Alpha-1 Lung Vocabulary
ABG Arterial Blood Gases
Arterial Blood Gas analysis typically measures:
pH Acidity
pCO2 Partial pressure of carbon dioxide
pO2 Partial pressure of oxygen
CO2 Carbon dioxide content
BE (base excess) The loss of buffer base to neutralize acid
And may include:
SO2 Oxygen saturation
These measurements are often used to evaluate oxygenation of the tissues and pulmonary function. Normal Adult Arterial Values Normal Adult Venous Values pH..................................7.35-7.45 pH................................7.31-7.41 pCO2..............................35-45 torr pCO2............................41-51 torr pO2...................................>79 torr pO2..............................30-40 torr CO2............................23-30 mmol/L CO2.........................23-30 mmol/L Base Excess/Deficit............± 3 mEq/L Base Excess/Deficit.........± 3 mEq/L SO2.......................................>94% SO2......................................75%
Blood Gas Abbreviations
BE Base Excess (positive number) or Base Deficit (negative number) HCO3 Bicarbonate H2CO3 Carbonic Acid pO2 Partial Pressure of Oxygen paO2 Partial Pressure of Oxygen in Arterial Blood pvO2 Partial Pressure of Oxygen in Venous Blood pCO2 Partial Pressure of Carbon Dioxide paCO2 Partial Pressure of Carbon Dioxide in Arterial Blood pvCO2 Partial Pressure of Carbon Dioxide in Venous Blood SO2 Oxygen Saturation SaO2 Oxygen Saturation in Arterial Blood SvO2 Oxygen Saturation in Venous Blood TCO2 Total Carbon Dioxide Content
pH Acidity
is a measurement of the acidity of the blood, reflecting the number of hydrogen ions present. Lower numbers mean more acidity; higher number mean more alkalinity.(1) pH is elevated (more alkaline, higher pH) with pH is decreased (more acid, lower pH) with Hyperventilation Strenuous physical exercise Anxiety, pain Obesity Anemia Starvation Shock Diarrhea Some degrees of Pulmonary disease Ventilatory failure Some degrees of Congestive heart failure More severe degrees of Pulmonary Disease Myocardial infarction More severe degrees of Congestive Heart Failure Hypokalemia (decreased potassium) Pulmonary edema Gastric suctioning or vomiting Cardiac arrest Antacid administration Renal failure Aspirin intoxication Lactic acidosis Ketoacidosis in diabetes
pCO2 Partial Pressure of Carbon Dioxide
pCO2 reflects the the amount of carbon dioxide gas dissolved in the blood. Indirectly, the pCO2 reflects the exchange of this gas through the lungs to the outside air.
Two factors each have a significant impact on the pCO2:
1. How rapidly and deeply the individual is breathing
Someone who is hyperventilating will "blow off" more CO2, leading to lower pCO2 levels
Someone who is holding their breath will retain CO2, leading to increased pCO2 levels
2. The lungs capacity for freely exchanging CO2 across the alveolar membrane
With pulmonary edema, there is an extra layer of fluid in the alveoli that interferes with the lungs' ability to get rid of CO2. This leads to a rise in pCO2.
With an acute asthmatic attack, even though the alveoli are functioning normally, there may be enough upper and middle airway obstruction to block alveolar ventilation, leading to CO2 retention.(1) Increased pCO2 is caused by Decreased pCO2 is caused by Pulmonary edema Hyperventilation Obstructive lung disease Hypoxia Anxiety Pregnancy Pulmonary Embolism* * This leads to hyperventilation, a more important consideration than the embolized/infarcted areas of the lung that do not function properly. In cases of massive pulmonary embolism, the infarcted or non-functioning areas of the lung assume greater significance and the pCO2 may increase.
pO2 Partial Pressure of Oxygen
pO2 reflects the amount of oxygen gas dissolved in the blood. It primarily measures the effectiveness of the lungs in pulling oxygen into the blood stream from the atmosphere.(1) Elevated pO2 levels are associated with Decreased pO2 levels are associated with Increased oxygen levels in the inhaled air Decreased oxygen levels in the inhaled air Polycythemia Anemia Heart decompensation Chronic obstructive pulmonary disease Restrictive pulmonary disease Hypoventilation
CO2 Carbon dioxide
CO2 is a measurement of all the CO2 in the blood.
