Download 10 Renal Acid-Base Balance

Renal Physiology
PART
THREE
Renal Acid-Base Balance
1
Acid
•
•
•
•
An acid is when hydrogen ions accumulate in a solution.
It becomes more acidic
[H+] increases = more acidity
CO2 is an example of an acid.
HCl
2
H+
H+
Cl-
H+
H+
ClH+
7
ClpH
ClCl-
As concentration of hydrogen
ions increases, pH drops
2
Base
• A base is chemical that will remove hydrogen ions from
the solution
• Bicarbonate is an example of a base.
NaOH
Na+ OH- H +
ClH+
ClNa+ OHH+
ClCl- Na+ OHH+
ClNa+ OH-
H+
2
7
pH
Acids and basis
neutralize each
other
3
A change of 1 pH unit corresponds to
a 10-fold change in hydrogen ion
concentration
7
Na+
ClNa+
H+
Na+
OH-
Na+
Cl-
2
Cl-
pH
H2O
Cl-
4
Acids are being created constantly
through metabolism
•
•
•
•
Protein breakdown produces phosphoric acid
Anaerobic respiration of glucose produces lactic acid
Fat metabolism yields organic acids and ketone bodies
Carbon dioxide is also an acid. Transporting CO2 as
bicarbonate leads to a release of H+ (an acid)
5
Acid/Base Balance
• There is a pH differential between arterial
blood (pH=7.4) and intracellular fluid (pH =
7.0).
• Most metabolic reactions liberate H+, and a
buffer system is needed to maintain
physiological pH.
6
Buffers
• “Buffers are solutions which can resist
changes in pH when acid or alkali is
added.”
7
Acids must be buffered, transported away from
cells, and eliminated from the body.
These are the most important buffers.
Phosphate: important renal tubular buffer
HPO4- + H+
H2PO4
Ammonia: important renal tubular buffer
NH3 + H+
NH4+
Proteins: important intracellular and plasma buffers
H+ + Hb
HHb
Bicarbonate: most important Extracellular buffer
and is also another important renal tubular
buffer.
H2O + CO2
H2CO3
H+ + HCO3 - 8
BUFFERING SYSTEMS
BUFFERS USED BY THE BUFFERING SYSTEMS
Bicarbonate
Respiratory System
Proteins
Bicarbonate
Phosphate
Blood
Bicarbonate
Kidneys
Phosphate
Ammonia
9
Phosphate Buffer System
•
•
•
It is mainly an intracellular buffer and a renal tubular buffer.
Its concentration in plasma is very low.
The phosphate buffer system operates in the internal fluid of all cells. This
buffer system consists of dihydrogen phosphate ions (H2PO4-) as hydrogenion donor (acid) and hydrogen phosphate ions (HPO42-) as hydrogen-ion
acceptor (base). These two ions are in equilibrium with each other as
indicated by the chemical equation below.
H2PO4-
•
H+ + HPO42-
If additional hydrogen (H+) ions enter the cellular fluid, they are consumed
in the reaction with HPO42-, and the equilibrium shifts to the left. If additional
hydroxide (OH-) ions enter the cellular fluid, they react with H2PO4-,
producing HPO42-, and shifting the equilibrium to the right.
10
Ammonia Buffer System
• Important renal tubule buffer.
• Excess H+ can be picked up by the
ammonia system in a complicated set of
reactions.
• The kidney makes ammonia by breaking
down glutamine (an amino acid).
• Ammonium is secreted into the filtrate
while the good products are reabsorbed.
11
Ammonia as a Buffer
12
Protein buffer system
• Most important buffer system in body cells.
Also important in the blood.
• There are 16 histidine (amino acid)
residues in albumin and 38 histidines
residues in hemoglobin.
• These amino acids can accept a H+ and
act as a buffer in the RBC’s and plasma.
13
BICARBONATE BUFFER SYSTEM
• Most important buffer system in the plasma
• Accounts for 65% of the buffering capacity in
plasma
• Accounts for 40% of the buffering capacity in the
whole body
14
Bicarbonate as a Buffer
15
Phosphate and Bicarbonate
Buffers
• The phosphate buffer is very effective but not
found in high concentrations in all tissues.
• The bicarbonate buffer is also very effective and
there are high levels of bicarbonate in all tissues
that contain carbonic anhydrase (red blood cells,
kidney, pancreas, stomach and brain):
carbonic anhydrase
H2O + CO2
H2CO3
Carbonic
acid
HCO3(-) + H+
Bicarbonate
16
Buffering Capacity in Body
• 52% of the buffering capacity is in cells
• 5% is in RBCs
• 43% of the buffering capacity is in the
extracellular space
– of which 40% by bicarbonate buffer, 1% by
proteins and 1% by phosphate buffer system
17
Buffering Systems
• The three different buffering systems are:
1) Respiratory buffering system
• Uses bicarbonate
2) Blood buffering system
• Uses bicarbonate, phosphate, and protein
3) Renal buffering system
• Uses bicarbonate, phosphate, and ammonia
18
BUFFERING SYSTEMS
BUFFERS USED BY THE BUFFERING SYSTEMS
Bicarbonate
Respiratory System
Proteins
Bicarbonate
Phosphate
Blood
Bicarbonate
Kidneys
Phosphate
Ammonia
19
Respiratory Buffering System
• The respiratory buffering system uses bicarbonate.
