in much
greater amounts
than H+
INFLUENCES ON K+ LEVELS
K+
K+K+K+K+K+K+
Na+Na+Na+Na+Na+Na+
H+

23.  If H+ concentrations are high (acidosis) than H+ is
secreted in greater amounts
 This leaves less K+ than usual excreted
 The resultant K+ retention can affect cardiac function
and other systems
INFLUENCES ON K+ LEVELS
K+K+K+
Na+Na+Na+Na+Na+Na+
H+H+H+H+H+H+H+
K+K+K+K+K+

24. Balance maintained by:
Buffering systems
Lungs
Kidneys
Maintenance of Balance

25. Chemical Buffers
 The body uses pH buffers in the blood to guard against sudden
changes in acidity
 A pH buffer works chemically to minimize changes in the pH of a
solution
ACID-BASE REGULATION
H+
OH-
H+
H+
OH-
OH-
Buffer

26.  Prevent major changes in pH
 Act as sponges…
 3 main systems
1) Bicarbonate-carbonic acid buffer
2) Phosphate buffer
3) Protein buffer
Buffer Systems
H+
H+
H+

27.  Bicarbonate buffer- most important
Active in ECF and ICF
 Phosphate buffer
Active in intracelluar fluid
 Protein buffer- Largest buffer store
Albumins and globulins
Hemoglobin
Buffer Systems

28. Body’s major buffer
Carbonic acid - H2CO3 (Acid)
Bicarbonate - HCO3 (Base)
1 20
pH = 7.4
Bicarbonate-Carbonic Acid
H2CO3 ……………… HCO3
24 mEq/L1.2 mEq/L

29.  Key concept
 Carbonic anhydrase equation
CO2 +H2O H2CO3 H+ + HCO3
Carbon Carbonic Bicarbonate
Dioxide Acid
(ACID) (BASE)
Regulation

30.  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 <7.35)

31.  As HCO3 increases, H+ decreases
 pH rises, becomes more alkaline
CO2 +H2O H2CO3 H+ + HCO3
Carbonic Bicarbonate
Acid
(pH Basic >7.45)

32. Lungs control CO2
Kidneys control HCO3
Respiratory & Renal Regulation

33.  Respiratory Regulation
 When breathing is increased, the blood carbon
dioxide level decreases and the blood becomes more
basic
 When breathing is decreased, the blood carbon
dioxide level increases and the blood becomes more
acidic
 By adjusting the speed and depth of breathing, the
respiratory control centers and lungs are able to
regulate the blood pH minute by minute
Respiratory Regulation

34. Mechanism of control
 Excretion or retention of
H+ or HCO3
Regulation….. Slow
 Hours to days to change pH
Renal Regulation

35.  Ratio of 20 to 1 out of balance
 Acidosis (acidemia)
 pH falls below 7.35
 Increase in blood carbonic acid
or
 Decrease in bicarbonate
Acid-Base Imbalances

36.  Alkalosis (alkalemia)
 pH greater than 7.45
 Increase in bicarbonate
or
 Decrease in carbonic acid
Acid-Base Imbalances

37.  Acidosis and Alkalosis can arise in two fundamentally
different ways:
 1) Excess or deficit of CO2
(Volatile Acid)
 Volatile Acid can be eliminated by the respiratory system
 2) Excess or deficit of Fixed Acid
 Fixed Acids cannot be
eliminated by the
respiratory system
ACIDOSIS / ALKALOSIS

38. Primary cause or origin:
 Metabolic
Changes brought about by systemic
alterations (cellular level)
 Respiratory
Changes brought about by
respiratory alterations
Acid-Base Imbalances

39. 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
Acid-Base Imbalances

40.  Respiratory Acidosis
 Respiratory Alkalosis
 Metabolic Acidosis
 Metabolic Alkalosis
Four Basic Types of Imbalance

41.  Carbonic acid excess
 Exhaling of CO2 inhibited
 Carbonic acid builds up
 pH falls below 7.35
 Cause = Hypoventilation
Respiratory Acidosis
H2CO3

42.  Caused by hypercapnia due to hypoventilation
 Characterized by a pH decrease and an increase in
CO2
RESPIRATORY ACIDOSIS
CO2
CO2
CO2
CO2 CO2
CO2
CO2
CO2
CO2
CO2
CO2
CO2
CO2
pH
pH

