π©Ί Nursing Question of the Day
Challenge yourself with one exam-style nursing question every day.
β Think carefully β’ β Choose your answer β’ β Then scroll down to check the explanation.
π Today’s Question:
Q: A patientβs ABG result showed a pH of 7.28, HCO3- of 18 mEq/L, and a PaCO2 of 30 mmHg. What may be the most likely condition?
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π©Έ Reading ABG: Metabolic Acidosis
The pH is low, the bicarbonate is low, and the PaCOβ is also low because the lungs are trying to remove more carbon dioxide to bring the pH back toward normal.
π Start With the pH
The first step in reading an ABG is always to look at the pH.
Below 7.35 = Acidosis
Above 7.45 = Alkalosis
Here, the pH is 7.28, so the blood is acidic.
π§ͺ Now Look at HCOββ»
HCOββ» means bicarbonate. It is an important base that helps control the acidβbase balance of the blood.
Normal bicarbonate is approximately 22β26 mEq/L. Here it is only 18 mEq/L, so bicarbonate is decreased.
π¬οΈ What Is the PaCOβ Telling Us?
PaCOβ means the partial pressure of carbon dioxide in arterial blood. Carbon dioxide acts like an acid in the body.
Normal PaCOβ is about 35β45 mmHg. The patient’s PaCOβ is 30 mmHg, which is low.
Why is it low? Because the patient is likely breathing faster or deeper to remove extra COβ. This is the body’s respiratory attempt to correct the metabolic problem.
π¬οΈ Low PaCOβ = Respiratory compensation
π What Does βCompensationβ Mean?
Compensation means the body tries to correct an acidβbase disturbance using another system.
When bicarbonate falls and causes metabolic acidosis, the lungs respond quickly by increasing ventilation. This removes COβ and helps raise the pH toward normal.
So, the kidneys/metabolic process created the primary problem, while the lungs are trying to help correct it.
π§ Understand the Medical Terms
Acidosis: A condition in which the blood becomes more acidic than normal. The word comes from acid + the medical suffix -osis, meaning a condition or process.
Metabolic: Related to the body’s chemical processes. Metabolism comes from the Greek metabolΔ, meaning change or transformation.
Respiratory: Related to breathing. It comes from Latin respirare, meaning to breathe again.
Compensation: The body’s attempt to reduce the effect of an abnormal acidβbase change.
β Why the Other Options Are Wrong
Respiratory alkalosis would primarily have a high pH and low PaCOβ. Here, the pH is clearly acidic.
Metabolic alkalosis is associated with increased HCOββ» and usually an increased pH. Here, HCOββ» is low.
Respiratory acidosis occurs when COβ is retained, so PaCOβ becomes high. Here, PaCOβ is only 30 mmHg.
π©Ί Common Causes of Metabolic Acidosis
- Diabetic ketoacidosis (DKA)
- Lactic acidosis from poor tissue perfusion
- Severe diarrhea causing bicarbonate loss
- Kidney failure with reduced acid excretion
- Certain toxic ingestions
A patient with significant metabolic acidosis may develop deep, rapid breathing. This is an important clinical clue because the body is trying to eliminate COβ.
β‘ Quick ABG Method
Step 2: HCOββ» β β Metabolic cause
Step 3: PaCOβ β β Respiratory compensation
ROME β Respiratory Opposite, Metabolic Equal.
In metabolic acidosis, pH and HCOββ» move in the same direction: both are low.
When you see low pH + low HCOββ» + low PaCOβ, don’t automatically call it respiratory alkalosis. First identify the primary problem: low HCOββ» is pointing to metabolic acidosis, while the low PaCOβ represents the body’s respiratory response.
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