Download 10 Renal Acid Base Balance

Renal Acid Base Balance
Acid
•
•
Base
•
•
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.
A base is chemical that will remove hydrogen ions from the solution
Bicarbonate is an example of a base.
pH
A change of 1 pH unit corresponds to a 10-fold change in hydrogen ion concentration
Acids are being created constantly through metabolism
o Anaerobic respiration of glucose produces lactic acid
o Fat metabolism yields organic acids and ketone bodies
o Carbon dioxide is also an acid. Transporting CO2 as bicarbonate leads to a release of H+
(an acid)
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.
Buffers
• “Buffers are solutions which can resist changes in pH when acid or alkali is added.”
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Phosphate Buffer System
• It is mainly an intracellular 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 hydrogen-ion 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.
H2PO4H+ + HPO42• If additional hydrogen ions enter the cellular fluid, they are consumed in the reaction with
HPO42-, and the equilibrium shifts to the left. If additional hydroxide ions enter the cellular fluid,
they react with H2PO4-, producing HPO42-, and shifting the equilibrium to the right.
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.
• Ammonium is secreted into the filtrate while the good products are reabsorbed.
Protein buffer system
• Most important buffer system in body cells. Also important in the blood.
• There are 16 histidine 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.
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
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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):
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
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
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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 even if pH receptor is sensing high
pH.
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.
Renal Buffering System
• The renal buffer system uses bicarbonate, ammonium, and phosphate. 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.
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Buffering is good, but it is a temporary
solution. Excess acids and bases must be
eliminated from the body
gas
H2O + CO2
aqueous
CA
Lungs eliminate
carbon dioxide
H2CO3
H+ + HCO3 Kidneys can remove excess
non-volatile acids and
bases
Excessive Acids and Bases can cause
pH changes---denature proteins
• Normal pH of body fluids is 7.40
• Alkalosis or alkalemia – arterial blood pH rises above
7.45
• Acidosis or acidemia – arterial pH drops below 7.35
(physiological acidosis)
• For our class, we will stick to 7.40 as normal!
• Acidosis:
– too much acid
– Too little base
• Alkalosis
– Too much base
– Too little acid
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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.
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
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)
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
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What would happen if the respiratory
system had a problem with ventilation?
Respiratory Acidosis and Alkalosis
Normal PCO2 fluctuates between 35 and 45 mmHg
•
•
•
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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)
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•
•
•
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Respiratory Alkalosis (less
than 35mmHg- lowered CO2)
Hyperventilation syndrome/
psychological (fear, pain)
Overventilation on mechanical
respirator
Ascent to high altitudes
Fever
What if your metabolism changed?
• Metabolic acidosis
• Bicarbonate levels
below normal (22
mEq/L)
• Ingestion, infusion or
production of more
acids (alcohol)
• Salicylate overdose
(aspirin)
• Diarrhea (loss of
intestinal bicarbonate)
• 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 ingestion,
infusion, or renal
reabsorption of bases
• Loss of gastric juice
during vomiting
• Intake of stomach
antacids
• Diuretic abuse (loss of
H+ ions)
• Severe potassium
depletion
• Steroid therapy
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How can you tell if the acid-base
balance is from a kidney disorder
or a lung disorder?
Acidosis: pH < 7.4
- Metabolic:
- respiratory:
HCO3 pCO2
Alkalosis: pH > 7.4
- Metabolic: HCO3 - respiratory: pCO2
pH Imbalances
• Let’s summarize so we can apply this to clinical conditions!
• Acidosis
– Can be metabolic or respiratory
• Alkalosis
– Can be metabolic or respiratory
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).
• 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.
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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+:
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 were the breathing
muscles are damaged (causing decreased ventilation), airway obstruction, or lung disease
(pneumonia, cystic fibrosis, emphysema, etc.).
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.
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.
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
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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.
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.
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.
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.
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).
• 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.
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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.
Compensation
• The body will reduce the breathing rate, and the kidney will excrete bicarbonate.
• If there is no H+ excreted in the kidneys, therefore cannot reabsorb of bicarbonate and will be
excreted.
• 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.
• The pH can revert to normal from compensation in chronic respiratory alkalosis.
Symptoms
• Iirritability
• Muscle twitching
• Muscle cramps
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).
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.
• *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.
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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.
• 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.
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)
Treatment
• 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.
COMPENSATION OF PH IMBALANCES
• 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.
• 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+.
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+
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.
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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.
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.
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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?
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'
• If the pH is low, it is acidosis.
• If it is high, it is alkalosis.
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.
• 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, we need to evaluate it further. Go to step 3.
