A 52-year-old man is evaluated in the intensive care unit for worsening hypoxemia. He was … — USMLE Step 2 CK

A 52-year-old man is evaluated in the intensive care unit for worsening hypoxemia. He was admitted 48 hours ago with severe right lower lobe pneumonia and was intubated yesterday due to progressive respiratory failure. He is currently receiving continuous intravenous norepinephrine. His temperature is 38.2°C (100.8°F), blood pressure is 94/58 mm Hg, pulse is 112/min, and respirations are 28/min. A bedside echocardiogram shows normal left ventricular systolic function with an estimated ejection fraction of 60%. A portable chest radiograph reveals new diffuse bilateral alveolar opacities. He is deeply sedated and receiving volume-cycled assist-control ventilation.

Current ventilator settings and arterial blood gas (ABG) results are as follows:

Parameter	Value
Tidal volume ( $V_T$ )	600 mL
Respiratory rate	28/min
Fraction of inspired oxygen ( $FiO_2$ )	0.90
Positive end-expiratory pressure (PEEP)	8 cm $H_2O$

The measured plateau pressure is 35 cm $H_2O$ . The patient's predicted body weight is calculated to be 65 kg (143 lb).

ABG on current settings:
pH: 7.26
$PaCO_2$ : 58 mm Hg
$PaO_2$ : 55 mm Hg
$HCO_3^-$ : 25 mEq/L

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

Decrease the tidal volume to 390 mLCevap
Increase the positive end-expiratory pressure (PEEP) to 14 cm $H_2O$ Cevap
C
Administer intravenous furosemide to induce negative fluid balance
D
Administer an intravenous sodium bicarbonate infusion
E
Add empiric intravenous micafungin to the antimicrobial regimen

Cevap

The most appropriate next steps are to decrease the tidal volume to 390 mL and increase the PEEP to 14 cm H2O.

This patient has severe Acute Respiratory Distress Syndrome (ARDS), defined by acute onset, bilateral opacities, exclusion of cardiogenic causes (normal EF), and a

PaO_2

FiO_2

ratio less than 100 mm Hg (55 / 0.90 = 61). The current tidal volume of 600 mL is roughly 9.2 mL/kg of predicted body weight, which is excessively high and contributes to an elevated plateau pressure of 35 cm

H_2O

. Lung-protective mechanical ventilation requires lowering the tidal volume to 6 mL/kg (390 mL) to maintain the plateau pressure below 30 cm

H_2O

, preventing volutrauma. Furthermore, the patient remains severely hypoxemic despite a high

FiO_2

. According to the ARDSNet protocol, oxygenation should be improved by increasing PEEP (e.g., to 14 cm

H_2O

), which recruits collapsed alveoli, decreases intrapulmonary shunting, and allows for subsequent weaning of toxic oxygen concentrations.

Adım Adım Çözüm

Calculate the P/F ratio and assess the plateau pressure to confirm ARDS severity and evaluate current ventilator settings.

The

PaO_2

FiO_2

ratio is 61 mm Hg (55 / 0.90), indicating severe ARDS. The plateau pressure is 35 cm

H_2O

(target is < 30 cm

H_2O

Establishing severity and recognizing that current settings are causing alveolar overdistension (barotrauma) is required for protocolized intervention.

Determine the optimal tidal volume based on predicted body weight (PBW).

Target

V_T

is 6 mL/kg

\times

65 kg = 390 mL.

Lung-protective ventilation significantly reduces mortality in ARDS by preventing volutrauma.

Address the patient's severe hypoxemia while on a dangerously high

FiO_2

The current PEEP of 8 cm

H_2O

is inappropriately low for an

FiO_2

of 0.90; PEEP must be increased (e.g., to 14-16 cm

H_2O

Higher PEEP recruits collapsed alveoli (reducing shunting), thereby improving oxygenation without worsening overdistension.

Assess the need for fluid removal or acid-base correction.

Diuretics and bicarbonate are withheld.

The patient is in shock (requiring norepinephrine), making diuresis dangerous. The pH is 7.26, which is an acceptable limit for permissive hypercapnia.

Anahtar Kavram

Management of Acute Respiratory Distress Syndrome (ARDS) requires lung-protective ventilation (tidal volume 6 mL/kg predicted body weight, plateau pressure < 30 cm H2O) and optimization of PEEP to manage refractory hypoxemia.

Soru

Cevap

Adım Adım Çözüm

Anahtar Kavram

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