Page 118 - Critical Care Notes

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RESP
■ Alveolar-arterial (A-a) gradient (PAO 2 / PaO 2 )
■ PAO 2 represents the partial pressure of alveolar O 2 (mm Hg).
■ PaO 2 represents the partial pressure of arterial O 2 (mm Hg).
■ Value is used to calculate the percentage of the estimated shunt.
■ Value represents the difference between the alveolar and arterial oxygen
tension.
■ Normal A -a gradient value <15 mm Hg.
■ Value is increased in atrial or ventricular septal defects, pulmonary
· ·
edema, ARDS, pneumothorax, and V/Q mismatch.
■ a/A ratio (PaO 2 /PAO 2 ):
■ If ratio <0.60, shunt is worsening.
■ Estimation of shunt using PaO 2 /FIO 2 (P/F) ratio:
■ P/F ratio 500 indicates a 5% shunt.
■ P/F ratio 300 indicates a 15% shunt.
■ P/F ratio 200 indicates a 20% shunt.
Management
■ Treatment of underlying cause and symptoms
■ Continuous positive airway pressure (CPAP), PEEP, or bilevel positive airway
pressure (BiPAP)
Ventilator-Associated Pneumonia (VAP)
VAP is an airway infection that develops more than 48 hr after the patient is
intubated. It is associated with increased mortality, prolonged time spent on a
ventilator, and increased length of ICU/hospital stay.
Pathophysiology
VAP is usually caused by gram-negative bacilli or Staphylococcus aureus via
microaspiration of bacteria that colonize the oropharynx and upper airways or
bacteria that form a biofilm on or within an endotracheal tube (ETT). The pres-
ence of an ETT also impairs cough and mucociliary clearance. Suctioning also
contributes to VAP.
Clinical Presentation
VAP manifests with:
■ Increased RR, HR, and temperature (>38.3°C or 101°F)
■ Increased WBC (>10,000/mm 3 )
■ Increased purulent tracheal secretions
■ Crackles
■ Worsening oxygenation, hypoxemia, PaO 2 /FIO 2 changes
Diagnostic Tests
■ CXR showing new or persistent infiltrates
■ Tracheal aspirate and blood cultures
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