renal physiology

Renal Physiology

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PART THREERenal Acid-Base Balance

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.

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pH

HCl

H + Cl-

H + Cl-

H + Cl-

H + Cl-

H + Cl-

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.

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pH

H + Cl-

H + Cl-

H + Cl-

H + Cl-

H + Cl-NaOH Na+ OH-

Na+ OH-

Na+ OH-

Na+ OH-

Acids and basis neutralize each other

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7

2

pH

Na+ Cl-

Na+ Cl-

Na+ Cl-Na+ Cl-

H+ OH- H2O

A change of 1 pH unit corresponds to a 10-fold change in hydrogen ion concentration

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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)

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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.

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Buffers

• “Buffers are solutions which can resist changes in pH when acid or alkali is added.”

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Acids must be buffered, transported away from cells, and eliminated from the body.

These are the most important buffers.

Phosphate: important renal tubular bufferHPO4

- + H+ H2PO4

Ammonia: important renal tubular bufferNH3 + H+ NH4

+

Proteins: important intracellular and plasma buffersH+ + Hb HHb

Bicarbonate: most important Extracellular buffer and is also another important renal tubular buffer.

H2O + CO2 H2CO3 H+ + HCO3 - 8

Phosphate

Bicarbonate

Proteins

Ammonia

Blood

Respiratory System

Bicarbonate

BicarbonatePhosphate

Kidneys

BUFFERING SYSTEMS BUFFERS USED BY THE BUFFERING SYSTEMS

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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 hydrogen-ion donor (acid) and hydrogen phosphate ions (HPO4

2-) as hydrogen-ion acceptor (base). These two ions are in equilibrium with each other as indicated by the chemical equation below.

H2PO4- H+ + HPO4

2-

• If additional hydrogen (H+) ions enter the cellular fluid, they are consumed in the reaction with HPO4

2-, and the equilibrium shifts to the left. If additional hydroxide (OH-) ions enter the cellular fluid, they react with H2PO4

-, producing HPO4

2-, and shifting the equilibrium to the right.

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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 (NH3) by breaking down glutamine (an amino acid).

• Ammonium (NH4) is secreted into the filtrate while the good products are reabsorbed.

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Ammonia as a Buffer

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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.

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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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Bicarbonate as a Buffer

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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):

carbonic anhydrase H2O + CO2 H2CO3 HCO3

(-) + H+

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Carbonic acid

Bicarbonate

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

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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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Phosphate

Bicarbonate

Proteins

Ammonia

Blood

Respiratory System

Bicarbonate

BicarbonatePhosphate

Kidneys

BUFFERING SYSTEMS BUFFERS USED BY THE BUFFERING SYSTEMS

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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 (in the brain stem) causes an increase in ventilation.

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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.

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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.

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Buffering is good, but it is a temporary solution. Excess acids and bases must be

eliminated from the body

H2O + CO2 H2CO3 H+ + HCO3 -

Lungs eliminate carbon dioxide

Kidneys can remove excess non-gas acids and bases

gas aqueous

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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

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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. 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

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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)

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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

HPO4-

NH3

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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

• 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

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What if your metabolism changed? • Metabolic acidosis • Bicarbonate levels

below normal (22 mEq/L)

• Metabolic alkalosis• bicarbonate ion levels higher

(greater than 26mEq/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

• 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

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Acidosis: pH < 7.4

- Metabolic: HCO3 -

- respiratory: pCO2

Alkalosis: pH > 7.4- Metabolic: HCO3 -

- respiratory: pCO2

How can you tell if the acid-base imbalance is from a kidney disorder

or a lung disorder?

Or normal

Or normal31

pH Imbalances

• Acidosis–Can be metabolic or respiratory

• Alkalosis–Can be metabolic or respiratory

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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).

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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+:

carbonic anhydrase CO2 H2CO3 HCO3

(-) + H+

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• 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.).

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• 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.

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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.

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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

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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.

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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.

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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.

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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).

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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.

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• Compensation

• The body will reduce the breathing rate, and the kidney will excrete bicarbonate.

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• 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.

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• Symptoms

• Irritability

• Muscle twitching

• Muscle cramps

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• 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).

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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.

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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.

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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.

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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.

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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)

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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.

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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.

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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+.

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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+

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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.

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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?

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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'

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Assessment Step 1

• If the pH is low, it is acidosis.

• If it is high, it is alkalosis.

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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.

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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.

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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.

• If one is normal and the other is too high or low, the patient is not compensating.

• You will never have a case where one is high and one is low.

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• 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.