43.  The speed and depth of breathing control the amount of CO2 in
the blood
 Normally when CO2 builds up, the pH of the blood falls and the
blood becomes acidic
 High levels of CO2 in the blood stimulate the parts of the brain
that regulate breathing, which in turn stimulate faster and
deeper breathing
RESPIRATORY ACIDOSIS

44.  Normal
1 20
7.4
Acid-Base Imbalances
H2CO3 ……………… HCO3
24 mEq/L1.2 mEq/L

45. 1 13
7.21
Respiratory Acidosis

46. Compensation: How?
Opposite regulating mechanism
Problem = depressed breathing,
build up of CO2 in blood
Response - Kidney retains HCO3
(Response ….. Slow)
Respiratory Acidosis

47. RESPIRATORY ACIDOSIS
-body’s compensation
-kidneys conserve HCO3
- ions to restore the normal
40:2 ratio
-kidneys eliminate H+ ion in acidic urine
2 30:
HCO3
-
H2CO3
HCO3
-
H+
+
acidic urine

48. RESPIRATORY ACIDOSIS
- therapy required to restore metabolic balance
- lactate solution used in therapy is converted to
bicarbonate ions in the liver
H2CO3 HCO3
-
2 40:
Lactate
Lactate
LIVER
HCO3
-

49.  The treatment of respiratory acidosis aims to improve
the function of the lungs
 Drugs to improve breathing may help people who
have lung diseases such as asthma and emphysema
RESPIRATORY ACIDOSIS

50.  Carbonic acid deficit
 Increased exhaling of CO2
 Carbonic acid decreases
 pH rises above 7.45
 Cause = hyperventilation.
Respiratory Alkalosis
H2CO3

51.  Cause is Hyperventilation
 Leads to eliminating excessive amounts of CO2
 Increased loss of CO2 from the lungs at a rate faster
than it is produced
 Decrease in H+
RESPIRATORY ALKALOSIS
CO2 CO2 CO2
CO2
CO2
CO2
CO2
CO2
CO2
CO2
CO2
CO2

52. Normal
1 20
7.4
Acid-Base Imbalances
H2CO3 ……………… HCO3
24 mEq/L1.2 mEq/L

53. 1
40
7.70
Respiratory Alkalosis

54.  Compensation:
 Problem = excess “blowing off” of CO2
 Result = decrease in carbonic acid and increase in
HCO3
 Response: Kidney excretes excess bicarbonate
Respiratory Alkalosis

55.  Usually the only treatment needed is to slow down
the rate of breathing
 Breathing into a paper bag or holding the breath as
long as possible may help raise the blood CO2 content
as the person breathes carbon dioxide
back in after breathing it out
RESPIRATORY ALKALOSIS

56.  Kidneys
compensate by:
 Retaining hydrogen
ions
 Increasing
bicarbonate
excretion
RESPIRATORY ALKALOSIS
H+
HCO3
-
HCO3
-
HCO3
-
HCO3
-
HCO3
-
HCO3
-
HCO3
-
HCO3
-
HCO3
-
HCO3
-
H+
H+
H+
H+
H+
H+
H+
H+
H+
H+

57. RESPIRATORY ALKALOSIS
- Body’s compensation
- Kidneys conserve H+ ions and eliminate HCO3
- in alkaline
urine
0.5 15:
HCO3
-
Alkaline Urine

58.  Decreased CO2 in the
lungs will eventually
slow the rate of
breathing
 Will permit a normal
amount of CO2 to be
retained in the lung
RESPIRATORY ALKALOSIS

59.  Base-bicarbonate deficit
 Low pH (< 7.35)
 Low plasma bicarbonate (base)
 Cause = relative gain in H+
(lactic acidosis, ketoacidosis)
or actual loss of HCO3
(renal failure, diarrhea)
Metabolic Acidosis

60.  Any acid-base imbalance not attributable to CO2
is classified as metabolic
 Metabolic production of Acids
 Or loss of Bases
METABOLIC ACIDOSIS

61.  If an increase in acid overwhelms the
body's pH buffering system, the
blood can become acidic
 As the blood pH drops, breathing
becomes deeper and faster as the
body attempts to rid the blood of
excess acid by decreasing the
amount of carbon dioxide
METABOLIC ACIDOSIS

62.  Eventually, the kidneys also
try to compensate by
excreting more acid in the
urine
 However, both mechanisms
can be overwhelmed if the
body continues to produce
too much acid, leading to
severe acidosis and eventually
a coma
METABOLIC ACIDOSIS