Most of this is in the form of bicarbonate (HCO3), controlled by the kidney. A small amount (5%) of the CO2 is dissolved in the blood, and in the form of soluble carbonic acid (H2CO3).
For this reason, changes in CO2 content generally reflect such metabolic issues as renal function and unusual losses (diarrhea). Respiratory disease can ultimately effect CO2 content, but only slightly and only if prolonged.(1) Elevated CO2 levels are seen in Decreased CO2 levels are seen in Severe vomiting Renal failure or dysfunction Use of mercurial diuretics Severe diarrhea COPD Starvation Aldosteronism Diabetic Acidosis Chlorthiazide diuretic use
BE Base Excess or Base Deficit
Whenever there is an accumulation of metabolically-produced acids, the body attempts to neutralize those acids to maintain a constant acid-base balance. This neutralizing is achieved by using up various "buffering" compounds in the blood stream, to bind the acids, disallowing them from contributing to more acidity. About half of these buffering compounds come from HCO3, and the other half from plasma and red blood cell proteins and phosphates. The words "base deficit" and "base excess" are equivalent and are generally used interchangeably. The only difference is that base deficit is expressed as a positive number and base excess is expressed as a negative number. A "Base Deficit" of 10 means that 10 mEqu/L of buffer has been used up to neutralize metabolic acids (like lactic acid). Another way to say the same thing would be the "Base Excess is minus 10." (1) Negative values of BE may indicate Positive values of BE may indicate Lactic Acidosis Loss of buffer base Ketoacidosis Hemorrhage Ingestion of acids Diarrhea Cardiopulmonary collapse Ingestion of alkali Shock
SO2 Oxygen saturation
SO2 measures the percent of hemoglobin which is fully combined with oxygen.
While this measurement can be obtained from an arterial or venous blood sample, it's major attractive feature is that it can be obtained non-invasively and continuously through the use of a "pulseoximeter."
Normally, oxygen saturation on room air is in excess of 95%. With deep or rapid breathing, this can be increased to 98-99%. While breathing oxygen-enriched air (40% - 100%), the oxygen saturation can be pushed to 100%.(1) SO2 will fall if SO2 will rise if Inspired oxygen levels are diminished, such as at increased altitudes. Deep or rapid breathing occurs Upper or middle airway obstruction exists (such as during an acute asthmatic attack) Inspired oxygen levels are increased, such as breathing from a 100% oxygen source Significant alveolar lung disease exists, interfering with the free flow of oxygen across the alveolar membrane.
6 Easy Steps to Accurately Interpret ABGs
What is an ABG?
ABG is the abbreviation for Arterial Blood Gas. This is a measure of certain characteristics of arterial blood. The first is the pH. The pH designates the acid-base balance of arterial blood. Ideally, blood pH would be 7.4. However, many variables affect the pH of the blood. If one of these variables forces the pH too far from 7.4, the cells of the body will be unable to function properly. Therefore, the body has two main buffering systems: the respiratory system and the renal system. These systems generally balance each other to provide an optimum environment within the body. They can be thought of as being on either side of a seesaw. When one side moves in one direction the other will move in the opposite direction to maintain balance.
The balancing component of the respiratory system is the dissolved carbon dioxide (CO2) that is produced by cellular processes and removed by the lungs. The balancing component of the renal system is the dissolved bicarbonate (HCO3) produced by the kidneys. The kidneys also help control pH by eliminating hydrogen (H+) ions. The way the two systems interact is through the formation of carbonic acid (H2CO3). Movement through the carbonic acid system is fluid and constant. What this means is that water (H2O) can combine with CO2 and form carbonic acid. If necessary, carbonic acid (H2CO3) can then break up to form hydrogen ions (H+) and bicarbonate (HCO3). This balance works in both directions. By balancing back and forth, pH balance is achieved. The respiratory system balances pH by manipulating the CO2 level. Increasing or decreasing respiratory rate does this. Faster and deeper breathing “blows off” more CO2. Conversely, slower and shallower breathing “retains more CO2. The renal system balances pH by producing HCO3 or by eliminating hydrogen ions (H+).