Assessment Step 3
• Determine if the body is attempting to compensate for the imbalance or not.
• If they are both high or both low, the patient is compensating. You can tell if it is respiratory
or metabolic by the pH (check the table at the bottom of this page)
•
You will never have a COMPENSATED case where one is high and one is low.
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 acidosis.
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•
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•
•
•
•
•
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•
•
•
•
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.
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 elevated.
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 low.
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.
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.
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.
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).
• Number Two:
• What is the 'primary problem?
• If the patient is acidotic with a PaC02 greater than 45 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 PaC02 less than 35 mmHg it is RESPIRATORY!
• If the patient is alkalotic with a HC03 greater than 26 mEq/L it is METABOLIC!
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•
Number Three:
Is the patient compensating?
• Are both components (HCO3 and PaCO2) shifting in the same direction?
• Up or down the continuum?
• Above or below the normal ranges?
If this is noted, you know that the patient’s buffering systems are functioning and are trying to bring the
acid-base balance back to normal.
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.
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Conditions
Metabolic
acidosis
pH
Low
Problem
Low HCO3
Compensation in
progress
Lungs
hyperventilate
(Kussmaul
breathing)
Lab Values if
compensating
Lab values if not
compensating
Blood pCO2 is
low
Blood pCO2 is
normal
Blood HCO3
Blood HCO3 is
levels will be high normal to low
Kidneys reabsorb
HCO3 and secrete
H+
Lungs increase
pCO2
(hypoventilation)
Metabolic
alkalosis
Respiratory
acidosis
Respiratory
alkalosis
High
Low
High
HCO3
High pCO2
High Low pCO2
Kidneys secrete
HCO3 and stop
secreting H+
Kidneys reabsorb
HCO3 and secrete
H+
Blood pCO2 is
high
Blood HCO3
levels will be low
Blood pCO2 is
high
Blood HCO3
levels will be high
Kidneys secrete
HCO3 and stop
secreting H+
Blood pCO2 is
low
Blood pCO2 is
normal
Blood HCO3 is
normal to high
Blood pCO2 is
high
Blood HCO3 is
normal
Blood pCO2 is low
Blood HCO3 is
normal
Blood HCO3
levels will be low
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.
Kussmaul Breathing
• Kussmaul breathing is a form of hyperventilation often associated with severe metabolic
acidosis, particularly diabetic ketoacidosis (DKA) but also renal failure.
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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. Compensated Respiratory Acidosis
2. Uncompensated Metabolic Acidosis
3. Compensated Metabolic Alkalosis
4. Uncompensated Respiratory Acidosis
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. Compensated Respiratory Alkalosis
2. Uncompensated Metabolic Acidosis
3 Compensated Metabolic Acidosis
4 Uncompensated Respiratory Acidosis
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 2hours) 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. Compensated Respiratory Alkalosis
2. Uncompensated Metabolic Acidosis
3. Compensated Metabolic Acidosis
4. Uncompensated Metabolic Alkalosis
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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. Compensated Metabolic Acidosis
2. Uncompensated Metabolic Acidosis
3. Uncompensated Respiratory Alkalosis
4. Uncompensated Respiratory Acidosis
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. Compensated Respiratory Alkalosis
2. Uncompensated Metabolic Acidosis
3. Compensated Respiratory Acidosis
4. Uncompensated Respiratory Alkalosis
Case Study 6
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?
1. metabolic acidosis
2. metabolic alkalosis
3. respiratory acidosis
4. respiratory alkalosis
Case Study 7
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?
1. metabolic acidosis
2. metabolic alkalosis
3. respiratory acidosis
4. respiratory alkalosis
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. metabolic acidosis
2. metabolic alkalosis
3. respiratory acidosis
4. respiratory alkalosis
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Case Study 9
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?
1. metabolic acidosis
2. metabolic alkalosis
3. respiratory acidosis
4. respiratory alkalosis
Case Study 10
12 year old diabetic presents with Kussmaul breathing
• pH
:
7.05 (low)
• pCO2: 12 mmHg (very low)
• pO2:
108 mmHg (normal)
• HCO3: 5 mEq/L (low)
– Compensating metabolic acidosis without hypoxemia due to ketoacidosis
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
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 breath 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
Case Study 13
7 year old post op presenting with chills, fever and hypotension
• pH:
7.25 (low)
• pCO2: 32 mmHg (high)
• pO2:
55 mmHg (low)
• HCO3: 10 mEq/L (low)
– Uncompensated metabolic acidosis due to low perfusion state and hypoxia causing increased
lactic acid
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