2. How to navigate this tutorial:
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3. Objectives:
Define acid base balance/imbalance
Explain the pathophysiology of organs
involved in acid base balance/imbalance
Identify normal/abnormal and
compensated/uncompensated
lab values
Explain symptoms related to acid base
imbalances and compensated vs.
uncompensated
Appropriate interventions and expected
outcomes
4. Main Menu:
Acid-Base Pretest The Buffer Systems
ABG Interpretation
& Case Studies
Acid-Base Review test
Diagnostic Lab Values
Metabolic Distubances
Respiratory Disturbances Acid-Base Compensation
5. Acid-Base Pretest:
What is the normal
range for arterial
blood pH?
7.38 – 7.46
7.40 – 7.52
7.35 – 7.45
6. Acid-Base Pretest:
What 2 extracellular substances work together
to regulate pH?
Sodium bicarbonate
& carbonic acid
Carbonic acid
& bicarbonate
Acetic acid & carbonic acid
7. Acid-Base Pretest:
Characterize an acid & a base based on the
choices below.
Acids release hydrogen (H+) ions
& bases accept H+ ions.
Acids accept H+ ions & bases
release H+ ions
Both acids & bases can release
& accept H+ ions
8. Acid-Base Pretest:
Buffering is a normal body mechanism
that occurs rapidly in response to acid-
base disturbances in order to prevent
changes in what?
HCO3
-
H2CO3
H+
9. Acid-Base Pretest:
What are the two systems in the body that
work to regulate pH in acid-base balance &
which one works fastest?
The Respiratory & Renal systems
Renal
The Respiratory & Renal systems
Respiratory
The Renal & GI systems
Renal
10. Acid-Base Balance:
Homeostasis of bodily fluids at a normal
arterial blood pH
pH is regulated by extracellular carbonic
acid (H2CO3) and bicarbonate (HCO3
-)
Acids are molecules that release
hydrogen ions (H+)
A base is a molecule that accepts or
combines with H+ ions
11.
12. Acids and Bases can be
strong or weak:
A strong acid or base is one that
dissociates completely in a solution
- HCl, NaOH, and H2SO4
A weak acid or base is one that
dissociates partially in a solution
-H2CO3, C3H6O3, and CH2O
13.
14. The Body and pH:
Homeostasis of pH is controlled through
extracellular & intracellular buffering
systems
Respiratory: eliminate CO2
Renal: conserve HCO3
- and eliminate
H+ ions
Electrolytes: composition of extracellular
(ECF) & intracellular fluids (ICF)
- ECF is maintained at 7.40
Protein
Buffer
system
HCO3
-
Buffer
system
K+ - H+
Exchange
15.
16. Quick Review: Click the Boxes
A donator of H+ ions An acceptor of H+
w/ pH <7.0 ions w/ pH >7.0
Regulated by EC Controlled by EC
H2CO3 & HCO3
- & IC buffer systems
Eliminates CO2 Conserves HCO3
-
Eliminates H+ ions
An Acid is: A Base is:
pH is:
Respiratory System:
pH is:
Renal System:
17. Respiratory Control Mechanisms:
Works within minutes to control pH; maximal in
12-24 hours
Only about 50-75% effective in returning pH to
normal
Excess CO2 & H+ in the blood act directly on
respiratory centers in the brain
CO2 readily crosses blood-brain barrier
reacting w/ H2O to form H2CO3
H2CO3 splits into H+ & HCO3
- & the H+
stimulates an increase or decrease in
respirations
18. Renal Control Mechanisms:
Don’t work as fast as the respiratory
system; function for days to restore pH
to, or close to, normal
Regulate pH through excreting acidic or
alkaline urine; excreting excess H+ &
regenerating or reabsorbing HCO3
-
Excreting acidic urine decreases acid in
the EC fluid & excreting alkaline urine
removes base
H+ elimination
& HCO3-
conservation
19.
20. Mechanisms of Acid-Base
Balance:
The ratio of HCO3
- base to the volatile H2CO3
determines pH
Concentrations of volatile H2CO3 are regulated
by changing the rate & depth of respiration
Plasma concentration of HCO3
- is regulated by
the kidneys via 2 processes: reabsorption of
filtered HCO3
- & generation of new HCO3
-, or
elimination of H+ buffered by tubular systems to
maintain a luminal pH of at least 4.5
Phosphate
Buffer
system
Ammonia
Buffer
system
21. Acid-Base Balance Review test:
The kidneys regulate pH by excreting
HCO3
- and retaining or regenerating H+
TRUE
FALSE
22. Acid-Base Review test:
H2CO3 splits into HCO3
- & H+ & it is the
H+ that stimulates either an increase or
decrease in the rate & depth of
respirations.