The renal system will reflect changes in metabolic activity within the body. For example, a patient who becomes hypoxic will undergo anaerobic metabolism, which produces lactic acid. The production of lactic acid will bind or use up available HCO3 and will be manifested by a decrease in the HCO3 level. Therefore, the HCO3 level is an indicator of metabolic acid-base balance.
Balance must always be achieved by the opposite system. If an adult were on one side of a seesaw and a small child on the other, we would expect the child’s side of the seesaw to go up and the adult’s side to go down. We cannot make the child go down by adding another adult to the adult’s side. In the same way, our body regulates pH by using the opposite system to balance pH. So if the pH is out of balance because of a respiratory disorder, it will be the renal system that makes the corrections to balance the body pH. Conversely, if the renal system is to blame for the pH disorder, the respiratory system will have to compensate. This process is called compensation. Compensation may not always be complete. Complete compensation returns the pH balance to normal. There are times when the imbalance is too large for compensation to return the pH to normal. This is called incomplete compensation.
System causing pH imbalance Compensating system Respiratory (pCO2) Metabolic (HCO3) Metabolic (HCO3) Respiratory (pCO2)
OK, let’s review what we’ve done so far… • ABGs measure blood acid-base balance • Carbon dioxide (CO2) is the respiratory component in acid-base balance • Bicarbonate (HCO3) is the renal component in the acid-base balance • CO2 and HCO3 work through carbonic acid to balance pH • Compensation for pH imbalance comes from the opposite system • Compensation attempts to bring pH back to normal
There are two sets of information that can be obtained from an ABG. The first is the blood acid-base balance, and the second is blood oxygenation. The measures of blood oxygenation are the oxygen (pO2) and the oxygen saturation (O2 sat). The dissolved oxygen in the blood is called the pO2 and is measured in mmHg. The second measure is the oxygen saturation, which represents the amount of hemoglobin sites with attached oxygen. Oxygen saturation is expressed as a percentage of the total sites that have hemoglobin. The O2 sat can be continually monitored non-invasively with pulse oximetry.
An ABG can detect four main states other than normal. These are: metabolic acidosis, metabolic alkalosis, respiratory acidosis, and respiratory alkalosis. Use the "6 Easy Steps to ABG Analysis" to help determine which state exists in your patient.
The Six Steps to ABG Analysis
In order for our analysis to be effective, notes will have to be written next to the results on our lab slip. Alternately, the ABG results can be transcribed onto another paper for analysis (see example one below). 1. The first step in analyzing ABGs is to look at the pH. Normal blood pH is 7.4, plus or minus 0.05, forming the range 7.35 to 7.45. If blood pH falls below 7.35 it is acidic. If blood pH raises above 7.45, it is alkalotic. If it falls into the normal range, label what side of 7.4 it falls on. Lower than 7.4 is normal/acidic, higher than 7.4 is normal/alkalotic. Label it. 2. The second step is to examine the pCO2. Normal pCO2 levels are 35-45mmHg. Below 35 is alkalotic, above 45 is acidic. Label it. 3. The third step is to look at the HCO3 level. A normal HCO3 level is 22-26 mEq/L. If the HCO3 is below 22, the patient is acidotic. If the HCO3 is above 26, the patient is alkalotic. Label it. 4. Next match either the pCO2 or the HCO3 with the pH to determine the acid-base disorder. For example, if the pH is acidotic, and the CO2 is acidotic, then the acid-base disturbance is being caused by the respiratory system. Therefore, we call it a respiratory acidosis. However, if the pH is alkalotic and the HCO3 is alkalotic, the acid-base disturbance is being caused by the metabolic (or renal) system. Therefore, it will be a metabolic alkalosis. 5. Fifth, does either the CO2 or HCO3 go in the opposite direction of the pH? If so, there is compensation by that system. For example, the pH is acidotic, the CO2 is acidotic, and the HCO3 is alkalotic. The CO2 matches the pH making the primary acid-base disorder respiratory acidosis. The HCO3 is opposite of the pH and would be evidence of compensation from the metabolic system. 6. Finally, evaluate the PaO2 and O2 sat. If they are below limits there is evidence of hypoxemia.