The respiratory system controls CO2 levels, while the
kidney can excrete bicarbonate.
• Hyperventilation leads to loss of CO2 and creates
alkaline conditions, while hypoventilation creates acid
conditions.
• Peripheral receptors detect CO2 concentration changes
and send the appropriate signal to the respiratory
system.
• When CO2 builds up, a central receptor increases
ventilation.
20
Blood Buffering System
• The blood buffering system uses three
different chemical buffers: phosphate,
bicarbonate and proteins. The phosphate
buffer is not abundant in blood. Blood
contains a high concentration of proteins.
21
Renal Buffering System
• The renal buffer system uses bicarbonate,
phosphate and ammonium. In the kidneys, the
bicarbonate buffer may increase plasma pH in
three ways: secrete H+, "reabsorb" bicarbonate,
or produce new bicarbonate.
• H+ secretion occurs mostly in the proximal
tubule by the carbonic anhydrase reaction.
• In acidic conditions, CO2 diffuses inside tubular
cells and is converted to carbonic acid, which
the dissociates to yield a H+ which is then
secreted into the lumen by the Na+/H+ shuttle. 22
Buffering is good, but it is a temporary
solution. Excess acids and bases must be
eliminated from the body
gas
H2O + CO2
aqueous
H2CO3
H+ + HCO3 Kidneys can remove excess
non-gas acids and bases
Lungs eliminate
carbon dioxide
23
Excessive Acids and Bases can cause
pH changes---denature proteins
• Normal pH of plasma is 7.40
• Alkalosis (alkalemia) – arterial blood pH rises above 7.45
• Acidosis (acidemia) – arterial pH drops below 7.35
• Acidosis:
– Too much acid
– Too little base
• Alkalosis
– Too much base
– Too little acid
24
Compensation for deviation
• Lungs (only if not a respiratory problem)
– If too much acid (low pH)—respiratory
system will ventilate more (remove CO2) and
this will raise pH back toward set point
– If too little acid (high pH)—respiratory will
ventilate less (trap CO2 in body) and this will
lower pH back toward set point
• Kidneys
– If too much acid (low pH)—intercalated cells
will secrete more acid into tubular lumen
and make NEW bicarbonate (more base)
and raise pH back to set point.
– If too little acid/excessive base (high pH)proximal convoluted cells will NOT reabsorb
filtered bicarbonate (base) and will eliminate
it from the body to lower pH back toward
normal.
25
Acid-Base Balance
• How would your ventilation change if you
had excessive acid?
– You would hyperventilate
• How would your ventilation change if you
had excessive alkalosis?
– Your breathing would become shallow
26
How can the kidneys control acids
and bases?
• Bicarbonate is filtered
and enters nephron at
Bowman’s capsule
• Proximal convoluted
tubule
– Can reabsorb all
bicarbonate (say, when you
need it to neutralize
excessive acids in body)
OR
– Can reabsorb some or
NONE of the bicarbonate
(maybe you have too much
base in body and it needs
to be eliminated)
27
How can the kidneys control acids
and bases?
• Acidosis
• Intercalated cells
– Secrete excessive
hydrogen
– Secreted hydrogen
binds to buffers in the
lumen (ammonia and
phosphate bases)
– Secretion of hydrogen
leads to formation of
bicarbonate
HPO4NH3
28
What would happen if the respiratory
system had a problem with ventilation?
Respiratory Acidosis and Alkalosis
Normal PCO2 fluctuates between 35 and 45 mmHg
• Respiratory Acidosis (elevated
CO2 greater than 45mmHg)
• Depression of respiratory centers
via narcotic, drugs, anesthetics
• CNS disease and depression,
trauma (brain damage)
• Interference with respiratory
muscles by disease, drugs,
toxins
• Restrictive, obstructive lung
disease (pneumonia,
emphysema)
• Respiratory Alkalosis (less
than 35mmHg- lowered CO2)
• Hyperventilation syndrome/
psychological (fear, pain)
• Overventilation on mechanical
respirator
• Ascent to high altitudes
• Fever
29
What if your metabolism changed?
• Metabolic acidosis
• Bicarbonate levels
below normal (22
mEq/L)
• Diarrhea (loss of
intestinal bicarbonate)
• Ingestion, infusion or
production of more
acids (alcohol)
• Salicylate overdose
(aspirin)
• Accumulation of lactic
acid in severe Diabetic
ketoacidosis
• starvation
• Metabolic alkalosis
• bicarbonate ion levels
higher (greater than
26mEq/L)
• Excessive loss of acids
due to loss of gastric
juice during vomiting
• Excessive bases due to
ingestion, infusion, or
renal reabsorption of
bases
• Intake of stomach
antacids
• Diuretic abuse (loss of
H+ ions)
• Severe potassium
depletion
• Steroid therapy
30
How can you tell if the acid-base
imbalance is from a kidney disorder
or a lung disorder?