TRUE
FALSE
23. Acid-Base Review test:
Plasma concentration of HCO3
- is
controlled by the kidneys through
reabsorption/regeneration of HCO3
-, or
elimination of buffered H+ via the tubular
systems.
TRUE
FALSE
27. Metabolic Alkalosis:
Caused by an increase in pH (>7.45)
related to an excess in plasma HCO3
-
Caused by a loss of H+ ions, net gain in
HCO3
- , or loss of Cl- ions in excess of
HCO3
-
Most HCO3
- comes from CO2 produced
during metabolic processes,
reabsorption of filtered HCO3
-, or
generation of new HCO3
- by the kidneys
Proximal tubule reabsorbs 99.9% of
filtered HCO3
-; excess is excreted in
urine
28. Metabolic Alkalosis
Manifestations:
Signs & symptoms (s/sx) of volume
depletion or hypokalemia
Compensatory hypoventilation,
hypoxemia & respiratory acidosis
Neurological s/sx may include mental
confusion, hyperactive reflexes, tetany
and carpopedal spasm
Severe alkalosis (>7.55) causes
respiratory failure, dysrhthmias, seizures
& coma
29. Treatment of Metabolic Alkalosis:
Correct the cause of the imbalance
May include KCl supplementation for K+/Cl-
deficits
Fluid replacement with 0.9 normal saline
or 0.45 normal saline for s/sx of volume
depletion
Intubation & mechanical ventilation may
be required in the presence of
respiratory failure
30. Metabolic Acidosis:
Primary deficit in base HCO3
- (<22
mEq/L) and pH (<7.35)
Caused by 1 of 4 mechanisms
Increase in nonvolatile metabolic acids,
decreased acid secretion by kidneys,
excessive loss of HCO3
-, or an increase in
Cl-
Metabolic acids increase w/ an
accumulation of lactic acid,
overproduction of ketoacids, or
drug/chemical anion ingestion
31.
32. Metabolic Acidosis Manifestations:
Hyperventialtion (to reduce CO2 levels),
& dyspnea
Complaints of weakness, fatigue,
general malaise, or a dull headache
Pt’s may also have anorexia, N/V, &
abdominal pain
If the acidosis progresses, stupor, coma
& LOC may decline
Skin is often warm & flush related to
sympathetic stimulation
33. Treatment of Metabolic Acidosis:
Treat the condition that first caused the
imbalance
NaHCO3 infusion for HCO3
- <22mEq/L
Restoration of fluids and treatment of
electrolyte imbalances
Administration of supplemental O2 or
mechanical ventilation should the
respiratory system begin to fail
34. Quick Metabolic Review:
Metabolic disturbances indicate an
excess/deficit in HCO3
- (<22mEq/L or
>26mEq/L
Reabsorption of filtered HCO3
- &
generation of new HCO3
- occurs in the
kidneys
Respiratory system is the compensatory
mechanism
ALWAYS treat the primary disturbance
35. Respiratory Disturbances:
Alkalosis: low PaCO2 (<35 mmHg)
Caused by HYPERventilation of any
etiology (hypoxemia, anxiety, PE,
pulmonary edema, pregnancy, excessive
ventilation w/ mechanical ventilator, etc.)
Acidosis: elevated PaCO2 (>45 mmHg)
Caused by HYPOventilation of any etiology
(sleep apnea, oversedation, head trauma,
drug overdose, pneumothorax, etc.)
Compensation is metabolic-related
36. Respiratory Alkalosis:
Characterized by an initial decrease in
plasma PaCO2 (<35 mmHg) or
hypocapnia
Produces elevation of pH (>7.45) w/ a
subsequent decrease in HCO3
- (<22
mEq/L)
Caused by hyperventilation or RR in
excess of what is necessary to maintain
normal PaCO2 levels
37.
38. Respiratory Alkalosis
Manifestations:
S/sx are associated w/ hyperexcitiability
of the nervous system & decreases in
cerebral blood flow
Increases protein binding of EC Ca+,
reducing ionized Ca+ levels causing
neuromuscular excitability
Lightheadedness, dizziness, tingling,
numbness of fingers & toes, dyspnea, air
hunger, palpitations & panic may result
39. Treatment of Respiratory
Alkalosis:
Always treat the underlying/initial cause
Supplemental O2 or mechanical
ventilation may be required
Pt’s may require reassurance,
rebreathing into a paper bag (for
hyperventilation) during symptomatic
attacks, & attention/treatment of
psychological stresses.
40. Respiratory Acidosis:
Occurs w/ impairment in alveolar
ventilation causing increased PaCO2
(>45 mmHg), or hypercapnia, along w/
decreased pH (<7.35)
Associated w/ rapid rise in arterial
PaCO2 w/ minimal increase in HCO3
- &
large decreases in pH
Causes include decreased respiratory
drive, lung disease, or disorders of
CW/respiratory muscles
41.