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Arterial Blood Gas problems when compensation is present

Respiratory Acidosis

Acid

Metabolic Alkalosis

Base

Metabolic Acidosis

Acid

Respiratory Alkalosis

Base

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pH PCO2 HCO3

• 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.

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Acid

Metabolic Alkalosis

Base

Metabolic Acidosis

Acid


Base

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pH PCO2 HCO3

• 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.

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Acid

Metabolic Alkalosis

Base

Metabolic Acidosis

Acid


Base

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pH PCO2 HCO3

• 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.

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Acid

Metabolic Alkalosis

Base

Metabolic Acidosis

Acid


Base

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pH PCO2 HCO3

• 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.

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Acid

Metabolic Alkalosis

Base

Metabolic Acidosis

Acid


Base

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pH PCO2 HCO3

• 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.

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Acid

Metabolic Alkalosis

Base

Metabolic Acidosis

Acid


Base

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pH PCO2 HCO3

• 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.

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Acid

Metabolic Alkalosis

Base

Metabolic Acidosis

Acid


Base

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pH PCO2 HCO3

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!

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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.

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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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http://www.wikihow.com/Interpret-Blood-Gas-Results

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http://www.wikihow.com/Interpret-Blood-Gas-Results

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.

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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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Acid

Metabolic Alkalosis

Base

Metabolic Acidosis

Acid


Base

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pH PCO2 HCO3

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

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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 Acidosis2. Uncompensated Metabolic Acidosis3. Compensated Metabolic Alkalosis4. Uncompensated Respiratory Acidosis

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Answer

• The answer is #4

uncompensated respiratory acidosis

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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 Alkalosis2. Uncompensated Metabolic Acidosis3 Compensated Metabolic Acidosis4 Uncompensated Respiratory Acidosis 102

Answer

• Answer is #3

• Compensated Metabolic Acidosis

• (you know that by looking at the history. Diarrhea is like squirting baking soda into the toilet, so acid is left in the blood.)

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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. Compensated Respiratory Alkalosis 2. Uncompensated Metabolic Acidosis 3. Compensated Metabolic Acidosis 4. Uncompensated Metabolic Alkalosis

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Answer

• Answer is #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

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. Compensated Respiratory Alkalosis 2. Uncompensated Metabolic Acidosis 3. Compensated Respiratory Acidosis 4. Uncompensated Respiratory Alkalosis

108



Acid

Metabolic Alkalosis

Base

Metabolic Acidosis

Acid


Base

109

pH PCO2 HCO3

Answer

• Answer is #3

• Compensated Respiratory Acidosis

110

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 111

Answer

• Correct answer is #3

• Respiratory Acidosis

112

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? Note: Potassium makes blood more acidic.

1. metabolic acidosis

2. metabolic alkalosis

3. respiratory acidosis

4. 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. metabolic acidosis 2. metabolic alkalosis 3. respiratory acidosis 4. respiratory alkalosis

115

Answer


• Metabolic Acidosis

116

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

117

Answer


• Respiratory Alkalosis

118

Case Study 10

12 year old diabetic presents with Kussmaul breathing

• pH : 7.05 (low)

• pCO2: 30 mmHg (low)

• HCO3: 5 mEq/L (low)

• pO2: 108 mmHg (normal)– What is the diagnosis? Is he compensating?

What caused the problem?

119



Acid

Metabolic Alkalosis

Base

Metabolic Acidosis

Acid


Base

120

pH PCO2 HCO3

Answer12 year old diabetic presents with Kussmaul breathing

• pH : 7.05 (low)



• pO2: 108 mmHg (normal)– 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)



• pO2: 60 mmHg (low)– What is the diagnosis? Is he compensating?


122



Acid

Metabolic Alkalosis

Base

Metabolic Acidosis

Acid


Base

123

pH PCO2 HCO3

Case Study 11

17 year old w/severe kyphoscoliosis, admitted for pneumonia

• pH: 7.37 (normal)



• pO2: 60 mmHg (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)• HCO3: 22 mEq/L (normal)• pO2 35 mmHg (very low)

– 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)• HCO3: 22 mEq/L (normal)• pO2 35 mmHg (very low)

– 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: 7.25 (low)

• pCO2: 36 mmHg (normal)


• pO2: 55 mmHg (low)– What is the diagnosis? Is he compensating?


127

Case Study 13

7 year old post-op presenting with chills, fever and hypotension

• pH: 7.25 (low)

• pCO2: 36 mmHg (normal)


• pO2: 55 mmHg (low)– Uncompensated metabolic acidosis due to

low perfusion state and hypoxia causing increased lactic acid

128

renal physiology

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intracellular buffer

excess h

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important extracellular

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phosphate buffer systemit

h ohh2oa change