Study topic
Labs and acid-base
NCLEX labs chapter: critical value priorities, platelet and ANC precautions, heparin aPTT response, and primary acid-base disorder patterns.
Lab items ask who gets a phone call now, which precautions match the count, and whether the ABG is a lung problem or a metabolic one.
Critical values and blood counts
| Result pattern | Nursing priority |
|---|---|
| Critically high/low K+, glucose, Na, etc. | Protect client; notify provider now |
| Platelets very low | Bleeding precautions |
| ANC / WBC critically low | Infection precautions; fever is an emergency |
| Heparin aPTT ~3× control | Hold/adjust per protocol; notify |
| Na 150 mEq/L | Hypernatremia — correlate with fluids/neuro status |
Safety
When several labs are abnormal, treat the one that can kill in minutes first (airway, extreme K+, symptomatic hypoglycemia, active bleed with crashing platelets).
Primary acid-base disorders
| Disorder | ABG fingerprint | Common cause on exams |
|---|---|---|
| Respiratory acidosis | ↓pH, ↑PaCO2 | Hypoventilation, opioids, COPD |
| Respiratory alkalosis | ↑pH, ↓PaCO2 | Hyperventilation, panic, pain |
| Metabolic acidosis | ↓pH, ↓HCO3 | DKA, diarrhea, renal failure, lactic acidosis |
| Metabolic alkalosis | ↑pH, ↑HCO3 | Vomiting, NG suction, diuretic losses |
- Uncompensated means the pH is still abnormal and the secondary system has not fully moved yet.
- Panic attack with tingling: slow the breathing; paper-bag tricks are not the modern default — follow current ordered coaching.
- DKA treatment trends: falling glucose/ketones and improving pH/HCO3 mean the plan is working.
Priority map
| Picture | First move |
|---|---|
| Four labs, one critical K+ | Notify; cardiac/safety actions |
| Platelets 30,000 | Bleeding precautions |
| pH 7.29, CO2 61 after opioid | Respiratory acidosis; support breathing |
| pH 7.51, CO2 28 in panic | Respiratory alkalosis; slow breathing |
| aPTT 3× on heparin | Hold/reduce per protocol; notify |
Must know
- 1Critical values (extreme K+, glucose, platelets, ANC, etc.) need prompt provider notification after you protect the client.
- 2Platelets ~30,000: bleeding precautions. Severe neutropenia: infection precautions and fever = emergency.
- 3Heparin aPTT about 3× control with no bleeding: anticipate hold/reduce per protocol, notify — do not ignore.
- 4Na 150 = hypernatremia. Match the number to the imbalance name.
- 5ABG first look: pH low = acidosis; pH high = alkalosis. Then see if CO2 or HCO3 matches the direction.
- 6Respiratory acidosis: high CO2 (hypoventilation, opioids, COPD). Respiratory alkalosis: low CO2 (hyperventilation/panic).
- 7Metabolic acidosis: low HCO3 (DKA, diarrhea, renal failure). Metabolic alkalosis: high HCO3 (vomiting, NG suction, diuretics).
- 8Panic hyperventilation: coach slow breathing; do not leave them alone with numb lips and ignore the ABG pattern.
Memory hooks
ROME
Respiratory Opposite (pH and CO2 move opposite). Metabolic Equal (pH and HCO3 move same direction).
Opioids hold the CO2 in
RR of 8 after opioids with low pH and high CO2 is respiratory acidosis — support ventilation.
Vomit the acid out
Prolonged vomiting or NG suction loses acid and trends toward metabolic alkalosis.
How it's tested
Stems ask which lab to call first, what precautions fit platelets 30k, or which ABG matches panic breathing. Distractors treat critical K+ as routine or call hyperventilation metabolic acidosis.