Objectives:

1. Identify the components of the ABG and their normal ranges.
2. Interpret ABG values and determine the acid base abnormality given.
3. Identify the major causes of acid base abnormalities.
4. Describe symptoms associated with acid base abnormalities.
5. Describe interventions to correct acid base abnormalities.
6. Identify the acceptable O2 level per ABG and Pulse Oxymetry.
7. Identify four causes of low PaO2.

      The body tries to maintain homeostasis with Acid-Base Balance using Acids
      and Bases. (The Alkaline part of your ABG) to counter balance each other.
      The body enzymes cannot work outside of this balance.
      The ABG is an Arterial Blood measurement of this Acid-Base status.

  A.  (Acid) The Respiratory System

        CO2 is a volatile acid.

1. If you increase your respiratory rate (hyperventilation) you "blow off" CO2 (acid) therefore decreasing your CO2 (acid)--giving you Alkalosis.

2. If you decrease your respiratory rate (hypoventilation) you retain CO2 (acid) therefore increasing your CO2 (acid)--giving you Acidosis.

  B.  (Base) The Renal System

      The Kidneys rid the body of nonvolatile acids (H+=Hydrogen ions) and maintain a constant HCO3 (bicarbonate = base).

1. You have Acidosis when you have excess H+ and decreased HCO3 (base) causing a decrease in pH.
          The Kidneys try to adjust for this by excreting H+ and retaining HCO3 (base).
          The Respiratory System will try to compensate by increasing ventilation to blow off CO2 (acid) and therefore decrease the Acidosis.

3. You have Alkalosis when H+ decreases and you have excess (or increased) HCO3 (base).
          The Kidneys excrete HCO3 (base) and retain H+ to compensate.
          The Respiratory System tries to compensate with hypoventilation to retain
          CO2 (acid) to decrease the Alkalosis.

4. There are other "buffers" involved here--like Carbonic Acid, Ammonia, and Protein. (Hgb)

C.  Compensation

      The Respiratory System can effect a change in 15-30 minutes.
      The Renal System takes several hours to days to have an effect.
      II.  The Big Four

  A.  Respiratory Acidosis     pH < 7.35 (Normal = 7.35-7.45)
                                            CO2 > 45 (Normal = 35-45)

    1. Causes:

     --Hypoventilation

      a. Depression of the Respiratory Center (sedatives, narcotics, drug overdose, CVA, cardiac arrest, MI)
      b. Respiratory muscle paralysis (spinal cord injury, Guillian-Barre, paralytics)
      c. Chest wall disorders (flail chest, pneumothorax)
      d. Disorders of the lung parenchyma (CHF, COPD, pneumonia, aspiration, ARDS)
      e. Alteration in the function of the abdominal system (distention)

    2. Signs and Symptoms:

     a. CNS depression (decreased LOC)
     b. Muscle twitching which can progress to convulsions
     c. Dysrhythmias, tachycardia, diaphoresis (related to hypoxia secondary to hypoventilation)
     d. Palpitations
     e. Flushed skin
     f. Serum electrolyte abnormalities including elevated K+ (K+ leaves the cell to replace the H+ buffers leaving the cell)

3. Treatment:

     a. Physically stimulate the pt to improve ventilation
     b.Vigorous pulmonary toilet (chest PT, coughing and deep breathing, inspirometer, respiratory treatments with Bronchodilators)
     c. Mechanical Ventilation (to increase the respiratory rate and tidal volume
     d. Reversal of sedatives and narcotics
     e. Antibiotics for infections
     f.  Diuretics for fluid overload
     (Note: beware of NAHCO3--Sodium Bicarbonate--can overcompensate and cause Metabolic Alkalosis. Also, if pt has been hypoxic and this is a Lactic
      Acidosis--NAHCO3 can be dangerous)
 

  B. Respiratory Alkalosis        pH > 7.45
                                               CO2  < 35

   1. Causes:

    --Alveolar Hyperventilation

    a.   Psychogenic (fear, pain, anxiety)
    b.   CNS stimulation (brain injury, ETOH, early salicylate poisoning, brain tumor)
    c.   Hypermetabolic states (fever, thyrotoxicosis)
    d.   Hypoxia (high altitude, pneumonia, heart failure, pulmonary embolism)
    e.   Mechanical overventilation (ventilator rate too fast)

    2. Signs and Symptoms:

     a. Headache
     b. Vertigo
     c. Paresthesias (numb fingers/toes/circumoral, carpal pedal spasms and tetany)
     d. Tinnitus (ringing in the ears)
     e. Electrolyte abnormalities (decreased Ca+, K+)

    3. Treatment:  (treat the underlying cause)

     a. Sedatives or analgesics
     b. Correction of hypoxia (possible diuretics, mechanical ventilation to also decrease respiratory rate and decrease the tidal volume)
         (Note: Brain Injury pt. may need hyperventilation)
     c. Antipyretics for fever
     d. Treat hyperthyroidism
     e. Breathe into a paper bag for hyperventilation

