Acid Base Balance
Recognize the role that the lungs and kidneys play to maintain the pH within normal range
Classify the acid-base status of a blood gas
The two components of acid-base regulation (pH) are the respiratory and renal systems. The respiratory system eliminates acids by eliminating CO2 out of the lungs. The renal system maintains adequate level of buffers (mainly bicarbonate) and eliminates excess hydrogen ions (H+) or fixed acids. The respiratory and renal systems work together to maintain the pH within a narrow physiologic range.
Respiratory System
Ventilation is defined as the exchange of gases between the lung and the atmosphere. As atmospheric air is breathed into the alveoli, with practically no CO2, pulmonary capillary blood diffuses out its rich CO2 content. The result is CO2 equilibrium between the alveoli and the blood. The CO2 rich air is then exhaled and leaves the body. The resulting carbon dioxide level of the blood is reported in a blood gas analysis as the PaCO2.
Chemical receptors that monitor the CO2 and hydrogen ion levels in the blood are located in the pons medullary center of the brainstem and send signals to the respiratory system to adjust ventilation. The primary stimulus for the respiratory center of the brain is the CO2 level in the arterial blood. Since the adjustment of CO2 levels is a neurologic response, the respiratory rate and tidal volume will change immediately to keep carbon dioxide levels within the appropriate range.
Renal/Metabolic System
The bicarbonate level reported from blood gas analyzers is a calculated number. The blood gas machine utilizes the measured pH and PCO2 measurements to derive the HCO3- level. Since the blood gas HCO3- can be affected by addition or loss of fixed acids along with loss or increase of bicarbonate, it is a representation of metabolic effects. Any alteration of the bicarbonate level is considered a metabolic problem, whether it is related to the renal system’s ability to manage bicarbonate levels or the body’s addition of acid or base.
If either system is inadequate in helping to maintain the pH, the other system can compensate to help bring the pH within normal limits. Remember these two systems; working together must equalize acid elimination to acid production by the body. If one system fails the other must work harder to maintain the proper pH range.
ABG Interpretation standard naming format:
Uncompensated Respiratory Acidosis + oxygenation evaluation
Uncompensated Respiratory Alkalosis + oxygenation evaluation
Uncompensated Metabolic Acidosis + oxygenation evaluation
Uncompensated Metabolic Alkalosis + oxygenation evaluation
Compensated Respiratory Acidosis + oxygenation evaluation
Compensated Respiratory Alkalosis + oxygenation evaluation
Compensated Metabolic Acidosis + oxygenation evaluation
Compensated Metabolic Alkalosis + oxygenation evaluation
Partially compensated Respiratory Acidosis + oxygenation evaluation
Partially compensated Respiratory Alkalosis + oxygenation evaluation
Partially compensated Metabolic Acidosis + oxygenation evaluation
Partially compensated Metabolic Alkalosis + oxygenation evaluation
Mixed respiratory and metabolic acidosis + oxygenation evaluation
Mixed respiratory and metabolic alkalosis + oxygenation evaluation
Normal + oxygenation evaluation
Prompt
In your own words, provide detailed responses to the following:
First, list all the normal values for all the items on an ABG result.
There are eight different patients below. Analyzing and interpreting each of the acid-base examples below separately. Address their acid-base, ventilation, and oxygenation status.
Identify which system is causing the acid-base problem if applicable.
Explain how you arrived at each of the conclusions as if you are explaining it to one of your fellow students.
Give the ABG interpretation with the standard format as shown below.*
In the case of any ‘partially’ or ‘fully’ compensated result, describe how you came to determine that compensation was present.
If the case of any metabolic acidosis ABG results, determine if the anion gap should be calculated. Discuss the additional information that is provided by calculating the anion gap for ABG results that are metabolic acidosis. Include the formula for the anion gap.
Mr. Archer
pH = 7.25, PaCO2 = 55 mmHg, PaO2 = 100 mmHg, HCO3- = 22 mEq/L
Ms. Hass
pH = 7.53, PaCO2 = 44 mmHg, PaO2 = 95 mmHg, HCO3- = 30 mEq/L
Mr Galloway
pH = 7.25, PaCO2 = 40 mmHg, PaO2 = 90 mmHg, HCO3- = 16 mEq/L
Ms. Bray
pH = 7.53, PaCO2 = 25 mmHg, PaO2 = 100 mmHg, HCO3- = 23 mEq/L
Mr. Petty
pH = 7.33, PaCO2 = 48 mmHg, PaO2 = 78 mmHg, HCO3- = 24 mEq/L
Mrs. Kaufman
pH = 7.25, PaCO2 = 56 mmHg, PaO2 = 65 mmHg, HCO3- = 25 mEq/L
Mr. Holden
pH = 7.59, PaCO2 = 27 mmHg, PaO2 = 100 mmHg, HCO3- = 26 mEq/L
Ms. Hays
pH = 7.32, PaCO2 = 50 mmHg, PaO2 = 79 mmHg, HCO3- = 29 mEq/L
Requirements:
In your own words, submit your responses, in essay form, complete sentences, in at least 400 words on a Word document. Explain how you arrived at the interpretations. The word count does not include the prompt, title, cover page, citations/references, “quotations.” Grammar and spelling count. You must include at least two references (the course text being one of your references) to defend and support your position.
