Acid-Base Balance
Interactive Tutorial
Emily Phillips
MSN 621
Spring 2009
E-mail:
emmalemmaRN@hotmail.com
All images imported from
Microsoft Clipart & Yahoo Image gallery
How to navigate this tutorial:
 To advance to the next slide click on the
box
 To return to the previous slide click on
the
box
 To return to the Main Menu: click the
box
 Hover over underlined text for a
definition/explanation
 To return to the last slide viewed click on
the
button
 Click the
for additional information
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
Main Menu:
Acid-Base Pretest
The Buffer Systems
Acid-Base Review test
Metabolic Distubances
Respiratory Disturbances
Acid-Base Compensation
Diagnostic Lab Values
ABG Interpretation
& Case Studies
Acid-Base Pretest:
 What is the normal
range for arterial
blood pH?
7.38 – 7.46
7.40 – 7.52
7.35 – 7.45
Acid-Base Pretest:
 What 2 extracellular substances work together
to regulate pH?
Sodium bicarbonate
& carbonic acid
Carbonic acid
& bicarbonate
Acetic acid & carbonic acid
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
Acid-Base Pretest:
 Buffering is a normal body mechanism
that occurs rapidly in response to acidbase disturbances in order to prevent
changes in what?
HCO3-
H2CO3
H+
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
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
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
The Body and pH:
 Homeostasis of pH is controlled through
Protein
Buffer
system
HCO3Buffer
system
K+ - H+
Exchange
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
Quick Review: Click the Boxes
A donator of H+ ions
An Acid is:
w/ pH <7.0
An acceptor of H+
A Base is:
ions w/ pH >7.0
Regulated by EC
pH is: H2CO3 & HCO3
Controlled by EC
pH is:
& IC buffer systems
Eliminates CO2
Conserves HCO3Renal System:
Eliminates H+ ions
Respiratory System:
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
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
& HCO3conservation
Mechanisms of Acid-Base
Balance:
 The ratio of HCO3- base to the volatile H2CO3
Phosphate
Buffer
system
Ammonia
Buffer
system
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
Acid-Base Balance Review test:
 The kidneys regulate pH by excreting
HCO3- and retaining or regenerating H+
TRUE
FALSE
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
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
Acid-Base Review test:
 The ratio of H+ to HCO3- determines
pH.
TRUE
FALSE
Acid-Base Review test:
 Secreted H+ couples with filtered HCO3-
& CO2 & H2O result.
TRUE
FALSE
Metabolic Disturbances:
 Alkalosis: elevated HCO3- (>26 mEq/L)

Causes include: Cl- depletion (vomiting,
prolonged nasogastric suctioning),
Cushing’s syndrome, K+ deficiency,
massive blood transfusions, ingestion of
antacids, etc.
 Acidosis: decreased HCO3- (<22 mEq/L)

Causes include: DKA, shock, sepsis, renal
failure, diarrhea, salicylates (aspirin), etc.
 Compensation is respiratory-related
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
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
Treatment of Metabolic Alkalosis:
 Correct the cause of the imbalance