Acidosis: pH < 7.4
- Metabolic:
- respiratory:
HCO3 - Or normal
pCO2
Alkalosis: pH > 7.4
- Metabolic: HCO3 - respiratory: pCO2 Or normal
31
pH Imbalances
• Acidosis
–Can be metabolic or respiratory
• Alkalosis
–Can be metabolic or respiratory
32
Acidosis
• Acidosis is excessive blood acidity caused
by an overabundance of acid in the blood
or a loss of bicarbonate from the blood
(metabolic acidosis), or by a buildup of
carbon dioxide in the blood that results
from poor lung function or slow breathing
(respiratory acidosis).
33
Acidosis
• Blood acidity increases when people ingest substances
that contain or produce acid or when the lungs do not
expel enough carbon dioxide.
• People with metabolic acidosis have nausea, vomiting,
and fatigue and may breathe faster and deeper than
normal.
• People with respiratory acidosis have headache and
confusion, and breathing may appear shallow, slow or
both.
• Tests on blood samples show there is too much acid.
• Doctors treat the cause of the acidosis.
34
Respiratory acidosis
• Respiratory acidosis is due to an
accumulation of CO2 in the blood stream.
This pushes the carbonic anhydrase
reaction to the right, generating H+:
carbonic anhydrase
CO2
H2CO3
HCO3(-) + H+
35
Respiratory acidosis
• Cause
• The increase in CO2 in the blood is often caused by
hypoventilation.
• This can be caused by asthma, COPD, and overuse of
sedatives, barbiturates, or narcotics such as valium,
heroin, or other drugs which make you sleepy.
• It can also be caused by other things wrong with the
lungs: an accident where the breathing muscles are
damaged (causing decreased ventilation), airway
obstruction, or lung disease (pneumonia, cystic fibrosis,
emphysema, etc.).
36
Respiratory acidosis
• Compensation
• Even if the peripheral receptors sense the change in pH,
the lungs are unresponsive.
• The kidneys will compensate by secreting H+.
• If H+ excretion cannot restore the balance, the kidneys
will also generate bicarbonate.
• Since the primary abnormality is an increase in pCO2,
the compensatory response is intracellular buffering of
hydrogen (by hemoglobin) and renal retention of
bicarbonate, which takes several days to occur.
37
Respiratory acidosis
• Symptoms
• May have no symptoms but usually experience
headache, nausea, vomiting, and fatigue.
• Breathing becomes deeper and slightly faster (as the
body tries to correct the acidosis by expelling more
carbon dioxide).
• As the acidosis worsens, people begin to feel extremely
weak and drowsy and may feel confused and
increasingly nauseated.
• Eventually, blood pressure can fall, leading to shock,
coma, and death.
• The most common clinical intervention is IV bicarbonate
and applying an oxygen mask.
38
Respiratory acidosis
• Treatment
• Treatment is aimed at the underlying disease,
and may include:
• Bronchodilator drugs to reverse some types of
airway obstruction
• Noninvasive positive-pressure ventilation
(sometimes called CPAP or BiPAP) or a
breathing machine, if needed
• Oxygen if the blood oxygen level is low
• Treatment to stop smoking
39
Metabolic acidosis
• Metabolic acidosis is the gain of acid or the loss of
bicarbonate.
• Cause
• Usual causes are the generation of ketone bodies in
uncontrolled diabetes mellitus, diarrhea (loss of
bicarbonate), excess protein consumption (breakdown
products are amino ACIDS), or excess alcohol
consumption:
(alcohol
formaldehyde
acetic acid).
• Can also be caused by ingestion of an acid (aspirin,
ethanol, or antifreeze).
• Exercise creates a milder, transient metabolic acidosis
because of the production of lactic acid.
40
Metabolic acidosis
• Compensation
• The body will compensate with hyperventilation and
increased bicarbonate reabsorption in the kidney.
• Since the primary abnormality is a decrease in HCO3,
the compensatory response includes extracellular
buffering (by bicarbonate), intracellular buffering (by
phosphate and proteins), respiratory compensation and
renal hydrogen excretion.
• Metabolic acidosis stimulates an increase in ventilation
(reducing pCO2).
• This hyperventilation is called Kussmaul's respiration.
41
Metabolic acidosis
• Symptoms
• Most symptoms are caused by the underlying
disease or condition that is causing the
metabolic acidosis.
• Metabolic acidosis itself usually causes rapid
breathing.
• Confusion or lethargy may also occur.
• Severe metabolic acidosis can lead to shock or
death.
• In some situations, metabolic acidosis can be a
mild, chronic (ongoing) condition.
