The rapid response team is urgently called to evaluate a 58-year-old male due to sudden cl… — USMLE Step 2 CK

The rapid response team is urgently called to evaluate a 58-year-old male due to sudden clinical deterioration. The patient was admitted 48 hours ago with right lower lobe community-acquired pneumonia. He has a history of heart failure with preserved ejection fraction and a 30-pack-year smoking history. His admission blood cultures are currently growing *Streptococcus pneumoniae*, and he has been receiving targeted intravenous ceftriaxone.

Upon evaluation, the patient is lethargic and oriented only to person.

Vital signs are:
- Temperature: $38.6^\circ\text{C}$ ( $101.5^\circ\text{F}$ )
- Heart Rate: $122\text{/min}$
- Blood Pressure: $88/56\text{ mmHg}$
- Respiratory Rate: $34\text{/min}$
- $SpO_2$ : $84\%$ on a high-flow nasal cannula

Physical examination reveals profound use of accessory respiratory muscles. Lung auscultation demonstrates diffuse bilateral crackles and expiratory wheezing. Jugular venous pressure is normal.

Arterial blood gas analysis and relevant laboratories reveal:

Parameter	Value
$pH$	$7.15$
$PaCO_2$	$50\text{ mmHg}$
$PaO_2$	$52\text{ mmHg}$
$HCO_3^-$	$16\text{ mEq/L}$
Serum lactate	$5.2\text{ mmol/L}$

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

Perform endotracheal intubation and mechanical ventilationAnswer
B
Switch current antimicrobial therapy to intravenous vancomycin and cefepime
C
Administer an intravenous sodium bicarbonate infusion
D
Administer intravenous furosemide and a nitroglycerin infusion
E
Administer nebulized albuterol and intravenous methylprednisolone

Answer

The most appropriate next step is to perform endotracheal intubation and mechanical ventilation.

This patient is in distributive (septic) shock and is exhibiting clear signs of impending respiratory failure. He has severe hypoxemia (

PaO_2 = 52\text{ mmHg}

) and clinical signs of respiratory muscle fatigue (use of accessory muscles, lethargy). Furthermore, his acid-base status confirms a mixed metabolic and respiratory acidosis. He has a metabolic acidosis driven by elevated lactate (

5.2\text{ mmol/L}

). According to Winter's formula (

Expected\ PaCO_2 = 1.5 \times HCO_3^- + 8 \pm 2

), his expected

PaCO_2

should be between

30

and

34\text{ mmHg}

. His actual

PaCO_2

50\text{ mmHg}

, indicating a severe superimposed respiratory acidosis due to inadequate alveolar ventilation. Given his altered mental status (lethargy) and hemodynamic instability, noninvasive positive pressure ventilation is strictly contraindicated, making definitive airway management via endotracheal intubation the most critical next step.

Step-by-Step Solution

Evaluate the patient's clinical status and vital signs.

The patient is lethargic, hypotensive, hypoxemic, and using accessory muscles, indicating septic shock and impending respiratory failure.

Recognizing the signs of respiratory muscle fatigue and altered mental status is critical for determining the urgency of airway intervention.

Analyze the arterial blood gas using Winter's formula to determine the acid-base disorder.

The patient has a primary metabolic acidosis (

HCO_3^-

16\text{ mEq/L}

). Expected

PaCO_2

(1.5 \times 16) + 8 \pm 2 = 32 \pm 2\text{ mmHg}

. Since the actual

PaCO_2

50\text{ mmHg}

, there is a severe concurrent respiratory acidosis.

Identifying the mixed acid-base disorder confirms that the patient's respiratory drive is failing to compensate, necessitating mechanical support.

Select the appropriate method of respiratory support.

Invasive mechanical ventilation via endotracheal intubation is selected.

Non-invasive positive pressure ventilation (NIPPV) is contraindicated due to the patient's lethargy (inability to protect the airway) and hemodynamic instability.

Key Concept

Impending respiratory failure characterized by altered mental status, hypoxemia, and mixed metabolic and respiratory acidosis requires immediate endotracheal intubation.

Question

Answer

Step-by-Step Solution

Key Concept

Common Mistakes

Topics

More questions from this topic