Now let’s try an example:
pH 7.30 acidotic pCO2 58 acidotic pO2 50 low O2 Sat. 80% low HCO3 26 normal Step 1. The pH is acidotic Step 2. The CO2 is acidotic Step 3. The HCO3 is normal Step 4. The CO2 matches the pH, therefore the imbalance is respiratory acidosis Step 5. The HCO3 is normal, therefore there is no compensation Step 6. The PaO2 and O2 sat are low indicating hypoxemia
The full diagnosis for this ABG is: Uncompensated respiratory acidosis.
Case Studies
Additional ABG Practice Examples:
1. Mr. Frank is a 60 year-old with pneumonia. He is admitted with dyspnea, fever, and chills. His blood gas is below: pH 7.28 CO2 56 PO2 70 HCO3 25 SaO2 89%
What is your interpretation?
What interventions would be appropriate for Mr. Frank?
2. Ms. Strauss is a 24 year-old college student. She has a history of Crohn's disease and is complaining a of a four day history of bloody-watery diarrhea. A blood gas is obtained to assess her acid/base balance: pH 7.28 CO2 43 pO2 88 HCO3 20 SaO2 96%
What is your interpretation?
What interventions would be appropriate for Ms. Strauss?
3. Mr. Karl is a 80 year-old nursing home resident admitted with urosepsis. Over the last two hours he has developed shortness of breath and is becoming confused. His ABG shows the following results: pH 7.02 CO2 55 pO2 77 HCO3 14 SaO2 89%
What is your interpretation?
What interventions would be appropriate for Mr. Karl?
4. Mrs. Lauder is a thin, elderly-looking 61 year-old COPD patient. She has an ABG done as part of her routine care in the pulmonary clinic. The results are as follows: pH 7.37 CO2 63 pO2 58 HCO3 35 SaO2 89%
What is your interpretation?
What interventions would be appropriate for Mrs. Lauder?
5. Ms. Steele is a 17 year-old with intractable vomiting. She has some electrolyte abnormalities, so a blood gas is obtained to assess her acid/base balance. pH 7.50 CO2 36 pO2 92 HCO3 27 SaO2 97%
What is your interpretation?
What interventions would be appropriate for Ms. Steele?
6. Mr. Longo is a 18 year-old comatose, quadriplegic patient who has the following ABG done as part of a medical workup: pH 7.48 CO2 22 pO2 96 HCO3 16 SaO2 98%
What is your interpretation?
What interventions would be appropriate for Mr. Longo?
7. Mr. Casper is a 55 year-old with GERD. He takes about 15 TUMS antacid tablets a day. An ABG is obtained to assess his acid/base balance: pH 7.46 CO2 42 pO2 86 HCO3 29 SaO2 97%
What is your interpretation?
What interventions would be appropriate for Mr. Casper?
8. Mrs. Dobins is found pulseless and not breathing this morning. After a couple minutes of CPR she responds with a pulse and starts breathing on her own. A blood gas is obtained: pH 6.89 CO2 70 pO2 42 HCO3 13 SaO2 50%
What is your interpretation?
What interventions would be appropriate for Mrs. Dobins?
9. After resuscitating Mrs. Dobins, you find Mr. Simmons to be in respiratory distress. He has a history of Type-I diabetes mellitus and is now febrile. (Wow, what a bad day). His ABG shows: pH 7.00 CO2 59 pO2 86 HCO3 14 SaO2 91%
What is your interpretation?
What interventions would be appropriate for Mr. Simmons?
