Are you an expert in interpreting ABGs?
TIC TAC TOE METHOD:
- Wales, who underwent post-abdominal surgery, has a nasogastric tube. The nurse on duty notes that the nasogastric tube (NGT) is draining a large amount (900 cc in 2 hours) of coffeeground secretions. The client is not oriented to person, place, or time. The nurse contacts the attending physician and STAT ABGs are ordered. The results from the ABGs show pH 7.57, PaCO2 37 mmHg and HCO3 30 mEq/L. What is your assessment?
The Correct Answer and Explanation is:
Yes, I can help interpret ABGs (Arterial Blood Gases), and we’ll use the Tic-Tac-Toe Method to systematically analyze this case.
Step-by-Step ABG Interpretation:
Given ABG values:
- pH: 7.57 (High – indicates alkalosis)
- PaCO₂: 37 mmHg (Normal)
- HCO₃: 30 mEq/L (High)
Step 1: Tic-Tac-Toe Grid Setup
We use three columns:
- Acid (↓ pH),
- Normal,
- Alk (↑ pH)
| Acid | Normal | Alk | |
|---|---|---|---|
| pH | X | ||
| PaCO₂ | X | ||
| HCO₃⁻ | X |
Step 2: Interpretation
- The pH is high (alkalosis).
- PaCO₂ is normal, so it’s not respiratory.
- HCO₃ is high, indicating metabolic alkalosis.
- Since PaCO₂ is normal, there’s no compensation happening.
✅ ANSWER: Metabolic Alkalosis (Uncompensated)
Explanation
The ABG results point to uncompensated metabolic alkalosis, evident from the elevated pH (7.57) and high bicarbonate (HCO₃⁻ = 30 mEq/L), with a normal PaCO₂ (37 mmHg). In this case, the pH being above the normal range (7.35–7.45) clearly indicates alkalosis. Since PaCO₂ remains within the normal range (35–45 mmHg), we can conclude that the lungs have not yet started to compensate. The elevated bicarbonate signifies that the kidneys have retained excess base, pointing to a metabolic cause.
The clinical context reinforces this interpretation. The patient has a nasogastric tube (NGT) draining a large amount of coffee-ground secretions — this suggests significant upper GI bleeding, potentially from a gastric ulcer or stress-related erosion. Prolonged nasogastric suction removes gastric acid (HCl), leading to a loss of hydrogen ions (acid), which in turn raises bicarbonate levels and the blood pH, resulting in metabolic alkalosis.
Moreover, the patient is not oriented, which could be a symptom of the alkalosis itself or due to hypovolemia from fluid loss. Neurological symptoms are common in alkalosis due to reduced ionized calcium levels and cerebral vasoconstriction.
Prompt intervention is crucial. This might include stopping or reducing NGT suction, replacing lost fluids and electrolytes (especially potassium and chloride), and monitoring for any worsening signs of shock or ongoing GI bleeding.
Final Diagnosis: Metabolic Alkalosis (Uncompensated) ✅