63.  The causes of metabolic acidosis can be
grouped into four major categories
 1) Ingesting an acid or a substance that is
metabolized to acid
 2) Abnormal Metabolism
 3) Kidney Insufficiencies
 4) Severe Diarrhea
METABOLIC ACIDOSIS

64. Normal
1 20
7.4
Acid-Base Imbalances
H2CO3 ……………… HCO3
24 mEq/L1.2 mEq/L

65.  Kidney failure (decrease in bicarbonate)
1 10
7.10
Metabolic Acidosis

66.  Lactic acidosis, keto acidosis (increase acid… no change
in bicarbonate)
1 10
7.10
Metabolic Acidosis

67.  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)
Metabolic Acidosis

68. METABOLIC ACIDOSIS
- body’s compensation
- hyperactive breathing to “ blow off ” CO2
- kidneys conserve HCO3
- and eliminate H+ ions in acidic urine
0.75 10:
CO2
CO2 + H2O
HCO3
- + H+
HCO3
-
+
H+
Acidic urine

69.  Metabolic acidosis may be
treated directly
 If the acidosis is mild,
intravenous fluids and
treatment for the underlying
disorder may be all that's
needed
METABOLIC ACIDOSIS

70.  When acidosis is severe,
bicarbonate may be given
intravenously
 Bicarbonate provides only
temporary relief and may
cause harm
METABOLIC ACIDOSIS

71. METABOLIC ACIDOSIS
- therapy required to restore metabolic balance
- lactate solution used in therapy is converted to
bicarbonate ions in the liver
H2CO3 HCO3
-
0.5 10:
Lactate
Lactate
containing
solution

72.  Bicarbonate excess
 High pH (> 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
Metabolic Alkalosis

73.  Reaction of the body to alkalosis is to lower pH
by:
 Retain CO2 by decreasing breathing rate
 Kidneys increase the retention of H+
METABOLIC ALKALOSIS
CO2
CO2
H+
H+
H+
H+

74. METABOLIC ALKALOSIS
- pH = 7.7
- HCO3
- increases because of loss of chloride
ions or excess ingestion of NaHCO3
1 40:

75. METABOLIC ALKALOSIS
- body’s compensation
- breathing suppressed to hold CO2
- kidneys conserve H+ ions and eliminate HCO3
- in
alkaline urine
1.25 30
CO2 + H2O
HCO3
- + H+
HCO3
-
H+
+
Alkaline urine
:

76. Normal
1 20
7.4
Acid-Base Imbalances
H2CO3 ……………… HCO3
24 mEq/L1.2 mEq/L

77. 1
30
7.58
Metabolic Alkalosis

78.  Compensation:
 Problem = too much base
 Response: Lungs compensate by
hypoventilating
 Retain CO2, increase PaCO2
 Increase acid level in blood
Metabolic Alkalosis

79.  pH 7.35 - 7.45
 PaCO2 35 - 45 mmHg
 HCO3 22 - 26 mEq/L
 Base Excess -2 - +2 mEq/L
 PaO2 75 - 100 mm Hg
 O2 saturation 93 - 100 %
Assessing ABGs

80.  pH
 Measurement of acidity or alkalinity, based on the hydrogen (H+)
ions present.
 The normal range is 7.35 to 7.45

 PaO2
 The partial pressure of oxygen that is dissolved in arterial blood.
 The normal range is 75 to 100 mm Hg.

 SaO2
 The arterial oxygen saturation.
 The normal range is 93% to 100%.

 PaCO2
 The amount of carbon dioxide dissolved in arterial blood.
 The normal range is 35 to 45 mm Hg.

Components of the Arterial Blood Gas

81.  HCO3
 The calculated value of the amount of bicarbonate in
the bloodstream.
 The normal range is 22 to 26 mEq/liter

 B.E.
 The base excess indicates the amount of excess or
insufficient level of bicarbonate in the system.
 The normal range is –2 to +2 mEq/liter.
 (A negative base excess indicates a base deficit in the
blood.)