42
Metabolic acidosis
• Treatment is give i.v. of sodium
bicarbonate.
•
•
•
The HCO3- deficit can be calculated by using the following equation:
HCO3- deficit = deficit/L (desired serum HCO3- - measured HCO3-) x 0.5 x
body weight (volume of distribution for HCO3-)
This provides a crude estimate of the amount of HCO3- that must be
administered to correct the metabolic acidosis; the serum HCO3- level or pH
should be reassessed frequently.
43
Alkalosis
• Alkalosis is excessive blood alkalinity
caused by an overabundance of
bicarbonate in the blood or a loss of acid
from the blood (metabolic alkalosis), or by
a low level of carbon dioxide in the blood
that results from rapid or deep breathing
(respiratory alkalosis).
44
Alkalosis
• People may have irritability, muscle
twitching, or muscle cramps, or even
muscle spasms.
• Blood is tested to diagnose alkalosis.
• Metabolic alkalosis is treated by replacing
water and electrolytes.
• Respiratory alkalosis is treated by slowing
breathing.
45
Respiratory alkalosis
• Respiratory alkalosis is generally caused by
hyperventilation, usually due to anxiety. The primary
abnormality is a decreased pCO2.
• Cause
• Caused from a decrease in CO2 in the blood because
the lungs are hyperventilating (anxiety, but not panting).
• Fever or aspirin toxicity may also cause respiratory
alkalosis.
46
Respiratory alkalosis
• Compensation
• The body will reduce the breathing rate,
and the kidney will excrete bicarbonate.
47
Respiratory alkalosis
• Compensation
• The compensatory response to a respiratory alkalosis is
initially a release of hydrogen from extracellular and
intracellular buffers.
• This is followed by reduced hydrogen excretion by the
kidneys.
• This results in decreased plasma bicarbonates.
• In chronic respiratory alkalosis, compensation can lead
to pH returning to normal.
48
Respiratory alkalosis
•
•
•
•
Symptoms
Irritability
Muscle twitching
Muscle cramps
49
Respiratory alkalosis
• Treatment
• Treatment for hyperventilation is to breathe into
a paper bag for a while, as the person breathes
carbon dioxide back in after breathing it out.
• For severe cases, need to replace the water and
electrolytes (sodium and potassium).
50
Metabolic alkalosis
• Metabolic alkalosis is due to the gain of base
or the loss of acid. The primary abnormality is an
increased HCO3.
• Cause
• Caused from an increase in bicarbonate in
the blood because of ingestion of excess
bicarbonate in the form of an antacid (Tums),
eating excess fruits (vegetarian diets and fad
diets*), loss of acid from vomiting, or loss of
potassium from diuretics.
51
FYI
• *Fruits are the normal source of alkali in the diet.
They contain the potassium salts of weak
organic acids.
• When the anions are metabolized to CO2 and
removed from the body, alkaline potassium
bicarbonate and sodium bicarbonate remain.
• Metabolic alkalosis may be found in vegetarians
and fad dieters who are ingesting a low-protein,
high fruit diet.
52
Metabolic alkalosis
• Compensation
• This is initially buffered by hydrogen buffers (such as
plasma proteins and lactate).
• Chemoreceptors in the respiratory center sense the
alkalosis and trigger hypoventilation, resulting in
increased pCO2.
• The respiratory system will hypoventilate but this will not
be effective because CO2 will accumulate and the CO2
receptors will override the pH receptors.
53
Metabolic alkalosis
• Compensation
• Naturally, the extent of respiratory compensation will be
limited by the development of hypoxia with continued
hypoventilation. The kidney will make more of a
difference by not reabsorbing bicarbonate.
• In addition to respiratory compensation, the kidneys
excrete the excess bicarbonate. However, this takes
several days to occur.
54
Metabolic alkalosis
•
•
•
•
•
•
•
•
Symptoms
Confusion (can progress to stupor or coma)
Hand tremor
Light-headedness
Muscle twitching
Nausea, vomiting
Numbness or tingling in the face, hands, or feet
Prolonged muscle spasms (tetany)
55
Metabolic alkalosis
• Treatment is to give an anti-emetic if the problem is from
vomiting. If not, give an i.v. of normal saline to increase
the blood volume.
• If potassium is also low, would have to add that to the i.v.
56
Compensation
• If the kidneys are the problem, the
respiratory system can compensate.
• If the kidneys are secreting too much
H+(which makes too much bicarbonate,
causing metabolic alkalosis), breathing will
become slower so that less CO2 (an acid)
is lost.
• If the kidneys are reabsorbing too much
H+(metabolic acidosis), breathing will
become faster.
57
Compensation
• If the respiratory system is the problem,
the kidneys can compensate.
• If breathing is too rapid (too much CO2, an
acid, is lost, leaving the blood in
respiratory alkalosis), Kidneys respond by
reabsorbing more H+.
• If breathing is too shallow (not enough
CO2 is lost, leaving the blood in respiratory
acidosis), Kidneys respond by secreting
more H+.
