DFT-MEDICINE D4- 11-10-2025 - MAXEMO

Following an aspirin overdose, a patient presents with tinnitus and tachypnea. An ABG shows: pH 7.42, PaCO2 20 mmHg, and HCO3- 12 mEq/L. Which acid-base disturbance best explains this clinical picture?

• Mixed respiratory alkalosis and metabolic acidosis

• Chronic respiratory alkalosis

• Partially compensated metabolic acidosis

• Acute metabolic alkalosis

Answer explanation

Salicylates cause a primary respiratory alkalosis (low PaCO2) by stimulating the medullary respiratory center and a primary metabolic acidosis (low HCO3-) by uncoupling oxidative phosphorylation. The near-normal pH with drastically low PaCO2 and HCO3- is characteristic of this mixed disorder.

A 68-year-old male with a history of invasive bladder carcinoma, treated with a ureterosigmoidostomy 10 years ago, presents with progressive lethargy. His laboratory results show a pH of 7.29 and an anion gap of 8 mEq/L. To further investigate the etiology of his acid-base disturbance, urine electrolytes are ordered. Which of the following findings would be most consistent with his clinical condition?

• Negative urine anion gap.

• Positive urine anion gap.

• Urine pH of 7.0.

• Glucosuria with normal serum glucose.

Answer explanation

Ureterosigmoidostomy causes a normal anion gap metabolic acidosis (NAGMA) due to colonic loss of bicarbonate in exchange for chloride. With intact renal function, the kidney compensates by excreting excess acid (NH₄Cl), leading to high urine chloride and a negative urine anion gap (UAG = [Na⁺ + K⁺] - Cl⁻).

A patient with a traumatic brain injury is in circulatory failure requiring noradrenaline. Given the arterial blood gas finding of pH 7.10, which intervention is most urgently indicated to improve the efficacy of the vasopressor therapy?

• Intravenous sodium bicarbonate infusion.

• Administration of intravenous calcium gluconate.

• Rapid infusion of 0.45% saline.

• Starting an insulin and dextrose infusion.

Answer explanation

Severe acidemia (pH < 7.15) significantly impairs myocardial contractility and diminishes the vasoconstrictive response to catecholamines like noradrenaline. Correcting the pH is crucial to restore hemodynamic stability.

The development of circulatory failure and severe lactic acidosis in this patient with a head injury is most likely mediated by which pathophysiological mechanism?

• Systemic catecholamine storm.

• Cushing reflex.

• Cerebral salt wasting syndrome.

• Parasympathetic hyperactivity.

Answer explanation

Severe traumatic brain injury can trigger a massive sympathetic surge, leading to intense vasoconstriction, myocardial dysfunction (neurogenic stunned myocardium), and organ hypoperfusion, which explains the profound shock and lactic acidosis.

A 22-year-old male presents with recurrent episodes of carpopedal spasm and generalized fatigue. His blood pressure is 110/70 mmHg. Lab results show persistent hypokalemia, metabolic alkalosis, and significant hypomagnesemia. A 24-hour urine collection reveals markedly decreased calcium excretion. The pathophysiology of this patient's condition is most analogous to the chronic use of which class of diuretic?

• Thiazide diuretics

• Loop diuretics

• Potassium-sparing diuretics

• Carbonic anhydrase inhibitors

Answer explanation

This clinical picture is classic for Gitelman syndrome, a salt-losing tubulopathy caused by a mutation in the NCC transporter. This defect mimics the chronic pharmacologic effect of thiazide diuretics, which also block the Na-Cl cotransporter in the distal convoluted tubule, leading to hypokalemia, metabolic alkalosis, hypomagnesemia, and hypocalciuria.

A patient is brought in from a rural area with altered sensorium. Examination reveals a temperature of 40°C, tachycardia, mydriasis, and a palpable, distended bladder. The skin is notably flushed, warm, and completely dry. Which of the following is the most likely causative agent?

• Datura stramonium

• Cocaine

• Organophosphate insecticide

• Paraquat

Answer explanation

This presentation is the classic anticholinergic toxidrome ("hot as a hare, blind as a bat, red as a beet, dry as a bone"). Datura is a well-known plant containing atropine and scopolamine, potent anticholinergic alkaloids.

A 68-year-old male with a history of symptomatic BPH and recurrent gout presents for management of newly diagnosed Stage 2 hypertension. His blood pressure is 164/98 mmHg, and his serum uric acid is 8.5 mg/dL. Which of the following antihypertensive agents would be the most appropriate single-drug therapy for this patient?

• Prazosin

• Hydrochlorothiazide

• Metoprolol

• Clonidine

Answer explanation

 Prazosin, an alpha-1 blocker, effectively treats hypertension and concurrently alleviates urinary symptoms of BPH by relaxing smooth muscle in the bladder neck and prostate. It does not adversely affect uric acid levels.

A patient with a history of myocardial infarction five years ago is currently managed for hypertension. Echocardiography shows a left ventricular ejection fraction of 35%. Which class of antihypertensive drugs is absolutely indicated for its proven mortality benefit in this patient?

• Beta-blockers

• Dihydropyridine calcium channel blockers

• Alpha-blockers

• Central sympatholytics

Answer explanation

Beta-blockers (e.g., carvedilol, metoprolol succinate) are a cornerstone of therapy in patients with heart failure with reduced ejection fraction (HFrEF) post-MI, as they have demonstrated a significant reduction in mortality.

A patient receiving prophylaxis for Pneumocystis jirovecii pneumonia develops acute flank pain and oliguria. Urine microscopy reveals crystals described as 'sheaves of wheat.' Which of the following is the most appropriate initial advice for managing this condition?

• Ensure adequate hydration and alkalinize the urine

• Administer penicillamine and restrict dietary methionine

• Start allopurinol to inhibit xanthine oxidase

• Administer a potent loop diuretic to flush the crystals

Answer explanation

"Sheaves of wheat" crystals are characteristic of sulfonamide drugs (used for PCP prophylaxis). Their precipitation is favored in acidic urine, so management involves increasing fluid intake and urinary alkalinization to enhance solubility.

A patient is brought to the emergency department after ingesting an unknown substance. On examination, the patient is tachypneic and fundoscopy reveals optic disc hyperemia. An arterial blood gas analysis shows a pH of 7.20, bicarbonate of 10 mEq/L, and a calculated anion gap of 30 mEq/L. Which substance is the most likely cause of this presentation?

• Methanol

• Acetaminophen

• L-Lactate

• Bicarbonate-rich fluid

Answer explanation

The patient has a severe high anion gap metabolic acidosis (HAGMA). The specific finding of optic disc hyperemia is a classic sign of methanol toxicity due to the formic acid metabolite.