82.  The anion gap (AG) estimates the presence of unmeasured
anions. Excess inorganic and organic anions that are not readily
measured by standard assays are termed unmeasured anions.
The AG is a tool used to further classify a metabolic acidosis as
an AG metabolic acidosis (elevated AG) or a non-AG metabolic
acidosis (normal AG). This distinction narrows the differential
diagnosis.
 The AG is the difference between the major serum cations and
anions
 that are routinely measured:
 AG = Na-(HCO3+CL)
 A normal value is 12 mEq/L 4 mEq/L.
The anion gap

83.  Nonanion gap metabolic acidosis results from loss of Na and K or
accumulation of Cl. The result of these processes is a decrease in
HCO3:
 Iatrogenic administration of hyperchloremic solutions
(hyperchloremic metabolic acidosis)
 Alkaline gastrointestinal losses
 Renal tubular acidosis
 Ureteric diversion through ileal conduit
 Endocrine abnormalities
MAJOR CAUSES OF A NONANION
GAP METABOLIC ACIDOSIS

84. 1. Start with pH
 Normal?
 Acidosis?
 Alkalosis?
___/______/___/______/___
6.8 7.35 7.45 8.0
Acidosis Alkalosis
Interpreting ABGs

85. 2. Assess PaCO2
(respiratory value)
_____/________/______
35 45
Respiratory Respiratory
Alkalosis Acidosis
Interpreting ABGs

86. 3. Evaluate metabolic indicators
Bicarbonate (HCO3) 22-26
and
Base excess (-2 to +2)
Interpreting ABGs

87. HCO3
_______/_______/________
22 26
BE ______/_______/_________
-2 +2
Metabolic Metabolic
acidosis alkalosis
Interpreting ABGs

88. 4. Determine level of compensation
Has the body tried to readjust the
pH?
 Uncompensated
 Partly compensated
 Compensated
Interpreting ABGs

89. 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)
Interpreting ABGs

90. 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

91. Compensated
 pH normal
 Other values abnormal in
opposite directions
 One is acidotic the other alkaline
Interpreting ABGs

92.  Determine amount of hypoxemia present
 Normal PaO2 (adults - room air)
 < 70 years = 75-100 mm Hg
70-79 = 70-100 mm Hg
 Drops 10 mm Hg for each decade
Interpreting ABGs

93.  Hypoxemia = < 70 mm Hg
(for adult < 70 years old)
 Mild = 60-75 mm Hg
 Moderate = 40-60 mm Hg
 Severe = < 40 mm Hg
Interpreting ABGs

94.  Oxygen saturation (pulse oximetry)
 93-100%
 < 91% confusion
 < 70% life threatening
Interpreting ABGs

95.  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%
Case 1

96. What is the problem?
Acidosis or alkalosis?
Respiratory or metabolic?
Compensated or not?
Level of hypoxemia?
Diagnoses?
Interventions?
Practice Problems

97. ACID NORMAL ALKALINE
_pH__________________________
_PaCO2_______________________
HCO3
Problem: _Respiratory acidosis___
Compensated? _Uncompensated_____

98.  Level of hypoxemia?
mild to normal….
 Diagnosis?
 Impaired gas exchange
 lung congestion Dx pneumonia.

99.  Assessment of breath sounds and respiratory rate
 Maintain patent airway
 Oxygen support, ventilation
 Positioning/turning 2 hrs
 Pulmonary hygiene
 IV antibiotic
Nursing Management

100.  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
Assessment (cont.)

101.  Ineffective breathing pattern
 Impaired gas exchange
 Altered tissue perfusion (cerebral)
 Activity intolerance
 Altered thought processes
 Risk for injury
Diagnoses

102.  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).
Interventions

103.  Assessment of breath sounds and respiratory rate
 Maintain patent airway
 Oxygen support, ventilation
 Positioning/turning q 2 hrs
 Pulmonary hygiene (postural drainage, chest
clapping)
Nursing Management
Respiratory Acidosis

104.  Teach how to relieve/ prevent anxiety
 Calm environment
 Positioning for comfort
 Assist with relaxation techniques
 Protection from injury
 Education re: drug overdose, esp aspirin
Nursing Management
Respiratory Alkalosis

105.  Frequent assessment of vital signs esp respiratory
rate and rhythm (compensatory mechanisms)
 Safety precautions for confusion
 For ketoacidosis, sodium bicarbonate IV
 Education about diabetes
Nursing Management
Metabolic Acidosis

106.  Monitoring LOC and confusion
 Monitor serum electrolytes, ABG’s
 Administer K and Cl replacement as ordered
 Antiemetics to relieve vomiting
 Seizure precautions
 Teaching/monitoring of diuretic therapy
 Referrals re: eating disorders
Nursing Management
Metabolic Alkalosis

107.  Burn patient 70% (2nd & 3rd degree),with respiratory
distress on 2nd day arterial blood sampling shows:
Case 2

110.  According to ABG results so decision for mechanical
support was made.
 CPAP mode was chosen from start then changed to
fully assisted mode (APRV).
 Another sample was drawn from patient`s radial
artery & showed:

113. Thank you