58
How the kidneys secrete H+
• The intercalated cells secrete H+ if the
blood is too acidic. If the blood is too
alkaline, the intercalated cells stop
secreting H+
59
How the kidneys make new
bicarbonate
• If there is bicarbonate (HCO3) in the filtrate, the secreted
H+ will combine with it to form carbonic acid (H2CO3).
This is taken into the tubular cells.
• If the blood is too acidic, the carbonic acid will dissociate
into bicarbonate, which is sent to the plasma, and the H+
will be excreted. This will raise the blood pH.
• If the blood is too alkaline, the H+ will enter the plasma
instead, and the bicarbonate will be excreted.
60
How the kidneys reabsorb
bicarbonate
• CO2 and water in the filtrate enter the tubular cells by
diffusion and are transformed into carbonic acid and then
into bicarbonate plus H+.
• Bicarbonate can then be transported into the plasma to
raise pH, or H+ is transported into the plasma to lower
pH.
• The other product is then excreted. The kidneys also
make bicarbonate at the collecting duct. This reaction is
also driven by the diffusion of CO2 into the cell.
61
62
Definitions
• Normal pH is 7.35 - 7.45
– If this value is normal, but one of the below values is
abnormal, the patient has compensated.
• Normal C02 is 35 -45 mmHg
– If this value is abnormal, the patient has respiratory
acidosis or alkalosis.
• Normal HC03 is 22-26 mEq/L
• If this value is abnormal, the patient has metabolic acidosis
or alkalosis
• Normal O2 Saturation is 80-100 ml/dl
– If this value is normal in a respiratory pH problem, patient
is compensating.
63
Interpreting Arterial Blood
Gases (ABG)
• This blood test is from arterial blood, usually from
the radial artery.
• There are three critical questions to keep in mind
when attempting to interpret arterial blood gases
(ABGs).
First Question: Does the patient exhibit acidosis or
alkalosis?
Second Question: What is the primary problem?
Metabolic? or Respiratory?
Third Question: Is the patient exhibiting a
compensatory state?
64
Assessment Step 1
• Step One: Determine the acid/base status of the
arterial blood.
• If the blood's pH is less than 7.35 this is an acidosis,
and if it is greater than 7.45 this is an alkalosis.
You may hear nurses or doctors say: "The patient is
'acidotic' or 'alkalotic'
65
Assessment Step 1
• If the pH is low, it is acidosis.
• If it is high, it is alkalosis.
66
Assessment Step 2
• Once you have determined the pH, you
can move on to determine which system is
the 'primary' problem: respiratory or
metabolic.
• To do this, examine the pCO2 and HCO3
levels.
67
Assessment Step 2
• If the pCO2 is the only one that is
abnormal, it is respiratory.
• If the HCO3 is the only one that is
abnormal, it is metabolic.
• If they are both abnormal, they are
compensating, so we need to evaluate it
further. Go to step 3.
68
Assessment Step 3
• Determine if the body is attempting to
compensate for the imbalance or not.
• If both CO2 and Bicarbonate are high or
both low, the patient is compensating.
• You will never have a case where one is
high and one is low.
69
• If both the pCO2 and HCO3 are high, what
does it mean?
• If the pH is low, it is compensated
respiratory acidosis.
• If the pH is high, it is compensated
metabolic alkalosis.
70
Arterial Blood Gas problems
when compensation is present
pH
Respiratory
Acidosis
Acid
Metabolic
Alkalosis
Base
Metabolic
Acidosis
Acid
Respiratory
Alkalosis
Base
PCO2
HCO3
71
• If both the pCO2 and HCO3 are high, and
the pH is low, why do you know it is
compensated respiratory acidosis instead of
compensated metabolic acidosis?
• In respiratory acidosis, the first thing to go
wrong is the pCO2 will become high. To
compensate, the HCO3 will become
elevated.
• If it was metabolic acidosis, the first thing to
go wrong would be the HCO3 levels would
be too low. To compensate, the pCO2 levels
would start dropping to raise the pH.
72
Arterial Blood Gas problems
when compensation is present
pH
Respiratory
Acidosis
Acid
Metabolic
Alkalosis
Base
Metabolic
Acidosis
Acid
Respiratory
Alkalosis
Base
PCO2
HCO3
73
• If both the pCO2 and HCO3 are low, and
the pH is low, why do you know it is
compensated metabolic acidosis instead
of compensated respiratory acidosis?
• In metabolic acidosis, the first thing to go
wrong is the HCO3 will become low. To
compensate, the pCO2 will become low to
raise the pH to compensate.
• If it was respiratory acidosis, the first thing
to go wrong is the pCO2 will become high.
To compensate, the HCO3 will become
74
elevated.
Arterial Blood Gas problems
when compensation is present
pH
Respiratory
Acidosis
Acid
Metabolic
Alkalosis
Base
Metabolic
Acidosis
Acid
Respiratory
Alkalosis
Base
PCO2
HCO3
75
• If both the pCO2 and HCO3 are high, and
the pH is high, why do you know it is
compensated metabolic alkalosis instead
of compensated respiratory alkalosis?
