WGU D236 UNDERSTANDING ACID-BASE IMBALANCES: CASE STUDIES
IN RESPIRATORY
Patho study pages
CASE STUDY 1
Patient A is enduring an asthma attack and is brought into the emergency department. The patient’s vital
signs are: Temp: 98.4°F, Pulse: 110 beats/min, Resp rate: 24 shallow breaths/min, BP: 136/86 mm Hg.
ABGs are:
• Blood pH: 7.30
• PCO2: 58 mm Hg
• PO2: 88 mm Hg
• HCO3−: 28 mEq/L
• SaO2: 88%.
Step 1. Does the blood pH show an acidotic, alkalotic, or normal bloodstream?
In this problem, the blood is acidic at pH 7.30, which is less than 7.35; therefore the condition is acidosis.
Step 2. What is the PCO2?
A PCO2 of 58 mm Hg is elevated beyond the normal range of 35–45 mm Hg.
Step 3. Is the acid–base imbalance caused by a respiratory or metabolic source?
pH (low) and PCO2 (high) are moving in opposite directions. The high PCO2 is causing the low pH,
indicating it is a respiratory disturbance and therefore respiratory acidosis.
The high PCO2 indicates a ventilation problem, and the PO2 and SaO2 are also low, further confirming a
lung problem.
Step 4. Is this a compensated or uncompensated problem?
The pH is abnormal; therefore the condition is uncompensated. The body is attempting to compensate
by reabsorption of HCO3− at the kidney. HCO3− is slightly elevated at 28 mEq/L vs. the normal range of
22–26 mEq/L.
Result
Because of the low blood pH and high PCO2, this is uncompensated respiratory acidosis. The kidney is
attempting to compensate through the reabsorption of HCO3−.
, CASE STUDY 2
Patient B is unconscious and brought into the emergency department because of suspected drug toxicity.
Vital signs include: Temp: 97.8°F, Pulse: 90 beats/min, Resp rate: 12 breaths/ min, BP: 100/70 mm Hg.
The patient’s ABGs are:
• Blood pH: 7.29
• PCO2: 32 mm Hg
• PO2: 95 mm Hg
• HCO3−: 13 mEq/L
• SaO2: 98%.
Using the previous step-by-step process:
Step 1. Does the blood pH show an acidotic, alkalotic, or normal bloodstream?
In this problem, the pH is less than 7.35; therefore the condition is acidosis.
Step 2. What is the PCO2?
The PCO2 is 32 mm Hg, which is low. This indicates the lungs are eliminating CO2 excessively.
Step 3. Is the acid–base imbalance caused by a respiratory or metabolic source?
As pH (low) and PCO2 (low) are moving in the same direction, PCO2 is not contributing to the acid–base
imbalance. The acid–base disturbance is metabolic in nature. Also, because the PO2 and SaO2 are
normal, the lungs are functioning well.
Step 4. Is this a compensated or uncompensated problem?
The pH is abnormal, so the condition is uncompensated. The lungs in this case are trying to compensate
for the low pH in the bloodstream by exhaling CO2, but the compensation is inadequate.
Result
Because of the low blood pH and low PCO2, the condition is uncompensated metabolic acidosis. The
lungs attempt to compensate for the acidosis by increasing ventilation to decrease CO2. In cases of
metabolic acidosis, a further step would be to calculate the anion gap to help narrow the list of
possible causes.
IN RESPIRATORY
Patho study pages
CASE STUDY 1
Patient A is enduring an asthma attack and is brought into the emergency department. The patient’s vital
signs are: Temp: 98.4°F, Pulse: 110 beats/min, Resp rate: 24 shallow breaths/min, BP: 136/86 mm Hg.
ABGs are:
• Blood pH: 7.30
• PCO2: 58 mm Hg
• PO2: 88 mm Hg
• HCO3−: 28 mEq/L
• SaO2: 88%.
Step 1. Does the blood pH show an acidotic, alkalotic, or normal bloodstream?
In this problem, the blood is acidic at pH 7.30, which is less than 7.35; therefore the condition is acidosis.
Step 2. What is the PCO2?
A PCO2 of 58 mm Hg is elevated beyond the normal range of 35–45 mm Hg.
Step 3. Is the acid–base imbalance caused by a respiratory or metabolic source?
pH (low) and PCO2 (high) are moving in opposite directions. The high PCO2 is causing the low pH,
indicating it is a respiratory disturbance and therefore respiratory acidosis.
The high PCO2 indicates a ventilation problem, and the PO2 and SaO2 are also low, further confirming a
lung problem.
Step 4. Is this a compensated or uncompensated problem?
The pH is abnormal; therefore the condition is uncompensated. The body is attempting to compensate
by reabsorption of HCO3− at the kidney. HCO3− is slightly elevated at 28 mEq/L vs. the normal range of
22–26 mEq/L.
Result
Because of the low blood pH and high PCO2, this is uncompensated respiratory acidosis. The kidney is
attempting to compensate through the reabsorption of HCO3−.
, CASE STUDY 2
Patient B is unconscious and brought into the emergency department because of suspected drug toxicity.
Vital signs include: Temp: 97.8°F, Pulse: 90 beats/min, Resp rate: 12 breaths/ min, BP: 100/70 mm Hg.
The patient’s ABGs are:
• Blood pH: 7.29
• PCO2: 32 mm Hg
• PO2: 95 mm Hg
• HCO3−: 13 mEq/L
• SaO2: 98%.
Using the previous step-by-step process:
Step 1. Does the blood pH show an acidotic, alkalotic, or normal bloodstream?
In this problem, the pH is less than 7.35; therefore the condition is acidosis.
Step 2. What is the PCO2?
The PCO2 is 32 mm Hg, which is low. This indicates the lungs are eliminating CO2 excessively.
Step 3. Is the acid–base imbalance caused by a respiratory or metabolic source?
As pH (low) and PCO2 (low) are moving in the same direction, PCO2 is not contributing to the acid–base
imbalance. The acid–base disturbance is metabolic in nature. Also, because the PO2 and SaO2 are
normal, the lungs are functioning well.
Step 4. Is this a compensated or uncompensated problem?
The pH is abnormal, so the condition is uncompensated. The lungs in this case are trying to compensate
for the low pH in the bloodstream by exhaling CO2, but the compensation is inadequate.
Result
Because of the low blood pH and low PCO2, the condition is uncompensated metabolic acidosis. The
lungs attempt to compensate for the acidosis by increasing ventilation to decrease CO2. In cases of
metabolic acidosis, a further step would be to calculate the anion gap to help narrow the list of
possible causes.
