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Difficulty: MediumPulmonary and Critical Care

A 72-year-old man is evaluated in the intensive care unit for increasing lethargy and rapid breathing. He was admitted two days ago for urosepsis and has been receiving intravenous ceftriaxone. Urine cultures returned earlier today growing *Escherichia coli* that is susceptible to ceftriaxone. His medical history includes severe chronic obstructive pulmonary disease and heart failure with preserved ejection fraction.

Upon admission, an advance directive was placed in his chart explicitly stating his desire for all life-sustaining interventions, including intubation and mechanical ventilation, in the event of critical illness. However, his wife, who is at the bedside, is distressed by his deterioration and requests that no breathing machine be used.

Vital signs are temperature 37.5°C (99.5°F), blood pressure 110/70 mm Hg, pulse 115/min, and respirations 28/min. Physical examination reveals a lethargic patient who only briefly opens his eyes to painful stimuli. His breathing is labored with prominent use of accessory muscles, prolonged expiration, and faint bilateral expiratory wheezes. Jugular venous distention is absent and trace pedal edema is present.

Laboratory TestResult
Sodium139 mEq/L
Potassium4.8 mEq/L
Chloride104 mEq/L
Bicarbonate14 mEq/L
Blood urea nitrogen35 mg/dL
Creatinine1.6 mg/dL
Lactate5.1 mmol/L

Arterial blood gas (on room air):

ParameterResult
pH7.23
PaCO235 mm Hg
PaO260 mm Hg

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

  1. Perform endotracheal intubation and initiate mechanical ventilationAnswer
  2. B
    Administer intravenous furosemide
  3. C
    Broaden antibiotic therapy to intravenous vancomycin and piperacillin-tazobactam
  4. D
    Withhold intubation and initiate comfort care measures as requested by the wife
  5. E
    Continue current management and reassess arterial blood gases in 2 hours

Answer

The most appropriate next step is to perform endotracheal intubation and initiate mechanical ventilation.
This patient is in impending hypercapnic respiratory failure secondary to a chronic obstructive pulmonary disease (COPD) exacerbation and sepsis. His arterial blood gas reveals a primary metabolic acidosis (bicarbonate 14 mEq/L, pH 7.23). Using Winter's formula (1.5×14+8±21.5 \times 14 + 8 \pm 2), his expected PaCO2\text{PaCO}_2 should be between 27 and 31 mm Hg. His actual PaCO2\text{PaCO}_2 of 35 mm Hg represents a superimposed primary respiratory acidosis, demonstrating an inability to mount an adequate respiratory compensation due to respiratory muscle fatigue. Clinically, this manifests as increasing lethargy and labored breathing. Immediate airway protection with endotracheal intubation is required. Ethically, his previously documented advance directive explicitly requesting mechanical ventilation must be honored over the contradictory wishes of his wife, as it represents his competent, autonomous choice.

Step-by-Step Solution

1
Analyze the primary acid-base disturbance.
The patient has a primary anion gap metabolic acidosis (pH 7.23, HCO3−\text{HCO}_3^- 14 mEq/L) likely secondary to lactic acidosis from sepsis.
Identifying the primary disorder is required to calculate the expected compensatory response.
2
Calculate the expected respiratory compensation.
Using Winter's formula (1.5×14+8±21.5 \times 14 + 8 \pm 2), the expected PaCO2\text{PaCO}_2 is between 27 and 31 mm Hg.
This determines if the patient's respiratory drive is adequate for the degree of metabolic acidosis.
3
Compare actual and expected PaCO2\text{PaCO}_2.
The actual PaCO2\text{PaCO}_2 (35 mm Hg) is higher than expected, indicating a superimposed primary respiratory acidosis.
This unmasks impending respiratory failure due to respiratory muscle fatigue.
4
Evaluate the ethical priority of decision-makers.
The patient's advance directive requests mechanical ventilation, which overrides the wife's contradictory request.
An advance directive represents the patient's autonomous, competent wishes and is legally binding.
5
Determine the appropriate clinical intervention.
Emergent endotracheal intubation must be performed.
The patient requires definitive airway management for respiratory failure, in accordance with his wishes.

Key Concept

Management of acute respiratory failure with mixed acid-base disorders and the ethical priority of advance directives over surrogate wishes.
Estimated Time:1m 30s
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Topics

Pulmonary and Critical Care

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