• In metabolic alkalosis, the first thing to go
wrong is the HCO3 will become high. To
compensate, the pCO2 will become high
to lower the pH to compensate.
• If it was respiratory alkalosis, the first thing
to go wrong is the pCO2 will become low.
To compensate, the HCO3 will become
76
low.
Arterial Blood Gas problems
when compensation is present
pH
Respiratory
Acidosis
Acid
Metabolic
Alkalosis
Base
Metabolic
Acidosis
Acid
Respiratory
Alkalosis
Base
PCO2
HCO3
77
• If both the pCO2 and HCO3 are low, and
the pH is high, why do you know it is
compensated respiratory alkalosis instead
of compensated metabolic alkalosis?
• In respiratory alkalosis, the first thing to go
wrong is the pCO2 will become low. To
compensate, the HCO3 will become low.
• If it was metabolic alkalosis, the first thing
to go wrong would be the HCO3 levels
would be too high. To compensate, the
pCO2 levels would start elevating to lower
the pH.
78
Arterial Blood Gas problems
when compensation is present
pH
Respiratory
Acidosis
Acid
Metabolic
Alkalosis
Base
Metabolic
Acidosis
Acid
Respiratory
Alkalosis
Base
PCO2
HCO3
79
• If the pCO2 is high and HCO3 is low, the
pH will always be low. But how do you
know if it is uncompensated respiratory or
metabolic acidosis?
• Look at the breathing rate.
Uncompensated respiratory acidosis will
have hypoventilation, while
uncompensated metabolic acidosis will
have normal ventilation.
80
Arterial Blood Gas problems
when compensation is present
pH
Respiratory
Acidosis
Acid
Metabolic
Alkalosis
Base
Metabolic
Acidosis
Acid
Respiratory
Alkalosis
Base
PCO2
HCO3
81
• If the pCO2 is low and HCO3 is normal,
the pH will always be high. But how do you
know if it is uncompensated respiratory or
metabolic alkalosis?
• Look at the breathing rate.
Uncompensated respiratory alkalosis will
have hyperventilation, while
uncompensated metabolic alkalosis will
have normal ventilation.
82
Arterial Blood Gas problems
when compensation is present
pH
Respiratory
Acidosis
Acid
Metabolic
Alkalosis
Base
Metabolic
Acidosis
Acid
Respiratory
Alkalosis
Base
PCO2
HCO3
83
Review the three essential
steps of ABG analysis
• Number One:
Determine if the patient is demonstrating an acidotic (remember: pH
less than 7.35) or alkalotic (pH greater than 7.45) condition.
• Number Two:
• What is the 'primary problem?
• If the patient is acidotic with a pC02 greater than 45 mmHg it is
RESPIRATORY
• If the patient is alkalotic with a pC02 less than 35 mmHg it is
RESPIRATORY!
• If the patient is acidotic with a HC03 less than 22 mEq/L it is
METABOLIC!
• If the patient is alkalotic with a HC03 greater than 26 mEq/L it is
METABOLIC!
84
Review the three essential
steps of ABG analysis
• Number Three:
Is the patient compensating?
• Are both components (HCO3 and pCO2) shifting in
the same direction?
• Both going up or both going down?
• If so, the patient is compensating. Their buffering
systems are functioning and are trying to bring the
acid-base balance back to normal.
85
Rules for compensation
• Compensation does not produce a normal
pH (except in a chronic respiratory
alkalosis, in which compensatory
metabolic acidosis can correct the pH).
• Overcompensation does not occur.
• Sufficient time must elapse for
compensation to reach steady-state,
approximately 24 hours.
86
http://www.wikihow.com/Interpret-Blood-Gas-Results
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Sleep Apnea
• Sometimes patient wakes up confused or
lethargic.
• Oxygen saturation quickly returns to
normal, but blood CO2 levels are high.
• That is evidence of respiratory acidosis
from sleep apnea.
96
Kussmaul Breathing
• Kussmaul breathing is a form of
hyperventilation often associated with
severe metabolic acidosis, particularly
diabetic ketoacidosis (DKA) but also renal
failure.
97
Arterial Blood Gas problems
when compensation is present
pH
Respiratory
Acidosis
Acid
Metabolic
Alkalosis
Base
Metabolic
Acidosis
Acid
Respiratory
Alkalosis
Base
PCO2
HCO3
98
Condition
pH
Resp
CO2
Bicarb
Compensating?
