A 72-year-old man is brought to the emergency department by his family due to a 3-day hist… — USMLE Step 2 CK

A $72$ -year-old man is brought to the emergency department by his family due to a $3$ -day history of worsening shortness of breath, generalized weakness, and increased production of clear sputum. He has a past medical history of ischemic cardiomyopathy with a left ventricular ejection fraction of $35\%$ and severe chronic obstructive pulmonary disease (COPD).

On arrival, he is obtunded and responds only to painful stimuli. His temperature is $37.1^\circ\text{C}$ ( $98.8^\circ\text{F}$ ), heart rate is $122/\text{min}$ , blood pressure is $76/48 \text{ mmHg}$ , respiratory rate is $30/\text{min}$ , and oxygen saturation is $84\%$ on room air. Physical examination reveals flat neck veins while supine. Cardiac examination shows a rapid, regular rhythm with no murmurs or gallops. Pulmonary auscultation reveals poor air movement and diffuse expiratory wheezing bilaterally, without crackles. His extremities are cool with a capillary refill time of $4$ seconds.

Laboratory results are as follows:

Component	Value
Sodium	$140 \text{ mEq/L}$
Chloride	$96 \text{ mEq/L}$
Bicarbonate	$24 \text{ mEq/L}$
Lactate	$6.5 \text{ mmol/L}$
Procalcitonin	$0.08 \text{ ng/mL}$ (normal $<0.1$ )

Arterial blood gas analysis on room air:

Component	Value
pH	$7.14$
$PaCO_2$	$75 \text{ mmHg}$
$PaO_2$	$48 \text{ mmHg}$

Which of the following are the most appropriate next steps in the management of this patient? (Select all that apply)

Endotracheal intubation and invasive mechanical ventilationAnswer
Rapid intravenous infusion of isotonic crystalloidsAnswer
C
Administration of intravenous furosemide
D
Administration of intravenous sodium bicarbonate
E
Initiation of intravenous piperacillin-tazobactam and vancomycin

Answer

The most appropriate next steps are endotracheal intubation and invasive mechanical ventilation, and rapid intravenous infusion of isotonic crystalloids.

The patient presents in severe respiratory failure and shock. The correct approaches involve securing the airway and restoring perfusion. Endotracheal intubation and invasive mechanical ventilation are required because the patient is obtunded, unable to protect his airway, and has profound acidemia (

pH = 7.14

) driven by severe hypercapnia (

PaCO_2 = 75 \text{ mmHg}

). Non-invasive positive pressure ventilation (NIPPV) is contraindicated in patients with altered mental status and hemodynamic instability. Additionally, the patient is in hypovolemic shock, evidenced by hypotension (

76/48 \text{ mmHg}

), tachycardia, elevated lactate (

6.5 \text{ mmol/L}

), cool extremities, and flat neck veins. Rapid intravenous infusion of isotonic crystalloids is the critical first step to restore intravascular volume and improve tissue perfusion.

Step-by-Step Solution

Analyze the patient's hemodynamic and volume status.

The presence of hypotension, tachycardia, flat neck veins, cool extremities, and lactic acidosis indicates hypovolemic shock, rather than cardiogenic shock from his known heart failure.

Identifying the type of shock dictates initial fluid management, favoring crystalloid resuscitation over diuresis.

Evaluate the respiratory status and arterial blood gas.

The patient is obtunded with a

pH

7.14

and a

PaCO_2

75 \text{ mmHg}

, indicating severe acute-on-chronic respiratory failure.

This establishes the need for definitive airway management (intubation) rather than non-invasive ventilation, which is absolutely contraindicated in patients with altered mental status.

Calculate the anion gap and assess the acid-base pathophysiology.

The anion gap is

20 \text{ mEq/L}

(

140 - [96 + 24]

), indicating a high anion gap metabolic acidosis. The concurrent high

PaCO_2

confirms a mixed disorder.

Recognizing the respiratory component determines that bicarbonate administration would be harmful, as it would generate excess

CO_2

that the patient cannot expire.

Key Concept

Management of severe mixed acid-base disorders and undifferentiated shock in patients with concurrent COPD and heart failure.

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