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Zorluk: Çok zorGeneral Internal Medicine

A 67-year-old woman is brought to the emergency department by her daughter due to increasing confusion, rapid breathing, and generalized weakness that started yesterday. The daughter notes that the patient has been complaining of a "constant buzzing" in her ears for the past 24 hours. The patient has a history of ischemic cardiomyopathy with a left ventricular ejection fraction of 35%, type 2 diabetes mellitus, and severe bilateral knee osteoarthritis. Her current medications include metoprolol, lisinopril, empagliflozin, and several over-the-counter analgesics that she has been taking frequently due to a recent pain flare.

Vital signs are:
Temperature: 38.3°C (100.9°F)
Heart rate: 118/min
Respiratory rate: 32/min
Blood pressure: 105/65 mm Hg
Oxygen saturation: 97% on room air

Physical examination reveals a disoriented patient taking deep, rapid breaths. Chest auscultation demonstrates scattered bilateral basilar crackles. Cardiac examination shows a regular, rapid rhythm with no murmurs, gallops, or jugular venous distention. Trace bilateral pedal edema is present.

Laboratory results:
Serum sodium: 142 mEq/L
Serum potassium: 3.4 mEq/L
Serum chloride: 100 mEq/L
Serum bicarbonate: 14 mEq/L
Blood urea nitrogen: 32 mg/dL
Serum creatinine: 1.6 mg/dL (baseline 1.1 mg/dL)

Arterial blood gas on room air:
pH: 7.46
PaCO2: 20 mm Hg
PaO2: 88 mm Hg

Which of the following is the most appropriate next step in the management of this patient?

  1. Intravenous sodium bicarbonateCevap
  2. B
    Endotracheal intubation and mechanical ventilation
  3. C
    Intravenous furosemide
  4. D
    Intravenous ceftriaxone and azithromycin
  5. E
    Measurement of serum thyroid-stimulating hormone

Cevap

Intravenous sodium bicarbonate
The correct intervention is intravenous sodium bicarbonate. This patient's presentation of tinnitus, hyperthermia, noncardiogenic pulmonary edema, altered mental status, and a history of excessive over-the-counter analgesic use is highly suspicious for salicylate toxicity. The diagnosis is confirmed by her arterial blood gas and basic metabolic panel, which reveal the hallmark mixed acid-base disorder of salicylate poisoning: a primary respiratory alkalosis (due to direct stimulation of the medullary respiratory center) and a primary high anion gap metabolic acidosis (due to uncoupling of oxidative phosphorylation and accumulation of organic acids). Intravenous sodium bicarbonate acts to alkalinize both the serum and the urine. Serum alkalinization keeps the salicylate molecule in its ionized (deprotonated) state, preventing it from crossing the blood-brain barrier and causing central nervous system toxicity. Urine alkalinization promotes 'ion trapping' in the renal tubules, significantly increasing renal clearance of the drug.

Adım Adım Çözüm

1
Analyze the arterial blood gas (ABG) to determine the primary acid-base disorder.
The pH is 7.46 (alkalemia). The PaCO2PaCO_2 is 20 mm Hg (low). The HCO3−HCO_3^- is 14 mEq/L (low). Since the pH is high and the PaCO2PaCO_2 is low, the primary disorder is a respiratory alkalosis.
Establishing the initial primary disorder is the first step in diagnosing complex acid-base abnormalities.
2
Calculate expected compensation to evaluate for mixed acid-base disorders.
For acute respiratory alkalosis, expected HCO3−HCO_3^- drops by 2 mEq/L for every 10 mm Hg drop in PaCO2PaCO_2. The PaCO2PaCO_2 dropped by 20 (from 40 to 20), so HCO3−HCO_3^- should drop by 4. Expected HCO3−=24−4=20HCO_3^- = 24 - 4 = 20 mEq/L. The actual HCO3−HCO_3^- is 14 mEq/L. Because the actual bicarbonate is much lower than the expected compensatory level, there is a concomitant primary metabolic acidosis.
Whenever actual compensatory values differ significantly from expected values, a secondary primary disorder is present.
3
Calculate the anion gap to characterize the metabolic acidosis.
Anion Gap (AG) =Na+−(Cl−+HCO3−)=142−(100+14)=28= Na^+ - (Cl^- + HCO_3^-) = 142 - (100 + 14) = 28 mEq/L. This confirms a high anion gap metabolic acidosis (HAGMA).
HAGMA narrows the differential diagnosis to specific causes such as ketoacidosis, lactic acidosis, renal failure, or ingestions (MUDPILES).
4
Synthesize the laboratory data with the clinical presentation.
The patient has a primary respiratory alkalosis + primary HAGMA. Clinically, she presents with tinnitus ('buzzing' in ears), hyperthermia, tachypnea, and noncardiogenic pulmonary edema (crackles without JVD/S3) after taking over-the-counter analgesics. This is the classic presentation of severe salicylate (aspirin) toxicity.
Salicylates directly stimulate the medullary respiratory center (causing respiratory alkalosis) and later uncouple oxidative phosphorylation (causing lactic acidosis/HAGMA).
5
Determine the definitive treatment for the diagnosed condition.
The treatment for severe salicylate toxicity is intravenous sodium bicarbonate.
Sodium bicarbonate alkalinizes the blood, keeping salicylate in its ionized form so it cannot cross the blood-brain barrier. It also alkalinizes the urine, trapping the salicylate ion in the renal tubules and promoting its excretion.

Anahtar Kavram

Diagnosis and management of a mixed primary respiratory alkalosis and primary high anion gap metabolic acidosis secondary to salicylate toxicity.
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General Internal Medicine

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