Review Question - QID 104309

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Analgesics Analgesic Drug Table Antirheumatic Agents Name Mechanism of Action Key Indication Key Toxicity TNFα Inhibitors Infliximab Monoclonal antibody against TNF-alpha (infliximab, adalimumab, certolizumab) Decoy receptor for TNF-alpha (etanercept) Disease QID: 104309 (M2.PH.14.35)

QID 104309 (Type "104309" in App Search)

A 58-year-old man presents to the emergency department with a chief complaint of ringing in his ears that started several hours previously that has progressed to confusion. The patient denies any history of medical problems except for bilateral knee arthritis. He was recently seen by an orthopedic surgeon to evaluate his bilateral knee arthritis but has opted to not undergo knee replacement and prefers medical management. His wife noted that prior to them going on a hike today, he seemed confused and not himself. They decided to stay home, and roughly 19 hours later, he was no longer making any sense. Physical exam is notable for a confused man. The patient's vitals are being performed and his labs are being drawn. Which of the following is most likely to be seen on blood gas analysis?

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pH: 7.30, PaCO2: 15 mmHg, HCO3-: 16 mEq/L

17%

4/23

pH: 7.31, PaCO2: 31 mmHg, HCO3-: 15 mEq/L

26%

6/23

pH: 7.37, PaCO2: 41 mmHg, HCO3-: 12 mEq/L

17%

4/23

pH: 7.41, PaCO2: 65 mmHg, HCO3-: 34 mEq/L

22%

5/23

pH: 7.47, PaCO2: 11 mmHg, HCO3-: 24 mEq/L

2/23

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This patient's presentation of tinnitus in the setting of excessive use of over-the-counter pain medications is suggestive of aspirin toxicity. A mixed metabolic acidosis and respiratory alkalosis is expected late in disease presentation.

Salicylates stimulate the respiratory center leading to hyperventilation and an ensuing respiratory alkalosis. Early in the presentation of aspirin overdose, patients may present with an isolated respiratory alkalosis. Concomitant production of endogenous acids (not the aspirin itself) leads to a metabolic acidosis. Salicylates uncouple oxidative phosphorylation leading to numerous end-organ effects. The diagnosis of aspirin toxicity is suggested by characteristic history and a presentation with consistent arterial blood gas results; however, the diagnosis is confirmed with serum salicylate levels. Treatment involves administration of sodium bicarbonate and dialysis.

Incorrect Answers:
Answer 2: pH: 7.31, PaCO2: 31 mmHg, HCO3-: 15 mEq/L corresponds to a metabolic acidosis with appropriate respiratory compensation (rather than a respiratory alkalosis which would be seen in this patient).

Answer 3: pH: 7.37, PaCO2: 41 mmHg, HCO3-: 12 mEq/L is a normal pH with a metabolic acidosis without respiratory compensation. This is an unlikely pattern to be seen in most diseases.

Answer 4: pH: 7.41, PaCO2: 65 mmHg, HCO3-: 34 mEq/L represents a normal pH with an elevated bicarbonate and an elevated PaCO2 suggestive of a chronic respiratory condition such as COPD where there is time for the kidney to adapt to this chronic disease.

Answer 5: pH: 7.47, PaCO2: 11 mmHg, HCO3-: 24 mEq/L represents a respiratory alkalosis without metabolic compensation. This may be seen early in the course of aspirin overdose but would not be seen late (several hours later) in a confused/altered patient.

Bullet Summary:
Aspirin overdose presents with a mixed respiratory alkalosis and overwhelming metabolic acidosis.

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