10. Ms. Berth was admitted for a drug overdose. She is being mechanically ventilated and a blood gas is obtained to assess her for weaning. The results are as follows: pH 7.54 CO2 19 pO2 100 HCO3 16 SaO2 98%
What is your interpretation?
What interventions would be appropriate for Ms. Berth?
Answers:
Answers to the ABG Practice Examples:
Mr. Frank has an uncompensated respiratory acidosis with hypoxemia as a result of his pneumonia. This is due to inadequate ventilation and perfusion. The treatment goals for Mr. Frank would be to improve both ventilation and oxygenation. Ventilation may improve with the use of bronchodilators and pulmonary hygiene. If not, Mr. Frank may require CPAP, BiPAP, or intubation and mechanical ventilation. Oxygen therapy should consist of only the minimal amount necessary to increase his oxygen saturation to normal (95%).
Ms. Strauss has an uncompensated metabolic acidosis. This is due to excessive bicarbonate loss from her diarrhea. It is interesting to note that she has no compensation. Normally, the respiratory center compensates quickly for metabolic disorders. However, in Ms. Strauss' case she would have to hyperventilate in order to compensate. This may not be possible in her present condition, and should be evaluated further. Treatment would consist of control of the diarrhea and bowel rest. It should not be necessary to administer bicarbonate in her present condition.
Mr. Karl has a metabolic and respiratory acidosis with hypoxemia. The metabolic acidosis is caused by his sepsis. The respiratory acidosis is secondary to respiratory failure. This presentation of sepsis and associated respiratory failure is consistent with ARDS. Treatment must be aggressive, because his acidosis is severe. His respiratory status needs to be stabilized, and would probably require mechanical ventilation. If hypotension exists, aggressive fluid and vasopressor support would be warranted. This patient is at high risk for further complications and should be managed in an ICU. Bicarbonate should not be administered until the underlying sepsis and respiratory failure is treated.
Mrs. Lauder has a fully-compensated respiratory acidosis with hypoxemia. Full compensation is evidenced by the normal pH in spite of her acid/base disorder. This is her baseline and doesn't require treatment.
Ms. Steele has an uncompensated metabolic alkalosis. This is due to vomiting that results in excessive loss of stomach acid. Treatment consists of fluids, anti-emetics, and management of her electrolyte disorders.
As a result of his neurologic condition, Mr. Longo has chronic hyperventilation syndrom. His blood gas shows a fully-compensated respiratory alkalosis. This is a chronic and stable condition for him and probably requires no treatment.
Mr. Casper has overmedicated himself with TUMS, effectively absorbing too much stomach acid. His ABG shows a partially-compensated metabolic alkalosis. Treatment consists of better control of his GERD, possibly with H2-blockers (Pepcid®) or proton-pump inhibitors (Prilosec®).
Mrs. Dobins has a severe metabolic and respiratory acidosis with hypoxemia. The metabolic component comes from her decreased perfusion, and the respiratory component comes from inadequate ventilation. Treatment would consist of intubation, mechanical ventilation, blood pressure and circulatory support.
Wow, Mr. Simmons too! He, like Mrs. Dobbins, has a metabolic and respiratory acidosis with hypoxemia. However, the cause is different. His respiratory acidosis is probably the result of pneumonia (also causing the fever). His pneumonia has altered his glucose metabolism, causing hyperglycemia and diabetic ketoacidosis. Treatment should be three-pronged: 1) increase his oxygenation with oxygen therapy; CPAP, BiPAP, or mechanical ventilation, 2) treat his pneumonia with antibiotics, antipyretics, and good pulmonary hygiene, and 3) administer insulin and IV fluids to decrease his blood glucose and treat his DKA.
Mrs. Berth is being overventilated which caused a partially-compensated respiratory alkalosis. Treatment would consist of decreasing ventilatory support, or trying other modes of ventilation to decrease her minute volume. She will be difficult to wean from the ventilator in this condition due to the metabolic compensation. Therefore attempts should be made to allow her CO2 to increase back to normal before weaning can proceed.
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