A 54-year-old woman is evaluated in the intensive care unit for worsening respiratory stat… — USMLE Step 2 CK

A 54-year-old woman is evaluated in the intensive care unit for worsening respiratory status. She was admitted 24 hours ago for severe community-acquired pneumonia and septic shock. She has been receiving targeted intravenous antibiotics, fluid resuscitation, and a continuous infusion of norepinephrine. Her current blood pressure is 88/58 mm Hg, pulse is 122/min, and respirations are 34/min. Temperature is 38.6°C (101.5°F). Pulse oximetry shows 91% on a high-flow nasal cannula delivering 60% oxygen. Physical examination reveals a lethargic patient with prominent use of accessory muscles of respiration. Lung auscultation reveals diffuse crackles over the right hemithorax.

Laboratory results obtained 15 minutes ago:

Test	Result
Sodium	138 mEq/L
Potassium	4.2 mEq/L
Chloride	102 mEq/L
Bicarbonate	12 mEq/L
Blood urea nitrogen	34 mg/dL
Creatinine	1.8 mg/dL
Lactate	6.5 mmol/L

Arterial blood gas analysis on current oxygen settings:

Parameter	Result
pH	7.20
pCO2	34 mm Hg
pO2	64 mm Hg

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

A
Administration of furosemide
B
Computed tomography angiography of the chest
Endotracheal intubationCevap
D
Administration of sodium bicarbonate
E
Addition of empiric fluconazole

Cevap

Endotracheal intubation is the most appropriate next step to secure the airway in this patient with impending respiratory failure.

The correct answer is endotracheal intubation. This patient has septic shock with a severe high anion-gap metabolic acidosis (lactic acidosis). According to Winter's formula (

Expected \ pCO_2 = 1.5 \times [HCO_3^-] + 8 \pm 2

), her expected

pCO_2

should be between 24 and 28 mm Hg. Her actual

pCO_2

is 34 mm Hg, which is inappropriately elevated and indicates a superimposed respiratory acidosis. Clinically, her lethargy, tachypnea, and prominent use of accessory muscles demonstrate diaphragmatic fatigue. She is in impending respiratory failure and requires immediate airway protection and mechanical ventilation.

Adım Adım Çözüm

Identify the primary acid-base disorder.

The patient has a pH of 7.20 and bicarbonate of 12 mEq/L, indicating a primary metabolic acidosis (lactic acidosis from septic shock).

Establishing the primary disorder is required before evaluating for secondary compensation.

Calculate the expected respiratory compensation.

Using Winter's formula (

pCO_2 = 1.5 \times [HCO_3^-] + 8 \pm 2

), the expected

pCO_2

for a bicarbonate of 12 mEq/L is 24 to 28 mm Hg.

This determines if the patient's respiratory response to the metabolic acidosis is appropriate.

Compare expected and actual

pCO_2

values.

The measured

pCO_2

is 34 mm Hg, which is higher than the expected range of 24-28 mm Hg.

An actual

pCO_2

higher than expected indicates a concomitant primary respiratory acidosis.

Synthesize laboratory and clinical findings to determine management.

The combination of relative hypercapnia, tachypnea (RR 34/min), accessory muscle use, lethargy, and hemodynamic instability points to impending respiratory failure. The patient must be intubated.

The patient's respiratory muscles are failing to maintain the extreme minute ventilation required, necessitating immediate mechanical support.

Anahtar Kavram

In a patient with severe metabolic acidosis, a 'normal' or slightly low

pCO_2

that remains higher than the value predicted by Winter's formula indicates a superimposed respiratory acidosis. In the context of increased work of breathing and altered mental status, this signals impending respiratory failure requiring endotracheal intubation.

Soru

Cevap

Adım Adım Çözüm

Anahtar Kavram

Sık Yapılan Hatalar

Konular

Bu konudan daha fazla soru