  C. Metabolic Acidosis        pH < 7.35
                                           HCO3 < 22  (normal = 22 – 26)

   1. Causes:

    --Increased H+, excess loss of HCO3

    a. Overproduction of organic acids (starvation, ketoacidosis, increased catabolism)
    b.   Impaired renal excretion of acid (Renal Failure)
    c.   Abnormal loss of HCO3 (diarrhea, biliary fistula, Diamox)
    d.   Ingestion of acid (salicylate overdose, oral anti-freeze)

   2. Signs and Sypmtoms:

    a. CNS depression (confusion to coma)
    b. Cardiac Dysrhythmias (elevated T wave, wide QRS to Ventricular Standstill)
    c. Electrolyte abnormalities (elevated K+, Cl-, Ca+)
    d. Flushed skin (arteriolar dilitation)
    e. Nausea

   3. Treatment:  (treat the underlying cause)

    a. NAHCO3 (Sodium Bicarbonate) based on ABGs only and with caution
    b. IV fluids and Insulin for DKA
    c. Dialysis for Renal Failure
    d. Antibiotics, increased nutrition for tissue catabolism
    e. Increase cardiac output and tissue perfusion for low C.O. states
    f.  Rehydrate, monitor I & O
    g. Treat Dysrhythmias, support hemodynamic and respiratory status

  D. Metabolic Alkalosis            pH > 7.45
                                                HCO3 > 26

1. Causes:

 --Loss of H+ or increased HCO3

     a. Large losses of gastric contents (vomiting, NG suction)
     b. Loss of K+ (diarreah, vomiting)
     c. Ingestion of large amounts of bicarbonate (antacids, resuscitation)
     d. Prolonged use of diuretics (distal tubule lose ability to reabsorb Na+ and Cl-  therefore Na+, Cl-, K+,
         Ammonia are lost in the urine and these bind with H+)
      (Note: al-K+-low-sis means K+ value is low when pt is alkalotic)

    2. Signs and Symptoms:  (similar to the associated disease process)

     a. Diaphoresis
     b. Nausea and Vomiting
     c. Increase neuromuscular excitability (Ca+ binds with protein)
     d. Shallow breathing (Respiratory Compensation)
     e. EKG changes (increased QT, Sinus Tachycardia)
     f.  May also see confusion progressing to lethargy to coma
     g. Electrolyte abnormality (decreased Ca+, normal or decreased K+, increased Base Excess on the ABG)

    3. Treatment:  (treat the underlying cause)

     a. Replace KCL losses in 0.9% NaCl (rehydrates and increases HCO3 excretion)
     b.   Diamox (Acetazolamide) (increases HCO3 excretion)
     c.   Monitor neuro status, re-orient, seizure precautions, monitor I & O
 
 

*based on a concept by Laura Gasparis Vonfrolio, RN,PHD

Once upon a time there was a land known as ABG.
Everyone there was related with only a limited number of names for the population.
They were also very polite and had their own etiquette for learning each other’s names.
Now I would like to introduce you to your patient. Let’s figure out what her name is:
All of the people in the land of ABG have a  first name, a middle name, and a last name. You just have to look at them one name at a time.
 

A. The Last Name

1.   First, look at her pH. (Normal = 7.35-7.45)
2. If her pH is < (less than) 7.35; her last name is ACIDOSIS.
3. If her pH is > (greater than) 7.45; her last name is ALKALOSIS.

(Note:  To be an absolutely perfect last name--her pH needs to be 7.40. So, keep in mind, that if her pH is 7.35-7.39--she’s thinking about marrying into the ACIDOSIS family.  If her pH is 7.41-7.45--she’s thinking about marrying into the ALKALOSIS family.)
 

B. The First Name

 Now that you know your patient’s last name, you would like to also learn her first name.

1. Look at her pH again.
2. If it is 7.35-7.45 (normal) then her first name is COMPENSATED.
3. If the pH is <7.35 or >7.45--then her first name is UNCOMPENSATED.
 

C. The Middle Name

    Now that you know your patient’s first and last name, you would like to know
    her middle name.

    (Name Alert: These people are all related and you have many patients with the
    same first and last name. A middle name will give you more information to go
    on.)
 

1. First you need to look at the CO2 and HCO3.
      (Remember: Normal CO2 = 35-45.  Normal HCO3 = 22-26)
2. The middle name will either be Respiratory or Metabolic.
3. If the CO2 is <35 or >45--her middle name is RESPIRATORY.
4. If the HCO3 is <22 or >26--her middle name is METABOLIC.
 

D. The Family Feud

1. pH and HCO3 are "kissin’ cousins"--they like to go in the same direction.
2. But CO2 is the "black sheep"--pH runs the opposite direction when it sees him coming.