Resp acidosis
Low
Hypoventilating
High
High
Yes
Resp acidosis
Low
Hypoventilating
High
Norm
No
Resp alkalosis
High
Hyperventilating
Low
Low
Yes
Resp alkalosis
High
Hyperventilating
Low
Norm
No
Metab acidosis
Low
Normal
Low
Low
Yes
Metab acidosis
Low
Normal
High
Norm
No
Metab Alkalosis
High
Normal
High
High
Yes
Metab Alkalosis
High
Normal
Low
Norm
No
99
Case Study 1
A patient recovering from surgery in the post-anesthesia care unit is
difficult to arouse two hours following surgery. The nurse in the PACU
has been administering Morphine Sulfate intravenously to the patient for
complaints of post-surgical pain. The patient’s respiratory rate is 7 per
minute and demonstrates shallow breathing. The patient does not
respond to any stimuli! The nurse assesses the ABCs (remember Airway,
Breathing, Circulation!) and obtains ABGs STAT! The STAT results
come back from the laboratory and show:
pH = 7.15 (low)
C02 = 68 mmHg (high)
HC03 = 22 mEq/L (normal)
1.
2.
3.
4.
Compensated Respiratory Acidosis
Uncompensated Metabolic Acidosis
Compensated Metabolic Alkalosis
Uncompensated Respiratory Acidosis
100
Answer
• The answer is #4
uncompensated respiratory acidosis
101
Case Study 2
•
An infant, three weeks old, is admitted to the Emergency Room.
The mother reports that the infant has been irritable, difficult to
breastfeed and has had diarrhea for the past 4 days. The infant’s
respiratory rate is elevated and the fontanels are sunken. The
Emergency Room physician orders ABGs after assessing the
ABCs.
•
The results from the ABGs come back from the laboratory and
show:
pH = 7.37 (normal)
C02 = 29 mmHg (low)
HC03 = 17 mEq/L (low)
1.
2.
3
4
Compensated Respiratory Alkalosis
Uncompensated Metabolic Acidosis
Compensated Metabolic Acidosis
Uncompensated Respiratory Acidosis
102
Answer
• Answer is #3
• Compensated Metabolic Acidosis
103
Case Study 3
•
A patient, 5 days post-abdominal surgery, has a nasogastric
tube. The nurse notes that the nasogastric tube (NGT) is
draining a large amount (900 cc in 2 hours) of coffee ground
secretions. The patient is not oriented to person, place, or time.
The nurse contacts the attending physician and STAT ABGs are
ordered.
•
The results from the ABGs come back from the laboratory and
show:
pH = 7.52 (high)
C02 = 35 mmHg (normal)
HC03 = 29 mEq/L (high)
1.
2.
3.
4.
Compensated Respiratory Alkalosis
Uncompensated Metabolic Acidosis
Compensated Metabolic Acidosis
Uncompensated Metabolic Alkalosis
104
Answer
•
•
Answer is #4
Uncompensated Metabolic Alkalosis
105
Case Study 4
•
A patient is admitted to the hospital and is being prepared for a
craniotomy (brain surgery). The patient is very anxious and
scared of the impending surgery. He begins to hyperventilate
and becomes very dizzy. The patient looses consciousness and
the STAT ABGs reveal:
•
•
•
•
The results from the ABGs come back from the laboratory and
show:
pH = 7.57 (high)
C02 = 26 mmHg (low)
HC03 = 24 mEq/L (normal)
1.
2.
3.
4.
Compensated Metabolic Acidosis
Uncompensated Metabolic Acidosis
Uncompensated Respiratory Alkalosis
Uncompensated Respiratory Acidosis
106
Answer
•
•
The answer is #3
Uncompensated Respiratory Alkalosis
107
Case Study 5
•
A two-year-old is admitted to the hospital with a diagnosis of
asthma and respiratory distress syndrome. The father of the
infant reports to the nurse that he has observed slight tremors
and behavioral changes in his child over the past three days.
The attending physician orders routine ABGs following an
assessment of the ABCs. The ABG results are:
•
•
•
pH = 7.36 (normal)
C02 = 69 mmHg (high)
HC03 = 36 mEq/L (high)
1.
2.
3.
4.
Compensated Respiratory Alkalosis
Uncompensated Metabolic Acidosis
Compensated Respiratory Acidosis
Uncompensated Respiratory Alkalosis
108
Arterial Blood Gas problems
when compensation is present
pH
Respiratory
Acidosis
Acid
Metabolic
Alkalosis
Base
Metabolic
Acidosis
Acid
Respiratory
Alkalosis
Base
PCO2
HCO3
109
Answer
• Answer is #3
• Compensated Respiratory Acidosis
110
Case Study 6
•
•
1.
2.
3.
4.
A young woman, drinking beer at a party, falls and
hits her head on the ground. A friend dials "911"
because the young woman is unconscious,
depressed ventilation (shallow and slow
respirations), rapid heart rate, and is profusely
bleeding from both ears.
Which primary acid-base imbalance is this young
woman at risk for if medical attention is not
provided?
metabolic acidosis
metabolic alkalosis
respiratory acidosis
respiratory alkalosis
111
Answer
• Correct answer is #3
• Respiratory Acidosis
112
Case Study 7
•
•
1.
2.
3.
4.
