A 64-year-old woman is evaluated in the emergency department for severe shortness of breat… — USMLE Step 2 CK

A $64$ -year-old woman is evaluated in the emergency department for severe shortness of breath and increasing leg swelling over the past week. She has a history of severe chronic obstructive pulmonary disease (COPD) requiring home oxygen therapy. Her temperature is $37.0^\circ\text{C}$ ( $98.6^\circ\text{F}$ ), blood pressure is $105/68\text{ mm Hg}$ , pulse is $118\text{ /min}$ , and respirations are $28\text{ /min}$ . Jugular venous pulsation is visible at $15\text{ cm H}_2\text{O}$ . Cardiac examination reveals a prominent parasternal heave and a loud $P_2$ . Lung auscultation shows significantly prolonged expiration and diffuse wheezing, with no crackles. The liver edge is palpable $4\text{ cm}$ below the right costal margin and is tender. Moderate pitting edema is present in the lower extremities. Arterial blood gas on $2\text{ L/min}$ supplemental oxygen shows:

pH: $7.31$
$PaCO_2$ : $62\text{ mm Hg}$
$PaO_2$ : $54\text{ mm Hg}$
$HCO_3^-$ : $31\text{ mEq/L}$

A trial of non-invasive positive pressure ventilation (NIPPV) is initiated for acute-on-chronic hypercapnic respiratory failure. Ten minutes later, the patient becomes lethargic and her blood pressure drops precipitously to $70/40\text{ mm Hg}$ . Which of the following is the most appropriate immediate next step in management?

Remove the non-invasive positive pressure ventilation maskCevap
B
Perform emergent endotracheal intubation
C
Administer an intravenous bolus of furosemide
D
Initiate an intravenous infusion of sodium bicarbonate
E
Administer intravenous piperacillin-tazobactam and vancomycin

Cevap

Remove the non-invasive positive pressure ventilation mask

The correct answer identifies that the sudden onset of profound hypotension following the initiation of non-invasive positive pressure ventilation (NIPPV) is due to a precipitous drop in venous return. The patient's physical exam (JVD, hepatomegaly, edema, clear lungs) reveals severe right ventricular failure (cor pulmonale) secondary to COPD. The failing right ventricle requires high filling pressures (preload) to maintain adequate stroke volume. When NIPPV is applied, the positive pressure is transmitted to the intrathoracic cavity, compressing the intrathoracic veins and sharply reducing venous return. This sudden loss of preload drastically drops right ventricular output, leading to reduced left ventricular filling and systemic shock. The immediate, life-saving intervention is to remove the NIPPV mask to restore venous return.

Adım Adım Çözüm

Analyze the patient's baseline clinical presentation.

The patient has signs of isolated right ventricular failure (JVD, parasternal heave, hepatomegaly, peripheral edema, clear lungs) secondary to chronic lung disease. This confirms a diagnosis of cor pulmonale.

Establishing the baseline hemodynamic state is required to predict how the patient will respond to cardiopulmonary interventions.

Evaluate the arterial blood gas results.

The ABG shows a pH of 7.31, PaCO2 of 62, and HCO3- of 31, indicating acute-on-chronic respiratory acidosis. NIPPV is a standard appropriate initial therapy for this gas exchange derangement.

Understanding the indication for NIPPV clarifies why it was started, setting up the subsequent complication.

Identify the mechanism of the sudden hemodynamic collapse after NIPPV initiation.

NIPPV delivers positive pressure to the airways, which transmits to the intrathoracic cavity. Increased intrathoracic pressure compresses the vena cava, reducing venous return (preload) to the right atrium.

Connecting the intervention to its physiological consequence is necessary to identify the cause of the shock.

Determine the effect of reduced preload on a failing right ventricle.

A failing right ventricle (cor pulmonale) is highly dependent on elevated filling pressures to maintain stroke volume. The sudden reduction in preload leads to a precipitous drop in right ventricular output, subsequent loss of left ventricular filling, and profound systemic hypotension.

This explains why the blood pressure dropped to 70/40 mm Hg and why the patient became lethargic.

Select the appropriate immediate intervention.

The inciting cause of the shock must be immediately reversed by removing the NIPPV mask to restore negative intrathoracic pressure and venous return.

Reversing the mechanical obstruction to venous return is the only way to immediately restore cardiac output in this scenario.

Anahtar Kavram

Patients with right ventricular failure (cor pulmonale) are highly dependent on adequate preload; initiating positive pressure ventilation increases intrathoracic pressure, which can precipitously reduce venous return and cause profound hypotensive shock.

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