42. Respiratory Acidosis
Manifestations:
Elevated CO2 levels cause cerebral
vasodilation resulting in HA, blurred
vision, irritability, muscle twitching &
psychological disturbances
If acidosis is prolonged & severe,
increased CSF pressure & papilledema
may result
Impaired LOC, lethargy/coma, paralysis
of extremities, warm/flushed skin,
weakness & tachycardia may also result
43. Treatment of Respiratory
Acidosis:
Treatment is directed toward improving
ventilation; mechanical ventilation may
be necessary
Treat the underlying cause
Drug OD, lung disease, chest
trauma/injury, weakness of respiratory
muscles, airway obstruction, etc.
Eliminate excess CO2
44. Quick Respiratory Review:
Caused by either low or elevated PaCO2
levels (<35 or >45mmHg)
Watch for HYPOventilation or
HYPERventilation; mechanical
ventilation may be required
Kidneys will compensate by conserving
HCO3
- & H+
REMEMBER to treat the primary
disturbance/underlying cause of the
imbalance
45. Compensatory Mechanisms:
Adjust the pH toward a more normal
level w/ out correcting the underlying
cause
Respiratory compensation by
increasing/decreasing ventilation is
rapid, but the stimulus is lost as pH
returns toward normal
Kidney compensation by conservation of
HCO3
- & H+ is more efficient, but takes
longer to recruit
46. Metabolic Compensation:
Results in pulmonary compensation
beginning rapidly but taking time to
become maximal
Compensation for Metabolic Alkalosis:
HYPOventilation (limited by degree of rise
in PaCO2)
Compensation for Metabolic Acidosis:
HYPERventilation to decrease PaCO2
Begins in 1-2hrs, maximal in 12-24 hrs
47.
48. Respiratory Compensation:
Results in renal compensation which
takes days to become maximal
Compensation for Respiratory Alkalosis:
Kidneys excrete HCO3
-
Compensation for Respiratory Acidosis:
Kidneys excrete more acid
Kidneys increase HCO3
- reabsorption
52. Acid-Base pH and HCO3
-
Arterial pH of ECF is 7.40
Acidemia: blood pH < 7.35 (increase in H+)
Alkalemia: blood pH >7.45 (decrease in
H+) If HCO3
- levels are the primary
disturbance, the problem is metabolic
Acidosis: loss of nonvolatile acid & gain of
HCO3
-
Alkalosis: excess H+ (kidneys unable to
excrete) & HCO3
- loss exceeds capacity of
kidneys to regenerate
53. Acid-Base PCO2, TCO2 & PO2
If PCO2 is the primary disturbance, the
problem is respiratory; it’s a reflection of
alveolar ventilation (lungs)
PCO2 increase: hypoventilation present
PCO2 decrease: hyperventilation present
TCO2 refers to total CO2 content in the
blood, including CO2 present in HCO3
-
>70% of CO2 in the blood is in the form of
HCO3
-
PO2 also important in assessing respiratory
function
54. Base Excess or Deficit:
Measures the level of all buffering
systems in the body – hemoglobin,
protein, phosphate & HCO3
-
The amount of fixed acid or base that
must be added to a blood sample to
reach a pH of 7.40
It’s a measurement of HCO3
- excess or
deficit
55. Anion Gap:
The difference between plasma
concentration of Na+ & the sum of
measured anions (Cl- & HCO3
-)
Representative of the concentration of
unmeasured anions (phosphates,
sulfates, organic acids & proteins)
Anion gap of urine can also be
measured via the cations Na+ & K+, & the
anion Cl- to give an estimate of NH4
+
excretion
56. Anion Gap
The anion gap is increased in conditions
such as lactic acidosis, and DKA that
result from elevated levels of metabolic
acids (metabolic acidosis)
A low anion gap occurs in conditions that
cause a fall in unmeasured anions
(primarily albumin) OR a rise in
unmeasured cations
A rise in unmeasured cations is seen in
hyperkalemia, hypercalcemia, hyper-
magnesemia, lithium intoxication or
multiple myeloma
57.
58. Sodium Chloride-Bicarbonate
Exchange System and pH:
The reabsorption of Na+ by the kidneys
requires an accompanying anion
- 2 major anions in ECF are Cl- and
HCO3
-
One way the kidneys regulate pH of ECF is
by conserving or eliminating HCO3
- ions in
which a shuffle of anions is often necessary
Cl- is the most abundant in the ECF & can
substitute for HCO3
- when such a shift is
needed.
59. Acid-Base Interpretation
Practice:
Please use the following key to interpret
the following ABG readings.
