Sixty minutes after a patient is extubated, an arterial blood gas sample is drawn; the results are: pH = 7.20, PaCO2 = 60 mm Hg, PaO2 = 55 mm Hg, SaO2 = 80%, HCO3? = 23 mEq/L with a 2 L/min nasal cannula

The patient is SOB and complaining of chest pain. His blood pressure is 92/50 mm Hg. The most likely cause of this weaning failure is which of the following?
a. Chronic obstructive pulmonary disease
b. Acute left ventricular failure
c. Ventilatory muscle weakness
d. Hypophosphatemia

ANS: B
Patients who do well for 30-60 minutes after extubation and then fail weaning because of acute respiratory acidosis, hypoxemia, hypotension, and chest pain are likely to have acute left ventric-ular failure. This occurs because of increased preload, which is due to the decreased pulmonary capillary compression that occurs when intrathoracic pressure is reduced as a result of being off the ventilator.