Acid–Base And Electrolyte Emergencies
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USMLE Step 2 CK › Acid–Base And Electrolyte Emergencies
A 44-year-old woman presents 36 hours after thyroidectomy with tingling and muscle spasms. She has stridor and is anxious. Labs:
| Test | Result |
|---|---|
| ABG | pH 7.46, PaCO2 33 mm Hg, HCO3− 23 mEq/L |
| Ionized Ca2+ | 0.78 mmol/L |
| K+ | 4.1 mEq/L |
| Mg2+ | 1.8 mg/dL |
Time-sensitive context: airway symptoms are worsening, and IV access is available.
Which of the following is the most appropriate initial treatment for this electrolyte imbalance?
IV calcium gluconate administration
Oral sodium polystyrene administration
Oral calcium carbonate administration
Fluid restriction and observation
IV insulin with dextrose administration
Explanation
This question tests the ability to diagnose and manage acid-base and electrolyte emergencies in critical care settings. Understanding acid-base balance is critical for managing patients with metabolic acidosis and alkalosis, as well as electrolyte imbalances like hyperkalemia or hyponatremia. In this vignette, the patient's symptoms and lab results provide crucial clues for identifying the underlying condition. The correct answer, choice A, is justified by the acute severe hypocalcemia causing laryngospasm and stridor, requiring immediate IV calcium to stabilize neuromuscular function. Choice B is incorrect due to oral calcium being insufficient for rapid correction in emergent airway-compromising symptoms. To improve student understanding, emphasize the importance of correlating clinical symptoms with laboratory findings and encourage the use of diagnostic algorithms to guide management decisions.
A 58-year-old woman with hypertension and CKD stage 3 takes lisinopril and spironolactone. She presents with progressive muscle weakness and palpitations for 2 hours. BP 148/86, HR 54. ECG shows peaked T waves and QRS widening. Labs:
| Test | Result |
|---|---|
| ABG | pH 7.36, PaCO2 40 mm Hg, HCO3− 22 mEq/L |
| Na+ | 138 mEq/L |
| K+ | 7.2 mEq/L |
| Cl− | 104 mEq/L |
| BUN/Cr | 44/2.6 mg/dL |
| Glucose | 118 mg/dL |
Time-sensitive context: telemetry shows intermittent runs of ventricular ectopy. Differential includes medication effect vs hemolysis vs acidosis.
Management steps being considered:
- Stabilize myocardium
- Shift potassium intracellularly
- Remove potassium from body
- Stop offending agents
Which of the following is the most appropriate initial treatment for this electrolyte imbalance?
Nebulized albuterol administration
IV furosemide administration
Oral sodium polystyrene administration
IV calcium gluconate administration
IV sodium bicarbonate infusion
Explanation
This question tests the ability to diagnose and manage acid-base and electrolyte emergencies in critical care settings. Understanding acid-base balance is critical for managing patients with metabolic acidosis and alkalosis, as well as electrolyte imbalances like hyperkalemia or hyponatremia. In this vignette, the patient's symptoms and lab results provide crucial clues for identifying the underlying condition. The correct answer, choice B, is justified by the ECG changes of peaked T waves and QRS widening in hyperkalemia, requiring immediate myocardial stabilization with calcium gluconate. Choice A is incorrect due to albuterol being a temporizing measure for shifting potassium but not the initial step when ECG changes indicate urgent membrane protection. To improve student understanding, emphasize the importance of correlating clinical symptoms with laboratory findings and encourage the use of diagnostic algorithms to guide management decisions.