Normal Values
| pH | 7.35–7.45 |
| PaCO₂ (resp) | 35–45 mmHg |
| HCO₃ (metabolic) | 22–26 mEq/L |
| PaO₂ | 80–100 mmHg |
| O₂ Sat | 95–100 % |
The ROME Rule
| Respiratory | pH & CO₂ move OPPOSITE directions |
| Metabolic | pH & HCO₃ move the SAME direction |
Match pH to CO₂ or HCO₃ to name the problem.
The 4 Disorders
| Resp acidosis | ↓pH ↑CO₂ — hypoventilation, COPD, opioids |
| Resp alkalosis | ↑pH ↓CO₂ — hyperventilation, anxiety, pain |
| Metab acidosis | ↓pH ↓HCO₃ — DKA, diarrhea, shock |
| Metab alkalosis | ↑pH ↑HCO₃ — vomiting, NG suction |
Step-by-Step
| 1 | pH: acidosis (<7.35) or alkalosis (>7.45)? |
| 2 | Which matches — CO₂ (resp) or HCO₃ (metabolic)? |
| 3 | Compensating? other value shifting toward normal |
Compensation
| Uncompensated | pH abnormal; one value off |
| Partial | pH abnormal; both values off |
| Full | pH normal; both values abnormal |
Worked Examples
| pH 7.30 / CO₂ 50 / HCO₃ 24 | uncompensated respiratory acidosis |
| pH 7.50 / CO₂ 30 / HCO₃ 24 | respiratory alkalosis |
| pH 7.30 / CO₂ 38 / HCO₃ 16 | metabolic acidosis |
Educational quick-reference only; values/ranges vary by source. Verify against your facility and the current NCSBN test plan.
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