May include KCl supplementation for K+/Cldeficits
 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
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
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
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
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
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
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
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
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.
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
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
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
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
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
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
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
DIAGNOSTIC LAB VALUES &
INTERPRETATION
Normal Arterial Blood Gas (ABG)
Lab Values:
 Arterial pH: 7.35 – 7.45
 HCO3-: 22 – 26 mEq/L
 PaCO2: 35 – 45 mmHg
 TCO2: 23 – 27 mmol/L
 PaO2: 80 – 100 mmHg
 SaO2: 95% or greater (pulse ox)
 Base Excess: -2 to +2
 Anion Gap: 7 – 14
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
HCO3Alkalosis: excess H+ (kidneys unable to
excrete) & HCO3- loss exceeds capacity of
kidneys to regenerate
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
HCO3PO2 also important in assessing respiratory
function
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
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
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, hypermagnesemia, lithium intoxication or
multiple myeloma
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.
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
Acid-Base w/o Compensation:
Parameters:
pH
PaCO2
Metabolic
Alkalosis
Normal
Metabolic
Acidosis
Normal
Respiratory
Alkalosis
Respiratory
Acidosis
HCO3-
Normal
Normal
Interpretation Practice:
 pH: 7.31
Resp.
Acidosis
Right!
 PaCO2: 48
Resp.
Try Alkalosis
Again
 HCO3-: 24
Try Again
Metabolic
Acidosis
 pH: 7.47
Resp.Again
Alkalosis
Try
Metabolic
Alkalosis
Right!
Metabolic
Acidosis
Try Again
 PaCO2 : 45
 HCO3- : 33
Back to Key
Interpretation Practice:
 pH: 7.20
 HCO3-: 14
Try
Again
Metabolic
Alkalosis
Try
Again
Resp.
Acidosis
Metabolic
Right! Acidosis
 pH: 7.50
Try Again
Metabolic
Alkalosis
 PaCO2 : 29
Right!
Resp. Alkalosis
Resp.Again
Acidosis
Try
 PaCO2: 36
 HCO3- -: 22
Back to Key
Acid-Base Fully Compensated:
Parameters:
pH
Metabolic
Alkalosis
Normal
>7.40
Metabolic
Acidosis
Normal
<7.40
Respiratory
Alkalosis
Respiratory
Acidosis
Normal
>7.40
Normal
<7.40
PaCO2
HCO3-
Interpretation Practice:
 pH: 7.36
 PaCO2: 56
Compensated
Resp. Alkalosis
Try Again
Compensated
Metabolic Acidosis
Try Again
 HCO3-: 31.4
Right!Resp. Acidosis
Compensated
 pH: 7.43
Compensated
Resp. Alkalosis
Right!
 PaCO2 : 32
Compensated
Metabolic Alkalosis
Try Again
 HCO3: 21
Try Again
Compensated
Metabolic Acidosis
Back to Key
Acid-Base Partially Compensated:
Parameters:
Metabolic
Alkalosis
Metabolic
Acidosis
Respiratory
Alkalosis
Respiratory
Acidosis
pH
PaCO2
HCO3-
Interpretation Practice:
 pH: 7.47
Partially Compensated Metabolic Alkalosis
 HCO3-: 33.1
Right!
PartiallyTry
Compensated
Again Resp. Alkalosis
Partially Compensated
Try AgainMetabolic Acidosis
 pH: 7.33
Partially Compensated
Try AgainMetabolic Alkalosis
 PaCO2: 49
 PaCO2 : 31
PartiallyTry
Compensated
Again Resp. Acidosis
 HCO3- : 16
Right! Metabolic Acidosis
Partially Compensated
Back to Key
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
PaCO2: 32
HCO3-: 18
The=pH
is:
Low, WNL
7.35-7.45
The PaCO
Low, WNL
= 35-45mmHg
2 is:
The HCO
Low, WNL
= 22-26mEq/L
3 is:
 Assess the pH, PaCO2 & HCO3-. Are the
values high, low or WNL?
Case Study 1 Continued:
 What is Mrs. D’s acid-base imbalance?
Partially Compensated
Right!Metabolic Acidosis
Try Again
Fully Compensated
Resp. Acidosis
 Remember the difference between full &
partial compensation. Go back & use
the appropriate key if necessary.
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
PaCO2: 52
HCO3-: 50
The pH is:
WNL = 7.35-7.45
The PaCO
High, WNL
= 35-45mmHg
2 is:
The HCO
High, WNL
= 22-26mEq/L
3 is:
 Assess the above labs. Are they
abnormal or WNL?
Case Study 2 Continued:
 What is Mr. M’s acid-base disturbance?
Fully Compensated
Metabolic Acidosis
Try Again
Fully Compensated
Right!Resp. Acidosis
 Think about appropriate interventions- if
the problem is metabolic, the respiratory
system compensates & vice versa
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
PaCO2: 32
HCO3-: 25
The=pH
is:
High; WNL
7.35-7.45
The PaCO
Low; WNL
= 35-45mmHg
2 is:
The HCO
High; WNL
= 22-26mEq/L
3 is:
 What is the significance of her ABG
values?
Case Study 3 Continued:
 What is Miss L’s imbalance?
Resp.
Alkalosis
Right!
Try Again
Metabolic
Alkalosis
 Great Job! You’ve reached the end of
the tutorial & I hope you found it helpful.
Thank you!
REFERENCES:
http://www.healthline.com/galecontent/acid-basebalance?utm_medium=ask&utm_source=smart&utm_campaign=article
&utm_term=Acid+Base+Equilibrium&ask_return=Acid-Base+Balance.
Retrieved 3/5/09.
Porth, C.M. (2005). Pathophysiology Concepts of Altered Health States (7th
ed.). Philadelphia: Lippincott Williams & Wilkins.
http://en.wikipedia.org/wiki/Dissociation_(chemistry). Retrieved 3/6/09.
http://www.clt.astate.edu/mgilmore/pathophysiology/Acid and Base.ppt#1.
Retrieved 3/6/09.
http://www.uhmc.sunysb.edu/internalmed/nephro/webpages/Part_E.htm.
Retrieved 3/6/09.
http://medical-dictionary.thefreedictionary.com/Volatile+acid. Retrieved
3/6/09.
REFERENCES
http://wiki.answers.com/Q/How_does_the_phosphate_buffer_system_help_
in_maintaining_the_ph_of_our_body. Retrieved 3/10/09.
Alspach, J.G. (1998). American Association of Critical-Care Nurses Core
Curriculum for Critical Care Nursing (5th ed.). Philadelphia: Saunders.
http://medical-dictionary.thefreedictionary.com. Retrieved 4/14/09.
Acid-Base Balance & Oxygenation Power Point. (2007). Milwaukee:
Froedtert Lutheran Memorial Hospital Critical Care Class.