       Therefore:

3. Decreased pH with Decreased HCO3 = ACIDOSIS.
4. Increased pH with Increased HCO3 = ALKALOSIS.
5. Decreased pH with Increased CO2 = ACIDOSIS.
6. Increased pH with Decreased CO2 = ALKALOSIS.
 
 

A. Respiratory Therapy gives you an ABG with the following numbers:

pH  = 7.60  CO2 = 30  HCO3 = 22

1. What is her last name?
(Her pH is >7.45 so her last name is ALKALOSIS.)

2. What is her first name?
(Her pH is not in the normal range of 7.35-7.45 so her first name is UNCOMPENSATED.)

3. What is her middle name?
(Her CO2 is <35 and her HCO3 is normal so her middle name is RESPIRATORY.)

4. You have now been introduced to UNCOMPENSATED RESPIRATORY ALKALOSIS.
 
 

B. pH = 7.31  CO2 = 50  HCO3 = 25

1. What is her last name?
(Her pH is <7.35 so her last name is ACIDOSIS.)

2. What is her first name?
(Her pH is not in the normal range so her first name is UNCOMPENSATED.)

3. What is her middle name?
(Her CO2 is >45 and her HCO3 is normal so her middle name is RESPIRATORY.)

5. You have now been introduced to UNCOMPENSATED RESPIRATORY ACIDOSIS.
 
 

C.  pH = 7.55  CO2 = 40  HCO3 = 30

1. What is her last name?
(Her pH is >7.45 so her last name is ALKALOSIS.)

2. What is her first name?
(Her pH is not in the normal range so her first name is UNCOMPENSATED.)

3. What is her middle name?
(Her CO2 is normal but her HCO3 is >26 so her middle name is METABOLIC.)

4. You have now been introduced to UNCOMPENSATED METABOLIC ALKALOSIS.
 
 

D. pH = 7.35  CO2 = 45  HCO3 = 21

1. What is her last name?
(Her pH is normal--but it is <7.40. So her last name might be ACIDOSIS. She hasn’t decided if she wants to get married yet.)

2. What is her first name?
(Her pH is normal so her first name is COMPENSATED.)

3. What is her middle name?
(Her CO2 is normal but her HCO3 is <22. So her middle name is METABOLIC. Note:  Because she has a middle name--she has decided to get married. Talk about a good reason to marry!)

4. You have been introduced to COMPENSATED METABOLIC ACIDOSIS.
 
 

E.  Now practice doing some yourself:

Click HERE  and a new window will open with practice problems.
 

F. Now try some harder ones:

In these ones, both the CO2 and the HCO3 are abnormal. Choose the middle name that is the same as the pH. (You can’t have a middle name in the Land of ABG unless you get married and can share a last name.)
Click HERE  and a new window will open with practice problems.

G. Now try some combined disorders:

Click HERE  and a new window will open with practice problems.
 
 

   Did you notice that I haven’t mentioned O2?  The O2 number has nothing to do with your acid-base ABG interpretation!

A. What does the PaO2 mean?

1. The O2 tells us if the patient has HYPOXEMIA (decreased oxygen in the blood).
2. Normal PaO2 = 80-100. (Hypoxemia = PaO2<80)
3. PaO2 assesses Perfusion (gas exchange).
4. PaCo2 asseses the adequacy of Ventilation (breathing pattern).
5. The PaO2 is very important in determining your patient’s oxygen status and needs—but it is not necessary in determining the Big Four.
 

B. What is saturation?

1. SaO2 (oxygen saturation) measures the percent of oxygen bound to hemoglobin. This tells weather the patient has HYPOXIA (decreased O2 in the tissues).
2. Normal SaO2 = Greater that 95%
3. Acceptable SaO2 will vary between MDs; but PaO2 dramatically drops when it is less that 92%.
4. This is a noninvasive measurement via pulse oxymetry and can be less accurate due to hypothermia, hypotension, hypovolemia, or vasoactives.
5. Note: In Carbon Monoxide Poisoning—the HGB is saturated with Carbon Monoxide. Although the patient is hypoxemic because there is no room on the HGB for O2 to be carried—the Saturation looks good because it can’t distinguish between the two.
 

C. What are some causes of low PaO2?

1. Hypoxic Hypoxia--there’s just not enough of a supply of O2
( COPD, pneumonia, ARDS, suffocation)

2. Anemic Hypoxia
There’s plenty of O2—but not enough HGB to carry it to the tissues

3. Stagnant Hypoxia
There may be enough O2 coming in and enough HGB to carry it--but the circulation is stagnant due to a decreased Cardiac Output. The O2 is not being adequately carried to the tissues.

 4.   Histotoxic Hypoxia
Poisoning like Carbon Monoxide or Cyanide. Either the blood can’t carry the O2 or the cells can’t receive the O2 from the blood.
 

VI. If you want contact hours--you have to take the test. 
(Just grin and bear it.)
 
 
 

VII.     You also need to fill out the evaluation to keep the state happy!
 
 
 

VIII.  Check out the "cheat sheet" after the test!