An 11-year old boy is admitted to the hospital with
vomiting (losing acid!), nausea and overall
weakness. The nurse notes the laboratory results:
potassium: 2.9 mEq (low).
Which primary acid-base imbalance is this boy at risk
for if medical attention is not provided? Note:
Potassium makes blood more acidic.
metabolic acidosis
metabolic alkalosis
respiratory acidosis
respiratory alkalosis
113
Answer
• Correct Answer is #2
• Metabolic Alkalosis
114
Case Study 8
• An elderly gentleman is seen in the emergency
department at a community hospital. He admits to taking
many tablets of aspirin (salicylates) over the last 24-hour
period because of a severe headache. He complains of
an inability to urinate. His vital signs are: Temp = 98.5;
apical pulse = 92; respiration = 30 and deep.
• Which primary acid-base imbalance is the gentleman at
risk for if medical attention is not provided?
1.
2.
3.
4.
metabolic acidosis
metabolic alkalosis
respiratory acidosis
respiratory alkalosis
115
Answer
• Correct Answer is #1
• Metabolic Acidosis
116
Case Study 9
•
•
1.
2.
3.
4.
A young man is found at the scene of an automobile accident in
a state of emotional distress. He tells the paramedics that he
feels dizzy, tingling in his fingertips, and does not remember
what happened to his car. Respiratory rate is rapid at
34/minute.
Which primary acid-base disturbance is the young man at risk
for if medical attention is not provided?
metabolic acidosis
metabolic alkalosis
respiratory acidosis
respiratory alkalosis
117
Answer
• Correct Answer is #4
• Respiratory Alkalosis
118
Case Study 10
12 year old diabetic presents with Kussmaul breathing
•
•
•
•
pH :
pCO2:
pO2:
HCO3:
7.05 (low)
30 mmHg (low)
108 mmHg (normal)
5 mEq/L (low)
– What is the diagnosis? Is he compensating?
What caused the problem?
119
Arterial Blood Gas problems
when compensation is present
pH
Respiratory
Acidosis
Acid
Metabolic
Alkalosis
Base
Metabolic
Acidosis
Acid
Respiratory
Alkalosis
Base
PCO2
HCO3
120
Answer
12 year old diabetic presents with Kussmaul breathing
•
•
•
•
pH :
pCO2:
pO2:
HCO3:
7.05 (low)
30 mmHg (low)
108 mmHg (normal)
5 mEq/L (low)
– Compensating metabolic acidosis without
hypoxemia due to ketoacidosis
121
Case Study 11
17 year old w/severe kyphoscoliosis, admitted for
pneumonia
•
•
•
•
pH:
7.37 (normal)
pCO2: 25 mmHg (low)
pO2:
60 mmHg (low)
HCO3: 14 mEq/L (low)
– What is the diagnosis? Is he compensating?
What caused the problem?
122
Arterial Blood Gas problems
when compensation is present
pH
Respiratory
Acidosis
Acid
Metabolic
Alkalosis
Base
Metabolic
Acidosis
Acid
Respiratory
Alkalosis
Base
PCO2
HCO3
123
Case Study 11
17 year old w/severe kyphoscoliosis, admitted for
pneumonia
•
•
•
•
pH:
7.37 (normal)
pCO2: 25 mmHg (low)
pO2:
60 mmHg (low)
HCO3: 14 mEq/L (low)
– Compensated respiratory alkalosis due to
chronic hyperventilation secondary to hypoxia
124
Case Study 12
9 year old w/hx of asthma, audibly wheezing x 1 week,
has not slept in 2 nights; presents sitting up and using
accessory muscles to breathe w/audible wheezes
•
•
•
•
pH:
7.51 (high)
pCO2: 25 mmHg (low)
pO2
35 mmHg (very low)
HCO3: 22 mEq/L (normal)
– What is the diagnosis? Is he compensating?
What caused the problem?
125
Case Study 12
9 year old w/hx of asthma, audibly wheezing x 1 week,
has not slept in 2 nights; presents sitting up and using
accessory muscles to breathe w/audible wheezes
•
•
•
•
pH:
7.51 (high)
pCO2: 25 mmHg (low)
pO2
35 mmHg (very low)
HCO3: 22 mEq/L (normal)
– Uncompensated respiratory alkalosis with
severe hypoxia due to asthma exacerbation
126
Case Study 13
7 year old post-op presenting with chills, fever and
hypotension
•
•
•
•
pH:
pCO2:
pO2:
HCO3:
7.25 (low)
36 mmHg (normal)
55 mmHg (low)
10 mEq/L (low)
– What is the diagnosis? Is he compensating?
What caused the problem?
127
Case Study 13
7 year old post-op presenting with chills, fever and
hypotension
•
•
•
•
pH:
pCO2:
pO2:
HCO3:
7.25 (low)
36 mmHg (normal)
55 mmHg (low)
10 mEq/L (low)
– Uncompensated metabolic acidosis due to
low perfusion state and hypoxia causing
increased lactic acid
128