Click on the blue boxes to reveal the
answers
Use the button to return to the key at
any time
Or use the “Back to Key” button at the
bottom left of the screen
60. Acid-Base w/o Compensation:
Parameters: pH PaCO2 HCO3
-
Metabolic
Alkalosis
Normal
Metabolic
Acidosis
Normal
Respiratory
Alkalosis
Normal
Respiratory
Acidosis
Normal
61. Interpretation Practice:
pH: 7.31 Right!
PaCO2: 48 Try Again
HCO3
-: 24 Try Again
pH: 7.47 Try Again
PaCO2 : 45 Right!
HCO3
- : 33 Try Again
Back to Key
Resp. Acidosis
Resp. Alkalosis
Metabolic Acidosis
Resp. Alkalosis
Metabolic Alkalosis
Metabolic Acidosis
62. Interpretation Practice:
pH: 7.20 Try Again
PaCO2: 36 Try Again
HCO3
-: 14 Right!
pH: 7.50 Try Again
PaCO2 : 29 Right!
HCO3
- -: 22 Try Again
Metabolic Alkalosis
Resp. Acidosis
Metabolic Acidosis
Metabolic Alkalosis
Resp. Alkalosis
Resp. Acidosis
Back to Key
63. Acid-Base Fully Compensated:
Parameters: pH PaCO2 HCO3
-
Metabolic
Alkalosis
Normal
>7.40
Metabolic
Acidosis
Normal
<7.40
Respiratory
Alkalosis
Normal
>7.40
Respiratory
Acidosis
Normal
<7.40
64. Interpretation Practice:
pH: 7.36 Try Again
PaCO2: 56 Try Again
HCO3
-: 31.4 Right!
pH: 7.43 Right!
PaCO2 : 32 Try Again
HCO3: 21 Try Again
Compensated Resp. Alkalosis
Compensated Metabolic Acidosis
Compensated Resp. Acidosis
Compensated Resp. Alkalosis
Compensated Metabolic Alkalosis
Compensated Metabolic Acidosis
Back to Key
66. Interpretation Practice:
pH: 7.47 Right!
PaCO2: 49 Try Again
HCO3
-: 33.1 Try Again
pH: 7.33 Try Again
PaCO2 : 31 Try Again
HCO3
- : 16 Right!
Partially Compensated Metabolic Alkalosis
Partially Compensated Resp. Alkalosis
Partially Compensated Metabolic Acidosis
Partially Compensated Metabolic Alkalosis
Partially Compensated Resp. Acidosis
Partially Compensated Metabolic Acidosis
Back to Key
67. Case Study 1:
Mrs. D is admitted to the ICU. She has
missed her last 3 dialysis treatments.
Her ABG reveals the following:
pH: 7.32 Low, WNL = 7.35-7.45
PaCO2: 32 Low, WNL = 35-45mmHg
HCO3
-: 18 Low, WNL = 22-26mEq/L
Assess the pH, PaCO2 & HCO3
-. Are the
values high, low or WNL?
The pH is:
The PaCO2 is:
The HCO3
- is:
68. Case Study 1 Continued:
What is Mrs. D’s acid-base imbalance?
Right!
Try Again
Remember the difference between full &
partial compensation. Go back & use
the appropriate key if necessary.
Partially Compensated Metabolic Acidosis
Fully Compensated Resp. Acidosis
69. Case Study 2:
Mr. M is a pt w/ chronic COPD. He is
admitted to your unit pre-operatively.
His admission lab work is as follows:
pH: 7.35 WNL = 7.35-7.45
PaCO2: 52 High, WNL = 35-45mmHg
HCO3
-: 50 High, WNL = 22-26mEq/L
Assess the above labs. Are they
abnormal or WNL?
The pH is:
The PaCO2 is:
The HCO3
- is:
70. Case Study 2 Continued:
What is Mr. M’s acid-base disturbance?
Try Again
Right!
Think about appropriate interventions- if
the problem is metabolic, the respiratory
system compensates & vice versa
Fully Compensated Metabolic Acidosis
Fully Compensated Resp. Acidosis
71. Case Study 3:
Miss L is a 32 year old female admitted
w/ decreased LOC after c/o the “worst
HA of her life.” She is lethargic, but
arouseable; diagnosed w/ a SAH.
Her ABG reads:
pH: 7.48 High; WNL = 7.35-7.45
PaCO2: 32 Low; WNL = 35-45mmHg
HCO3
-: 25 High; WNL = 22-26mEq/L
What is the significance of her ABG
values?
The pH is:
The PaCO2 is:
The HCO3
- is:
72. Case Study 3 Continued:
What is Miss L’s imbalance?
Right!
Try Again
Great Job! You’ve reached the end of
the tutorial & I hope you found it helpful.
Thank you!
Resp. Alkalosis
Metabolic Alkalosis